One other reported a similar problem on his loop
antenna. The radio station he reported the problem
with transmits on 840khz. 1/4 wave on 840 is 278ft.
If his loop is full wave on 3.6 mhz its length is
about 278ft. Suspicious to say the least. In fact I
think it is a red herring. On a resonant antenna a
couple of miles from a 50kw transmitter, I am not
surprised significant voltage could be present on the
antenna terminals of the Orion. Neither am I
surprised that a 6db pad might be enough to clear the
problem. In fact I would predict such a conclusion.
So what makes the loop so special? He did not say he
had trouble on all antennas, only on his loop which
he said was a very challanging antenna for BCI. He
also noted that the problem went away when he used a
tuner, which would give attenuation to the 840khz
signal, the same as a pad. So my guess what makes the
loop so special is that is has a resonance on 840khz.
This has not been a commonly reported problem with
this radio on this list. In fact just the opposite is
true. Many operate these radios in full tilt multi
station and SO2R contesting situations with success.
If it was a common problem that a couple of stray
volts on the antenna terminals made the clamp diodes
go non linear, people would be howling to the hills
about how bad the Orion is for contesting. This is
not the case. So given that the experiment has been
done in contests repeatedly and is probably being
conducted this weekend during the WPX test, it makes
me wonder why you have the situation and most others
do not.
So given your RF engineering background you might
consider seeing if you lost bias on the diodes, just a
suggestion of course.
Another tact might be to poll the membership of the
list and see just how common the problem is. I'm sure
there are many hams who live within a few miles of a
broadcaster. If it is a design flaw you would expect
the problem to be common since every radio would
contain the precursor to the problem. So that's the
null hypothesis, a design flaw should lead to a
predominance of BCI problems. The alternate
hypothesis would be that the problem is not common and
therefore not a design flaw. I have an Orion, I live
3 miles from a broadcast station on 880khz, and I have
no problem like you describe. So put that bit of data
in the "not common therefore not a design flaw"
column.
73 W9OY
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