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Re: choice of IF frequencies



50 MHz can be used as an IF with a high Q helical or interdigital filter on
the mixer output. IFs down to 2% of the RF frequency will work nicely -- you
just need better and better filters at the RF frequency as the IF frequency
goes down. 435 MHz to 1270 MHz can also be made to work and will be about
the same level of difficulty as a 50 MHz IF. You just need a 20 MHz wide 2-3
pole filter at 1265 MHz. The disadvantage compared to a wideband design like
that used by DEM is that you can't use it for 1296 MHz by changing crystals.

John
KD6OZH

----- Original Message -----
From: "Estes Wayne-W10191" <Wayne_Estes-W10191@email.mot.com>
To: "John Stephensen, KD6OZH" <kd6ozh@AMSAT.Org>; <amsat-bb@AMSAT.Org>
Sent: Friday, 08 December 2000 15:45 UTC
Subject: RE: [amsat-bb] choice of IF frequencies


> John, thanks for the explanation why 435 MHz isn't a suitable IF for a
1270 MHz transmit converter.  I hadn't thought of that.
>
> A 435 MHz IF for the 2400 MHz down converter also wouldn't be particularly
desirable because then I couldn't operate mode US.
>
> I suppose I'll do a double up conversion to use 28 MHz as the IF for my
1270 MHz TX converter.  Then I can operate every combination of V, U, L, and
S modes except for VS which will probably never be used.
>
> Out of curiosity, is there any reason why a single conversion from a 50
MHz IF wouldn't be viable for a 1270 MHz TX converter?  Would the filtering
be too difficult to attenuate the 2xIF spur?
>
> Wayne Estes W9AE
> Mundelein, IL, USA

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