Re: Topband: Short radials?
Richard The data is indisputable but I think for the average ham about a dozen 45 degree radials will produce about 3 DB less than theoretical. That is less than an S unit. The other difference is that all this information is based on ground wave propagation. There is nothing that addresses higher angle sky wave propagation common for 160 M operation. Sent from my iPad On Sep 27, 2012, at 7:38 PM, "Richard Fry" wrote: > Guy Olinger wrote: > >> Can you pass along your source of information that BL&E was done over 4 mS/m >> soil, ... Or are you using the FCC map for typical soil conductivities and >> presuming a common New Jersey value and no variation at the site? > > It is my presumption that for their cost and logistics, and with my 15 years > of insight as an RCA Broadcast field engineer (1965-1980), the BL&E > measurements were made near Princeton, NJ. I'll try to confirm that, and > advise. Princeton was the corporate facility containing the office/laboratory > of George H. Brown. > > If those tests had been made at some physical location where earth > conductivity at/near the test site was significantly better than in New > Jersey, this would have been evident in their measured data. > > For an example of this, if earth conductivity at/near the test site was 30 > mS/m, then even relatively few/relatively short buried radials in contact > with that earth would enable higher radiated fields than shown in the BL&E > data for those radial numbers and lengths. This is illustrated by the NEC4 > study using a short monopole on 1.85 MHz at this link: > http://i62.photobucket.com/albums/h85/rfry-100/10m_Vert32Buried_Radials.jpg . > > Even for an earth conductivity of 4 mS/m, the BL&E data show that monopoles > ranging from about 45 to at least 90 degrees in physical height, driven > against an r-f ground system consisting of at least 113 x 0.412-wave buried > radials, produces a groundwave field at 3/10 of a mile that is within several > percent of the maximum theoretical value possible for a perfect monopole > driven against a perfect ground plane, for that applied power. > > The bottom line in all of this is that the worse the earth conductivity > within 1/2-wavelength of the base of a monopole (especially a short monopole) > while driving that monopole against a set of buried radials, the more > important it becomes to use a large number of such radials of lengths > approaching 1/2 of a free space wavelength. > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: elevated counterpoise and lightning
A one or two inch form and #12 wire. On 7/30/12 12:23 PM, Jim Hoge wrote: > Then what would you recommend for homebrewing a choke? > > Tnx, > Jim W5QM > > ---- > *From:* W2XJ > *To:* topband@contesting.com > *Sent:* Monday, July 30, 2012 11:12 AM > *Subject:* Re: Topband: elevated counterpoise and lightning > > True but they are pretty wimpy. > > > On 7/30/12 12:10 PM, donov...@starpower.net > <mailto:donov...@starpower.net> wrote: > > Array Solutions (WX0B) sells static drain chokes at much lower cost > than AM broadcast equipment suppliers. > > > > http://www.arraysolutions.com/Products/staticsurgecoils.htm > > > > Or you can easily wind your own. > > > > 73 > > Frank > > W3LPL > > > > Original message > >> Date: Mon, 30 Jul 2012 11:49:09 -0400 > >> From: W2XJ mailto:w...@nyc.rr.com>> > >> Subject: Re: Topband: elevated counterpoise and lightning > >> To: topband@contesting.com <mailto:topband@contesting.com> > >> > >> Static drain chokes and ground rods should be SOP. The chokes drain > >> static build up which usually prevents direct hits. The chokes are > >> available from various broadcast suppliers. > >> > >> > >> On 7/30/12 11:40 AM, DAVID CUTHBERT wrote: > >>> Bob, do you have ground rods for lightning? > >>> > >>> The stub should be ok for static discharge but not for near or direct > >>> strikes. > >>> > >>> Dave WX7G > >>> On Jul 29, 2012 7:04 PM, "Bob Kupps" <mailto:n...@yahoo.com>> wrote: > >>> > >>>> Hi in this thread I mentioned using a 1/4 wave shorted stub at > the feed > >>>> points of our 4 square for static drain. Since we want to farm > the paddy > >>>> land we will use a non-resonant counterpoise of 48 radials > connected to a > >>>> perimeter wire about 1.5m above the flooded ground. The only galvanic > >>>> connection to earth would be back through the RG6 feed line to > the center > >>>> control box. So would adding an RF choke to the earth ground at > the element > >>>> base be a good idea in this case? Does anyone have any experience > with the > >>>> behavior of elevated radials in a lightning strike? > >>>> > >>>> 73 Bob HS0ZIA > >>>> ___ > >>>> UR RST IS ... ... ..9 QSB QSB - hw? BK > >>>> > >>> ___ > >>> UR RST IS ... ... ..9 QSB QSB - hw? BK > >>> > >> ___ > >> UR RST IS ... ... ..9 QSB QSB - hw? BK > > ___ > > UR RST IS ... ... ..9 QSB QSB - hw? BK > > > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: elevated counterpoise and lightning
True but they are pretty wimpy. On 7/30/12 12:10 PM, donov...@starpower.net wrote: > Array Solutions (WX0B) sells static drain chokes at much lower cost than AM > broadcast equipment suppliers. > > http://www.arraysolutions.com/Products/staticsurgecoils.htm > > Or you can easily wind your own. > > 73 > Frank > W3LPL > > Original message >> Date: Mon, 30 Jul 2012 11:49:09 -0400 >> From: W2XJ >> Subject: Re: Topband: elevated counterpoise and lightning >> To: topband@contesting.com >> >> Static drain chokes and ground rods should be SOP. The chokes drain >> static build up which usually prevents direct hits. The chokes are >> available from various broadcast suppliers. >> >> >> On 7/30/12 11:40 AM, DAVID CUTHBERT wrote: >>> Bob, do you have ground rods for lightning? >>> >>> The stub should be ok for static discharge but not for near or direct >>> strikes. >>> >>> Dave WX7G >>> On Jul 29, 2012 7:04 PM, "Bob Kupps" wrote: >>> >>>> Hi in this thread I mentioned using a 1/4 wave shorted stub at the feed >>>> points of our 4 square for static drain. Since we want to farm the paddy >>>> land we will use a non-resonant counterpoise of 48 radials connected to a >>>> perimeter wire about 1.5m above the flooded ground. The only galvanic >>>> connection to earth would be back through the RG6 feed line to the center >>>> control box. So would adding an RF choke to the earth ground at the element >>>> base be a good idea in this case? Does anyone have any experience with the >>>> behavior of elevated radials in a lightning strike? >>>> >>>> 73 Bob HS0ZIA >>>> ___ >>>> UR RST IS ... ... ..9 QSB QSB - hw? BK >>>> >>> ___ >>> UR RST IS ... ... ..9 QSB QSB - hw? BK >>> >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: elevated counterpoise and lightning
Static drain chokes and ground rods should be SOP. The chokes drain static build up which usually prevents direct hits. The chokes are available from various broadcast suppliers. On 7/30/12 11:40 AM, DAVID CUTHBERT wrote: > Bob, do you have ground rods for lightning? > > The stub should be ok for static discharge but not for near or direct > strikes. > > Dave WX7G > On Jul 29, 2012 7:04 PM, "Bob Kupps" wrote: > >> Hi in this thread I mentioned using a 1/4 wave shorted stub at the feed >> points of our 4 square for static drain. Since we want to farm the paddy >> land we will use a non-resonant counterpoise of 48 radials connected to a >> perimeter wire about 1.5m above the flooded ground. The only galvanic >> connection to earth would be back through the RG6 feed line to the center >> control box. So would adding an RF choke to the earth ground at the element >> base be a good idea in this case? Does anyone have any experience with the >> behavior of elevated radials in a lightning strike? >> >> 73 Bob HS0ZIA >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: More Amplifier info
A while back on another list there was a discussion about a robust amp can not be built in a table top size. I believe this applies to solid state amps as well. The key to building a gutsy solid state amp is the use of multiple devices and distributing the heat over a larger area. All solid state broadcast transmitters are comprised of multiple modules. Sometimes multiple fans are used to cool the modules. I am not aware any amateur linears with a modular design but there is nothing beyond economics to prevent one from being built. On 7/8/12 10:18 AM, Tom W8JI wrote: > Hi Larry, > > All of the links and data agree with what I found here in my measurements. I > think the real issue is some very creative marketing is being done, and the > factory data sheets can be a bit confusing. They certainly do not contain > linear data. > > Here are the main points: > > 1.) The "1250 watt device" is actually about a 800 watt PEP maximum device > in linear service. At 800 watts, it is right on the edge of what we are > accustomed to for Ham product IMD. > > 2.) A major problem is heat. Because all heat is in one small footprint, it > needs a very thick machined copper spreader or liquid cooling, even at just > 800 watts PEP. > > 3.) Like any other device, they will fail with mismatch at high power. They > absolutely will require SWR shutdown and temperature monitoring. > > If we read all of the links carefully enough to cut through the marketing > fluff, we will see every reference link listed (where they have actually > tested) agrees with all of this. > > I think what has really happened, is many home or first-time builders have > taken the data sheet at face value. They have convinced themselves this is a > 1250 watt output device that can be run right into almost any load without > worry. Of course, neither of those things are remotely true. > > I understand it is tough to let go of the magic of a single 1250-watt device > that slapped on a heatsink without protection, and can be run into a 65:1 > SWR without failing. But this is really a 800 watt PEP linear device that > comes with all the long term baggage of any other similar device, as ALL of > those links also seem to agree with. > > At 600 watts it will be pretty clean. At 800 watts about at the lower limit > of what cheap tube amps can do. All of this requiring getting the heat out, > and shutting it off if SWR goes high. > > 73 Tom > > full power in normal amateur service due to the heat issues. Maybe some > energetic person will build one up for 1.8 MHz using cryogenic cooling and > let us know how that works out... > > 73, > > Larry - W7IUV > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: TX ANT TO RX ANT COUPLING
Probably part has to do with the fact that your vertical is 1/8 wavelength and rule of thumb is 1/8 wavelength or less do no have a significant influence unless extremely close. On 6/17/12 5:34 PM, Bill and Liz wrote: > I have been following the thread with interest. I have a K9AY and a DO loop > located within 60 to 75 ft of the TX vertical at our summer home. > Interestingly, I find both these antennas very quiet with no sign of noise > being coupled to them via the TX antenna. I work a lot of DX from this > location on topband using these loops as well as a pair of Beverages, both > of which also pass fairly close to my TX vertical and both of which are very > quiet. > > So, why am I not hearing this noise many are experiencing? The TX vertical > is a 60 ft toploaded affair and I do not de-tune it on receive. All I have > done is to run all the feedlines for both RX antennas and the TX vertical > underground in different conduits to a remote switching location. Someone > please tell me why I am missing out on all the fun of having noise on my RX > antennas. > > Bill, VE3CSK > > > > - > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2012.0.2180 / Virus Database: 2433/5075 - Release Date: 06/17/12 > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: full wave horiz loop
EZNEC is your friend. On 6/16/12 9:35 PM, Tom W2MN wrote: > A couple of us in the radio club were discussing the possibility of > installing a full wave horizontal loop antenna (for Rx and Tx) on top of a > building we have access to. The loop would be about 20ft above the building > roof, making it about 100ft above ground. The loop could be a rectangle > approx. 180ft x 110ft (adjusted for a full wavelength on 160m). We were > thinking of using it on 160m as well as 80m. We would use steel / copper > clad wire and there in NO possibility of support except at the corners; so > it will sag under its own weight. > > > > Would appreciate any comments concerning its usefulness. Is it going to be > worth the effort?? > > > > Tom > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Receiving loops
Sensitivity is not always important. Small loops in general receive less noise and the real exercise is balancing the internal noise floor against the actual signal received. In some cases a loss up to 20 db can be acceptable the numbers are easy enough to run. On 6/16/12 8:17 PM, Brian Miller wrote: > Hi Tim > > I also agree with the previous comments on this thread about detuning the > transmit antenna (or any other wires/cables that are resonant on 160M) and > isolating the coax feed line from the RX loop. > > It is also important to identify the direction of the main source of the > noise and orientate the loop accordingly so that is being properly nulled. I > use a small portable tuned loop to identify the direction of the noise.. > > Of course, if the noise is coming from the same direction as the DX then you > are not going to see much (or any ) improvement in the signal-to-noise > ratio. Also, if the noise sources are in multiple directions then it will > also be difficult to null the noise properly. I have found that small tuned > loops (with their bidirectional nulls) are often more effective in such a > situation. > > One of the problems with small tuned loops made from wire is their low > sensitivity. Rather than using a pre-amp you can boost the output by making > the loop larger (e.g., a circumference of 0.1 wavelength or even larger). > The larger loop maintains a directional pattern similar to the smaller one > but also exhibits a higher radiation radiation resistance and hence lower > losses. > > Good luck with the experiments and let us know how you get on. > > 73, Brian VK3MI ZL1AZE > >> From: tsho...@wmata.com >> To: topband@contesting.com >> Date: Sat, 16 Jun 2012 13:28:38 + >> Subject: Topband: Receiving loops >> >> I want to try a new receiving antenna for the summer Stew Perry. Last >> winter was my first foray onto 160M and I really felt like an alligator. I >> could work everyone I could hear, with just 100W. I think that means I >> need a better receive antenna. If you look at my score in the winter Stew >> Perry I think I did great QSO-number wise, but my average distance was >> very poor, I'm guessing typical alligator. >> >> I have tried pennants and K9AY's over the winter with little success. >> Compared to my transmitting antenna (A "T" with a poor radial system) most >> signals were still better, S/N wise, on my transmitting antenna. I feel >> like I must've been doing something wrong. Still the fact that a few >> signals came in on the loop with by ear much better S/N, maybe I was on >> the right track and just didn't try hard enough. >> >> I will be trying a small tuned magnetic loop tonight (e.g. the last one at >> http://www.w8ji.com/magnetic_receiving_loops.htm with the 9:1 transformer) >> . And maybe a terminated beverage but I'm limited to about 150'... well >> maybe I could run something longer down the driveway as long as I clean it >> up before the sun comes up and the neighbors see. >> >> I was fairly impressed with small tuned magnetic loops when I was doing >> some BCB DX'ing several years ago. I wasn't comparing with beverages or >> anything. >> >> Tim N3QE >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Detuning transmit antenna in receive
There is no single solution for detuning an antenna it depends on electrical length. For verticals a quarter wavelength or less it is common to have a contactor between the network and the radiating element and open the connection to float that element. This is the practice in commercial directional arrays where some tower are not used in a day or night mode. This does not work well on taller towers and I do not know offhand how it would work with the T. It is easy enough to model in EZNEC. On 6/16/12 3:02 PM, Shoppa, Tim wrote: > OK, several folks came back and recommended detuning my transmit antenna in > receive. > > Certainly any receive antenna I have is going to be in the shadow of my > transmit antenna, a 130-foot flat-top about 85 feet up, fed against ground. > (Really it's an 80 meter doublet fed with ladder line. I tie the ladder line > together at the bottom and feed against ground.) > > Trying to figure out what "detune" is. > > I match the transmit antenna to 50 ohm coax with a L network at the bottom. > If I want to detune, then I can open up the connection between the > antenna and the L network at the bottom? Unhook the L or C in the L network? > Short out the antenna where it comes into the L network? I could rig up a > relay contact to do any of those. > > Tim N3QE > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: radial wire source
You really do not need stranded wire. Bare solid wire is typically used for grounds. and while the standard of 120 radials spaced 3 degress is a well known standard for ground systems, it is very rare in amateur radio. Anything beyond 12 1/8 wavelength radials is a plus. I would check an electrical wholesaler and price bare copper in bulk. Usually #10 is used but I see no serious reason why #12 or even #14 would work in this application. I prefer a buried ground (or at least on the surface) over elevated for various reasons. Having installed many MW systems, I can tell you the ideal is not always achieved. At the end of the day, get as much wire in the ground wherever it is possible. On 6/5/12 9:01 AM, Dan Bookwalter wrote: > I think I asked something similar last fall , but , circumstances changed > and I couldn't do anything about it at the time... > > So , here I am again looking for a source of radial wire I was thinking > of either going with K2AV's FCP or a radial field If i go with the > radials I was thinking of using #14 stranded for about 15 radials that in > theory would help absorb any lightning impulses (per W8JI website) , then I > was going to use whatever wire I can find for the remaining 40 or 50 radials. > My radial field can only cover from about SW thru North over to East. > > > Is there a better source for wire than Lowes/Home Depot ? I will check with > the local electrical distibutor , but , if I recall correctly they weren't > much better Lowes currently has 500' of #14 THHN for $50 I would need > about 3000 feet. > > Dan > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Monopole Radiation Patterns, takeoff angles etc
Subject: Date: From: Reply-To: To: Having worked in the business over 54 years with LW MW and SW transmission systems up to 2 megawatts and having built numerous MW arrays to 12 towers I would respectfully suggest a quick check of fundamental broadcast history. Google is your friend. BTW most early stations broadcast from rooftops, not mountain tops, and some diamond towers (Blau Knox) are still in service at legendary stations. On 5/6/12 9:40 PM, ZR wrote: > Carl has nothing backwards, best do your research the next time. > > - Original Message - > From: "W2XJ" > To: > Sent: Sunday, May 06, 2012 7:40 PM > Subject: Re: Topband: Monopole Radiation Patterns, takeoff angles etc > > >> I think Carl may have his time line backwards. In the 20s and early 30s >> many stations used various forms of wire antennae including dipoles and >> various cage designs. During the 30s Dr Brown and colleagues studied and >> tested various vertical radiators and ground systems. The result of that >> work remains the underpinning of most MW radiators and a substantial >> amount of it ultimately became part of FCC rules and standards in many >> other parts of the world. Some stations continued with their wire >> antenna into the 40s and some paid a penalty of having stations moved >> into the natural nulls of a dipole. >> >> On 5/6/12 6:18 PM, Kevin wrote: >>> WHO-AM (1040 KHz) still uses the modified Franklin. >>> Their 50KW covers the entire state of Iowa + during the day and goes >>> international at night. >>> >>> >>> On 05/06/2012 11:31 AM, ZR wrote: >>>> The BCB stations migrated from 1/2 and 5/8 wave antennas, diamond shaped >>>> towers, and mountain tops by the early to mid 30's as they started to >>>> understand how things worked...or didnt. >>>> >>>> Carl >>>> KM1H >>>> >>> -- R. Kevin Stover AC0H >>> ___ >>> UR RST IS ... ... ..9 QSB QSB - hw? BK >>> >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> >> >> - >> No virus found in this message. >> Checked by AVG - www.avg.com >> Version: 10.0.1424 / Virus Database: 2411/4981 - Release Date: 05/06/12 >> > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Monopole Radiation Patterns, takeoff angles etc
I think Carl may have his time line backwards. In the 20s and early 30s many stations used various forms of wire antennae including dipoles and various cage designs. During the 30s Dr Brown and colleagues studied and tested various vertical radiators and ground systems. The result of that work remains the underpinning of most MW radiators and a substantial amount of it ultimately became part of FCC rules and standards in many other parts of the world. Some stations continued with their wire antenna into the 40s and some paid a penalty of having stations moved into the natural nulls of a dipole. On 5/6/12 6:18 PM, Kevin wrote: > WHO-AM (1040 KHz) still uses the modified Franklin. > Their 50KW covers the entire state of Iowa + during the day and goes > international at night. > > > On 05/06/2012 11:31 AM, ZR wrote: >> The BCB stations migrated from 1/2 and 5/8 wave antennas, diamond shaped >> towers, and mountain tops by the early to mid 30's as they started to >> understand how things worked...or didnt. >> >> Carl >> KM1H >> > -- R. Kevin Stover AC0H > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Monopole Radiation Patterns, takeoff angles etc
One has to be careful with 5/8 wavelength verticals. A radiator that is physically 5/8 wavelength is already electrically too tall. That is why a 300 foot BC tower would not work well at low angles on 160. There are too things to considers one is that towers have velocity factor just like coax and the other is guy wires and anything else attached to the tower will have a loading effect. The size of the tower face also has an effect. I knew someone who without doing the necessary engineering built a 225 degree BC radiator and had horrible results because he did not take the above factors into consideration. It is difficult to say what a safe physical height might be without fairly precise modelling. A significant number of 50KW former clear channel stations use 195 degree radiators. Part of the logic is that above that height a minor high angle lobe becomes significant and causes sky wave cancellation of the ground wave which is a concern to broadcasters. But the other point is that 195 degrees is far enough away from 225 degrees that the mechanics of the install is not important unless that tower is also supporting some beam antennas. There is one true Franklin on the BC band in Sacramento CA. There are several other sectionalized radiators in service but the generally tend to be high maintenance. On 5/6/12 5:07 PM, Herb Schoenbohm wrote: > In 2006 Tom Rauch, W8JI mentioned the disappointment with 3/8 wave > vertical antennas and Carl mention today abut how "BCB stations migrated > from 5/8 wave and 1/2 wave antennas." I added to Tom's rejoinder that > several AM stations spent considerable amounts of money with the > Franklyn design which was claimmed to lay more radiation at lower > angles. This is possible if the two is insulated and a phasing device > is place between the upper and lower tower sections. Presumably it can > be accomplished even with reduced height or a squashed design of the > true Franklyn. Admittedly I have yet to hear of any TB'er to use this. > However a 3db signal enhancement at low angles in all directions may be > something to consider. I would also wonder if putting to much RF below > the critical angle (since DX-ers) are not particularly interest in > ground wave coverage and need sky wave instead) would be detrimental. > There are times when a higher angle take off is the difference between > being heard or not especially, I think, during SR/SS Grey line > enhancements, and maybe on some skews and spotlights. I post the > Franklyn information just the same for those who may have missed the > original post. > > > Herb Schoenbohm, KV4FZ > > Quoting Tom Rauch: > > >> / Some of the biggest failure antennas I have used were 5/8th/ >> / wave verticals at broadcast stations. We loaded one AM tower/ >> / that happened to be a 5/8th wave on 160, and it was poor/ >> / compared to a short vertical./ > The balloon lengths has increased my curiosity in learning what principles are > working here. Theoretically, very low angle radiation could be obtained by a > balloon supported long wire with "controlled current distribution". (ARRL > Antenna Compendium Vol. 2 pp. 132-135) > > As I mentioned before in my case the 5/8 vertical 308 foot insulated tower, > totally surrounded by sea water was a big disappointment on 160 meters. I > tried it for 5 years and the lower antennas were always noticeably better. > > I once worked for KUOM which shared a tall tower with KSTP 1500 kHZ in > Minneapolis. Stan Hubbard, owner of KSTP was convinced to erect a Franklin > antenna design which was supposed to modify the current distribution on tall > towers to lay out a stronger ground wave then the 1/4 wave or smaller AM > radiators. All the theory, the engineer and construction cost, sort of like a > Ringo Ranger for the broadcast band were very disappointing. Years of A/B > testing driving across the Dakotas, WCCO (although lower in frequency) was the > king of signals from the Twin Cities by a significant margin. Both were 50KW > clear channel stations. (KSTP bragged 100KW Effective Radiated Power) Some > claimed > this was due to sky wave and ground wave out of phase arrivals in which case > the > Franklyn actaully redued the sky-wave component, at least in theory. > > The Franklin concept can be found in Jasik's First Edition Antenna Engineering > Handbook pp. 4-35 and 4-36. A traditional Franklin was two half waves stacked > end to end and fed in phase. KNBC (Los Angles)built one in 1949 as a means > of lowering the angle of radiation, but used a 550 foot tower since at 680 Khz > a true Franklin would have been 1500 feet tall. They were apparently able to > design a much shorter structure since their top portion was top loaded with a > capacity hat and only 150 feet tall. (Put "KNBC Franklin Antenna" in your > search engine for some awesome pictures of this antenna.) Did it actually > improve coverage for KNBC? Are they still using it today? > > It would be int
Re: Topband: Skywave for LF
True 500 KHz did it for Marconi 111 years ago. On 2/22/12 2:25 PM, Robert Kavanagh wrote: >> 630 meter propagation will be almost entirely groundwave as ionospheric >> conditions generally do not support skywave (a primary reason for the >> use of LF and low MF for NDB). > Not true. > > As G5VU has already noted, NDBs are routinely propagated via skywave, > e.g. IPA in Easter Island has been frequently heard here (8700 km) after > dark. > > Bob > VE3OSZ > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: EIRP Measurement
That is not what I said. The skywave would only be stronger if field measurements on the ground were used to determine power due to various ground losses, ground conductivity, etc. when an RF ammeter is used for measurement (standard practice for MW installations) The maximum EIRP before ground losses is at the zero degree azimuth. Skywave will have a lower EIRP. Having designed and built MW facilities for over the last 40 years, I and anyone else who has can attest to the irregularity in field strength when radials are measured. When the measurements are matched to the best fit ground conductivity curve the variations in signal strength above and below the theoretical can be significant in many cases. On 2/21/12 8:58 PM, Rick Karlquist wrote: > W2XJ wrote: >> >> >> If you can find a used FIM 22 it goes from 200 KHz to 550 KHz. That said >> I can not see determining EIRP by field measurement. There are just two >> many variables and a degree of engineering skill not posessed by the >> average amateur. The various national authorities must have a means of >> measurement accessible to the average operator and is easy to enforce. >> Then as I stated previously there is the interference problem. The >> signal measured along the ground will be less than at higher angles. >> Skywave interference will be greater because the real EIRP will be >> exceeded and by a large amount in some cases. > The RF ammeter test merely measures the total radiated power. > It does not account for the effective signal strength at some > skywave angle. If it is true that the skywave is stronger than > the ground wave, then the power would need to be backed off, > but there is no way to determine how much to backoff without > a helicopter field measurement. It would depend on ground conductivity, > so there would be no way to calculate it or model it accurately. > > Rick N6RK > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: EIRP Measurement
I would disagree. The signal measured along the ground is affected by ground losses and is subject to ground conductivity even though the charts show maximum gain along the ground. The signal radiated at angles above about 10 degrees is governed by inverse distance and therefore less loss. An attempt to determine EIRP by measurement on the ground will be subject to local conditions thus more loss than higher angle radiation not subject to the same attenuation. What can be assumed for an amateur 600M installation is: The radiator will be electrically very short. The ground system will be far from optimum for most installations. There will be other losses not usually found in full size MW installation This will all contribute to more losses on the ground than in the air. This is different than what is shown for radiators greater than .64 wavelength where the radiating element starts to transition to being an end fed array. On 2/21/12 10:23 PM, Joe Subich, W4TV wrote: >> If it is true that the skywave is stronger than the ground wave, then >> the power would need to be backed off, > Fortunately, it is not true with short ground mounted monopole > antennas. In order for the skywave to exceed the groundwave, the > monopole needs to be longer than half wave (somewhere in the area > exceeding 0.64 wave). > > 73, > > ... Joe, W4TV > > > On 2/21/2012 8:58 PM, Rick Karlquist wrote: >> W2XJ wrote: >>> >>> >>> If you can find a used FIM 22 it goes from 200 KHz to 550 KHz. That said >>> I can not see determining EIRP by field measurement. There are just two >>> many variables and a degree of engineering skill not posessed by the >>> average amateur. The various national authorities must have a means of >>> measurement accessible to the average operator and is easy to enforce. >>> Then as I stated previously there is the interference problem. The >>> signal measured along the ground will be less than at higher angles. >>> Skywave interference will be greater because the real EIRP will be >>> exceeded and by a large amount in some cases. >> The RF ammeter test merely measures the total radiated power. >> It does not account for the effective signal strength at some >> skywave angle. If it is true that the skywave is stronger than >> the ground wave, then the power would need to be backed off, >> but there is no way to determine how much to backoff without >> a helicopter field measurement. It would depend on ground conductivity, >> so there would be no way to calculate it or model it accurately. >> >> Rick N6RK >> >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: EIRP Measurement
Ahh but I think the FCC will see things much differently. I base this on the existing 60M regs where an ERP is specified: (i) No station may transmit with an effective radiated power (ERP) exceed- ing 50 W PEP on the 60 m band. For the purpose of computing ERP, the trans- mitter PEP will be multiplied by the antenna gain relative to a dipole or the equivalent calculation in decibels. A half-wave dipole antenna will be pre- sumed to have a gain of 1. Licensees using other antennas must maintain in their station records either the an- tenna manufacturer data on the an- tenna gain or calculations of the an- tenna gain. This can give a pretty good indication of how the FCC thinks. I think 600M installations might be allowed to assume a certain amount of losses and a means to measure power into the radiating element. They will not create a regulatory nightmare. Notice in the case of 60M the feedline is not considered. Any losses their are at the amateur's expense. The same will likely be the case for 600 M ground loss. There are possibly a handful of amateurs in the world that will be able to install a full ground system and will gain an advantage but the rest will just have to be as clever as possible in reducing losses. The height of the tower is not that important as the radiation pattern does not change from 1/4 wave for a short element. What does happen is a dramatically lower resistance resulting in higher losses. Matching systems losses are unimportant since they would precede the point of measurement. One would expect transmitter powers of at least 100 to 200 watts in order to achieve to EIRP limit. Many broadcasters would gladly operate with much shorter towers and less ground if the FCC would allow. But the FCC is and always has been all about what makes it easier for them to administrate. On 2/21/12 7:36 PM, Joe Subich, W4TV wrote: > On 2/21/2012 4:17 PM, W2XJ wrote: >> In broadcast work the antenna impedance is first determined by >> calculation (now modeling) then the actual impedance are measured >> when the station is tuned up. Loading coils are not used at least not >> by that name. > The methods used in broadcast work are not applicable to amateur use > for a lot or reasons. First, broadcast towers are generally a far > greater fraction of a wavelength than 0.05 wave where an amateur > antenna for 630 meters will almost certainly be no more than 0.05 > wave. Second, broadcast ground systems are extensive - 120 half > wave radials ... an amateur ground system for 630 meters is likely > to be no more than .04-.05 wave! Losses in the ground system alone > - not counting losses in the matching system are going to be very > high. > > The only way an amateur is going to get *accurate* EIRP numbers is > to measure the field strength at 1 KM or other known distance well > beyond the near field/far field transition range - that means 1 km > or more and compare that to the theoretical field intensity for 5W > EIRP. > > Anyone who does not have the capability to make accurate field > intensity measurements will simply be guessing. > > 73, > > ... Joe, W4TV > > > On 2/21/2012 4:17 PM, W2XJ wrote: >> In broadcast work the antenna impedance is first determined by >> calculation (now modeling) then the actual impedance are measured when >> the station is tuned up. Loading coils are not used at least not by that >> name. The current is measured after the antenna matching unit which is >> often a T network but could easily be an L or even PI.. In broadcast >> rules a loss resistance of one ohm is assumed and the maximum allowed >> but all losses attributed to matching are eliminated due to the >> measurement location.. This will be an issue in amateur operation since >> the actual losses would be higher and more difficult to determine. A >> short vertical will show a gain of about 4.78 dbi regardless of height. >> Tapering and top loading are taken into account when the feed point >> impedance is measured. >> >> At least in the US and probably Canada the FCC and Industry Canada might >> possibly used a simplified version of the broadcast methods they have >> used for over 80 years. It could be something like assuming a 4.78 db >> gain over isotropic, base impedance measurements and ignoring ground and >> other system losses. This would assure that no station would actually >> exceed EIRP and is easy to measure upon inspection. It would be >> necessary for each amateur to develop a chart that equates allowable >> antenna current to frequency as the drive impedance could change >> drastically on such a short radiator. >> >> On 2/21/12 3:31 PM, Rick Karlquist wrote: >>> W2XJ wrote: >>> >>>> This m
Re: Topband: Topband list and 630 Meters - the decision
The sign up procedure fails. There seems to be a problem with the majordomo address. On 2/22/12 1:17 AM, Mike Waters wrote: > Thanks. That must be it. http://www.500kc.com/Maillists.htm > > On Tue, Feb 21, 2012 at 9:59 PM, Tod Olson wrote: > >> http://www.500kc.com/ >> >> > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: EIRP Measurement
If you can find a used FIM 22 it goes from 200 KHz to 550 KHz. That said I can not see determining EIRP by field measurement. There are just two many variables and a degree of engineering skill not posessed by the average amateur. The various national authorities must have a means of measurement accessible to the average operator and is easy to enforce. Then as I stated previously there is the interference problem. The signal measured along the ground will be less than at higher angles. Skywave interference will be greater because the real EIRP will be exceeded and by a large amount in some cases. I could see where if there were a sufficient market a device that was sort of a combination of a vector impedance meter and an ammeter could calculate EIRP on the fly. It would have to be located remotely at the antenna feed. On 2/21/12 5:22 PM, Jack/W6NF wrote: > On 2/21/2012 11:51 AM, W2XJ wrote: >> The Potomac Analog FIM is no longer available, nor are the parts to >> repair them and calibration service is no longer available. The new >> meters are expensive digital units. But in broadcast we do not use them >> to determine power but rather coverage usually when directional systems >> are tuned. >> >> On 2/21/12 1:05 PM, Jack/W6NF wrote: >>> On 2/21/2012 8:26 AM, Joe Subich, W4TV wrote: >>>> > On Mon, 2012-02-20 at 19:04 -0700, Tod - ID wrote: >>>> > >>>> > The important thing is to have a way to assure that when >>>> someone >>>> > measured the same field at the same point with the same type >>>> of >>>> > measurement device they would get the same measurement result. >>>> > That would allow us to compare measurements between different >>>> > people even if we did not know the absolute field strength >>>> value. >>>> >>>> I think simple, repeatable and accurate are a difficult triad. What >>>> you are talking about is an accurate Field Intensity Meter (FIM) and >>>> getting stable calibrations with home constructed equipment is not >>>> going to be easy - let along easy to duplicate. The closest solution >>>> is to use standard antennas (not simple whips) and calibrate them >>>> against broadcast signals at known locations and known field strengths. >>>> >>>> This will still require separate antennas for 160 and 630 meters and >>>> separate calibration sources on the appropriate ends of the standard >>>> broadcast band (due to the antennas). >>>> >>>> 73, >>>> >>>> ... Joe, W4TV >>>> >>>> >>>> ___ >>>> UR RST IS ... ... ..9 QSB QSB - hw? BK >>>> >>> It's been many years since I have had to make any AM broadcast field >>> measurements. I don't recall if the Potomac Instruments, or other, FIMs >>> go much below 550kHz. >>> >>> 73, >>> >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> > Yes, I am aware of that, having been CE at several DAs, including one > critical night-time array. I was thinking that, if the FIMs covered the > necessary frequencies, EIRP could be inferred by measuring field strength. > > I'd still be curious if any of the new FIMs have extended coverage that > would make them useful. > > Oops, I guess this is now OT, right? ;>) > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: EIRP Measurement
In broadcast work the antenna impedance is first determined by calculation (now modeling) then the actual impedance are measured when the station is tuned up. Loading coils are not used at least not by that name. The current is measured after the antenna matching unit which is often a T network but could easily be an L or even PI.. In broadcast rules a loss resistance of one ohm is assumed and the maximum allowed but all losses attributed to matching are eliminated due to the measurement location.. This will be an issue in amateur operation since the actual losses would be higher and more difficult to determine. A short vertical will show a gain of about 4.78 dbi regardless of height. Tapering and top loading are taken into account when the feed point impedance is measured. At least in the US and probably Canada the FCC and Industry Canada might possibly used a simplified version of the broadcast methods they have used for over 80 years. It could be something like assuming a 4.78 db gain over isotropic, base impedance measurements and ignoring ground and other system losses. This would assure that no station would actually exceed EIRP and is easy to measure upon inspection. It would be necessary for each amateur to develop a chart that equates allowable antenna current to frequency as the drive impedance could change drastically on such a short radiator. On 2/21/12 3:31 PM, Rick Karlquist wrote: > W2XJ wrote: > >> This method is virtually universal for MW power measurement. There are >> calibrated RF ammeters available since they are required at each AM >> broadcast station (directional stations may use as many as a dozen >> depending on the array). Alternatively the voltage can be measured. In > Why is this method bulletproof? So you measure the RF current, which > by the way is different below the loading coil than above the loading > coil. How do you determine the radiation resistance of the antenna? > By modeling? You have to correctly take into account tapering, > top loading, etc. How do you know the counterpoise isn't radiating? > > Rick N6RK > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: EIRP Measurement
As I posted earlier field measurement is not an accurate method of determining power. I seriously doubt an administration permit such a technique unless it was very dumbed down and produced very 'safe' results or in other words less power than could otherwise be achieved. On 2/21/12 2:54 PM, Tod Olson wrote: > Joe, et. al > > I am quite certain that there will need to be different sense antennas for > 160m and 630m. I would not be surprised if we did not also need bandpass > filters for each of the bands as well. > > As I recall there were several circuits in QST using a single analog > Devices unit to measure RF input levels. I think that it have several > decades of measurement and the output was on a log scale. Since the input > of those circuits was broadband something would need to be altered to make > it usable on 160m and/or 630m for measuring rf at those specific > frequencies. > > There is a device called a Helmholtz pair that might be used on low > frequencies to help with calibration. > > See → www.ets-lindgren.com/page/?i=6402M > > I have been advised by Dave Bowker, K1FK, that such a device might be > constructed for quite low cost. > > > > Thanks for the suggestions Joe. > > Tree, if this is going over the edge let me know. It was not my intention > to subvert the TopBand reflector. > > Tod, K0TO > > > > > > > On 2/21/12 10:26 AM, "Joe Subich, W4TV" wrote: > >>> On Mon, 2012-02-20 at 19:04 -0700, Tod - ID wrote: >>> >>> The important thing is to have a way to assure that when someone >>> measured the same field at the same point with the same type of >>> measurement device they would get the same measurement result. >>> That would allow us to compare measurements between different >>> people even if we did not know the absolute field strength value. >> I think simple, repeatable and accurate are a difficult triad. What >> you are talking about is an accurate Field Intensity Meter (FIM) and >> getting stable calibrations with home constructed equipment is not >> going to be easy - let along easy to duplicate. The closest solution >> is to use standard antennas (not simple whips) and calibrate them >> against broadcast signals at known locations and known field strengths. >> >> This will still require separate antennas for 160 and 630 meters and >> separate calibration sources on the appropriate ends of the standard >> broadcast band (due to the antennas). >> >> 73, >> >>... Joe, W4TV >> >> > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: EIRP Measurement
The Potomac Analog FIM is no longer available, nor are the parts to repair them and calibration service is no longer available. The new meters are expensive digital units. But in broadcast we do not use them to determine power but rather coverage usually when directional systems are tuned. On 2/21/12 1:05 PM, Jack/W6NF wrote: > On 2/21/2012 8:26 AM, Joe Subich, W4TV wrote: >>> On Mon, 2012-02-20 at 19:04 -0700, Tod - ID wrote: >>> >>> The important thing is to have a way to assure that when someone >>> measured the same field at the same point with the same type of >>> measurement device they would get the same measurement result. >>> That would allow us to compare measurements between different >>> people even if we did not know the absolute field strength value. >> >> I think simple, repeatable and accurate are a difficult triad. What >> you are talking about is an accurate Field Intensity Meter (FIM) and >> getting stable calibrations with home constructed equipment is not >> going to be easy - let along easy to duplicate. The closest solution >> is to use standard antennas (not simple whips) and calibrate them >> against broadcast signals at known locations and known field strengths. >> >> This will still require separate antennas for 160 and 630 meters and >> separate calibration sources on the appropriate ends of the standard >> broadcast band (due to the antennas). >> >> 73, >> >> ... Joe, W4TV >> >> >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> > It's been many years since I have had to make any AM broadcast field > measurements. I don't recall if the Potomac Instruments, or other, FIMs > go much below 550kHz. > > 73, > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: EIRP Measurement
The link provided below shows how to calculate EIRP. I think each administration will spell out the requirements of how to legally calculate EIRP. To me it is fairly straight forward. 60M in the US is an example. While there is an EIRP limitation, the FCC simplified the determination by assuming a dipole and the amount of power fed to it. On 600M, one could easily put up as much tower as reasonable and then measure the tower's impedance. Once the impedance is known it is easy to calculate the input power to the radiator and therefore the current. This method is virtually universal for MW power measurement. There are calibrated RF ammeters available since they are required at each AM broadcast station (directional stations may use as many as a dozen depending on the array). Alternatively the voltage can be measured. In either case it is relatively easy to build and calibrate a voltage or current sampling device. That will establish the actual power input to the antenna. An 80 foot tower on 600M has around .6 ohms impedance therefore 1 amp will produce about 600 milliwatts into the antenna. 1.3 amps would be 1 watt in this example. The antenna has 4.78 db gain over an isotropic radiator so this needs to be reduced to .75 amps which is 340 milliwatts into the antenna (or 1.7 watts if a 5 W EIRP limit , slightly more than 1.5 Amps). This method eliminates having to calculate matching network losses as the ammeter is at the antenna feed point. I also think that actual field measurement is a bad idea and probably not allowed by most administrations. The reason is that the losses near the ground will be higher than the skywave component which is where there will be the possibility of interference. We will all have to wait and see how the rules are written. On 2/21/12 12:09 PM, Brad Rehm wrote: > I also think this topic is worth addressing, but Bill is probably > right in saying it could gobble all the bandwidth on this reflector. > Maybe someone would be willing to be the moderator of a new reflector. > > In the mean time, we should acknowledge that a lot of the work has > already been done by the hams who've been experimenting on 136 kHz. > See http://www.strobbe.eu/on7yd/136ant/#Loops for example. > > BTW, the three-antenna method is not considered the best way to make > field strength measurements at these frequencies. Since the field is > magnetic, loops, monopoles, helmholz coils, and other kinds of probes > are normally used. > > I wonder how many 160 ops are considering trying the new band. I > wouldn't be surprised if the answer were "very few." Although the new > band is just below AM broadcast frequencies, instead of just above > them, this is the region in which transmitters and antennas begin to > look very different from conventional HF setups. After we've made > substantial investments in time and resources in decent 160m stations, > moving down will present new challenges which may only interest > "experimenters." > > Brad > KV5V > > On Tue, Feb 21, 2012 at 8:49 AM, Bill Cromwell wrote: >> On Mon, 2012-02-20 at 19:04 -0700, Tod - ID wrote: >>> In thinking about the measurement of EIRP for the new band it occurred to >>> me that this might be the time for a few folks to think about how we could >>> fabricate a "commonly calibrated" field strength meter. Such a device might >>> well be used on both 160m and the 600 kHz band. By commonly calibrated in >>> mean a device that has an agreed upon standard way to calibrate it that can >>> be done with simple methods. One thing that always intrigued me about the >>> HeathKit products was the fact that they used very simple methods to allow >>> the builder to adjust the device without expensive equipment. Sometimes >>> that meant a special circuit built into the product which was only used for >>> adjusting the device. >>> >>> The important thing is to have a way to assure that when someone measured >>> the same field at the same point with the same type of measurement device >>> they would get the same measurement result. That would allow us to compare >>> measurements between different people even if we did not know the absolute >>> field strength value. >>> >>> An interesting idea might be to make such a field strength meter have an >>> interface to Wi-Fi so that it could be positioned at a remote point and >>> send its readings to one's local network. There are a lot of ways to do >>> that of course, but planning to have it part the device initially would >>> simplify taking measurements. I am sure that there are others who could >>> contribute ideas that eventually could be used to formulate design >>> objectives for such a device. If there was enough interest I can imagine >>> that a single PCB could created and a lot of such devices built to allow us >>> to add to our collection of measurement devices that help us fabricate >>> better antennas and stations. >>> >>> I wonder if I am the only one who
Re: Topband: Radials help
That makes a lot of sense. The FCC has never allowed any form of parasitic directional array. They want something that has positive control. In the 60s there was no computer modeling so the effect of a slant wire would be basically guessing. For hams running a slant into the window is an excellent approach. It permits matching where it should be without having an outdoor tuner. On 2/10/12 6:37 PM, Herb Schoenbohm wrote: > > No papers that I know of Guy, just the word of a consulting engineer > who said he applied in the 60's and said it would not be considered as a > solution for even a slight pattern control to protect another station. > He finally had to go to a two tower array, another ground system, a > phaser, a day night switching control and a lot of bucks for the owner. > Station now are allowed lowering power to accomplish protection but back > then it was 250w, 500w, or 1KW, etc. Nothing in between for a single > tower set up. Now they permit single tower daytimers to operate at > night with very low power levels as low as a few watts to keep their > station on at night. I am sort of certain that some ham has modeled the > pros and cons of a slant wire feed for a grounded tower but I have never > seen such results published. Some hams tell me they do this to bring the > feed wire into the shack so they can use the tuner there to get a decent > match across the band. > > > Herb, KV4FZ > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Radials help
Here is a link to that paper. It is easy see what field a radiator of X height will produce with varying number of radials from 2 to 113. From the graphs 15 radials and a 45 deg tower gets reasonably close to the ideal. It also shows a 45 deg tower with 113 radials is almost as good as a 90 deg. http://rfry.org/Software%20Download/Ground%20Systems%20-%20Brown,%20Lewis%20and%20Epstein%201937.pdf On 2/10/12 4:03 PM, Guy Olinger K2AV wrote: > The 120 comes from the watershed 1937 Brown Lewis and Eppstein study now > found in the IEEE journals. There were distinct characteristics to 120 > times 0.4 wl (actually 115) that improved results even vs. 60. > > That a deficient radial system on one side has any significant reduction in > that direction alone VS THE OTHER DIRECTIONS is a fairly well debunked > idea. That the missing radials reduce radiation in all directions, due to > diminished efficiency, is not disputed. > > 73, Guy. > > On Fri, Feb 10, 2012 at 2:54 PM, Herb Schoenbohm wrote: > >> >> On 2/10/2012 1:11 PM, Milt -- N5IA wrote: >>> If that is the case, WHY do the pro broadcasters install all 120 radials >> at >>> full length; even bare wire buried a couple of inches underground? >> Answer: >> >> Because the FCC requires it as part of your AM application. Some >> stations that were required to protect a distant station on the same >> channel but away from the area they wanted to cover, even applied for a >> waivers with a deliberately poor ground system in the protected >> direction ...but the FCC said no way Jose. Another consulting engineer >> when modeling a slant wire shunt fed and running test FSM noticed some >> cancellation in the opposite direction of the slant wire shunt fed >> tower. This appeared a sensible solution to enhanced protection without >> the addition of another tower and expensive pahser, not to mention the >> cost of additional real estate. Again the boys at 1919 M Street said >> no. (The Portals today) >> >> With the price of copper skyrocketing the amount of theft in some parts >> of the country is unbelievable. AM stations are immediate targets as >> thieves just pull up the systems with a winch or just hook it to the >> bumper and drive off into seclusion and roll it up in the back of a >> truck. Some station owners in PR have opted to plow in barbed wire as a >> lower cost alternative to bare copper. So far none of the barbed wire >> buried ground systems have not been touched. >> >> >> Herb Schoenbohm, KV4FZ >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Topband: Fwd: Re: Radials help
Most stations just follow tradition. No station I have built has ever had any radials stolen. They are buried 3 feet down. It takes heavier equipment to do it but it is worth the effort. On 2/10/12 2:54 PM, Herb Schoenbohm wrote: > > On 2/10/2012 1:11 PM, Milt -- N5IA wrote: >> If that is the case, WHY do the pro broadcasters install all 120 radials at >> full length; even bare wire buried a couple of inches underground? > Answer: > > Because the FCC requires it as part of your AM application. Some > stations that were required to protect a distant station on the same > channel but away from the area they wanted to cover, even applied for a > waivers with a deliberately poor ground system in the protected > direction ...but the FCC said no way Jose. Another consulting engineer > when modeling a slant wire shunt fed and running test FSM noticed some > cancellation in the opposite direction of the slant wire shunt fed > tower. This appeared a sensible solution to enhanced protection without > the addition of another tower and expensive pahser, not to mention the > cost of additional real estate. Again the boys at 1919 M Street said > no. (The Portals today) > > With the price of copper skyrocketing the amount of theft in some parts > of the country is unbelievable. AM stations are immediate targets as > thieves just pull up the systems with a winch or just hook it to the > bumper and drive off into seclusion and roll it up in the back of a > truck. Some station owners in PR have opted to plow in barbed wire as a > lower cost alternative to bare copper. So far none of the barbed wire > buried ground systems have not been touched. > > > Herb Schoenbohm, KV4FZ > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Radials help
I think this is all being way over thought. It would be good to go back and study the work of Dr. Brown of RCA in the early 30s. At the time broadcast stations were using various iterations of wire antennas as we still use today on our HF bands. Dr Brown developed the theory and the math underlying what came to be the standard practice for MW broadcasting world wide. There have been numerous studies that build on that work including some in QEX that document the effect of varying numbers and lengths of radials. In a nutshell virtually no commercial broadcast is reasonant nor is that even part of the design criteria. A sterotypical idealized antenna would consist of a quarter wave vertical with 120 ground radials a quarter wavelength or more. In the real world this can be reduced to a 45 degree mast and 4 to 8 ground radials with some loss of efficiency but not as much as one might think. My advice for the top band put up as much tower as possible with 60 feet being a desireable minimum and about 360 feet the maximum. Use a buried ground system. In broadcast we usually use #10 bare copper. Put in as many as is pratical and as long as practical. The key is to have a proper matching network at the antenna. In broadcast we always have an outdoor ATU at the tower base (or a dog house). For simplicity an L network will do the job although a T network is better. Either network can be adjusted to match any frequency in the 160 M band. There are also more elaborate network design that can flatten out the reactance slope to create a much broader match without retuning. On 2/10/12 1:21 PM, Guy Olinger K2AV wrote: >> According to either the ARRL "ANTENNA HANDBOOK", or ON4UN's "LOW-BAND DX >> HANDBOOK", the velocity factor of insulated wire placed atop the ground is >> 50%... >> > Unfortunately, and inconveniently, not to cast aspersions on anyone, BUT > actual measurements in the Raleigh area showed that velocity factor of a > wire laying on the ground and used for 160 meters was nothing like a > uniform 50%. Measurements were taken with a 151' (46m) dipole on ground, > with an analyzer to find primary resonance (and therefore velocity factor > with a formula) and RF resistance at zero reactance, half of this being the > effective series resistance of an electrical 1/4 wave radial identically > installed in that spot. > > The measured velocity factor ranged from 45% to 80%, with the effective > series resistance ranging from 30 to over a hundred ohms. There were wild > variations both in velocity factor and effective series resistance on the > same property, often had just by reorienting the DOG 90 degrees. > > These measurements were extremely dependent on the actual height above the > dirt. Notching the wire down just into the dirt (not waiting for the grass > to gradually bury it) produced the most repeatable measurements. If the > end was not specifically insulated (like dipping in liquid tape, etc), the > ends had to be bent up to get a measurement, because the ends are voltage > nodes, even at the tiny antenna analyzer output voltages. Having an > uninsulated end down just down in the damp botched the measurement. > > If any of you think an insulated radial field can just plopped down based > on a formula on just any plot of land and be efficient, think again. All > that is necessary to be abysmally INefficient is for the construction > ground fill underneath your sod to be variable in composition, or contain > metallic pipes or buried wires or a septic system. In this case your > radials are no longer ELECTRICALLY dense and uniform, current distribution > becomes wacky, effectively removing radials from the system, and the radial > system has become an unbalanced ground heater, and quite inferior to an > elevated counterpoise. (Sound familiar?) > > Have a read on W7ADC's (the excellent Mr. Archibald Doty) work in NCJ on > radials. 1983 and 2011. Note the variability in the SAME dense radial > field, and his conclusions. Largely ignored, and price paid for ignoring. > > Measurements made out in the convenient middle of a plowed and disc'd Iowa > cornfield are idyllic because the dirt is uniform and wonderfully > conductive, and UNAVAILABLE to the tortured topbanders trying to get > anything to work on the only and the MF-dreadful plot of land they own. >The starting presumption on a given plot of land should be that > on/in-ground radials will NOT work well unless PROVEN otherwise. The odds > are simply dreadful against it. I doubt they are even as good as one in a > hundred that they could beat a well-designed elevated counterpoise. > > If one is stuck with in/on ground, then DEAL with the variability and > INDIVIDUALLY PRUNE radials, notched into the dirt to their final resting > place, to equal effective series resistance to FORCE the UNIFORM in "dense > and uniform". And if you're not willing to bother with dense, you're going > to need an
Re: Topband: Radials help
They have stray radiation that the FCC's computer can not model. On 2/10/12 5:43 PM, Guy Olinger K2AV wrote: > Off top my head, it would seem the slant wire would work to create a > directional effect of one sort or other, depending on the specifics, but I > have no clue why the FCC dissed that one. They usually attach some > technical explanation to rulings. You have access to the specific > proceedings? I could come up with a dozen speculations about it, but > that's all they'd be. > > -- Guy. > > On Fri, Feb 10, 2012 at 5:13 PM, Herb Schoenbohm wrote: > >> On 2/10/2012 5:03 PM, Guy Olinger K2AV wrote: >>> The 120 comes from the watershed 1937 Brown Lewis and Eppstein study now >>> found in the IEEE journals. There were distinct characteristics to 120 >>> times 0.4 wl (actually 115) that improved results even vs. 60. >>> >>> That a deficient radial system on one side has any significant reduction >> in >>> that direction alone VS THE OTHER DIRECTIONS is a fairly well debunked >>> idea. That the missing radials reduce radiation in all directions, due >> to >>> diminished efficiency, is not disputed. >>> >>> 73, Guy. >>> >> Guy, >> >> What about the slant wire cause at least some directive component in the >> direction of the slant wire? >> >> >> Herb, KV4FZ >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Shunt fed tower
I would ditch the GDO and measure R and J. On 12/15/11 6:45 PM, Larry wrote: > Herb, > > I tried measuring the tower resonance with a GDO as suggested > by ON4UN's book but my GDO wouldn't go low enough in frequency > to find resonance. It appears to be below 1.5MHz (100 ft 45G with > a KT36XA at 100.5 ft, 80M rotatable dipole at 108 ft, and a 2 el 40M > yagi at 117 feet). > > I was thinking about a 6 wire cage 6 inches in diameter probably about > 2-3 feet out but I will rethink that in light the comments by you, Carl. and > Guy. It may need to be further out. ON4UN's book suggests an > omega match in such circumstances but after measuring with the cage in > place I'll see what it actually needs. > > I am hoping to get a better 160 signal out of the shunt fed tower. I > currently > have an inverted V that is OK but certainly is not great. I used to have > a sloper attached to the 100 foot tower that seemed to work better - > most of the time - but it was finicky to tune. > > I am in the process of putting up another tower which by coincidence(?) > is 128 feet from the 100 footer but the new tower is only 70 feet. At some > point I will look at phasing them as a 2 el vertical array for 160. The 70 > foot tower may a bit short for that service. I need to do some reading and > experimenting before I get there though. The line through the towers is > pointed right at Europe (NE) or Australia (SE). > > Thanks all for the comments. > > 73, Larry W6NWS > - Original Message - > From: "Herb Schoenbohm" > To: "Larry"; "TopBand List" > Sent: Thursday, December 15, 2011 5:49 PM > Subject: Re: Topband: Shunt fed tower > > >> Larry, >> >> Because of the complexity of modeling without going crazy, although in >> simple situations it will get you in the ball park, I would highly >> recommend a 3 or 4 wire cage space at least 24 inches from the area near >> the rotor plate on a, let's say, 70 to 80 foot tower. The drop wires >> should be #8 or #6 copper and tied together in a ring supported by >> porcelain insulators (PVC not recommended in some circles) around at the >> base with one wire connected from the ring going to your proposed ATU. >> With a MFJ bridge measure the feed wire's reactance and impedance against >> ground. With one climb have your tower climb buddy work his way from the >> top in 2 foot increments jumpering the cage to the tower with large >> alligator clips (nothing fancy for this purpose) and tell him or her to >> keep coming down until you get close to 50 ohms. (It can be 40 to 60 ohms >> as that is sweet point enough you me) Then back a better connection using >> split copper bolts with three jumpers to the tower. Whatever the >> reactance is you can tune out that inductive reactance with an equal value >> of capacitance. As Guy said forget about the tower being resonant >> anywhere since in such circumstances you may never get that. A tap coil >> to ground will get you with a simple L network and series cap should get >> your SWR to 1:1 even if the sweet point is a bit off. Again the components >> should be, flat wound coil with correct tap connections, a vac of at least >> 750pf with broadcast mica paders if required for more C. >> >> I have found that single wire shunt feeds are the most problematic to work >> with, especially when the beams are on multiple levels. A larger diameter >> cable, if you must only use a single wire shunt can be obtained from using >> a length of CATV .750 which is 3.5 inch in diameter. But a big shunt >> doesn't look all that hot and a three wire cage is beautiful, looks like >> it will work, and in fact does. >> >> Good luck, >> >> >> Herb Schoenbohm, KV4FZ >> >> >> >> >> >> >> >> >> On 12/15/2011 5:14 PM, Larry wrote: >>> I haven't done much modeling in the past.I have a KT36XA which would be >>> very >>> ugly if I had to model it precisely. I also have a linearly loaded 2 el >>> 40M >>> yagi. >>> I suspect that the loading wires probably are negligible in the overall >>> scheme >>> of things at 160M. So I would guess that there some approximation that >>> would >>> give reasonable results as a place to start on the tower. Suggestions? >>> >>> 73, Larry W6NWS >>> - Original Message - >>> From: "W2XJ" >>> To: >>> Sent: Thursday, December 15, 2011 10:34 AM >>> Subject: Re: Topband: Shunt fed tower >>> >>> >>> V
Re: Topband: Shunt fed tower
For most of us a precise model is not possible. EZNEC will give you an approximation. The tower is represented as a cylinder equal to the cross section of the real tower. You could measure the existing R and J and then in EZNEC just keep adding loading until EZNEC agrees with your measurements. Then move the shunt wire around in EZNEC until you hit 50 ohms. The result will give you a ballpark but it saves a lot of climbing and rearranged real wires. A yes, to be clear that 50 ohms is at the bottom of the shunt feed. On 12/15/11 4:14 PM, Larry wrote: > I haven't done much modeling in the past.I have a KT36XA which would be very > ugly if I had to model it precisely. I also have a linearly loaded 2 el 40M > yagi. > I suspect that the loading wires probably are negligible in the overall > scheme > of things at 160M. So I would guess that there some approximation that would > give reasonable results as a place to start on the tower. Suggestions? > > 73, Larry W6NWS > ----- Original Message - > From: "W2XJ" > To: > Sent: Thursday, December 15, 2011 10:34 AM > Subject: Re: Topband: Shunt fed tower > > > Vertical antennas have been shunt fed for over 70 years. There is no > magic involved. Very few MW verticals are ever resonant and resonance is > irrelevant. The only important thing is to match the TX so it is happy. > The easiest way to deal with matching is to first model on EZNEC which > will give an approximation of where the shunt should be connected and > then physically moving the shunt to find the 50 ohm point which should > be determined by measurement. Once that is accomplished, measure the J > and calculate the necessary C to cancel it. > > On 12/15/11 10:17 AM, Joe Subich, W4TV wrote: >> On 12/15/2011 7:27 AM, W2RU - Bud Hippisley wrote: >> >>> Of course, a grounded, shunt-fed, top-loaded tower isn't exactly the >>> same as a full-size half-wavelength Yagi driven element, but the >>> comparison is at least a good starting point. >> That is true but a 100 foot tower with decent sized 20M monobander or >> 24 foot boom tribander with the front/back elements grounded and a >> short 40 meter yagi will most certainly have a natural resonant point >> below 1.8 MHz. Additional side mounted yagis will further lower the >> resonant point. A tower with resonant point below 1.8 MHz will have >> a higher impedance which will transform badly in a "gamma" with high >> "element to rod ratio" and narrow spacing. >> >>> I don't support the weight of the entire rod -- which consists of >>> stepped diameters of plumbing tubing -- that way — I simply "steady" >>> the top portion while making electrical connection to the tower at >>> the tap point. >> R and L Electronics (www.randl.com) has insulators for "cage" dipoles. >> They are about 3.5" OD with 12 1/4" holes on a roughly 3" diameter and >> make excellent insulators for a "fat" gamma rod. One can use 3, 4, or >> 6 wires in the cage and achieve effective diameters between 2 and 3 >> inches. >> >> 73, >> >> ... Joe, W4TV >> >> >> On 12/15/2011 7:27 AM, W2RU - Bud Hippisley wrote: >>> Many shunt-fed, loaded towers on 160 exhibit narrow bandwidth and are >>> difficult to match with a single series capacitor for one simple >>> reason: >>> >>> The gamma rod (shunt wire) is TOO CLOSE to the tower. >>> >>> A few years ago, after struggling with Omega matches in conjunction >>> with MANY trips up my tower, I modeled my system with EZNEC. For me, >>> the "sweet spot" was to position the gamma rod SEVEN (7) FEET from >>> the tower! >>> >>> For my tower (92 feet of Rohn 45, 8 feet of mast above it, shorty 40 >>> at 97 feet and 4-el. 20-m monobander at 92 feet), the tap point is 57 >>> feet up. >>> >>> My minimum SWR (in a 50-ohm system) at my center frequency is around >>> 1.4:1, but my 2.0:1 SWR bandwidth increased (with no change in my >>> skimpy radial field) to over 75 kHz as a result of my modeling >>> efforts. >>> >>> Having struggled with Omega matches for years before that, the >>> present setup is a joy. >>> >>> One way to get in the ballpark without doing any serious modeling is >>> to think about the gamma matches you've probably seen (and maybe even >>> used) on your 20-meter beams. Very roughly, since 160 meters is 1/8 >>> the frequency of 20 meters, all things being equal, the gamma rod >>> spacing on 160 should be eigh
Re: Topband: Shunt fed tower
Agreed, my bad semantics. That said I was thinking more of a sloping shunt similar to was was used in broadcast. I don't think many will have a "too tall" problem on 160 M unless some lucky person has around 300 feet or more. On 12/15/11 10:59 AM, Joe Subich, W4TV wrote: > On 12/15/2011 10:34 AM, W2XJ wrote: >> Vertical antennas have been shunt fed for over 70 years. There is no >> magic involved. Very few MW verticals are ever resonant and resonance >> is irrelevant. > All true but one does not want a tower that is "too tall" that the > pattern deteriorates. > > > The easiest way to deal with matching is to first model on EZNEC which > > will give an approximation of where the shunt should be connected and > > then physically moving the shunt to find the 50 ohm point which should > > be determined by measurement. > > The shunt is *not* connected to the 50 Ohm point. It is connected to > the point that is *transformed to 50 Ohms* by the effects of the gamma. > The key is to find a combination of tap point, gamma spacing and rod > diameter that result is 50-jx Ohms at the bottom of the rod with a > usable bandwidth so the -jx can be cancelled by a single capacitor. > > 73, > > ... Joe, W4TV > > > On 12/15/2011 10:34 AM, W2XJ wrote: >> Vertical antennas have been shunt fed for over 70 years. There is no >> magic involved. Very few MW verticals are ever resonant and resonance is >> irrelevant. The only important thing is to match the TX so it is happy. >> The easiest way to deal with matching is to first model on EZNEC which >> will give an approximation of where the shunt should be connected and >> then physically moving the shunt to find the 50 ohm point which should >> be determined by measurement. Once that is accomplished, measure the J >> and calculate the necessary C to cancel it. >> >> On 12/15/11 10:17 AM, Joe Subich, W4TV wrote: >>> On 12/15/2011 7:27 AM, W2RU - Bud Hippisley wrote: >>> >>>> Of course, a grounded, shunt-fed, top-loaded tower isn't exactly the >>>> same as a full-size half-wavelength Yagi driven element, but the >>>> comparison is at least a good starting point. >>> That is true but a 100 foot tower with decent sized 20M monobander or >>> 24 foot boom tribander with the front/back elements grounded and a >>> short 40 meter yagi will most certainly have a natural resonant point >>> below 1.8 MHz. Additional side mounted yagis will further lower the >>> resonant point. A tower with resonant point below 1.8 MHz will have >>> a higher impedance which will transform badly in a "gamma" with high >>> "element to rod ratio" and narrow spacing. >>> >>>> I don't support the weight of the entire rod -- which consists of >>>> stepped diameters of plumbing tubing -- that way — I simply "steady" >>>> the top portion while making electrical connection to the tower at >>>> the tap point. >>> R and L Electronics (www.randl.com) has insulators for "cage" dipoles. >>> They are about 3.5" OD with 12 1/4" holes on a roughly 3" diameter and >>> make excellent insulators for a "fat" gamma rod. One can use 3, 4, or >>> 6 wires in the cage and achieve effective diameters between 2 and 3 inches. >>> >>> 73, >>> >>>... Joe, W4TV >>> >>> >>> On 12/15/2011 7:27 AM, W2RU - Bud Hippisley wrote: >>>> Many shunt-fed, loaded towers on 160 exhibit narrow bandwidth and are >>>> difficult to match with a single series capacitor for one simple >>>> reason: >>>> >>>> The gamma rod (shunt wire) is TOO CLOSE to the tower. >>>> >>>> A few years ago, after struggling with Omega matches in conjunction >>>> with MANY trips up my tower, I modeled my system with EZNEC. For me, >>>> the "sweet spot" was to position the gamma rod SEVEN (7) FEET from >>>> the tower! >>>> >>>> For my tower (92 feet of Rohn 45, 8 feet of mast above it, shorty 40 >>>> at 97 feet and 4-el. 20-m monobander at 92 feet), the tap point is 57 >>>> feet up. >>>> >>>> My minimum SWR (in a 50-ohm system) at my center frequency is around >>>> 1.4:1, but my 2.0:1 SWR bandwidth increased (with no change in my >>>> skimpy radial field) to over 75 kHz as a result of my modeling >>>> efforts. >>>> >>>> Having struggled with Omega matches for years before that,
Re: Topband: Shunt fed tower
Vertical antennas have been shunt fed for over 70 years. There is no magic involved. Very few MW verticals are ever resonant and resonance is irrelevant. The only important thing is to match the TX so it is happy. The easiest way to deal with matching is to first model on EZNEC which will give an approximation of where the shunt should be connected and then physically moving the shunt to find the 50 ohm point which should be determined by measurement. Once that is accomplished, measure the J and calculate the necessary C to cancel it. On 12/15/11 10:17 AM, Joe Subich, W4TV wrote: > > On 12/15/2011 7:27 AM, W2RU - Bud Hippisley wrote: > >> Of course, a grounded, shunt-fed, top-loaded tower isn't exactly the >> same as a full-size half-wavelength Yagi driven element, but the >> comparison is at least a good starting point. > That is true but a 100 foot tower with decent sized 20M monobander or > 24 foot boom tribander with the front/back elements grounded and a > short 40 meter yagi will most certainly have a natural resonant point > below 1.8 MHz. Additional side mounted yagis will further lower the > resonant point. A tower with resonant point below 1.8 MHz will have > a higher impedance which will transform badly in a "gamma" with high > "element to rod ratio" and narrow spacing. > >> I don't support the weight of the entire rod -- which consists of >> stepped diameters of plumbing tubing -- that way — I simply "steady" >> the top portion while making electrical connection to the tower at >> the tap point. > R and L Electronics (www.randl.com) has insulators for "cage" dipoles. > They are about 3.5" OD with 12 1/4" holes on a roughly 3" diameter and > make excellent insulators for a "fat" gamma rod. One can use 3, 4, or > 6 wires in the cage and achieve effective diameters between 2 and 3 inches. > > 73, > > ... Joe, W4TV > > > On 12/15/2011 7:27 AM, W2RU - Bud Hippisley wrote: >> Many shunt-fed, loaded towers on 160 exhibit narrow bandwidth and are >> difficult to match with a single series capacitor for one simple >> reason: >> >> The gamma rod (shunt wire) is TOO CLOSE to the tower. >> >> A few years ago, after struggling with Omega matches in conjunction >> with MANY trips up my tower, I modeled my system with EZNEC. For me, >> the "sweet spot" was to position the gamma rod SEVEN (7) FEET from >> the tower! >> >> For my tower (92 feet of Rohn 45, 8 feet of mast above it, shorty 40 >> at 97 feet and 4-el. 20-m monobander at 92 feet), the tap point is 57 >> feet up. >> >> My minimum SWR (in a 50-ohm system) at my center frequency is around >> 1.4:1, but my 2.0:1 SWR bandwidth increased (with no change in my >> skimpy radial field) to over 75 kHz as a result of my modeling >> efforts. >> >> Having struggled with Omega matches for years before that, the >> present setup is a joy. >> >> One way to get in the ballpark without doing any serious modeling is >> to think about the gamma matches you've probably seen (and maybe even >> used) on your 20-meter beams. Very roughly, since 160 meters is 1/8 >> the frequency of 20 meters, all things being equal, the gamma rod >> spacing on 160 should be eight times what it is on 20. If your >> 20-meter gamma rod is 7 or 8 inches from your driven element, that's >> equivalent to 5 or 6 feet on 160. Of course, a grounded, shunt-fed, >> top-loaded tower isn't exactly the same as a full-size >> half-wavelength Yagi driven element, but the comparison is at least a >> good starting point. >> >> Construction: My local ACE hardware store stocks 8-foot lengths of >> angle aluminum, which is what I used for my horizontal tap rod. >> Their heaviest-duty stock is more than strong enough to support >> itself plus the top of my gamma rod. I don't support the weight of >> the entire rod -- which consists of stepped diameters of plumbing >> tubing -- that way — I simply "steady" the top portion while making >> electrical connection to the tower at the tap point. (The nearest >> Lowe's has even heavier aluminum stock, but if you're using wire >> instead of heavy tubing, the ACE stock is plenty strong enough.) >> The bottom of my gamma rod sits on a single piece of 2x8 >> pressure-treated lumber from the scrap bin. I use a couple of scrap >> lengths of 1x2 furring strips between one face of the tower and the >> gamma rod to maintain spacing along the length of the rod. It ain't >> pretty, but it works...I apologize to no one about my signal on 160! >> >> Bud, W2RU >> >> >> ___ UR RST IS ... ... ..9 >> QSB QSB - hw? BK >> > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Changes To My Shunt Fed Tower
The best way to handle the problem is to assume the new antenna made an impact on the match. The first step would be to measure the actual resistance and if it is not 50 ohms, reset the tap for 50 ohms. Then measure the J again and you can easily calculate the amount of C required to cancel the J. Anything else is just guessing. On 12/12/11 11:38 AM, DL2OBO wrote: > AFAIK all Optibeam elements are always isolated from the boom. So there > shouldn't be any additional toploading from them (elements), just the > loading from the boom should be considered > > 73 Tom > > > DL2OBO (T88DL) > Carsten-Thomas Dauer ( Tom ) > c/o Hotel Hellers Krug > Altendorfer Str. 19 > D-37603 Holzminden > > www.dl2obo.com Ham-Radio > www.hotel-hellers-krug.de my hotel / rent-a-shack > www.carstendauer.dephotografy > > -Ursprüngliche Nachricht- > Von: topband-boun...@contesting.com [mailto:topband-boun...@contesting.com] > Im Auftrag von Mike& Coreen Smith > Gesendet: Montag, 12. Dezember 2011 16:30 > An: topband@contesting.com > Betreff: Re: Topband: Changes To My Shunt Fed Tower > > Hi Bob, > > If I recall (correctly). The D40 is completely > isolated from the mast, so it would be nearly invisible to your 160m > RF...given all the other loading you have going on there. > I don't know a thing about the Optibeam...is it also isolated or grounded? > I am guessing grounded, as you now have a change. > If that IS the case, you'll need more capacitance to counteract the loading > you've added. As to the amount, I could only hazard a guess. If you've > maxxed out your 1000pF air variable, you can add some random length of > RG-214 or other coax in parallel and start hacking off a foot at a time, and > > then tweak with the cap as neccessary. > It's cheap and saves climbing ! I forget at the moment how many pF RG-214 > or other similar dielectric coax is, but maybe 10-15pF per foot springs to > mind. Try adding 10 or 15' on and see what you can do with your cap. > > My brain is still numb from ARRL-10 CW this weekend...I keep hearing "T E S > T, V E 9 A A" in my ears , hi ! > > DIT dit, > > MIke > >- Original Message - >From: Bob Garrett >To: 'Jim F.' ; 'top Band' >Sent: Sunday, December 11, 2011 1:21 PM >Subject: Topband: Changes To My Shunt Fed Tower > > >Hello Topbanders, > >It is getting cold in the Northeast and as I get older, I dislike the cold >even more. > >In April of this year, I replaced my Cush craft D40 40 meter rotable > dipole >with an OptiBeam OB-4030 dipole for 30 and 40 meters right at the top of > the >mast. The overall length of the antenna is about ten feet longer and I am >assuming that it has added some additional capacitance to my 100 foot > shunt >fed tower with a Cush craft X7, A3WS, 5 EL M2 6 meter yagi and the new >OptiBeam dipole. > >My match on the tower went from 1.0 x 1. To 1.9 x 1 after I installed the >new antenna. In terms of loss, this isn't a huge change but my amplifier >doesn't like the change. Before I spend a lot of time running back and >forth to the tower making random changes, any thoughts as to what I can do >to improve the match. I'm currently using one series capacitor 1000PF for >the matching network. I have attempted to adjust this capacitor but it >looks like the 1.9 x 1 is the low point. Perhaps some thoughts - increase >or decrease the spacing of the shunt wire? Move the connection up or down >on the tower? > >Before I get to crazy, just wanted to look to the base of knowledge on > this >reflector for your input. > >73 and tnx in advance. > >Bob K3UL > > >___ >UR RST IS ... ... ..9 QSB QSB - hw? BK > > > > -- > > > >No virus found in this incoming message. >Checked by AVG - www.avg.com >Version: 8.5.454 / Virus Database: 271.1.1/4071 - Release Date: 12/09/11 > 20:51:00 > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: no response to query: feeding phased verticals at half wave spacing
This is quite true although some patterns will be closer to theory than others. In a commercial phasor as is used for broadcast there are several elements that must be taken into account. The first is the matching at each vertical element. It must take the actual drive impedance of the elements and match to the transmission line (usually 50 ohms). These networks all have phase shift which must be taken into account as a part of the total system design. The next important element is the power divider. There are various designs but in the end they all permit the adjustment of power to each element so the currents are correct. The ARRL patterns are idealized examples where the current in both elements are equal but in the real world this is not often the case. A power divider also has phase shift. The final element is the means of making the phases of each tower the desired value while taking into account the fixed phase shift of the matching network and the power divider. There are two common methods used. The first is a lumped constant network which adds or subtracts phase to achieve the correct values after transmission line phase delay is added into the system. The other method is to use the transmission line to achieve the proper phase relationships. Even when transmission lines are used it is necessary to have a small lumped constant network to trim for minor variations in phase. It is apparent that such a system is very sensitive to a change in frequency. Adjusting a typical phased array requires a means of measuring impedance and typically there is a phase monitor which shows the phase and current ratio of each tower. This is all verified by field measurements that require a calibrated field intensity meter and a lot of paperwork to plot the pattern or a more complex (and expensive) GPS based measurement system. It should be obvious at this point that no amateur phased arrays are built as described above and do not have the same requirements. Commercial arrays are usually designed to provide protection to other stations on the same or adjacent frequencies. Amateur arrays are generally intended for gain in a desired direction and must have at least a small amount frequency agility. While the ARRL patterns are very much theoretical a few can be implemented for practical amateur use. The broadside two tower array spaced 180 degrees is probably the best if space is available. One drawback is the figure 8 pattern has zero db front to back ratio. This could be handled with a parasitic reflector but at the expense of more complexity and space. The bottom line is that practical amateur arrays will not achieve performance close to theoretical. On 11/24/11 10:59 AM, Rik van Riel wrote: > On 11/22/2011 08:06 PM, Gerry Treas, K8GT wrote: >> Hi Dale, >> >> I'm no antenna expert, but certainly read as much of the experts >> publications as I can get my hands on, but having a Teflon brain, it doesn't >> stick very well. >> >> That said, the ARRL Antenna Book has a page that shows the patterns of >> various spacings and phasings of vertical antennas, which I found very >> enlightening. >> > Enlightening, but also somewhat misleading... > > The patterns in the ARRL Antenna Book are correct if the > current in both elements is the same. > > However, if you feed an array of antennas with delay lines, > those delay lines will act as impedance transformers for > the antenna impedance of each element (like all feedlines do). > > This can result in each element getting different currents, > and the pattern no longer being what it was. > > This makes feeding a phased array with delay lines much > trickier than one would imagine at first glance. > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: 1/2 wave spacing vs. 1/4 wave
That would be a function of a number of things unrelated to array topology. It could reflect difference in electrical tower height or how the array is phased. A properly designed vertical array will always have maximum vertical angle gain near zero degrees elevation. Theoretically the maximum gain is at zero but in the real world ground conductivity affects gain near zero degrees. When I say 'properly designed' it is not any reflection on any Ham's design. Vertical arrays can take a lot of work and design effort when built for professional use which is almost always broadcast. Another aspect of such an array is that they only work correctly at one frequency. A half wave spaced broadside array is probably the best for amateur use because the matching is very simple, just two 90 degree lines fed in parallel. As the frequency changes the pattern remains essentially the same except for some added side lobes but the match at the feed point changes. A tuner solves this problem and IMHO the feed lines should be open wire. In line arrays interact in a much more complex manner in part because of the closer element spacing. On 11/23/11 1:21 PM, Dr. Wolf Ostwald wrote: > hi reflectees ! > I guess i was not specific enough. I was stating that my 2 el broadside > array`s signal with 1/2 spacing must have lower angle of radiation than > my 3 el 1/4 wave spacing in line array. The farther the shot, the more > signal i get and produce with the 2el versus the 3 el in-line array. > East coast is neck to neck, westcoast up to 3 db in favour of the 2 el > half-wave spaced array in broadside config. > Again. i am not talking forward gain at any angle of radiation, i am > talking gain at a specific angle. > 73 de wolf df2py > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: 1/2 wave spacing
But that is Apples to Oranges. Three elements will usually yield more gain than two. Typical broadcast arrays use a combination of the two topologies a two row of three in a line with the second row spaced 180 or so degrees is common in broadcast and yields excellent gain as well as FB ratio. On 11/23/11 12:36 AM, Dr. Wolf Ostwald wrote: > Hi reflectees ! > I currently have the setup to try 3el in line against 2 el halfwave > spaced broadside. I run this comparingly for about two years now and my > findings are : the broadside radiation from 2el /halfwave is lower than > the endfire radiation from 3 el 1/4 spaced. E.g. westcoast USA is > easier to work with my 2el broadside than with 3 el endfire, not by > much, but some 2 dbs on the long hauls is frquently encountered, which > is a lot on 160. This is also commonly described in antenna design books. > Just a short message from the "been there, done that" department :-) > 73 de wolf df2py > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: no response to query: feeding phased verticals at half wave spacing
A wide spaced array offers many benefits when possible. In general the is less coupling between the elements results in better less mutual impedance interdependence. When enough space is available a simple Ham array would be 1/2 wave spaced elements fed from the center point with open wire. This will produce familiar figure 8 pattern where the major lobe is perpendicular to the line of the towers. Basically the energy if equal from both towers will cancel along the line of the towers but since the towers are in phase, points perpendicular, beginning at 45 degrees between the line of the towers will add in phase with the resultant lobe at 90 degrees. If the phasing is 180 degrees the energy will add along the line of the towers and also produce a figure 8 but rotated 90 degrees. A useful unidirectional mode with 180 degree spaced towers is 45 degree phasing which produces a wide forward lobe with deep nulls at an angle to the rear and a 'tail' peaking up at the rear. Towers spaced around 90 degrees produce better cardioid patterns. The ARRL Antenna Handbook goes into pretty detailed explanation of phased arrays and gets into multitower arrays, showing three and four tower designs. I would also suggest EZNEC as good entry modelling software. while with modeling the devil is always in how close to life the modeling details are, simple two towers models play out pretty well with basic models. If I had the space I would consider a 180 deg spaced two tower array with as I mentioned earlier open transmission with 4 positions. The first in the center for normal figure 8 operation, the second a transmission line to either one of the towers to rotate the figure 8 90 degrees and the third and forth to taps in either direction along the TX line to achieve 45 degree phasing for quasi unidirectional operation along the line of the towers in either direction. This would be one of the least expensive arrays that could be built with a minimum parts count. But have 360 deg coverage. On 11/22/11 8:06 PM, Gerry Treas, K8GT wrote: > Hi Dale, > > I'm no antenna expert, but certainly read as much of the experts publications > as I can get my hands on, but having a Teflon brain, it doesn't stick very > well. > > That said, the ARRL Antenna Book has a page that shows the patterns of > various spacings and phasings of vertical antennas, which I found very > enlightening. > > 73, Gerry, K8GT > > > Dale Long wrote: > > = > Gentlemen: > > > > I am not one who thinks the whole world revolves around my concerns. And I > recognize that some research on my part may be necessary. ( I have read > ON4UN's Low-Band Dxing) > > > > But I do think this is a reasonable question, and think that there are > knowledgeable folks who might provide some advice. Unfortunately I have > never done any antenna modeling. > > > > Please let me know your thoughts. > > > > Thanks, > > > > Dale N3BNA > > > > From: Dale Long [mailto:dale.l...@prodigy.net] > Sent: Saturday, November 19, 2011 3:05 PM > To: 'Topband@contesting.com' > Subject: feeding phased verticals at half wave spacing > > > > Gentlemen: > > > > I have been told repeatedly that phased verticals should be spaced 1/4 > wavelength apart. Ok, I am willing to accept that. > > > > My question is if you have verticals that are 1/2 wave apart, would it not > give some pattern, whatever that should be? > > > > If you were looking for an endfire pattern how should you feed such > verticals? > > > > If you have specific questions, you may contact me directly at > dale.l...@prodigy.net > > > > Thanks and 73, > > > > Dale N3BNA > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
