EEVblog #368 - EPIRB Teardown - Page 1
Forum section: electronics / general

author: Wytnucls
author_rank: Super Contributor
timestamp: October 09, 2012, 07:46:28 pm
content: Gosh, I hate that sound!Hear it quite often, while overflying Italy, on guard frequency.

author: DarkPrince
author_rank: Regular Contributor
timestamp: October 10, 2012, 03:13:17 am
content: So I thought of an aspect that wasn't tested. Remove the RF detection feedback component(s), replace the antenna, and run test mode again. Assume to fail then, but didn't test. Ah well. Great video and loved the simpler RF stuff (not that black magic 13GHz stuff).

author: jrg
author_rank: Newbie
timestamp: October 10, 2012, 06:34:23 am
content: Hi, this is my first time. Always have to be oneI work at an airport in electronics maintenance. Air traffic controllers usually have those two frequencies selected in their console, so if you are close to an airport, be careful. The UHF one (243.0) is for military use.When you are testing the equipment, try to charge the output with a dummy load of 50ohm instead of the aerial, so reflected power won't bother your meassurements.

author: kyndal
author_rank: Regular Contributor
timestamp: October 10, 2012, 08:02:02 am
content: i agree that you missed the "test feature" without the feedback disabled..but in "live mode" if i was stuck somewhere..it might be useful information if you expect to get picked up "any time now"...maby the piezo would give off a warning about it ?i actually have a "no micro all discrete through hole" circuit board from a far older aviation one. somewhere around here.....Edit: yup.. it was around here somewhere. All discrete. missing part in the top middle is the 121.500mhz xtaland not that i have ever had it turned on of course....... or well if i had.. i would have done so in the approvedshort ELT Test periode of the first 5 minutes of every UTC Hour....hrmph.. anyway "mod" is where the modulated sweap might be foundoh and ya... even with the antenna disconnected.... im pretty sure an overflying airplane would hear it...the new digital 406mhz ones still give the same analog burst on 121.5 and 243mhzfor local homing using existing equipment. and for aircraft flying overhead.that are still monitoring 121.5 because its used not only for these transmitters.but also for aircraft distress "mayday, panpan" calls, and intercept proceduresQuote/Kyndal

author: Dread
author_rank: Regular Contributor
timestamp: October 10, 2012, 09:54:10 am
content: If I remember correctly that varying tone in the modulation is used by aircraft to determine distance to target. Some sort of dopler effect is extrapolate from comparing the slight compression of the audio versus a template reference and the delta T of each freq Step when compared indicates a rough distance. At least that's what I had heard.

author: KaZjjW
author_rank: Newbie
timestamp: October 10, 2012, 01:10:38 pm
content: Quote from: jrg on October 10, 2012, 06:34:23 amHey! I used to do the same job as you (ATSEP).A lot of airport control towers were equipped with portable radio range finders that were supposed to be used to locate the source of a distress signal (especially in smaller GA airports).I would have loaded the antenna connexion too, but it could be something else than 50 Ohms. This way, you're sure you are not emitting anything.The airport VHF radio receivers are usually set to squelsh around -105dBm, which is quite low. And yes, the 121,5MHz is still monitored for emergency calls.Am I the only one to think the antenna up/down detection is done by this track on the top of the PCB, with a lot of vias? (close to the LEDs).The grounded rod could act as a reflector or parasitic element to bounce the antenna signal to this track (and shift the signal frequency?). When the antenna is down and emitting, the signal is received by the track and detected by the uC. When the antenna is up, at an angle of 90°, plus the track is shielded by the grounded rod, makes the track receive little signal.This way, you can detect the position of the antenna and also check if the system is working OK, if you can demodulate the RF signal and feed it to an ADC..Well, my guess.

author: PeteInTexas
author_rank: Frequent Contributor
timestamp: October 11, 2012, 04:13:40 am
content: This was very interesting. I was going to watch this in two parts but ended up watching the whole video in one go. Anyway, I think your friends missed an opportunity for a good prank where they come swarming in to your lab, dressed in emergency rescue gear, to drag you away in an air lift rescue harness at the end of the video!

author: PA3BNX
author_rank: Regular Contributor
timestamp: October 11, 2012, 07:42:18 pm
content: Hello Everybody,Nice video Dave.EPIRB is something like ham radio fox hunting hi.I would take my SuperSimpleSoundDoppler software to track it hi.Just change the x-tal and its ready for 2 meter foxhunting.See my thread on this forum Radio Direction Finding.I am stil working on the hard and software.http://www.pi4wag.nl/index.php/pseudo-doppler-radio-direction-finderhttp://members.chello.nl/~w.hofman/pa8w/dopplerRDF.htm

author: Mr J
author_rank: Regular Contributor
timestamp: October 12, 2012, 03:37:28 am
content: hey Dave,Great video, brought back a lot of memories. I was the guy who went out at 3 to 4 in the morning knocking on doors finding ELT and EPIRBs and yes even inside the sats can pick it up. I was in the Civil Air Patrol USAF Aux. for many years tracking down these devices, I even did a capstone project for an pager size ELT/EPRIB detector back in 1999/2000 Detectorhttp://www.n1ir.com/2011/03/blast-from-past-elt-detector.htmlIve also attached a ELT schematic, it's not your model but is' an analog version, I use to convert abandoned ELT/EPRIB into trainers on 121.775, not sure if Australia has a similar training frequency or not. We used the Little L-Per by L-Tronics to DF them on the ground and in the air, we even found one in the back of a trash truck while it was moving, someone thew out and EPRIB in the trash. Typically it would take about 12 hours for us to show up at the site with the old 121.5/243 analog system, with the new 406 GPS response was about 15 min to 1 hour in my area. Lots of funny stories when we would pull up to a house or airport, especially in BDU fatigues. Found 70 of them total with 2 real emergencies the rest were false, but with the old system the false ones could mask or block a real one so it was important to shut the false ones off fast.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 13, 2012, 07:15:51 am
content: Here is the old US military version. Not sure if the same model is still in use. I doubt it, as it weights a ton. It fits in the survival vest, with the folded aerial connected.I opened it up and there isn't much to see, just a long pcb, with 2 sealed cans for transmitter and receiver. The whole thing is housed in a cast aluminium body, with a large sealed plate on the back of it. Probably water resistant and possibly waterproof.There is a pushbutton on top, to start the distress tone on either frequency.