> afaik all analogue frequency shifters, no matter which brand,
> share the same problem. please somebody correct me if i'm wrong.
> the modulator signal cannot be suppressed for 100%, there is
> always a portion of the modulator signal intruding the shifted
> output. with careful calibration this bleedthru can be minimized,
> but not totally eliminated. some designs have a sort of automatic
> noise gate (bode used the term "squelch"), which mutes the output
> when the input signal level drops below a certain threshold,
> consequently cutting out the bleedthru and other unwanted
> artifacts during signal intermissions.
> this trick can be done easily by using an a119, a vca and maybe
> a slew limiter or envelope to get smoother transitions between
> "on" and "off".
>
> best wishes
>
> ingo

You are right. No matter which multipliers are used in the ring modulators
(e.g. MC1496, AD633, AD534 ...) there is always some feedthrough of the
carrier signal. Only the squelch circuit you mentioned will cancel the
feedthrough. After all it's the question if such a sqelch circuit has to be
an integral part of a ring modulator or frequency shifter or not.

Best wishes
Dieter Doepfer