[Milsurplus] bc-348 design question

[C.Whitaker]

de WB2CPN
First, You'll have to run the Audio Gain up, and run the RF Gain down.
Use the RF Gain to control the audio volume.  This is true of all the
old receivers.  Set the BFO about 1.5 KHz to one side or the other
depending on whether you're running USB or LSB.
In 1962 I modified an SP-600 to incorporate a "Hot Carrier" SSB
demodulator.  Info from QST or CQ or something.  Used a 6BE6
with the CW oscillator output connected to the control grid, and the
IF output connected to the other grid.  The receiver AVC needs to
have a very large capacitor placed across it.
Run the RF Gain wide open.  No distortion.
Trivia:  Space for the 6BE6 was found by replacing the 6AL5 which
is on the rear side with a couple of diodes.  Minimum Hacking.
Also, I did 22 years with AT&T Long Lines where I learned that almost
all their multichannel carrier systems used SSB.  With a Hot Carrier
Bridge demodulator.  There was no AGC or AVC in their equipment.
73  Clete


On 12/11/2011 11:58 PM, hwhall at compuserve.com wrote:
>
>
>
>> 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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