[Elecraft] K1 with 4 bands

[Tom Hammond]

Hi Don:

WA9TGT / Don wrote:
>I have heard that if you choose 80 meters as one of the 4 bands you want 
>to use with a 4 band K1 filter board it will limit you to only being able 
>too use 3 bands in total.  Any one have any information on this that they 
>can share?

Each of the (2) bandpass filters on the KFL-4 board must work for two 
bands. As a result the frequencies of the two bands must be close enough 
together than the higher of the two frequencies is NOT an integral multiple 
(harmonic) of the lower frequency. If it was, and the filter was designed 
to pass it, it'd also pass any harmonic energy of the lower band... which 
comes under than heading of "Bad Things Will Happen".

So, if you chose 80M as your lower band, then the filter would have to have 
its cutoff BELOW 7 MHZ (40M) in order to not pass 80M harmonic energy. This 
precludes you using that particular bandpass filter for two bands, since 
(ignoring 60M for the moment) 80M and 40M are the only two ham bands which 
are commonly used and which are next to each other.

40M and 30M works because the BPF has its cutoff BELOW 14MHz, so it 
attenuates harmonic energy from both 40M and 30M.

Hope this helps.

73,

Tom Hammond    N0SS