Beacon Puzzler (a la Car Talk)

[Jonathan S.]

[cross posted to ttips avy forum]
Okay, so maybe the answer is immediately obvious, but I had to think a little bit before figuring out the explanation . . .

*****

So Crusty the beacon mechanic is testing a fleet of old F1 beacons.
First he uses a DSP to test the frequency drift -- all the F1 units are low by 60 to 70, so still within spec.
Then Crusty tests with an S1: frequency is fine (although the S1 just says whether it's ok or not, without giving the amount of any drift).
But the S1 fails the F1 in its additional tests for both "On" time and "On + Off" time.
Crusty is, well, puzzled!
Holding the S1 while still in testing mode, he happens to step back a bit from the F1 -- and now the transmission is testing out as okay.
He repeats this several times, and finds that the S1 consistently fails the F1 within about 50cm, yet passes the F1 outside of that distance.
Other beacon models pass both within and outside of the 50cm distance.
Then Crusty realizes that this is caused by . . . ?

[Scroll down for additional hints, although in a way they're almost more like additional puzzlers!]



















*****
Hint #1:
-- The explanation can be determined by (among other means) searching for the F1 with the Barryvox Pulse in backup search mode with analog accoustics, but *not* in regular search mode even when the accoustics are set to analog.
[keep scrolling for another hint/puzzler]
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Hint #2:
-- The answer to the puzzler is related to why the DSP often will count >3 victims even when only a single old F1 is transmitting.
*****

[stuckathuntermtn]

Analog sucks?

[Jonathan S.]

Analog sucks?

The answer is entirely unrelated to the F1's capacity for searching only via analog accoustics plus a few LED lights.

[Tye 1on]

F1 antenna is so directional that the signal doesn't hit it up close? Wait, the transmitting signal is very directional up close?

so this blonde walks into the doctors office, i don't know what's wrong, i hurt everywhere i touch. Touch your knee, doc says, does that hurt? Blond checks, yes, it does! Touch your arm, that hurt? Oh, yes it does! You're a natural blond aren't you? Blond blushes, why yes, why do you ask? Cuz you broke your finger...

[summit]

There is nothing wrong with analogs if you know how to use one and practice. If you use an analog beacon with an analog pulsing system, then they are still fine as long as they are tuned and in spec.

Guess 1: Without seeing receiver diagrams, my guess is that the front end of the S1 at close range. S1 wasn't meant to test at 50cm. One should conduct spaced out beacon testing at 20m minimum, preferably having people walk in and out of range of the tester one by one at the trail head.

Guess 2: That particular F1 had a pulse duration out of spec on the long side (which can make the Peips DSP's DSP assume overlapping signals and therefor a multiburial) but at close range the S1's DSP goes "Hey, this presumed overlap is of constant and high power and is therefor an over length pulse duration, not overlapping multiple signals."

F1 antenna is so directional that the signal doesn't hit it up close? Wait, the transmitting signal is very directional up close?

All beacons use only one antenna to transmit
Yes they are all very directional up close until you are so close that the flux lines are very dense from all aspects.

[~mikey b]

here's what I understand about F1 and DSP - F1 will always have a bit of background signal when transmitting, even between the beeps, which can account for digi transcievers like the DSP picking up "ghost" signals from them -

I'm guessing that there is some sort of initial signal spike and then a drop off when the F1 beeps -

think of it using the word BEEP ---> B (signal spike) EE (audible signal) P (signal spike and drop)

[Jonathan S.]

here's what I understand about F1 and DSP - F1 will always have a bit of background signal when transmitting, even between the beeps, which can account for digi transcievers like the DSP picking up "ghost" signals from them -

I'm guessing that there is some sort of initial signal spike and then a drop off when the F1 beeps -

think of it using the word BEEP ---> B (signal spike) EE (audible signal) P (signal spike and drop)

Correct! (Although you still need to send in your answer written on a Dynafit Manaslu ski mounted with Dynafit F12 bindings.)

The F1 "continuous carrier" (which is unrelated though to the analog-only search capabilities of the F1) at very close range in the S1's test mode is so loud that the S1 never senses any "Off" time.
Same reason the DSP often displays incorrect victim counts when searching
for an F1.
However, the S1 and Pulse are very reliable in searching for F1 units, although they can take a bit longer than usual to get it right at first.
The Pulse can illustrate this problem in backup search mode, because with the volume cranked up all the way (and ditto when searching with an F1 or M2 or any older analog beacon or Barryvox Opto 3000 or ARVA ADvanced) at close range the F1 sounds like a continuous beep with a rhythmical spike (and never any silence).
But when the Pulse is in regular search mode even with analog accoustics, the volume is automatically modulated to enhance searching, which means that even at close range the volume is turned down such that the continuous carrier can never be heard.

[Jonathan S.]

One should conduct spaced out beacon testing at 20m minimum, preferably having people walk in and out of range of the tester one by one at the trail head.

Just to clarify: both the S1 and Barryvox (current Pulse and older Opto 3000) have a special check mode that drastically shortens the receive range so that a group need not space out that much for one person to check all the beacons. The Barryvox just searches as usual (within the shortened range) whereas the S1 shows whether the beacon is within spec.
By contrast, the DSP frequency drift tester is designed to be used at close range, but I don't think it can really be used as a shorterned-range group beacon checker in the same way as the S1 and Barryvox. (I'm not saying this is a big deal, but just clarifying the different way all these features work -- and yes, this is confusing keeping it all straight!)

[summit]

when the Pulse is in regular search mode even with analog accoustics, the volume is automatically modulated to enhance searching, which means that even at close range the volume is turned down such that the continuous carrier can never be heard.

I believe you are mistaken. In regular (digital) search mode for the Pulse, there are no true analog sound output. It is a digitally generated accoustic signal from the processed signal data.

That's what remember from playing with a Pulse.

[Jonathan S.]

In regular (digital) search mode for the Pulse, there are no true analog sound output. It is a digitally generated accoustic signal from the processed signal data.

That's what remember from playing with a Pulse.

The Pulse's default setup is a digitally generated accoustic signal, but that can be changed over to an analog signal via the menu. This is distinct from the backup mode, with uses a 180-degree rotating arrow in conjunction with analog volume control, and a multi-burial indicator, but no signal separation and marking.
(One of the Pulse's strengths is the amazing range of user customization, although then again, it's a potential drawback in that a rescuer trying to assist someone else with another Pulse has no way of knowing beforehand how it is set up. Also, my understanding is that Barryvox does sell a system to groups -- patrols, SAR teams, heli/cat ops, etc. -- that allows a fleet of beacons to be set up a certain way and then lock out the individual user from making any changes.)

[LeeLau]

OT - how does one check for frequency drift in a Barryvox Opto 3000 and an Ortovox F1?

[Jonathan S.]

Find an S1 (any generation) or DSP (with software current as of at least Fall 2006 -- I forget exactly which # that was, but note that many beacons purchase in Fall 2006, or sometimes even later, lack the Fall 2006 software).

[~mikey b]

what is a Dynafit?

[rideit]

Don't you have to hold it directly OVER the stud?