[Milsurplus] bc-348 design question

[jcoward5452 at aol.com]

You can use a LM or BC-221 as a SSB external BFO. Works great and far less "drifty".
Jay KE6PPF



-----Original Message-----
From: hwhall <hwhall at compuserve.com>
To: Milsurplus <Milsurplus at mailman.qth.net>
Sent: Sun, Dec 11, 2011 8:58 pm
Subject: Re: [Milsurplus] bc-348 design question





 When receiving SSB signals, with the BFO on, seems that strong signals 
 swamp the injected BFO signal.
 
 Seems I recall reading in some old literature that good SSB reception depended 
n having a stronger BFO than normally designed for CW operation. 
Wayne
B4OGM
 
-----Original Message-----
rom: WA5CAB <WA5CAB at cs.com>
o: jphutch60bj <jphutch60bj at gmail.com>; Milsurplus <Milsurplus at mailman.qth.net>
ent: Sun, Dec 11, 2011 9:15 pm
ubject: Re: [Milsurplus] bc-348 design question

he BC-224, of which the BC-348 was an offshoot, was designed in the mid 
0's.  SSBSC didn't come into general use until the mid 50's, by which time 
lmost all BC-348's had been retired.  The squelch box for the BC-348 in the 
N/MRC-20 was part of a stop-gap or ad hoc system that was not expected to 
emain in service more than a short time before it was replaced by newer 
quipment.  There is no logical reason why the Air Force should have spent any 
ime or money improving the SSB performance of the BC-348.
In a message dated 12/11/2011 21:44:40 PM Central Standard Time, 
phutch60bj at gmail.com writes: 
 When receiving SSB signals, with the BFO on, seems that strong signals 
 swamp the injected BFO signal.
 
 I wish I had an opportunity to  talk, read, about the design 
 considerations  made by the RCA designers on the BC-348.   After some 
 time looking at the circuit and playing with the restored R version; 
 Questions formed -
 
 Why was the 2 IF not set to some predefined gain ,  with the cathode 
 resistor to ground,  and with and AGC-AVC directly applied to the grid 
 of the second IF; regardless of the MVC-AVC switch position ?
 
 IMO this would have stabilized the BFO circuit since I can hear a slight 
 pitch change when adjusting the MVC when listening to SSB transmissions?
 
 The military wen to the trouble of adding in  a squelch circuit.  Why 
 was there not a mod for the BFO  / 2 IF circuit to make SSB reception a 
 bit better?
 
 Hutch
 
Robert & Susan Downs - Houston
a5cab dot com (Web Store)
VPA 9480
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