[CQ-Contest] Stubs - 40 & 15 meters

[Jukka Klemola]

>> Pretty simple - see W2VJN's book on stubs "Managing Interstation
>> Interference"
>>
>> My copy is not at hand here, but as I recall it involves a quarter
...
>> But, check the book for more details.  I tried it back when I did a book
>> review of
>> it for NCJ and it worked FB.
>
> Thinking about that logically, it appears it would still pass 40 meters to
> me.
>
...
> I don't see how that would reject 40 at all.
>
> I have ran the stub impedances to get exact values, but off the top of my
> head I can't see why that would null 40. It should pass both 15 and 40.
>
> 73 Tom


In my systems the 40m signal entering 15m is attenuated by band filters.
Even ICE with old school micas is OK, after which FT1000MPs survive no problem.
I use always band filters if I have more than one HF radio connected
and I have experienced no problems due to this combination.


If, after this, you are still worried and want to attenuate / mismatch
a 40m signal trying to enter a 15m system, you could use a shorted 7'
8" of RG213 that passes 15m.

It will attenuate the 40m signal to 'some' extent.


Actual nulling of F/3 is explained on page 28 of VJN's book Managing
Interstation Interference.
http://www.qth.com/inrad/book.htm
Building one is not as straightforward as the other stubs we have been
writing about.


..when thinking about these, I bumped into
http://www.yccc.org/Articles/K3NA_stubs.pdf
and also
http://www.e73m.com/NotchCoax15m.php.


One thought that came into my mind would be to see what would happen
reversing the 40m passing but 15m nulling stub. So, to make it the
other way around, like:
7' 8" .. short
15' 3" .. open

If I would need such 40m nulling 15m passing stub, I would start by
simulating this one.
= I have not tested this idea. It probably will not work.


73,
Jukka OH6LI