[TowerTalk] coax stubs /bandpass filter

[Stan Stockton]

Rag,

Sometimes it seems there is a big difference between theory and practice in dealing with solutions to inter-station interference.

I am guessing you would not be as concerned if you just had a strong second harmonic, equivalent to yet another 40 over S9 signal on the band. Instead, perhaps you have a trashy out of band signal all over the other band?
   
There are many other factors that can come into play than what stubs you use and the length of those stubs.  Other cables and devices that you think are not a problem could be the entire problem.  Unfortunately there is not as much written about the real world, testing and solutions as there is about textbook theory.

As an example, I have a homebrew coaxial filter made from an article in NCJ for 40M that makes absolutely no difference  
in attenuating harmonics from 40M when the SWR goes SKY HIGH above about 8.5 Mhz.  Same experience when I borrowed a high power bandpass filter from W3NQN a few years ago. 
 
Perhaps try your stubs away from the station in a temporary set up on someone's kitchen counter-top  
with a very simple antenna setup to see if they are more effective.  If  they are start looking at why they don't work at the big station. 
 
Stan, K5GO 
www.cycle-24.com

 
---- Stein Roar  LA6FJA-K3RAG <s-roabr at online.no> wrote: 
> Hi
> 
> I have made a set of coaxstubs for bandpass filter, but it is not enough attunation..
> Is it normal with 20-30 db attunation ??
> 
> 
> We had big problems during WPX SSB as LN5O we experienced that the stubs didnt attunate enough between 20 40 & 15m...
> 
> Have anyone idea about kits or assembled coils for making bandpassfilters ?
> 
> Is there anyone having a old bandpassfilter(s) box collection dust or having ideas how to build contact PM to la6fja at gmail.com
> 
> 73 LA6FJA Rag