Receivers - Low vrs High
 

I was looking at what transmitter I was wanting to get and the receivers that you can get.

What caught my eye was that on the same receiver. Let's say the R127DF FM receiver for the Futaba 6XAS it has a low and high. What is the differences between the 2? Does one reach further then the other? I just can't see the difference and at tower hobbies it doesn't explain the differences between the low and high.

Thanks!

RE: Receivers - Low vrs High
 

Go to the Futaba site www.futaba-rc.com they will be a lot more helpful.
But basically the difference is where they are tuned to operate. The high for the channels 31 thru 60 and the low is for channels 11 thru 30.
[&:]

RE: Receivers - Low vrs High
 

Steve there is no difference in the way high/low band works. Futaba "tunes" it's receivers to a low band range 11 to 30 and high band range 31 to 60, no other manufacture does this that I'm aware of. check out your area and find out what end of the frequency range is used most... then go to the other end:D

John

RE: Receivers - Low vrs High
 

So in other words, a futaba transmitter can do both the high and low receiver? You just need to have the right high or low crystal to go along with it?

I have rc cars and the one receiver would work for which ever crystal you put in it. I will go the the Futaba website for further info.

RE: Receivers - Low vrs High
 

YES and NO, the transmitter module is tuned for what ever frequency it's on, it is illegal to change the crystal in a module,you can however put in any channel module you like as long as it on the right band. if you don't have a module you need to send in the transmitter to futaba and have it tuned for what ever frequency you want too switch to. futaba receivers are tuned into high and low band groups, if the receiver is low range you can only use crystals from 11 to 30 in that receiver according to futaba... if you put a low band crystal into a high band receiver or vice versa it will not be tuned to optimum performance and could cost you a plane.


John

RE: Receivers - Low vrs High
 

It is illegal to swap crystals in the transmitter. (any brand.)

It is OK to swap the modules. The module contains the complete "RF Deck" and is tuned for the crystal that is installed.

Each TX is individually tuned to the crystal installed. It takes about 30 sec at the factory. (clip 2 wires on... turn on... tweak the tuning capacitor.... put on the sealing wax.... unclip the leads... pass the TX to the next guy.) The guy that tunes the TX's tunes a couple of hundered a day easilly. (then he goes and does other tasks... they don't need him to tune 1200 radios a day.)

RE: Receivers - Low vrs High
 

It is legal to change the entire RF Module like FHHuber said, it is also legal to change the crystal in the reciever only. The idea behind legal and illegal has been covered in many posts. Since recievers only recieve signals, there is no danger (to others in the frequency range) of messing up their systems (only to your own by having the reciever system not work correctly) with a change. In short, only when you send OUT a signal does the FCC really care. Thus, I would like to have and keep legal by having an extra module on hand (only around $50) and matching reciever crystal to change channels if need be for whatever reason. Safe, legal and a nice backup.

RE: Receivers - Low vrs High
 

Or buy one of the newer radios with synthesizers. They can be switched between channels within the radio. No crystals and perfectly legal. You can also buy receivers that can be changed to the channel you want without a crystal change.
Dennis-.

RE: Receivers - Low vrs High
 

By the way, just so you don't go running off on a tangent, Low band is considered channels 11 through 35, not just 11 through 30 and High band is considered 36 and up. In a lot of cases the recievers are not all that particular but sometimes they are. Therefore, it is a good idea to pay attention and make sure you buy the proper reciever to match your assigned transmitter frequency.

RE: Receivers - Low vrs High
 

be carefull with the R127DF when i was putting the xtral in, i messed up and broke lots of bits. i sent it back and paid £35 for repairs[:@].
is the 6XAS any good, i mate at my club got it, gave it back and got a FF6 (he said it crap!)

RE: Receivers - Low vrs High
 

I'm very happy with my XAS, don't know what's "crap" about it. The one thing I don't like is having to use number for models in the memory instead of names. Even three letters would be enough.

It's easy enough to remember the 4* is Model # four, and I can move the J3 Cub to three I suppose, but the Super Sporster, Great Lakes, Skybolt or Phaeton??
Dennis-

RE: Receivers - Low vrs High
 

ok.....just a quick question!!!!!

if you were to take the crystal out of your radio, but not the reciever, and put it into another radio, will it affect anything??[&:]

RE: Receivers - Low vrs High
 

Transmitters are tuned to a specific frequency. The crystal itself is only one component in obtaining that frequency. Believe it or not, crystal frequencies are not the stated frequency of a given channel. The crystal acts as an occillator which is then mixed by means of a "tank" circuit in the radio in order to obtain a given channel frequency. Changing one crystal to another affects the tune and as a result the range and "trueness", of the frequency. An example is you have a transmitter that is tuned to channel 56. The frequency of 56 is 72.930 mhz. You change out the crystal for a channel 54 crystal. The transmitter doesn't know that the crystal is different and as a result is still trying to achieve 72.930 mhz. only it can't because the crystal occillator is now different. The transmitter will now broadcast on the challel 54 freq. except it won't be right on the frequency it will be off by a little bit. The sensitivity of the reciever will then determine how the range is affected, and the other people at your flying field on adjacent channels may be affected as well. I know some people get away with it but it should never be done and doing so may affect others even if you are not affected. Bad idea. The only acceptable way to change the channel of your transmitter is to have it retuned to the new frequency by a qualified technician.

Hope I said it so you can understand.

RE: Receivers - Low vrs High
 

My R127DF FM receiver for the Futaba 6XAS it has a round sticker on it that has the number 80 on it. Is this the channel number and would this be a High? Also the crystal in the reciever says (I believe) 72.50, or something like that.

If I go and buy another receiver i.e. a Futaba R127DF and buy the same crystal number to put in it I should be OK to fly it a second plane with it, right?

IF it is illegal to take crystals out then why do I see so many at eBay that are sold that way? I must totally be missing something here.

RE: Receivers - Low vrs High
 

Channel 80 is not an aircraft channel, it's a surface channel on 75Mhz. Since the crystal you have says 72.50, the "80" is something besides the channel.

72.50 is not a currently valid channel!! It's half way between channel 35 (72.490Mhz) and 36 (72.510Mhz) DON'T USE IT. I'm hoping you typo'd the frequency there. Could you check and see what it actually says?

If it actually says 72.50, then I'm not sure, but I suspect your crystal is really old. Sometime in the mid-80's, when the 72Mhz band was opened up, there were only a few channels, on rather wide spacing. Some of those old channels are now "between" our current ones. I think you have one of those.

I don't use Futaba RX's, I find that whole low/high thing to be entirely too annoying to deal with.

What cstevec said is right on about transmitter crystals and tuning, at least for most transmitters. And he is absolutly right about the FCC rules that make it illegal to just swap TX crystals. However, in other countries, it's not illegal at all. And, further more, some TX's are actually designed to stay on frequency with different crystals within their band (such as on 72Mhz). So, some TX's will NOT drift or cause anyone any problems or lack of range if you do, in fact, change the TX crystal. Now, which will and which won't is a hard call.

Either way, if you change the TX crystal, you are breaking the FCC regs, and if you have a crash that causes injury or property damage that is related to a radio failure, you can pretty much bet that your insurance isn't going to cover you, it will be considered negligent.

RE: Receivers - Low vrs High
 

I got some of the 1/2" vinyal numbers. I put the number of the plane on each side of the vertical stab . Solves the problem of which plane is which and doesn't look bad either. Just remember to change the model number in the transmitter to the correct one.

RE: Receivers - Low vrs High
 

Like I was saying though is that I am not positive about the crystal number being 72.50, It just may be 75.250. I will check tonight.

What is the difference between air and surface channels? I bought my Futaba 6XAS with the intent of using her for planes from a "Plane" hobby store.

RE: Receivers - Low vrs High
 

Aircraft use 72Mhz, surface (cars and boats) use 75Mhz, they are on totally different bands. It's not legal to use one for the other.

Btw, the surface radios on 75Mhz usually have a lower power output than aircraft transmitters on 72Mhz. I'm not sure if there is a lower legal limit on the output power, but there might be.

RE: Receivers - Low vrs High
 

I've searched for the tx output in watts but didn't find anything so i gave up.
*Take a trucker that runs east to west coast and i'm willing to bet he has a lot more channels than the standard or "legal" 40 channel radios,i'm also willing to bet he is pushing a lot more power than the "legal" 4 watts which is limited on his cb radio,i'll also bet some of them have a linear,so careful if your near Interstates*
I found this out yesterday while talking to a rc'er.

RE: Receivers - Low vrs High
 

OK I just figured it out that my receiver is a 18 channel with a 72.150 crystal. Now how do you see if it is a high or low... does it say it on the receiver... if so I didn't see it.

RE: Receivers - Low vrs High
 

IF your receiver is one of the ones that is tuned to either the upper or lower part of the band, then, since you are channel 18, which is on the low end, you'd have a "low band" receiver. Low band is channel 35 and lower, high band are channel number above 35.

RE: Receivers - Low vrs High
 

Wondering about the fact that Futaba sells crystal cases. Why does Futaba sell crystal cases when the hot-swapping of crystals is not allowed?

Cruising around the car forums, many people change the crystal on their 75mHz radio... How come we can't do it?

RE: Receivers - Low vrs High
 

Thanks everyone. Now I get it. Sometimes I am very thick headed and just don't get something till it hits me square on the nose.

Thanks again.

RE: Receivers - Low vrs High
 

I have never heard of it being illegal to change crystals. I used to race rc cars and we changed crystals in and out of transmitters between races. I have also changed the crystal out of two of my plane transmitters, with no negative effects.

We used the crystal cases to hold our extra crystals. We had about 5 different channels for our cars and transmitters.

With car races if you were on the same channel as someone else you were asked to change crystals.

Just my experiances

RE: Receivers - Low vrs High
 

I honestly don't know if the rules are different on 75Mhz, they very well might be.

But it IS against FCC regs to change crystals on 72Mhz. You can change the module if the radio has one, but just a crystal is not legal.

Just because it's common practice to chang the crystals at races doesn't mean it's leagl. I've seen lots and lots of things done as common practice that were against some rule or another.

It's also worth noting that if a car has a couple of radio hits, it's usually not as bad as with an airplane. Not that a car can't hurt or kill someone, I've seen enough nitro cars get airborne at head-level to know someone could be hurt by one. But with a car, if you have a suspect radio while running and start having intermitent control, you can kill the engine and just stop. Airplanes don't have that option, and they can travel a lot farther to reach out and touch someone. So, I'd personally be willing to do more stuff with the radio with a car than I would with my planes.

You're right about the crystal sales being inconsistant. So is having the crystals right there where you can easily change them. Believe it or not, to pass the FCC acceptance, some radio companies claim to glue the crystals in so they aren't "user replaceable". The "reason" crystals are available is so that people who are licensed to work on radios can get them to make the change for you. You don't have to be the factory service center, just have the right license to legally change the crystal.

And, like I said, outside of the US, the rules are different. So it makes sense for the manufacturers to just make the same product and ship the same parts everywhere.

And, frankly, the FCC has better things to do than chase around RC guys swapping crystals. So you can be pretty sure the FCC isn't going to actually enforce the rule anytime soon.

If you have an accident, though, you should at least know what you did is not techically OK.

But, as you guessed, most of it is a bunch of nonsense, at least with MOST current transmitters. I won't say "all" however, there could be some that won't take kindly to a crystal swap.

Personally, if I wanted to change my TX to another channel, I'd just do it as well. But I'd make the change a small one, just in case. And I'd carefully range check the radio before and after the change, to make sure the range didn't change. If you notice a drop in range, you know why. (But, since I own a Polk Traker synth radio, I can just pick a channel, no crystals. Hitec and others have this kind of thing as well. I suspect eventually crystals will be a thing of the past).