I got a nice e-mail from Jack Burchfield at Ten Tec about the AM distortion
problem. He listened to my recording and agreed that the Orion II didn't sound
as good as it should, and explained that the dual-loop AGC system with the new
adjustable hang time has to be slowed down to sound good in AM. He suggested
using a hang of 3 to 4 seconds.
I increased the hang time to 4 seconds and that cured the distortion! I didn't
realize that the two AGC loops were so independent and I had been thinking that
a slow decay time coupled with a hang time of more like .5 seconds would
eliminate AGC distortion from the equation. It does take a very long hang to
clean up the sound. The short hang time is apparently what was causing the
clipping and the "crunched" sound due to severe loss of dynamic range.
I made a new recording that I will place on my website later that demonstrates
how AM sounds when the settings are changed. I recorded a 40 meter short-wave
broadcast station on both receivers simultaneously with the 870 in the left
channel and the O2 in the right. I split the channels and made separate MP3
files of each radio. I also backed off the bandwidth of 870 and matched the O2
so the -3 dB points were at the exact same frequency. Both receivers were fed
from a T connector to the same antenna. The results were outstanding! The
only noticeable difference is the AGC action, and that the O2 handled the
really deep fades better than the 870.
Good work TT! I'll mark that off the 'fix' list...
Ron N6IE
www.N6IE.com
(Formerly N6AHA)
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