August
2004, Issue 169
Ham
Radio Repeater Locator
by
Glen Worstell
Ham
radio enthusiasts no longer have to manually tune
the radio as new repeaters come into range. Glen’s
Ham Radio Repeater Locator consists of a Zilog microcomputer
with the locations and frequencies of several thousand
repeaters stored in its flash memory. The system displays
the distance to the nearest eight repeaters and more.
On
a recent drive through several western states, I took
along a 2-meter amateur (ham) transceiver to relieve
the monotony. I enjoyed chatting with other hams along
the route, and often obtained useful information about
local attractions and road conditions.
Because
2-m communications (144 to 148 MHz) are normally line-of-sight,
the amateur radio community has, over the years, built
repeaters at many strategic locations throughout the
U.S. and in some other countries. These repeaters allow
amateurs to communicate over much longer distances than
would otherwise be possible. The repeaters receive transmissions
and simultaneously rebroadcast them on a frequency 600
kHz away.
In
order to program the radio for the frequencies of the
nearby repeaters, I had to consult an American Radio
Relay League (ARRL) book that gives repeater locations
and frequencies. After driving some distance, I had
to reprogram the ham transceiver for the new nearby
repeater frequencies. The repeater locations are given
as cities or mountain names, and they have to be found
on a map to see which ones are nearby. This is time-consuming,
difficult, and dangerous to do without stopping.
During
one long stretch in Montana, it occurred to me that
there must be a better way, and so the Ham Radio Repeater
Locator (HRRL) was born. The HRRL consists of a Zilog
Z8 Encore! microcomputer with the locations and frequencies
of several thousand repeaters stored in its flash memory,
an interface to a GPS receiver that gives the current
location of the car, and the ubiquitous 4 × 16 alphanumeric
LCD, which shows the selected repeaters.
The
system displays the distance to the nearest eight repeaters,
and a detail line shows the frequency and tone for the
selected repeater. An interface to my ham radio transceiver
is used to automatically program its scan memory to
scan the nearest repeaters, eliminating the need to
change the tuning of the radio as new repeaters come
into range.
Winning
the Z8 Encore! International Design Contest inspired
me to work on a second version of the HRRL, which is
presented here. If you’re implementing the first version,
I encourage you to switch to this one because I added
several nice features.
DISPLAY
AND OPERATION
The
display’s top two lines show the distances in miles
to the nearest eight repeaters (see Photo 1). The third
line shows detailed information for one of the eight
repeaters. The first digit shows the number that corresponds
to one of the eight repeaters. Pressing the station-select
button results in the next repeater being selected,
cycling back to the first after the eighth is selected.
The rest of the third line shows the repeater frequency
and the tone information if the repeater requires tone
access.
|
(Click
here to enlarge)
|
Photo
1—The display’s top two lines show the distances
in miles to the nearest eight repeaters. Pressing
the station-select button (the red button on the
left) selects the next repeater. The third line
shows the repeater frequency and the tone information
for the selected repeater. The forth line gives
the UTC, the call sign of the selected repeater,
and an update counter that changes with each new
GPS position. |
The
last line shows the current time (UTC) on the left,
the call sign of the selected repeater, and a counter
on the right. The counter increments each time the GPS
position changes by enough to affect the distances.
If GPS information is lost, the UTC is replaced by a
“NO GPS” message, alerting you that the information
is no longer current. A red LED blinks once per second
to assure you that that the system is still alive. This
is an extremely useful feature during debug!
A
single character following each of the distances in
the first two lines shows the approximate bearing to
the corresponding repeater. Bearings, which are given
as “n,” “s,” “e,” and “w,” are only accurate to ±45°.
When
listening to a repeater with an interesting conversation,
it’s annoying to lose it when another repeater comes
closer. So, there is a “sticky bit” for each of the
eight repeaters currently being scanned. To toggle the
bit for a particular repeater, first select the repeater
with the station-select switch, and then toggle the
bit with the “sticky bit” switch. When the sticky bit
is on for a particular repeater, the direction display
changes to uppercase letters (N, S, E, and W), and the
station will not be replaced even when another station
becomes closer.
