Hi Paul,
I've done a lot of reading through the reflector archives on this
topic lately. You are going to run into the same problem I have - my
plan is 80 / 40 / 20 / 10.
The 4-band filter board only uses two low-pass filters. The filters
are shared, so the 40 and 30 meter bands share one filter and the 20
and 17 meter bands share the other filter. This is possible because
the first harmonic of the low frequency is higher than the high
frequency. In other words, the 30/40 meter filter cuts off below
14MHz but above 10MHz - thus passing both 30 and 40 meters but not
allowing the 1st harmonic of 40 meters to get through. The same
thing on the 20 & 17 side.
So if you were to pair 80 and 40 meters, or pair 40 and 20 meters,
you're going to let out the 1st harmonic of the lower of the two bands.
One solution you could do is go ahead and build your board for
80-40-20-17 if you want, then build an external low-pass filter for
80 meters. You could fit it in a small enclosure with BNC connectors
in and out, then just remember to pop that on before you transmit on
80, and remove it before you switch to the other bands. It would
probably impact the internal ATU, and it's an external device, but it
would do the job.
I can let you know what changes I've made to my 4-band filter board,
to replace the 40/30 side with 80/40 if you like.
Stephanie Maks
va3uxb
K1 # 02132
On 26-Dec-2005, at 17.07.41, Paul Webb wrote:
> HI
>
> Having now got my K1 running correctly its time to mod it!
>
> I have the 4 band card fitted on 40/30/20/17m but being in the UK I
> find
> that 80m is the best bet at night, I know I could fit a 2 band card
> but I
> would prefer to keep 40/20m too,
>
>> From reading the archive I see that there as been some talk about
>> fitting
> 80m onto a 4 band card, but I understand if you do you can only use
> the 4
> band module on 3 bands.
>
> Anyone done this and if so what bands can you get? 80/40/20??
>
> All the best
>
> Paul
>
> M0BMN
>
> K1 #2139
>
>
>
>
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