Animal tracking frequency

[bee]

Hi

I am trying to make a underground animal tracking system , I have used a setup from a previous project using the 433mhz module for transmit and receive , However that frequency is not very good underground works well down to about 2 foot , So my question is this can i change the freq of these cheap modules down to around 457 khz (avalanche beacon freq),, Or can a module be puchased around that freq ,, The max depth would be around 10 foot

Regards
Bernie

 

[JimB]

So my question is this can i change the freq of these cheap modules down to around 457 khz (avalanche beacon freq)

Sorry, but there is no chance of that. You would be changing the frequency by the order of 1000:1, that is a lot!

Or can a module be puchased around that freq

I don't know of any, but at 457khz it would be quite easy to build an oscillator using bits from an old AM radio where the IF is about 455khz.

JimB

 

[bee]

I thought it was a big ask to alter the modules i have , I thought it might be just change the crystal freq , This electronics caper is never easy hey

I will have to look into building my own then ,all it has to do is transmit a signal ,

Thanks

Bernie

 

[dougy83]

If you can live with a transmitter frequency 540–1610 kHz, then you can use a standard AM radio to receive the signal. Transmission will need to contain some modulation of course.

 

[bee]

I have read somewere about transmitting with a pic micro , That would be good i could program the frequency i needed then , I will do some more googleing on that

Am radio that would be good for receiving the signal , Just got to get the signal out of the ground first

Bernie

 

[dougy83]

You could use the CLKOUT or FOSC4 pin on some PICs, or a PWM channel on others to generate the frequency. If you're using the internal RC oscillator, you can then tune it or introduce modulation by adjusting the OSCCAL register.

 

[MikeMl]

Let me guess, ferrets...

450kHz may propagate through the earth better than UHF, but it is going to be hard to get out a signal with a tiny antenna. The efficiency of a transmitting antenna is a function of its size relative to a half-wavelength( 1/2λ) at the operating frequency. A 1/2λ center-fed dipole antenna has a slight gain over a theoretical isotropic radiator. At 450kHz, 1/2λ = 3e8/(2χ450e3) = 333meters. I'm guessing that you want an antenna no longer than several cm, so be prepared for an antenna gain (loss) of 0.001 or worse. tens to hundreds of mW at your transmitter becomes a field strength equivalent to uW, which wont travel far in air, let alone dirt...

You would do better to use a resonant 10cm ferrite loopstick, with several hundred turns of wire on it, similar to what is used in an old transistor AM radio. That produces an h-field which might couple to a similar loop stick in your receiver. However, the orientation of the loopsticks must not be orthogonal, otherwise you get no signal. This is what the avalanche beacons do. The null is used to locate the buried skier.

 

[RadioRon]

You could learn what components make sense by researching the RFID industry and tags that operate at 150Khz. I think they also use loop antennas on ferrite. Range on those is pretty dismal though.

 

[bee]

This is indeed for my ferrets good guess was it the frequency that gave it away haha,, I spent a lot of time training these stinkys not to bite , so i dont want to lose any

Thanks all for the ideas , I am looking at a micro similar to what dougy was talking about ,, only a few components so will give it a crack

Bernie

 

[MikeMl]

... I am looking at a micro similar to what dougy was talking about ,, only a few components so will give it a crack

It is dirt simple to generate a signal at 450kHz; it is damn hard to make it radiate very far without using a proper antenna. Unfortunately, at that frequency, any reasonable antenna has to be tens to hundreds of meters long...

 

[bee]

I am going to try it at 1mhz from the clkout pin on a 12f675 ,Then add a signal via a mosfet ,, it has to be better than the 433 mhz signal i have tried already,, Yes the antenna is going to be a problem , I have scoured google and there is very little information around, A few folks on elec forums trying to get something goingbut nothing so far

Bernie

 

[bee]

I got this working with the 12f675 at 1mhz , Then fed in a square wave , And i picked it up on my radio , I will generate the 457khz freq in software rather than use the clkout pin at 1 mhz , However i think i will need to amplify this signal as it is quite weak ,, I dont think the circuit is very efficient i will post a pic see what you think

Thanks
Bernie

 

[MikeMl]

...However i think i will need to amplify this signal as it is quite weak ,, I dont think the circuit is very efficient...

What are you using as the "antenna"? Likely, the circuit is efficient, but the antenna you are using is not...

 

[dougy83]

What are you using as the "antenna"? Likely, the circuit is efficient, but the antenna you are using is not...

Is there any reason that you can't use the microcontroller driving a MOSFET/BJT with a tuned ferrite tank circuit? This would be basically a class-C amp. with the resonant circuit described by MikeMl in post #7.

 

[bee]

The antenna was a 300m/m length of wire ,, I will look into the tank circuit/Amp dougy , Ran out of time lastnight, I will do some more on this tonight

Thanks

 

[bee]

Whats the best way to generate the 457 khz ,should i go for a pic with the pwm built in,, or stick with the 12f675 i am not sure on programming this yet in mikro c

Thanks
Bernie

 

[scubadog]

I actually have a commerciqly made one. The transmitter is very small. max 1CM x 1cm size so it is possible.

I am trying to tune an old radio i to pick this up but im not having much luck.

 

[bee]

So did you get a transmitter going yet scuba ,
I have a old mark1 transmitter and collar also but i would like to put one on every ferret i own

Bernie

 

[scubadog]

no. i have only looked at the receiver.

Though havent spent much time on it.

I may have time to try again over the next few weeks.
Perhaps if there is some intereat between us we can get sonething
working.

Have you looked inside the mk1 transmitter?

 

[bee]

No i havent looked inside cause they are the ones cast in green epoxy resin with the coax plug for the battery , And doing so would wreck it ,, The thing i have got going at the moment is picked up by the mk1 receiver, on the bench have not tried it down a hole yet ,, I am going to drop the frequency a little but thats another pic micro learning curve for me ,,

B