[BC] R Orban's comments

DHultsman5@aol.com DHultsman5
Thu Dec 21 08:41:57 CST 2006


 
In a message dated 12/20/2006 5:50:48 PM Central Standard Time,  
rorban at earthlink.net writes:

When you  modulate the audio on RF in the form of double sideband suppressed  
carrier, you can now use a single variable-mu tube to change gain. The  gain 
control signal will appear as low frequency thumps at the output of  the 
tube. However, when the DSB suppressed carrier signal is changed back  to 
audio via a product detector, the thumps get frequency-shifted outside  the 
audio band (to approximately the carrier frequency) and can be readily  
filtered out.

As an interesting side-effect, this process does not  add harmonic 
distortion even though the variable-mu tubes, being nonlinear  devices, 
always add nonlinear distortion to the audio. If the carrier is  at 1 MHz, 
for example, the second harmonic caused by nonlinearity in the  gain-change 
tube will appear at 2 MHz. After product detection, this  harmonic will 
appear at 1 MHz and can be readily filtered out. This also  happens to be 
the operating principle of a RF clipper, which is another  audio processing 
technique that produces no harmonic distortion. (Some of  our processors 
have used a "computed RF clipper" using Hilbert transforms  to exploit this 
fact. See US Patent  4,495,643.)



*********************************
 
Bob:
 
>From your recollection and Mark's schematic,  it appears that the  audio 
delay line in the General Electric BA-5  was a passive delay  line.    The GE BA-6 
 had the DSB Generator built-in.   This was the unit that gave me some 
problems with my old Western transmitter  which would pass DC to light  (well 
nearly).
 
Does anyone have on file a diagram of the last GE Peak Limiter the single  
chassis BA-6?
 
Thanks
 
Dave Hultsman


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