Vetical Antennas
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Hi All,
I've moved to a new house and I'm trying to get a Hustler 5BTV working really well with my K2 in my new location. I plan to install the antenna in a ground plane configuration on a 2 storey home and feed it with coax. I was planning to use a few quarter wave radial for each of the bands of interest. I've had problems with TVI using this antenna before, so this time I will use some sort of a choke to block currents on the outer surface of the coax braid. Any suggestions on what I should use? How should I protect myself from lightning? I initially thought about running a lead from the base of the antenna to ground, but the length of this would probably turn the antenna into a vertical dipole. I was reading some doco for this antenna and read the following: Never use an antenna tuner to tune the antenna.Use of a tuner only fools the transmitter and does not correct a problem at the antenna. This doesn't seem right can I use my K2's tuners? Finally, I've been reading Moxon's HF Antennas for All Locations, and he doesn't seem to recommend quarter wave radials for ground planes. I'm not sure I comprehend why. Is anyone familiar with his concerns? Mike VK1KCK, K2 #2599 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Hi Mike,
I just want to respond to one aspect of your post which, co-incidentally, I have been discussing elsewhere this week. Thats the business of using an ATU. Essentially the document you read is correct; any adjustments to obtain a good match to the transmitter in an aerial of this type (trapped vertical, yagi, dipole etc.) should be done by adjusting the aerial itself. Placing an ATU at the tx end of the feeder (or built in as in the K2) is fine for small adjustments at, for example, band edges to prevent the SWR protection circuit from reducing the power out whilst still protecting the PA. Attempting to compensate for large mismatches with an ATU at the tx end of the feeder may result in an apparently good match, but will in most cases cause the feeder to radiate. Exceptions to this are when the feeder is of the balanced variety, eg. open wire, where the feeder carries a 'balanced' standing wave as a matter of course. In your case, adjust the vertical for best match on each band, starting with the highest frequency band, and without using the ATU in the K2. Once you are happy you have the best match you can on each band, then the K2's ATU can be used to perfect the match before operating. HTH Trev G3ZYY In message <007701c75cb9$5ba76270$0501a8c0@LAPTOP>, Mike Walkington <[hidden email]> writes >Hi All, > >I've moved to a new house and I'm trying to get a Hustler 5BTV working >really well with my K2 in my new location. I plan to install the antenna in >a ground plane configuration on a 2 storey home and feed it with coax. I was >planning to use a few quarter wave radial for each of the bands of interest. > >I've had problems with TVI using this antenna before, so this time I will >use some sort of a choke to block currents on the outer surface of the coax >braid. Any suggestions on what I should use? > >How should I protect myself from lightning? I initially thought about >running a lead from the base of the antenna to ground, but the length of >this would probably turn the antenna into a vertical dipole. > >I was reading some doco for this antenna and read the following: Never use >an antenna tuner to tune the antenna.Use of a tuner only fools the >transmitter and does not correct a problem at the antenna. >This doesn't seem right can I use my K2's tuners? > >Finally, I've been reading Moxon's HF Antennas for All Locations, and he >doesn't seem to recommend quarter wave radials for ground planes. I'm not >sure I comprehend why. Is anyone familiar with his concerns? > > >Mike >VK1KCK, K2 #2599 > >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com -- Trevor Day Sunny Saltash _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Walkington-3
-----Original Message-----
From: Mike Walkington I was reading some doco for this antenna and read the following: Never use an antenna tuner to tune the antenna.Use of a tuner only fools the transmitter and does not correct a problem at the antenna. This doesn't seem right can I use my K2's tuners? ------------------------- Yep, that's pretty much it. This is nothing new and nothing specific to the K2 or the 5BTV antenna. An ATU at the rig does NOT change the impedance of the antenna or provide any sort of match between the coax and the antenna. Instead it provides a match between the rig and the coax. Any standing waves on the coax due to impedance mismatch between the antenna and the 50 ohm coax will remain. But, again, this is nothing specific to the K2 or 5BTV. So yes, you can use your K2 tuner. It will do what it can to transform the who-knows-what impedance is seen at the rig end of the coax into a 50 ohm resistive load to keep the rig happy. You'll have loss in the coax due to the SWR and resulting reduced efficiency in the antenna system but clearly that is a compromise that most of us have been happy to live with for many years. My antenna system consists of a 32' vertical in the back yard with a remote tuner in the garage. 35' of RG-213 connects the tuner to the base of the vertical and often carries rather high SWR. RG-8x connects the rig to the remote tuner and that section is always at SWR 1.5 or below thanks to the action of the tuner. The whole thing seems to work just fine. - Keith N1AS - - K2 5411.ssb.100 - _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Trevor Day
-----Original Message-----
Attempting to compensate for large mismatches with an ATU at the tx end of the feeder may result in an apparently good match, but will in most cases cause the feeder to radiate. Exceptions to this are when the feeder is of the balanced variety, eg. open wire, where the feeder carries a 'balanced' standing wave as a matter of course. --------------------------- Actually I believe this is one of the great myths of amateur radio. Standing waves on the feedline do not create feedline radiation. What standing waves do is to increase the loss in the feedline. Open wire feeder is used to reduce feedline loss. - Keith N1AS - - K2 5411.ssb.100 - _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Walkington-3
Mike,
I suggest you may want to do some reading at L B Cebik's website www.cebik.com about vertical antennas. It would seem that what you have been reading/hearing has some 'garbage content' to it, or may be information specific to one installation. Start with basic antenna principles and work to apply that to your situational constraints and you will reward yourself with a better performing antenna system. For a multiband elevated quarterwave vertical, I recommend using 2 electrical quarter wave radials for each band of use. Each radial pair should be oriented in opposing directions to cancel the horizontal component in the radiation pattern. If you do not wish to cancel the horizontal component, then a single radial for each band is all that is needed. Since you will have the base of the antenna well above ground, you must create a ground plane with the radials. A vertical monopole with its base on the ground will behave nicely with untuned radials buried in the ground and forming a ground screen, but with an elevated quarterwave vertical monopole, you must create 'the other half of the antenna' at the base - that is what the radials accomplish. An elevated monopole may be tuned by either trimming the length of the radiator or the length of the radials or both. Yes, think of the vertical and each of the radials as a dipole, bent at the feedpoint - in other words, as an upright "L" antenna fed at the corner. If you have multiple radials for each band, tune each one of them individually. for zero reactance at the base if you are using an antenna analyzer, but you can also tune for minimum SWR. Remember that a vertical monopole operating against a perfect ground (or complete radial screen) will have a feedpoint impedance of 35 ohms. If the radials slope downward instead of perpendicular to the vertical, the feedpoint impedance will be increased because the antenna system is approaching a dipole (which has a theoretical feedpoint impedance of 72 ohms). If you are feeding the antenna system with 50 ohm coax, you can expect some SWR on the line, so that part can be tuned out at the transmitter end. To keep radiation from the feedline to a minimum, run the feedline away from the antenna in-line with the radiator - it should drop for at least a quarterwave under the ground plane. Accomplishing that feat is usually not possible with the antenna roof mounted, so you will have to provide some in-line decoupling on the feedline. A balun (or unun) at the base will not accomplish all the decoupling required because the feedline will pick up radiation beyond the balun and try to act as a radial. A W2DU type current balun placed along the feedline will help a lot. I would suggest placing it at the point where the feedline exits the roof and changes direction. For lightning protection, yes use a heavy wire to ground from the base of the antenna. The radials should stop the radiation from this ground wire (BTW, there is nothing wrong with a vertical dipole). If your antenna already has a DC path to ground at the base, you will be all set, but if there is no DC path, you can install an RF choke there. An RF choke will also bleed off any static that will tend to build up on the antenna. 73, Don W3FPR > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]]On Behalf Of Mike Walkington > Sent: Friday, March 02, 2007 5:56 AM > To: Elecraft-Reflector > Subject: [Elecraft] Vetical Antennas > > > Hi All, > > I've moved to a new house and I'm trying to get a Hustler 5BTV working > really well with my K2 in my new location. I plan to install the > antenna in > a ground plane configuration on a 2 storey home and feed it with > coax. I was > planning to use a few quarter wave radial for each of the bands > of interest. > > I've had problems with TVI using this antenna before, so this time I will > use some sort of a choke to block currents on the outer surface > of the coax > braid. Any suggestions on what I should use? > > How should I protect myself from lightning? I initially thought about > running a lead from the base of the antenna to ground, but the length of > this would probably turn the antenna into a vertical dipole. > > I was reading some doco for this antenna and read the following: Never use > an antenna tuner to tune the antenna.Use of a tuner only fools the > transmitter and does not correct a problem at the antenna. > This doesn't seem right can I use my K2's tuners? > > Finally, I've been reading Moxon's HF Antennas for All Locations, and he > doesn't seem to recommend quarter wave radials for ground planes. I'm not > sure I comprehend why. Is anyone familiar with his concerns? > > > Mike > VK1KCK, K2 #2599 > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.446 / Virus Database: 268.18.5/706 - Release Date: > 2/28/2007 4:09 PM > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.446 / Virus Database: 268.18.5/706 - Release Date: 2/28/2007 4:09 PM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Darwin, Keith
I agree with Kieth wholeheartedly. SWR on the feedline does NOT cause
feedline radiation - ever. The thing that causes feedline radiation is common mode currents - most commonly observed as current flowing on the outside of a coax line. Properly placed current baluns can eliminate common mode current, but should not change the SWR, 73, Don W3FPR > -----Original Message----- > > -----Original Message----- > Attempting to compensate for large mismatches with an ATU at the tx end > of the feeder may result in an apparently good match, but will in most > cases cause the feeder to radiate. > > Exceptions to this are when the feeder is of the balanced variety, eg. > open wire, where the feeder carries a 'balanced' standing wave as a > matter of course. > --------------------------- > > Actually I believe this is one of the great myths of amateur radio. > Standing waves on the feedline do not create feedline radiation. What > standing waves do is to increase the loss in the feedline. Open wire > feeder is used to reduce feedline loss. > > - Keith N1AS - > - K2 5411.ssb.100 - > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.446 / Virus Database: 268.18.5/706 - Release Date: > 2/28/2007 4:09 PM > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.446 / Virus Database: 268.18.5/706 - Release Date: 2/28/2007 4:09 PM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Trevor Day
My observations. 2 years go, I put up a homebrew made of leftover
tubing 33 ft vertical using an old Hustler 5BTV mount. A 3-1/2 inch galvanized pipe, hacksawed at one end into a 30 degree (angle) point was sledge driven into the ground as a mount stake. It is guyed with 3 ropes at the 18-ft level and secured with wood stakes. I feed it directly at the bottom with RG8X small coax. I have put down 32 radials. Since 6/2005, I have worked 212 countries and worked all states numerous times, including QRP. I run a IC756 Pro III. I also work plenty of DX using my Elecraft K1 which I just finished building. I used the vertical on 40 where it works the best and has a 1:1 SWR. I also use it on 30, 17 and 15 meters. I am amazed how well it works on 17 and 15 meters. I use a Palstar AT1500CV. I can work anything I hear and I hear plenty. I don't get too excited about SWR. If the transmitter sees a 1:1 on TX side of the tuner using the Palstar, I will see what the antenna can do. Other antennas are 133ft inverted-L. G5RV. And A3 at 40 feet. My K1's antenna tuner matches to the vertical just fine. When the weather warms up, I'm going to hit the mountain tops of Vermont (my home) with a disposable party helium canister and float a 66ft vertical on 40 meters. Being 1/2 wavelength it should not need any radials. BTW, the vertical ad RG8X takes 600 watts using a Yaesu FL2100B just fine, for those times when I want to run an indefinite string of DX QSOs back-to-back. I am CW only. Jozef WB2MIC Wells VT Trevor Day wrote: > Hi Mike, > I just want to respond to one aspect of your post which, > co-incidentally, I have been discussing elsewhere this week. Thats > the business of using an ATU. Essentially the document you read is > correct; any adjustments to obtain a good match to the transmitter in > an aerial of this type (trapped vertical, yagi, dipole etc.) should be > done by adjusting the aerial itself. > > Placing an ATU at the tx end of the feeder (or built in as in the K2) > is fine for small adjustments at, for example, band edges to prevent > the SWR protection circuit from reducing the power out whilst still > protecting the PA. > Attempting to compensate for large mismatches with an ATU at the tx > end of the feeder may result in an apparently good match, but will in > most cases cause the feeder to radiate. > > Exceptions to this are when the feeder is of the balanced variety, eg. > open wire, where the feeder carries a 'balanced' standing wave as a > matter of course. > > In your case, adjust the vertical for best match on each band, > starting with the highest frequency band, and without using the ATU in > the K2. Once you are happy you have the best match you can on each > band, then the K2's ATU can be used to perfect the match before > operating. > > HTH > Trev G3ZYY > > In message <007701c75cb9$5ba76270$0501a8c0@LAPTOP>, Mike Walkington > <[hidden email]> writes >> Hi All, >> >> I've moved to a new house and I'm trying to get a Hustler 5BTV working >> really well with my K2 in my new location. I plan to install the >> antenna in >> a ground plane configuration on a 2 storey home and feed it with >> coax. I was >> planning to use a few quarter wave radial for each of the bands of >> interest. >> >> I've had problems with TVI using this antenna before, so this time I >> will >> use some sort of a choke to block currents on the outer surface of >> the coax >> braid. Any suggestions on what I should use? >> >> How should I protect myself from lightning? I initially thought about >> running a lead from the base of the antenna to ground, but the length of >> this would probably turn the antenna into a vertical dipole. >> >> I was reading some doco for this antenna and read the following: >> Never use >> an antenna tuner to tune the antenna.Use of a tuner only fools the >> transmitter and does not correct a problem at the antenna. >> This doesn't seem right can I use my K2's tuners? >> >> Finally, I've been reading Moxon's HF Antennas for All Locations, and he >> doesn't seem to recommend quarter wave radials for ground planes. I'm >> not >> sure I comprehend why. Is anyone familiar with his concerns? >> >> >> Mike >> VK1KCK, K2 #2599 >> >> _______________________________________________ >> Elecraft mailing list >> Post to: [hidden email] >> You must be a subscriber to post to the list. >> Subscriber Info (Addr. Change, sub, unsub etc.): >> http://mailman.qth.net/mailman/listinfo/elecraft >> >> Help: http://mailman.qth.net/subscribers.htm >> Elecraft web page: http://www.elecraft.com > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Mike, others have given what I consider good advice on several of the points
you asked about. I'll take a crack at your question about Moxon's counterpoise advice. I'm slowly going through Moxon's book. Its fascinating reading, by the way, for those looking for new antenna ideas or new ways of looking at old antennas. But his writing style isn't always very clear and easy to comprehend. And some of his "contraptions" with multiple feedlines coming into the shack seem overly complicated to me. But, all in all, I still recommend the book. His point about the conventional ground plane with 3 or 4 sloping counterpoise wires goes as follows. The assumption that all 3 CP wires will carry equal current is bogus. Since they all vary slightly in length or in coupling to surrounding objects, their impedance as seen at the feedpoint will also vary widely. The net result is that one of them will take a large percentage of the current while the others will be mostly ineffectual, and the hoped for symmetrical pattern will not in fact occur. To obtain the desired symmetry, he suggests using CP wires cut to less than 1/4 WL (even substantially less) and then putting an inductance between the common feedpoint of the CP wires and the return side of the feedline. This inductance is then adjusted to obtain resonance of the CP wires at the operating frequency. This way, they will share the RF current much more equally. I have not tried this approach, but it seems to make sense to me. Another point he and others make, that I can confirm from experience, is that 3 or 4 CP wires and a symmetrical pattern really aren't needed in practice anyhow. I use a BuddiPole in a vertical arrangement with one sloping CP wire per band and it works just fine and seems to work stations in all directions without a problem. I don't have his book in front of me right now, but somewhere in it is a nice table or graph that compares ground plane performance vs. number of CP wires, and hardly anything is lost by reducing the number. 73 ... Craig AC0DS _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Walkington-3
Mike
you already have received some excellent advice from others, so i will keep this brief. (1) understand that mounting a vertical above the ground works best with resonant (quarter wave length radials) while on the ground it does not require resonant radials, but is more challenging as it wants as much metal as possible over the ground. (2) mounting something that tall (around 26 feet) onto a house is no small undertaking! remember your house is more vital than your ham radio experience (and more costly to repair than the antenna). some people have adequately installed such an antenna onto a house, but its a big effort to do it sufficiently well (understatement). (3) the TVI cure you allude to is to reduce feed line radiation. if the feedline is closer to the TV's than your antenna, this is a greater help. its certainly good practice to work to minimize feed-line radiation, but it is not a fix-all. antenna installations have lots of challenges, so don't push the envelope beyond your capabilities. and don't rule our wire antennas, as this might get you in business quicker while working the vertical more. 73, curt ----- Original Message ---- From: Mike Walkington <[hidden email]> To: Elecraft-Reflector <[hidden email]> Sent: Friday, March 2, 2007 5:55:54 AM Subject: [Elecraft] Vetical Antennas Hi All, I've moved to a new house and I'm trying to get a Hustler 5BTV working really well with my K2 in my new location. I plan to install the antenna in a ground plane configuration on a 2 storey home and feed it with coax. I was planning to use a few quarter wave radial for each of the bands of interest. I've had problems with TVI using this antenna before, so this time I will use some sort of a choke to block currents on the outer surface of the coax braid. Any suggestions on what I should use? How should I protect myself from lightning? I initially thought about running a lead from the base of the antenna to ground, but the length of this would probably turn the antenna into a vertical dipole. I was reading some doco for this antenna and read the following: Never use an antenna tuner to tune the antenna.Use of a tuner only fools the transmitter and does not correct a problem at the antenna. This doesn't seem right can I use my K2's tuners? Finally, I've been reading Moxon's HF Antennas for All Locations, and he doesn't seem to recommend quarter wave radials for ground planes. I'm not sure I comprehend why. Is anyone familiar with his concerns? Mike VK1KCK, K2 #2599 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ____________________________________________________________________________________ Have a burning question? Go to www.Answers.yahoo.com and get answers from real people who know. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Walkington-3
Mike,
Don makes a lot of good points in his post. I've played quite a bit with elevated verticals with tuned radials. They radiate well, but I am not sure it is worth the effort and trouble they present. I would suggest that you ground mount the vertical and use radials that do not necessarily have to be a quarter wave. I've seen very little difference between the elevated and the ground mounted vertical...but...with one exception. A gound mounted vertical needs more radials. There is a very large difference in radiation resistance etc...from 8 radials to 16 to 24 to 32. Now, no installation is perfect...but the idea is to radiate a signal. So, do the best you can to get down as many radials as you can...and they do not have to be a quarter wave. I have a 40 meter quarter wave with just 16 radials under it...right on the ground. Works very well. Most of the radials are a quarter wave in length, but to the east they are not because of my placement in my backyard. I have down two radials that are short to the east....and two radials that are quarter wave on 40 meters but are bent at 90 degrees to follow the fence line. In addition you can put down a 8 foot ground rod for even more "grounding" when you are ground mounted. That would help on 80/75 meters as well. There is a lot to be said about this kind of antenna and the literature is out there to read about...so take some time and read about it. I just found it is easier to ground mount verticals and they work the same. Your mileage my vary. Lee - K0WA In our day and age it seems that Common Sense is in short supply. If you don't have any Common Sense - get some Common Sense and use it. If you can't find any Common Sense, ask for help from somebody who has some Common Sense. Is Common Sense devine? _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Don Wilhelm-3
Ouch!
Thanks all, I am suitably chastened :-) In my defence, I believe the basis of my advice (tune the aerial in the first instance) remains sound. Trev G3ZYY In message <[hidden email]>, Don Wilhelm <[hidden email]> writes >I agree with Kieth wholeheartedly. SWR on the feedline does NOT cause >feedline radiation - ever. > >The thing that causes feedline radiation is common mode currents - most >commonly observed as current flowing on the outside of a coax line. >Properly placed current baluns can eliminate common mode current, but should >not change the SWR, > >73, >Don W3FPR > >> -----Original Message----- >> >> -----Original Message----- >> Attempting to compensate for large mismatches with an ATU at the tx end >> of the feeder may result in an apparently good match, but will in most >> cases cause the feeder to radiate. >> >> Exceptions to this are when the feeder is of the balanced variety, eg. >> open wire, where the feeder carries a 'balanced' standing wave as a >> matter of course. >> --------------------------- >> >> Actually I believe this is one of the great myths of amateur radio. >> Standing waves on the feedline do not create feedline radiation. What >> standing waves do is to increase the loss in the feedline. Open wire >> feeder is used to reduce feedline loss. >> >> - Keith N1AS - >> - K2 5411.ssb.100 - >> _______________________________________________ >> Elecraft mailing list >> Post to: [hidden email] >> You must be a subscriber to post to the list. >> Subscriber Info (Addr. Change, sub, unsub etc.): >> http://mailman.qth.net/mailman/listinfo/elecraft >> >> Help: http://mailman.qth.net/subscribers.htm >> Elecraft web page: http://www.elecraft.com >> -- >> No virus found in this incoming message. >> Checked by AVG Free Edition. >> Version: 7.5.446 / Virus Database: 268.18.5/706 - Release Date: >> 2/28/2007 4:09 PM >> >-- >No virus found in this outgoing message. >Checked by AVG Free Edition. >Version: 7.5.446 / Virus Database: 268.18.5/706 - Release Date: 2/28/2007 >4:09 PM > >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com -- Trevor Day Sunny Saltash _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Ouch indeed. I found out that SWR does not contribute to feedline
radiation when I posted in an internet group that it does ... and received a response similar to yours :-) Been there, done that LOL! - Keith N1AS - - K2 5411.ssb.100 - -----Original Message----- From: Trevor Day Ouch! Thanks all, I am suitably chastened :-) _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by k0wa@swbell.net
Ground vs.roof mount - here's my experience.
I have a 32' vert on the ground over a field of 16 radials, each about 20 feet long. Remote tuner, 35' away, allows it to work on multiple bands. I also have a 16' vert on the roof of my garage with 4 radials. I tuned this antenna by connecting 1 radial at a time and then trimming the radial until I got the same impedance (more or less). Then I connected all 4 radials and adjusted the vertical radiator to finalize it. I've done a lot of A/B switching between them on 20 meters. The 1/2 wave on the ground over 16 radials performs equal to or slightly WORSE than the 1/4 wave on the roof. I've checked both domestic and DX on it and, as much as I want the 1/2 wave to be better, it just isn't. At one time I had a Cushcraft MA5V on the roof. The 32' vertical outperformed it most of the time. - Keith N1AS - - K2 5411.ssb.100 - _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Walkington-3
Mike Walkington wrote:
> Finally, I've been reading Moxon's HF Antennas for All Locations, and he > doesn't seem to recommend quarter wave radials for ground planes. I'm not > sure I comprehend why. Is anyone familiar with his concerns? He argues that unbalanced currents in radials will result in radiation at very high angles, which is essentially wasted. He says that resonant quarter wave radials are likely to be affected by nearby objects, so unless take special care to measure the current in the radials and adjust them, the currents are likely to be unbalanced. For that reason he recommends shortening the radials and feeding them through a common inductance (it can be a coil or a stub) to resonate the whole system; that is much more likely to result in equalized currents in the radials. I have a 33-foot vertical with four radials made of tubing, each 8 feet (2.4m) long. All of the radials are connected together at the base, and fed through a small coil. I adjusted it with an MFJ analyzer (the adjustment was somewhat critical) and I get an SWR of about 1.2:1 at resonance, and it's broad enough to cover most of the 40 m band with SWR under 2:1. It's not far from another 45-foot tower, so there's some interaction. Modeling it with EZNEC indicated that the gain was about 1 db lower than full-size resonant radials (of course this assumes that the radial currents are perfectly balanced). I also use a choke balun at the feedpoint which consists of a bunch of ferrite toroids that fit tightly on a piece of coax. I bought a kit to make it from The Wireman <http://thewireman.com/index.shtml>. This is advisable for two reasons: 1) without it, current flows on the outside of the coax which causes radiation upwards as discussed before, and 2) without it, noise generated in the shack from computer equipment, etc. can flow up the coax and enter the system at the antenna. I also have an inverted V with the center at 40 feet with a balun at the center. Comparing these two antennas I find that the dipole is always quieter, and is usually better for stations closer than about 1500 miles. For stations 2500 miles away it's a tossup, and for DX usually the vertical is better. A whole lot of the time there's no difference. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Feedline radiation (WAS: Vetical Antennas)
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In reply to this post by Don Wilhelm-3
Another source of radiation-causing common-mode currents is an *unbalanced*
two-wire feeder, such as when ladder, window or twinlead is used to feed an off-center fed dipole. A balun at the transmitter will do little or nothing to improve the balance. It's caused by the unbalanced load at the antenna. That radiation is not always bad if the system is designed to make use of it. The version of the Windom that uses open wire or twinlead feeders is a good example (the original Windom used a single wire feeder). In this case the considerable radiation from the feeder is part of the effectiveness of the antenna, adding a fair bit of vertical radiation (if the feed line runs vertically). The challenge is to recognize that the "feeder" in such antenna systems is actually part of the radiating antenna and must be run in the clear. It can be a source of severe RFI if it's run where it can induce heavy RF currents into nearby conductors, such as TV antenna leads, house power wiring, etc. Even though a two-wire line might be used, when it's unbalanced it has to be treated with the same consideration one would give to running a simple end-fed wire into the shack. An that's why coaxial lines are so popular in spite of the need to hold down the SWR to avoid excessive losses. Ron AC7AC -----Original Message----- I agree with Kieth wholeheartedly. SWR on the feedline does NOT cause feedline radiation - ever. The thing that causes feedline radiation is common mode currents - most commonly observed as current flowing on the outside of a coax line. Properly placed current baluns can eliminate common mode current, but should not change the SWR, 73, Don W3FPR _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Walkington-3
Lots of good discussion here, some of it relevant to mounting a 5BTV on the
roof, some of it not :-) To the original poster: you might want to take a look at http://www.dimebank.com/cak/k6dbg/k6dbg_hf.html About halfway down, I go into a lot of detail of my elevated 6BTV installation, including tuned radials, feedpoint choke, common mode chokes, and grounding. I've been very pleased with mine. 73 de chris K6DBG _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Darwin, Keith
Keith, I suggest you get Walter Maxwells book Reflections II and read it
cover to cover a few times. It takes time to grasp all the good antenna info he has in there. But, it corrects the many myths most hams have heard. The tuner really tunes your line and antenna as a system! Reflections II can be ordered from the World Radio website, as I recall. It also is on the web as some QST past articles, but he added to it for the second edition of the book which compiled the QST series on SWR, reflections, etc. Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Curt Milton
I'm just catching up reading this thread and have some questions:
What is the best way to feed a 1/2 wave or 5/8 wave vertical at ground level? I'm guessing a link coupled matching network would be better than an L match and would perhaps obviate the need for a feedline choke? What would constitute an efficient 'ground' for such an antenna? I assume the requirement for lots of close in radials is not so important as it would be for a 1/4 wave vertical? I await any comments with interest. Thanks and 73 Fraser G4BJM _________________________________________________________________ Get Hotmail, News, Sport and Entertainment from MSN on your mobile. http://www.msn.txt4content.com/ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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A half wave needs no ground at all. Since virtually no current is flowing
into the antenna when fed at the end, no current needs to flow into a ground. From my second-story window I use a parallel tuned circuit with the power fed from the rig in via a link at one end, and the 1/2 wave antenna connected to the other end. An L-network would work just as well. In that case, since the high-impedance is at the antenna end of the inductor, that's where the capacitor goes. An L-network is a simple parallel-tuned resonant circuit with the connection between the tuning cap and the inductor opened to connect the low-impedance circuit - in this case the low-impedance coax connection to the rig. The high-impedance load at the other end is across the tuned circuit that includes the rig in series with the coil and capacitor. Here's a rough schematic: >---coil---|-----> high impedance antenna 50 ohm | <---cap----| A 5/8 wave does draw current at the base and it'll look inductive since it is longer than its naturally resonant 1/2 wave. You'll need capacitive reactance equal to the inductive reactance to bring the 5/8 wave radiator to resonance. Again that can be done with either L-network or a link-coupled parallel tuned network. When the load shows inductive or capacitive reactance, that reactance detunes the circuit, so you adjust the value of the coil or cap to compensate and bring the system, including the antenna, back to resonance while providing the required impedance transformation. That's what is happening when you adjust an L-network or a parallel tuned link-coupled network for a low SWR on the 50-ohm link to the rig. Whether you'll need to worry about a balun or feed line choke will depend entirely upon whether there's RF currents flowing on the outside of the coax and, if so, whether they are a nuisance. You are quite right that in both cases the demands upon a low-impedance ground system are greatly reduced over that needs of a 1/4 wave (or shorter) vertical for equal efficiency. With the antenna oriented vertically, you'll still have the added far-field ground losses inherent in such antennas compared to a horizontal antenna at a good height (0.2 wave or higher). But you can't do anything about that short of locating next to the sea shore <G>. Even so, a vertical will generally outperform a low (0.2 wave high or less) horizontal, especially for lower angles of radiation generally desirable for DX. The horizontal really shines for DX when it approaches 1/2 wavelength above ground. Under those conditions you'll see 3 dB to 6 dB gain over a vertical - equivalent to doubling or quadrupling your transmitter power. Down at 0.2 wave above the ground, the horizontal will show a very strong vertical lobe that isn't present with the vertical, although most verticals show some radiation straight up anyway. That strong vertical lobe from the low horizontal is what provides the short skip or "NVIS" characteristic of those antennas that is generally superior to verticals. Below 0.2 wavelength the amount of current induced in the ground by a horizontal causes excessive losses that reduce its gain. That's why verticals really outshine low horizontals on the lower-frequency bands. To be a really effective DX antenna, an 80 meter dipole needs to be >70 feet up and something around 120 feet up is ideal. A 40 meter dipole needs to be about half that height. For a lot of us, that simply isn't practical. Ron AC7AC -----Original Message----- I'm just catching up reading this thread and have some questions: What is the best way to feed a 1/2 wave or 5/8 wave vertical at ground level? I'm guessing a link coupled matching network would be better than an L match and would perhaps obviate the need for a feedline choke? What would constitute an efficient 'ground' for such an antenna? I assume the requirement for lots of close in radials is not so important as it would be for a 1/4 wave vertical? I await any comments with interest. Thanks and 73 Fraser G4BJM _________________________________________________________________ Get Hotmail, News, Sport and Entertainment from MSN on your mobile. http://www.msn.txt4content.com/ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Fraser Robertson
Both the half wave and 5/8 wave antennas are complete resonant structures
without the need for radials. See L. B. Cebik's web site, www.cebik.com for his discussion modeling half wave verticals, and little was gained by modeling radials under them. The reflections you are concerned about are in the range beyond the Fresnel Zone, some 5 or more wavelengths out from the vertical. Short 1/4 wave verticals need radials to complete the circuit and return RF current to the feedpoint. You can feed with a link, and possibly not need the cable choke. But, the cable choke is good insurance in any case. The whole issue is one of balance and if the feeder leads off vertically under the vertical, there is minimal pickup of RF by its outer conductor. Of course, if it is at right angles to the vertical directly at the feed point, there is more chance of current reaching the outer conductor inducing unbalance. An efficient ground for a 1/2 wave vertical is any whose impedance is say 1/10 of the feedpoint impedance of the vertical conductor, which is typically around 3000 ohms, depending on how close it is to RF earth at the base of antenna. So, a ground of 300 ohms would work in this case, while it would way inefficient for a quarter wave vertical, which needs a return conductors impedance of less than 3.6 ohms or so. (36 ohms base impedance on theoretical quarter wave vertical, base fed.) You want the ground to be a much more attractive path for RF than the other impedances in the system. 73, Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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