Portable GPS on commercial flight

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Dave Dixon
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Portable GPS on commercial flight

Post by Dave Dixon » Tue Jan 29, 2008 5:50 am

Hi all, Seems like I have seen this discussed here once. I'm taking a trip via commercial airliner, and would like to use my handheld GPS. It doesn't have an external antenna jack that I can find, and I am wondering if anyone has had any luck using one from the cabin during a flight. Mine doesn't always do well in the car, unless it is on or near the dashboard, and I won't be riding in the "jump seat" or have cockpit access :) Any tips, ideas, experience with this? Thanks! Dave

wd5gnr
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Post by wd5gnr » Tue Jan 29, 2008 10:26 am

Mine (a Mio) works fine. Although the speedometer goes crazy. Also it is best if you turn off the option that makes it keep your track on the street.

Al Williams
http://www.awce.com/gp3ez <--- video!

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Dave Dixon
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Post by Dave Dixon » Tue Jan 29, 2008 10:32 am

Thanks, I'll give it a try.

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haklesup
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Post by haklesup » Tue Jan 29, 2008 1:28 pm

GPS recievers (PNA's = Portable Navagation Assistant) work just fine in an airplane particularly near the windows but they are technially prohibited by FAA rules (not FCC, they don't care if you use one) being a type of radio reciever. The flight attendant will ask you to turn it off if you they observe you using it. If you fail to comply by pulling it out later, they could fine you if they have a mind to. FWIW.

IMO It's unlikly they are in fact harmful to flight operations but it is the law. Just like cell phones, FM radios and bluetooth devices, all banned.

Have you unlocked your Mio? To access the underlying WinCE operating system? You can install a bunch of other GPS S/W, Maps, games, MP3, videos etc. (some cracked, some freeware) Just search on Unlocking Mio and you will find plenty. You will need to download Active Sync from Microsoft to communicate with the device.

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jwax
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Post by jwax » Tue Jan 29, 2008 4:07 pm

I wonder if you could get an "elevation" readout?

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haklesup
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Post by haklesup » Tue Jan 29, 2008 4:40 pm

I wonder if you could get an "elevation" readout?
Of course you can. Or was that Off Course (pun)

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dacflyer
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Post by dacflyer » Wed Jan 30, 2008 4:42 am

i used my garmin before,,but i had to keep it held up to the window, and the antenna extension cable i made didn't work for some reason, it was a straight thru cable,using RG-56 cable, and only 2 ft long.
but anyway when i got to germany i had difficulty getting satalites, seemed like it took forever to get any locks. but after a while it would work.

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Dave Dixon
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Post by Dave Dixon » Wed Jan 30, 2008 5:44 am

Thanks Dac! I think it must be your previous post that I was thinking of. I remember your extension, but didn't know if it worked. I guess I'll just give it a try "as is". Gonna be in Vegas for the SuperBowl!!! I BET I come home lighter than when I leave here! Dave

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GPS in flight

Post by Mark Arnold » Wed Jan 30, 2008 6:36 am

Until recently Southwest Airlines allowed using GPS in flight as well as Satellite Radio. This is no longer allowed. I used to use my Garmin E-Map and it worked perfectly. Speed, altitude, time to destination ect. I just held it up to the window.

RG-56 won't work very well as an extension cable it is a 75 ohm coax use rg58 or 174 which are 50 ohm.

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haklesup
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Post by haklesup » Wed Jan 30, 2008 12:44 pm

My older Garmin GPS3 isn't very sensitive and does require a good clear view of the sky and takes forever to acquire in a new location. It worked on a plane but needed to be held in the window. I also have the original model eTrex and it does a little better (never tried on plane) but the SirfIII chipset in the newest recievers is quite remarkable. With my v7 Nav730 I can get a 5 sattelite fix 12' from a window inside my house and never looses lock in the trees and worked fine from my lap in a window seat. It dosen't work well 3' from my office window which is coated with a metallic thin film for energy efficiency.

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dacflyer
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Post by dacflyer » Wed Jan 30, 2008 1:28 pm

mark >> thanks for the tip, i'll try it..

speaking of cables.. i never understood 50ohm - 75 ohm cables..
i never could detect a resistance.. whys it called that ?

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Post by Bigglez » Wed Jan 30, 2008 2:14 pm

Greetings dacflyer,
dacflyer wrote:i never understood 50ohm - 75 ohm cables..
i never could detect a resistance.. whys it called that ?
The cables in question are transmission lines used
to convey RF energy (or high speed digital data).

There are two important characteristics of a transmission
line.

One is that the source impedance and load impedance
are the same. This is not "resistance" as
AC circuits have complex notation with both real
and imaginary components. The process is called
matching and allows the most efficient transfer
of energy over the transmission line. Long distance
high voltage powerlines have a charateristic impedance
to match the generator and sub-station transformers
at 60Hz (or 50Hz elsewhere).

The second one is that the transmission line is
not reactive at the desired operating frequency,
as energy will be reflected or attenuated at the
boundaries of the different impedance sections.

Measuring any cable with an ohmmeter will only
reveal it's DCR (DC resistance) which increases
with length. To measure the impedance of the
cable would require a TDR (Time Domain Reflectometer)
or NA (Network Analyzer) or similar RF test
equipment to measure complex impedances.

A transmission line can be an open feeder for
a broadcast transmitter tower for example, or a
cable that is designed to have a known, or
"Charactersistic", impedance that can be used
in a circuit with the same impedance.

Cables come in different styles and sizes, the
popular ones are coax and twisted pairs, and
they may also have shields or be bundled with
other conductors. Coax operates as a shielded
single-ended line, as the shield is usually also
system ground. Twisted pairs are not grounded
and each line has an equal and opposite signal
that cancels (balances) out. Twisted pairs are
used by the phone company and for professional
microphones. Other uses are for high speed
digital data.


The most abundant is coax for TV antennae and
cable TV feeds in the home, and these
are 75 ohms impedance. Coax replaced
twin-lead open feeders of 300 ohms impedance,
and so 4:1 balun transformers are often found
in adapters to go between the two cable types.

Professional video systems use a standard 75
ohms impedance cable, and require long runs
and high performance in broadcast plants that
in turn require qood quality connectors and cables.


Coax in 50ohm impedance was used for radio
applications originally on Navy ships as the
shorter antenna wire required lower feeder
impedances.

Modern instruments have 50 ohms connectors
for RF, TV and consumer appliances use 75
ohms, and high speed digital data cables (CAT5,
etc.) are 120 ohms characteristic impedance.

Cable impedance is only critical in instrumentation
to prevent measurement errors, and in both
low power and high power RF to prevent signal
loss. The GPS signals are low power and
high frequency as are cellphone receivers so in
both cases the circuits require good matching
and low-loss (gold or silver plated) connectors.

In the digital world the cable impedance only
shows up on long runs and is measured as BER
(bit error rate) rather than amplitude (dB) scales
used for analog signals.

Comments Welcome!

wd5gnr
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Post by wd5gnr » Thu Jan 31, 2008 6:20 am

Yep its unlocked. Truth be told I liked my old street pilot a little better. The Mio maps seem to have more out of date/errors in them I miss it telling me what side of the street my destination is on.

BUT for the money, the feature set is fantastic. The SirfIII chip set is amazing as someone else said. Having the media player built in means one less thing to carry around on travel. The bluetooth is disappointing though.

X-ray
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Re: Portable GPS on commercial flight

Post by X-ray » Thu Jan 31, 2008 3:46 pm

Dave Dixon wrote:Hi all, Seems like I have seen this discussed here once. I'm taking a trip via commercial airliner, and would like to use my handheld GPS. It doesn't have an external antenna jack that I can find, and I am wondering if anyone has had any luck using one from the cabin during a flight. Mine doesn't always do well in the car, unless it is on or near the dashboard, and I won't be riding in the "jump seat" or have cockpit access :) Any tips, ideas, experience with this? Thanks! Dave
I have a Garmin iQue3600 which works well on commercial flights, so long as I am at a window. People are impressed when I can show the average speed for all my trips to be over 500 MPH! Good luck.

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MicroRem
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GPS

Post by MicroRem » Thu Jan 31, 2008 3:51 pm

I used my Garmin 550 yesterday (30 Jan 2008)on a flight from Portland to Salt Lake City.
Worked like a champ, 23 foot accuracy at 597 knots at 26,000 ft (tailwind assisted). Southwest does not prohibit GPS, but Alaska Airlines does. Go figure.

I did get the best signal strength sitting near a window but didn't use an external antenna and it worked great.

I did find that having a destination inputed renedered it useless because it wanted me to follow streets, and every tiome i missed a "turn" it had to recalculate, and then while recalculating I missed another and another.



Regards

Tom

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