Re: [amsat-bb] choice of IF frequencies

[Robert Snyder <kd1vv@xxxxxxxxxxxx>]

I think the problem isn't receiving (AO-40 doesn't have an L-band
downlink) but transmitting.  You have to meet FCC spurious emissions
requirements.  Also, it's not the image frequency (that's way away for a
435 MHz IF) it's the 3x1 mixer spur.  But some manufacturers (e.g.
Parabolic AB) are advertising a 435/1268 MHz up converter, so how are
they dealing with the problem?

73
Bob KD1VV


laura halliday wrote:
> 
> 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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