On 5/3/22 23:34, David Hopkins wrote:
A preamp can be a help BUT remember the preamp is only there to overcome the feed line loss.
I respectfully disagree. The LNA, sometimes called a "preamp", is there to set the noise figure (NF in dB) of your receive system. Your NF determines, ignoring interference, the signal-to-noise (SNR) ratio of the signal going into your demodulation setup (FoxTelem).
https://www.rfcafe.com/references/electrical/noise-figure.htm https://www.microwaves101.com/encyclopedias/noise-figure
SNR is what actually determines how many packets are decoded. You can have a strong signal which has a terrible SNR and no packets will be decoded. Conversely, you can have a very weak/faint signal with a great SNR and you'll get 100% decodes.
https://en.wikipedia.org/wiki/Bit_error_rate
(SNR and Eb/N0 are different ways of expressing the same ratio: https://en.wikipedia.org/wiki/Eb/N0)
Putting a preamp at the receiver end of the coax is a waste of time.
I agree, assuming usual feedline losses which would add directly to the NF of your receive system.
Summing up, If you want peak performance then you need to put the effort into maximising your receive system. Long Yagies, low loss coax, N type connectors and tracking yagies. Anything less than this degrades your performance.
Type N connectors are not necessary for good/excellent performance at sub-1GHz frequencies. The clunky-but-common SO/PL-259 connector will work just fine, as it represents a minimal impedance bump in the line.
https://www.iz2uuf.net/wp/index.php/2016/01/08/pl-259-vs-n-on-430-mhz/
Sure, if you're wanting to eek out that last 0.1dB in your setup, go whole hog with N connectors. However, that shouldn't stop the casual amateur who just wants a workable setup on 2m/70cm.
--- Zach N0ZGO