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Field Day and Using a Weather Balloon
by: Ron, N9EE
July, 2004
The below is experience of using a weather balloon for a Field Day antenna project.
As we announced for our 64 group Field Day here at the Werner Boyce Salt Springs State Park (not open yet) here in west Pasco last month one item of interest to many was the use of a weather balloon for erecting some HF antennas. The following is some history and info of the balloon we choose, legal information and results of our experience. Hope it might help for those who want to give it a try.
>From the internet, the source for all knowledge of which most sane people have little use for, we found some good info on using balloons. The FAA has a publication of regulation at www.faa.gov/avr/AFS/FARS/far-101.txt. It explains what one can and cannot do. One item of interest is the balloon is limited to a 5 lb payload. Also one must notify the FAA if going above 200 ft even if you are simply letting the balloon go such as in the use for ATV projects which typically carries a video camera with a transmitter to as high as 100,000 ft.
Another good site is www.nordicdx.com/antenna/special/baloon.html which give some good info from experience on using a balloon for antennas.
Also some good info came from ebay.com. There are many listings for balloons. Most are party or advertising custom type and range in price from $1 to over $5000. I found info on a balloon I was trying to use. It was an official weather balloon made for the NWS. I had obtained a ML541/A shaped as a sphere which was used until the mid 90s. The last buy by the NWS was 5000 units at $191 each, about $1,000,000 worth. It can be inflated up to 12 ft diameter which requires about 900 cubit ft of air. Helium here goes for about $75 for 210 cubit ft. The equation for determining the volume of a sphere is:
Volume = V(S) = 4/3 x 3.14 x r cubed (3.14 is pi and r is sphere radius)
volume = 75 cubit ft for 5 lb = 4/3 x 3.14 x r cubed means r= 2.616 ft or 5.2 ft diameter
Fifteen cubit ft of helium can lift 1 lb so to lift 5 lb requires about 75 cubit ft. The ML541 was purchased in Tampa, FL surplus new in it original sealed pack for $32. On ebay with shipping it goes for about the same.
Field Day Experience
The problem with this balloon for antennas is that it is a sphere. This gives a large face to the wind which kept trying to, and often did, blow the balloon down into the ground. Also the weather balloon was not made to have it tied down and simply lift a payload, but rather to be let go and rise on its own. The balloon eventually became damaged after a couple hours of the wind tugging at it. The winds were I would say mostly at only 5 mph.
The solution seems to be a cigar shaped balloon with rear fins which will cause it to face into the wind and have a small face. Thus the wind will not affect it much. Most balloons one sees at say car dealers are this type and for good reason. If you are in an area with no wind then this should not be a problem.
Getting the Balloon Ready
First we filled the balloon with about 110 cubit ft of helium. This can be puzzling due to the balloon did not look like what one would expect. The fill valve was at the top with a skirt about 5 ft long to hang from the bottom. Also due to the very thin rubber material of .0035 inch much care must be taken to protect the balloon.
Then after getting the balloon off the ground we tied it down but again the wind kept it low, less than 25 ft with at least 50 ft of rope.
Another problem with this balloon is helium is 2nd only to Hydrogen in the size of a molecule. Hydrogen is one proton and one electron and Helium has 2 of each. Hydrogen has more lifting power, but for obvious reasons is not used much, but it is used some. This small molecule has the problem of being able to leak through many materials. If you ever got a helium balloon and took it home one sees it stay up, but after a day or so it is laying on the floor. The weight of the material becomes too much for the helium left after some leaked. For balloons ment to be used for long periods of time the lining is most often thicker rubber. The lining in the weather balloon is 0.0035 inches and was made for a short flight.
The Antenna
The antenna we planned on using was 80, 40 & 20 meter dipoles fed in the center with RG58. We calculated we could go to 200 ft with this weight. Some have used long wires with a tuner with success. I wanted a real Field Day antenna meaning tune and talk; don't tune the rig up, but tune only the freq and transmit. Of course an automatic antenna tuner would help.
Well we did not get off the ground because of the wind and the sphere shaped balloon. If I can get the right type I would like to try again. The total cost for this project was about 6 hours and $80, but we still had fun. Heck that is what ham radio is about and as for Field Day learning the dos and don'ts might just help when the real reason we have Field Day come along.