At 01:45 AM 2/20/2012, Ralph W5JGV wrote:
> Surprised at your observation, I checked my 5000a and noticed that if
> RX1 preamp is off, I get same results on both RXes at 485 KHz, but if
> RX1 preamp is on, the baselines are different and I see an apparent
> difference of 30-something dB.
>
> Are you using the same settings on both receivers?
Hello Jerry,
Yes, I am. See this screen shot:
http://w5jgv.com/special/RX1-RX2.jpg (177 kB)
It shows that both RX's are set for USB reception, with a 2.7 KHz bandwidth.
A 50 Ohm dummy load is connected to the ANT1. The signal on the screen is my
PSK31 200 watt transmitter while it is on the air.
Looks like rx1 BW is 2.4 and rx2 BW is 2.9 KHz, but that shouldn't
make a difference. Also, AGC-T is set differently, but that shouldn't
make a difference either.
Since some minor difference in internal rx shielding could affect the
receivers differently with a local signal, I would compare using a
distant signal or no signal at all - just using the noise baseline.
When I look at your baseline, I see only a few dB difference - maybe 5-6.
The antenna connections are:
RX1 to ANT1 connector
RX2 to ANT1 TAP
You can see the signal level difference between the RX's. The gain of RX2 is
about the same as both of my Yaesu FT-747GX's. I therefore conclude that RX1
is deaf.
As for the preamps, in my F5K, the preamps on both RX's are grayed out and
not available at frequencies at or below 2.000 MHz.
My rx1 preamp is available at 485 kHz, and I can turn it on/off.
Makes a big difference in the baseline. My rx2 preamp will not turn
on at 485 kHz. Your rx1 preamp button is blue - this means it is off?
I am not familiar with the skin you are using, but I see that your
other function buttons go blue when they are on. You might want to
recheck the status of your rx1 preamp.
When I look at a distant AM station on 580 KHz, I see an apparent
difference in rx sensitivity when I switch rx1 preamp on/off - it
looks like rx2 is more sensitive by about 30 dB with rx1 preamp on.
They are the same when off.
GL
Jerry W4UK
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