Topband: BC Images

[Tom Rauch]

> I've seen a few posts about AM BC band images at frequencies evenly
> divisible by 10 Khz ... makes sense, I guess, however I do not hear
> any of them.  Should I?  I'm beginning to wonder if there's something
> wrong with my receiving setup?

I would think anyone in or near the USA would hear some 
harmonics, unless their noise floor is covering them up. Most of the 
harmonics and spurious are fairly weak here however. I hear 
multiple stations from multiple directions on 1800, 1820, 1830, 
1840...although most are weak.

I also hear a few Airport NDB harmonics. 

I've made it a point to identify some of the stronger stations and 
report them. So far it has been a 100% hit as they've checked 
stations, and found them out of spec. A few of the stronger stations 
have disappeared. Several more stations are on a list for FCC 
visits, including two stations in Alabama.

On the topic of reporting problems, we have to be very careful to be 
sure the spurious signals we hear are actually transmitter 
problems. A test would be installing a good highpass filter ahead of 
any potentially non-linear devices like preamplifiers or diode 
"clamps", use of a step attenuator to make sure the harmonic 
decreases at the same rate as the attenuation that is added (make 
sure you know your "S" meter's real accuracy), and trying a couple 
different type of receivers and antennas if possible.


73, Tom W8JI
W8JI@contesting.com