Clever antenna tuning ideas wanted
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OK, here is what I want to do:
I have a 33' (10m) vertical with the base about 10' (3.3m) above ground. It has four 8' (2.4m) radials which are connected to the feedpoint through a coil which resonates the system on 7 MHz. It works as well or better than any vertical that I've used on 40m -- low SWR and good results. It's fed through a relatively short (20', 6m) length of RG-213. I would like to use it on 80m and 30m as well. My first try was to simply use the KAT100 to tune it. It tunes fine on both bands (1:1 at the rig), but results are fair-to-poor on 30 and poor-to-worthless on 80. On 30m, the coax losses are reasonable (the SWR on the coax is about 8 to 1, but it's very short). I suspect the problem is that the radial ground system is very poor on this band (on the other hand, the long vertical radiator should provide a slight amount of gain). So I may try paralleling a set of radials tuned for 30m. They will also be short, but resonated with a coil or stub. Does this sound like a good analysis/solution? On 80m, it's more complicated. The ground system is terrible, the radiation resistance of the vertical very low, and the SWR and losses on the coax very high. No wonder it's a dummy load! I guess the way to deal with it is to add more tuned radials in parallel and a switchable base network, but I would like to avoid any more control wires that have to go through my lightning suppression panel (I can't pass DC through the coax, either). Does anyone have any suggestions? -- 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 |
RE: Clever antenna tuning ideas wanted
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My antenna is similar. 28.5' tall, ground mounted over twelve 28' long
radials. Fed with 30 feet of RG-213. With a tuner the system works well enough on 40, 30, 20, 15. 80 Meters is the pits. Dummy Load City! I'm considering putting a remote ATU at the base of the antenna. Basically, eliminating the 30 feet of coax feed line and all the high VSWR losses it entails. I picked 28 feet for the vertical to make it a reasonable impedance on each of my bands of interest (as well as to increase wind survivability). Another thought I've had is to put a Hustler 80 M resonator on top of it to raise the feed point impedance on 80. For now, I'll have to stick with 40 meters. - Keith KD1E - -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Vic K2VCO Sent: Wednesday, December 07, 2005 4:20 PM To: Elecraft Reflector Subject: [Elecraft] Clever antenna tuning ideas wanted OK, here is what I want to do: I have a 33' (10m) vertical with the base about 10' (3.3m) above ground. It has four 8' (2.4m) radials which are connected to the feedpoint through a coil which resonates the system on 7 MHz. It works as well or better than any vertical that I've used on 40m -- low SWR and good results. It's fed through a relatively short (20', 6m) length of RG-213. I would like to use it on 80m and 30m as well. My first try was to simply use the KAT100 to tune it. It tunes fine on both bands (1:1 at the rig), but results are fair-to-poor on 30 and poor-to-worthless on 80. On 30m, the coax losses are reasonable (the SWR on the coax is about 8 to 1, but it's very short). I suspect the problem is that the radial ground system is very poor on this band (on the other hand, the long vertical radiator should provide a slight amount of gain). So I may try paralleling a set of radials tuned for 30m. They will also be short, but resonated with a coil or stub. Does this sound like a good analysis/solution? On 80m, it's more complicated. The ground system is terrible, the radiation resistance of the vertical very low, and the SWR and losses on the coax very high. No wonder it's a dummy load! I guess the way to deal with it is to add more tuned radials in parallel and a switchable base network, but I would like to avoid any more control wires that have to go through my lightning suppression panel (I can't pass DC through the coax, either). Does anyone have any suggestions? -- 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 _______________________________________________ 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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Darwin, Keith wrote:
> My antenna is similar. 28.5' tall, ground mounted over twelve 28' long > radials. Fed with 30 feet of RG-213. With a tuner the system works > well enough on 40, 30, 20, 15. 80 Meters is the pits. Dummy Load City! > > I'm considering putting a remote ATU at the base of the antenna. > Basically, eliminating the 30 feet of coax feed line and all the high > VSWR losses it entails. I thought of this. A tuner would help by reducing the coax loss, as you say, but at 80 meters the radiation resistance of the radiator is very low, and so it's necessary to improve the ground system -- either by making it more extensive, of resonant length, or loading it to resonance. Since the effective ground resistance is in series with the radiation resistance, the efficiency suffers when the ground or counterpoise system is poor. Also, the usual autotuner is not very efficient when loading a short whip -- that's why the mobile guys use big bugcatchers. -- 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 |
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In reply to this post by Vic K2VCO
Vic
Here's an idea that I haven't seen anyone else use, but it might just do the trick for you. Lower your vertical and connect a 33 ft piece of good wire at the top. Put a good egg insulator at the free end of the wire and attach a long nylon string. When you want to work 80m, draw the wire away from the vertical until it is as horizontal as possible. When you want to work 40 or 30m, lower the wire so it is right up against the vertical. This will cancel the effect of the wire, making it as if it wasn't there. As a belt and suspenders approach, you could even put an alligator clip at the end of the wire and clip it to the bottom of the vertical when the wire is down. You will have to improve the radial system for 80m. At least get some radials that are full size for 40m. These don't have to be run straight, either. Remember the function of the radials, to collect the current radiated by the vertical and return it to the feed point. Resonant lengths collect more current because they are longer and intercept more current. A second function of the radial system is to mask the lossy ground below the radial system, thus giving the return current the lowest loss return path possible. You can do a lot to improve your setup, just by working on the radial system. You will not be adding gain, but you will be reducing losses, which will have the same effect on your signal. Hope this gives you some ideas, Vic. Good luck and 73 Bob N6WG The Little Station with Attitude -----Original Message----- From: [hidden email] [mailto:[hidden email]]On Behalf Of Vic K2VCO Sent: Wednesday, December 07, 2005 1:20 PM To: Elecraft Reflector Subject: [Elecraft] Clever antenna tuning ideas wanted OK, here is what I want to do: I have a 33' (10m) vertical with the base about 10' (3.3m) above ground. It has four 8' (2.4m) radials which are connected to the feedpoint through a coil which resonates the system on 7 MHz. It works as well or better than any vertical that I've used on 40m -- low SWR and good results. It's fed through a relatively short (20', 6m) length of RG-213. I would like to use it on 80m and 30m as well. My first try was to simply use the KAT100 to tune it. It tunes fine on both bands (1:1 at the rig), but results are fair-to-poor on 30 and poor-to-worthless on 80. On 30m, the coax losses are reasonable (the SWR on the coax is about 8 to 1, but it's very short). I suspect the problem is that the radial ground system is very poor on this band (on the other hand, the long vertical radiator should provide a slight amount of gain). So I may try paralleling a set of radials tuned for 30m. They will also be short, but resonated with a coil or stub. Does this sound like a good analysis/solution? On 80m, it's more complicated. The ground system is terrible, the radiation resistance of the vertical very low, and the SWR and losses on the coax very high. No wonder it's a dummy load! I guess the way to deal with it is to add more tuned radials in parallel and a switchable base network, but I would like to avoid any more control wires that have to go through my lightning suppression panel (I can't pass DC through the coax, either). Does anyone have any suggestions? -- 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 _______________________________________________ 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 |
RE: Clever antenna tuning ideas wanted
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In reply to this post by Vic K2VCO
Vic,
For those bands, I would recommend that you use a higher frequency adaptation of the DXPeditioner's Battle Creek Special antenna (see ON4UN's Low Band DXing). Add a 30 meter trap in the vertical section and put a 40 meter trap at the top, then use a wire from the top of the 40 meter trap to create an inverted L antenna for 80 meters. Since the base is already above ground, I would believe you should be successful with elevated radials - but they have to be tuned to the vertical portion to work properly - use 2 (or 4) diametrically opposed radials each for the 30 and 40 meter bands to cancel the horizontally polarized component of the radiation and on 80 meters you can get away with one because the horizontal portion of the antenna already has some horizontal radiation to its pattern, so a bit more horizontal polarization won't hurt. You can instead install a very good on (or in) ground radial system, but that will likely take a minimum of 16 radials to perform as well as the raised radials. With the raised radials, experiment with and without an actual connection to ground to see which gives the better results - often it is better to keep the elevated radials isolated from earth ground (except connected through an RF Choke to keep things at DC ground potential). Tune the radials one at a time until you get the reactive part of the feedpoint impedance at zero, then observe the resistive part after all radials are in place - you can accept the resulting SWR or install a matching network at the antenna base to bring it into line with the feedline losses you are willing to accept. Good luck with it. 73, Don W3FPR > -----Original Message----- > > > OK, here is what I want to do: > > I have a 33' (10m) vertical with the base about 10' (3.3m) above ground. > It has four 8' (2.4m) radials which are connected to the feedpoint > through a coil which resonates the system on 7 MHz. It works as well or > better than any vertical that I've used on 40m -- low SWR and good > results. It's fed through a relatively short (20', 6m) length of RG-213. > > I would like to use it on 80m and 30m as well. My first try was to > simply use the KAT100 to tune it. It tunes fine on both bands (1:1 at > the rig), but results are fair-to-poor on 30 and poor-to-worthless on 80. > > On 30m, the coax losses are reasonable (the SWR on the coax is about 8 > to 1, but it's very short). I suspect the problem is that the radial > ground system is very poor on this band (on the other hand, the long > vertical radiator should provide a slight amount of gain). So I may try > paralleling a set of radials tuned for 30m. They will also be short, > but resonated with a coil or stub. Does this sound like a good > analysis/solution? > > On 80m, it's more complicated. The ground system is terrible, the > radiation resistance of the vertical very low, and the SWR and losses on > the coax very high. No wonder it's a dummy load! I guess the way to > deal with it is to add more tuned radials in parallel and a switchable > base network, but I would like to avoid any more control wires that have > to go through my lightning suppression panel (I can't pass DC through > the coax, either). Does anyone have any suggestions? > > -- > 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 |
Re: Clever antenna tuning ideas wanted
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In reply to this post by Darwin, Keith
On Dec 7, 2005, at 4:34 PM, Darwin, Keith wrote: > My antenna is similar. 28.5' tall, ground mounted over twelve 28' > long > radials. Fed with 30 feet of RG-213. With a tuner the system works > well enough on 40, 30, 20, 15. 80 Meters is the pits. Dummy Load > City! One idea - there was an article in QST some years ago about using a trap to make an inverted L. Fellow had an 80m vertical. He added a trap for 80m and then ran a wire out horizontally. You could probably do the same thing for 40m/80m. One pretty foolproof way to make a trap is to wind coax on a PVC form. There's even a freeware program out there to compute the length of the coax - Coaxtrap. Google for it. If you're going to make 80m a habit, some 50-60 foot radials would be nice. K2VCO should also consider some longer radials. Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email] Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 _______________________________________________ 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 |
Re: Clever antenna tuning ideas wanted
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In reply to this post by Vic K2VCO
Vic Rosenthal wrote:
> OK, here is what I want to do: > > I have a 33' (10m) vertical with the base about 10' (3.3m) above ground. > It has four 8' (2.4m) radials which are connected to the feedpoint through > a coil which resonates the system on 7 MHz. It works as well or better > than any vertical that I've used on 40m -- low SWR and good results. It's > fed through a relatively short (20', 6m) length of RG-213. > > I would like to use it on 80m and 30m as well. My first try was to simply > use the KAT100 to tune it. It tunes fine on both bands (1:1 at the rig), > but results are fair-to-poor on 30 and poor-to-worthless on 80. > > On 30m, the coax losses are reasonable (the SWR on the coax is about 8 to > 1, but it's very short). I suspect the problem is that the radial ground > system is very poor on this band (on the other hand, the long vertical > radiator should provide a slight amount of gain). So I may try > paralleling a set of radials tuned for 30m. They will also be short, but > resonated with a coil or stub. Does this sound like a good > analysis/solution? ................................................................................................... Hi Vic, Do you have EZNEC or any other form of NEC? I had a quick look at what you have, making many assumptions such as element / radial diameters, slope of radials, azimuth of radials, ground type etc etc etc, and I think that on 30m the vertical element + radials + radial loading coil looks more like an offset fed "dipole" with a drive point impedance around 120 +j something. The vertical pattern is still good, with a little gain over a monopole. On 80m the vertical pattern broadens with the take-off angle increasing to 26 - 28 degrees, but still with a deep null at 90 degrees although the gain is poor. The drive point impedance is VERY low and Complex. The actual orientation and slope of the existing radials will have great effect on all bands, and some form of additional 80m radials could be required if the vertical portion is not top loaded. If you want to add or remove parts when changing bands, you might like to consider "passive switching". Parallel tuned traps are one form of "switch", but there is also the series tuned form. For example if you wanted to remove the tuned coil used with the radials on 40m when going to 30m, a series LC tuned to 30m placed across the 40m "radial coil" would do this. Some fiddling is needed because there would be some interaction between the 40m and 30m circuits. All sorts of games can be played with passive switching although there is a limit as to how many bands can be handled by one switching module, and you don't want to introduce loss by using dinky little coils etc. If you would like to continue, I suggest that we do it off-list to avoid using List Bandwidth. 73, Geoff. GM4ESD _______________________________________________ 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 Vic K2VCO
I'd like to thank everyone for their suggestions on how to make my 32'
vertical with 8' elevated loaded radials perform on 80 and 30 meters as well as 40. It's clear I will have to do some major surgery on the antenna to add 80 meters, such as a trap plus a toploading wire, or a movable wire (N6WG). Otherwise, the high reactance and low radiation resistance at the base will remain a problem. AB9CA pointed out that a tuner at the base could efficiently handle a low resistance if the reactance were tuned out by some top-loading. For 30 meters there seem to be some elegant solutions. W3FPR mentioned that two symmetrical radials are enough, and EZNEC agrees that the difference in overall gain between two and four is less than 0.1 db! One approach would be to separate the two pairs of radials and feed them each through an appropriate inductance (about 11.5 uh on 40 and 1.7 uh on 30). This would resonate the system on both 40 and 30 meters. I also noticed (thanks, EZNEC) that with all four radials connected together, all I would have to do is short out the existing 40 meter inductance to obtain a low SWR on 30! But that would require a switch or relay which I want to avoid. -- 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 |
RE: Clever antenna tuning ideas wanted
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Vic,
A series circuit resonant at 30 meters will do a good job of shorting out the 40 meter inductance (no relay) - but the inductor used for 40 meters would have to be modified to compensate for the effect of the series circuit when on 40 and produce the same resultant inductance. 73, Don W3FPR > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]]On Behalf Of Vic K2VCO > Sent: Thursday, December 08, 2005 11:30 AM > To: Elecraft Reflector > Subject: Re: [Elecraft] Clever antenna tuning ideas wanted > > > I'd like to thank everyone for their suggestions on how to make my 32' > vertical with 8' elevated loaded radials perform on 80 and 30 meters as > well as 40. > > It's clear I will have to do some major surgery on the antenna to add 80 > meters, such as a trap plus a toploading wire, or a movable wire (N6WG). > Otherwise, the high reactance and low radiation resistance at the base > will remain a problem. AB9CA pointed out that a tuner at the base could > efficiently handle a low resistance if the reactance were tuned out by > some top-loading. > > For 30 meters there seem to be some elegant solutions. W3FPR mentioned > that two symmetrical radials are enough, and EZNEC agrees that the > difference in overall gain between two and four is less than 0.1 db! > > One approach would be to separate the two pairs of radials and feed them > each through an appropriate inductance (about 11.5 uh on 40 and 1.7 uh > on 30). This would resonate the system on both 40 and 30 meters. I also > noticed (thanks, EZNEC) that with all four radials connected together, > all I would have to do is short out the existing 40 meter inductance to > obtain a low SWR on 30! But that would require a switch or relay which > I want to avoid. > > -- > 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 > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.371 / Virus Database: 267.13.12/194 - Release Date: 12/7/2005 > > _______________________________________________ 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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Don Wilhelm wrote:
> A series circuit resonant at 30 meters will do a good job of shorting out > the 40 meter inductance (no relay) - but the inductor used for 40 meters > would have to be modified to compensate for the effect of the series circuit > when on 40 and produce the same resultant inductance. GM4ESD also suggested this and I am going to try this, since it will require the least modification to my existing antenna. I will build up the circuit on my bench and adjust it for the reactance shown by EZNEC with my MFJ analyzer. Then I'll hook it up and make final adjustments on the antenna. It will be interesting to see if the antenna appears to perform better. -- 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 |
re: Clever antenna tuning ideas wanted
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In reply to this post by Vic K2VCO
Vic K2VCO <[hidden email]> wrote : > I would like to use it on 80m and 30m as well. My first try was to > simply use the KAT100 to tune it. It tunes fine on both bands (1:1 at > the rig), but results are fair-to-poor on 30 and poor-to-worthless on > 80. Can you clarify are the radials elevated above ground or are they on or below the ground ? It sounds like they are tuned so my guess is elevated? > > On 30m, the coax losses are reasonable (the SWR on the coax is about 8 > to 1, but it's very short). I suspect the problem is that the radial > ground system is very poor on this band (on the other hand, the long > vertical radiator should provide a slight amount of gain). So I may > try > paralleling a set of radials tuned for 30m. They will also be short, > but resonated with a coil or stub. Does this sound like a good > analysis/solution? I suspect that this would help. You could also just try a single elevated tuned radial for 30m to make it into an L antenna with some directionality in the direction of the radial. > > On 80m, it's more complicated. The ground system is terrible, the > radiation resistance of the vertical very low, and the SWR and losses > on > the coax very high. No wonder it's a dummy load! I guess the way to > deal with it is to add more tuned radials in parallel and a switchable > base network, but I would like to avoid any more control wires that > have > to go through my lightning suppression panel (I can't pass DC through > the coax, either). Does anyone have any suggestions? > Well, one trick to put this sort of antenna on 80 is to make it into an inverted L by running a horizontal (or nearly horizontal) wire off the top of the antenna. Since it doesn't sound like it is practical to switch the wire maybe you could add an 80M trap and enough wire to get it close to resonance on 80m. I'm thinking something like the Unadilla traps (http://www.unadilla.com/traps.htm). You could always tack the second of the pair of traps to the single 30m tuned radial I suggested above and more wire on the other side of the trap to make it a dual-band radial on 30m / 80. If you don't have space to run in in a straight line bend it as necessary to make it fit your lot. Michael VE3WMB _______________________________________________ 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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