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Lots of radio questions!

Old 04-03-2003, 10:55 PM
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Default Lots of radio questions!

Hi, Im new to the hobby, and dont even have a car yet. Im gettin an evader st (I Think), but I have questions about radios. How do cristals work. Can I switch my radio without changing reciever or servo? What all would I have to do if all I wanted to do was just change the radio, and nothing else?

Can you help?
thanks alot,
Dan
Old 04-03-2003, 11:38 PM
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Default Lots of radio questions!

Not quite sure what you are asking here. The crystal is in both the transmitter and reciever. If you use a different transmitter, it must be the same brand and freq to work. Some will work with others like hitec and futaba. If you want to use the same trans and different rec, then you need to consider the same thing, brand and freq.
Old 04-03-2003, 11:42 PM
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Default Lots of radio questions!

If your transmitter uses modules (small boxes about 1/2 the size of a pack of cigarettes) then you can change channels by changing modules. Your receiver must match the channel you're transmitting on. If your transmitter simply uses crystals (the crystals control the channel you're transmitting on) you may not change them unless licensed by the FCC. It is illegal in the US for you to make channel changes by changing crystals. (Modules ok) It is ok to change crystals in receivers, no government problem there, but some brands, Futaba for example, say channel changes are restricted to what are called High and Low bands. Check on this site for discussions about this, they abound.
Old 04-03-2003, 11:56 PM
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Default Lots of radio questions!

Also, even though it is common practice among RC Car drivers, in North America it is illegal to change transmitter crystals. Only the receiver crystal may be changed legally.

If you wish to change the channel on a transmitter you have 4 choices:
1.) Change crystals, then send it in to a service center for re-tuning
2.) Use a radio with exchangable RF modules (a crystal is not a module)
3.) Use a radio with a synthesized RF signal, since these can be changed without changing a crystal
4.) Change crystals illegaly without a re-tune, and hope no-one reports you to the FCC. The fines are VERY expensive.

For a copy of the FCC regulations pertaining to RC, click here and read Subpart C and Subpart E (95.218, 95.222, and 95.645)
Old 04-04-2003, 12:09 AM
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Default Lots of radio questions!

wow....um....., Im still a bit confused, but thanks for trying. If the crystals have to match then how can you do it with out changing the one in the transmitter?
Old 04-04-2003, 12:21 AM
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Default Lots of radio questions!

When you buy extra receivers, in order to control multiple vehicles with the same transmitter (not at the same time), you can change the receiver to match the transmitter.

Let's say you forget your transmitter at home (or it's broken) and you borrow or buy another transmitter which is on a different channel than your previous one. Obviously, the easiest is to change the transmitter, but that's illegal, so you change the crystals in the receivers you want to use with the new transmitter.

The main problem is that in North America, the air waves are so crowded, that RC is a SECONDARY user on our frequencies. The FCC is trying to protect the PRIMARY users who pay thousands (or maybe millions) for the right to use these frequencies. Since changing the transmitter crystal without re-tuning could cause the unit to interfere with industrial equipment on the PRIMARY users equipment, the FCC disallows it. Receivers don't transmit, so the FCC doesn't care if they are out of tune.

Does that help clarify things a bit?

Since you said you don't even have a car yet, before you order your radio, find out what channels (frequencies) are being used by others you might drive together with, and order your radio on a different channel. Either that, or get a radio with removable modules. Then you can buy additional modules for alternate channels.
Old 04-04-2003, 12:29 AM
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Default Lots of radio questions!

thanks, that helps but i still dont see how you can change the frequency of both, by only changing the one in the receiver. Lets say I start racing my truck. but somebody has the same frequency as me. I cant change it without using a new transmitter?
Old 04-04-2003, 12:37 AM
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Originally posted by dan1220
Lets say I start racing my truck. but somebody has the same frequency as me. I cant change it without using a new transmitter?
That is correct. Or use one of the methods mentioned above. Option #3 "Use a radio with a synthesized RF signal" is the best choice, since that allows you to use ANY channel you want (legally) with no additional cost.
Old 04-04-2003, 12:39 AM
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are those expensive? what would be a good inexpensive one?
Old 04-04-2003, 12:48 AM
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The least expensive are the ones from Polk's Hobby and Hitec makes one also. The Hitec one is $225 or thereabouts for transmitter only. It has what is called a Spectra Module which allows you to select the frequency you're transmitting on. Check the web, you can find both.
Old 04-04-2003, 12:51 AM
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Quoted from the FCC regulations
95.218 (R/C Rule 18) What are the penalties for violating these rules?
(a) If the FCC finds that you have willfully or repeatedly violated the Communications Act or the FCC Rules, you may have to pay as much as $10,000 for each violation, up to a total of $75,000. (See Section 503(b) of the Communications Act.)
(b) If the FCC finds that you have violated any section of the Communications Act or the FCC Rules, you may be ordered to stop whatever action caused the violation. (See section 312(b) of the Communications Act.)
(c) If a federal court finds that you have willfully and knowingly violated any FCC Rule, you may be fined up to $500 for each day you committed the violation. (See section 502 of the Communications Act.)
(d) If a Federal court finds that you have willfully and knowingly violated any provision of the Communications Act, you may be fined up to $10,000, or you may be imprisoned for one year, or both. (See section 501 of the Communications Act.)
Now you can see just how expensive the fines can be...

Unfortunately, I can't make suggestions for which radio to use for your truck. I only fly RC planes, and our radios are somewhat different. The laws are the same though.

I would suggest you ask for suggestions in the RC Car Radio Equipment forum. Keep in mind, many RC car enthusiasts either don't know or don't care about the FCC laws I have mentioned. Some will tell you it is OK to change the crystals in the transmitter, but just remember the fines mentioned in my quote...

In the end, it's your choice. I just want to help prevent you from breaking the law and facing stiff fines or jail time (95.218d).
Old 04-04-2003, 12:56 AM
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Default Lots of radio questions!

thanks for all the help guys. I dont think i will be breaking those laws. Just to make sure though, The only thing crystals do is allow you do use the same transmitter for more than one car right?
Old 04-04-2003, 12:57 AM
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Default Lots of radio questions!

Originally posted by Jim Schwagle
The least expensive are the ones from Polk's Hobby and Hitec makes one also. The Hitec one is $225 or thereabouts for transmitter only. It has what is called a Spectra Module which allows you to select the frequency you're transmitting on. Check the web, you can find both.
Jim,
I think you've overlooked the fact Dan is talking about RC cars / trucks. He probably wants a pistol style of transmitter. Hitec makes a couple pistol grip versions, and at least one of them should support the Spectra module. The Tracker II from Polk's is a 2 stick version.
Old 04-04-2003, 01:00 AM
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Too true, look for the Hitec radios, I think you're right, one of them, at least, supports the Spectra module.
Old 04-04-2003, 01:02 AM
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Dan - The crystals determine which channel you are using. Modules have the crystal built inside, together with the tuned RF circuitry, which is why you may swap them legally.

Hitec makes the Lynx 3D in a pistol grip, and it can use their spectra module. Click here to see it.
Old 04-04-2003, 01:05 AM
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thanks for all the help. I think I understand it.
Old 04-04-2003, 01:08 AM
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Dan - you can get the Lynx 3D from Tower Hobbies by clicking here or, if you also want a receiver which has no crystal, click here

You can probably get them from other online retailers, this is just the first place I looked.

Don't forget to check if they include servos and receiver batteries - Tower Hobbies doesn't with these kits.
Old 04-04-2003, 01:09 AM
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alright. Thanks again for all your help.
Old 04-04-2003, 01:15 AM
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For more info on all of Hitec's products, goto: http://www.hitecrcd.com/product_fs.htm . They even include an MSRP price list.

Welcome to the hobby, and a great source of info (RCUniverse). :spinnyeye

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