RE: Motor wires too close to Rx??
Rick you are taking the right approach, do change out the receiver only but keep the antenna with the same routing. That way the only variable is the receiver (and well the transmitter as well).
However since the servos are jumping with or without motors on then you can almost eliminate the motor noise as a problem. It sounds like a pure range problem which changing receivers would check.
I have a 3 channel Hitec that I bought 5 years ago as my first 72 mh smaller rig. I had been using old old 72mh rigs when we had the 6 channels and then some 50mh rigs - all big old equipment. I just took a look at the receiver - it is a big brown setup with green label that has AM embossed in the plastic where the 4th and 5th channels would go in the newer Hitec 555 receivers.
I don't know if it is dual conversion or not - it is buried under the servos and battery plate in the airplane, all I can see is near the servo plugins and not the info written on the top of the receiver. I don't know if it is the same as your setup or not. One thing though is that it has range as far as I have ever flown the airplane (which is pretty high).
Every month or so I fly the airplane several hundreds of feet high so it is small but I can see how it responds, collapse the antenna and point the antenna at the airplane. That assures you getting the lowest signal at the airplane and have time to pull out the antenna and recover from the maneuver (no doubt a straight down full power dive) if the rig isn't working.
350 feet is pretty poor range. Check that each motor has a arc suppression capacitor on it. Wait, you said it was working OK with one ESC/motor but with two motors it isn't working. You need to determine if it is a receiver or ESC problem that isn't happy with two motors for some reason. If all you varied was adding a motor to the ESC and found yourself with no range then it would seem to be motor ESC oriented. Disconnect one motor and see what happens to the range.
But do change out components until you find a reason why it worked before with one motor and doesn't now. And be sure and report back the results.
Side comment, With the old Hitec (before I went with Futaba equipment) I decided to see how many motors I could fly on one of my stick and foam models (I had an open field just across the street). I had some very small surplus motors that had good brushes on them. I ended up with 6 of the little motors in parallel across the wing on the same ESC and it was a medicore success at best. I never had a range problem as it would make one small circle around the field and run out of power!
I agree jooNorway, the need to make the receivers light and cheap does cause a lot of compromises in the design. There are a some manufacturers using single conversion in their top of the line radios but they are using the top of the line signal processing techniques also. It makes a difference for sure.
My dad was an electronic tech for the FAA and several times took my brother and I out when he had to make an emergency run to fit the ILS system that was around 45 years ago. No computers to make simulations though!!