On 2019-12-30 20:20, John Kludt via AMSAT-BB wrote:
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.
I'll chime in with my usual "it depends" statement: Spending a bunch of money on coax and neglecting a good LNA located _at the antenna_ is a shame.
If you have a big spool of RG-8X (or even RG-8) and some few dollars for a preamp (LNA), go for the preamp! 100' of LMR400 has a loss of 2.7dB at 70cm. Without a preamp, you now have an instant 2.7dB (or worse) noise figure, even before you get to the radio's front-end, and you've spent 3x on coax.
Yes, RG-8X loss at 70cm is 8.1dB, which means your radio's 100W signal is only ~15W at the antenna, but that's more than enough to reach a satellite before antenna directional gain is accounted for.
One can always make more TX power (and today's radios are overpowered anyway), but one can never recover signals already lost.
A prototypical LNA for 20 EUR ($22 USD) at http://lna4all.blogspot.com/, and a determined amateur can construct one for less.
Back to building..
--- Zach N0ZGO