Search and Rescue Technology Question

[Fishbowl]

I recently watched the movie "6 Below, Miracle On The Mountain", about the hockey player Eric LeMarque, who survived eight days in the Mammoth back country in 2004. During his ordeal, LeMarque uses a small MP3 with an FM tuner, to try to locate the Mammoth Village, by using the signal strength from a local radio station. That makes sense, but, his is finally located by search and recuse when they "detect a signal" from his FM tuner? Just to be clear, this is not a phone, two way radio, GPS or transmitter of any kind, just an MP3 with a radio receiver. The scene in the movie shows a rescue worker in the lodge looking at a screen, then declaring that he has detected a signal. Looking through the numerous "true story" sites, there is a reference that claims the National Guard detected LeMarque from a "signal from his equipment". However, the official account of the event describes LeMarque as being found after signs of his route, like tracks, clothing and a failed fire, were discovered.

I've done all the research I reasonably can, and cannot find any reference to technology that can detect the use of a receiver. Does this type of technology exist, and is it used but search and rescue to locate lost skiers/snowboarders?

 

[DanoT]

So you saw this amazing FM radio receiver technology that pinged and saved the lost guy in a Hollywood movie and you expect it to accurately reflect real world technology? It is called "theatrical license" and it allows them to make stuff up for the sake of the story telling even in "true stories".

Movies are not like the internet where everything you see is true.

 

[Fishbowl]

Considering that it’s a true story, and that LeMarque himself was onset, yes, I expected factual accuracy. Theatrical license should enhance the story, not inherently change it. Plus, an independent source quotes this as military technology, so I think it’s fair to ask, especially as I am not an expert in search and rescue.

Did you really have to be so condescending in your reply ?

 

[DanoT]

Sorry, I didn't mean to be condescending although I am a skeptic even when it comes to documentaries which one would think would be more about presenting factual information but in reality are often just a reflection of the movie maker's point of view or set of values.

 

[oldschoolskier]

The short answer is yes this type of technologies exists (for a long time actually). Example RF signal strength meters (old transistor radios used to have them), Doppler tracking units (not small if you want portable, huge if it’s a base station). The list goes on.

Having not seen the movie I can’t comment on the methodology and supposed equipment used.

 

[François Pugh]

It would not surprise me. Receivers typically receive and amplify signals (electro-magnetic waves). I am not a radio technician and have not studied this field, but any such amplification process would produce a detectable signal. How good S&R or some other government agency is at detecting such a signal is most likely a secret not to be divulged in a movie.

That being said, "based on" a true story is never a true story.

 

[graham418]

Back in the day, before GPS or other fancy navigation systems, out on the lake we would use a radio direction finder (RDF) to assist in navigation. It would indicate the location of known radio towers by way of a signal strength gauge and a directional antenna. It was only a rudimentary aid, and only sometimes helpful. Atmospheric interferences could play against you, and you might be just as well off looking at the stars, or a Ouija board . It is quite possible you could work backwards and find someones radio signal. Especially nowadays, with advances in snooping technology

 

[mdf]

I never thought about it before, but a receiving antenna works by resonating with the incoming radio waves. This creates a locally stronger voltage that the radio works with. Most of it is meant to wind up in the receiver circuit, but some will escape and create a larger reflected signal than the ambient "stuff" that is not tuned to those radio waves. The level would still be low and require a strong stimulus and sensitive search receiver. Doing a narrow-band search on known frequencies would help.

So I think that in principle you could detect a passive, receive-only radio. Without googling for confirmation, I think this is how Recco works. They have a strong, narrow, search transmitter paired to the search receiver, which drastically improves the signal to noise over opportunistic signals.

 

[kayco53]

We have been practicing with Recco system. Its interesting that you also pickup cell phones,key fobs etc when sweeping the area. We found you had to get rid of your keys,phones and radio to use it and your jacket if Recco equiped that as well . We would notice people about a 100 ft away skiing up to us if they had a cellphone.I know its a bit off topic but not far off.

 

[pchewn]

The FM superheterodyne receiver has one or two local oscillators operating at an intermediate frequency. These may be detectable using another receiver/antenna.

 

[fatbob]

We have been practicing with Recco system. Its interesting that you also pickup cell phones,key fobs etc when sweeping the area. We found you had to get rid of your keys,phones and radio to use it and your jacket if Recco equiped that as well . We would notice people about a 100 ft away skiing up to us if they had a cellphone.I know its a bit off topic but not far off.

But isn't that just because Recco relies on passive reflection so anything which is a substantial chunk of metal can reflect a signal as well as official reflectors. Do you pick up pylons, metal fence posts etc?

 

[kayco53]

Seems to pickup anything electronic. Ski poles aren't a problem or skis and they have metal edges and bindings.And my pack has a sam splint in it.

 

[cantunamunch]

The FM superheterodyne receiver has one or two local oscillators operating at an intermediate frequency. These may be detectable using another receiver/antenna.

^this.

https://ieeexplore.ieee.org/document/5699393/

But isn't that just because Recco relies on passive reflection so anything which is a substantial chunk of metal can reflect a signal as well as official reflectors. Do you pick up pylons, metal fence posts etc?

It's not just passive reflection. It's reflection of energy, not the stimulating wave itself, at a harmonic of the original stimulus.

Kinda like playing a huge organ pipe and then listening for a cymbal to ring.