General Radio Coverage

The VAST majority (99.9%) of EOSS payloads transmit on VHF and above frequencies. This means that line of site is required to hear the payloads and transmit to them.

footprint at 90,000 ft. ASL
Mapping Software - Street Atlas V 8.0

In order to hear the balloon payload systems you must be within this footprint. A footprint is simply, the area beneath the balloon which can "see" the balloon above the receiver's local horizon. 

This map shows the size of a radio footprint for one of our flights once the balloon and payload have reached an altitude of 90,000 feet above sea level. At that altitude the footprint of the balloon's VHF/UHF transmitters is approximately 392 miles in radius. As you can see, this footprint takes in a good chunk of the central US. A slightly magnified view of this footprint is available on the Cross Band Repeater Page. The Cross Band Repeater Page also has footprint maps for 20,000 feet and 45,000 feet as well as timelines to reach these altitudes. That page may be of interest to people concerned with signals from other EOSS payloads.

Take the above map as a guideline as to the size of the footprint. The actual footprint's geographic center will naturally be dependent on the location of the balloon once it reaches 90,000 feet.

Generally, you should be able to hear the balloon's payloads without the use of high gain antennas. A simple 5/8ths wave antenna should be ample for most VHF/UHF narrow band FM transmissions.

The exception to this "rule" is ATV. ATV is transmitted at 5 watts output. However that 5 watts is spread over a signal bandwidth of 4.5 MHz and so it is extremely weak. Gain antennas are required for just about all stations.