Topband: BC filters - the rest of the story

[donovanf at starpower.net]

Paul,

There were two confusing typos in my prior e-mail.  Lets try again!

I'm sorry to hear about your furnace RFI problem.  I have similar furnace RFI, in my case the furnace is more than 1/2 mile away!  My Beverages limit the problem to the southeast direction only.

Your skywave interference intermod should be easy to resolve, since most of us have little or no problem at all.  There should be no need for a very sophisticated brick wall BC band filter.

I use inexpensive W3LPL bandpass filters 
http://www.k1ttt.net/technote/w3lplfil.html

to protect relatively inexpensive ARR P1-30/20VD preamplifiers
http://www.advancedreceiver.com/page46.html

I've never had any trace of AM broadcast intermods with this simple setup.

Good luck, I'm sure you'll find a solution to your intermod problem.

73
Frank
W3LPL


>---- Original message ----
>>Date: Thu, 05 Jan 2012 18:26:28 -0500
>>From: N1BUG <paul at n1bug.com>  
>>Subject: Topband: BC filters - the rest of the story  
>>To: Topband <topband at contesting.com>
>>
>>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
>>
>>
>>_______________________________________________
>>UR RST IS ... ... ..9 QSB QSB - hw? BK
>_______________________________________________
>UR RST IS ... ... ..9 QSB QSB - hw? BK