[amsat-bb] When exactly is a non-conductive mast necessary?

[Zach Metzinger]

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