Re: {Collins} Crystal Filter



Correction to my previous filter type should read F455B3. Sorry


Clarence G. Marshall
K5CGM
AC10-12553

Tube radios keep your shack warm in the winter...




-----Original Message-----
From: Collins [mailto:collins-bounces+bonaire=olp.net@xxxxxxxxxxxxx] On
Behalf Of Bill Carns
Sent: Sunday, August 25, 2013 2:49 PM
To: 'Richard Knoppow'; collins@xxxxxxxxxxxxx
Subject: Re: {Collins} Crystal Filter

Excellent contribution

-----Original Message-----
From: Collins [mailto:collins-bounces+wcarns=austin.rr.com@xxxxxxxxxxxxx] On
Behalf Of Richard Knoppow
Sent: Sunday, August 25, 2013 2:43 PM
To: collins@xxxxxxxxxxxxx
Subject: {Collins} Crystal Filter

     Perhaps somewhat OT.  The crystal filter used in Collins A line
receivers up to the 75A-3 and in the 51J receivers was a slightly modified
version of the patented Hammarlund filter.  This filter was introduced in
the Hammarlund HQ-120-X and made available later in the Super-Pro 200
series.  The same filter appears to have been used in some TMC receivers and
perhaps others.  The filter was designed to eliminate some of the
shortcomings of the original James Lamb filter which was introduced in the
mid 1930s and used by National, Hallicrafters, and several others.  For
those interested the patent is:
USP 2,222,043 and there is a good description of the circuit by its
inventor, Donald K. Oram, of Hammarlund, in the December, 1938 edition of
QST.
     The main virtue of this filter is that its passband stays symmetrical
as its bandwidth is changed and the center frequency does not vary with the
notch frequency (phasing adjustment).


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
 

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