General Frequency Usage

by Mike, W5VSI with updates by Nick, NØLP

On each flight we fly two beacons: a "bottom" and a "top." The bottom is the primary tracking beacon. It transmits an APRS beacon every 30 seconds. The top is the backup APRS beacon. It transmits an APRS beacon every 60 seconds and transmits a 30 second DF tone each minute also. The top is also command receptive and can be used to cut the balloon away if necessary.

The frequencies used by the bottom and the tops are shown below. 

Frequency EOSS Usage
144.340 MHz Bottom Beacon Packet APRS
144.360 MHz Occasional Bottom Beacon Packet APRS
144.905 MHz Top Beacon Packet APRS, DF Tone and Balloon Cutaway
144.045 MHz Top Beacon Packet APRS, DF Tone and Balloon Cutaway
145.535 MHz Top Beacon Packet APRS, DF Tone and Balloon Cutaway
145.645 MHz Top Beacon Packet APRS, DF Tone and Balloon Cutaway
145.710 MHz Top Beacon Packet APRS, DF Tone and Balloon Cutaway
145.765 MHz Top Beacon Packet APRS, DF Tone and Balloon Cutaway

EOSS flights usually get airborne between 0700 and  0900 local, and are back on the ground by 1130. We most often schedule flights for a Saturday, with Sunday as a weather date.

Weight considerations limit our ERP (effective radiated power) to 4 Watts (W), and we more commonly fly 350 milliWatt (mW) HTs (handi-talky) or a dedicated "radio module" with vertical omni directional antennas. 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.

Due to receiver de-sense concerns, we have never used more than three 2m downlink frequencies on the same balloon string. We currently fly up to three balloons per flight day, but have the capability to fly four.

We use the national aprs.si network of APRS servers to relay our APRS beacons to the FAA controllers at Denver Center. The ground station, Internet-capability trackers, and various volunteer stations in the Denver metro region I-Gate the balloon packets up to the aprs.is servers. If the APRS beacons 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.

For communications between the trackers and the ground station, 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 446.050 MHz for simplex communications at the ground station and in the field near the recovery site. For general Track and Recovery communications we use 446.100 and move to 446.150 MHz and 446.200 MHz as the traffic increases.

We occasionally run an HF net on 40m, somewhere between 7227 KHz and 7240 KHz, to keep interested folks beyond 400 miles apprised of flight status and once in a great while to talk with the trackers from the ground station. Of course cell phones are available also.


Webmaster note: taken from an email Mike sent out (circa 2003). I was so impressed I thought it might make a nice addition to the Web Pages.

NØLP updated the write-up to be compatible with today's (2018) opertions.