Tips, Hints, Explanations, or Whatnot......
Started January 2003

This is not intended to be a comprehensive guide to using a GPS receiver.  Check the page of links for sites that have guides, manuals, and other information.  This is intended to cover consumer type GPS receivers not survey grade receivers.  I hope to address the subject from a different perspective.  Sometimes "viewing" a subject from a different point of view helps in grasping the meaning.   Or, if nothing else, reading it again can help to get it to "sink in".

Software (and firmware) is often changed or upgraded.  What was true for one version may not be true for another version.  The comments made here usually apply to the version that was current at the time the comment was written.  A feature may have been present in a prior version, removed in a current version and added back in a future version.

Basic Tips, Hints, Explanations, or Whatnot......

Primarily Garmin Tips, Hints, Explanations, or Whatnot......

External Antennas and Hats
Don't take this section too seriously but it might give you some ideas about using the receiver for hiking for better reception.

For Magellan try the Yahoo group for the Meridian

Learn More About Garmin Receivers in the Test Section.....

If you are out in the "middle of nowhere" and the electronics in your GPSR fail or the batteries die, will you be able to find your way back?  A GPSR in conjunction with a map is very handy - try thinking in terms of a map and compass and GPSR.  The plain common compass does not need batteries to work!  It helps to print a map showing the locations of the waypoints stored in your GPS receiver.

Also did you calibrate your electronic compass after the batteries were changed?  Even if you calibrated it correctly, it may not be as accurate as the standard compass.


Battery Run Time Specification
GPS Receiver to Computer
GPS Receiver to PDA
Latitude and Longitude Formats
Navigation, Bearing, and Course
Radio Frequency Interference
At Start of Trip
Track Logs and Saving Them

Connecting the GPS Receiver (GPSR) to a Personal Computer
Older GPSR's had RS232 serial (often just called "serial") interfaces.  More recent ones may have only a USB interface or both.  If your computer only has a USB port you will need to get a USB to serial converter if you have a receiver that only has RS232.  Not all USB to serial converters work well for this application.  The new (2004) Garmin Legend C, Vista C, 76C, and 76CS have a USB port.  The Legend C and Vista C do not have "RS232" serial ports.

A USB interface is either a "host" or a "client".  A "host" is always connected to a "client".  Two "clients" or two "hosts" are not connected together.  The computer is usually a "host".  The peripherals are usually "clients" which are connected to the computer "host".  For example printers, digital cameras, PDAs, GPS receivers, etc. are usually "clients".   So in some cases you can't connect a GPS receiver to a PDA.  The exception occurs when the PDA also has a USB "host" port.

RS232 Serial Connections

You will be plugging the appropriate serial cable into a serial port on your computer.  You may have more than one hardware serial port, which usually consists of a DB9 connector - 9 pins in two rows, one row of 5 and one row of 4. You need to figure out which logical port it is from the computer's point of view - COM1, COM2, COM3, and so on.  Make sure no other program is configured to use that port.  This could be a mouse driver, modem driver, network driver, handheld hotsync program, IrDA port (infrared port), etc.  For Windows check the Settings/Control Panel and be careful you don't turn something off (disable) that you don't really want to turn off.

The National Marine Electronics Association (NMEA) issues standards for interfacing marine electronics devices.  GPS receivers can be one of those electronic devices that support NMEA protocols.  When the GPS receiver is set to NMEA, it usually sends a "steady stream" of current position data to whatever is listening.  This is often used for real time tracking on a laptop computer running a mapping program.

If you are having trouble getting your GPS receiver to communicate with your computer program that supports GPSRs try setting the GPS receiver to NMEA mode (serial data format).  When the receiver has a lock or is in simulator mode, it should send out NMEA data strings (ASCII text) which you should be able to see with a terminal program (i.e. HyperTerminal with Windows) on the computer.  The default speed is usually 4800 bps on the GPS receiver so make sure that the terminal program is set to the same speed.  If you receive the NMEA strings then you know you have the correct port and the cable is good for sending data in at least one direction.  It doesn't necessarily mean sending data from the computer (handheld) to the GPS receiver will work.

Navigation and Bearing and Course Lines
For many GPS receivers, a "course" is from your starting location to the destination or from the previous route point to the next route point.  A bearing is from your current location to the destination or, more properly, a bearing is the direction from one point to another point.

The GPS receiver does not know what is in between you and your destination.  When it gives you a line pointing to your destination that doesn't mean you can walk the straight line to it.  There may be all sorts of obstacles in the way.  I hope this is obvious!

This is partially true of maps. A map may show you some obstacles but not others.  For instance an impassable cliff may not be noticeable on a topographic map.  A cliff may be smaller than the contour interval of the map and hence, may not be noticeable.  Also a bog/swamp may not be shown on the map, there may be a beaver pond where there wasn't one before, and vegetation may be too thick to get through easily or at all.

Use routes or draw your own track log(s) to show you where to travel to get around obstacles.  You can create these on a computer with appropriate background maps and any other materials you can obtain ahead of time such as guidebooks.  Of course, expect that you didn't find out about all the obstacles so you may not be able to follow your "trail track log" exactly.

Battery Run Time Spec.
Manufacturers usually give you the best possible run time.  They assume that power (battery) save mode is on and that any optional features are turned off and the backlight too.  Your actual running time is almost guaranteed to be less.  You probably bought the receiver with the optional features to use them; although some, such as a compass, might be turned on briefly and not very often. 

In some cases battery (power) save mode consists of shutting down the receiver (not the whole unit) and only waking up every few seconds to get a fix.  If you are in a difficult reception area it will take some time to get a fix and the receiver will end up running most of the time thus consuming power for little or no savings.  In addition the receiver will perform poorly since it doesn't have a fix most of the time.  Out on the open road battery save mode can work well but then I'm running off the car's power, so I don't care.  I never use battery save mode while hiking or any other time.

So your actual run time may very well be less than the manufacturers specification. 

At Start of a Hike (or Trip)
Some things you might want to do:
  • Mark the location of your parked vehicle or the location of your camp!
  • Reset (clear) the track log if you didn't store a predetermined log as a trail map to follow or a track log for boundary information (coastline, private property, country, etc.).
  • Check the track logging settings: On/Off, Interval, etc.  With Garmin receivers when you get to your destination you can save the track log and do a "TracBack®".   Then the receiver can give you information about your return trip. Some Magellan models can back track the recorded log.
  • Reset the trip odometers, time, averages, maximum speed, etc.   Don't reset the waypoints or routes.  You preloaded the receiver with this information for your trip - right?
  • Let the receiver run with good view of the sky for around 5 to 15 minutes.  Use the longer time if the receiver hasn't been used for awhile so it can get current satellite almanacs.  Do this if you are interested in the best accuracy.  Otherwise you might just wait until the receiver is using the obvious set of satellites. If you are about to enter a forested area, it is especially important to wait until the receiver has picked up the satellites that are in view.
  • If you have a receiver with a barometric altimeter, you might want to calibrate the altimeter to either the known elevation or the GPS elevation.  This might be done even if you have an auto calibration function turned on because the GPS elevation or actual elevation may be a bit different from the initial barometric elevation and it may take awhile before the auto calibration brings the barometric elevation into sync with the GPS elevation.

Tracks or "Trails" and Saving Them
Garmin handheld receivers have one track log called the "Active Log".  It holds about 2,047 track points on many models.  The basic eTrex stores about 1536 track points and recent firmware releases for the GPSmap 76, 76S, Legend, and Vista store about 10,000 track points.  The GPS 76 and eTrex Venture still have 2047 points.  Most Garmin handhelds have "Auto", Time, and Distance logging options including five levels of "Auto".

The Garmin receivers do not really have a save track function although that is what it is called.  The operation is a reduce and then store function.  It is used for a detailed back track route that Garmin calls "TracBack®".  It only stores the most significant points of your route (up to 250 points on most current models and is being increased to 750 in some new firmware releases).  These track storage areas are good for storing trail maps, coast lines, boundary lines, etc.  You can create the line set on the computer (but not necessarily with MapSource) and send them to the receivers storage areas.  Besides the horizontal coordinates the elevation, time, and date are recorded in the track log.  The times and dates are removed when a "save" is done.  There are exceptions.

With Garmin receivers, you do not need to "save" the active log to transfer it to a computer.  The active log and all the stored logs in the Garmin receivers are transferred to the computer when a track log transfer is done.  For more on Garmin models see:  Primarily Garmin Tips, Hints......

Lowrance's name for track logs is "trails" or "plot trails".  The Lowrance iFinder can save up to 10 trails of 9,999 points in the iFinder's memory and additionally save this data to MultiMedia Cards (MMC) or Secure Digital (SD) Cards.  I understand that "10" trails is not a fixed limit.  You might be able to save say 20 trails of 4,999 points (can't exceed a maximum 99,999 points).  The iFinder has "Auto", Time, and Distance logging options and it has a "navigate a trail" function.

Magellan Meridian series holds about 2,000 track points and can store the track in an SD card. The Meridian has Fixed Rate, "Auto", and "Auto Detailed" track logging options and can navigate a back track route created from a track log.

The Magellan SporTrak series holds about 2,000 track points and doesn't have SD card support.  It has a save track to route function.

Many GPS receiver cases are rated waterproof to IEC 529-IPX-7 standards.  That means you can probably place it under one meter of water for 30 minutes (if the gaskets are not old and crumbling, etc.) without damaging the electronics.  Others are rated IPX-2 (light mist, do not immerse) such as a Garmin eMap.  If a receiver falls into a lake or stream, check the battery compartment to make sure it and the batteries are dry before operating even if it is rated IPX7.  Also make sure there is no water around buttons, etc.

A water "splash" can exceed a GPSR's "waterproofness".  A wave (splash) hitting the GPSR while riding some rapids can exceed the pressure exerted by one meter of water.  There's a difference between a static, submerged water specification and a dynamic one.  Hydrodynamic pressure during a splash can be greater than the hydrostatic pressure of IPX7 specifications.  A water damaged GPSR that was splashed won't necessarily be covered by the manufacturer's warranty.

GPSR to PDA Connections
There are three general combinations here.  One combination consists of PDA's that output proper RS232 signal levels.  This combination shouldn't be too difficult to get to work because it only needs the appropriate wire only cables.

The second combination consists of PDA's that supply a high enough voltage to a powered serial cable so that the cable generates proper (well "marginal" is a better term) RS232 signal levels.  The PDA either has an internal voltage regulator that supplies a high enough voltage or it has a battery supply that is high enough (possibly rechargeable batteries over 4V).  This combination will work without much trouble with the correct cables.

The third combination consists of PDA's that don't have internal voltage regulators to generate the voltage necessary to drive the RS232 signal lines and their battery voltage is too low.  This combination needs a serial cable with an internal voltage doubler or so to generate RS232 signal levels that will work.  Most cable makers don't bother with that kind of expense.  They only put line buffers in the cable and supply them with power from the computer's RTS and/or DTR signal line.  This will usually work for the PDA to PC connection but not for the PDA to GPSR connection - many GPS receivers don't have RTS and DTR signal lines.  The information in the link below is intended for this combination - you add the power that the PC would otherwise be providing.

Generally speaking, you need a serial hot sync cable to connect to the PDA and a null modem adapter to connect to the serial cable for the GPSR.  The null modem feature would likely be incorporated in the design of a cable made for this purpose.  The PDA serial hot sync cables may be designed to use power from the computer's serial port.  If this is the case, you will need some arrangement to supply power to the cable because the GPSR will not supply it.  Also the PDA probably won't send unless its "Clear to Send" input is "true".  The GPSR probably doesn't provide this signal either.  See the link listed below.

Some commercial cables that are made to connect a PDA to a GPSR will not work with some combinations of PDA's and GPSR's that you might think would work based on the description of the cable.  For instance I bought a cable to connect the Sony CLIÉ T/NR series PDAs to Garmin receivers.  It worked when an SL10 was connected to a Venture or a GPSmap 76 but not when the SL10 was connected to a GPS 76 or a 12XL.  Looking at the signal levels, I would say it was very marginal when used with the Venture and GPSmap 76.  That might be why the GPSmap 76 worked and the GPS 76 didn't.

What's this about supplying power to a cable?  Isn't a cable just wire?

Some PDA's (especially new ones) input/output the serial data at the PDA's internal logic levels.  They expect the cable to provide the circuitry to change these logic levels to RS232 logic levels.  Just about everyone (with regard to the devices discussed here) takes some sort of shortcut in implementing the handling of RS232 logic levels.  This has created a nightmare with regards to getting things to work together.

For additional information (especially connecting a Sony Clie SL10 to a Garmin GPS receiver) including a wiring diagram:

"Connecting a PDA to a GPS Receiver"

RFI - Radio Frequency Interference
RFI emitted by various electronic devices can interfere with GPS signal reception.  If you lose your position lock you might try turning off nearby electronic devices or try moving the GPSR away from the radio, the DVD player, the cell phone, etc.  You might lose your position lock when you drive by a transmission tower for radar, pagers, communications, etc.

Go To
Don't worry about using the "GoTo" function.  There won't be a flash of light nor a loud boom nor should there be a puff of smoke.  Also don't trade in your car since the "GoTo" function will not automatically transport you to the location specified.  You will need the super deluxe model for that and it isn't available yet.

(Idea from posting by Richard Mitchell on sci.geo.satellite-nav newsgroup)

WAAS is a system that is specific to the U.S.A.  The more general term is SBAS - Satellite Based Augumentation System.  Other systems are being developed in other parts of the world.  DGPS, Differential GPS, requires a DGPS receiver to receive local broadcasts of correction data.  The DGPS receiver is probably a separate device from the GPS receiver and connects to the GPS receiver via a cable.

The Wide Area Augmentation System (WAAS) is being developed to bring precision guidance to aircraft at airports and airstrips where there is no precision landing capability (so check the FAA for additional information).  However it's also useful to those of us with handheld receivers provided that we are in a location where the correction signals from the WAAS geo-stationary satellites (fixed points above the Equator) can be received.  Currently the WAAS satellite constellation is being changed.  The satellite with ID 35 (NMEA convention) used to be above the Atlantic (~Brazil) but has been moved above the Pacific Ocean.  The satellite with ID 47 is above the Pacific Ocean (~Hawaii) and and hasn't been changed.  These satellites are fairly low on the horizon for parts of the US, particularily the middle and eastern parts - California should have great views of them.  This means WAAS is not so useful in mountainous areas, heavily forested areas, or areas with other kinds of obstructions because you can't receive (or it's intermittent) the transmissions from the satellites sending the correction data. However if you are on "top of the mountain" or in a valley that's open in the right direction it might work.  This Fall 2006, two new satellites should be operational that will bring much better coverage for all areas of the US.  It will probably take longer to get another satellite operational near the spot that AOR-W operated.  Those in the eastern US will appreciate a replacement near 54 deg. west.

AOR-W (PRN 122, NMEA 35) and POR (PRN 134, NMEA 47) are to stop sending WAAS signals on July 30, 2007.

The NMEA satellite ID, which is the value displayed on Garmin satellite screens, equals the PRN number minus 87.

Satellite / Location PRN Number Garmin Satellite ID Location
WAAS: AOR-W (?) (this was moved from
the Atlantic Region to the Pacific)
122 35 142 W (was at 54 deg. W)

POR / Pacific Ocean Region
134 47 178 deg. E

The FAA leases to use the satellites listed above expire in July 2007.
AOR-W (PRN 122, NMEA 35) and POR (PRN 134, NMEA 47) are to stop sending WAAS signals on July 30, 2007.

WAAS uses a system of ground stations to provide tracking data to master stations on the U.S. East and West coasts.  The master stations compute a set of correction data for the U.S. that is sent to the satellites for re-transmission to GPS receivers.  If you are more than about 500 miles from a ground station, the correction data is probably invalid.  So if you are in Central America, you can receive the data from the WAAS satellites but the correction information is not applicable to that area.  You should disable WAAS in your GPS receiver when you're not in a coverage area or when you can't get reliable WAAS signal reception.

In Garmin receivers the letter "D" is put in the satellite strength bar (or above if the bar is short) when WAAS correction data is being applied to the signal from that GPS satellite.  When WAAS is enabled the satellites that don't have a "D" are not being used in the position computation (but could be different on newer receivers/models).  So you can get a "2D Differential" location indication with solid indications on eight satellites but with only three satellites receiving differential corrections.  Hopefully this will change in a future firmware release.  Disabling WAAS will cause the use of all eight satellites and probably a "3D GPS Location" fix.

Other countries are developing satellite-based differential GPS systems.  The Japanese are implementing the Multi-Functional Satellite Augmentation System (MSAS).  And Europe is creating the Euro Geostationary Navigation Overlay Service (EGNOS).  It may be usable (non-critical applications) in the summer of 2003.  Note:  As of May 2006, people have been receiving EGNOS (ESTB) test signals but it isn't fully operational yet.

Satellite / Location PRN Number NMEA (Garmin)
 Satellite ID

53 deg. W
not going to use??

INMARSAT 3F4 (AOR-W changed??)
142 deg. W
moved 2006 from 54 W





127, 128
40, 41

63 deg. E
Not currently in use for SBAS



Maybe around
53 deg. W
To be launched end 2006

178 deg. E

PanAmSat Galaxy 15
133 deg. W

8 deg. E

Telesat ANIK F1R 138
107.5 deg. W

EGNOS: INMARSAT 3F2, AOR_E / Atlantic East 120 33 15.5 deg. W

21.5 deg. E

25 deg. E

INMARSAT 3F1, IOR-E / Indian Ocean 131 44 64 deg. E
EGNOS shut down

MSAS: MTSAT -1R 129 42 TBD

MTSAT -2 137 50 TBD

Telesat and PanAmSat should be broadcasting a test signal in the Spring 2006 and be operational around Oct./Nov. 2006.  As of May 17, both satellites are sending test signals.  There are interruptions!  They are undergoing tests!!

Latitude and Longitude Formats
The standard formats for specifying latitude are: DD.DDDD, or DDMM.MMM, or DDMMSS.SS
North (N) is positive (+) and South (S) is negative (-).

The standard formats for specifying longitude are: DDD.DDDD, DDDMM.MMM, and DDDMMSS.SS
East (E) is positive (+) and West (W) is negative (-).
Leading zeros are required in both cases.

For example 5 deg 7 min 42.06 seconds N and 31 deg 45' 7.19" W becomes

An additional number appended to the above would be the altitude in meters and the string may end with a "/".

The United States Coast Guard uses the form "DDDMM.MMM" (degrees, minutes, decimal minutes) for a common standard.

TIP: If you have a Garmin 76 series GPS receiver and the location format is set to something other than degrees/minutes, you can change the location display on the satellite page to degrees/minutes by pushing the rocker key up or down.  Pushing the rocker key up or down again will change it back.

There are 60 minutes in one degree and there are 60 seconds in one minute.  Latitude runs from 0 degrees at the Equator to 90 deg. at the poles.  It is 0 to 360 deg. around the Earth with 0 (and 360) deg. being the Prime Meridian that goes through Greenwich (pronounced gren'ich), England.  Normally numbers greater than 180 degrees are not used.  Instead positive numbers up to 180 deg. are used going east from the Prime Meridian and negative numbers are used when going west.  Note that "37.87" can't be deg.minutes since "87" can't be minutes - sometimes the "decimal" point is put in the wrong place and/or used as a separator instead of as a decimal point.  Note that comma and decimal point usage is different in Europe and the U.S.

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