[TenTec] Omni V Product Detector Mod Feedback Please

[George Stern]

Was wondering if anyone in the group has ever heard of or tried the mod described below and if so could you share your comments about wheter it was worthwhile doing.
 
Regards,
George
 
Subject: [omni_V_562] product detector improvement 





The CA3053 product detector (U3 on the IF/AF board) has been the subject of several mods intending to improve intermodulation distortion in the audio passband. W3TS has written about this at length.
The CA3028 is the same part as the CA3053, so I did some research and found a Harris Application Note AN5337 discussing the CA3028 in RF applications. In studying this info I noticed that Harris always biases pin 5 at 2/3 of Vcc, as opposed to 1/2 Vcc in the O-V. The datasheets also show this if you look close enough.

R14 and R15 form a voltage divider to provide this bias, so I put a 10K resistor in parallel with R14 to get the bias level to 2/3 of Vcc. The voltage at pin 5 in my radio is now about 5.6v, up from about 3.6v before the change.

The result is that the distortion goes away. Pile-ups now sound so clean and clear that it's hard to believe one little resistor can make such a difference.

Try it! You'll like it!