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Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
They are just a crystal oscillator, not a full transmitter as the description would imply. You still need some kind of rf amp and antenna and impedance matching and all that.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Crystal oscillators will give off radiation so they are transmitters in that sense. They are just not very good transmitters.
One problem is the square wave output that will make it transmit on multiple frequencies unless you filter it. With a good and well matched antenna you gan get quite impressive range from one of those.
Just buy the cheapest crystal oscillator you can find that has the right frequency. Remember that a crystal alone will not oscillate so you need one of those chips with a built in oscillator or make the oscillator yourself since the crystals are much cheaper.
... not Russel! Registered Member #1
Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052
I have used similar devices. They are generally just keyed using the output enable pin, rather than the power, as shown, to reduce chirp.
They aren't the greatest thing in the world. There's generally always a small amount of chirp as you key down, and as Bjorn pointed out, the output is a square wave, so you'll need to filter the output.
You can use a high speed CMOS buffer as an amplifier for one of these chips, and get a half watt or so out. You can then also key the CMOS output enable, and get rid of most of the chirp.
As they are now, don't expect much range. A few hundred yards, maybe more with a good antenna. With a CMOS acting as an amp for 250-500mW out, into a good antenna, anything within line of site and perhaps a little beyond should be possible with CW, assuming they are paired with a good receiver.
Note that the AM modulation scheme shown is a bad idea. These things are not frequency stable with respect to input voltage, so it will FM as well as AM, and the signal won't be very nice.
For the price, I probably wouldn't bother unless you have something specific in mind. If you want a one-chip low-parts transmitter, check out something like this: . If you use sockets or switches for the crystal and filters, it can operate over many bands.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
I found a place locaklly that sells crystal oscillators and all the stuff I need to filter the output (and amplify it) and the total parts are cheaper than this (minus the keyer) :P
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ebay - QRP transmitters-on-a-chip?
