Re: receiving a carrier

"jhon1" <aomarenator@xxxxxxxxx> wrote in message
news:1166722851.167874.109410@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I am working on a project that needs to transmite a clock signal (just
binary
sequence or a square wave), and one of the options is to send a sine
wave ( high frequency carrier) and squarising it at the other side, so
how I can achieve like this task?, as you know radio modules do't
really fit in such application, I don't need to transmit data (the rate
of it is a small), I need only to transmit a clock signal.

I agree with Michael T. -- radio modules would work quite well for this
application if you're just looking to build a single unit and get something
working.

Will that suffice? If not, if you actually *have to* design and build your
own radio, from what you've said so far I think you're looking at a
significant amount of work. One way to reduce this is to build at the
"functional" level: Use filters, mixers, power amplifiers, etc. from the likes
of Mini-Circuits, Hittite, Analog Devices, Maxim, etc.

Do you have a spectrum analyzer around? You can learn a lot by just hooking
up an antenna (which can be as simple as a, say, foot long wire) and
"sniffing" around -- you'll see your local radio stations, TV stations, etc.
In your case, try something like the following:

-- Set a function generator to a frequency where it's *legal* to transmit in
your country. Set the power to, say, 0dBm (1mW).
-- Connect an "antenna" -- just a wire, make it roughly 68/f mm long, where f
is in MHz -- see http://en.wikipedia.org/wiki/Dipole_antenna for details;
you're making a dipole antenna using the function generator as a crude ground
plane
-- Connect another such antenna to a spectrum analyzer and find the
transmitted signal
-- Move a few hundred meters away and see if you can still find the
transmitted signal. If not, try bumping up the function generator's power
output or adding an outboard amplifier... after you look up with the legal
power limit is in the band you've chosen (here in the U.S., it's usually not
more than 100mW or so in the unlicensed bands, unless you get fancy with
spread spectrum techniques where you can have a watt).

Now... start trying to replace all that expensive test equipment with your own
circuit!

The transmitter is almost always easier than the receiver, because you don't
have to deal with interfering signals, absurdly weak power levels, etc.

If possible, you might want to get yourself something like an AM/FM radio kit
to play with... something like http://www.esssales.com/elenco/radio-kit.html
.... although as you can see that's a superheterodyne architecture. (The main
problem without some sort of heterodyning is providing selectivity... at
100MHz you're not just going to open up the DigiKey catalog and find a really
good resonator at that exact frequency... although you might find one at, say,
90MHz, since that's sometimes used as an IF. For your purposes, you can use
an air core coil and capacitor -- an LC tank -- to provide a filter, but your
Q will probably be limited to no more than ~100 [1MHz bandwidth]).

---Joel


.

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