[1000mp] 1000MP-MV Filter choice

Thu, 28 Mar 2002 06:46:11 -0000

Be aware that, when two filters are cascaded---and essentially that is what
you are doing in the 2nd and 3rd IF's--the total response is  due to both
filters. So, if you have two "500 Hz" filters, each of which is -6dB at
f0+/-250 Hz, the combo will be -12 dB at f0+/-250 Hz. Similarly, the
transition and stopband attenuations add, as well, but the passband width
for the pair will be narrower than for one.

The transition to the stopband and the stopband depth are usually more
dramatic in the 3rd IF filter, because it is "easier" to accomplish at 455
kHz and not 8.2 MHz. So, all other things being equal, the 3rd IF filter
will provide the most selectivity, although the 2nd IF filter is important
for reducing the crud that gets to the 3rd IF filter.

Be aware that, in the MP, two 2nd IF filters--500 and 2400 Hz--are wired in,
and must be desoldered to be replaced. I am not sure if the Mk V is the
same. Desoldering requires detachment of many connectors, and removal of the
circuit board, and is not a quick, easy operation. If you are not
technically adept at such work, either have it done for you, or leave the
filters be and add only the snap-in filters.

You can move the 500 Hz Collins mechanical filter from the main 3rd IF to
the sub-receiver 2nd IF and install a 400 Hz INRAD in its place. The
combination of the wired-in 500 Hz in the 2nd IF and the sharp INRAD in the
3rd IF should suffice--the 400 Hz filter then essentially defines the
passband, while both define the stopband. If you need to spend more money,
add a 250 Hz CW INRAD filter to the 3rd IF band, and/or a pair of 2.0 kHz or
1.8 kHz INRADs for SSB.

In my case, I added a pair of 2.0 kHz INRAD filters for SSB, moved the
mechanical filter to the sub-RX, and added 400 and 250 Hz 3rd IF filters for
CW and RTTY.

Garry, NI6T

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Thomas Rudolph
> Sent: Wednesday, March 27, 2002 12:46
> To: [email protected]
> Subject: Re: [1000mp] 1000MP-MV Filter choice
>
>
> Hello again,
>
> please let me answer my question myself ;-)
>
> I digged a little bit more in the list archives and the web, and IMHO the
> best way is to use complete
> INRAD filter pairs. So I think I'll use 1.8k and 400Hz pairs +
> 70MHz IF mod
> , and that's it.
>
> Of course I'm still interested in further experiences and hints.
>
> 73 de DK3DUA
> Thomas
>
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