Hi Lawrence,
Not wishing to duplicate what I have written elsewhere, but there may be others here, following this thread, who haven't read the thread elsewhere to which you refer.
One modification to the RA-17 that does eliminate the 'BFO signal appearing on the R.F. level metering' is the conversion of the BFO to a product detector. I fitted such (based on a 6BE6) to my RA-17W. That mod. was primarily fitted to improve the resolution of SSB - which it does very well. The disappearance of the 'BFO signal appearing on the R.F. level metering' just happens to be a fortunate by-product.
The technical bit . . .
The modulated SSB signal still passes through the A.M. detector and its load and filter, so the resultant current that is fed to the R.F. level metering is a measure of the instantaneous amplitude of the SSB signal. The modulated SSB signal is simultaneously and separately demodulated in the product detector (using the original BFO oscillator cct.) and the resultant audio is thus extracted. The carrier injection signal thus never 'escapes' into the rest of the circuitry of the receiver. A simple switching arrangement (ganged to the 'BFO' H.T. on / off switch) simply selects the appropriate detector source: A.M. or SSB - and feeds that selected audio to the A.F. amplifier, via the A.F. volume control.
The one real problem in implementing the modification is simply one of fitting all the components that comprise the P.D. into the existing BFO housing: there is very little room to spare and a good deal of 'shuffling things around' in that housing is necessary. So it's more than a 'five minute job', but well worthwhile and once fitted, you tend to forget that the receiver's metering ever 'worked' in a different way, plus the improved SSB resolution. You can set the I.F. gain control to any 'comfortable' setting, depending of the strength of the received signal, noise & QRM, etc. Turning down the I.F. gain and advancing the A.F. gain, when receiving SSB, then becomes a thing of the past.
Al.
Not wishing to duplicate what I have written elsewhere, but there may be others here, following this thread, who haven't read the thread elsewhere to which you refer.
One modification to the RA-17 that does eliminate the 'BFO signal appearing on the R.F. level metering' is the conversion of the BFO to a product detector. I fitted such (based on a 6BE6) to my RA-17W. That mod. was primarily fitted to improve the resolution of SSB - which it does very well. The disappearance of the 'BFO signal appearing on the R.F. level metering' just happens to be a fortunate by-product.
The technical bit . . .
The modulated SSB signal still passes through the A.M. detector and its load and filter, so the resultant current that is fed to the R.F. level metering is a measure of the instantaneous amplitude of the SSB signal. The modulated SSB signal is simultaneously and separately demodulated in the product detector (using the original BFO oscillator cct.) and the resultant audio is thus extracted. The carrier injection signal thus never 'escapes' into the rest of the circuitry of the receiver. A simple switching arrangement (ganged to the 'BFO' H.T. on / off switch) simply selects the appropriate detector source: A.M. or SSB - and feeds that selected audio to the A.F. amplifier, via the A.F. volume control.
The one real problem in implementing the modification is simply one of fitting all the components that comprise the P.D. into the existing BFO housing: there is very little room to spare and a good deal of 'shuffling things around' in that housing is necessary. So it's more than a 'five minute job', but well worthwhile and once fitted, you tend to forget that the receiver's metering ever 'worked' in a different way, plus the improved SSB resolution. You can set the I.F. gain control to any 'comfortable' setting, depending of the strength of the received signal, noise & QRM, etc. Turning down the I.F. gain and advancing the A.F. gain, when receiving SSB, then becomes a thing of the past.
Al.
