A Fun Experiment I did

Very interesting and thanks for sharing. I am finding that many electronic goodies one can buy at retail stores can be adapted for other purposes which is a lot easier and cheaper than ordering parts and such on-line.

There are several frequency bands which can be used under the Part 15 rules, some with restrictions on duty cycle and some not. I am experimenting with the 930 MHz band for a telemetry system I am developing for my own use.

I also play with microwaves in the 10 GHz ham band but the old standby Gunnplexer(R) is getting expensive and hard to find. A commonly available device which is used for motion detection can be had for about $15 at retail and inside there is a X band transmitter and receiver which does essentially the same thing as a $120 Gunnplexer(R).

Some brands of wireless thermometers have their schematics posted on the FCC site. They can be found from the FCC ID on the device. These could be used to monitor other things but their duty cycle is around 1 second on, 30 seconds off.

Thanks for indulging me as I throw out some random thoughts about the topic but I hope I can stimulate some ideas such as your post did for me.

Neil

Hi Mr. Crow and Neil:

That's a really good idea using an RC transmitter
to get on 49 MHz. I could be wrong, but if
memory serves me correctly, most of the radio
controlled toys use one channel, and the baby
monitors use the other channels(?)

Also, it seems that the baby monitors use FM,
while the R/C toys use AM. I think this is true
because the really inexpensive R/C toy receivers
are regenerative types, and would not hear FM
well. I'll have to check on this.

Well, anyway, that's a really good idea. That could
be the transmitter end of a 49 MHz link, which was
mentioned in that other thread about solar power
repeaters.

Are there any inexpensive 900 MHz voice transmitters
and receivers for Part 15? I know people have attempted
to use the audio portion of those old TV links on about 915 MHz.

Well, it's stuff to think about.

Best Wishes,
Bruce, MICRO1690/1700

I have in my hand a Sony WCS-990T Transmitter, part of a 900mHz wireless microphone set that costs just over $100 from MCM Electronics, and there's an updated version available.

My version uses 2-AAA batteries and the newer model uses AA batteries.

I was very impressed when I got these for TV work. The mic that came with them sounded very tinny and poor, but I added a better mic and the quality matched a $900 Lectrosonic wireless (186mHz) in both sound quality and reception stability.

It would be quite easy to build an attenuator so this could be driven by line-level audio, keeping in mind there is 5VDC on the mic input for powering condenser mics. A 10uF or 100uF NP capacitor would provide the isolation needed.

Each unit has a selection of 2-channels: 912.6mHz and 916.2mHz

Thanks, Carl, for bringing me up to date
on that. I had no idea that there were
wireless mikes on 900 MHz. And the
cost isn't bad.

I tend to accumulate a little bit of electronics
equipment at a time. That started in 1962.

Gee, I think I have too much stuff now.

Oh well. What's a few more items?

What will the wife say?

Uh oh.

Bruce,
MICRO1690/1700