On 4/7/2011 9:26 AM, TexasRF@aol.com wrote:
> I guess I am wondering how much of the 160m QRM is cross mod vs radio
> station harmonics.
>
Good question. When I lived in Chicago, I heard occasional mixes that
I'm pretty sure were NOT generated at any of the stations involved.
They came and went as if switched at random times, and not at times that
corresponded to pattern or power changes. My QTH was about 20-25 miles
from WBBM, 50kW Non-DA on 780. Their second harmonic was audible on
1560 during the day when there wasn't enough skywave to cover it. I was
more or less equidistant from WGN and WMAQ (720 and 670, also 50kW,
Non-DA), but never heard their harmonics. .
My first job in broadcasting (in 1960) was working for a 1kW 4-tower DA
on 930 kHz that was 5kW daytime. Nulls were pretty tight, and hard to
maintain, and the Chief worked pretty hard on that. I grew up about a
mile away, and during my early days as a ham, had to contend with a loud
mix on 3870 between them and a 5kW rig on 1470.
Later, I worked for Pete Johnson in his consulting office, plotting his
calcs for new DAs on maps, and doing some of the calcs for complete
patterns. Pete, along with Carl Smith, wrote the FCC technical rules
for AM broadcasting after WWII. Carl ran a tech school in Cleveland.
Never met him. Pete was quite sharp.
73, Jim K9YC
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