very small low power simple transmitter (ideally single chip)?

megoodsen · 2006-08-18T09:00:21+00:00

I'd like to build a very small, low power RF transmitter circuit thatis small and light enough (and cheap enough not to worry about) to beattached to a cats collar.I just want it to transmit either a constant or pulsed carrier (pulsedprob best for battery life) of a known frequency, that I can monitorwith a receiver and DF antenna.There must be single chip transmitters about these days?Anyone suggest suitable circuit?

J

John - KD5YI 20 years ago

You are correct about antenna gain. The FCC spells out many of the test conditions.

I cannot answer your question about RF modems without much more study of the regulations. Most likely they are manufactured to meet some other part of the regulations and have probably been submitted to the FCC for approval. In some of these cases, it is illegal for the end user to tamper with any part of the device, including attaching an external antenna.

Presumably you mean 13 nW. I estimate that the signal strength would be about -115 dBm at the receiver (isotropic source in free space) at 300 meters. I wouldn't try it.

That band is regulated in other parts of the rules. I do not remember the appropriate section. I am certain that higher power is permitted for those specific frequencies.

See (a) above. There are exceptions listed elsewhere in part 15. For example, they allow 100 mW input power to the final stage in a transmitter on the AM broadcast band (with not more than 3 meters of antenna, lead-in, and ground combined). In the 88-108 MHz (commercial FM) band, 250 uV/m at 3 meters is allowed. The OP asked about the 144-146 MHz band which is alloted to licensed amateur use (covered by Part 97 rules). Unlicensed operation in that band is limited to 150 uV/m at 3 meters per the above table.

It is important to wade through all applicable regulations to discover what is permitted.

Cheers to you, too. John

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J

John - KD5YI 20 years ago

Part 95 (

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) covers the 72 MHz R/C frequencies. As you can see, power output can be up to

0.75 watts (95.210). That's high power!

See 95.201 through 95.225 (R/C Rules).

Note that an R/C transmitter must be FCC certified. You may make no modifications to the transmitter.

Cheers, John

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J

John - KD5YI 20 years ago

Read Title 47 and decide for yourself. In the meantime, I will ask them if there is a reward for reporting lawbreakers such as yourself.

John

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John - KD5YI 20 years ago

Hi, Mark -

AFAICT, only on the commercial AM broadcast band.

I have a feeling that the belief that 100 mW is legal came from the FCC's rule that you may transmit using 100 mW on the AM broadcast band (510-1705 kHz) which is very popular with the hobbyist home broadcasting group and it got erroneously applied to all frequencies.

By the way, the FCC says

"Sec. 15.219 Operation in the band 510-1705 kHz.

(a) The total input power to the final radio frequency stage (exclusive of filament or heater power) shall not exceed 100 milliwatts."

Note the reference to filaments indicating it is a rather old rule. In addition, note that it is *input* power to the final stage. With less than

100% efficiency in the final, it will be less at the antenna (which, at 3 meters for antenna, lead-in, and ground) will give very low radiated power.

AFAIK, this is the only reference to 100 mW in the FCC regulations. However, I have not been through them all and I may someday be corrected.

Cheers, John

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Tim Auton 20 years ago

[radio licensing]

[snip table]

I think the only important bit of that quote from the FCC is this bit: "Except as provided elsewhere in this subpart". Elsewhere in the subpart you'll find the limits for the ISM bands, RC frequencies etc. and they are of course much higher.

Tim

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Michael A. Terrell 20 years ago

snipped-for-privacy@fcc.gov is the address to report suspected illegal use of RF equipment to the FCC. I contacted them to ask where to report the people spamming cell phone jammers and snipped-for-privacy@fcc.gov is where I was told to make reports.

Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida

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John - KD5YI 20 years ago

My comment was in the same vein as Luhan's. I should learn how to put in smiley faces, I guess.

If I were to report Luhan, I would also have to report all those other lawbreakers who drive around with their headlights on.

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Michael A. Terrell 20 years ago

I wasn't suggesting you report him. Like I said, it is the link if there is a real need to report anything to the FCC.

Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida

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Rich Grise 20 years ago

In what state is it illegal to turn your headlights on?

Thanks, Rich

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Ancient_Hacker 20 years ago

Yep, that's a good transmitter circuit. If you need longer batery life, you can add a 74HC14 and set it up as a short pulse oscillator, say 10 seconds on, a minute or two off.

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RST Engineering (jw) 20 years ago

The state of insobriety?

Jim

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megoodsen 20 years ago

In fact, yes I do have the appropriate licence for operation on 144MHz (and all others) amatuer bands.

I doubt the cat has though, and he will be the one 'transmitting'...

I suspect at the RF output levels the cat will be transmitting, he won't need one. Here.

I asked originally for a simple circuit, knowing this sort of thing would have been done already, why re-invent the wheel...

And just a comment following the er, expansion of the thread.

As far as I know the FCC is only the American radio regulatory body.

There IS life outside the US of A you know!!

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Alan 20 years ago

Have a search for animal tracking collars/transmitters. Usually a simple one or two transistor crystal controlled oscillator circuit normally used at about 152MHz so easily modified for 2m.

Alan

-- Sell your surplus electronic components at

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Search or browse for that IC, capacitor, crystal or other component you need.

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Rich Grise 20 years ago

Well, I suggested looking into key fob transmitters, that you could hack into and bypass the button with a little CMOS pulser, but you seem to have ignored my suggestion.

RS has a transmitter/receiver set (the receiver is like a coffee timer, but without the knob) for about $15.00. Or they did when I went there a few years ago.

Good Luck! Rich

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