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Old Sep 18, 2004, 09:26 AM
LexTalionis is offline
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Range problems with my 4-yr old Son's 27mhz AM RTF...


Hi all,

I got my 4 year old son an RTF 27mhz AM airplane (really cheap, but that's the point). I want to get him started early.

The range is only about 30ft before the engines start to sputter. I've checked the RX/ESC combo and the antenna connections looks good and the TX batteries are topped off. The Nimh pack is topped off too. Since I can't return this (bought a year ago), I was wondering if I could electrically lenghten the antenna by putting a coil of wire in series with the antenna.

The 27mhz AM antenna is, by default, 18 inches on this plane. Is this long enough? Any suggestions here would be great. Thanks!
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Old Sep 18, 2004, 10:44 AM
Foamaholic is offline
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You could experiment with antenna length, but it's only likely to shorten range futher. The problem with 27 mhz is that it can pick up all kinds of stray signals. See how the range is in a different location. How is the antenna routed? Keep it away from other electronics, receiver, servos, etc. and make it as straight as possible.
Old Sep 18, 2004, 10:57 AM
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The 27 Mhz tx's are designed to have a low range.
Old Sep 18, 2004, 11:08 AM
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Designed for low range...hummm...30ft is pretty low. There are no servos in this one...dual engines left/right is accomplished via the motors.

I'll try to lengthen it a bit. Thanks!

Lex
Old Sep 18, 2004, 12:17 PM
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I had a "Wal-mart" special car when I was younger on 27 Mhz... 30 feet was about max. The 49 Mhz is a little better.
Old Sep 18, 2004, 12:26 PM
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Humm...we'll I now know the general range of 27mhz AM...thanks guys!

Lex
Old Sep 18, 2004, 12:57 PM
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which plane is it?
Old Sep 18, 2004, 01:17 PM
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Lengthening won't do anything. I'm not sure what the proper length for a 27mhz antenna bit it is specific.

mw
Old Sep 18, 2004, 06:08 PM
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I don't remember the name of it, but it was bought at Wal-Mart about a year ago and it was a flimsy Delta type wing with two small (about have the size of IPS motors) in the center of each wing half. It was yellow and black. I've taken the motors out and esc/rx out and put them on a small 25" foam glider and it flys fine if the motors would stay on past 30ft...after about 30ft the motors loose signal and begin to cut out because of range issues. I'll try a coil and call it then and just have an on/off switch for the motors and just have my boy fly it w/o r/c, at least then it would fly futher...just don't know where to ;-)

Thanks,
Lex
Old Sep 18, 2004, 08:44 PM
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The prob is most likly not the RX but the TX. Try adding another cell to it. The guys in indoor forum have gotten improved range on the Bit charger type cars like this.

I also read somewhere about hanging a copper wire the same length as the ant. from the neg battery connection. Not sure on this but is cheap to try.
Old Sep 18, 2004, 09:04 PM
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Well, I just added a coil made from 30awg magnet wire in series with the antenna and the range improved about 4 fold. I have thought about the TX since it's only 6 AA cells.

copper wire from the neg battery connection????? just slap a wire the same length to any neg terminal in the battery compartment and try? sound like pfm to me if it does work. I'll give it a try too.

Thanks,
Lex
Old Sep 23, 2004, 05:49 PM
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The length of the antenna is a tuned feature.
if you are planning to lengthen it, it would be best to double the length, instead of adding e.g.50% extra as the tuning is less interfered with .
Also the transmitter is low power compared to the usual equipment used by model flyers. So the Tx is limiting range also, but more difficult to improve.
It would be wise to check out insurance considerations if you are using 27AM in a built up area, because FM is considered a minimum standard for safety in most countries. FM is of course more interference resistant.
In any case you will probably find that interference mostly comes from within your own model, and reducing throtle is very effective at reducing interference, and thus increasing effective range.
Old Sep 24, 2004, 04:40 PM
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Adding an equal length wire to the -ve terminal can improve the radiation from the antenna. When you hold the transmitter, you actually become part of the circuit. The whip antenna forms one part of the dipole, and you become the other half. If the intercapacitance between you and the groundplane in the transmitter is poor, then it becomes effectively a lopsided dipole. Hence the addition of the wire to the -ve side, this makes the set see a full dipole.


Old Sep 24, 2004, 04:51 PM
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mac_man,

Could you please describe this in more general terms? How long of a piece of wire should I connect to one of the negative battery terminals and where should the other end connect to?

Thanks,
Lex
Old Sep 24, 2004, 04:57 PM
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The way I do it, is to cut a length of wire the same as the extended transmit antenna. If you have a charge socket on the side of the transmitter, the obtain a plug to fit and solder one end of the wire to the -ve side of the connector. The other end just dangles loose, you could weight it with anything non-metallic.


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