[ARC5] OT? bc-348 bfo question

[Christopher Bowne]

My BC-348s (have used 2) both are poor in the AVC position for either CW or SSB,.  Using MVC  gives perfromance similar to other sets of that vintage, none to my knowledge had good CW or SSB reception with AGC engaged.  at the time it was mainly used to combat fading on AM signals.




________________________________
 From: Fernando - LU2DFM <lu2dfm at gmail.com>
To: arc5 at mailman.qth.net 
Sent: Saturday, September 14, 2013 9:03 AM
Subject: Re: [ARC5] OT? bc-348 bfo question
 

On Sat, Sep 14, 2013 at 08:29:10AM -0400, D. Platt wrote:
> All of you guys have it right.  The BFO injection needs to be
> upwards of 25% to 50% of the received signal level, at the point of
> mixing.  Unfortunately, the BFO signal is fixed and one must use the
> RF gain to bring that ratio back into some sort of reasonable

At full level, the BFO just gets in the verge of 50% of FI signal level
only for mid level signals at the antenna. But this is perhaps ok.

The BFO level, however, is not fixed in MVC position, the Vp
of the BFO osc. triode is the MVC line controlled voltage.

> number, but at the expense of gain.  Increasing the BFO injection
> will certainly help.  Its only when signals are at or near the
> receiver MDS that too much BFO can be a negative factor.  Truth
> told, I really don't know what the actual ratios are in these old
> radio sets.  I read somewhere that only a very small percentage of
> signal voltage is required to provide a usable CW note.   I'd be
> curious to know what results you find in the BC-348.  I know that in
> receivers such as the S-40( ) and the SX-99, twisting the gimmick to
> twice the turns does, in fact, help.

I'm suspecting same thing here. Besides that, the gimmick in my rx is
barely 1/2 turn.

Thanks.

-- 
73 de Fer, LU2DFM
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