Wednesday, 19 November 2014

Signal Overlap & "Marking"

I thought it worth re posting this little experiment I did with a Canadian SOS F1 (re boxed Ortovox) analogue with a couple of digital beacons pre season. Always worth being aware of these little glitchy things!
video

If you have a beacon with a "mark" feature beware of signal overlap. Listen to the audio signals from this old analog beacon. Analog is good for demonstrating signal overlap because of the audio picking up and letting you hear all signals. This short home experiment I did illustrates overlap, as two pulses merge to become one for a time.  Imagine you have four vehicles on a track. One travelling at 20mph, one at 30, one at 40 and one at 50mph.  At some point all 4 would be in line and seem as one. So like the vehicles the more beacons on transmit the more chance of signal overlap.  There is a risk when you "mark", that you mark two as one therefore missing one victim, or more if its a really big scenario.  Manufacturers try and address this by varying the pulse rate. Imagine what would happen in a large group with the same Beacon pulsing at the same rate!  But - there is a limit to how much they can do this before performance is affected. Therefore there is still very realistic possibility of synchronisation of the signal and marking two. Click this link also:
 HTTP://vimeo.com/23539827

Signal overlap is more frequent with 3 and even more with 4 beacons. For that reason on training session limit your transmitting beacons to less than 4 as you might confuse them. Establishing as soon as possible how many are in a party, how many have beacons, and how many victims are left out off the tip can help the rescue leader establish if the search is compromised and the searchers can try and separate any overlapping signals.

Many folk have failed the North American ski guide test because of signal overlap. The test usually consists of one fairly easy to find beacon and two that are in close proximity. It's these two close proximity that can catch folk out. For this reason its safer to use a simple 3 antenna beacon and search in micro strips or if its flat the DAV three circle method.  I have an obvious vested interest being a BCA retailer but hope I am being objective. I find the Tracker 1 and 2 both superior for this type of test with the SP mode invaluable.

I can't say much about Pieps which is the only make I have not tested but have seen in action in multiples and it does well. The Barryvox pulse has great advanced features especially with V 3.04 software but seems to want you to stop and stand still a lot. The one beacon that does really well is the ARVA "Neo" and is the only one with a mark feature which I have found reliable in mark/flagging. Like all of the beacons with this feature you need to be aware of overlap.  However if you want a beacon with that feature its a remarkably well priced beacon at £225 from me.

Obviously I am in the market to sell transceivers but you can see the Neo's 5 star review here
http://beaconreviews.com/transceivers/Specs_ArvaNeo.asp
A very reliable avalanche beacon with a mark feature and a very good price indeed at £225. 5* Rating

It beats a lot of more highly priced rivals hands down. Oddly the guts of the Neo are made by Barryvox, so its from a reliable and long standing company with technical expertise so it seems off pitching it against the Mummut branded Barryvox Pulse.  Yet it performs the basic functions better in my opinion. The Pulse is possibly more aimed at rescuers with it's many advanced features such as "Rescue Send" etc


No comments:

Post a Comment