[R-390] 60 Hz on Audio

[Jon Schlegel]

All,

Please check out these photos of the output of my R-390A IF Module.

This first image shows the audio output from the Diode Load signal 
line.  Input to the IF module is 455 kHz modulated 30% with a 1 kHz 
tone.  The 16 kHz mechanical filter is selected in this image.  The 
audio looks pretty clean.  Any 60 Hz that might be there really isn't visible.

http://www.vecnav.com/R-390A_IFmodule/DiodeLoadOut_16kHzMechFilter.jpg



This second image was made with the identical conditions as above 
except that the selected mechanical filter is now 8 kHz.  A 60 Hz 
component is now easily visible.  In fact it's about 25 dB or a 
factor of about 18 times worse than with the 16 kHz setting.

http://www.vecnav.com/R-390A_IFmodule/DiodeLoadOut_8kHzMechFilter.jpg



Is this kind of behavior acceptable for these receivers?

If not acceptable, what could be causing the distinct difference of 
60 Hz level just by changing the BW setting?


Thanks and regards,
Jon Schlegel WA3MVM