On 2020-01-13 08:37, Wes Baden via AMSAT-BB wrote:
given the 9700's extraordinary sensitivity and built in preamp. Would a 2M mast mounted preamp be overkill and an unneeded expense?
Hello Wes,
The built-in preamp doesn't make any sense unless you connect your antenna directly at the rig (inches) or have super-expensive zero-loss coax.
As I outlined a few months ago on this list, a fairly inexpensive LNA at the antenna is the best way to improve your station noise figure.
Once the system noise figure has been set, the coax back to the shack doesn't really matter too much other than wasting a bit of transmit power if you use the same coax for TX and RX.
Original message included here:
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.
--- Zach N0ZGO