Cathryn,
And if you pay attention to all of the caveats in his paper. One saving grace about all of this is it is not EME. If you were working with 250 +/- dB path loss and a passive reflector like the moon you might come to a different conclusion. Just be careful of all of the those 1/2 wavelengths and 1 wavelengths that he speaks about. Especially for the 70 cm uplinks as that isn't very many inches.
The other thing I have seen folks trip over is coax selection. Satellites are not the place to be using RG-8X. Others may have other thoughts I think you are looking at LMR400 or its equivalent or better if it is a permanent installation.
John
On Mon, Dec 30, 2019 at 7:57 PM Cathryn Mataga via AMSAT-BB < amsat-bb@amsat.org> wrote:
Oh, thanks guys. This is eye-opening. It looks like even circular polarized antennas will work with metal masts, if you rotate them 45 degrees.
On 12/30/2019 2:31 PM, Gary wrote:
The short answer is almost never. Here is a link to an AMSAT Symposium
paper form antenna guru Kent Britain, wa5vjb (inventor of the famous cheap yagis). He actually measured the effects.
http://www.kk0sd.net/metalboom/metalboom.htm
73, Joe kk0sd
-----Original Message----- From: AMSAT-BB amsat-bb-bounces@amsat.org On Behalf Of Cathryn Mataga
via AMSAT-BB
Sent: Monday, December 30, 2019 3:27 PM To: amsat-bb@amsat.org Subject: [amsat-bb] When exactly is a non-conductive mast necessary?
I'm trying to understand, under what circumstances is a non-conductive
mast necessary at VHF/UHF frequencies. Thinking of the following installs.
- Circular polarized antenna mounted to the mast at the center of the
boom. This is clear, see this advice all the time, fiberglass mast.
Same antenna but mounted at the rear end of the boom.
Vertical Yagi, elements parallel to a vertical mast, mounted at the
center of the boom. I guess, non-conductive wold be required here.
Same antenna but rear mounted.
Horizontal Yagi, elements perpendicular to a vertical mast, mounted
at the center of the boom. I think this is pretty normal install, so a conductive mast would be okay?
- Same antenna but mounted at the rear of the boom.
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Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb