Re: [Discuss-gnuradio] Fixed frequency Mixer?

[Mark Smith]

On Tue, Dec 10, 2002 at 12:59:55AM -0800, Saeed Beyty wrote:
> Hi folks
> 
>  I got to a problem making my own GNURaido Hardware 
> It's about the fixed frequency mixer you commonly use after the TV 
> tuner module.  I think it must be capable of interchanging 45Mhz 
> into 5Mhz or something like this.

Yep.  A mixer is a device that has the neat property that its output
is the two inputs as well as the sum and difference of those two inputs.
If you have a 45MHz signal that you want down at 5MHz, you make either a
40MHz or a 50MHz signal on the other input (depending on whether you want
a positive or a negative image of the 45MHz signal.)  On the output,
you'll have the two input signals (45MHz and (eg) 40MHz), and the sum
(85MHz) and the difference (5MHz).  Filter off everything above what
you're looking for (say, at 6MHz) and you're left with a 5MHz signal.
If that image is spectrally inverted compared to what you want, then mix 
with 50MHz instead of 40MHz.

For more details on this, I'd check any good RF design reference.  I'm
a Ham Radio Operator and have had pretty good luck with the ARRL Handbook
as a reference.  I'm sure there are plenty of others out there that will
do just as good a job.

There are other ways of sampling a 5MHz wide signal at 45MHz without
having to down convert to base band.  Has anyone played with 
undersampling?

> Is it a commercial module ( just like the TV tuners ! )  or a self 
> designed board?

I've not done a lot of RF design so I'm probably the wrong person to
talk to here, but I know they can be made pretty easily from amplifier
chips (like a high speed Op-Amp).  I'm sure that these days there are
mixer chips that will do it easier and in a single package.

> If so, is there any schematics, or guidelines available?
> Send me some info if possible.

I'm sure there are.  www.google.com is your friend.  :)

-Mark
-- 
Mark Smith - finger address@hidden for GPG v1.0.1 public key

pgplLZNPnd7F0.pgp
Description: PGP signature