> One of those, in particular, is that (approximated to the 2nd
> harmonic), distortion in a square law detector is actually
> lower when a steady state AM signal is tuned to remove most
> of one sideband than when the carrier is centered in the
> passband. ... Blah blah
Actually, that's not correct. Lankford adjusted the square law equations to
the case of diode (half-wave detector) multiplying by the Fourier series for
half-wave rectification.
Some preliminary tests done at 7 Khz with a 1000 Hz AM signal modulated at
50% on the Orion II subreceiver does indeed show some increase in 2nd order
harmonic distortion when the passband is shifted.
Generator 8640B at 7 Mhz; modulated 50% at 1 Khz.
BW: 6000 Hz, PBT: 0 No discernable 2nd harmonic
Following are the 2nd order products relative to the fundamental for various
settings of PBT. Total AUDIO bandwidth is 5000 Hz at 2K shift and 5500 Hz
at 2500 shift.
PBT
- 2000 Hz: -45dB
- 2500 Hz: -33dB
+ 2000 Hz: -33dB
+ 2500 Hz: -34dB
The largest of these (-33dB) represents 0.05% harmonic distortion. A
relatively small number. 3rd order products were visible but well below 2nd
order, and I didn't take the reading.
Grant/NQ5T
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|