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Fall 2007 Issue |
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Building a Beacon
Amateur radio operators who use weak-signal propagation on the microwave bands like having beacons available in order to determine whether or not a band opening is under way. Here W3HMS and K3VDB discuss theur 2401-MHz beacon project. Significant portions of this article also appeared in the Proceedings of the 2007 AMSAT-NA Space Symposium.
By John
Jaminet, W3HMS, |
. Photo A. Inside view of the beacon. |
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With no high-earth-orbit satellite to use as
a signal source for quite some time, we thought a 24/7 beacon might be
useful to folks around south-central Pennsylvania. The microwave community makes extensive use of beacons for checking equipment equipment and propagation on all bands from 50 MHz to 24 GHz. Therefore, why not do the same for satellite users? Thus, we set about building a dual beacon for 1296.064 MHz horizontal polarization and 2401 MHz circular polarization, both in the same box.
The “we” in this case is Fred Lowe, W3MMV,
Joe Lockbaum, WA3PTV, John Jaminet, W3HMS, and Charlie Heisler, K3VDB.
We defined the tasks to be done and the purchases to be made and then
shared the jobs among our group. I (W3HMS) have operated a Kuhne
Electronics beacon on 10 GHz for about six years now and am so very
pleased with the dependability of it, which is consistent with the
company’s other products that I use for contesting on VHF, UHF, and the
microwave bands. The heart of the two beacons is the Kuhne Electronics of Germany “Bakensenders” for each band. Each was ordered with the frequency specified. Each uses F1 FSK keying in lieu of classic “make and brake” keying, as this promotes better short-term stability. The frequency will change a few kHz over time as the crystal ages. W3MMV volunteered to fabricate “from scratch” the horizontally polarized Alfred Slot antenna for 23 cm. Likewise, K3VDB volunteered to fabricate the 13-cm circularly polarized Lindenblad antenna. The slot antenna gain is about 4 dB and the Lindenblad about 3 dB; both antennas are housed in radomes.
The 10-GHz experience told us that we wanted
to use a WW2R keyer with telemetry so that we could remotely monitor the
health of each beacon, keyed by the same keyer. We use two blowers both
for air flow and dependability, and they are turned on and off by a
thermostat set to about 80 degrees. All is mounted in a waterproof box
designed for the electrical trade to house both beacons. The 23-cm
antenna is below in the box and the 13-cm antenna is on top. A single
coax cable feeds 13 VDC to the beacons. The 23-cm beacon has an output
power of 1.5 watts and the 13-cm MHz beacon 1 watt.
The TLM has four positions of information.
It was designed, built, and the PIC programmed by Doug Robinson,
G4FRE/WW2R, in Texas. All the details are available on his website:
<http://g4fre.com/radio.htm>. In the past, W3HMS and WA3PTV have used
several of Doug’s keyers for various functions, all with superb results.
The keyer with telemetry is called an “Intelligent Keyer,” and it is
viewable on his site under this title with schematic. Doug programs your
desired message at purchase time. It is possible to send any TLM sensor
value that can be expressed in the range 0–5 VDC. |
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