Using Aluminum Window Screen As Counterpoise For Portable Antenna (
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- Опубликовано: 4 июн 2023
- Conrad, KN6VMK, told me that KB9VBR made a video where he used aluminum window screen instead of radio wires. Watch to learn more on why this works. Here is the link to KB9VBR video: • Window screen antenna ...
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This much like mobile operation where the car body acts not only as a counterpoise but also capacitive couples into the earth. It works real well on a concrete slab or parking lot that has some rebar in it. You can often hear the difference driving over a steel bridge.
I have been using the window screen for my POTA activations since Michael's videos. Probably 4 or 5. Works well; the thing I like is the rapid deployment and teardown compared to my 3 bunches of 4-16' radials. It isn't that much of a time saver but it is a few minutes. And, when it degrades as you mention, just get a new one for $8.
I just use stainless steel window screen of a fairly fine mesh so it's easy to roll. This eliminates the maintenance problems you were talking about.
I saw Michael’s video and Dave has made some great points as well.
I’ve read countless articles, & watched hours of videos on the subject of ground radials and counterpoises’. Yes there is a difference depending on whether the vertical is elevated and the radials have to be elevated or ground mounted with the radials lying on the ground. Using the Buddistick and one elevated counterpoise wire on an elevated tripod I’ve had zero issues tuning for resonance by lengthening or shortening the counterpoise.
But when I’ve tried multiple coils and a 17’ SS whip ground mounted on a tripod (less than 6” off the ground) I started with 12 16.5’ radials lying on the ground the SWR was 5:1 or more on 40m. So I removed a set of 4 and the SWR went down to about 4:1. So I removed another set of 4 and the SWR went down to 2.5:1. I folded the last set in half and the SWR went down to 1.5:1 or less across the entire general voice portion of 40m. I tried this with multiple lengths and multiple types of coax RG8X 50’, RG58U 25’, and RG316 25’ and got the same results with each. So it can’t be any of the coax cables I was using. It was even worse using a SS tent stake pounded at least 12” into the ground and a SS jaw mount, where I couldn’t get the antenna to resonate at all.
After reading and watching the general consensus was, when ground mounted, the more shorter radials are better than less longer ones and it doesn’t matter how long they are or how many you use. I have not seen this to be true based on my analysis above. So what is going on then? Because basically a 17’ SS whip with the WRC Sporty Forty I could only obtain resonance using 4 8.25’ radials.
The more radials the closer you get to the ideal 36.5 ohms Z of a 1/4 wave vertical. That's why the SWR goes up as you add wire.
@@Philip-KA4KOE isn’t the SWR supposed to go down there more ground radials you lay down? I was also under the impression that the length didn’t matter lying on the ground?
Length of radials on the ground does matter, but they do not have to be tuned (by being a specific % of a wavelength at frequency of operation). Short radials are electrically longer on 10m/20m than on 40m. I wouldn’t expect very good capacitive coupling to ground (contributing to good signal reflection for) 40m with only 4 short radials of that length. It would work better the higher in frequency you go.
That being said, a 4:1 or 5:1 SWR is really not expected with the sporty40 and 17’ whip fully extended with a number of ground radials. While 36 ohms characteristic of a perfect 1/4 wave vertical is not 1:1, it’s still under 2:1.
I have only used the 17’ whip on 20m ground mounted, (40m only mounted on a 4’ tripod, and then with 1 tuned and fully elevated counterpoise)… and am able to get
@@Kinetic79 thank you for all of your help. I have tried it in multiple locations and still get the same results. As far as continuity you would think it wouldn’t be the issue as 40m is the only band that gives me trouble. Not only that but the 4 16.5’ radials work on 40m and if there was a continuity issue it wouldn’t, at least as far as SWR is concerned.
I swapped out the 3 long wires that came with that kit with 9 wires, 3 per group and 1/3 the length (about 10 or 11 ft I think). I got it in bright orange and silicone coated so it is flexible. Put three alligator clips on it and I'm done. The whole antenna goes up in about 10 minutes.
Just got an idea to try metal window screen (pretty rare here in Europe, or, at least, in Slovakia - most of them are plastic) as a part of artificial ground (normally, it tunes up a wire).
I don't have any possibility for a good RF ground, living at 9th floor, so artificial ground was my only choice. Fortunately, it is not always needed.
Hey Dave. I was thinking that that plastic-coated wire-mesh would be a better solution. I have used it to build out a mini-fence around my veggie garden to keep my pups from trampling it. You can get matching posts for it. The mesh are squares about 1 inch spaced (or so). The plastic coating does a super job of protecting the steel. Now, while I am an engineer of "osmosis" (learning from others), I would guess that this mesh would do every bit as well as screen, given we are talking about HF frequencies.
Just my 2 cents and 73,
Marc, N6UNX
Need to make sure you have good conductivity between the weave and between the shield connection of your coax and any metal underneath the plastic protective coating. May be tricky.
What about faraday cloth?
Michael recently presented at our club; Chippewa Valley Amateur Radio Club, and he gave a fantastic presentation. I know he got several members excited about trying POTA. Great guy.
Chip W9OQI
What about hardware cloth 1/4 or 1/2 mesh?
Chicken wire work as well.
Possible stupid question: would this work on those military surplus portable antennas?? I'm eyeing one nearby, just got to figure out how to tell the XYL...
Yes it will. I've done this with a resonant vertical antenna and a non-resonant vertical (Chameleon MPAS 2.0). The effects are the same with the resonant and non-resonant antennas.
I guess chicken wire would serve the same purpose.
When I was a Boy Scout (~55 years ago) I was part of one of the first JOTA's.
The hams that came to my town (Montreal, Canada) and set up in an outdoor parking lot did just that.
They had a large vertical antenna with a 30-40 foot square area of chicken wire tent-pegged onto the parking lot gravel surface.
I remember talking to a fellow scout in Sweden, so it must have worked OK. 😀😀
Chicken wire is twisted together. Those contact points will corrode quickly on the ground I’m told.
@@halcollins4293 so you can put them on the roof.