im about to change crystals in a jr rx from 21 to 45 so does anyone know if the hi-low band thing applys. or will this be ok?

All the current JR RX's that I'm aware of do not have the high/low band problem. I do have some nearly 20year old AM RX's from JR that ARE labeled as "low band" . (no, I don't fly them. In fact, I don't know whey I haven't tossed them, but I haven't)

I just got a futaba 7cap that has an 18 transmitter crystal, I have a futaba r-114fm reciever, and I tried to put my old channel 52 crystals in to try them and nothing works on the plane. I think I need the low band crystal as stated in the manual, I will get correct channel 18 crystal tomorrow and see what happens.

I too am confused by this. Some here say any crystal between 11 and 60 will work, but the manual says 11 thru 35 and 36 thru 60 are differant and will not work. Sure seems that way to me. Any more input out there on this issue?

I would go by the manusl. You might get qway with using the "wrong" range crystal, but why take the chance, all the crystals cost the same, high or low range. If you use a Hi-tech reciever it is different, they are not high - low selective.

The high band/low band thing is the receivers, not the crystals. A crystal is made to a specific frequency/channel. Futaba tunes many of their receivers to a high or low band, which in theory made them a bit more acccurate. If you have a high band receiver, you should not put a low band crystal in it, or visa-versa, because the reception may not be as good. You can read more about the high/low band thing here: http://www.futabarc.com/faq/faq-receivers.html

The more important issue is that Futaba makes several different models of crystals. If you do not have the correct model for the transmitter and receiver, they will not work. This page has more information on crystal models: http://www.futabarc.com/radioaccys/futl20.html

OK, first the HI/LO thing for Futaba. The RX are tuned to optimize in the center of the bands specified. Therefore if you cross bands HI to LO or Vice versa there will be a slight loss of performance (read range/sensitivity). The LATEST Futaba FM RX on the market
R168DF
http://www2.towerhobbies.com/cgi-bin...p?&I=LXLSX4&P=
are NOT restricted to HI/LO separation and can use any appropriate crystal.
OK, now single/dual conversion, these recievers end up operating on the same frequencies of course but the crystals actually oscillate on different freqs because there is another step of intermodulation(mixing) in a dual conversion RX. I do not know if all brands of RX use the same IM freqs or not. I always recommend buying the correct crystal from the mfg of the RX. If you can't afford a $13 XTAL after buying a $600+ plane, then park it for a week or two.