Just replaced my antannae in the RX and it's about a foot longer than the stock Futaba 6ch one. Can I shorten it to match the original length?

Don't quote me on this, but if your using a 72MHz freq I've read the antenna length is suppose to be 39" or close to it.

Yeah, the new one is 36"....stock one was 28", very strange.
(reciever is Futaba R156)

I definately wouldn't cut it, especially before you do the math on it.

468/freq you are using, and that will give you feet, probably something around 6.5' for a half wave antenna. The receivers can either be 1/4 or 1/6 wave, so then you take that number you got and convert it from 1/2 to either 1/4 or 1/6. That is gona be the descrepency between the two antenna's.

for example say you are on ch50, or freq 72.790, that works out to be 468/72.790 = 6.43' or 77.153", so that's 1/2 wave, so to get to 1/4 wave divide that # by 2 and you get 38.577" and for 1/6 wave you divide the 1/2 wave # by 3 or 25.718"

I definately would not cut that =)

BTW I learned this from vec over on bladecprepair.com

"If you divide 468 / frequency, you get the half wave length of your antenna. If you were to take 468 / 75.890 = 6.16 feet. The antenna's on the helis are normally about 2 to 3 feet long, which makes the short wire on the receiver a 1/4 wave, or even a 1/6 wave wire. You could wind a third of that in magnet wire around a wooden dowel rod, and achieve the same thing as a base loaded antenna, having the wound part about 4 to 6 inches away from the receiver, and a solid spring wire antenna 1 foot long attached to the end of the coil. And when you do your calculations, be sure to include all the antenna wire from where it goes into the receiver."

You should always have an antenna length configured for what frequency you want to receive (and transmit). This is why there are so many different types of antennas ... If you want a kick-butt antenna for your heli, find a ham friend of yours. He/she will be an expert and can configure an antenna that will be outstanding! Here are antenna lengths for 1/4, 1/2 and full wave lengths for all the channels that come with Axe CP:

[ul][*] Channel 36
[ul][*] 1/4 wave length:
[ul][*] 38.73 inches (3.2 feet)
[/ul][*] 1/2 wave length:
[ul][*] 77.45 inches (6.45 feet)
[/ul][*] Full wave length:
[ul][*] 162.85 inches (13.57 feet)
[/ul]
[/ul][*] Channel 40
[ul][*] 1/4 wave length:
[ul][*] 38.68 inches (3.22 feet)
[/ul][*] 1/2 wave length:
[ul][*] 77.37 inches (6.44 feet)
[/ul][*] Full wave length:
[ul][*] 162.67 inches (13.55 feet)
[/ul]
[/ul][*] Channel 42
[ul][*] 1/4 wave length:
[ul][*] 38.66 inches (3.22 feet)
[/ul][*] 1/2 wave length:
[ul][*] 77.32 inches (6.44 feet)
[/ul][*] Full wave length:
[ul][*] 162.58 inches (13.54 feet)
[/ul]
[/ul][*] Channel 44
[ul][*] 1/4 wave length:
[ul][*] 38.64 inches (3.22 feet)
[/ul][*] 1/2 wave length:
[ul][*] 77.28 inches (6.44 feet)
[/ul][*] Full wave length:
[ul][*] 162.49 inches (13.54 feet)
[/ul]
[/ul][*] Channel 54
[ul][*] 1/4 wave length:
[ul][*] 38.53 inches (3.21 feet)
[/ul][*] 1/2 wave length:
[ul][*] 77.07 inches (6.42 feet)
[/ul][*] Full wave length:
[ul][*] 162.04 inches (13.50 feet)
[/ul]
[/ul][*] Channel 56
[ul][*] 1/4 wave length:
[ul][*] 38.51 inches (3.20 feet)
[/ul][*] 1/2 wave length:
[ul][*] 77.03 inches (6.41 feet)
[/ul][*] Full wave length:
[ul][*] 161.95 inches (13.49 feet)
[/ul]
[/ul]
[/ul]

Antenna length and loading are more important on the xmit side than the recv side (that's why they warn you not to operate the xmitr without the antenna screwed in).

Basicly, on the recv side, the longer the antenna, the better off you are for range (pulsed digital and the like sometimes suffer in an unbalanced antenna though and you risk flooding the rcvr with more interferance). If you try wrapping the antenna wire around, say the landing gear or some structure, don't if the structure is ferous metal, and wrap excess in figure eight, not loop.

Splat