What is under heat shrink tube on 6/8ch receiver antenna?

[Spoogy]

Just wanted to ask if someone can clarify me what is under the heat shrink tube in these 6ch/8ch receiver antennas? Asking because I'm wonderning why 3ch receiver doesn't have this small "tube" on its antenna.

[gohsthb]

You must be talking about the flysky receivers.
The antenna type is a dipole. What that means is at the end of the coax 2 antennas split off and need to be parallel to each other but going in opposite directions. See http://en.wikipedia.org/wiki/Dipole_antenna The 3ch was intended for ground based stuff, I think I don't think they ever specify that. The 3ch has less range than either the 6 or 8ch versions, probably because of the different antenna.
-Gohst

[ShowMaster]

The "sleeve" is the second half of the dipole antenna configuration. A dipole is center fed and in this case the exposed center coax conductor is one half of the dipole. The sleeve is the other half and because of it being slipped over and connected to the coax shield at the point where the center conductor exits it becomes a center fed dipole. The sleeve being slipped over the coax this way and being cut the correct length also decouples it from the longer coax cable run that's not the correct length so the antenna tuning ignore the longer coax. All in all this makes the antenna more efficient in radiation and reception than just having the center conductor exposed. It does make for a larger bulkier antenna so it's avoided by many brand radio.
Under normal range line of sight flying and true diversity RX's there is more than enough sensitivity and selectivity provided by the "cats wisker" dual antennas to fly without link loss. Less bulk for mini and micro installations without the sleeve.
One good rule to remember with antennas, never run them close parrallel to any other wiring in your plane or you run the risk of detuning them or shading them from seeing your TX.
Always try and make the antenna(s) cross the wiring at 90 degrees instead. This can issolate the antenna by as much as 20 db from the internal wires and any induced interfierance.
SM

[Spoogy]

Thank you guys (I assume that you are guys ) for your answers. That clarify me a lot. Thanks!!