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1. 01:34 PM - Re: ADS-B and Transponder antenna... (Charlie England)
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| Subject: | Re: ADS-B and Transponder antenna... |
On Thu, Oct 1, 2020 at 8:59 AM andymeyer <meyerkc135@gmail.com> wrote:
> >
>
> So, all this chatter about the ELT antennas got me thinking about the
> ADS-B antenna I made. I dove into the math, made some estimates, and
> designed two on Upverter and had parts made. I got luck in that my SlimJim
> ADS-B antenna has picked up airborne traffic over 100 miles away connected
> to a Stratux (I have both SDR radios tied into a single antenna - criminal
> - I know, but it works and it's small and light.)
>
> Attached are the layouts of the two antennas and links to the actual
> designs on Upverter.
> I had 5 of each made. Anyone interested in testing and sharing data -
> maybe make this a shared design as well. Cost is just a few bucks.
>
> Slim Jim: https://upverter.com/eda/#tool=pcb,designId=1d1c59be761e9901
> DiPole: https://upverter.com/eda/#tool=pcb,designId=9eb3fbd043861e96
>
>
> (Upverter is a pretty awesome cloud based schematic and layout tool that
> allows collaboration on designs, etc... Think Google Docs for circuit
> design.)
>
>
> Hello group,
Andrew sent me a couple of the antennas he mentioned, above, to play with
(Thanks, Andy), which got me motivated to take my 1st dive into using a
nanoVNA.
I promised Andrew I'd share results of testing the two antennas. Let me
remind everyone that while I consider myself reasonably adept at
electronics troubleshooting (3 or 4 'lives' in electronics maintenance),
I'm not formally educated in the field nor am I a HAM operator. I hope the
attached images will be viewed more as an invitation to teach me more about
how to use the nanoVNA than an actual analysis of the antennas.
Starting from a knowledge level of near zero, here we go: Since Andrew is
splitting the signal using one antenna to feed two SDRs that are tuned to
978MHz & 1090MHz, I set the center frequency on the VNA at the midpoint
between the two freqs (1034MHz), & span to 200MHz. On the *very* slim
chance that I set up the VNA correctly, It looks like the dipole has a
worst case SWR of around 4.6 & the Slim Jim was basically off the chart at
1090MHz.Measurements were taken with the antennas hanging on the 6" long
cable that came with the nanoVNA.
Even if I did the tests correctly, I'm not sure if the above has any real
meaning for a receive-only antenna. If there's a better test that can be
accomplished with the nanoVNA and someone is willing to walk me through the
setup, I'll be happy to run the test(s), or I can forward the antennas to
someone with more RF-foo. Shoot me a direct email if you're interested.
Charlie
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