[TenTec] Orion AM RX Performance Measurements

[Grant Youngman]

> Orion can deliver up to 1.4 W into 4 Ohm load with less than 
> 0.5 % THD, using HANG of 0.3 seconds and 5 dB/s.

Higher THD with rapid decay rates can be reduced, nearly to baseline, by
increasing Threshold, and keeping the the signal under the point where AGC
begins to operate.  Clearly, as the measurements show,  fast AGC is
interacting with the signal to raise THD.


> An attempt to shift PBT by 1200 Hz in order to obtain wider 
> response, results in response being DOWN by almost 6 dB from 
> 1850 Hz up.

As the shift is increased, the point at which the output falls off moves
lower in frequency.  For example, at 1900 HZ shift, the response drops
between 1000-1250 Hz, and then remains reasonably flat out to about 4800.
Hz.

THD also increases significantly in roughly the 2000 Hz shift region, moving
from fractional %THD to the order of 6% at 2000 Hz and 10-12% at 2500 Hz (50
uV, 7.0Mhz, modulated 90% at 1 Khz)

I also observed that engaging the 6 Khz roofing filter (selected in AUTO)
rather than manually selecting the 20Khz filter raises THD at 0 shift into
the 4% range.  By 1000 Hz shift, the THD numbers are back in line with the
20 Khz filter, then rising to about 6% at 1800 and 10% at 2000 Hz shift.

So --- on the Main receiver it's certainly a good idea to manually select
the 20 Khz roofing filter for AM.  And on either, and if you off-center tune
or use PBT, keep it 1900 Hz or so below.

Grant/NQ5T