Transmiter 173.243 Mhz

[LukeAlden]

I have recently become interested in Falconry however a common problem with this hobby, especially at the start, is loosing the bird...
you can get around this by fixing a transmiter (at 173.243Mhz) to the birds tail and wonderering around with a reciever hoping you can find it. I dont really want to loose a £350 pound bird so this seams like a sensible option right?

I'm a bit of a budding electronics enthusiast but I am new to it all. So when I found out that these transmiters were prohibitivly expensive I figured I could just build one myself? I asked around and someone supplied me with a broken (it has been run over) transmiter.

Now in front of me I have a Hartly ? transmiter circuit that uses coil (about 5:1) ratio, resistors, capacitors a transistor and what looks like a hc-49 quartz resonator (smashed) to produce the required frequency. As the crystal is smashed I dont know of any way to work out what I should buy to replace it. I assume with the values of that other components I could work out what crystal I need. I hoped that maybe the people here could give me a few hints on where to start looking and what I should be looking for to get me started.

The values of the components I have here are:
1 x 820r @5% tol resistor
1 x 850r @1% tol resistor
1 x 3E transistor (PNP transistor?) my search brought up BC857A as a p/n
1 x 102 capacitor (ceramic)
1 x 15k (?) ceramic capacitor
1 x coil setup at aprox 5:1 ratio
1 x broken HC-49 crystal (might be different)
1 x 3.7v silver cell 720mAh

Anything you could tell me would be much appreciated as it is a very interesting subject for me and I have not long discovered it!

another option is to create the circuit from scratch though to do that I need to think about battery life and weight.

Cheers in advance

Luke Alden

 

[MikeMl]

The transmitter likely uses a third or fifth overtone crystal, followed by a tuned circuit at the operating frequency. The oscillator bias network causes the transmitter to pulse on/off with a low duty-cycle to reduce battery life.

 

[MikeMl]

Google is your friend "animal tracking transmitter"

 

[LukeAlden]

Thanks Mike

That was a great help, not sure how i missed that to be honest.
The only thing is that I'm not sure why that circuit is 220MHz or 150MHz, what controls it in the circuit?

And also is there a reason that coils are used? seams like a long winded way of doing what a colpitts does with capacitors.

Thanks again

Luke

Ninja edit: i need it to be 173.243 MHz or i need to build or modify my reciever too... =)

 

[MikeMl]

The frequency is dictated by the regulations that apply in the country you are in. There are specific frequency bands allocated to this purpose. You do not just pick a frequency at random and build a transmitter! In the US, the FCC frowns on it, as do the legitimate licensees of the frequency...

An overtone oscillator requires an LC circuit tuned to the operating frequency to trick a third or fifth overtone crystal to oscillate at the overtone; otherwise it would oscillate at the fundamental.

 

[Shax]

Falconry transmitters are used by a few UK rocketry enthusiasts.
They are very small, and have a decent range, but the quality does come at a price.
I very much doubt that you will be able to design a stable transmitter, that has a long life using a tiny battery pack, and is small enough not to annoy the bird.
Don't forget that birds need feathers for flight and guidance, and a heavy transmitter could easily yank the tail feathers out when the bird is doing high G avian aerobatics!

Do the bird a favour, and buy the correct kit.

 

[LukeAlden]

Thanks for the input guys.
Obviously i know you cant just pick a frequency at random, thats why I need the 173.243MHz as that is the standard in the UK. Looks like i need to do some more research into LC circuits

An Shax, thanks for the vote of confidence. I'm not designing it myself so to speak, just copying an already existing homebuilt broken transmiter. and this transmiter was on a bird before. Obviosuly if the project bears no fruit then I will have to buy one. but thats just not fun is it?


any other helpful info?

Luke

 

[marcbarker]

any other helpful info?

M15m Tracking Transmitter 147

 

[MikeMl]

... Looks like i need to do some more research into LC circuits.

Actually, look into "Overtone Crystal oscillators"