• First thick nylon line, then copper wire
• Be extremely careful about static
• My balloon and kite antenna system
• Kite antenna - watch out!
• Balloon antennas - a theoretical approach
• Excellent supports for LF antennas

First thick nylon line, then copper wire

Last month there was a discussion about balloon antennas, mainly about using 2 balloons instead of one for a vertical antenna.
Two persons mentioned their concerns after having read articles on the subject relating about wind-induced static shock hazard and reception high noise level.
One participant replied that if one would shunt the antenna with carbon resistor (~4.7k-22k) to local ground, high enough not to upset antenna caracteristics but still, low enough to discharge the beginning of charge buildup, one would be able to cope with this problem.

On the same subject, a second participant with actual balloon and kite antenna experience (300 ft - 100 meter) did report the reality of shock hasard, but eventualy got around the problem by shunting an antenna tuner inductor to ground or shunting the antenna directly with a 100k resistor. He reported that in these conditions, he was able to get signals that sounded great. Also in light wind conditions, he said that static was not much of a problem.

On the structural aspect, for security reasons, personally I would't try to tie a thin copper wire directly to the balloon, as some may have suggested. I'd rather use high strenght nylon or alike line (fishing line type for exp., I've seen some with 40 lbs capacity) to cary the all strain the holding line may be subject to in presence of higher ds than expect winds. The thin wire copper line would only be ' brought along ' for its antenna role. To avoid any wobbling of the 2 lines, I would knot, using short lenght of holding wire (trimmed after knotting), every 5 feet or so.
For example, if one want to jack a 300 feet vertical up and chooses a nylon line of 20 lb capacity (lets say it's 2000 feet/lb (.0005 lb/foot) and AWG #28 copper wire at 2081 feet/lb (again, ~.0005 lb/foot) and 65 ohms/1000 feet (ARRL handbook), one would end up with a line at .001 lb/foot for a total payload of .3 lb. So the balloon would need, at least, this 'net' boyancy (preferably a bit more let say .4 lb). By net boyancy I mean the payload the balloon can handle, after lifting its own weight. A 3.5 to 4 feet diameter ballon should be able to handle this charge, depending on its enveloppe weight.

The balloon envelope material quality his also something one should consider before attempting any lift off. If not, one may experience a short lived project.
We've all air blew party rubber balloons to their max, just to realize that the next day they had shrinked to half their size. The reason being that, due to pressure differential between inside and outside of the streched enveloppe, air will just sift through it. Rubber is an elastomeric material build around long organic molecular chain attatched one to the other through ramifications (something like a tree), and there are 'holes' between these chain elements. Air (that is, molecular oxygen, nitrogen (and carbon dioxide if you blew the balloons yourself... pfiew!!)) eventualy finds its way through. So if molecular elements like O2 and N2, that are many time the size of atomic helium (He) can do that, you can imagine how helium would act considering the wide open barn doors these 'holes' are, relative to its size. I dont think one would be able to retain it for more than a couple of hours. So not any off the shelf stock will suffice.

I've done a few phone calls, a couple of weeks ago to see what's available, mentioning I was looking for a balloon to be inflated with helium, that was able to retain its content for at least a couple of days.
The only source I found was the Party Decoration retailers. I eventualy found someone that told me they had 42 inches size balloons, the enveloppe of wich is made of unstreachable material (vynil???) made for that purpose (helium inflating) for $5. They would inflate them for $5 each. One can also get pressured helium portable refill thanks, good for ~25(?) of these balloons, at $60. They were not able to specify the enveloppe weight or the ' net boyancy '.
Another retailer told me the he could supply me with a 7 feet balloon (that's 9 times the volume of 42" diam.), again the unstreachable kind used for outside advertizing, hence relativaly long lasting, with a 4 lb lifting capacity for CAN$342 + helium...
Ooops, this time my budget was blown!!!

Be extremely careful about static

First: Hugh Caron's post concerning static charges on the balloon wire are accurate. I was one of the guys he spoke about and, yes, when flying kites with a wire antenna, one must be extremely careful to bleed off the static charge. My friend Tony, was practically thrown across the deck of his boat when he touched the ungrounded wire on one of our kite- antenna experiments.

Two: Helium is much easier to buy and transport than hydrogen. It may not be cheaper, but at least you don't get anything close to the HAZMAT paperwork you'd get if it were hydrogen.

Three: Although latex balloons do deflate more readily than, say, mylar balloons, the surface area to size ratio of an eight foot weather balloon will guarantee that it will stay up for quite a while.

Four: The FAA's relevant regulation on this subject of tethered kites and balloons is Part 105. When I last read it three years ago, it said that anything with a total weight of under five pounds empty is exempt from most regulations.

You do have to know where the airports are, and don't fly your kite or balloon where it may get in the way. A call to the local Flight Standards District Office (in the United States) will go a long way toward clarifying whether the place and altitudes you wish to fly the antenna are appropriate. Even if you might fly it so high that it could interfere, they'd be more than willing to accomodate you by issuing a NOTAM, or NOtice To AirMen, with adequate notice, and then issue you a permit for a certain time and place.

My balloon and kite antenna system

Since the discussion is going this way I'll go in to more detail as to how I handled the Balloon and Kite antenna systems.
First, all flights were made from a boat, a few miles south of the Middle River in the Chesapeake Bay. All lines were 400' or less.
The kites and balloons all had empty weights of under five pounds (thus not requiring notification under part 105). Prior to conducting these tests, I contacted the Baltimore Flight Standards District Office for advice on how to proceed.

We thought briefly about using a strobe light. The problem was two fold: first, the strobe itself sometimes put us over the part 105 weight limit (depending on which kite we used). Second, the strobe light could easily have been mistaken for a life-vest strobe light on the water (because that's what it was). We decided to keep the line to about 200' instead, and to forget the strobe light.

There are few standards for this sort of activity. Kites and tethered balloons are usually not a problem for most aircraft, especially those over open water. I caution you, however, to know the area where the airports are, to know where the instrument approaches are and to avoid those places. This is something I'm already aware of, since I am an instrument rated pilot.

In any case, low flying aircraft don't often go over open water, so the risk of collision is low (the big sky, small target theory).
Obviously, these details are things you should consider well before purchasing that kite or balloon...

Kite antenna - watch out!

Using a kite, or balloon, to launch a long-wire antenna is a risky business, even on a clear day with no clouds around. The danger arises from the electric field between the earth and ionosphere. This field is about one hundred volts per meter (in the vertical direction), and is always present. Any antenna launched into the clear blue yonder will aquire a charge large enough to wipe out a final transistor, or a receiver front end.

So what's the difference between ordinary outdoor antennas and one attached to a kite?
Earth's electric field is easily distorted by objects attached to ground, like a tree, or mast, or house (your tower doesn't have a few kilovolts between top and bottom). A kite-bourne antenna protrudes into wide open spaces, where it very likely gets charged up. Your earth-bound antenna is attached to a mast or tree or house, where earth's electric field is greatly reduced.

Here are some precautions for kite experimenters, or anyone who uses temporary outdoor antennas:

Add a choke coil to the antenna connector between centre pin and ground. This will leak away any charge that tries to accumulate. I see that most modern rigs don't provide a D.C. discharge path from antenna connector to ground - this is dangerous to your equipment.

This choke won't save you if you connect a charged antenna to your rig after you've put it up: either discharge the antenna to ground or connect the rig to antenna before putting it up.

A few years ago I put up a two-meter 1/4 wave antenna on top of my tower. The coax snaked thru the window had no connector. When it started snowing, I noticed a snapping sound every twenty seconds or so. The end of the coax was arcing over from the charge accumulating in the coax capacitance. That cable was being charged five or ten kilovolts in only twenty seconds!

Balloon antennas - a theoretical approach

The discussion about the possibility of erecting a balloon supported long vertical and/or inverted L type thin wire antennas has raised concerns about potential shock hasards and high noise levels resulting from wind-induced static. Solution replies were proposed, through the use of bleading resistor (and/or inductor) to a good ground, high enouph to discharge the static buildup at adequate rate while preserving electrical caracteristics of the antenna. r > 4700 ohms. inductor = ?

Concern was also raised about the trouble of putting up a 2 balloon setup over a single one as high (or even higher) vertical, on the base that inverted L would behave as top loaded vertical, which is omnidirectional by nature. On this, I replied it may and would only be worth the trouble if, considering the multiple wavelenght in hight and lenght for a large part of the SW band, such a setup would show directivity caracteristics that would approach that of a long wire. As I could't answer this question myself, I left it open for comment. If there were any, I have not seen them, yet.

Lastly, concerns were also expressed about the physical (structural) ' reality ' and security of such a setup. To this I brought the idea it should take the shape of a trapezoidal figure (as seen from the side). I also stated that I will try to determine through mathematical (mecanical) equations, proper sizing of such a setup along with constrains the wiring would be submit under different wind loads.
This is what will now follow.

Sizing for still-air conditions

I choosed to evaluate a 200'H x 200'L feet trapezoidal setup, ABCD c.c.w. with base angle at A and D = 60 deg.
XY locations

			   Q		 Q   <--- Balloons
	 (115.47,200) 	B *  	 ---	 * C (315.47,200) 
				  ^
				  |
			         H = 200' 
				  |
				  |
Gd. lv   -------    ( 0, 0 ) A *	---          * D (430.94, 0 ) --

A cable or wire suspended between to horizontal points, such as points B and C in the above figure is called a ' Catenary ' in a Mathematical and Mechanical sense. A cable or wire such the ones that links A and B or C and D (sides) is more simply call a ' Flexible Cable Suspended from Two Differents Levels ', at least in the Mechanical engineering texbook I refered. (1952 ed., but the logic still good, even after iron curtain fall ;-))

I will limit here the results resolution of the proposed equations brought, in the case of this problem. I would suggest to those interested by the details of these equations to refer to similar book as mentionned above. They are long, dry and require the use of minimal graphic support, beyond the limit of this media, to have any meaningfull sense. I will just mention they are of the recursive type, that one can resolve with a spreadsheet such as Excel with relative ease.

The resulting figures were found to be:

Top section BC (Catenary):
Actual wire lenght: 202.97'
Sag                   15.0'
Tension at B and C .3508 lb at 16.82 deg with horizontal axe
                   .3358 lb along x axis
                   .1015 lb along y axis (down)

Side sections AB an CD
Actual wire lenght: 231.22' (to compare with 230.94' above, thus
                             very little sag on those)
Tension at B and C .7790 lb at 64.47 deg with horizontal axis
                   .3358 lb along x axis
                   .7030 along y axis (down) 

Tension at A and D .5790 lb at 54.55 deg with horizontal axis
                   .3358 lb along x axis
                   .4717 along y axis (up)

At B and C vertical down force combine .1015 + .7030 to give .8045 lb which is the vertical upward force (net boyancy) that is required by the balloons, at each site, to maintain the setup aloft at desired location.

The Baloons

Let suppose that a 40 inches (3.33' ) diameter of .5 lb envelope weights is available.

Density of air at 500' ASL = .0754 lb/pi3, at 700 ASL = .0750 lb/pi3

Volume = .5236 x d3 = 19.39 pi3

At 700' ASL ; Weight of air = 19.39 x .0750 = 1.454 lb
At 500' ASL ; Weight of helium = 19.39 x .0754 x .1308 = .191 lb

Net boyancy at 700' ASL = 1.454 - .191 - .4 = .863 lb

In this case, 2 of these balloons would be ok for the proposed setup. The top part would be a bit flatter (but, not by much) than calculated

Effects of the wind

Fd : drag force ( lb ) Cd : drag coefficient (no dimension)
V2 : Velocity of the wind squared ( f2/sec2 )
A : Center area of the sphere ( f2 )

Cd = .4 for Re ( Reynold number) < 350,000
Cd = .2 for Re > 350,000

Re = D V / u

D diametre of the spere (feet)
V Speed of the wind (feet/sec)
u (nu) Kinematic viscosity of air = ~.00016 (f2/sec)

Below a table that shows the evolution of horizontal pressure (in ponds) induced by various wind velocities (mph) on various balloon diameter (feet)

Table 1.
Horizontal wind-induced pressures on a spherical balloon: Fd (pounds)

Diam-->	  3'	3.33'	  4'	  5'	  6'
V (mph)
10		.71	.88	.66	1.02	1.5
15		.83	1.03	1.5	2.3	3.33
20		1.5	1.83	2.63	4.1	5.9
30		3.33	4.1	5.9	9.2	13.3
40		5.9	7.3	10.5	16.5	23.7

Here, I will limit the analysis to a worst case senario, where I will use only common sense to evaluate resulting strain on support wire AB.
Examining the trapezoidal shape of the proposed setup, one can observe that a wind blowing from the left would induce the highest strain on line AB, resulting from the combine effect of the pressure on balloon C 'added' to the one on balloon B through wire BC.
To get these 'exact' values one would have to develop some kind of program that would require to first compute the relative reposi- tionning of each balloon wit varying wind condition and then apply vector computation to get this value. Developping such a program would be time consuming.

Common sense evaluation should suffice to get acceptable ballpark values. One can see that wind blowing from the left will tend 'push' balloon B along a circonference of radius AB, thus going down. At the same time, balloon C would be ' forced ' to travel up along the circonference of radius DC. Those 2 opposite forces would tend to oppose, resulting in reduced displacement of point B as to compare to a single vertical balloon. In any case one can see that balloon B moves at all, the effect will be to reduce the angle at A.

Hence, If one directly adds the horizontal wind induced pressure on B and C balloons (or doubles the value at B) and divide the result by cosine 60 deg, one would get a value of the strain induced in wire AB higher than reality, but still representative for evaluation purpose. I did that to Table 1 above to generate Table 2 below. Let's keep in mind these values are somewhat on the overestimated side.

Table 2.
Estimated side wind-induced strain on wire AB: T ( pounds)

Diam-->    3'    3.33'   4'    5'     6'
V (mph)
10       3.9     4.1    3.1   4.7    6.9
15       3.9     4.8    7.0  10.7   15.4 Safe zone
20       7.0     8.5   12.2  19.0   27.4
                            -------------------
30      15.4    19.0   27.4 |42.7   61.8
                     -------|            Risk zone
40      27.4    33.9 | 48.8  76.7  110.

One last table (some useful physical properties of air)

Altitude(ASL)   Air pressure   Air density   Air viscosity
   feet            lb/f2          lb/f3          f2/sec
     0             2116.2         .0765         .000156
   1000            2040.9         .0743         .000162
   2000            1967.7         .0720         .000164

Well those are my findings. I hope those infos will be of some help for anyone who would like to tackle (or proceed) with the idea of erecting some kind of balloon antenna.

A Skyhook for the '90s

Balloons, shaped like small blimps, are in relatively common use for advertising purposes. Such a blimp, of 10- to 12-foot (3.3 to 3.7 m.) length and 3- to 4-foot (0.9 to 1.2 m.) diameter can easily be used to support a vertical antenna for temporary use, such as in Field Days. K4ZA has successfully used them, and in this article, offers the benefit of his experiences for others who might want to follow his example.

A balloon of such size, when filled with helium, will provide a lift of about two pounds, ample for a quarter-wavelength wire on the 160-meter band. The balloon should be tethered in the center of an open space of such size that the perimeter is at least as far in all directions from the tether as the length of the antenna. For safety and good results, one should select an area of relatively flat ground with no buildings, towers, trees, fences, or overhead wires within it.
The balloons are commonly made of polyurethane film of 2- or 3-mil (50- to 75-micron) thickness. The film is relatively strong but must be protected from puncture. The author suggests laying a 20- by 20-foot (6- by 6-m.) tarpaulin around the tether where the blimp will be inflated, to protect it from twigs or sharp weeds.

The tethering line should be 100-pound test fishing line or 1/8-inch (3-mm.) nylon rope. Stranded wire or aluminum welding wire is light and amply strong for the radiator. A good quality ball-bearing swivel should be used to attach the tether to the balloon's halter, since the wind will cause it to turn, pitch, and roll in all directions. Gloves should always be worn when the blimp is being launched and retrieved. In all cases, one should avoid dangerous situations, such as operating near power lines, in wet or stormy weather, or near airports or areas congested with people. Do not attempt to use heights greater than a simple quarter-wave monopole. Finally, remember that an adequate ground system is at least as important as the antenna; use either four elevated, or up to 60 ground radials for best results.

Two suppliers of these inflatable blimps are: Toy-Tex Novelty Company, 7315 N. Linder, Skokie, IL 60077, tel (847) 673-6600; The Blimp Works, 156 Barnes Airship Drive, Statesville, NC 28677, tel (704) 876-6705; web http://www.msmall.com/blimp.