by Mike Manes, W5VSI
|144.340 MHz||Packet Telemetry and APRS|
|145.600 MHz||Occasional Packet APRS and beacon|
|147.555 MHz||Voice Output of the Crossband Repeater
|426.250 MHz||ATV AM (can be received locally by a cable receiver on ch 58|
|445.975 MHz||Voice Input for Crossband Repeater
Occasional Packet APRS output
|several freqs||Repeaters used by Tracking and Recovery vary from flight to flight.|
note: ATV via Cable Receiver ... locally means very close (under a mile).
We use 144.34 MHz for packet APRS and telemetry on nearly every flight, and those are going at a pace of about one per month lately. The flights usually get airborne by 0900 local, and are back on the deck by 1130. We schedule flights for a Saturday, with Sunday as a weather date.
We also always carry along a backup DF beacon/cutdown command system, usually on 147.555 MHz; this is also the downlink frequency for the crossband repeater, which flies on perhaps 10 - 20% of the flights.
If we need a third 2m downlink, it's on 145.600 MHz, which could be a beacon or combined command and telemetry link.
Weight considerations limit our ERP (effective radiated power) to 4 Watts (W), and we more commonly fly 350 milliWatt (mW) HTs (handi-talky) with vertical omni directional antennas - "line of sight is a magic thing!" Since we get up to about 100,000 ft MSL where the radio horizon is about 400 miles out, we hear stuff that never shows at the ground station. This is a real concern for critical command links. But so far, we haven't encountered any serious problems; we can hit our ground station 18 dB yagi with 20W, which usually captures the command receiver limiter.
Our ATV module, which goes on about half the flights is 1 W DSB AM on 426.250 MHz, horizontally polarized. Eventually, we hope to move ATV to 1286 MHz WBFM, but that project is moving very slowly.
Due to receiver de-sense concerns, we have never used more than 3 2m downlink frequencies on the same balloon string. But we have done some two-fer launches where de-sense isn't an issue. And we are going to have some 3-fer's this year as well, which will compel us to try some new frequency territory, or time share some of the packet frequencies .
We first used a new www.findu.com feature to relay our APRS beacons all the way to the FAA controllers at Denver Center on our flight on 30 Mar 2003. They loved it! And now of course, they are insisting on it for future flights. The backup is a cell phone or autopatch position report every 10,000 ft or so below 60,000 ft. If the APRS beacon fails, we use DF fixes and either barometric telemetry or dead reckoning for altitude. Needless to say, the fastest and most accurate position and altitude reports are preferred to let the FAA steer aircraft around us.
The only 70 cm narrow band FM frequency we've used is 445.975 MHz, but we may try some new ones in the FM simplex subband.
For ground communications, we prefer the 448.450 MHz PPFMA repeater for southern flights and 449.450 MHz RMRL for the north. We always ask permission to use those machines for our flights, since our traffic loading can be pretty heavy. We also have RMHams OK to use the 449.225 MHz autopatch for T - 30 trajectory forecasts and enroute position reports to the FAA.
We use 146.550 MHz for simplex communications at the ground station and in the field near the recovery site. The Tracking and Recovery Team may also QSY (change frequency) to any nearby 2m or 70cm repeater out east if they get out of range of the primary machines.
We usually run an HF net on 40m, somewhere between 7227 KHz and 7240 KHz, to keep interested folks beyond 400 miles apprised of flight status.
webmaster note: taken from an email Mike sent out. I was so impressed I thought it might make a nice addition to the Web Pages.