frequency shifter - BFO problems

[Steven Cook]

> 
> I'd love to get some ideas, hints etc. what could be wrong.
> I'd always love to get some experience shared from people who already
> use frequency shifters (commerciall ones, or home built ones), if they
> also have some unsteady level when the frequency shift is near zero.
> 
> Thanks for listening, many thanks in advance for any helpful hint!
> 
> JH.

I've heard about similar problems before using 2 hf oscillators. I'm not
sure what the cause is! Have you tried using a simpler design of
frequency shifter?

I've built one using a 90degree phase network (4 opamps), Quadrature VCO
(LM13700) 2 multipliers (MC1495) and summing amp (1 opamp).

Of course it's not possible to get a through zero shift with this
arrangement, but it is possible to have a stable shift of 0.1 Hz or even
less, up or down, which I think is more usefull (?).

Swap the outputs of the VCO to switch between up and down shift, or have
both at once using sum and difference amps.

Add feedback for ultradeep phasing. Improves my girlfriend's cds no end!

Good luck,

Steven Cook.