Originally Posted by Polwart
Would a little very short ariel (like a handheld) give nearly as good performance as a big whippy one (which have storage/snapping issues) if mounted on a suitable pole/frame?
Now there lies a bit of radiographic geometry....... I forget the physics behind this, but the theory is the longer the antenna, the more "disc" shaped the transmitted signal will be.
So, two extremes - a 3" stubby and a 4m whip which somehow manages to defy gravity & stay vertical. The stubby will produce a more "ball" like transmission patern,whereas the 4m will produce a near disc, which in theory gives better power density as it;s only going in "one direction" as opposed to going everywhere.
This is where practicality comes in - on a rib you are not perfectly aligned to the horizon at all times, and even less so with a handheld, so the fact that the stubby on the handheld is nice & compact also helps because you dont need a spirit level down the side of your handset!
Conversely, a lo-o-o-ong whip on a rib will maybe fire it's signal straight over the top of the recieving set's antenna..... should the rib be at an angle when transmitting becaue of rolling in big waves, the transmitting "disc" will roll with it.
Somewhere in the middle is a bhappy medium. I have both a 1.25m whip with a patch panel under the consol so I can easily swap to to a Vtronix raider. Haven't noticed a difference in either in either TX or RX.
(And before you ask, it's a phased introduction of technology - eventually one will be the AIS stick & double as the VHF backup antenna. At the moment, I'm swapping them around to find out which works best with the VHF.)