[R-390] re: Call for measurements - 100dB carrier reading

[Roy Morgan]

At 09:00 PM 8/30/2007, Jim M. wrote:
>..."pulling" of the 17 Mhz 1st crystal oscillator by strong signals with 
>AGC turned on.  As the AGC varies, the osc. pulls 50-80 Hz causing a chirp 
>or whoop on CW

I have not dealt with this one, but here are my ideas:

  - The 17 mc signal goes to a mixer - that mixer may be affected by the 
level of incoming signal and change the load on the oscillator.  Part of 
the oscillator-mixer design is to minimize this effect.

- The AGC is likely reducing the load on the B+ used by the RF and/or IF 
stages. This B+ may well be affecting the oscillator itself.  Test by 
measuring carefully the oscillator B+ level.  Is the oscillator fed from 
regulated B+?  Test by pulling the regulator and feeding the regulator tube 
output pin with a separate, preferably regulated, supply.

  - there may well be some component in the oscillator such as a bypass 
cap, that is B+ sensitive.

  - If you have another R-390A, you might feed the 17 mc from the other 
radio, or feed a 17 mc signal into the crystal oven socket from a stable 
signal generator.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
13033 Downey Mill Road, Lovettsville, VA 20180
Phone 540-822-5911   Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-975-6097
roy.morgan at nist.gov --