[Elecraft] KX-1 BC interference on 20m

[Jim Wiley]

Stephen -


Some of those SW BC stations are pretty strong - as in hundreds of KW.  
It is possible that what you were hearing is the 2nd harmonic from these 
stations operating in the 41-meter (7.10 - 7.35 MHz) Shortwave Broadcast 
(SW BC) band.


Given a 100 KW transmitter, with 2nd harmonics 40 dB down from the 
fundamental (which would be considered reasonably good suppression)  is 
still 10 watts at the 2nd harmonic, or roughly 5 times the output power 
of a 2-watt KX1.  Since the European (ITU Region 1) 40-meter SW BC band 
starts at 7100 KHz, I think,  then it would be normal to hear such 
signals starting at 14.200 and continuing up in frequency across the 
rest of the 20 meter band.


100 KW is probably more or less a "median" power level for SW BC 
stations, with some running less, and some quite a bit more - as in 500 
KW.   And, this is "real" power from the PA.  Add to this the fact that 
some stations get another 10 dB or more from antenna gain in whatever 
direction they happen to be beaming and we're talking big time 
competition with amateur signals.  Another consideration is that SW BC 
stations are usually designed to be frequency agile,  and so they often 
have antennas that can be used on multiple frequencies.  Such antennas 
can be efficient radiators of harmonic energy. 


So, the best hope is to wait for a few more years until the 40 meter 
broadcasters move above 7300 KHz, which I think is in the works, but I 
have forgotten just when it is supposed to happen.  In any case, the 
problem you describe will be with us for a few more years.


- Jim, KL7CC



Stephen Prior wrote:
As I have mentioned before, I really enjoyed using the KX-1 on holiday in
Europe this year but found that there were several broadcast stations
appearing across 20m from about 14.20MHz upwards.  I was using a roughly 
5/8
wave vertical antenna with counterpoise and the internal ATU.

Is this normal operation, or should I delve into the manual for alignment
procedures? I am at a disadvantage in that I did not build the unit.  The
radio suffered a pretty bad knock whilst camping and I am wondering if
something is adrift.

Thanks and 73

Stephen G4SJP


Stephen Prior wrote:
> As I have mentioned before, I really enjoyed using the KX-1 on holiday in
> Europe this year but found that there were several broadcast stations
> appearing across 20m from about 14.20MHz upwards.  I was using a roughly 5/8
> wave vertical antenna with counterpoise and the internal ATU.
>
> Is this normal operation, or should I delve into the manual for alignment
> procedures? I am at a disadvantage in that I did not build the unit.  The
> radio suffered a pretty bad knock whilst camping and I am wondering if
> something is adrift.
>
> Thanks and 73
>
> Stephen G4SJP
>
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft    
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>
>