[Hi-zreceivingarraydiscussions] BC IMD

[Paul Christensen]

Lee,

N4CC and I installed the new Hi-Z preamps on our 160m 8-cicle array.
Balance is better than with the old preamps and while listening last night,
F/B was excellent with no signs of skewing.  However, starting at 6:15am
this morning, I heard significant broadcast band IMD every 10 kHz on 160m.
We have a Hi-Z HPF between the controller and Hi-Z final preamp.  

The main culprit seems to be WBOB-AM.  In a prior life I was Director of
Engineering at the station.  It operates with 5KW on 600 kHz.  ND daytime,
and 5-tower DA inline array at night with a very narrow lobe to the east,
right over Jacksonville.  Our site is about 15 miles NW of WBOB-AM and as
such, the nighttime pattern has very little effect on us.  But the ND
daytime field strength is very strong.  I don't recall the post-sunrise
switch time for the month of November, but I'm guessing it's at 6:15 am.

I see that Jeff, AC0C is using a notch filter right at each Hi-Z whip
antenna preamps.   I will do some more investigating but if it turns out
that we need the filters, do you supply these?  Any impact on system balance
with these filters?  Also, I am not sure if 600 kHz is the only Jacksonville
station causing a problem.  It's certainly the main cause at the moment.
Others that are potential candidates in Jacksonville are at 690 kHz and 1460
kHz.  

By the way, I don't recall having the BC IMD issue with the prior antenna
preamps.  Just an observation.

Paul, W9AC