[Milsurplus] bc-348 design question

[hwhall at compuserve.com]

> 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 on having a stronger BFO than normally designed for CW operation. 

Wayne
WB4OGM

 

-----Original Message-----
From: WA5CAB <WA5CAB at cs.com>
To: jphutch60bj <jphutch60bj at gmail.com>; Milsurplus <Milsurplus at mailman.qth.net>
Sent: Sun, Dec 11, 2011 9:15 pm
Subject: Re: [Milsurplus] bc-348 design question


The BC-224, of which the BC-348 was an offshoot, was designed in the mid 
30's.  SSBSC didn't come into general use until the mid 50's, by which time 
almost all BC-348's had been retired.  The squelch box for the BC-348 in the 
AN/MRC-20 was part of a stop-gap or ad hoc system that was not expected to 
remain in service more than a short time before it was replaced by newer 
equipment.  There is no logical reason why the Air Force should have spent any 
time or money improving the SSB performance of the BC-348.

In a message dated 12/11/2011 21:44:40 PM Central Standard Time, 
jphutch60bj 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
wa5cab dot com (Web Store)
MVPA 9480
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