[time-nuts] Finding lost items with GPS reporting

Bob Burchett bob.burchett at eeontheweb.com
Tue May 27 12:30:26 EDT 2014


Andrea;
I am a professional in this industry and I can tell you there is no need to
"invent" this; there are literally dozens of these products out there. There
are (as you figured out already) 2 parts to the product; the GPS "this is
where I am" component and the reporting component. While GPS location "where
am I" is the easy part; clearly defined, pretty much only one "source" of
the data (put in a GPS receiver and listen to the NMEA string) but the
reporting methods are based on YOUR end-result and defined by YOUR needs. 

Both need a "carrier" to report the GPS data back and battery life is tied
to two things; the power output on the transmission device (carrier
transmitter) and the interval it reports. Remember the flight recorder from
Flight 370 that got "lost" when the battery went dead? That issue is now
your issue....and since they never found the plane you may not find your
item either. 

If the battery is too big then the thief will SEE it and rip it off, leaving
the GPS tracker in the yard and the item gone; so it can't be too big right?
So if you MAKE it then you better be pretty good at engineering the
end-result into microelectronics. The 40 MHz is unworkable as the antenna
will be too long to radiate any distance (the higher the frequency the
shorter the antenna) so stick to 450 MHz and UP but that isn't the only
issue. 

If you buy the product like for example a PET TRACKER that is pre-built &
ready to go they virtually all work on GSM type of cellular RENTED carriers
so you pay a monthly data rate fee and in return get really GREAT coverage
with very low transmitter power so the thief can take the item all the way
to their home across town and you can track them on the Internet to their
door 25 miles away. That is good but you pay for service...is that bad? You
decide. 

If you buy and own it with NO rented carrier now the distance is tied to
your transmitter power; if the unit puts out say 1/2 of a watt then you can
track it for a short distance over a long period of time (recall the flight
recorder at the bottom of the ocean problem here). If you want more power
but small battery pack then you will get a longer distance but short battery
life AND with both of these cases you have to be "on notice" as to WHEN the
item was taken, then go start your search. 

If you put the tracker on the item, start it up PINGING and go to bed at say
9 PM and someone steals it at say 10 PM and you wake up at say 8 AM to
discover it is gone; rush out to track it by either means then the clock
started ticking for your battery when you turned it ON at 9 PM so you are
burning battery for 11 hours now....see the issue? 

They don't call you up and let you know they are gone UNLESS you have an
Internet based GPS/ Cellular tracker that is "FENCED" and when the GPS unit
sees that it has gone outside of its FENCE (say 200 feet around your home
for example) then it starts yelling at you, can probably be configured to
send you a TEXT message to your phone, you are awakened by the DING sound
and start following at 10 PM instead of 8 AM. 

Go look at
http://www.pocketfinder.com/gps-locator/pet-locator/gps-dog-collars-worth-in
vestment/ for example; there are lots of them; hunt for "pet tracker" as a
search term and good luck. I suggest you don't try and build it but check
back if you still want to create a new product someone else abandoned long
ago...

Each has their benefits; get the idea? 

Robert L. "Bob" Burchett
Certified Communications Engineer
Enterprise Electronics
22826 Mariposa Ave. 
Torrance CA 90502
Direct line: 310.534.4456
FAX: 310.534.1233
Website: www.EEonTheWeb.com



-----Original Message-----
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Sent: Tuesday, May 27, 2014 9:00 AM
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Subject: time-nuts Digest, Vol 118, Issue 58

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Today's Topics:

   1. Toy radiolocation and LORAN envelope (Andrea Baldoni)
   2. UK MSF off the air ... (David J Taylor)
   3. Over optimistic PN measurements (bruce at ko4bb.com)
   4. Re: Toy radiolocation and LORAN envelope (Graeme Zimmer)
   5. Re: Beginner question - unexpected possible jitter in 1	PPS
      (Jason Rabel)


----------------------------------------------------------------------

Message: 1
Date: Tue, 27 May 2014 11:12:32 +0200
From: "Andrea Baldoni" <erm1eaae7 at ermione.com>
To: time-nuts at febo.com
Subject: [time-nuts] Toy radiolocation and LORAN envelope
Message-ID: <20140527091232.GA27635 at sol.ermione.com>
Content-Type: text/plain; charset=us-ascii

Hello!

Years ago, I sometimes played the transmitter hunting game, probably known
to most of the members of this list.
A friend of mine recently suffered a theft so I thought about the
opportunity to embed little marker transmitters in some object usually left
in the yard (like bicycles for example), and have inside the house a system
that constantly monitors them for unwanted movement, while at the same time
be eventually able to recover them once "disappeared" using portable
equipment.
I think that the very simple RF power way to monitor movement is inadequate,
but at the same time I would like to keep things very simple, little and
really cheap, so no things like gps receivers on it: maybe just a 8 pin
microcontroller and a crystal.
Also, the battery life should be the maximum possible, so the RF power will
be little and this also exclude to put a transponder inside the gadget,
unless its on-time could be limited to short and precise slots, because a
constantly-on RX will consume more power than a low duty cycle (say, 0.1pps)
pulsed TX.

Obviously, the goal is to reach the best positional accuracy possible within
the constraints.
The frequency is yet to choose, but I think it should stay in the ISM band
around 40MHz.

The angle could be found with a directional antenna or inerferometry, but
about the distance? There is the need of a very good accuracy of the
transmitter pulses. It's obtainable at least in the short term (the time
needed to recover the object, for instance) for low power and low price? The
long term inaccuracy could tracked and offset when the system is aware that
the target is not moving.

By the way, the LORAN envelope, was so shaped just to limit harmonics, push
up energy efficiency, or there were other reasons not to transmit a square
one?

Best regards,
Andrea Baldoni


------------------------------

Message: 2
Date: Tue, 27 May 2014 10:32:44 +0100
From: "David J Taylor" <david-taylor at blueyonder.co.uk>
To: "Time-nuts mailing list" <time-nuts at febo.com>
Subject: [time-nuts] UK MSF off the air ...
Message-ID: <642642419E4840278740729A296B704C at Alta>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original

From:
 
http://www.npl.co.uk/science-technology/time-frequency/products-and-services
/time/msf-outages

"MSF signal off-air

"Please note that the MSF signal has had to be taken off-air from Saturday
evening, 24 May, until late Tuesday, 27 May, at the earliest, due to a
technical fault.

"Further updates will be posted here when received."

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk 



------------------------------

Message: 3
Date: Tue, 27 May 2014 06:31:52 -0400 (EDT)
From: "bruce at ko4bb.com" <bruce at ko4bb.com>
To: time-nuts at febo.com
Subject: [time-nuts] Over optimistic PN measurements
Message-ID:
	
<582894685.402.1401186712874.open-xchange at oxuslxltgw10.lxa.perfora.net>
	
Content-Type: text/plain; charset=UTF-8

There has been some controversy over the Phase noise of CMOS logic devices.
Perhaps the apparently anomalously low PN measures are due to the use of
cross
correlation in the phase noise measurement equipment and the occurrence of
phenomena detailed in the recent NIST papers:

http://tf.boulder.nist.gov/general/pdf/2697.pdf

http://tf.boulder.nist.gov/general/pdf/2698.pdf

Such collapse of the cross-spectral function may also be present in the PN
plots
shown in the datasheets for some OCXOs.

Bruce

------------------------------

Message: 4
Date: Tue, 27 May 2014 20:40:24 +1000
From: Graeme Zimmer <gzimmer at wideband.net.au>
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Toy radiolocation and LORAN envelope
Message-ID: <53846B98.7090503 at wideband.net.au>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hello Andrea,

> The angle could be found with a directional antenna or inerferometry, but
about
> the distance?

About the only reliable way to locate hidden transmitters is by field 
strength. The problem in built-up areas is reflections.

At one time Doppler DF systems were popular, but anybody who has used 
one will tell you they are usually more trouble than they are worth.

A simple beam or dipole is useful, but only when out in the open country

By simply gridding the area, and drawing a field strength map, you will 
soon cut the location down to a small area. Then with a field strength 
meter you can walk right up to it.

When doing professional DF work, I would use a scanner with an external 
S-meter and an effective attenuator in the antenna lead.

Regards........... Zim




------------------------------

Message: 5
Date: Tue, 27 May 2014 08:04:50 -0500
From: "Jason Rabel" <jason at extremeoverclocking.com>
To: <time-nuts at febo.com>
Subject: Re: [time-nuts] Beginner question - unexpected possible
	jitter in 1	PPS
Message-ID: <00dc01cf79ac$3fbc13e0$bf343ba0$@extremeoverclocking.com>
Content-Type: text/plain;	charset="us-ascii"

> My question is this: Under what conditions can the
> 1 PPS signal be relied on to meet its period uncertainty
> spec? The UT+ emits 1 PPS regardless of whether 
> satellites are visible or not 

Look under the TRAIM settings. You should have several choices:

1PPS disabled
1PPS always on
1PPS when tracking at least 1 sat
1PPS when TRAIM conditions are met


I would chose the last in the list as that would ensure your PPS is valid.



------------------------------

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