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Personal Locator Beacons (Spot, InReach, etc) in avy terrain

Rod9301

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I always have a place in my backpack when I go Backcountry skiing.

I have an inreach as well, but very seldom use it.
 

Joel

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Hi,

WRT my curiosity as to why PLB should or should not interfere with Avy beacons,

While waiting for my loaner beacon, I have been looking at some other things. I don't want to pollute this thread if folks are not interested in what I'm doing ( looking for signals from personal devices that can interfere with 457KHz beacons, where they are coming from....).

So if a couple of you are interested, I will post some stuff here, if not, I'll keep it to myself ( no offense will be taken ).

Let me know
 
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Monique

Monique

bounceswoosh
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Hi,

WRT my curiosity as to why PLB should or should not interfere with Avy beacons,

While waiting for my loaner beacon, I have been looking at some other things. I don't want to pollute this thread if folks are not interested in what I'm doing ( looking for signals from personal devices that can interfere with 457KHz beacons, where they are coming from....).

So if a couple of you are interested, I will post some stuff here, if not, I'll keep it to myself ( no offense will be taken ).

Let me know

I'm interested, but if it's not really PLB specific, a separate thread makes more sense. If the focus is on PLBs, by all means.
 

Joel

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My first look is with my cellphone because it's easier to do without risking a false SOS from my Spot. I expect the mechanisms from my phone to be similar to the Spot.

That work for you? The way I see it, this is your thread, so your rules ;)

I'm interested, but if it's not really PLB specific, a separate thread makes more sense. If the focus is on PLBs, by all means.
 
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Monique

Monique

bounceswoosh
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My first look is with my cellphone because it's easier to do without risking a false SOS from my Spot. I expect the mechanisms from my phone to be similar to the Spot.

That work for you? The way I see it, this is your thread, so your rules ;)

Go for it!
 

Joel

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First installment,

Disclaimer, I did this in my basement not an RF chamber but I did see some interesting results. When you look at this, the higher up the scale the signal is, the stronger it is.

First I turned off my phone and got a background measurement, the center is 457KHz the peaks you see are random in position
across the full spectrum. I'm looking at 250KHz on each side of center.

ambient.png


To get an idea of what the noise peaks to, I did a max hold measurement, this displays what all the random peaks look like over time
and sets the base line for what I want to look for.

ambientpeak.png


Next I just turn on the phone and see if it does anything, and it does, there's a burst just under 457KHz. The right edge of it is close
to the boarder of where the Avy receiver should be sensitive.

phoneidle.png


I let things sit for a bit and captured this burst.

phoneburst.png


I now turned on my phones data and play Bohemian Rhapsody with youtube. I do this with the phone about 6 inches from the analyzers antenna.
I'm using max hold. There is something going on.

phoneactive.png


To get perspective on how distance matters, I do the same measurement with the phone about a meter away. You can see the level is greatly reduced.

active1m.png



So, there are some interesting things going on. The peaks I saw were pretty random, but there. There was never a constant signal at 457KHz
but they do show up. So when I think about what I saw, I don't think it's the cell frequency that is the issue. In the phone there are probably voltage
regulators that are likely switching regulators ( turn an electrical switch on and off really fast to make a voltage ). These can run in the KHz to MHz range.
There is also the speed of the various clocks and data buses in the phones, high MHZ to GHZ. Given the levels of the noise I saw and the way the peaks
looked, I'm thinking it's the data that is moving in the phone along with other lower frequency events. It is not the cell RF, BT RF... thats in the GHz range.

So, If you are using a beacon trying to find someone, your personal devices might interfere, phone, BT wearable devices.... You are not likely to interfere
with someone a ways away from you.

To tie this to a PLB without trying mine yet, you have some of the same things going on to a lesser extent, probably have a voltage regulator along
with a CPU. You might have some but not the same type of data transfers going on. I'm going to try and see if I can sneak into the RF chamber where I work
and do some PLB measurements there. If not, I'll see if I can find a way to do it at home. At the very least, I can get an idle measurement.

all of the signal levels I measured were pretty low. So the next experiment is with the Avy receiver when I get it and see if I can determine it's sensitivity
and rejection.

So, based on what I see so far, at least if you are involved with a search, turn other stuff off. If you know a search is going on, maybe turn stuff off anyway for good mojo.
 
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Monique

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bounceswoosh
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So, based on what I see so far, at least if you are involved with a search, turn other stuff off. If you know a search is going on, maybe turn stuff off anyway for good mojo.

I'd be interested in what you see for the "send" mode. Your phone is on so that you can take selfies or listen to some tunes, and then you get caught in a slide ...
 

Joel

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By send I think you mean like sending a pic. I did this and it looks the same as just playing youtube. This is actually what I expect and backs up a bit that I think it has nothing to do with the actually GHz RF the phone uses and is more related to internal activity.

Was that what you were asking for?

sent a picture, had to send it several times to get the full composite.

send.png
 

SBrown

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By send I think you mean like sending a pic. I did this and it looks the same as just playing youtube. This is actually what I expect and backs up a bit that I think it has nothing to do with the actually GHz RF the phone uses and is more related to internal activity.

Was that what you were asking for?

sent a picture, had to send it several times to get the full composite.

View attachment 38650

No, she means the "transmit" mode on the beacon. My understanding has been that the main issue is with "search" mode, as you have shown.
 
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Monique

Monique

bounceswoosh
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No, she means the "transmit" mode on the beacon. My understanding has been that the main issue is with "search" mode, as you have shown.

Yes, sorry. Words are hard.
 

Joel

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I looked at my SPOT just being on and it has zero impact in the spectrum I have been looking at. As I was thinking about it, I don't have an active subscription for it, I'll have to check and see if it will send something ( I thought I would test by sending a message ) and it gets ignored without a subscription, or if the device just wont send.

With respect to that, if anyone is looking into a PLB, I think there are better choices. Some will have more upfront cost ( device ) but no subscription fees. At $200 a year for the spot, a couple years, you can pretty much take you pick. I would look at the ACR or Garmin inReach ( not sure what/if it costs to use the Garmin).
 

Rainbow Jenny

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I bought an InReach last summer and kick myself for not bringing it along on my current trip. Really wasn’t expecting to spend as much time touring as I am. Well, the basics of map and compass will have to do.

I’ve wanted to read more about radio, GPS, and PLB interference for a while now, thanks for this discussion thread.
 
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Monique

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bounceswoosh
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I looked at my SPOT just being on and it has zero impact in the spectrum I have been looking at. As I was thinking about it, I don't have an active subscription for it, I'll have to check and see if it will send something ( I thought I would test by sending a message ) and it gets ignored without a subscription, or if the device just wont send.

With respect to that, if anyone is looking into a PLB, I think there are better choices. Some will have more upfront cost ( device ) but no subscription fees. At $200 a year for the spot, a couple years, you can pretty much take you pick. I would look at the ACR or Garmin inReach ( not sure what/if it costs to use the Garmin).

My research definitely leaned InReach. It's more expensive than the Spot, but the ability to pre-program a bunch of text messages and recipients, as well as the ability to send custom text messages (and it talks to your phone over bluetooth, so you can actually type on a reasonable device), were definite winners. I have used my InReach to ask about the traffic situation when I was in a dead spot in stopped traffic. I don't think you can do that with a Spot. Then again, it was not exactly critical info. But other stuff could be.

I think this was the resource I used, primarily, in choosing InReach: https://www.outdoorgearlab.com/topics/camping-and-hiking/best-personal-locator-beacon

Note - I wonder if the Bluetooth has a big impact on beacon behavior.
 

Joel

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I think BT will impact the receive of your beacon similar to the data I have shown. It is not the phones radios ( WiFi, BT, Cell ) that is the issue, it is the other things going on inside. So if you are linked to your inreach with your phone, you will see the noise at 457KHz when ever the phone is busy. The things that keep the phone busy are, listening to music, taking pictures, sending data to from other devices.... Now keep in mind, this is not constant, it's only while there is activity going on in your phone. The busier you keep your phone, the more active the noise will be. It also isn't constantly at the beacon frequency, it jumps around.

Note - I wonder if the Bluetooth has a big impact on beacon behavior.
 

mikel

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Nice research @Joel. There is so much spurious crap and anymore with everything we use daily. There is a reason most HOA's have some transmitter verbiage in them. What I thought was pretty funny was some of the research on emissions from cell phones. In one test setup they used 2 identical Iphones. You would expect reasonably close results. Nope. Apples and Oranges.

There was a couple of reasons I said I wouldn't worry about a PLB and interference. As you mentioned, different systems and frequencies, the size of the antenna, and possible distance from each device. If I was using a PLB and going to hit the panic button I would not have it on my person if I was moving around or working an avalanche. I would want it stationary and put it in the clearest possible space to the sky and behind me and the work scene. Plus we're talking 406/121.5 and 457.

Turning everything off is absolutely the best way to avoid interference but I can tell you with my beacon I have never encountered any issues during my training or practice. I've had my cell and InReach turned on while using the beacon. They were in my pack.

Bluetooth can be a pita in a wifi environment. But with Bluetooth we are talking 2.4/ 5 ghz.

One of the reasons I went with InReach is I'm not a huge fan of PLB's. Certainly they have their place and can help. If you go PLB I wouldn't cheap out. I would get one with GPS and make sure you register it.

Bottom line is practice. If you typically carry electronic devices with you then you need to practice using your beacon with those devices in your pack or on your person also. It's the only true way to find out if you will have an issue.
 
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Monique

Monique

bounceswoosh
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Bluetooth can be a pita in a wifi environment. But with Bluetooth we are talking 2.4/ 5 ghz.

One of the reasons I went with InReach is I'm not a huge fan of PLB's. Certainly they have their place and can help. If you go PLB I wouldn't cheap out. I would get one with GPS and make sure you register it.

Two things:

1) Do you mean that I should turn off bluetooth on my InReach unless I need it?

2) Wait, unpack that for me - you went with InReach because you don't like PLBs - how should I read that? Do you mean you went with InReach because it's also a GPS device?
 

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