[Milsurplus] bc-348 design question

[C.Whitaker]

de WB2CPN
When we were trying to copy frequency-shift facsimile weather maps
on the RBP-2 Navy receivers a long time ago, we had the best results
by running the receiver in AM mode, and loosely coupling a BC-221
freq meter to the receiver antenna terminals.   Circuit from Tokyo to
Andrews AFB near Wash DC.
73  Clete


On 12/12/2011 11:26 AM, jcoward5452 at aol.com wrote:
> 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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