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The AGC characteristics of R-4C receivers depends on the version of the receiver. There were at least two that I know of. Furthermore, modifying agc time constant was something that may individuals tried way back when. There were several articles dealing with that subject including one in the March 1980 issue of CQ magazine in which the author modified his R-4C to mimic the Collins 75S3-B. Maybe this is because fast, medium, and slow is subjective and everyone has their own idea of what it should be. Nevertheless, the fast AGC position in the stock R-4C is much too fast for my taste and lacks filtering so I added a 0.05 uf capacitor from Q7 collector to ground to suit myself. As it is, the R/C combination of C43 a 0.01uf capacitor and R16, a 1 meg resistor as well as C75 a 0.0024 uf capacitor provide a bare minimum of filtering. If there is motorboating, I would check these components and make sure they are in the circuit and working properly. Additionally, C76 a 0.001 uf capacitor may also be opened. The fast AGC position is meant to be used on CW and possibly AM. It was never intended to be used on SSB. The R-4B agc is a similar design but with different values of gain and time constants. The fact that the R-4C has sharper bandpass IF filters accentuates the problem.
-----Original Message-----
Bob: I agree with Mark about the AGC issue you have described. The audio will have a somewhat distorted sound at times when in the fast AGC position. Slowing the AGC release time down just a bit will resolve that issue. I personally never use the Fast AGC position. I have owned many Drake receivers over the years and have found this to be common. I doubt you really have a problem.
73, Don / WA9TGT |
- RE: [drakelist] R4C agc problem Gerry
- Re: [drakelist] R4C agc problem Bob Henderson
