[ARC5] OT? bc-348 bfo question

[Fuqua, Bill L]

  That will work for CW just fine since distortion is not an issue.
It should be more for AM. Just depends how much of the muffled 
AM detected SSB you are willing to tolerate.
73
Bill wa4lav

________________________________________
From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on behalf of Fernando - LU2DFM [lu2dfm at gmail.com]
Sent: Sunday, September 15, 2013 7:46 PM
To: arc5 at mailman.qth.net
Subject: Re: [ARC5] OT? bc-348 bfo question

On Sun, Sep 15, 2013 at 07:37:49PM +0000, Fuqua, Bill L wrote:
>     A bit of information of copying SSB with diode detector and BFO.
> The BFO injection must exceed the peak signal at least several times.
> The diode detector is a square law device. The output is proportional to the square
> of the input voltage which works well for receiving AM.
>   So the output of the diode detector when two signals are provided is as follows.
> Iout = Vsquared.
> So
> I out=(Vsignal+Vbfo) squared
> Expanded you get
> I out= Vsignal Squared + 2xVsignalxVbfo+Vbfo squared
>
> The Vsignal Squared represents the AM detection of the signal
> The Vbfo squared term is DC from rectified BFO signal
> However,
> The 2xVsignalxVbfo is the part of the expression that is the product of the two signals (product detector)
> That detects the SSB signal.
>
> If the BFO injection is too low you get some AM detection and SSB detection. Thus it sounds bad.
> If you increase the BFO signal the product detected signal exceeds the AM detected signal and it
> sounds much better.

Ok Bill. I have to look in an old handbook but I'm quite sure my '61 or
'62 ARRL handbook recomends 25% to 50% or perhaps 75% more BFO voltage
thant IF signal peak level.

Thank you.

--
73 de Fer, LU2DFM
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