On 04/17/21 11:16, crohtun via AMSAT-BB wrote:
internal preamps are turned on. The 9700 is especially deaf on 70 cm without its preamp.
Compared to the FT-847, a standard satellite rig, the IC-9700 is not too far off in sensitivity (MDS, SSB/CW, dBm, ARRL):
FT-847 IC-9700 Freq / Preamp-> OFF ON OFF ON 432.02 MHz -139.1 -140.8 -133 -145
That 6dB power difference with the Preamp disabled is one S-unit.
As I've posted on this forum before, a preamp at the rig is a poor substitute for a quality LNA at the antenna, unless your coax is 0dB loss. Signal that has "burned up" in the coax can never be recovered.
If you turn on your preamp to make the background noise seem louder, you're really just using it as an audio amplifier. Even worse, you might be driving the receiver stages after the preamp into a more non-linear region, creating mixing products which show up as a higher noise floor.
The best situation is a high dynamic range LNA with a very low noise figure. Pointing your antenna at "cold" sky and turning on the LNA should result in little, if any, change in the noise floor (or audio level).
Carl tells me he has a good LNA (not currently in use) which he plans to put at the antenna. Based on my observations with the XW-2 satellites, an LNA is not necessary to hear or work them with a simple J-pole in the attic.
More is always better, but I don't think the preamp is the source of his problems.
73,
--- Zach N0ZGO