Topband: BC filters - the rest of the story

[N1BUG]

I have received MANY excellent responses and am still working my way 
through them. Quite a number asked for specifics of my problem. I 
thought I would post that here in case someone may have other 
helpful suggestions.

I have been plagued since last February with severe interference 
from a neighbor's furnace. There is no hope for a resolution. Trying 
to combat this I recently bought an MFJ-1026 noise canceller. It 
helps tremendously, BUT due to its inherently high noise floor I 
lose S/N ratio unless I run a preamp ahead of it. Some of my 
Beverages have rather low output due to a combination of mediocre 
grounds and the loss of WD-1A wire in the "reverse" direction.

I have a hommebrew W7IUV type preamp which solves that problem but 
creates another. Whenever I use it I get severe BCI mixes every 10 
kHz across 160 meters. They are so strong that I sometimes hear 
modulation splatter everywhere across the band! It is worth noting 
NONE of this is from local stations. It only appears at night and 
the strength of the BCI follows 160 meter propagation conditions 
very closely. I thought the preamp had a problem, but rebuilding it 
twice and fiddling with bias had no affect.

At this point I honestly don't know what is going on. I have a KD9SV 
160 meter band pass filter. Here are results of a test I ran:

Beverage>Receiver = NO trace of BCI

Beverage>Preamp>Receiver = S9+ BCI

Beverage>BP filter>Preamp>Receiver = S2 BCI

Beverage>Preamp>BP filter>Receiver = S5 BCI

I repeated the test several times and ensured levels were stable and 
repeatable. QSB was not a factor.

Even though I don't clearly understand the issue, I want to try a 
filter with more BC band attenuation in front of the preamp and see 
what happens.

73,
Paul N1BUG