Instruction manual

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From March 2009 QST © ARRL

beacon frequency, Smart Beacon features and

which GPS data to include in your transmis-

sions. When programming the operating fre-

quencies for the SRB-MX146, you can choose

the switch setting or a fixed frequency. (If you

might want to change transmit frequencies in

the field, set this to Switch, and then be sure

to write down the programmed frequencies.)

One interesting option is to tell the RTrak

to transmit on an alternate frequency every

x number of transmissions. Save the configu-

ration file on your computer so that several

alternate configurations can be reloaded later,

simply by calling up a file.

Is 500 mW Really Enough Power?

I was concerned that

⁄2 W may not be

enough power as I travel up and down

the low hills in eastern Con-

necticut, so I conducted

a two-part experiment.

For the first part, my

wife, Jean, WB3IOS,

sat in her car with a

portable APRS receiv-

ing station and watched

my progress as I drove

“around the block” with

the RTrak. Jean didn’t decode

every transmission from the RTrak, but she

captured enough information to roughly

track my movements. In general, if I was

more than about

⁄4 of a mile away, she was

not able to decode my beacons directly. The

second experiment was to get on the Web

and go to wulfden.org/APRSQuery.shtml

and see if my transmissions had been picked

up by any local APRS nodes and relayed

to the Internet. Sure enough, I was “in the

system.” My signal made it to the Internet

via the W1DX node on a hilltop about

⁄2 miles away. The route took me up and

down some low hills near my home, but not

over any substantial hilltops. The relayed

packets covered about half of my 4 mile

loop.

The RTrak’s relatively low output power

is more than compensated by its rugged

construction and operational convenience.

If you’re looking for a plug-and-play APRS

tracker, the RTrak is definitely worth con-

sidering.

Manufacturer: RPC Electronics, 4408

Running Brook Dr #104, Virginia Beach,

VA 23462; www.rpc-electronics.com.

$250.

RPC Electronics

RTrak All-In-One APRS Tracker

short takes

Larry Wolfgang, WR1B

QEX Editor

lwolfgang@arrl.org

Many readers are familiar with the Au-

tomatic Packet/Position Reporting System

(APRS), first developed by Bob Bruninga,

WB4APR. Bob’s recent QST article de-

scribes the many ways we can use APRS.

The RTrak unit is a complete APRS

tracker package, but does not receive or

decode APRS data. Instead, it receives

Global Positioning System data, encodes the

position information into APRS-compatible

data packets and transmits the packets on

2 meters. Receiving stations decode

the packets and display

your movements with

icons on computer-gen-

erated maps.

What’s In The Box?

Inside the package

I found the RTrak unit,

an external GPS magnet-

mount antenna, a car-lighter

power cord and a programming

cable to connect a computer serial port to

the RTrak. A CD contains the RTrak configu-

ration software and operating manual, along

with the operating manual PDF files for the

various circuits in the RTrak.

The RTrak is packaged in a 4

⁄4 × 3 ×

1 inch extruded aluminum box that looks

like you could safely drive over. (Maybe

in a tank!) The magic, of course, is inside

that box.

Remove the four screws holding the solid

end panel and the circuit board slides out

easily. On that circuit board you will find an

Argent Data Systems SMT Open Tracker +,

a Small RF Budget SRB-MX146 transmit-

ter and a Trimble Copernicus GPS receiver.

All of the connectors to interface the RTrak

with the outside world are lined up along the

back edge of the main circuit board. You may

need an SMA to BNC adapter to connect the

transmitter antenna.

The Argent Data Systems SMT Open

Tracker + is a small plug-in daughter board

that includes the full functionality of the

ADS Open Tracker + unit. The Copernicus

GPS unit is a full-featured GPS receiver on a

⁄4 inch square SMD IC.

The Small RF Budget SRB-MX146 block

transmits with a minimum of 500 mW of

power, and is capable of operating on any

frequency from 144 to 148 MHz at 2.5 kHz

channel spacing. You can program up to eight

different operating frequencies into the RTrak.

A 16 position rotary switch allows you to se-

lect one of the eight frequencies programmed

using the configuration software. The other

switch positions are reserved for future firm-

ware features. The SRB-MX146 was designed

with APRS tracker applications in mind.

Since you will be transmitting without

listening for activity on the frequency first,

the low power seems most appropriate. This

will limit the probability of interference from

packet collisions with other stations. It also

limits the effective range of the tracker, but

in an area with significant APRS activity

there should be stations to relay your position

beacons. For operation in an ARES event or

other public service activity, this transmit

power should be adequate, especially since

some of the other participating stations could

be set up as secondary relay stations.

Programming the RTrak

Plug the programming cable into a serial

port on your computer (or a USB-to-serial

adapter) and the RTrak programming jack.

Slide the

PROG/RUN

switch to

PROG

, add

power and start the configuration software.

The first screen will ask you to select the

appropriate COM port, and when the con-

nection has been established, you will see the

programming screen. I won’t go through all of

the possible configuration steps; suffice it to

say the options are plenty. Set your call sign,

transmission path, and other options such as

B. Bruninga, WB4PRS, “Maximizing the

Mobile Motorist Mission,” QST, Sep 2008,

pp 30-33.