radios

[norgale]

I have a question about radios for boats. It's my understanding that boats are considered surface vehicles which of course they are. So is it 27mhz or 75mhz that is for surface operation?
OK I see where it's 27mhz for boats so why did the lunkheads send me 75mhz for receivers? I'm tellin'ya----- oh well. Send em back.

[Kmot]

You can use 75 Mhz for surface vehicles only. You can use 27Mhz for anything, as it is a shared frequency.

What freq is your transmitter on?

[green-boat]

And to confuse you even more, 2.4 GHZ radios can be used for both air and surface.

[norgale]

I bought a 2 chan HiTec Ranger that came with a speed control and some servos and the frequency is 27.095.Then I ordered two more Rx's for two other boats but I got them in 75mhz and no crystals. Didn't realize they were dif from the Tx until I went to order crystals for them. So now I know what I want I can send back the 75's and get some 27's so all will work with one Tx. Thanks again for the usual great advice. Pete

[norgale]

I also have a Futaba FP-R-127DF dual conversion,seven channel Rx with 72.530 crystal
to swap for a like type Rx in HiTec 27.095 or a Futabe 27.095 crystal swap.

[CG Bob]

Some more radio info:
72 MHx (50 channels) aircraft only
75 Mhz (30 channels) surface models - boats, subs, cars, robots
The following are shared frequencies, and can be used by any type of model in the USA:
27 MHz (6 channels)
50 MHz (10 chanels) - requires FCC Amatuer Radio license
2.4 Ghz - doesn't work for submarines

Most of the RC rules are in Subpart C of the FCC regs (http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/cfr/1998/47cfr95.pdf); Subpart E has the tech specs. Technically, it's illegal to change crystals in the transmitter, as they aren't considered a "frequency module.

You can change crystals within a frequency band, like 75 MHz (say channel 61 to channel 89) without retuning the radio. You CANNOT change crystals from one frequency band to another, like a 27 MHz system to a 75 MHz channel, the radio won't work without being retuned by the factory service center. Futaba 72 MHz radios on the 72 MHz band are either low (11-35) or high (36-60). For these Futaba air radios, you can change crystals without retuning the radio in either the low or high band; to change from low to high requires retuning the radio.

The radio makers use either positive or negative shift of the frequency modulation to encode and send the signal between the tx and rx. Positive shift tx (or rx) will not work with a negative shift rx (or tx). Positive shift radio systems are: Jr; Airtronics; GWS; and Futaba Ham (50 MHz) radios. Negative shift radios are: Futaba (27, 72, & 75 MHz); Hitec; Tower Hobbies; GWS. Some manufactures do make receivers for both shifts, like GWS & FMA.

[norgale]

OK. That's great to know. I never did understand the dif between the two but that explains it. Actually I don't need to change my Tx now anyway. Just need to get the right extra Rx's onboard here. Thanks very much Bob. Pete