RC-CAM
Senior Heliman
Location: USA
| I vote for 41 inches outside the Rx case.| Quote |
| Well, I can tell you that the original antenna wasn't 5 feet long. That is why I'm asking. Is it 1/8 wave = 28.97" ( I still think it wasn't that long)
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Contrary to popular belief, model R/C antennas are usually NOT based on true 1/4 wavelengths. Rather, the lengths were chosen out of convenience for us modelers.
Regardless of the worldwide R/C freq (27Mhz, 35Mhz, 40Mhz, 50Mhz, 72Mhz and 75Mhz), the lengths of most aircraft aerials has been 39 to 42 inches.
Ground vehicles, such as the USA's 75Mhz band, use a length that is about half of that. Any longer and some R/C cars would be poking a few eyes out during use. 
I have heard other fellows claim that their Rx antenna wire length was "factory tuned," since theirs was an inch or so different from a buddy's Rx that was on a different channel. Actually, what is really going on is that the strain relief knot just got tied in a slightly different spot at the factory (or an assembler got sloppy with the wire cutters).
The magic behind all of this is really handled by the antenna matching transformer in the Rx. It is a tuneable slug device and it is one of the components that got factory tweaked to ensure the best reception. If you deviate from the aerial length that was installed at the factory then this coil will need to be tweaked. In the sixties it was common practice to tune the Rx's antenna matching coil for best range, but it is an act that has been eliminated from the hobby.
And before you ask, the answer is yes: A perfect 1/4 wave antenna with a precisely tuned matching xfmr/coil will offer best range. Having said that, I doubt that it will really add up to much (versus our current lengths).
Although it is best to ask Great Planes for confirmation, I believe that Futaba has chosen a 41 to 42 inch length (outside the rx case) for ALL their USA aircraft frequencies (six meters and 72Mhz). The raw antenna wire is about 43.5 inches long. Please see http://www.futabarc.com/faq/service-faq.html#q235
There is a chance that their six meter gear deviated a slight bit from the raw 1100mm wire length, so please ask them about this. Please tell us what they say.
For sure, do not sweat if your length is off by an inch or so. The Rx will be clueless.
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