Re: Topband: In search of resonance
Tom> It could be from a few things, but two closely spaced conductors, with the "parasitic" conductor resonant near the target band of the fed conductor, commonly behaves this way. You might never be able to get Inverted L "real part" (resistance part) high at that spacing and length. > There is probably some ideal point where the shunt capacitance is minimized, and that would be best. There are hundreds of points that will work, but they will have higher Q. > I don't know. I've never looked at doing that. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Compromise vertical loading questions
Thanks for all the input received. In short it seems like lifting the coil would not do much difference. Raising/increasing the angle of the top loading spokes might be the better option. Then of course moving the antenna to the water and improving the radials including some going into the water should make the most improvement. Unfortunately I can not move the antenna much more. Putting it on the beach would be hassle as it had to come down every morning and go up again in the evening. To much activity on the beach in daytime :) I will see what I can do with the top loading spokes. The wind has changed today, it might help or it might not. Thanks again for all the input received on the reflector and in private. 73 from the Maldives de Björn, SM0MDG 8Q7BM SE0X On 29 Jan 2014, at 12:47, Björn SM0MDG wrote: > Here are some question for anyone with more tech skills than me; > > My compromise vertical at 8Q7BM is made of thin wire attached to a DX-Wire 15 > meter glass fibre pole. The vertical wire goes all the way up, but as the > pole’s top sections are very thin/weak the three top loading spokes (each 12 > meter long) are attached at about 13 meter. The antenna has a 1/4 elevate > radial towards the water at 2-3 meter height. The whole structure is within > 1/4 wave of the water line. > > The antenna is self resonant at 2.2 MHz and I use a coil wound on a water > bottle to bring it down to 1.8. The coil appears to be about 8-10 uH > according to online calculators. > > My questions are; > > How much I can improve by moving the coil up. What improvement should I > expect if center loading at about 7 meter? How about moving the coil all the > way up to the top loading spokes? Is it worth the effort? (the pole won’t > support much up there). > > My top loading spokes are sloping more than the recommended angle. According > to the ON4UN Low Band book I got the impression that the difference should be > minimal when close to salt water. I have tried to slope them less, but easily > get in trouble with the weak pole in the wind. And there are pats to the > beach every where so options are few. > > Which one of the two above actions would be the most beneficial? Move the > loading coil higher up or rearrange the top loading spokes for a better angle? > > > 73 de Björn, > SM0MDG > 8Q7BM > SE0X > > > > > > > > > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 8Q7BM on Topband
Here is another update from 8Q7BM; Wednesday evening FT5ZM started so I moved away from 23.7 to 33.7. I was calling from about 1430 and on. Heard OH5KW 579 during the evening and logged VK3EW and A45XR. Other than that it was FT5ZM and their weak pileup heard here. On Thursday morning I started well ahead of my SR (at Wed 2315). I heard SM, OH, DL and OM stations around 539 in the FT5ZM pileup, but no luck hooking any of them on 33.7. At 0003 Thursday morning my PSU blew up. Fortunately I brought a spare as I don’t really trust the cheap Asian switch mode supplies. They are handy to carry, but they fail. This is my second of the same brand and model failing. I am now using a small “Gamma HPS-1a” PSU. It is minimalistic and I hope it will take the beating and survives to the end. Thursday evening there was no activity as we were celebrating my girlfriend's birthday with a many course fine dinner at the fancy hangout on the island. On Friday morning I heard LA1MFA call CQ and tried unsuccessfully to get though to him. Back on 33.7 LA1U called me a few minutes later and and got logged at 2335. After this nothing heard and nothing worked until my SR. I will be back tonight again then In my SR tomorrow. Look for me on 1833.7 +/- QRM. 73 de Björn, SM0MDG 8Q7BM SE0X _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
Thanks for this tidbit of information. As soon as this white manure melts (some people call it snow) I will do a re-check on my shunt fed tower. I think I did have at least one dip to zero and never did find a resonance point. Thanks Chet N4FX -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Thursday, January 30, 2014 1:34 PM To: Tree Cc: 160; Carl Braun Subject: Re: Topband: In search of resonance > You might be dealing with AM BCB being detected by the meter - and > masking what you are looking for. > No, because he gets a dip to zero reactance. If that happens anywhere, there is no BCI. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short receiving verticals question
On 01/30/2014 02:42 PM, Joe Subich, W4TV wrote: > A possible answer might be here: > > http://www.legupenterprises.com/ Doesn't faze the deer around here. They come right up to the house and the fenced kennels and munch on whatever they like. That stuff may do something with the small animals but the Eagle, Great Horned Owl, Red Tail Hawk and other birds of prey generally keep the rodents and small mammals in check. 73, ... Joe, W4TV Hi, Coyotes and foxes keep the small critters in check here AND they leave free samples of predator urine, too. 73, Bill KU8H _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short receiving verticals question
> A possible answer might be here: > > http://www.legupenterprises.com/ Doesn't faze the deer around here. They come right up to the house and the fenced kennels and munch on whatever they like. That stuff may do something with the small animals but the Eagle, Great Horned Owl, Red Tail Hawk and other birds of prey generally keep the rodents and small mammals in check. 73, ... Joe, W4TV On 1/30/2014 1:42 PM, Gary Smith wrote: The biggest problem with the top hat is deer catching the wire/string and bending the element or some rodent eating the string. A possible answer might be here: http://www.legupenterprises.com/ They sell predator urine which discourages animals from going near the smell. My YL uses it to keep the squirrels out of her flowers and it works extremely well. I just had my antenna wires clipped by a rabbit over last weekend (saw the tracks in the snow) and I put some coyote urine in a vial the company sells and have that at my radial plate. I'm sure it'll work as well for keeping them away here as it does in her garden. If it would have tried chewing the 160 Inv-L while I was working the contest I might have had a nice supper. Gary KA1J --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Speking of Hardline
I don't know about anyone else's cable company, but when the prices of scrap metal went up a few years ago Comcast emptied out their local scrap yard. Actually, I'm just supposing that's the reason. I got a lot of good stuff there while they were willing to let it go. 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. On 1/30/2014 1:32 PM, Ray Benny wrote: Have you tried the actual cable companies? My local Cableone cable service gave me a spool with about 800 ft on it. At the time, they had probably 6 - 8 spools with odds lengths in their yard, so giving one away was no big deal. Sometimes a case of beer helps make a deal! Ray, N6VR Chino Valley On Thu, Jan 30, 2014 at 11:25 AM, Gary Smith wrote: I've asked the local cable installers if they have any extra hardline & no cigar. I need around 400' of it so Andrews is out of the question. I'd like the 50 ohm line but will probably have to settle for aluminum jacketed 75 ohm line. Any suggestions where else I might look to find something used? 73, Gary KA1J --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short receiving verticals question
At the speeds that deer run across an open field, I doubt that repellant will help. Seven foot fence posts work perfectly, and they will last a lifetime! 73 Frank W3LPL - Original Message - From: "Gary Smith" To: Topband@contesting.com Sent: Thursday, January 30, 2014 6:42:57 PM Subject: Re: Topband: Short receiving verticals question > The biggest problem with the top hat is deer catching > the wire/string and bending the element or some rodent > eating the string. A possible answer might be here: http://www.legupenterprises.com/ They sell predator urine which discourages animals from going near the smell. My YL uses it to keep the squirrels out of her flowers and it works extremely well. I just had my antenna wires clipped by a rabbit over last weekend (saw the tracks in the snow) and I put some coyote urine in a vial the company sells and have that at my radial plate. I'm sure it'll work as well for keeping them away here as it does in her garden. If it would have tried chewing the 160 Inv-L while I was working the contest I might have had a nice supper. Gary KA1J --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short receiving verticals question
> The biggest problem with the top hat is deer catching > the wire/string and bending the element or some rodent > eating the string. A possible answer might be here: http://www.legupenterprises.com/ They sell predator urine which discourages animals from going near the smell. My YL uses it to keep the squirrels out of her flowers and it works extremely well. I just had my antenna wires clipped by a rabbit over last weekend (saw the tracks in the snow) and I put some coyote urine in a vial the company sells and have that at my radial plate. I'm sure it'll work as well for keeping them away here as it does in her garden. If it would have tried chewing the 160 Inv-L while I was working the contest I might have had a nice supper. Gary KA1J --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Speking of Hardline
Good suggestion Ray. When I moved to this QTH was TIGHT... I went to the local Cable Co. and spoke to the line Boss. He gave me all the cable ends I wanted I originally feed my 4 towers with 3/4" 75 ohm Catty hardline. Give'em a try . Wayne W3EA PS I also had permission to clean up there Stump Strand 1/4 EHS with most stumps below 120' worked for me :) as I broke my guys with insulators , > Date: Thu, 30 Jan 2014 11:32:12 -0700 > From: rayn...@cableone.net > To: g...@ka1j.com > CC: topband@contesting.com > Subject: Re: Topband: Speking of Hardline > > Have you tried the actual cable companies? My local Cableone cable service > gave me a spool with about 800 ft on it. At the time, they had probably 6 - > 8 spools with odds lengths in their yard, so giving one away was no big > deal. > > Sometimes a case of beer helps make a deal! > > Ray, > N6VR > Chino Valley > > > On Thu, Jan 30, 2014 at 11:25 AM, Gary Smith wrote: > > > I've asked the local cable installers if they have any extra hardline > > & no cigar. I need around 400' of it so Andrews is out of the > > question. I'd like the 50 ohm line but will probably have to settle > > for aluminum jacketed 75 ohm line. > > > > Any suggestions where else I might look to find something used? > > > > 73, > > > > Gary > > KA1J > > > > --- > > This email is free from viruses and malware because avast! Antivirus > > protection is active. > > http://www.avast.com > > > > _ > > Topband Reflector Archives - http://www.contesting.com/_topband > > > _ > Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Submerging variable caps in oil as substituteforvacuum variables
Very true but the RF is still in the oil "dielectric" from the coax connector to the hot end of the resistor. Not the same at all. Loss tangent is meaningless in the dummy load application because impedance is low (weak electric field). There is very little displacement current compared to current into the resistor. Loss tangent means everything in a capacitor in a coupling or tuning system, because displacement current is as high as or higher than the terminal current. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: oil-submerged variables
I might have some big micas that would work. What value would you need? Gary KA1J > Thanks, everyone. I had not thought about the possible difference > between 600M and 160 in terms of heating. Jon's suggestion of using big > old micas sure seems like a good one if I can find what I need. As a > refugee from the BC-610 era I'm amazed that any are still around! > > -- > 73, Pete N4ZR > Check out the Reverse Beacon Network at > http://reversebeacon.net, > blog at reversebeacon.blogspot.com. > For spots, please go to your favorite > ARC V6 or VE7CC DX cluster node. > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
You might be dealing with AM BCB being detected by the meter - and masking what you are looking for. No, because he gets a dip to zero reactance. If that happens anywhere, there is no BCI. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Speking of Hardline
Have you tried the actual cable companies? My local Cableone cable service gave me a spool with about 800 ft on it. At the time, they had probably 6 - 8 spools with odds lengths in their yard, so giving one away was no big deal. Sometimes a case of beer helps make a deal! Ray, N6VR Chino Valley On Thu, Jan 30, 2014 at 11:25 AM, Gary Smith wrote: > I've asked the local cable installers if they have any extra hardline > & no cigar. I need around 400' of it so Andrews is out of the > question. I'd like the 50 ohm line but will probably have to settle > for aluminum jacketed 75 ohm line. > > Any suggestions where else I might look to find something used? > > 73, > > Gary > KA1J > > --- > This email is free from viruses and malware because avast! Antivirus > protection is active. > http://www.avast.com > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Speking of Hardline
I've asked the local cable installers if they have any extra hardline & no cigar. I need around 400' of it so Andrews is out of the question. I'd like the 50 ohm line but will probably have to settle for aluminum jacketed 75 ohm line. Any suggestions where else I might look to find something used? 73, Gary KA1J --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short receiving verticals question
Hi Doug, A few notes about the short verticals in my 160M passive receive array. I use them in my W8JI broadside-endfire passive array described in detail on Tom's home page and on W5ZN's home page. Its important to understand that the loss in the radial system of a 160M passive receive array is of no importance, but variations in the base impedance of the verticals during wet and dry weather could affect the pattern of the array. You don't need many radials, but you do need "enough." I use eight 65 foot radials under each vertical. Several of my verticals are in wetlands that flood during wet weather and the variation in ground conditions under the verticals is unusually severe. I initially used four radials and found there was nearly ten ohms change in the resistive component of the feed point impedance between flooded conditions and extreme dry ground conditions. Four additional radials solved that problem. My radials are simply laid on the surface of the ground. While the deer traffic rearranges the location of the radials, that doesn't seem the affect the performance of the array. I use stranded copper wire, solid wire would easily entrap the legs of the deer. Dozens of deer inhabit the field where my verticals are located. I eliminated deer collisions with the umbrella wires by attaching the ends of bottom ends of the wires to the top of seven foot fence posts (through a porcelain insulator and short length of light rope). I've never had a deer collision since. While some users of short verticals install foundations, I've found it completely unnecessary with guyed (e.g. top loaded) verticals. I simply use a two foot length of one inch diameter rebar. The vertical is attached to a 1.25 inch o.d. aluminum tube that simply slips over the rebar. Rebar is very inexpensive and easy to install an remove and especially convenient for temporary installations like mine 73 Frank W3LPL - Original Message - From: "Doug Renwick" To: "topband" Sent: Thursday, January 30, 2014 3:04:02 PM Subject: Re: Topband: Short receiving verticals question I have used this same setup for my 4-square 160m receive array for years. Since I have to take down and put up this array every spring/fall, I have to re-tune each element for the 160m band. I have found that the base loading does not have to be exact for the system to 'work'. Last year I decided to make inductor substitution box for each element to easily tune each element close to 1.830 MHz. The biggest problem with the top hat is deer catching the wire/string and bending the element or some rodent eating the string. It's amazing how forgiving aluminum tubing is as I can straighten it many times without breaking. At the base I use a 2 ft ground rod and 4 short radials. I found the use of the ground rod makes a large change in the tuning of the element. Doug -Original Message- Jon, The reason I use the hats and do everything I do in the elements is bandwidth. Even at my quiet rural location on the quietest hour of the quietest day, almost any element of reasonable height will have more than enough signal level. This is why I base load and use a large hat. While the large hat tends to keep current more uniform throughout the element independent of coil location, and while more uniform current increases radiation resistance, that effect is meaningless to me. The entire goal for me is bandwidth, or a stable SWR vs. frequency. Bandwidth is also why I load the element with a series resistance for matching, instead of a network. I want to "swamp out" or dilute the effects of resonance, minimizing element phase shift vs. frequency change at the element terminals and preventing drastic changes in element feedpoint impedance from mutual coupling between elements. The hat is actually the bulk of the loading, and sets the current distribution. The coil just cancels reactance. Since it is a series network with the inductor forming a series tank with the termination reactance, the lower the reactance used (compared to termination resistance) the larger bandwidth becomes. You want the loading coil to be terminated in the lowest capacitive reactance possible, and that is at the antenna base. Because voltage and current are out-of-phase above the coil, even with high current, the impedance increases. This means the tradeoff in a bottom inductance is increased voltage above the inductor. The antenna is more "loss critical" above the coil for anything coupled via the electric field, including a lossy dielectric. This is a compromise of two things: 1.) Bandwidth 2.) Sensitivity to dielectrics around the element Getting rid of the hat while the element is close to a tree does nothing but bad things to both, but no one can say how much. The last resort for me would be no "hats". Perhaps you can use T elements with loading wires away from foliage that might change tuning
Topband: Topban: FT5ZM
I managed to work RI4ANF last fall with 100W and a hastily strung 90' EFW (w/essentially no RF ground), no part of which was hung higher than 15' off the deck. I can't imagine anything more NVIS than that. Mark -- WA9ETW > -- > > > > Some of my best Antarctic area contacts have been with a horizontal antenna > and the very best had the apex at only 50' and the end at 3blew the > pileup away with one call and was told later at Dayton I was at least 10dB > above the 10 KHz+ of callers. Not bad for a fast installed antenna at the > new home and 1200W. > > Ducting via NVIS? > > Carl > KM1H > > > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
You might be dealing with AM BCB being detected by the meter - and masking what you are looking for. On Thu, Jan 30, 2014 at 9:14 AM, Tom W8JI wrote: > I cannot get the inverted L to provide a dip on my MFJ 259 analyzer > anywhere in the 160 meter band. I get dips at 8.2 MHz (R=36 ohms X=0) with > reactance on each side of X=0. At 5 MHz R=40 ohms X=0 with reactance on > each side of X=0. I cant get any significant dips neat the 80 or 160 band. > However, when I approach 1.750MHz the resistance drops to 6 ohms and X is > off the scale...at 1.825 I'm at 10 ohms and X is off the scale. Its as if > my 140+ feet of wire is resonant on 8MHz.>>> > > Given you have dips on 8.2 and 5 MHz, the MFJ is working normally. > > With the tower so close to the Inverted L they are like one big coupled > system. I expect the "system" is resonant in the AM BCB, and that is why > you cannot find the low dip. > > I would look for resonance around 5MHz / 3 and or at 8.2MHz /5 MHz. So > look around 1650 kHz or. > > Another way to find the base frequency for Marconi resonance when a system > is out of band is to subtract the closest two dips and divide by two. (This > is what I use in the MFJ 259 firmware to find distance to fault.) > > 8.2 MHz - 5 MHz = 3.2 > > 3.2 / 2 = 1.6 > > So you have two different methods pointing to 1.6 MHz as the resonance. > This tells me your combination antenna is on 1.6 MHz. > It might not move like you think because the tower is fixed at a certain > frequency, and probably well down in the BCB, but you can try making length > 1.6/1.8 = .889 times what the L is now, or 129 ft. I wouldn't expect it to > move perfectly, but it should move. > > ***Ignore trying to determine resonance with a shunt wire. You are wasting > time, because that is a complex system. A shunt system consists of a > transmission line stub mode plus a common mode resonance, so you see the > combination of the two effects. It will NOT tell you where the tower is. *** > > > > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
I cannot get the inverted L to provide a dip on my MFJ 259 analyzer anywhere in the 160 meter band. I get dips at 8.2 MHz (R=36 ohms X=0) with reactance on each side of X=0. At 5 MHz R=40 ohms X=0 with reactance on each side of X=0. I cant get any significant dips neat the 80 or 160 band. However, when I approach 1.750MHz the resistance drops to 6 ohms and X is off the scale...at 1.825 I'm at 10 ohms and X is off the scale. Its as if my 140+ feet of wire is resonant on 8MHz.>>> Given you have dips on 8.2 and 5 MHz, the MFJ is working normally. With the tower so close to the Inverted L they are like one big coupled system. I expect the "system" is resonant in the AM BCB, and that is why you cannot find the low dip. I would look for resonance around 5MHz / 3 and or at 8.2MHz /5 MHz. So look around 1650 kHz or. Another way to find the base frequency for Marconi resonance when a system is out of band is to subtract the closest two dips and divide by two. (This is what I use in the MFJ 259 firmware to find distance to fault.) 8.2 MHz - 5 MHz = 3.2 3.2 / 2 = 1.6 So you have two different methods pointing to 1.6 MHz as the resonance. This tells me your combination antenna is on 1.6 MHz. It might not move like you think because the tower is fixed at a certain frequency, and probably well down in the BCB, but you can try making length 1.6/1.8 = .889 times what the L is now, or 129 ft. I wouldn't expect it to move perfectly, but it should move. ***Ignore trying to determine resonance with a shunt wire. You are wasting time, because that is a complex system. A shunt system consists of a transmission line stub mode plus a common mode resonance, so you see the combination of the two effects. It will NOT tell you where the tower is. *** _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Not seeing your posts?
I have been getting emails from KV4FZ talking about not being able to post to the list. Emails directly to him are bouncing. I will try this channel as the message applies to a few others who are having the same issue. If your email does not show up here right away - the most likely reason is that you are sending your email from an email address that does not match the one you are subscribed to the list as. In order to eliminate spam - you must use the same address for both. For example, if you have subscribed to the list as yourc...@arrl.net - messages from the list will get forwarded to you - but when you send a post from something like yourc...@gmail.com - it will not match up and your post will end up in the moderator pile. Depending on when I check that pile - it might take some time for your message to show up. There are some people who have demonstrated that their messages need to be moderated at all times and they end up in that pile as well. So - if you are not seeing your messages show up right away - I would suggest resubscribing to the list with your current email. If you then start seeing two messages for every post - you will need to delete the old one (I can help you with that if necessary). 73 Tree N6TR (currently enjoying the weather in Atlanta) _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Bad tower shunt capacitor
Jon: Thanks for this. This has crossed my mind since I use hose clamps to attach the wire from the top and bottom of the caps. I had used copper flashing between the two caps. I'll change that to a heavy insulated wire. Get out the NoAlOx too. :) Thanks again. 73, Jamie WB4YDL -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Jon Zaimes AA1K Sent: Thursday, January 30, 2014 3:21 AM To: James C. Hall, MD; topband@contesting.com Subject: Re: Topband: Bad tower shunt capacitor Look closely and you may see a hairline crack on the bad one. Also look for other possibilities. A number of times I've swapped out "bad" matching capacitors without solving the problem, only to find later it was simply an oxidized connection that needed to be cleaned up and tightened down. 73/Jon AA1K On 1/29/2014 7:26 PM, James C. Hall, MD wrote: > I have an omega matched 120 foot tower and I apparently have a bad vacuum variable capacitor. Upon applying more than about 300 watts, the SWR goes off scale. Tuning it out and trying again, yields the same thing. > > The question is which capacitor is the culprit. These are surplus Soviet caps obtained from the Ukraine and, as I recall, the larger value capacitor is the parallel one, not the series one. I could buy one of each and switch one at a time and have a spare left over. Any suggestions ? > > 73, Jamie > WB4YDL > > Sent from my iPad > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Submerging variable caps in oil as substituteforvacuum variables
That uses the thermal properties outside a resistor, not dielectric constant properties in a capacitor :-). Tim N3QE - Original Message - From: ZR [mailto:z...@jeremy.mv.com] Sent: Thursday, January 30, 2014 11:28 AM To: Tom W8JI ; HAROLD SMITH JR ; Shoppa, Tim; n...@contesting.com ; topband@contesting.com Subject: Re: Topband: Submerging variable caps in oil as substituteforvacuum variables The large Bird dummy loads use oil up into the low microwave region. Carl KM1H - Original Message - From: "Tom W8JI" To: "HAROLD SMITH JR" ; "Shoppa, Tim" ; ; Sent: Thursday, January 30, 2014 5:32 AM Subject: Re: Topband: Submerging variable caps in oil as substituteforvacuum variables > Still I am intrigued by the thought of a remote tuning capacitor via > hydraulic tubing :-). The capacitor plates could be as simple as two > concentric cylinder conductors with appropriate spacers. I betcha crud > collecting on the top of the oil would set voltage limit.>>> > > I would be as concerned, or more concerned, with the dissipation factor of > the oil at short wave frequencies. > > The thing that worries me is I cannot recall every seeing a single good > high-Q oil-dielectric capacitor above power line and audio frequencies. As > a matter of fact, many years ago I tried to use a surplus 20-40kV oil > capacitor from Fair Radio as a plate blocking capacitor, and it overheated > so badly it exploded. > > I looked for HF data on mineral oil as a dielectric and couldn't find > anything. That would be my main concern. I guess I could stick mineral oil > between the plates of a capacitor and see what happens to Q. > > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > > > - > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2014.0.4259 / Virus Database: 3684/7045 - Release Date: 01/30/14 > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short receiving verticals question
Ok Frank I will forward this to the Topband reflector. Bernie McClenny, W3UR Editor of The Daily DX and The Weekly DX www.dailydx.com 410-489-6518 Sent from my iPhone On Jan 30, 2014, at 10:56, donov...@starpower.net wrote: Hi Burny, When you have a chance, please forward this email to the Topband reflector. For some reason its spam filter is blocking emails from me! tks Frank From: donov...@starpower.net To: topband@contesting.com Sent: Thursday, January 30, 2014 3:52:24 PM Subject: Re: Topband: Short receiving verticals question Hi Doug, A few notes about the short verticals in my 160M passive receive array. I use them in my W8JI broadside-endfire passive array described in detail on Tom's home page and on W5ZN's home page. Its important to understand that the loss in the radial system of a 160M passive receive array is of no importance, but variations in the base impedance of the verticals during wet and dry weather could affect the pattern of the array. You don't need many radials, but you do need "enough." I use eight 65 foot radials under each vertical. Several of my verticals are in wetlands that flood during wet weather and the variation in ground conditions under the verticals is unusually severe. I initially used four radials and found there was nearly ten ohms change in the resistive component of the feed point impedance between flooded conditions and extreme dry ground conditions. Four additional radials solved that problem. My radials are simply laid on the surface of the ground. While the deer traffic rearranges the location of the radials, that doesn't seem the affect the performance of the array. I use stranded copper wire, solid wire would easily entrap the legs of the deer. Dozens of deer inhabit the field where my verticals are located. I eliminated deer collisions with the umbrella wires by attaching the ends of bottom ends of the wires to the top of seven foot fence posts (through a porcelain insulator and short length of light rope). I've never had a deer collision since. While some users of short verticals install foundations, I've found it completely unnecessary with guyed (e.g. top loaded) verticals. I simply use a two foot length of one inch diameter rebar. The vertical is attached to a 1.25 inch o.d. aluminum tube that simply slips over the rebar. Rebar is very inexpensive and easy to install an remove and especially convenient for temporary installations like mine 73 Frank W3LPL From: "Doug Renwick" To: "topband" Sent: Thursday, January 30, 2014 3:04:02 PM Subject: Re: Topband: Short receiving verticals question I have used this same setup for my 4-square 160m receive array for years. Since I have to take down and put up this array every spring/fall, I have to re-tune each element for the 160m band. I have found that the base loading does not have to be exact for the system to 'work'. Last year I decided to make inductor substitution box for each element to easily tune each element close to 1.830 MHz. The biggest problem with the top hat is deer catching the wire/string and bending the element or some rodent eating the string. It's amazing how forgiving aluminum tubing is as I can straighten it many times without breaking. At the base I use a 2 ft ground rod and 4 short radials. I found the use of the ground rod makes a large change in the tuning of the element. Doug -Original Message- Jon, The reason I use the hats and do everything I do in the elements is bandwidth. Even at my quiet rural location on the quietest hour of the quietest day, almost any element of reasonable height will have more than enough signal level. This is why I base load and use a large hat. While the large hat tends to keep current more uniform throughout the element independent of coil location, and while more uniform current increases radiation resistance, that effect is meaningless to me. The entire goal for me is bandwidth, or a stable SWR vs. frequency. Bandwidth is also why I load the element with a series resistance for matching, instead of a network. I want to "swamp out" or dilute the effects of resonance, minimizing element phase shift vs. frequency change at the element terminals and preventing drastic changes in element feedpoint impedance from mutual coupling between elements. The hat is actually the bulk of the loading, and sets the current distribution. The coil just cancels reactance. Since it is a series network with the inductor forming a series tank with the termination reactance, the lower the reactance used (compared to termination resistance) the larger bandwidth becomes. You want the loading coil to be terminated in the lowest capacitive reactance possible, and that is at the antenna base. Because voltage and current are out-of-phase above the coil, even with high current, the impedance increases. This means the tradeoff in a bottom inductance is increased voltage above the inductor. The a
Topband: In search of resonance
Hello to the group I'm a newbie to 160 having only participated in various contests over the course of the last two years. I used an 80 meter aluminum tube vertical with a Reyco trap affixed to the top with a horizontal "L: wire heading over to the palm tree. I've since converted that antenna into a pair of 40M verticals so I'm focusing my efforts on getting a resonant antenna on 60 and especially 160. Here's the hardware I'm working with... 90' Tri Ex Skyneedle tower with a Telrex 20 meter 5-element yagi on a 45' boom at 94'. Inverted L wire runs parallel to the tower and is spaced at 36" up to 85' and then out approx 60' or so. The tower is grounded via copper strap to three ground rods that are bonded to 1 ½" copper pipe that circles the perimeter of my tower and control panel base. The perimeter copper pipe is a 4' x 8' rectangle that currently has 16 radials screwed to it. Three of those radials are tied into my 40M phased array ground radial system with some of the radials as short as 30' and others as long as 100'. The ground screen for my 40M array uses 100 radials each 60-90' long. I'm adding radials as I have time. Half of the 16 radials are multi conductor rotor control cable that fans out to affix to the radial ring then converge back together for 10' across the driveway and then fan out. I do this to eliminate a lot of individual wires crossing my secondary driveway. I cannot get the inverted L to provide a dip on my MFJ 259 analyzer anywhere in the 160 meter band. I get dips at 8.2 MHz (R=36 ohms X=0) with reactance on each side of X=0. At 5 MHz R=40 ohms X=0 with reactance on each side of X=0. I cant get any significant dips neat the 80 or 160 band. However, when I approach 1.750MHz the resistance drops to 6 ohms and X is off the scale...at 1.825 I'm at 10 ohms and X is off the scale. Its as if my 140+ feet of wire is resonant on 8MHz. Also, I've experimented with shunt feeding the tower to see where the thing would resonate but got similar results. ON4UN says my 90' tower and 5 ele yagi should yield an antenna that is 110 to 115 degrees in total length so I followed his guidelines and tapped the tower at 67' with a gamma wire spaced at 36" . The tower had multiple dips at 27 MHz, 20 MHz, 14 MHz and at 7.5 MHz the resistance dropped to 6 ohms...the same low resistance I' m now seeing on the L at 1.750 or so. No dips were observed at 3.5 or 1.8 MHz. I plan to experiment with a gamma wire that goes all the way to the top of the tower to see where it resonates...if its still high in freq maybe I should consider an Omega match So all of that being said...why cant I find a resonant frequency on 160 with this L? Am I still too long? Is the tower causing that much interaction? I'd rather not cut the L long and insert a variable cap...I want it resonant at 1820 so I can use an unun to match the impedance and then run it into the shack. Any suggestions on getting the antenna to work? Thanks in advance for any help Carl AG6X _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Bad tower shunt capacitor
Wouldn't 1 5/8 hardline make a better HV RF capacitor? Herb, KV4FZ On 1/29/2014 11:34 PM, HAROLD SMITH JR wrote: Jamie, The VSWR would change because the arc would change the impedance at the Arc point. From perhaps several hundred or thousand ohms to near Zero during the Arc.. 73, Price W0RI Thanks Steve: Not bad - I may try that ! :) The question in my mind was if there was an arc outside the caps, why would the SWR change ? Anyway, I may be missing something. I haven't been inside the cap box at the tower for many months so I'll get into it - may be something easy. 73, Jamie WB4YDL Sent from my iPad On Jan 29, 2014, at 7:11 PM, wb6r...@mac.com wrote: Have someone hit the key while you watch which one flashes over. Steve WB6RSE _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: FT5ZM
Some of my best Antarctic area contacts have been with a horizontal antenna and the very best had the apex at only 50' and the end at 3blew the pileup away with one call and was told later at Dayton I was at least 10dB above the 10 KHz+ of callers. Not bad for a fast installed antenna at the new home and 1200W. Ducting via NVIS? Carl KM1H - Original Message - From: "Milt -- N5IA" To: Sent: Monday, January 27, 2014 9:26 AM Subject: Topband: FT5ZM He was first discernable here at 1350. In the log at 1400. It is now 1422 and he is fading with my sunrise. The signals peaked at S3 on the Beverages for about 20 minutes, but was good copy on ALL 16 Beverages. This indicates a VERY HIGH arrival angle here near the Amsterdam antipode. He was good copy (S1) on a full wavelength horizontal loop just 10 feet AGL. He is now working northern Scandinavian station as well as NA west coast as he fades away. Still 449 at 1427. 73, and good luck to all. de Milt, N5IA - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4259 / Virus Database: 3681/7035 - Release Date: 01/26/14 _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4259 / Virus Database: 3681/7037 - Release Date: 01/27/14 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short receiving verticals question
I have used this same setup for my 4-square 160m receive array for years. Since I have to take down and put up this array every spring/fall, I have to re-tune each element for the 160m band. I have found that the base loading does not have to be exact for the system to 'work'. Last year I decided to make inductor substitution box for each element to easily tune each element close to 1.830 MHz. The biggest problem with the top hat is deer catching the wire/string and bending the element or some rodent eating the string. It's amazing how forgiving aluminum tubing is as I can straighten it many times without breaking. At the base I use a 2 ft ground rod and 4 short radials. I found the use of the ground rod makes a large change in the tuning of the element. Doug -Original Message- Jon, The reason I use the hats and do everything I do in the elements is bandwidth. Even at my quiet rural location on the quietest hour of the quietest day, almost any element of reasonable height will have more than enough signal level. This is why I base load and use a large hat. While the large hat tends to keep current more uniform throughout the element independent of coil location, and while more uniform current increases radiation resistance, that effect is meaningless to me. The entire goal for me is bandwidth, or a stable SWR vs. frequency. Bandwidth is also why I load the element with a series resistance for matching, instead of a network. I want to "swamp out" or dilute the effects of resonance, minimizing element phase shift vs. frequency change at the element terminals and preventing drastic changes in element feedpoint impedance from mutual coupling between elements. The hat is actually the bulk of the loading, and sets the current distribution. The coil just cancels reactance. Since it is a series network with the inductor forming a series tank with the termination reactance, the lower the reactance used (compared to termination resistance) the larger bandwidth becomes. You want the loading coil to be terminated in the lowest capacitive reactance possible, and that is at the antenna base. Because voltage and current are out-of-phase above the coil, even with high current, the impedance increases. This means the tradeoff in a bottom inductance is increased voltage above the inductor. The antenna is more "loss critical" above the coil for anything coupled via the electric field, including a lossy dielectric. This is a compromise of two things: 1.) Bandwidth 2.) Sensitivity to dielectrics around the element Getting rid of the hat while the element is close to a tree does nothing but bad things to both, but no one can say how much. The last resort for me would be no "hats". Perhaps you can use T elements with loading wires away from foliage that might change tuning or losses? 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: oil-submerged variables
Thanks, everyone. I had not thought about the possible difference between 600M and 160 in terms of heating. Jon's suggestion of using big old micas sure seems like a good one if I can find what I need. As a refugee from the BC-610 era I'm amazed that any are still around! -- 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Submerging variable caps in oil as substitute forvacuum variables
Still I am intrigued by the thought of a remote tuning capacitor via hydraulic tubing :-). The capacitor plates could be as simple as two concentric cylinder conductors with appropriate spacers. I betcha crud collecting on the top of the oil would set voltage limit.>>> I would be as concerned, or more concerned, with the dissipation factor of the oil at short wave frequencies. The thing that worries me is I cannot recall every seeing a single good high-Q oil-dielectric capacitor above power line and audio frequencies. As a matter of fact, many years ago I tried to use a surplus 20-40kV oil capacitor from Fair Radio as a plate blocking capacitor, and it overheated so badly it exploded. I looked for HF data on mineral oil as a dielectric and couldn't find anything. That would be my main concern. I guess I could stick mineral oil between the plates of a capacitor and see what happens to Q. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short receiving verticals question
But what about an element loaded with a coil at the center or at the top? Would there be advantages to that approach that would come close to the short verticals with top-hat wires, or any serious disadvantages? Jon, The reason I use the hats and do everything I do in the elements is bandwidth. Even at my quiet rural location on the quietest hour of the quietest day, almost any element of reasonable height will have more than enough signal level. This is why I base load and use a large hat. While the large hat tends to keep current more uniform throughout the element independent of coil location, and while more uniform current increases radiation resistance, that effect is meaningless to me. The entire goal for me is bandwidth, or a stable SWR vs. frequency. Bandwidth is also why I load the element with a series resistance for matching, instead of a network. I want to "swamp out" or dilute the effects of resonance, minimizing element phase shift vs. frequency change at the element terminals and preventing drastic changes in element feedpoint impedance from mutual coupling between elements. The hat is actually the bulk of the loading, and sets the current distribution. The coil just cancels reactance. Since it is a series network with the inductor forming a series tank with the termination reactance, the lower the reactance used (compared to termination resistance) the larger bandwidth becomes. You want the loading coil to be terminated in the lowest capacitive reactance possible, and that is at the antenna base. Because voltage and current are out-of-phase above the coil, even with high current, the impedance increases. This means the tradeoff in a bottom inductance is increased voltage above the inductor. The antenna is more "loss critical" above the coil for anything coupled via the electric field, including a lossy dielectric. This is a compromise of two things: 1.) Bandwidth 2.) Sensitivity to dielectrics around the element Getting rid of the hat while the element is close to a tree does nothing but bad things to both, but no one can say how much. The last resort for me would be no "hats". Perhaps you can use T elements with loading wires away from foliage that might change tuning or losses? 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Bad tower shunt capacitor
Jamie, When I had a problem like that on a matching system, I had someone else key the transmitter and watched the feedpoint at night. It took ten seconds to see the problem ! Fireworks had nothing on what happened. 73 Don, G3BJ / G5W -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of James C. Hall, MD Sent: 30 January 2014 00:27 To: topband@contesting.com Subject: Topband: Bad tower shunt capacitor I have an omega matched 120 foot tower and I apparently have a bad vacuum variable capacitor. Upon applying more than about 300 watts, the SWR goes off scale. Tuning it out and trying again, yields the same thing. The question is which capacitor is the culprit. These are surplus Soviet caps obtained from the Ukraine and, as I recall, the larger value capacitor is the parallel one, not the series one. I could buy one of each and switch one at a time and have a spare left over. Any suggestions ? 73, Jamie WB4YDL Sent from my iPad _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Bad tower shunt capacitor
Look closely and you may see a hairline crack on the bad one. Also look for other possibilities. A number of times I've swapped out "bad" matching capacitors without solving the problem, only to find later it was simply an oxidized connection that needed to be cleaned up and tightened down. 73/Jon AA1K On 1/29/2014 7:26 PM, James C. Hall, MD wrote: I have an omega matched 120 foot tower and I apparently have a bad vacuum variable capacitor. Upon applying more than about 300 watts, the SWR goes off scale. Tuning it out and trying again, yields the same thing. The question is which capacitor is the culprit. These are surplus Soviet caps obtained from the Ukraine and, as I recall, the larger value capacitor is the parallel one, not the series one. I could buy one of each and switch one at a time and have a spare left over. Any suggestions ? 73, Jamie WB4YDL Sent from my iPad _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
