[ARC5] OT? bc-348 bfo question

[Fernando - LU2DFM]

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