[Hammarlund] Hammarlund Crystal Filter

[Richard Knoppow]

     Hammarlund introduced a patented crystal filter in the 
HQ-120-X. This filter has the advantage that its bandwidth 
can be varied over a wide range while maintaining a 
symmetrical shape and that the notch or phasing adjustment 
does not change the center frequency. Slightlyl modified 
versions of this filter were used in some Collins receivers 
and in some TMC receivers, and perhaps others. For those 
interested the patent is:
USP 2,222,043  issued to Donald K. Oram, who was chief 
engineer of Hammarlund. Oram also wrote an article in the 
December `1938 edition of QST describing the circuit.
     Another note:  It appears that one of the 
Hammarlund-Roberts receivers was called a Hi-Q and I wonder 
if the later HQ series of receivers perhaps inhereted their 
model designation from this early receiver.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com