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how short to cut my antenna?

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Old 12-22-2004, 09:59 PM
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Spaceclam
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Default how short to cut my antenna?

ok. i have a deans short antenna and it says to cut your antenna to anywhere between 4"-10". that's 6" of variables. that would make the difference between excellent reception and poor reception i would think. if i am on channel 22 and am using a hitec feather rx on 72 mhz, what length should i cut it to in order to have the optimum range?
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Old 12-23-2004, 02:41 AM
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Default RE: how short to cut my antenna?

That would make sense for a whip antenna but not a base loaded antenna, split the difference and go with 7 inches, range test, range test, range test If you have problems, tweak.
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Old 12-23-2004, 06:44 AM
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Default RE: how short to cut my antenna?

ORIGINAL: Spaceclam

ok. i have a deans short antenna and it says to cut your antenna to anywhere between 4"-10". that's 6" of variables. that would make the difference between excellent reception and poor reception i would think. if i am on channel 22 and am using a hitec feather rx on 72 mhz, what length should i cut it to in order to have the optimum range?
The Deans antenna has a loading coil in it. The length of your antenna between the receiver and the loading coil is not critical. The antenna length on the other side of the coil is critical, but that is the Deans part and they have tuned it to 72 MHz.
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Old 12-23-2004, 01:21 PM
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Default RE: how short to cut my antenna?

but it must make some kind of difference. see, i am not using it in an airplane as you know them. i am using it in a 4 rotored draganflyer thing that i made myself. there are 4 motors going at the same time and there is a lot of electrical noise so i need to tune it as well as possible. If it wont make the slightest difference at all, i will just cut it to whatever, but if there is ANY difference at all i need the optimum, because as it stands now with the regular arial it does glitch from time to time.
also, while we are on the subject, is ther any point in cross capping brushless motors? i know you can do + to ground, - to ground, and + to - on a brushed motor and it will eliminate a lot of electrical noise, but is that so on a brushless motor? that would obviously require 5 capacitors to do each wire to ground, and each wire to every other wire. what would that do?
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Old 12-23-2004, 02:56 PM
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Default RE: how short to cut my antenna?

ORIGINAL: Spaceclam

but it must make some kind of difference. see, i am not using it in an airplane as you know them. i am using it in a 4 rotored draganflyer thing that i made myself. there are 4 motors going at the same time and there is a lot of electrical noise so i need to tune it as well as possible. If it wont make the slightest difference at all, i will just cut it to whatever, but if there is ANY difference at all i need the optimum, because as it stands now with the regular arial it does glitch from time to time.
also, while we are on the subject, is ther any point in cross capping brushless motors? i know you can do + to ground, - to ground, and + to - on a brushed motor and it will eliminate a lot of electrical noise, but is that so on a brushless motor? that would obviously require 5 capacitors to do each wire to ground, and each wire to every other wire. what would that do?
Doesn't make any difference as to where it is used, antennas are the same. If it glitches with a regular antenna, it will glitch with the Deans antenna.

You must stop the noise at the source but I am not the one to recommend anything on brushless motors as I don't have any. However, I have never heard of caps on brushless motors.
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Old 12-24-2004, 03:22 AM
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Default RE: how short to cut my antenna?

Brushless motors are electrically controlled not mechanically. Put the caps on the controllers +/- Case ground rather than the motors connection. Caps on a brushless motors leads directly might actually cause interference rather that reduce it.
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Old 12-24-2004, 09:10 AM
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Default RE: how short to cut my antenna?

Spaceclam,
I one of my other careers I used to install car radios and burglar alarms. We had a motor home that came in one day with an awful whine on his radio whenever he used his speed control. This is back in the 70's, anyway this speed control used a brushed DC motor. I put a ferrite bead on the positive lead to the motor and the noise was gone. Beads are cheap they act as RF chokes. To use just put the wire through the bead. The bead should be held as close to the motor as possible.

http://www.palomar-engineers.com/Fer...ite_beads.html

John
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Old 12-24-2004, 11:03 PM
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Default RE: how short to cut my antenna?

no caps on a brushless motor. the caps are for brush noise and a brushless has no brushes to make noise.
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Old 12-25-2004, 03:07 AM
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Default RE: how short to cut my antenna?

Brushless motors still switch electrically betwen the individual poles, they still make noise. Just not the same kind.
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Old 12-25-2004, 12:52 PM
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Default RE: how short to cut my antenna?

can it be reduced? is it significant?
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Old 12-25-2004, 01:12 PM
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Default RE: how short to cut my antenna?

Group,

A brushless motor is an A/C motor (one reason why you can reverse the direction by changing any two leads). The three leads are NOT D/C power leads. If you place a capacitor across any of them, or to ground too, you will create a direct short circuit as capactiors are made to block D/C and pass A/C (the reason they are used on brushed motors, to ground the A/C noise created by the brushes). At the typical currents used on a brushless motor, at the very least you will pop the capacitor, and maybe even damage the brushless motor and the ESC. So, capacitors on a brushless motor are NOT recommended at all.

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