> Here is my problem. I was sent here for ideas. I have three loud
broadcast
> stations with in close proximity. The weakest is 810 and the strongest is
> 1540. The problem is that 1540 is the also the closest to me. For some who
> know what this means (I do not), here are the readings that I got:
> In the basement shack:
> 810 100 microvolt/meter
> 980 100 microvolt/meter
> 1540 350 microvolt/meter
> At the tower (with in a foot)
> 810 1 volt/meter
> 980 1.3 volts/meter
> 1540 10+volts/meter
Hi Will,
It is VERY unlikely common mode chokes, especially just adding a few beads
on the coax or some wires, will do anything at all. First the impedance of
any beads is generally far too low at BC frequencies, but most important the
problem is virtually never common mode.
Unless your radio is very poorly designed or you have very bad coax
connections virtually all of these types of problems are internal mixing in
the receiver front end. On much rarer occasions it is external mixing in
non-linear joints OUTSIDE your system.
Your signal strength readings are not helpful at all, because it sounds like
you are using a FS meter near the tower, which makes the tower an antenna
and any reading on the FSM totally useless since tower coupling is unknown.
I can go back to my 300 ft tower and read similar FS 2V/m reading on a 1kW
station 4-5 miles away, but the data is mostly meaningless.
What you need to measure is the POWER of the stations INSIDE the coaxial
feedline connected to the radio. That is almost 100% certainly where the
problem is.
You probably need a good highpass BCI filter. I think you are scaring or
confusing people by giving them too much information they don't quite
understand. The 10V/m only applies when the meter is out in the clear and
not directly coupled to large antennas, like your tower!!!!
The information needed to design a filter would be how much power is INSIDE
the coax at the radio. But if it were me, I'd stick a normal hi-pass cheap T
network tuner in line *at the radio output* to just see what happens, and
use a low value of C in the network. I'd also just try a standard ICE
broadcast filter.
73 Tom
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