Mark Lunday, WD4ELG wrote:
F3K, SDR 1.18.5
When I turn on the ARR, the noise floor jumps UP from -140 to -110, not what
I expected.
Actually, that is what I would expect, although 30dB sounds a bit much.
The F3K sees an increase in noise from turning on the pre-amp. Take a
conventional radio, for example. Turn on the pre-amp and you should hear
the noise level should increase; otherwise the advantages of the
outboard amp are being lost.
By using the internal pre-amps in the Flex, PSDR knows about them and
compensates accordingly for the displayed values. It is calibrated for
signal into the rig, and is actually very accurate. Almost a lab-grade
selective voltmeter. However, it has no knowledge about the outboard
amplifier so treats it just as something coming in to the antenna terminal.
Now, if you were listening to a weak signal, say a beacon, you should
see that the desired signal is also enhanced when turning on the
pre-amp. It should not be the case that it get gets swamped by the
pre-amp noise level. If the S/N reduces then the pre-amp may be bad.
Having said that, I measured my F3K to be in the order of 7dB noise
figure, which is completely dominated by external noise in my urban
location. I get about a 10dB increase in noise floor switching from a
good dummy load to my antenna. Having a pre-amp in place would only make
inter-mod a worse problem. Maybe you live out in the sticks where things
are quieter, so YMMV.
To summarize: I doubt you have a problem with either the F3K or your
pre-amp. You should do some on-air tests with weak signal sources to
verify this.
Good luck, and I hope to catch you on the Magic band. We have several
good openings to your area each summer E season.
73 Alf NU8I
Scottsdale AZ DM43an
160m > 24Gigs
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