Should have checked your location. I assumed that you were in the UK. Even when we first put a 40MHz PCM Rx we started with alot of problems. Most of the EMI came from the motors even with the suppression capacitors connected, try removing the brushes if you can and see what increased range you get without altering any of the wiring. I even went to the trouble of designing a filter to put on the motor wires to get rid of most of it. The probelm was the filter needed to cope with 120Amps and it was huge. We solved the probelm by simple putting everything to do with the Rx (battery,mixer) in one metal box and earthed the chasis to the Rx battery (not main battery). Got some SMB mini co-ax connectors and used co-ax right up to the point that the areial left the robot where we used piano wire (30-40cm long) and have had no probs since. The only reason to use piano wire is its strengh and when upsidedown our spiked wheels dont rip it off. The Rx is matched to the wire attached to it when you get it. Altering the length and even the thickness degrades the signal to the Rx but the wire is not strong enough for an areal so its a compromise.