Re: Topband: Receiving loops
Thanks. I wasn't referring to a magnetic loop that uses the shield for pickup. I was referring to the outer shield on the coax that runs from any antenna to the shack. If you use an antenna that was chosen for its specific directional and/or low-noise properties, and you don't isolate that antenna from the outer shield of the feedline, the shield itself becomes part of the antenna, spoils the directionality and picks up additional noise. Art DelibertKB3FJO Not necessarily. If the antenna is properly balanced, or properly unbalanced, that should be all the isolation necessary. Beverages are sensitive to common mode because people use autotransformers, or share a common shield and antenna ground, and the antenna almost always has a poor ground. So the antenna is nether balanced, no unbalanced, but is somewhere between and the shield has a connection to the antenna's ground. A small loop, if properly built, should be immune to common mode on the feeder. It is also more difficult to fix a problem in loop design by throwing beads on a cable, because loop common mode impedance is so high the beads are a tiny part of the CM system impedance. Adding a ground rod at the antenna, where the cable comes vertically to the earth, would probably be more effective with a small loop than beads. I never have needed additional isolation on a small loop, but I've never gapped the loop at the wrong place, or built a poorly balanced loop. PS Why do my posts take so long to appear on the reflector? Is this normal? 73 Tom ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: full wave horiz loop
have a 70 foot per side, elevation aprox 25 ft, corner supports only, 12 Ga solid copper, fed at the corner with open wire all the way to johnson match box here in shack for 80mtrs...works GREAT on 75/80, 40, 30,( on 20 and up- too many little lobes begin ..)it really is on the edge of my lot/ corners in rear set back in front. no way to really know till ya try it and see...my guess it should work..proof is in actual use... Renée, K6FSB W2XJ wrote: 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 ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Topband: Beverage Antennas Trees
I am preparing to install a reversible Beverage antenna, using 450 Ohm ladderline. All of the components are from DX Engineering. The maximum length I could fit on my property was 480ft. This would be the first of my receive antennas for my first venture into 160 and 80M. Here is my concern. To fit an antenna of that length, oriented in a N-E or S-W direction, it will have to go through a think grove of trees (many are over 75ft high) and an even thicker underbrush of younger trees and junk growth. Despite all of the trees, I think I can keep it pretty much in a straight line. How significant will the attenuation be caused by all of the branches and leaves? Thanks for your help to a newcomer to your band. Wayne, KK6BT ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Beverage Antennas Trees
Wayne, That's what mine does with the same components. Works fine. Les W2LK On 6/18/2012 2:45 PM, Wayne Willenberg wrote: I am preparing to install a reversible Beverage antenna, using 450 Ohm ladderline. All of the components are from DX Engineering. The maximum length I could fit on my property was 480ft. This would be the first of my receive antennas for my first venture into 160 and 80M. Here is my concern. To fit an antenna of that length, oriented in a N-E or S-W direction, it will have to go through a think grove of trees (many are over 75ft high) and an even thicker underbrush of younger trees and junk growth. Despite all of the trees, I think I can keep it pretty much in a straight line. How significant will the attenuation be caused by all of the branches and leaves? Thanks for your help to a newcomer to your band. Wayne, KK6BT ___ UR RST IS ... ... ..9 QSB QSB - hw? BK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Beverage Antennas Trees
Mine are installed thru the woods and I spent considerable time trimming out low growth plus interfering branches. The path doesnt deviate over a feet in order to pass to the side of trees and I had to reroute a few when I discovered my eyeball and compass werent in agreement! Nobody ever said it was easy but the end results are good with excellent patterns and noise reduction. The 2 wire reversible Beverages are mounted to trees using electric fence insulators found locally in bags of 25 at a feed and grain/pets/horsey set shop. Carl KM1H - Original Message - From: Wayne Willenberg wewill...@gmail.com To: Topband@contesting.com Sent: Monday, June 18, 2012 2:45 PM Subject: Topband: Beverage Antennas Trees I am preparing to install a reversible Beverage antenna, using 450 Ohm ladderline. All of the components are from DX Engineering. The maximum length I could fit on my property was 480ft. This would be the first of my receive antennas for my first venture into 160 and 80M. Here is my concern. To fit an antenna of that length, oriented in a N-E or S-W direction, it will have to go through a think grove of trees (many are over 75ft high) and an even thicker underbrush of younger trees and junk growth. Despite all of the trees, I think I can keep it pretty much in a straight line. How significant will the attenuation be caused by all of the branches and leaves? Thanks for your help to a newcomer to your band. Wayne, KK6BT ___ 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: 2433/5081 - Release Date: 06/20/12 ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: TX ANT TO RX ANT COUPLING
Hi Jim,
I just use a simple SPST open frame relay to ground the vertical section of the
antenna and no I do not use QSK ... yet ... (need to add it to the old amp)
The vertical section is about 60’ and the rest is horizontal at about 80’ up.
Yes, I have been very pleased with this for this lot. I have thought about the
flag antennas (Waller) and the Hi-Z antennas for rx and will experiment with
that in the future. Oh yes, I have a relay that grounds the feed on the K9AY
loop during transmit as to not get too much signal into the front end of the
rig (K3).
Just let the DX know you are in NM and they will come calling :) I grew up in
Hobbs, NM and it worked.
73, Mike
From: Jim Koshmider
Sent: Monday, June 18, 2012 12:09 PM
To: mikefur...@att.net
Subject: Re: Topband: TX ANT TO RX ANT COUPLING
Outstanding job, Mike...!
It's encouraging to hear about your successes. Your results are amazing.
I have a similar situation here, in Albuquerque, and am in the process of
setting up my Inverted L - essentially the same way as yours. I tried a
different configuration, using a shorter vertical component of the L (only
about 33 feet tall), but I am convinced that having a taller vertical component
(about 44 feet tall) will give me a better low-angle signal. Since I don't
have the benefit of having tall pines in my yard, the horizontal part of my L
will droop down to about 25 feet at the end. Still that's not too much of a
handicap.
About your relay for grounding your transmit antenna... do you use a
vacuum relay? { If you don't use QSK, I suppose a typical latching relay would
work just as well. }
I'm sure glad you commented on this issue. I was beginning to wonder if
I would ever be able to work outside the continental US on 160! (Ha!)
73, and best DX,
Jim, K8OZ
--- On Mon, 6/18/12, mikefur...@att.net mikefur...@att.net wrote:
From: mikefur...@att.net mikefur...@att.net
Subject: Re: Topband: TX ANT TO RX ANT COUPLING
To: topband@contesting.com
Date: Monday, June 18, 2012, 8:34 AM
I perhaps have maybe a worst case scenario ... I live on a 60' by 90'
lot in
Houston. Fortunately I have some very nice tall pine trees that support
my
inverted L. It has one elevated radial in the shape of an L about 20'
above
the ground and the antenna is fed through a current balun. One leg of
my
K9AY loop is within 6' of the elevated radial and 40' from the antenna.
Yes,
I get significant noise transferred from the transmit antenna to the
K9AY
loop on receive. As per ON4UN's book, he suggests to ground the TX
antenna
during receive and I set up a relay to do such and as a result, there
is a
significant decrease in the received noise from the loop. The power
line in
my area is underground, underneath and parallel for some distance with
that
radial.
Just what I have managed to do here and have worked 155 countries with
600
W.
73, Mike WA5POK
-Original Message-
From: W2PM
Sent: Monday, June 18, 2012 5:50 AM
To: Bill and Liz
Cc: wlmailhtml:/mc/compose?to=topband@contesting.com
Subject: Re: Topband: TX ANT TO RX ANT COUPLING
Do you have much noise in the first place to reradiate? Line noise also
is
very spotty along a power line - along the same line of wires any nasty
arcing noise can be very strong or very weak at certain spots so the
noise
level - if you have noise - may not be strong enough to reradiate with
any
affect.
Sent from my iPad
On Jun 17, 2012, at 17:34, Bill and Liz
wlmailhtml:/mc/compose?to=ma...@isp.ca 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.
Re: Topband: TX ANT TO RX ANT COUPLING
There are two potential problems with this. As general rules:
1.) Grounding any antenna which is dependent on a ground system to be
resonant will maximize reradiation.
2.) Resonant elevated radials, even without an antenna connected, are
resonant and re-radiate.
3.) Things that are not resonant can still re-radiate.
To minimize coupling from a resonant radial, the radial has to be
disconnected from ground and from other radials.
Different systems can be different, and in some cases re-radiation can
actually cause a null that reduces noise, but the general rule is
self-resonant antennas with a ground (Marconi), or nearly self-resonant
antennas when grounded, should be floated. Other antennas can be terminated
in an inductor, capacitor, or opened, depending on the system.
My 220 ft insulated tower, in the center of a four square, is opened by
shorting a specific length of coax to the L matching network. It has much
more radiation when open or grounded. radiation is minimal when detuned by a
proper impedance.
73 Tom
- Original Message -
From: mikefur...@att.net
To: Jim Koshmider k8...@yahoo.com; topband@contesting.com
Sent: Wednesday, June 20, 2012 1:06 PM
Subject: Re: Topband: TX ANT TO RX ANT COUPLING
Hi Jim,
I just use a simple SPST open frame relay to ground the vertical section
of the antenna and no I do not use QSK ... yet ... (need to add it to the
old amp) The vertical section is about 60’ and the rest is horizontal at
about 80’ up. Yes, I have been very pleased with this for this lot. I have
thought about the flag antennas (Waller) and the Hi-Z antennas for rx and
will experiment with that in the future. Oh yes, I have a relay that
grounds the feed on the K9AY loop during transmit as to not get too much
signal into the front end of the rig (K3).
Just let the DX know you are in NM and they will come calling :) I grew
up in Hobbs, NM and it worked.
73, Mike
From: Jim Koshmider
Sent: Monday, June 18, 2012 12:09 PM
To: mikefur...@att.net
Subject: Re: Topband: TX ANT TO RX ANT COUPLING
Outstanding job, Mike...!
It's encouraging to hear about your successes. Your results are
amazing.
I have a similar situation here, in Albuquerque, and am in the
process of setting up my Inverted L - essentially the same way as yours.
I tried a different configuration, using a shorter vertical component of
the L (only about 33 feet tall), but I am convinced that having a taller
vertical component (about 44 feet tall) will give me a better low-angle
signal. Since I don't have the benefit of having tall pines in my yard,
the horizontal part of my L will droop down to about 25 feet at the end.
Still that's not too much of a handicap.
About your relay for grounding your transmit antenna... do you use a
vacuum relay? { If you don't use QSK, I suppose a typical latching relay
would work just as well. }
I'm sure glad you commented on this issue. I was beginning to wonder
if I would ever be able to work outside the continental US on 160! (Ha!)
73, and best DX,
Jim, K8OZ
--- On Mon, 6/18/12, mikefur...@att.net mikefur...@att.net wrote:
From: mikefur...@att.net mikefur...@att.net
Subject: Re: Topband: TX ANT TO RX ANT COUPLING
To: topband@contesting.com
Date: Monday, June 18, 2012, 8:34 AM
I perhaps have maybe a worst case scenario ... I live on a 60' by
90' lot in
Houston. Fortunately I have some very nice tall pine trees that
support my
inverted L. It has one elevated radial in the shape of an L about
20' above
the ground and the antenna is fed through a current balun. One leg
of my
K9AY loop is within 6' of the elevated radial and 40' from the
antenna. Yes,
I get significant noise transferred from the transmit antenna to
the K9AY
loop on receive. As per ON4UN's book, he suggests to ground the TX
antenna
during receive and I set up a relay to do such and as a result,
there is a
significant decrease in the received noise from the loop. The power
line in
my area is underground, underneath and parallel for some distance
with that
radial.
Just what I have managed to do here and have worked 155 countries
with 600
W.
73, Mike WA5POK
-Original Message-
From: W2PM
Sent: Monday, June 18, 2012 5:50 AM
To: Bill and Liz
Cc: wlmailhtml:/mc/compose?to=topband@contesting.com
Subject: Re: Topband: TX ANT TO RX ANT COUPLING
Do you have much noise in the first place to reradiate? Line noise
also is
very spotty along a power line - along the same line of wires any
nasty
arcing noise can be very strong or very weak at certain spots so
the noise
level - if you have noise - may not be strong enough to reradiate
with any
affect.
Re: Topband: TX ANT TO RX ANT COUPLING
Tom, This is not encouraging news for those of us with towers already ground and are either shunt fed or cage fed. Even though they are not resonate, although top loaded and approaching resonance, it seems that even with some elaborate decoupling arrangements, and I hope I am wrong, not to much can be gained by even trying to get them detuned. This is crucial for me to know, and I would assume many others that have Beverage terminations or feed points 100 feet away, Thanks for the warning as this summer I was going to install a HV relay on the shunt cage to groundbut as you point out it may not help as the grounded shunt or cage fed tower is already a noise source for close proximity RX antennas. On 6/20/2012 2:09 PM, Tom W8JI wrote: There are two potential problems with this. As general rules: 1.) Grounding any antenna which is dependent on a ground system to be resonant will maximize reradiation. 2.) Resonant elevated radials, even without an antenna connected, are resonant and re-radiate. 3.) Things that are not resonant can still re-radiate. To minimize coupling from a resonant radial, the radial has to be disconnected from ground and from other radials. Different systems can be different, and in some cases re-radiation can actually cause a null that reduces noise, but the general rule is self-resonant antennas with a ground (Marconi), or nearly self-resonant antennas when grounded, should be floated. Other antennas can be terminated in an inductor, capacitor, or opened, depending on the system. My 220 ft insulated tower, in the center of a four square, is opened by shorting a specific length of coax to the L matching network. It has much more radiation when open or grounded. radiation is minimal when detuned by a proper impedance. 73 Tom ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Beverage Antennas Trees
On 6/20/2012 9:40 AM, ZR wrote: Mine are installed thru the woods and I spent considerable time trimming out low growth plus interfering branches. Mine are also DXE twinlead in a dense redwood forest with rather irregular terrain, and go through a lot of brush and scrub trees. When I installed them about five years ago, I used electric fence post stand-offs on trees, but after a few years most had fallen off or the twinlead had separated from the standoff. For several years, my Beverages have been supported by the brush and branches of low trees. They work. A year or so ago, I helped string a single wire Beverage along a dirt road in Bonnaire, again supporting it on the scrub trees and brush. it worked fine. Bottom line -- Beverages don't have to be ideal to work. What DOES matter is keeping common mode noise out of it, and also off of the feedline. That means a decent transformer and ferrite chokes formed by winding at least 14 turns of the coax around a #31 toroid. 73, Jim K9YC ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: TX ANT TO RX ANT COUPLING
Doesn't this suggest that there is a role here for cut and try? Take a set of clip leads to the base of the tower and experiment? 73, Pete N4ZR The World Contest Station Database, at www.conteststations.com The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com, spots at telnet.reversebeacon.net, port 7000 and arcluster.reversebeacon.net, port 7000 On 6/20/2012 3:45 PM, Herb Schoenbohm wrote: Tom, This is not encouraging news for those of us with towers already ground and are either shunt fed or cage fed. Even though they are not resonate, although top loaded and approaching resonance, it seems that even with some elaborate decoupling arrangements, and I hope I am wrong, not to much can be gained by even trying to get them detuned. This is crucial for me to know, and I would assume many others that have Beverage terminations or feed points 100 feet away, Thanks for the warning as this summer I was going to install a HV relay on the shunt cage to groundbut as you point out it may not help as the grounded shunt or cage fed tower is already a noise source for close proximity RX antennas. On 6/20/2012 2:09 PM, Tom W8JI wrote: There are two potential problems with this. As general rules: 1.) Grounding any antenna which is dependent on a ground system to be resonant will maximize reradiation. 2.) Resonant elevated radials, even without an antenna connected, are resonant and re-radiate. 3.) Things that are not resonant can still re-radiate. To minimize coupling from a resonant radial, the radial has to be disconnected from ground and from other radials. Different systems can be different, and in some cases re-radiation can actually cause a null that reduces noise, but the general rule is self-resonant antennas with a ground (Marconi), or nearly self-resonant antennas when grounded, should be floated. Other antennas can be terminated in an inductor, capacitor, or opened, depending on the system. My 220 ft insulated tower, in the center of a four square, is opened by shorting a specific length of coax to the L matching network. It has much more radiation when open or grounded. radiation is minimal when detuned by a proper impedance. 73 Tom ___ UR RST IS ... ... ..9 QSB QSB - hw? BK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: TX ANT TO RX ANT COUPLING
If one's tower does not have radials, is set in concrete, with minimal direct contact with earth (say less than a linear foot, with nothing more than the usual lightning treatment attached to the base, then the base connection is likely rather resistive RF, and strictly by itself the tower is a fairly impeded conductor at 160. The conductors you need to block current on are those going up the tower: coax, control leads, and possibly the lightning ground leads. You can get that done with various applications of #31 ferrite. Toroids, monster clamp-ons, and beads, without getting into specifics. Since house radio garbage stuff frequently comes out coax shields to and then up towers, it is not too hard to get a permanent infusion of junk into just about any RX antenna on a small lot and wind up blaming it on the antenna. If you put a block on **ALL** the coax and control conductors just before they go up the tower, you may solve a lot of problems. For 80 and 160, seven or eight turns of RG400 through a five stack of #31 ferrite FT240 form factor toroids will put a hefty block on stuff off the tower. Simply running eight turns of rotor cable through a five stack will block all the conductors, whether used or not. A good article on how this works is at http://audiosystemsgroup.com/RFI-Ham.pdf Do a search on #31 to go directly to the relevant material. We are developing some special uses of an FCP to substitute for radials where towers on a small lot either are the radiator or support the radiator, as in an inverted L. This allows one to pull all connections to the base of the tower other than lightning protection (through expendable #31 ferrite). These FCP methods will require current blocking treatment of ALL conductors on the tower. This will at one time substantially reduce noise induction, and reduce loss caused by these conductors becoming default lossy radials and significantly decouple all of them from the RX antennas. An FCP, its isolation transformer, and L supported by the tower, is detuned from affecting the RX antenna by breaking the contact between the isolation transformer's radiator connection post and the L. Rather than looking at it all as an unfortunate discovered disadvantage, look at it as there IS a way. It's just to do some stuff on a small lot is going to require a bunch of #31 ferrite. Cheaper than moving :) 73, Guy. On Wed, Jun 20, 2012 at 3:45 PM, Herb Schoenbohm he...@vitelcom.net wrote: Tom, This is not encouraging news for those of us with towers already ground and are either shunt fed or cage fed. Even though they are not resonate, although top loaded and approaching resonance, it seems that even with some elaborate decoupling arrangements, and I hope I am wrong, not to much can be gained by even trying to get them detuned. This is crucial for me to know, and I would assume many others that have Beverage terminations or feed points 100 feet away, Thanks for the warning as this summer I was going to install a HV relay on the shunt cage to groundbut as you point out it may not help as the grounded shunt or cage fed tower is already a noise source for close proximity RX antennas. On 6/20/2012 2:09 PM, Tom W8JI wrote: There are two potential problems with this. As general rules: 1.) Grounding any antenna which is dependent on a ground system to be resonant will maximize reradiation. 2.) Resonant elevated radials, even without an antenna connected, are resonant and re-radiate. 3.) Things that are not resonant can still re-radiate. To minimize coupling from a resonant radial, the radial has to be disconnected from ground and from other radials. Different systems can be different, and in some cases re-radiation can actually cause a null that reduces noise, but the general rule is self-resonant antennas with a ground (Marconi), or nearly self-resonant antennas when grounded, should be floated. Other antennas can be terminated in an inductor, capacitor, or opened, depending on the system. My 220 ft insulated tower, in the center of a four square, is opened by shorting a specific length of coax to the L matching network. It has much more radiation when open or grounded. radiation is minimal when detuned by a proper impedance. 73 Tom ___ UR RST IS ... ... ..9 QSB QSB - hw? BK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Beverage Antennas Trees
I agree with Jim. Beverages don't have to be ideal to work very well indeed, thank you. It's the matching transformers (and maybe their grounds) that are a more important thing to worry about. You need not worry that trees and bushes will attenuate the signal at HF. Lots of people have installed them in deep woods. If you installed two identical, separate Beverages pointed in the same direction --one in the woods and one in the clear-- I doubt if you would be able to tell any difference between the way they work. My Beverages run through the woods for a portion of their length, and they work fine. Although I don't have any leaves or other foliage actually touching my Beverage's bare open-wire line, there are plenty of places where the antenna runs past them. And one of them is supported by tree trunks for about half of its length. 73, Mike http://www.w0btu.com/Beverage_antennas.html On Wed, Jun 20, 2012 at 2:51 PM, Jim Brown j...@audiosystemsgroup.comwrote: Mine ... through a lot of brush and scrub trees. ... Bottom line -- Beverages don't have to be ideal to work. ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: TX ANT TO RX ANT COUPLING
Great idea Pete but I also may run head long into false positive results with so many Beverages (12) and each with a different possible indications. Here with the masking over of any subtle changes by strong ever present boiling tropical QRN yielding a possible infinite number of variables, each by themselves variable may not quickly yield any discernible results. If there was any time day or night when QRN did not run S-9 in almost every direction I would give it a try but I fear that with what i have I may be just peeing up a rope. Herb, KV4FZ On 6/20/2012 4:45 PM, Pete Smith N4ZR wrote: Doesn't this suggest that there is a role here for cut and try? Take a set of clip leads to the base of the tower and experiment? 73, Pete N4ZR The World Contest Station Database, at www.conteststations.com The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com, spots at telnet.reversebeacon.net, port 7000 and arcluster.reversebeacon.net, port 7000 On 6/20/2012 3:45 PM, Herb Schoenbohm wrote: Tom, This is not encouraging news for those of us with towers already ground and are either shunt fed or cage fed. Even though they are not resonate, although top loaded and approaching resonance, it seems that even with some elaborate decoupling arrangements, and I hope I am wrong, not to much can be gained by even trying to get them detuned. This is crucial for me to know, and I would assume many others that have Beverage terminations or feed points 100 feet away, Thanks for the warning as this summer I was going to install a HV relay on the shunt cage to groundbut as you point out it may not help as the grounded shunt or cage fed tower is already a noise source for close proximity RX antennas. On 6/20/2012 2:09 PM, Tom W8JI wrote: There are two potential problems with this. As general rules: 1.) Grounding any antenna which is dependent on a ground system to be resonant will maximize reradiation. 2.) Resonant elevated radials, even without an antenna connected, are resonant and re-radiate. 3.) Things that are not resonant can still re-radiate. To minimize coupling from a resonant radial, the radial has to be disconnected from ground and from other radials. Different systems can be different, and in some cases re-radiation can actually cause a null that reduces noise, but the general rule is self-resonant antennas with a ground (Marconi), or nearly self-resonant antennas when grounded, should be floated. Other antennas can be terminated in an inductor, capacitor, or opened, depending on the system. My 220 ft insulated tower, in the center of a four square, is opened by shorting a specific length of coax to the L matching network. It has much more radiation when open or grounded. radiation is minimal when detuned by a proper impedance. 73 Tom ___ 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: Chokes for Beverages
On 6/20/2012 1:16 PM, Herb Schoenbohm wrote: Jim, How about 7 turns of coax then an independent ground rod and on the other side another 7 turns on type 31 Two chokes with a rod in between is a great move, but you need at least 14 turns to get the choke resonance down to 160M, and more turns is better. Seven turns of RG6 on a 2.5 inch type 31 is about all I can get on a core.or what about stacking cores? would that be any better? Yes, it's OK to stack cores, but you still need a lot of turns. Inductance increases linearly with the number of cores, but increases as the square of the turns, capacitance increases linearly as turns but only slightly with number of cores, so turns move the resonance more than cores. Since it's an RX antenna, use smaller coax for the choke(s). RG58 or RG59 or even mini-coax. A small break in the Zo doesn't matter. Or wind one of the bifilar chokes (really a parallel wire line) shown in my RFI tutorial.16 turns of a pair of #12 THHN will give you a 5Kohm choke from 160M up to 15M with a Zo of about 100 ohms. Tape the wires together, then wind them on the core(s) and put SO239s on each end. Do the same thing with #12 or 14 enameled wire and you'll get about the same 5Kohms, but not as broadband, and a Zo of about 50 ohms. 73, Jim K9YC ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Beverage Antennas Trees
- Original Message - From: Mike Waters mikew...@gmail.com To: topband topband@contesting.com Sent: Wednesday, June 20, 2012 5:24 PM Subject: Re: Topband: Beverage Antennas Trees I agree with Jim. Beverages don't have to be ideal to work very well indeed, thank you. It's the matching transformers (and maybe their grounds) that are a more important thing to worry about. Since work very well is entirely subjective it means little unless there is an ideal benchmark to compare against. Yes, Ive stressed the transformer design and construction to you several times on here and elsewhere. That and isolated grounds and common mode rejection will allow digging to a new layer of DX. You need not worry that trees and bushes will attenuate the signal at HF. Lots of people have installed them in deep woods. If you installed two identical, separate Beverages pointed in the same direction --one in the woods and one in the clear-- I doubt if you would be able to tell any difference between the way they work. How do you know any of the above without fully testing? It only makes good sense to at least assume that a wire touching branches and low brush during full sap season that will also be rained on often in many parts of the world will have many impedance discontinuities that when added up will likely have a negative effect. I walk mine several times a year trimming off wandering growths that have touched the insulated wire of my Beverages, it seems to me to be smart PM. This year in particular and due to the warm winter I have a jungle type explosion of growth from bushes, small pine trees, nasty stuff with thorns and creeper things. I prefer to keep them far away thank you and its a cost free exercise. My Beverages run through the woods for a portion of their length, and they work fine. Although I don't have any leaves or other foliage actually touching my Beverage's bare open-wire line, there are plenty of places where the antenna runs past them. And one of them is supported by tree trunks for about half of its length. Since I rebuilt all mine are now 100% in the woods and well removed from verticals and radials. Local digital, switchers, and other crud noise has also been reduced but I have no idea what re-radiation has in thepast or is affecting now. Carl KM1H 73, Mike http://www.w0btu.com/Beverage_antennas.html On Wed, Jun 20, 2012 at 2:51 PM, Jim Brown j...@audiosystemsgroup.comwrote: Mine ... through a lot of brush and scrub trees. ... Bottom line -- Beverages don't have to be ideal to work. ___ 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: 2433/5081 - Release Date: 06/20/12 ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: TX ANT TO RX ANT COUPLING
This is not encouraging news for those of us with towers already ground and are either shunt fed or cage fed. Shunt fed towers can be detuned, or taken out of the picture by phasing a small sample of signals into the RX antenna. I could try a motor driven inductor or capacitor (small) just to see while QSX on various RX antennas. Is the required reactance likely to be inductive or capacitive reacatance? It depends on what is on the tower, the shunt system, and the grounding. It can be anything from open circuit on the drop wire to fairly high reactance. There are too many variables to guess. Outside of measurements, you could model the tower and add a distant vertical 300-500 feet away that is excited as a source. Then find a detuning value for minimum pattern distortion and current in the tower. You'll see considerable pattern distortion on 160 meters from a resonant structure even 500 feet or further away, so obviously there can be considerable interaction to receive antennas even at a fairly large distance. My small vertical reversible Europe array, with each cell 70 foot spacing between two verticals for endfire, and 350 foot broadside spacing, has one endfire cell about 250 feet from my transmitting 4 square. When it looks back into the four square, while watching W1AW, I can change the level of W1AW 20 dB or more by playing with the TX antenna termination in the house. A resistor is never good, but shorts and opens or reactances can be. Some of my RX antenna to TX antenna coupling data is at the bottom of this page: http://www.w8ji.com/antenna_coupling.htm Having two antennas in the nulls of each other is worth a whole lot more than distance. 73 Tom ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
