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Radio Direction Finding Forum - Discussions regarding direction finding and transmitter location

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Old 07-31-2012, 9:05 AM
wdhartman's Avatar
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Default Avalanche beacon project

Hi Guys!

I've got a 2 part project that I hope you can help me with.Avalanche S&R training includes use of a low frequency beacon. I usually have to bury a unit, than have a student find it. Lots of work for a large class. There are "beacon parks" available where pre-buried transmitters are remotely turned on and off, but they start at several thousand dollars. Presently, I'm using a Velleman R/C setup. The receiver turns on an attached beacon.

Problem is that the units are $50 apiece, and I would rather the beacon be in a student's possession. I don't have enough beacons or receivers to make a full blown park.


My training is primarily in digital logic circuits, not R.F.. Can someone come up with a transmitter circuit? An alternative R/C circuit would be great too!

Thanks!
Dave
The beacon stats are-transmit frequency: 457 +/- 0.1 kHz
transmit field strength: between 0.5 and 2.16 mA/m at 1 m
output
modulation: A1A (carrier on/off)
turn-on time: >70 ms
turn-off time: >200 ms
period: 0.9 +/- 0.4 s
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Old 08-22-2012, 3:51 PM
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Maybe this might help get you in the direction. I think you would use some sort of relay to remotely turn them on and off.

OZ2M - Beacon Keyer 16F84

n7ksb

Alan Yates' Laboratory - 30 Metre QRSS Beacon

This might help with the relay
DIY-Make A Secret Hidden RC Hard-Drive - YouTube
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Old 10-08-2012, 6:06 PM
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actually, the Velleman unit works excellently for turning the beacon on-off, and a timer function allows me to use the NC side of the relay. If for some reason I can't turn the beacon on remotely, it will revert to transmit after a set period. Also, if the RC power should fail, the beacon will transmit, and allow me to locate the failed unit. Beats the heck out of waiting for the spring thaw!

What I really need is a simple beacon simulator circuit that will allow me to replace the expensive beacon with a simple circuit. I had figured that a 555 circuit driving a looped ferrite antenna should work.
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Old 04-28-2016, 8:56 PM
RFI-EMI-GUY's Avatar
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Quote:
Originally Posted by xeno194 View Post
Maybe this might help get you in the direction. I think you would use some sort of relay to remotely turn them on and off.

OZ2M - Beacon Keyer 16F84

n7ksb

Alan Yates' Laboratory - 30 Metre QRSS Beacon

This might help with the relay
DIY-Make A Secret Hidden RC Hard-Drive - YouTube
I have to agree with the suggestion to use a 16F84 microchip or equivalent. I explored using 555 timers for a UHF rocket beacon and found the parts count and reliability very poor. I used specifically the PICAXE -08M chip and the programming editor from Revolution Education UK to program and compile a small program to turn on and off a LINX UHF ISM transmitter chip. The parts count was very small.

In this case, you could either use a carrier derived from a crystal and divided down using CMOS logic to 457 KHz and use the -08M to provide on off timing, or use the square wave or PWM features in a similar microchip to generate a 457 KHz carrier with on off modulation. You may want to use an external crystal with the microchip as the internal oscillator is less stable.

Here is a similar application note.

http://ww1.microchip.com/downloads/e...tes/00232B.pdf


From Wikipedia:
In 1986, IKAR adopted the frequency of 457 kHz. In 1996 ASTM adopted the 457 kHz standard.[3]

The following are the currently accepted international standards for Avalanche Transceivers operating on the 457 kHz frequency.[1][3][6][7]

457 kHz, frequency tolerance 80 Hz
200 hours transmitting at +10C (assumed inside protective clothing)
1 hours receiving at −10C (assumed handheld)
operation from −20C to +45C
carrier keying (pulse period) 1000300 ms

Last edited by RFI-EMI-GUY; 04-28-2016 at 9:04 PM..
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