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Re: choice of IF frequencies



An image-rejection mixer is limited to about 30 dB of rejection at UHF. This
is OK for reception in the case where there are few interfering signals but
on transmission, it results in too much interference to other services.

73,

John
KD6OZH

----- Original Message -----
From: "laura halliday" <marsgal42@hotmail.com>
To: <amsat-bb@AMSAT.Org>
Sent: Friday, 08 December 2000 21:23 UTC
Subject: Re: [amsat-bb] choice of IF frequencies


> John Stephensen, KD6OZH <kd6ozh@gte.net> wrote:
>
> >Yes, it can be done and most of the 1296 MHz transverters
> >in the 1960's and 1970's used a 28 MHz IF. However, they
> >all used fairly large narrowband interdigital filters built
> >up from sheet metal and tubing. This was required to get a
> >Q high enough to reject LO and image frequencies...
>
> There is of course nothing preventing you from building
> an image-reject mixer, in which case you can use any IF
> you want. Even baseband. All you need is enough image
> rejection to keep the image from killing the noise
> figure. If you can't be bothered, you can also just
> eat the noise figure hit. Based on what I've heard from
> AO-40 so far, this won't be much of a problem...
>
> Laura Halliday VE7LDH     "Que les nuages soient notre
> Grid: CN89mg               pied a terre..."
>                                    - Hospital/Shafte
>
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