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Old 18-Jul-2016, 9:58 PM   #11
acat
Junior Member
 
Join Date: Jun 2016
Location: Boulder, Colorado
Posts: 17
Back of the Envelope Calculations & Some Tentative Results

Thanks Rabbit73 & AdTech for the thoughtful insights & suggestions.

So some rough calculations...
Pinebrook Hills, a possible source of reflections is roughly 1 mile distant. At the speed of light that amounts to a ~5 microsecond delay. However, 1 cycle at 180 Mhz is 0.00555 microsec, and since the reflection delay is likely smeared over a range of times given that the reflecting surface is pretty ugly, interference with the digital signal seems to be a given. (if I had done this calculation first, I might not have started!)

This is just a tentative result, since the reliability of any solution so far has been poor...but... I did put a screen up to the side of the VHF antenna with the SiliconDust Receiver software running on channel 7 next to me on a laptop. Without the wire mesh, the symbol rate was Zero. With the wire mesh it went to 100%. I added and removed it several times and it SEEMED reproducible, but I am reluctant to bet the farm on it.

I'll need to give some thought to a more permanent construction for the shield as we have notoriously high winds in the mountains. I don't want the antenna to blow all the way to Kansas. I suppose some aluminum rods widely spaced as they are at the back of the 8-bay UHF and VHF antenna would be a good start along with some plastic pipe as a support.
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