9:1 Home Brewing
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9:1 Home Brewing
I am getting ready to build a QRP 9:1 unun as the basis for a random wire antenna. If anybody can answer a couple of questions, it would be greatly appreciated.
1. Conventional wisdom has the toroid wrapped with three conductors wrapped in parallel, then connected to give the correct final turns ratio. I understand that parallel wrapping helps to distinguish each of the conductors. Is there any reason that wrapping with three wires twisted together would not work (assuming that I can identify the ends of each of the wires before making final connections)?
2. I believe a capacitor connected between the coax center conductor and shield (ground) is not used for the 9:1 (as distinct from a 49:1 for an EFHW). Is it correct to wire the 9:1 without the capacitor?
Thanks and 73 de Brian - K3ES
1. Conventional wisdom has the toroid wrapped with three conductors wrapped in parallel, then connected to give the correct final turns ratio. I understand that parallel wrapping helps to distinguish each of the conductors. Is there any reason that wrapping with three wires twisted together would not work (assuming that I can identify the ends of each of the wires before making final connections)?
2. I believe a capacitor connected between the coax center conductor and shield (ground) is not used for the 9:1 (as distinct from a 49:1 for an EFHW). Is it correct to wire the 9:1 without the capacitor?
Thanks and 73 de Brian - K3ES
Re: 9:1 Home Brewing
So, I've only built a couple 9:1's, so I'm certainly not an expert. But, the ones I've built have worked, so FWIW ...
1. The wire I used to wrap the toroid (a 240-43) was a bit thick (maybe 14-gauge?) to twist all three strands together and then wrap the toroid. However, I have seen bifilar 9:1's made with a twisted pair and they seem to work.
2. Correct. I haven't used a capacitor and I haven't seen others use capacitors in 9:1's. The capacitor across the primary side of a 49:1 transformer supposedly reduces the SWR somewhat on the higher bands. I assume you're using your 9:1 on a random wire antenna and since that antenna is deliberately not resonant on anything (i.e., it's resonant on nothing and all of nothing's harmonics
), and will be using a tuner anyway, a slight tweak to the SWR on some select bands wouldn't seem to be necessary.
Good luck with the build!
73 Skip K4EAK
1. The wire I used to wrap the toroid (a 240-43) was a bit thick (maybe 14-gauge?) to twist all three strands together and then wrap the toroid. However, I have seen bifilar 9:1's made with a twisted pair and they seem to work.
2. Correct. I haven't used a capacitor and I haven't seen others use capacitors in 9:1's. The capacitor across the primary side of a 49:1 transformer supposedly reduces the SWR somewhat on the higher bands. I assume you're using your 9:1 on a random wire antenna and since that antenna is deliberately not resonant on anything (i.e., it's resonant on nothing and all of nothing's harmonics

Good luck with the build!
73 Skip K4EAK
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Re: 9:1 Home Brewing
Thanks, Skip.
73 de Brian - K3ES
73 de Brian - K3ES
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Re: 9:1 Home Brewing
I found this one being quite good
https://vk6ysf.com/unun_9-1_v3.htm
my only additional recommendation is to also wind this
https://vk6ysf.com/balun_choke_balun_hf_reisert.htm
and insert it in the same box, connecting the choke at the output of the 9:1, this will effectively stop the feedline from becoming part of the antenna (CMC) then, by the way, you'll need to use a counterpoise, but that shouldn't be a problem; a run of insulated wire laying down on ground will do
https://vk6ysf.com/unun_9-1_v3.htm
my only additional recommendation is to also wind this
https://vk6ysf.com/balun_choke_balun_hf_reisert.htm
and insert it in the same box, connecting the choke at the output of the 9:1, this will effectively stop the feedline from becoming part of the antenna (CMC) then, by the way, you'll need to use a counterpoise, but that shouldn't be a problem; a run of insulated wire laying down on ground will do
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- Joined: Sat Jun 11, 2022 2:59 pm
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- Posts: 200
- Joined: Sat Jun 11, 2022 2:59 pm
Re: 9:1 Home Brewing
alternatively, you may wind the 9:1 and the 1:1 choke in two separate boxes, that way, you may place the 9:1 at the feedpoint and the choke further down the coax, so using the coax braid (between the 9:1 and the choke) as a counterpoise (that is a part of your antenna in both tx and rx), this may be fine for SOTA/POTA where the coax won't meet a "noise cloud" but a "no go" for a permanent installation, where the braid would pick up all kinds of "domestic noise"Andrew (grayhat) wrote: ↑Wed Dec 07, 2022 5:53 pm I found this one being quite good
https://vk6ysf.com/unun_9-1_v3.htm
my only additional recommendation is to also wind this
https://vk6ysf.com/balun_choke_balun_hf_reisert.htm
and insert it in the same box, connecting the choke at the output of the 9:1, this will effectively stop the feedline from becoming part of the antenna (CMC) then, by the way, you'll need to use a counterpoise, but that shouldn't be a problem; a run of insulated wire laying down on ground will do
HTH
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Re: 9:1 Home Brewing
Thanks all! I am going to build a QRP 9:1 using tri-filar winding, and no capacitor. I'm not yet sure about radiator length. All I'm lacking now is a bit of shop time. When I get things together, I will let you know how it works.
Best 73 de Brian - K3ES
Best 73 de Brian - K3ES
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Re: 9:1 Home Brewing
I'll refrain itBrian - K3ES wrote: ↑Mon Dec 12, 2022 6:44 pm Thanks all! I am going to build a QRP 9:1 using tri-filar winding, and no capacitor. I'm not yet sure about radiator length. All I'm lacking now is a bit of shop time. When I get things together, I will let you know how it works.
Best 73 de Brian - K3ES
http://qrper.net/viewtopic.php?p=267#p267
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Re: 9:1 Home Brewing
forgot, as for the radiator length, check the link I posted, then decide based on the lowest band of interest and on the type of installation; I mean, if it's for a permanent installation (e.g. at home), then you may consider a longer antenna, if instead the antenna will be used for POTA or the like, a shorter one will be easier to deploy, but the lenght still is a factor; if you take the time to read these
http://qrper.net/viewtopic.php?p=267#p267
viewtopic.php?t=60
and to check the included links, you'll find this useful reference
https://udel.edu/~mm/ham/randomWire/
which shows the "good" lengths for a "random" wire antenna, now the author correctly states that, to be efficient on a given band, the antenna should be at least (around) 1/4 wave, this means that, for example, willing a random which will efficiently cover the 40m band, the length should be above 10m (33ft); this does not mean that one can't use a shorter antenna, just that such an antenna won't be as efficient; the "classic" size, that is 84ft for the random and 17ft for the counterpoise is a pretty good one, covering all the bands from 80 to 10 meters, but won't be so easy to deploy, operating in the field, in such a case, one may give up some bands and pick a shorter antenna, for example, a 35ft random will allow to operate on 40, 30, 20, 17, 15, 12, 10 meters and won't be difficult to deploy, add a decent counterpoise (which may still be 17ft if you want, or for example, two or three 10ft wires) and you'll be in business
http://qrper.net/viewtopic.php?p=267#p267
viewtopic.php?t=60
and to check the included links, you'll find this useful reference
https://udel.edu/~mm/ham/randomWire/
which shows the "good" lengths for a "random" wire antenna, now the author correctly states that, to be efficient on a given band, the antenna should be at least (around) 1/4 wave, this means that, for example, willing a random which will efficiently cover the 40m band, the length should be above 10m (33ft); this does not mean that one can't use a shorter antenna, just that such an antenna won't be as efficient; the "classic" size, that is 84ft for the random and 17ft for the counterpoise is a pretty good one, covering all the bands from 80 to 10 meters, but won't be so easy to deploy, operating in the field, in such a case, one may give up some bands and pick a shorter antenna, for example, a 35ft random will allow to operate on 40, 30, 20, 17, 15, 12, 10 meters and won't be difficult to deploy, add a decent counterpoise (which may still be 17ft if you want, or for example, two or three 10ft wires) and you'll be in business
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Re: 9:1 Home Brewing
I finished my build this month, and used the antenna for Winter Field Day... Er... used Winter Field Day to test the antenna. Particulars are:Brian - K3ES wrote: ↑Mon Dec 12, 2022 6:44 pm Thanks all! I am going to build a QRP 9:1 using tri-filar winding, and no capacitor. I'm not yet sure about radiator length. All I'm lacking now is a bit of shop time. When I get things together, I will let you know how it works.
Best 73 de Brian - K3ES
- 9:1 unun auto-transformer was built on a FT50-43 core, wrapped with 9 turns of tri-filar (3 twisted strands) 24 AWG magnet wire.
- I connected a 144 ft radiating wire, with the objective to enable tuning for CW on the 10m through 160m bands.
- I used a three 17 ft wires for a counterpoise.
- LDG Z-11Pro II tuner was successful matching 10m, 15m, 20m, 40m, 80m, and 160m bands with 1.5:1 or better SWR.
I am pleased with the results, and am working on a more complete field report, so more to follow. Thanks to all who helped with tips and advice.
73 de Brian - K3ES