I am trying to make a radio transmitter for practicing with an avalanche transceiver. The idea is that I can pick up this device with my transceiver simulating a buried skier. I do not know very much about rf in general. I do know that avalanche transceivers work at 457khz. I am more of a programmer myself so I should be able to get the coding side of it taken care of. I am just not sure what kind of hardware this would require. I see many transmitter modules available but none of them seem to go down into the khz range. Any help would be great, thanks!!
Hello
You should take a view on HAM-Radio sites, too.
Have a nice day and enjoy coding in C++.
The first thing to do would be to study the RF regulations for your part of the World.
You need to check if DIY manufacture of transmitters for that frequency is permitted or there may be specific licensing required.
Ignoring legalities/licensing issues, which I don't recommend, there exist software defined radios that will go down to 457 kHz (LimeSDR comes to mind), but it would be cheaper, easier, legal, and more practical to buy/borrow a second avalanche transceiver for training.
Look for information on making an OSCILLATOR! This can easily be done for any frequency in the range you are interested in. You will be working with very low power, so legality is not a concern. A receiver for avalanche search use will need to be very sensitive to find weak signals, so your oscillator does not need mush power.
Ok, I understand I will need to figure out how to make an oscillator and somehow hook that up to an antennae. This is turning into less of an Arduino project. How would I go about hooking it up to an antennae? Are there not purchasable oscillators for this frequency range? There isn't a chip out there that will simply produce the oscillation to feed the antennae? Thanks!
First tell us the actual distance your receiver needs to be from the transmitter. If no more than 10 feet, then the wiring for the oscillator will be the antenna. Tune an AM radio to 912 kHz and see if your receiver can hear the oscillator in the radio. It should be on 457kHz. The key is your receiver sensitivity,
The intermediate frequency of most AM radios is about 455 kHz. At close range, you should be able to pick that up no matter what station the radio is tuned to. Of course if the avalanche beacon receiver expects some particular modulation, it may not respond to the radio IF.
The Brits used to require AM radios to be licensed, for a fee. They would go around with a vehicle carrying an IF receiver, looking for unlicensed radios. Owners of same were fined.
There are any number Arduino Sine Wave Generator projects out there using the AD9850 DDS chip that would generate your signal without much work.
Again, "hooking that to an antenna" and making it a transmitter is regulated in most jurisdictions. Without the proper license it is probably not strictly legal and without proper test equipment there is risk your project is doing nasty things to other receivers in the environment.
I would probably want to be able to transmit up to ~30 ft more or less. What nasty things could happen to other receivers? I would likely be using this almost exclusively out in remote areas anyway.
I can use a transmitter that I have purchased at this frequency, but making my own makes it illegal? Again, I am new to all of this.
I cannot determine if the signal is modulated. There is not a lot of information out there about these kinds of details. I am guessing there is not any sort of affordable equipment (maybe an oscilloscope hooked up to an antennae? Probably expensive.) to pick up and read the signal of my existing transceiver.
No, but interfering with radio services and users certainly is, in most countries. Consult your country's rules and regulations.
So far, you have not been very clear about what you really want to do. There seems little point in proceeding with this project until you have more information, and can communicate that to us.
To give a more complete picture, when a skier gets buried by an avalanche, they are(should be) wearing an avalanche transceiver that is set to TRANSMIT mode. The other skiers will then turn their transceivers to RECEIVE mode to look for the buried skier. To avoid buying another ~$300+ transceiver just for the purpose of practicing, and simply for fun, I want to try to make a device to simulate an avalanche transceiver in TRANSMIT mode. I can then go out in the field and practice in different ways.
That is fine, but do you fully understand how to build a transmitter that will be frequency stable under changing temperature extreme and be able to perform just like the $300 unit?
In order for avalanche beacons to save lives, you need to be skiing with or near other people who have them.
Talk a skiing partner into buying one, then you both can practice, as well as both hope to live through being buried in an avalanche. Or, fork over the $300 for a practice unit, then sell it at a discount to someone who needs it.
From what you have posted so far, you are very, very far from being in a position to construct a working avalanche beacon transmitter.
Paul_KD7HB:
I do not fully understand how to do build this transmitter and really if it is actually something I am capable of doing. That is why I posted on this forum. You make great points mentioning temperature and frequency stability.
jremington:
I know I could get with a friend to practice. I am interested in being able to practice alone and, as I mentioned, It would be interesting and fun to build something like this myself. I appreciate your honesty, I am open to learning and that is why I am on here. I have mentioned several times that I am not that knowledgeable about the topic at hand.
I am looking for technical information from this forum. I understand there is some legal concern here and I appreciate you all mentioning that.
Do not assume that every task in electronics can be reduced to a simple ABC list of instructions that can be carried out by those with very limited to zero exeperience.
If you were to get this DIY build wrong, what would be the consequences ?
Please explain how I have asked for ABC instructions. The situation is very simple really, I am interested in seeing how I could do something like this. I would like to get a general idea of what all is involved. I am here to learn and I have clearly admitted to not being well educated on the topic. So instead of telling me reasons why I should not do something maybe a better approach would be to move to the next post or to share information in the way that most people do on forums.
If you or anyone else reading this post doesn't have anything supportive to say I would encourage you to move on. I do, however, appreciate those that have brought up legal concerns.
From poking around on the internet for a description of the signal, my understanding is that the transmitted signal is a continuous wave signal pulsed on/off nominally once per second with an on period of 70-400 ms. I'd expect the typical transmitter is 100 ms on/900 ms off.
One can look at radio frequency signals with an inexpensive Software Defined Radio and free software, but the inexpensive ones don't generally go down to 457 kHz. At that frequency one should be able to see the signal on an oscilloscope probing on the transceiver or with a suitable antenna and pre-amp.
If I felt the need build such a transmitter at reasonable expense and minimal effort, I'd base it on a AD9850 DDS board.
In a public forum we're obligated to point out that building radio transmitters is a regulated activity. I suspect more than a few of us have done so without strictly following the laws, but the laws are there because of the potential for things to go bad, particularly for someone with a limited background in radio electronics.
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