G4AKC - HF Pedestrian and Bicycle Mobile

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Balloon Antenna

Posted: 11 May 2020 03:06 AM PDT
https://www.g4akc.co.uk/balloon-ante...loo n-antenna



Well we have all been locked down for some time now and although I have a
high noise level at home I decided to try a balloon antenna on the flat
garage roof.




The balloon antenna was supported by an initial 30ft telescopic fishing
pole and then 170ft of floating lightweight wire was connected to the top
of the fishing pole.








The balloons were several 12 inch balloons treated with Hi Float and filled
with helium gas and all the balloons were bound together to provide
sufficient lift.




The wire used was simple stranded plastic coated hook up wire as its very
light.




At the bottom of the fibreglass fishing pole I used an MFJ Versa Tuner 2 to
match the antenna on the various frequencies of operation.








I used a 1 Meg Ohm discharge resistor to eliminate static build up from
creating unwanted noise on the 200ft balloon antenna.




I used a coax line feed from the Versa tuner back to the bicycle mobile
trailer which was in the back garden I also had a full sized quarter wave
vertical antenna for 20m on the bike trailer to compare the performance of
the balloon antenna against, although the location of the trailer meant
that the trailers quarter wave vertical antenna was in a very screened
position.








I had the facility to use radials if required but as expected with this
type of antenna the radials gave no benefit whatsoever.




I used my antenna analyser to roughly set resonance using the Versa tuner
to resonate the balloon antenna and any fine adjustments were made on air
using a low power carrier.




I had problems with balloons randomly bursting that was not linked to RF
transmissions and that did cause a few practical problems.




Simon N Wilton, VA3SII kindly sent me the EZNEC modelling of the 200ft
antenna which I have posted on here, including VSWR and resonance points
(without any ATU)












Firstly the noise level on 20m was high compared to the quarter wave
vertical and the performance difference was not as great as I was
expecting, specially seeing that the trailer quarter wave was in a poor
position (see video)




On 40m the 200ft antenna was a much better performer with some excellent
signal reports, one from the Orkney Islands was 59+45 I did rig up a
makeshift 33ft vertical on the bike trailer to compare the balloon antenna
against and there was a considerable advantage with the balloon antenna,
however no DX was worked on 40m as the noise level on the antenna was
anything up to S9!!




Finally I tried 80m speaking with David Roper, M0DAD but again the noise
level on the antenna was very high making it almost impossible to receive
with, had I not had the west mountain CLR DSP unit on board it would have
been impossible to use the antenna to receive on.




Conclusion The balloon antenna may seem simple but requires financial
investment of helium gas, several high quality balloons, Hi float sealer to
prevent gas loss, a fishing pole or similar to prevent the balloon from
drifting horizontal in the breeze and of course the antenna requires
effective base impedance matching.




The time effort and expense in my opinion did not not warrant the
performance, which generally was poor and although I have done the same
experiment 3 times over the last 40 years I will definitely not be doing it
at home again However as I still have some gas and balloons left I intend
to try it over sea water as we can now operate by the sea again after
Wednesday as the government have relaxed the restrictions for the moment.




Dave G4AKC