David AMA40795 / KC5UH <remove #$%^ from email address> wrote:
| Neither Tx nor Rx antennas in RC gear are "tuned". They are sized to
| get maximum signal strength for a nominal length that is kept
| reasonably short.
I'm not sure that's quite true ... sure, they're not *carefully*
tuned, but they do seem to at least aim for a 1/4 wavelength antenna,
which would be the proper length to aim for.
If you measure your 72 mHz receiver antennas, you'll find that just
about all of them, except for the cheap single conversion receivers,
are almost exactly one meter long, which corresponds almost exactly to
a 1/4 wave antenna for 72 mHz.
Now, I did measure some transmitter antennas (I removed the metal part
and measured that, because some is hidden inside the unit.) These
seemed to vary a lot more -- a JR radio was 1.16 m, Airtronics was
1.17 m, Futaba was 1.02 meters, and the Megatech transmitter was 0.97
A bit shorter than 1/4 wavelength I can understand -- there's a bit of
wire inside the transmitter that will radiate as part of the antenna,
but being longer than 1/4 wavelength suggests that they're just not
being very careful. But even so, they're sort of close to 1/4
I guess if they wanted much better performance, they'd go for exactly
1/4 wavelength at 72.5 mHz, and they'd include radials. You'd look
like a dork with those radials, running the risk of poking somebody in
the eye with them, but you'd have a nice strong signal :)
(For receivers, they'd go for a full dipole rather than a half dipole
whip antenna.But you'd also pick up more noise, so it may not help
In any event, since current systems will let you control your plane
much further away than you can see already, there's no real need to
Also, the 50 mHz equipment uses antennas that are exactly the same
lengths as that for 72 mHz. So either there's a loading coil in both
TX and RX, or they're *really*
letting things get sloppy.
And for 27 mHz, again, similar antenna lengths, but there really must
be a loading coil or it wouldn't work well at all.
Doug McLaren, firstname.lastname@example.org
Can anyone remember when the times were not hard, and money not scarce?
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