how hard can it be? small 457khz transmitter

[daz21470]

hello there im new to the site so was not sure where to post this.
ive been trying to find someone that could build/design a small 457khz transmitter..no frills a little box with an on and off switch.
not knowing who to approach with my project im hoping some of you could give me some pointers,thanks all.

[dhouston]

Why not just buy an avalanche beacon?

[daz21470]

hello houston i do already own avalanche beacons what id like to buy is schematics a prototype for a small transmitter.
i have already emailed several companys and they seem to complicate things with questions of what are your sale projections for the first year?????i dont see what any of that has to do with it.
at this time i would just like a one off ,test it and take it from there.

during my enquires ive had some great replies and advice but as easy as they make it sound im a long way off from being able to build the project my self.

i,ll put up a couple of responses ive had ,should make interesting reading thanks for your replies....

Hello Sir,
Interesting project.



Although I have very little time and it is hard to help all the people asking me for my advice.
I really would like to help all people but it is difficult as you may understand.
Anyhow, I do have a few ideas for you.

Lot about this project depends on which level you put the construction.
Simple, cheap, advanced....microcontroller.....

I will give an idea of a very simple unit.

I have choosen to use less parts as possible becasue it will be cheaper and consum less power (gives longer battery time)..

Alright, Imagine you have a crystal of 16Mhz.
By loading the crystal with a capacitor you will be able to lower the frequency to 15.995MHz

Divide this frequency with 35 and you get 457kHz signal.

Put this signal into a transistor which has a LC unit tuned to 457kHz at the collector and you have a small transmitter.

This transmitter will send continously. If you want a on/off pulsing you can add a toggling osc which turns on /off the transmitter...

How about power....

The 16MHz oscillator is based on a transistor ands the divider is cmos circuits... all together it consum very little power.

I read about the transmitters and most of them send out 0dbm = 1mW

1mW at 3V will give long battery time

A small chargabel battery will provide power for days.

If you add more circuits (making it more complex) they will consume current at that will lower battery time.

Well, this is the basic idea I came up with.


regards.......


And another..
Hello Darren,



A very interesting project, I hadn’t realized that that this application existed! My approach would be to use a microcontroller (PIC16LF88) with a 20MHz crystal and a R2R DAC, to generate square wave bursts at 457kHz. The DAC output would drive a small power FET (2N7000) with a tuned ferrite antenna as its load. The advantage of this approach is that the component count is very low, power consumption would also be low and the performance is set by software. Unfortunately we’re up to our necks with several projects at present and I can’t set the time aside to do any work on this but it is certainly an interesting one. From your experience is there a wide demand for this type of device?



Best Regards

[dhouston]

So what is your application? How much output power? Is it battery powered? If so, how long must it last? How much are you willing to pay for the design work? I'm not interested myself but these are the types of questions you'll need to answer.

The second response you cited is reasonable. It can probably be simplified even further by using PWM (although I haven't checked to see how close to the desired frequency PWM can get) and a PIC12F683 and its internal oscillator which costs a bit over a dollar.

[daz21470]

im just looking for an alternative to these in the links but the application and requirements are the same.
a company yesterday quoted me £2500 (a ball park) figure based on 5 days.
http://www.ortovox.com/content/en/products/safety_systems/dog_rescue/
https://www.bellmanandflint.co.uk/terrierlocation.aspx.
thanks

[dhouston]

Well, that's a bit more than just a simple transmitter.

If this is a commercial item, you can plan on spending several thousands of dollars for the testing required to meet CE, FCC, etc. regulations. That may explain the amount you were quoted.