AW: serge frequency shifters

[Haible Juergen]

>Seems that the way one would design a frequency shifter, there 
wouldn't
>be much difference in quality between having an internal or external 
>carrier, because the carrier enters at a specific insertion point. 
 The
>difficulty lies in designing the Hilbert transform circuit (90 deg.
>phase shift)
>to be viable over a large freq. range.  It would be interesting to 
find
>out what the problems were since I am interested in an ext. carrier
>someday. Anyway I have two internal carrier Serge freq. shifters + 
use
>them all the time, they are very high quality although I have never
>owned another type.  the only difficulty I have lies in getting very 
>small amounts of shift (<= 0.1 Hz), I have to use both F/S
>(signal->upshift->downshift).  As I said this configuration is useful 
in
>feedback situations.

>--Harvey


Interesting problem. Small amounts of shift are important - but how do 
this with
an external carrier? Does it have a quadrature input for an external 
carrier?

JH.