Range of VHF/UHF Transmissions

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A typical EOSS balloon will ascend at a rate of approximately 1000 to 1100 feet per minute to maximum altitude of around 95,000 feet.

At this rate of ascent, approximately 22 minutes into the flight the balloon will be at an altitude of 30,000 feet above sea level and the footprint will have a radius of approximately 205 miles. Remember, we launch at around 5,000 ASL.

Footprint at 30,000 ft. ASL

For all footprint shots
light green = good packet, excellent voice
red = boundary beyond which received signal is less than 0.4 uV

50 minutes into the flight the balloon will be at an altitude of 60,000 feet above sea level and the footprint will have a radius of 310 miles.

Footprint at 60,000 ft. ASL

From this altitude it will take approximately 32 minutes to reach an altitude of 95,000 feet above sea level (82 minutes into the flight). Most of our flights will ascend to that height. At that altitude the foot print of the cross band repeater will be approximately 399 miles in radius. 

Footprint at 95,000 ft. ASL
Propagation Software -
Radio Mobile
Map Overlay - MapBlast

You should be in no great hurry to make contacts while the balloon is below 80,000 feet. There will be ample opportunities to jump in and get net control's attention.

However, once the balloon rises above 80,000 feet the likelihood of a balloon burst becomes significantly greater. Therefore, as good operating practice, we suggest that only really distant stations attempt contacts at this point. Remember, the footprint is constantly growing. A station at the extreme edge of the footprint may not even hear the balloon until, literally, the last minute of ascent. Offering deference to those distant stations would be appreciated. 

Here is an example of how a voice net control station can be very helpful. In the above map, Pierre, SD would check in sometime within the last few minutes of the flight. Then at the very last minute, Albuquerque, NM would check in (assuming they found a high/hot spot). Net control would, hopefully, recognize this excellent opportunity for a really long distance QSO and tell Albuquerque to call Pierre. It takes Net Control to put this together because Albuquerque never heard the repeater or Pierre's check in since that event happened just prior to Albuquerque's reception of the repeater's signal. Of course, if Net Control misses this opportunity, hopefully Pierre will see the possibilities and request the QSO. If closer in stations are keeping clear of the repeater during the last few minutes of ascent this contact is much more likely to happen.

Try and be aware of your distance to all the stations checking into a net and plot any APRS positions your stations hears. In the above example, Albuquerque might not check in. Perhaps you are located in Pueblo, CO. You might be the station with the best chance for the maximum distance QSO during a flight by calling Pierre. But, with a lot of Colorado stations checked in, the Net Control might not pick up on this fact. In that case, you should try to get permission to make the contact. Just be sure to allow air time for more distant stations to check in. It's all a judgment call on your part. If you can make a contact of over 400 miles, you should elevate your own priority in your calculations and go for it.

Once the balloon bursts and falls below 80,000 feet net control will once again accept any contact requests. We've had our chance at long distance QSOs and now it's time to just have some fun.

The rate of ascent is a relatively constant factor. However, descent is entirely different. The only brake on descent speed is the parachute. And the parachute works against the surrounding air. And, obviously, the atmosphere is much less dense at high altitude. Therefore, the balloon begins its descent at a very high rate of speed. As the balloon moves into denser air, it continually slows its rate of descent. 

  • At 100,000 feet altitude the descent rate is around 12,000 feet per minute

  • At 60,000 feet around 4600 feet per minute

  • At 45,000 feet around 3200 feet per minute

And so, stations on the fringes of the footprint will rapidly lose the signal.

Also, since the Tracking and Recovery teams usually don't need the repeater until the last stages of the flight (below 45,000 feet) they may not need to commandeer the system until most of the distant stations have already fallen out of coverage.

Propagation models for each altitude based on the location:

  • Last Chance, Colorado

    • 39� 44.402' N

    • 103� 35.606' W