AEROSTAT October 2003

Glen Everett offers a selection of technical tips

Aerials are ‘centred’ on a particular frequency and operate less efficiently either side of that number, until eventually it will actually damage the radio, the same as will transmitting without an aerial at all. The wider diameter the rod/wire, the more efficiently it will operate away from this frequency and this is sometimes referred to as wideband capability. Fortunately, in the UK we mostly operate on one frequency, 122.475Mhz, and you can ‘tune’ your aerial to get the best out of it. Airband aerials for base stations are commonly magmount or gutter mount for your 4x4, the most common and practical being quarter wave. The length of the antennae is simply a calculation of the speed of light (in metres per second) divided by frequency (in hertz), all divided by 4 (for quarter wave):–

300000000 / 122475 / 4 = 612mm

A more efficient aerial can be made by using a 5/8 wave whip, but this works out around 5 feet long, so you have to think of somewhere to mount it!

Check the length of your magmount aerial from the unshielded base to the tip. I have seen many commercial off-the-peg aerials as much as 10cm short, either because some manufacturers centre

the aerial higher up the airband frequencies of 108 to 137Mhz, or because you have an aerial for the 2m amateur band.

Keep your balloon cleaner and safer from blown grass or alpine meet snow by obtaining an old nomex skirt/scoop and placing it in front of the fan during inflation.

Insist your crew switch off your fan fuel switch before they load it into the trailer. During the chase the carburettor float will bounce up and down, flooding the engine. This excess petrol can evaporate,

leaving gum and deposit inside its passageways which will cause poor starting.

Don’t look for leaks with a naked flame! A soapy solution is recommended by the factory. A commercial bottled propane supplier I know checks his thousands of cylinders using windscreen wash solution,

as it contains the same ingredients as the £12 a bottle commercial leak detector (and doesn’t perish rubber).

THE FLYTEC 3040 UNDER TEST

Being a man of gadgets, I liked the sound of being able to tell how loaded the balloon is by knowing the temperature at the crown. I had seen the wired versions but I had also heard about somebody hitting power lines and electrocuting themselves with the sensor cable.

The now affordable handheld infra-red emissivity thermometers seemed ideal, and were tried, but actually don’t work at all, so don’t waste your money on those unless you can get a variable one (most seem to be fixed at 0.95) and somebody can come up with the IR emissivity of balloon fabric.

I borrowed a wireless Flytec 3040 for this trial with an open mind and found it excellent. It is a vario, altimeter and measures envelope temperature. Ergonomically it is very good and the display is clear. I had heard from several sources that early units were unreliable, but I found no problems. My usual vario is a simple Flytec 4005 and operating it was very similar and relatively foolproof. The sensor requires a slight approved mod to a top panel by fitting some Velcro and a reinforced hole to pass the sensor through, the radio sender body being Velcroed to a load tape. A quirk I found was that it shuts off after not being used for 30 minutes, and therefore when tethering it keeps turning off! If I had a spare 1200 (wow!) quid I would probably buy one.  I have seen them on American websites for under £1000, if you have a relative over there to buy you one for Christmas. However, for now I guess I will be sticking to the load chart!

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