Grant:
What do you see at 100% modulation? I have noticed a fair bit of distortion
on AM on the O2, even on ground-wave commercial broadcast signals, and have
reported this to TT. I don't hear it at lower levels of modulation, and
it's most noticeable on peaks, particularly on voice. Sounds like
flat-topping of some sort.
Ron N6AHA
----- Original Message -----
From: "Grant Youngman" <nq5t@comcast.net>
To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
Sent: Friday, March 17, 2006 1:39 PM
Subject: Re: [TenTec] Further Orion Sub Receiver -- Some results
>> 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
>
>
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>
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