On Wed, Mar 23, 2005 at 09:44:43PM -0800, Larry Taylor wrote: | The Small Ant will not radiate off the end.
Rubber duckies do. That is what you're talking about, right? | The sailplane after a few flight may have the Ant wire all bunched | up next to the receiver from landing. Really, the antenna should not be allowed to do this. It should be installed better. (But mistakes do happen.) | The longer the TX Antenna the better it is for the sailplane. I think a better maxim is `the stock antenna is usually best' (unless you know what you're doing.) Taking your stock antenna, TX or RX, and replacing it with one that's somewhat longer will probably _reduce_ performance, not improve it. | I have seen many sailplanes that have added on wire to their RX | Antenna just to get better range. This is a `Bad idea', unless you know what you're doing. | (England) but we here (USA)can get so high just a speck in the sky | and still have control of it with our stock radios from the Hobby | Stores. I'm guessing they can speck it out over on the other side of the pond with stock equipment too. The minimum length for a good antenna is 1/4 wavelength, because that's where it becomes resonant. At 72 mHz, this is right at one meter, and you'll find that most antennas, receiver and transmitter, are right about one meter. This is not a coincidence. If your antenna isn't right at 1 meter, either 1) it's close enough to one meter to work well enough, 2) there's a matching network (perhaps the manufacturer had a nice supply of antennas that were slightly off, and so it's cheaper to just add a coil or capacitator and use the off-length antenna), or 3) the receiver is so bad at rejecting interference that they're deliberately reducing the range. *cough*Hitec Feather*cough*. A matching network can make an antenna that's not 1/4 wavelength long resonant, but it's still a compromise, and will reduce range. If the difference between the antenna length and 1/4 wavelength is small, then the range lost is very small. But if your antenna is electrically 1/4 wavelength long, but physically much smaller (like with a rubber ducky, or a reduced size receiver antenna), it will still be resonant, but the range loss is signifigant. But the range will still be much better than if you took the stock antenna and simply cut it to the shorter length (making it non resonant.) It seems that most non-72 mHz equipment (50 mHz, 27 mHz, 35 mHz, etc.) also uses antennas at about one meter. (Probably because these antennas are easy to get, and a 3 meter antenna at 27 mHz would be unwieldy anyways.) This equipment would almost certainly have a matching network, probably a loading coil. In any event, if you make this one meter antenna longer, you'll make it so it's not resonant anymore (not even close) and you'll _reduce_ range. (Now, if you add another 1/4 wavelength, or a multiple of that, you'll probably slightly improve range. But only slightly.) Either way, the range of our equipment seems to be around 1.5 miles -- at least that's what I've heard. I can't see my largest plane at over half a mile well enough to fly it, so there's a lot of room for small compromises or mistakes. But if you get enough of these going at once, it could result in the loss of a plane. | Larry Taylor KF6JBG Personally, I wish we could just get a frequency allocation in the 800 mHz or so range. Then a good antenna could be less than 4 inches long, making much of the need for small antennas moot. (It would also be ideal if the new radio equipment used spread spectrum rather than discrete channels, removing frequency conflicts forever. R/C heaven! But so much for dreaming ...) -- Doug McLaren, [EMAIL PROTECTED], AD5RH Why don't cannibals eat clowns? They taste funny. RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
