[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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