Hi Kevin, crystals aremost important as the home office has laid down accuracy figures that all radio control sets must conform tothe transmitter crystal set s the frequency that is radiated into the ether by your transmitter, and the receiver crystal tunes your receiver exactly to matcgh the transmitterthe two crystals make an exactly matched pairwithout which your radio would not workeach crystal would work in a radio of a different frequency, but the output would be very low indeed and the receiver would belooking for a very different frequency,so it too would not workThe frequencies not milligrammes but MegaHertzwere laid down by the AmericanFederal Communications Commission (Fccand were interlaced with the CB radio frequencies at exactly 10 KiloHertz apartso one could operate without being interfered with by an adjacent transmitterand if you care to look it up, the 27MHz channels are seen as gaps in the AM CB channelsand as far as I know there are two or three channels where CB and models were allocated identical frequenciesI think that the black channel was allocated to a CB channel and hospital paging systems accounting for the number of aero modellers claiming that a CB user caused a model to crash, it certainly did for me when I was giving a demonstration to disabled children in their theraputic swimming pooland I had sailed along one wall to give one section of kids to get a close viewand I was heading towards the other side to do a lengthfor the other kidswhen the boat dug her stern right in and accelerated flat out in a hard turn to starboard, sadly it collided with the tiled concrete wall knocking one propellor right off, the other engine took over propulsion and I brought her to a halt and steered her towards me so I could recoverethe wreckagewhich was not funny. I knew that there was nothing wrong with the boat so I switched off the batteriesand lifted the boat out of the water and on to her stand where she would be safeI looked out of a window, and saw a ford capri with a six foot long CB antemnna clamped to its roof parked outsideI went utside to speak to the driver and asked him what power he was using. it turned out he was using a 1000 watt linear amplifier andI warned him that he was breaking the law on several counts, but it turned out that propagation effects meant that a4 watt legal CB could reach the eastern seaboard of USA easily so lots of CB’ers were talking to Americansand loving every minute of itso I contacted the chairman of the CB club and asked if I could speak to the attendees of their next meetingat which I explained the things they could do legally without crashing radio controlled aircraft of boats, and I did the same at the model club of which I was chairman. After that, things ran a little more smoothly.I have just realised one thing you said in your post was somewhat incorrect,which wasthat you reversed your crystals if another person was using the same colour frequencythis would mean that your transmitter would send at a frequency 455Kilohertz lower than his and your receiver would produce an intermediate frequency455Kilohertz above, and not 455 below the transmitted frequencyas it should to match the settings of the tuned circuits withinthe combination could have worked I guess, but not nearly as well as if the crystals had been fitted to the correct units. I think the best way to eliminate interference is to use the peg system where an antenna would be mounted o the controller’s table with a load of coloured pegswhich you could take if you wanted to use that coloured frequencyWhat I did was to buy a nearly complete set of crystals so I could always fit a different pair of crystals to my rig and sail off into the sunset, no worriesIf you would like me to send you my paper which I wrote explainig how radio control works, send me your e-mail address, and I will send it to you as an attachment.Mike Davidson