457 khz Radio Transmitter

[norrabyelsew]

I would like 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 radio in general. I do know that avalanche transceivers work at 457khz and the only sort of signal modulation is a ~70ms pulse then 1s off. I am more of a programmer myself so I should be able to get the coding side of it taken care of assuming there is some involved if use of a microcontroller is necessary. I am just not sure what other kinds of hardware this would require. Maybe a signal generator along with a small antenna? Or maybe the use of a signal amplifier with that? I am really interested in doing this to learn about radio and to save the money of buying another transceiver. I understand there is some legal concern here. Is there a way to produce a weak enough signal to where this would not be of any legal concern? I would be happy if I could pick up the signal 100' away.

Here is a link with a little more detail on the signal produced by an avalanche transceiver:

ARVA9000 Avalanche transceiver Block Diagram ASTEELFLASH FRANCE

Avalanche transceiver Block diagram details for FCC ID O9BARVA9000 made by ASTEELFLASH FRANCE. Document Includes Block Diagram Block diagram

fccid.io

Any help would be great, thanks!!

 

[danadakk]

FCC part 47 would be a start to determining power limits.

Federal Register :: Request Access

Also consider posing the question at qrz.com, the amateur radio community.
I am sure someone over there could answer the FCC related questions.


Regards, Dana.

 

[FvM]

In the ETSI domain, we have a specific standard for 457 kHz avalanche beacons, ETSI EN 300 718, search www.etsi.org

I don't see a frequency assignment for avalanche beacons in FCC, in part 47 vol 5, 457 kHz is assigned to aviation direction finding purposes on the high sea.

 

[danadakk]

In the ETSI domain, we have a specific standard for 457 kHz avalanche beacons, ETSI EN 300 718, search www.etsi.org

I don't see a frequency assignment for avalanche beacons in FCC, in part 47 vol 5, 457 kHz is assigned to aviation direction finding purposes on the high sea.

Looks like Part 15C applies. I see that on proudct certs already files for 457 Khz.

FCC ID REMDSP01 Avalanche Beacon by Pieps GmbH

FCC ID application submitted by Pieps GmbH for Avalanche Beacon for FCC ID REMDSP01. Approved Frequencies, User Manuals, Photos, and Wireless Reports.

fccid.io

Regards, Dana.

 

[biff44]

commenting only on the block diagram, i am not sure you want the receiver to have an "automatic gain control".

the problem is, if you have a detectable signal that is weak, the gain is cranked to maximum.
if you have a detectable signal that is strong, the gain is cranked way down.
in either case, the signal at the end of the reciever chain now has a constant amplitude, and you can not physically tell which direction to walk. you want the "buzzer" to get louder as you get nearer, and quiter as you go away.

Now you might have some sort of dial indicator to show the "gain control setting", making a sort of power detector. If the gain control to the amplifier is a control voltage, basically a voltmeter will show the signal strength being received at the antenna.

but that might be problematic for various reasons. You mention a coil antenna....that will be very directional. you might be hand orienting the receiver in such a way that the receiver antenna coil nulls out the transmitter antenna coil, and falsely think you are walking away from the skier, even though you might be right on top of them. One solution might be to time average the indicated signal strength, or maybe use two antenna coils, oriented 90 degrees apart, that are automatically switched.

 

[BradtheRad]

Your project is not too different from a pet locator. You hold the directional antenna and aim it at various angles. Watch for changes in signal strength coming from the transmitter. Walk toward the direction of strongest signal strength.

Such a system is on the market. If you wish to build something similar, look at equipment used by radio clubs holding 'fox and hound' contests. Someone hides a transmitter, and members try to locate it using their directional receivers.