🚀 go-pugleaf

jgk@osc.COM (Joe Keane) writes:
>I want to buld a circuit to phase shift an audio signal by 90 
>degrees.  I also want this to work over a range of frequencies and 
>have fairly flat amplitude response...

>I also noticed a 90 degree phase shift is one way to make a SSB AM 
>signal. They don't say how to do this, other than that it's difficult 
>to get exactly right...

The phasing method of generating single sideband requires that the 
audio phase-shift network be accurate within a few degrees, else the 
unwanted sideband is insufficiently suppressed.

The best explanation I've ever seen of the phasing SSB method is in 
_QST_ magazine, January 1988: "A New Breed of Receiver" by Gary Breed 
(editor of _RF Design_ magazine).  The article contains plans for an 
all-pass 90-deg. audio network made of 8 op-amps with precision 
resistors and capacitors.

90^ audio phase-shift can also be done with a passive network of LOTS 
of resistors and capacitors.  See old ARRL SSB Handbooks.

--

Frank Reid     W9MKV     reid@ucs.indiana.edu