Radio without xtal

Hello group -

I bought a radio without battery or xtal to use just with computer simulation flight software. Now I'm wondering if I could use it with a plane I'm about to buy. The plane comes with engine, servos & receiver.

The radio is a Futaba T4YF. On the back there is a sticker that says 26,

72.310 MHz - so I'm thinking it was set up for channel 26, right? So if the receiver in the plane doesn't understand this I buy a new receiver and the system works, right?

Anyone see any problems with this plan?

Tnx - LeeH

Reply to
Lee Hopper
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Wouldn't it make more sense if you put a new or good nicad pack in the transmitter and plugged in a crystal ..in the transmitter..that matched your current receiver? Should work just fine. Buying another receiver would not be particularly cost effective...in my opinion.

Reply to
Frank Schwartz

Are you in the US? If so, the first problem is it's against FCC regulations to change the transmitter crystal on your own. You need to send it to a licensed repair person to be sure the transmitter is within specs with the new crystal. Many people will tell you it's ok to do it on your own. That's complete B.S. The FCC rule is in place to protect other people who share the narrowly spaced frequencies being used by R/C fliers. Including shipping, this will probably end up costing $30-50. Note, this assumes that they don't discover a problem with the transmitter while they're trying to tune it to the new crystal.

Moving on. You didn't say what kind of receiver you got. It may or may not be compatable with your transmitter. If it is, great, all you've bought is a couple crystals. However, if it isn't, you now need a new receiver and crystal too. Receiver crystal, $14 (including shipping), new receiver, $50 (an approximation, will not be much lower).

How about the batteries for the transmitter and receiver? Are those in good shape? If not, you'll be buying those too. Receiver battery $10-20, transmitter, $15-30.

This is adding up, isn't it? We haven't even talked about the servos and whether they are in good shape. Here's another option, which in the long run may be easier. You can buy a new 4 channel system for $90-130. This system will include a new transmitter, receiver, battery packs, crystals, servos, switch harness, charger, etc. You'll start off knowing everything is in perfect working order, and you'll still have the old transmitter to use with your simulator. Here's an example:

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**&P=1Use ad number 011T4 in on your shopping cart box and they'll knock $20 off your order.

Reply to
C G

| I bought a radio without battery or xtal to use just with computer | simulation flight software. Now I'm wondering if I could use it with a | plane I'm about to buy. The plane comes with engine, servos & receiver. | | The radio is a Futaba T4YF. On the back there is a sticker that says 26, | 72.310 MHz - so I'm thinking it was set up for channel 26, right? So if | the receiver in the plane doesn't understand this I buy a new receiver | and the system works, right? | | Anyone see any problems with this plan?

The plan is relatively sound, though there's a number of possible problems, mostly financial.

A battery for your transmitter will cost around $25 if you buy the standard one

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or could cost as little as $10 if you can make your own. Places like
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can make a pack for you as well, for less than Futaba will charge, and you'll probably get a better pack. You'll probably need a charger too -- looks like the stock one is $18 (!) --
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(You could probably find that a lot cheaper at a swap meet, or somebody might give you one, as these things seem to accumulate.)

A new transmitter crystal will cost around $25 -- Futaba doesn't seem to sell transmitter crystals by themselves, so you'll get a new Futaba receiver crystal too. You don't need to stay at channel 26, but it's not a bad idea, as if you get far away from that you ought to have the transmitter retuned.

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**&P=ML Depending on where the transmitter came from, it's transmitting circuitry may not even work. That may be why it was sold as a buddy box. The odds are good that it works, however.

That Futaba transmitter will only work with a Futaba or Hitec receiver. If it's JR or Airtronics, it will not work. (There's a few other brands that it'll work with too, but the odds are low that your plane has a receiver outside of thouse four brands.)

When you buy the transmitter/receiver crystal combo, do be aware that the receiver crystal will probably only work in a Futaba receiver. Not a Hitec one. And since your transmitter is FM, your receiver will need to be too. FM is the most common, but sometimes planes are sold with old AM receivers. And it's possible that this plane has an old wide-band receiver, which would need to be replaced.

So $25 battery + $20 charger + $25 crystal = $70 plus shipping. You could buy a new T4YF transmitter + receiver + two servos for $100 at

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**&P=0, and you'll know that works. Or the Tower Hobbies brand with no servos for $90 --
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**&P=0.Or there's a lot of other options.

Reply to
Doug McLaren

No, THAT is cxomplete BS. Provided you get te crystal that is matched to teh make of transmitter, it will be withing spec, especially if it matches the channel for which teh TX is set up.

In Europe we change crytsals all teh time qquite legally, and teh only problems are when a vrystal from one brand is used in another brand transmitter. These have been shown to sometimes be off frequency by half a channel or even more.

Whereas fiting the correct crystal is accuraet to a 100Hz or so,

The FCC rule is in place to protect

I suspect they don't actually tune *anything* to the new crystal. Just check that its on frequenc 0-m which it will be if te hcrystal is kosher, and the sideband emnssion is correct, which it will be if you are wihin half a dozen channels of where it was originally set up.

Reply to
The Natural Philosopher

Reply to
Chuck Jones

You are wrong, and it's not worth arguing with you. The US law says the user can't change the tx crystal. It's done because the tx may be out of spec with a new crystal.

That's nice. However, it appears we are just a bit more careful on this side of the pond. What you do over there really doesn't matter, the rules here are different. So, your advice is meaningless if the OP is in the US.

Reply to
C G

No, I'm one of the many who don't want my plane shot down because some clueless, irresponsible bubba thinks he can just switch tx crystals on his own. If you think it's ok to ignore the FCC requirement then you're the nut case. If you don't like the rule, take it up with the FCC.

Reply to
C G

CG

If it's so against US law why does every manufacture of radio systems sold in the US stock and sell crystals / crystal sets for installation by the user.

We own and operate a large midwest hobby shop and have obtained crystals and sold them or installed them for our customers for many years.

In the early days of RC we built hundreds of Royal Electronics systems for our customers and installed crystals in the TX deck.

If we replace crystals we do use a Tek. SA to check that the TX is on freq and that the sidebands are down where they are susposed to be. Have never had one fail in the last 20 plus years.

I suggest that you refresh your knowledge of the FCC requirements for changing crystals in current design consumer RC equipment.

To thje orig poster I suggest that you contact a good local hobby shop for assistance in what receiver and transmitter you have and if they are compatible and what is needed to get them working.

Hugh

Reply to
Hugh Prescott

You need the clue! You need to learn about the systems you use.

Modern radios are not tuned to the crystal frequency at the factory. They are tuned around a center frequency at the factory. The crystal is just plugged in later at some point of the assembly/distribution. Sometimes by the hobby shop that sells the unit.

Some manufacturers use a single center freq for the whole band while some split the band in two and use an upper or lower center freq to tune to. But even though, a radio tuned to the upper center will pass FCC specs with a crystal from the lower part of the band and vice versa.

As for the FCC? With an average of one field inspector per state, they have far bigger fish to fry than a bunch of overgrown children playing with toy airplanes at a paltry 100 mW of power. Go to the nearest boat pond and have a look. Don't be surprised if you see someone using a plane freq on a boat. Hell! Just yesterday I saw someone claiming to be on one of the old pre

1991 airplane freqs for a boat. It was posted on a club website on the internet.

Maybe you should chase them down and chastise them before they cause Big Daddy FCC to shut us all down!

Reply to
Chuck Jones

What the law says, and what will technically work and be with US legal specs are two different things.

Look at what your law says carefully. I would be fairly certain that what is actually prohibited is operating equipment that is out of spec. And that for this reason only 'competent people' can make crystal changes.

How you adjudge competence is propbably not defined.

Ther are two issues when changing crytsla. The fiorst is, will teh actual frequency be accurate? Test done here and elsewhere show that as long as the correct brand of crystal for the transmitter is chosen, the transmitter are indeed operating on the correct frequency. If a different brand is chosen the reults are unpredictable and may be out by up to 3khz - enough to be completely illegal in anyones book.

The second issue is what sidebands the transmitter is producing outside teh allowed spectrum. In general the power stages of transmitters are not so narrowly tuned that going a few channels one way or another will make any significanbt difference. Going from one end of teh whole band to the other however may result in slightly lower transmitted power and slightly higher out of band transmission. Its unlikely that these will be out of spec, but merely sub optimal. That's all.

Sadly, to be sure, you need a few thousand dollars of spectrum analsyer and the wit to use one.

Something very few TX repair shops have. Despite calling thesmelves competent etc.

They probably just tune it up for peak output and take it in trust tht the sidebands are withing spec.

Reply to
The Natural Philosopher

Indeed. I think you should never ever touch a crystal, for fear it might reveal more about your dark futire than you care to know.

Reply to
The Natural Philosopher

I am impressed. I suspect you are in a minority though!

Reply to
The Natural Philosopher

| You are wrong, and it's not worth arguing with you. The US law says the | user can't change the tx crystal. It's done because the tx may be out | of spec with a new crystal.

With all this arguing about the law, I'm surprised that nobody has yet actually given a link to the actual law in question. Just lots of chest pounding ...

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lets you read the actual laws (look for the R/C Rule links), and
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is a good link for the relevant bits with a little discussion.

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covers it as well, perhaps in a smaller and easier to read format than the vantec link.

Looking at the actual regulations, it looks like you can't legally change your crystals in the US. However it also says that internal repairs or internal adjustments should (not must!) be made by or supervised by `a person certified as technically qualified to perform transmitter maintenance and repair duties ... by an organization or committee representative of users in those service'.

So it's as clear as mud. :)

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is good too, and somebody actually asked the FCC to clarify the rules there, and the FCC said you _can't_ change crystals. This would seem to be pretty authoritative.

I saw a link somewhere where somebody had gone through the FCC regulations and determined that it *was* OK to change crystals. If I recall correctly, their argument was either based on the idea that everybody was technically qualified, or on the statement about `should be made' (and not `must be made'.) I can't seem to find this now ...

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't quite what I was thinking of, but it does suggest that it's OK to change crystals. Of course, the R/C regulations never said you needed a commercial radio operator license -- only that adjustments _should_ be made by a person certified as technically qualified ...

Of course, that's all about the legality of the matter. Practically, the FCC isn't going to care. They're spread very thin, and don't even usually go after the CBers using thousands of watts and operating out of band, they're certainly not going to go after somebody using 1/4 watt who changed a crystal.

The _only_ time it's likely to ever be an issue is if there's a serious accident. If somebody gets injured by an R/C plane and gets dollar signs in their eyes, their lawyer will start looking for violations of any sort to bolster their case, and they'll probably zoom right in on the transmitter's stated frequency not matching the crystal if that manufacturer mounted channel sticker is still there. Same goes for somebody getting killed and the police investigating.

Reply to
Doug McLaren

C G

You are so off base here my preferred next step would be to use a 2x4 attention getter. However!

Let me suggest you contact the newly elected Dist V DVP. He also owns a well known radio repair shop. Ask him, legalities aside, if he knows of any modern R/C transmitter that couldn't have the frequency changed from one end of the spectrum to the other and remain in FCC spec without being re-tuned?

Will you do that and then take the word of a professi>> C G wrote:

Reply to
Chuck Jones

You sir are no doubt thinking about crystal balls. But then I understand your confusion with that subject as well! Hard to know about something you lack!

Reply to
Chuck Jones

I quite agree!

Reply to
Sparky

No Chuckie, you need to get a clue about FCC regulations and show a bit of concern for your fellow modellers. It appears you have no clue and little concern for others.

Reply to
C G

The law is designed to ensure that the equipment stays within the bounds of what is needed to properly share the very closely spaced frequencies.

It defines who can make frequency changes.

I have looked at the law. And competence is defined, it's based on obtaining the proper licenses. Obtaining such licenses is based on passing tests which show competence.

Reply to
C G

No Chuckie, you are the one who is off.

You are showing your ignorance. Check with Futaba about your idea above.

I've talked to several pros. They all say the same thing, don't change the crystal, send it to an authorized center.

Reply to
C G

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