118 to 136MHz Airband Antennas
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Mobile One Airband antennas are centred on 124MHz unless otherwise requested

Stainless Steel Antennas

Stainless steel antennas are strong and durable, they are light and simple to tune but they are very hard to cut to tune. Steel is not as good radiator of energy than copper (fibreglass antennas) and so stainless steel antennas are usually longer after being tuned than tuned fibreglass antennas on the same frequency. Stainless Steel antennas have a 95% efficient transmit bandwidth of around 4MHz ie: the antenna can only work 96 to 100% effectively over 4MHz of the 118 to 136MHz airband, It is important to tune the antenna to the most used part of the airband, eg: If you tune your steel antenna to 124MHz then it will work from 122 to 126MHz at 96 to 100% efficiency and then will gradually reduce in efficiency on both sides of 122 & 126MHz frequency.

Fibreglass Antennas

Fibreglass antennas have larger a useable bandwidth of 5MHz (see stainless steel antennas) ie: the antenna can only work 96 to 100% effectively over 5MHz of the 118 to 136MHz airband, it is important to tune the antenna to the most used part of the airband, for example If you tune your steel antenna to 124MHz then it will work from 121.5MHz to 125.5MHZ at 96 to 100% efficiency and then will gradually reduce in efficiency on both sides of 121.5MHz & 125.5MHz frequency.

Issues

Ground Plane
Ground plane independent antennas are not suitable for Airband they are too narrow banded

King post
Antennas mounted on a king post will not tune well, The king post causes the antenna
to become a untuned dipole. You may be able to tune the antenna SWR <1.5 to 1
but the antenna will have a bad Return Loss, the result you will have a unnatural longer
antenna top but this length will be a compromise.  

Antennas mounted on a metal fuselage
If you are mounting the antenna on a metal airplane then you will have little problems you can use a SW2
or a M120-1 antenna and you will have no problems tuning these antennas.  

Antennas mounted on a fibreglass fuselage
If you are mounting the antenna on a fibreglass area then you will need to either create a ground plane
by the use of a metal surface such as wire mesh or you will need to use a Mobile One Airkit
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