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The R390A/URR |
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Ultimate Performance, General Coverage AM & CW Receiver |
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R390A/URR Receiver Site Pages Accessible from Left Hand Navigation Bar |
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Testing RF Deck Noise Power
This is an interesting test to demonstrate the effect of proper IF gain set up: Before running the above procedure, set the IF gain to maximum, i.e. fully CCW looking from the top. Set up as above except:
Set IF bandwidth to 8 kHz Set the "Line Gain" for 0VU on the "Line Level" meter. Then, tune the antenna trimmer for minimum When I did this with my receiver the noise dropped by only 3 dB in IF
Gain Setting Procedure, step 9. That means the noise from the receiver first RF amplifier, the place where the receiver noise floor should be established, is only 3 dB above the noise generated in the following stages.
With the maximum IF gain setting, half of the noise power heard in the output is coming from stages later than the first RF amplifier. Then I performed the adjustment as above and measured the difference between the
antenna trimmer peak and minimum settings. When I did this, I found the difference to now be 5 dB. Now only about 1/3 of the noise power heard in the output comes from the later stages. Your results may vary depending
on how much gain your receiver has ahead of the stages controlled by the IF Gain pot. If you can't hear the noise peak as the trimmer is rotated through resonance, there is something wrong with your RF deck. I would be
interested to hear your experiences running this procedure. Is my receiver typical, or do I need to give it a tune-up? Contribution by Joe Buch, N2JB |