Lennart Michaëlsson wrote:
>
>
> Actually, changing filters in the second rx is harder. To change the
> filter in rx 1, you can just lift rx 2 out of the way. But to change the
> filter in rx 2, you must remove it and take the board out of the shield
> box to get at the screw that holds the filter!
> --
> 73,
> Vic, K2VCO
> Fresno CA
>
> ... and what filters do the test pilots recommend?
> Presently I have 6, 2.8, 0.4 and 0.25 kHz - all being 8 pole.
> Would a 2.8 and a 0.4 be enough to keep cost down for a non FM/AM man?
> Len/SM7BIC
>
That should be fine Len. There are also a couple of other issues people
should be aware of, especially if you plan to use diversity:
1. I would not mix filters of different types that are near the same
bandwidth (i.e. a 2.7k 5-pole with a 2.8k 8-pole). Use both 5-poles or both
8-poles, not one of each. The reason is that you want the passband shape
and filter offset to match as closely as possible.
2. If you have 5-pole filters, it may be necessary to get matched sets from
Elecraft. The reason is that there will be a frequency difference in
diversity if the filters don't have the same offset. If you have two 500 Hz
5-pole filters with slightly different offsets (e.g. -0.89 and -0.85), it
may be possible to set them both to -0.87. Elecraft needs to do some more
testing and will provide more information about this issue.
3. Because of 1 and 2 above, 8-pole filters may be preferable to 5-pole
filters if you plan to use diversity. Now that there is only $25 difference
between the 5-pole and 8-pole filters, this may be a good reason to consider
8-pole filters when placing your order.
73, Bill
--
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