On 02/17/17 14:17, Frank Staffa Jr. via AMSAT-BB wrote:
Hello everyone. I just purchased a M2 leopack antenna system and I was reading about different coax cables to use for low loss. Since I am mounting the antenna only about 10 feet off the ground, 50 foot will be enough to go into the shack. I wanted to purchase RG8x but read that the best way to go is with LMR400. What I dislike about it is that its much wider and very stiff, and will make it difficult around bends. I also have the Az/alt rotator which I will have to loop each antenna to have enough for turns. Any other suggestions out there for an alternative to LMR-400?Thanks Frank KB2CWN
Hello Frank,
You could always consider a LNA at the antennas, which sets your system noise figure early on in the receive chain and allows the use of RG-8X or similar. It's best to buy a weatherproof LNA and mount it right at the antenna/rotator with a short section of high-quality, low-loss coax (or direct connect). You'll want to run DC up the coax to power the LNA, if possible. Make sure your LNA switches itself out of the way when you remove power!
Of course, you'll lose power as heat on transmit with the higher-loss cable, but I wouldn't that is much of a problem with today's radio output levels.
Remember that you only need enough LNA gain to offset cable losses and your receiver's noise figure (NF). More than that risks overloading the front-end of your receiver and causing undesirable non-linear operation (IMD). A good place to start is about 13-15 dB of gain, if you need a concrete number.
That's my view on it, and I'm definitely no expert. It works for me. YMMV. :-)
--- Zach N0ZGO