My own humble tracker.
Radios
Minimally, you need one VHF radio for data and one UHF radio for voice. Some think mono-band radios like these are ideal, since there is no way to accidentally use the unused band on the voice radio. This is also the cheapest way to go.Alternatively, you could use two identical dual-band radios. Dual-band radios allow you some latitude in configuration for environments other than B2V. Identical radios allows ease of programming in field environments.
Probably the best of both worlds is a bread of radio that has both UHF and VHF, though only one can be used at a time (probably best called a twin-band radio). To make cabling easier (explained later), look for unsquelched audio on the microphone jack for the data radio, or a dedicated packet jack. Also make sure it is 1200 baud packet capable. While a mono-band UHF radio is adequate, the pricing on them is nearly as high a low-end dual-band, so it often makes sense to get a dual-band for more versatility. If you use dual-band radios, look for ones that can have one of their bands turned off. This will save power if operated on battery and offer less chance for operator error.
The voice radio should have tone encode/decode, a memory mode, and the ability to lock the front controls. We generally use tone encode/decode to limit interference. We program the repeater frequencies used for the race into the voice radio for each tracker, so memory is required. We also like to use the lock feature, which makes it much harder for an operator in dark van at night to inadvertently change settings.
HRO and AES often have the Icom IC-2100H for $130, which makes a darned inexpensive data radio. (Note: These radios are no longer in production and will only be available while current stocks last.) New dual-band radios start at about $280. On eBay, you can get used VHF radios starting at about $100, and used dual-band radios for about $150.
Don't buy any used radio for which you cannot find a user's manual. Icom has most of their current manuals online here. You can also find online manuals for Kenwood and Alinco.
While Alinco used to be the low price-point leader, Icom seems to have now taken the lead. At $130, the IC-2100H is hard to beat for a mono-band VHF radio, though it has neither unsquelched audio on the microphone jack nor a dedicated packet jack. At $280, the Icom IC207H is about the lowest priced dual-band radio around, and it has a rear-panel jack for packet. ADI's AR-447 is about the cheapest mono-band UHF radio out there at $235.
Cost: Low end (used), about $250-300. High-end (two new dual-band) about $600.
Dual-band Antenna
Look for a quality, high-gain, mag-mount dual-band antenna. Avoid the cheap MFJ models. It should have a PL-259 connector and a good length of quality coax.Cost: About $50-75.
Duplexer
You need a duplexer to allow you to use both radios (one UHF and one VHF) on the same dual-band antenna. You can get them with or without coax pigtails. If your radios don't have pigtails, you probably want to get a duplexer that has them. Look for one that has mounting "ears", as that will allow you to mount it within the tracker enclosure.
Duplexers, with and without ears and coax pigtails.
Duplexers come in a variety of frequency splits. Make sure you get one that covers both the two meter and seventy centimeter bands.
Cost: You don't often see them used, and a new Comet CF-416 (such as the one pictured at right, above) costs about $45.
Global Positioning System (GPS)
The GPS unit sends information (latitude, longitude, speed, and direction) to the TNC which then transmits it out the data radio.Any GPS that has jacks for external power, external antenna, and NMEA data will do. Almost all new GPS's are 12-channel parallel, which acquire a fix faster than the old 8-channel serial units, particularly when turned on after being relocated more than 50 miles. Unless you are going to dedicate this GPS to your tracker, you might also like to investigate other GPS features useful for camping, hunting, or your outdoor activity of choice.
The workhorse GPS that many of us have used is the Garmin GPS-12XL. Older Garmin GPS-45 and GPS-45XL are the same form factor and take the same cables, though they are slower to acquire a fix.
Front and rear views of the Garmin GPS-12XL. Back view shows external antenna connector (top), and power/data connector (bottom).
One of the annoying "features" of most GPS's is that they beep to alert you when they cannot get a good fix, such as when you are under an overpass or in a parking garage. One way to avoid this is to get an OEM GPS, which is just the guts of a GPS, with no display or user interface. You have to buy your own box and wire it for data, antenna, and power. This can be done a lot cheaper than a standard GPS, but the lack of a user interface makes it less desirable for B2V field use. Below is a picture of such a GPS that part of my truck's APRS system.
New Garmin GPS-12XL's run about $200. An OEM GPS, along with all the parts to make a complete unit should cost less than $100. I recently bought a used Garmin GPS-45XL on eBay for $75.
Cost: Low end (used 8-channel serial) about $75. High-end (new GPS-12XL) about $200. (Note that you can spend well over $1000 for a mapping, dash-mount, differential marine GPS.)
GPS Antenna
The internal antenna on handheld GPS's is not adequate for a tracker.
You will need to buy an external antenna.At right is a Motorola patch GPS antenna with BNC connector and 20' coax.
Small (about 2" square) mag-mount GPS antennas can now be found for under $50. Make sure the connector matches your GPS, and that the coax is at least 12'. gpscity is a good source for GPS accessories.
I have a source, at least for now, who will sell me patch GPS antennas with 5 meter coax and either BNC or MCX connectors for just under $35. Let me know if you want one and I'll order it.
Cost: $35-50.
Terminal Node Controller (TNC)
The TNC is what interfaces the GPS to the radio. It is programmable via a terminal interface with a PC or laptop. This is how we configure the APRS network, and how we tell the tracker how often to send out its location.There are a variety of TNC's available, though two seem to be most ubiquitous for tracker use, the AEA PK-12 and the Kantronics KPC-3 Plus. The PK-12 appears to no longer be made, though you can still find them on eBay and at flea markets for about $50.
Far preferable is the venerable Kantronics KPC-3 Plus. Though not cheap at $170 new, these are wonderful TNC's with a couple of unique features that make them ideal for trackers. We've never had a KPC-3 Plus fail in the field. If buying used, look for firmware version 8.3 or better, as these have a feature we'll discuss later in wiring. If you find a good deal on one with an earlier firmware version, you can buy the 8.3 firmware upgrade from Kantronics.
Cost: Low-end (used KPC-3 Plus) around $90. High-end (new KPC-3 Plus) $170.
Tracker Box
We've had very good luck with the larger size orange sportsman's dry box you can get at West Marine or much cheaper at Walmart in Union City, in their automotive section. These measure 13"x9"x14" (LxWxD) are run about $15. The one pictured below is an "MTM Case-Gard Sportman's Dry Box".
You'll also need to build some kind of insert structure to go inside the box on which to mount things. If you get a box like the one pictured above, the following dimensions work well. Material can be either 1/4" or 3/8 inch plastic of plywood.
This creates a nice, removable insert on which to mount your equipment. The large hole allows you to pull cables from one side to the other.
Cost: $15, plus about $10-15 in material for an insert.
Various Cables
In general, you'll need power cables for two radios, one TNC, and the GPS. You will also need a cable to connect your GPS to TNC, and your TNC to the data radio. All of these are custom cables.See below under Wiring for specifics.
Component Wiring
Power
The power harness has to have a connector for outside power, and connect to all four powered components (voice radio, data radio, TNC, and GPS). We use .093 Molex connectors; you can search at DigiKey for 03-09-2021 (male) or 03-09-1027 (female) connectors. Radio Shack also carries them (rather pricey) and you can sometimes find them at Fry's.
Male connectors with female pins lead away from the power source. Female connectors with male pins receive power from the source. Each powered unit should have a power cable that ends in a female connector.
You will need to build a harness that has a female connector that will receive power from outside the tracker and splits that into four male connectors, that you will plug into each of your powered units.
TNC to Radio
You will have to consult the manuals for both your TNC and data radio to determine how to wire this cable. Generally, you will need to get PTT, TX audio, RX audio, and ground from the radio to the TNC.Most TNC's have a DB9 connector on the back for interface to the radio, and a DB25 for interface to either the GPS, or to a PC for programming. One very nice feature of the Kantronics KPC-3 Plus TNC's with firmware 8.3 or greater, is the ability to run your GPS data into the radio connector, freeing up the DB25 to be used at any time for programming. To those who have had to service trackers in the field, this is a extremely welcome feature.
In order for the TNC to be able to detect a busy frequency (so as not to trasmit when another tracker is transmitting), it needs to have audio from the radio. Unless your radio has a dedicated packet connector, or has unsquelched audio on the microphone connector, you will need to pull audio from the headphone jack and wire that through the DB9 to your TNC, as well.
GPS to TNC
GPS's seem to all have proprietary connectors, but you can generally buy a cable that connects to the GPS and has bare wires for +/-12VDC and data out. Again, gpscity is a good source for GPS accessories. This cable will have to be modified for your TNC and will vary depending on your choice of GPS and TNC. The data wires carry serial data in NMEA format and are often refered to as NMEA (ground) and NMEA+ (data).For the Kantronics KPC-3 Plus, you have two options. The older option is to use the DB25 connector on the TNC. This requires just two wires from the GPS to the DB25. The better way to wire it is documented in the release notes for the KPC-3 Plus with firmware version 8.3 or greater. This is three or four pages of 8 1/2 x 11, stapled together and tucked into the user's manual. Instead of using the DB25 for GPS data, you wire the GPS to unused pins on the DB9 connector coming from the radio.
Tracker Packaging
Now that you have all your parts and pieces, you need to put it all together into a clean, functional package. Tracker packaging owes a lot to personal taste, but must also be functional and serviceable. While the following description is based on my own tracker and is just one way of packaging a tracker, it does include a lot of the ideas proven in years of B2V tracker use.
The Box
As mentioned above, we generally use sportsman's dry boxes. While they are not submersible, they do have an o-ring seal in the lid which will keep out splashes and rain.We do not recommend cut-outs in the box for cables, or mounting anything on the outside wall of the box. Antenna connectors (or anything else) mounted on the outside of the box are susceptible to damage and make the boxes harder to stack next to each other.
Mounting Equipment
By far the easiest way to mount things is to use an insert, described above. This allows the entire thing to be pulled from the box, providing easy access for service and repair.Exactly where you mount each piece of equipment is a matter of taste. There are, however, some general rules of thumb that will make the tracker more functional.
Notice that the only field service function not easily accomplished from the top of this tracker would be swapping out the GPS antenna. That could be easily added by cabling the GPS antenna connector to a panel-mount BNC near the DB25 on the alluminum accessory box.
Space is tight in a tracker box. If you mount anything so close to the side
of the insert that you cannot get to the mounting screws, be sure to cut
holes in the insert to allow access to them (below left.)
If you get a duplexer with mounting ears (highly recommended), mount it such
that it is easy to get to from the top (below right.)
There are a number of ways to mount your GPS. You can velcro it in, use velcro cable wraps (below left), or use a custom mounting bracket (below right). Whatever means you use, make sure that the GPS (and everything else in the box) is securely attached. In the tracker previously pictured, the TNC is attached to the data radio with industrial grade velcro. There should not be anything in the box that is left to "float".
Sticking with the theme that everything should be top-accessible, consider adding a small hobby box with such things as the power input connector, a single fuse for the whole tracker (no digging through the tracker in the field to figure out which fuse blew), a main power switch, and an external DB25 connected directly to the TNC. Possible additional features for this box would be a small digital panel meter for voltage and amps, and a BNC connector for the GPS antenna.
Lastly, label everything. Every radio, TNC, GPS, duplexor, cable, etc., should be labeled with your call sign. In this photo you can also see small white B2V97 property tags on the radio and microphone. These were put there by Logistics when the equipments was checked in for the event.
TNC/GPS Configuration
TNC Programing
Please note that, even if you program a tracker ahead of time, it will be reprogrammed by the tech group in Las Vegas. The following assumes a KPC-3 Plus TNC. This is what we have found works best for us at B2V. You should study your TNC's manual and talk to local APRS users to find the best programming for use in your home area. The lines starting with a sharp (#) are comments and would not be typed into the TNC.
RESTORE DEFAULTS
# resets the TNC to factory defaults
INT TERM
# set the interface to terminal mode (it starts in NEWUSER mode)
MYCALL FFV
# sets a tactical call for Fremont Follow Van
ABAUD 4800
# set the interface baud rate at 4800 baud
BLT 1 EVERY 00:02:00
# beacon the contents of location text buffer #1 every 2 minutes
BTEXT KQ6TM Baker-to-Vegas 2002
# sets the beacon text
CD SOFTWARE
# handle collision detection in software, instead of hardware
GPSHEAD 1 $GPRMC
# use the GPRMC GPS NMEA data string for location text buffer #1
LTP 1 GPSLV VIA WIDE4-4
# sets the APRS icon to a van, and sets the APRS path to WIDE4-4
TXDELAY 50
# sets transmit delay to 50ms
XMITLVL 50
# sets modem drive level
UNPROTO APRS
# sets destination address as APRS
BEACON EVERY 9
# sends out the BTEXT every 9 minutes
PBBS 0
# turns off PBBS mode - TNC will reset
INT GPS
# sets interface to GPS MODE
Note: If you have a KPC-3 Plus with firmware version 8.3 or greater, and you have wired your GPS to the radio port of the TNC, do not use the INT GPS command. Instead, you will need to issue the following command:
GPSPORT 4800 NORMAL CHECKSUM
# tells the TNC to look for GPS data on the DB9 radio port at 4800 baud
This will allow you to hook a computer to the DB25 port at any time and connect to the TNC.
GPS Configuration
There are two things you need to set on your GPS: Interface protocol and baud rate. Most GPS's have a variety of protocols for the data sent out their data port. You need to configure yours for NMEA/NMEA. Additionally, you need to set the baud rate for 4800 baud.
That's it! With these notes you should be well on your way to building a functional tracker. Please keep in mind that both your TNC and radio will be reprogrammed in Las Vegas if you loan your tracker to B2V. Assume all memories will be lost.