> Telescoping but short and tested to show that it actually has
> better output than the stock full size.
This comes up from time to time. A manufacturer who makes such a claim
has to be viewed with suspicion.
One antenna can show gain over another only in two ways: One was is by
producing a directive signal, i.e. one that is concentrated in a given
direction and has nulls in other directions. This is not applicable to
the whip antennas we use. Old old timers may remember the McEntee 465
MHz transmitters with the little Yagi on top; if it wasn't pointed
directly at the plane, you lost contact.
The other way to show "gain" is by being less lossy. That is, if
antenna A is 50% efficient and antenna B is 25% efficient, then A will
have a 3 db louder signal.
But unless there is some gross mismatch in the output to the full-size
antenna, a shortened antenna is tremendously more lossy. A typical
figure is 10 db; in other words, 90% of the transmitter's output power
is wasted when using a shortened antenna.
This often does not matter, since in most cases our signals are about
30 db above the level needed for full control, so lots of flyers toss
away that 10 db with impunity, and never have any radio glitches. In
most circumstances you'll get satisfactory performance from a short
antenna, but you can't buy one that defies the law of conservation of
energy.
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