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All Forums >> Radios, Batteries, Clubhouse and more >> RC Radios, Transmitters, Receivers, Servos, gyros >> changing tx crystals
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changing tx crystals - 4/4/2003 9:34:42 PM   
flyboy11


 

Posts: 54
Joined: 4/2/2003
From: Sadler, TX,
Status: offline 		Hey guys I'm curious, why can you not change tx crystals without having someone retune it but you can change the rx crystals yourself? Also, why is it illegal?
Thanks
       Post #: 1

changing tx crystals - 4/5/2003 1:13:41 AM   
Phil Cole



Posts: 755
Joined: 1/27/2002
From: Redwood City, CA, USA
Status: offline 		It's illegal because the FCC wants it that way.

Most likely the "retuning" just involve checking that the transmitter is still on frequency and the modulation is OK. Most of the time it will be OK, but there is no guarantee, and the FCC wants to be sure that any transmitter let loose on the aether is functioning properly.

Malfunctioning receivers won't pollute the airwaves, and the FCC is not concerned about crashing due to faulty radios.

(in reply to flyboy11)
       Post #: 2

changing tx crystals - 4/5/2003 9:14:05 AM   
strato911



Posts: 1479
Joined: 9/17/2002
From: Winnipeg, MB, CANADA
Status: offline 		As Phil said, it is illegal to change Tx crystals because the FCC says so. The reason is because RC users are SECONDARY users of our radio frequency bands. The PRIMARY users (industrial) pay big $$$ for the right to can use their frequencies without interference. If a Tx is slightly out of tune, it could interfere with industrial equipment long before it affects the neighboring RC channel, since the Primary channels are in between each RC channel.

The reason it is legal to change the Rx crystal is simple - the Rx doesn't transmit, so if it's out of tune, it doesn't affect anyone except the RC pilot (and his/her plane).


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       Post #: 3

changing tx crystals - 4/5/2003 9:23:05 AM   
CAP232CM



Posts: 488
Joined: 4/21/2002
From: Parkville, MO, USA
Status: offline 		I don't understand this at all. I have a Hitec radio with a spectrum module and I can change it to any ch. I want. Why is this not illegal or is it? I have a JR radio with 2 different modules. Is it illegal to switch them to change the ch.? This makes no sense at all.

(in reply to flyboy11)
       Post #: 4

changing tx crystals - 4/5/2003 9:37:14 AM   
Flyfalcons



Posts: 6150
Joined: 7/27/2002
From: Bonney Lake, WA, USA
Status: offline 		Modules are cool. They are certified to be changed out. Same goes for synth modules. From what I understand they are 'self-tuned' in that the tuning of the Tx isn't critical but the tuning of the module is. It's just 'standard' crystal swapping that is illegal here.

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Cub flying - the new EXTREME SPORT!!! (evarrr)

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       Post #: 5

changing tx crystals - 4/5/2003 9:39:03 AM   
CAP232CM



Posts: 488
Joined: 4/21/2002
From: Parkville, MO, USA
Status: offline 		Oh I see thanks for the heads up.

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       Post #: 6

changing tx crystals - 4/5/2003 12:35:51 PM   
strato911



Posts: 1479
Joined: 9/17/2002
From: Winnipeg, MB, CANADA
Status: offline 		[QUOTE]Originally posted by CAP232CM
I don't understand this at all. I have a Hitec radio with a spectrum module and I can change it to any ch. I want. Why is this not illegal or is it? I have a JR radio with 2 different modules. Is it illegal to switch them to change the ch.? This makes no sense at all. [/QUOTE]Sorry to confuse you. What you are doing is the proper way to change channels.

Changing modules or changing channels on a synthesized transmitter is legal.


_____________________________

I try to learn from other people's mistakes...
I won't live long enough to make them all myself.

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       Post #: 7

changing tx crystals - 4/7/2003 3:34:56 AM   
Lynx



Posts: 1374
Joined: 9/19/2002
From: Rochester, NY, USA
Status: offline 		The spectrum module is designed from the ground up to be able to switch channels like that. If the module uses a crystal it wasn't, it was ment to work with that one crystal, if you change it it needs to be checked for tuneing to avoid spurios emitions on nearby channels (don't wany to hit primary users of the 72mhz band)

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       Post #: 8

changing tx crystals - 4/7/2003 7:12:17 PM   
strato911



Posts: 1479
Joined: 9/17/2002
From: Winnipeg, MB, CANADA
Status: offline 		Lynx - He's talking about changing the entire module, not the crystal within the module.

Modules contain the entire RF circuit, and are tuned for the crystals contained within them. That is why the FCC allows modules to be swapped - they are already tuned for the crystal.


_____________________________

I try to learn from other people's mistakes...
I won't live long enough to make them all myself.

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       Post #: 9

??? - 4/8/2003 9:26:09 PM   
Pete the Geek


 

Posts: 21
Joined: 3/3/2003
From: Russellville, AR
Status: offline 		So what you're saying is that if I took a Hitec 3 channel am focus that originally came with a removeable 26.995 crystal and swapped it out for a 27.045 crystal it is illegal?!?! Why even make the darned crystal removable then?

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       Post #: 10

Re: ??? - 4/8/2003 9:32:56 PM   
Steve Lewin


 

Posts: 904
Joined: 3/18/2002
From: Reading, UNITED KINGDOM
Status: offline 		[QUOTE]Originally posted by Pete the Geek
So what you're saying is that if I took a Hitec 3 channel am focus that originally came with a removeable 26.995 crystal and swapped it out for a 27.045 crystal it is illegal?!?! Why even make the darned crystal removable then? [/QUOTE]
Because it's not illegal in most of the world and Hitec are not going to make a special version just for you .

Steve

(in reply to flyboy11)
       Post #: 11

Changing Tx crystals - 4/8/2003 9:34:43 PM   
FlyinBrian


 

Posts: 54
Joined: 4/8/2003
From: NorthamptonNorthants, UNITED KINGDOM
Status: offline 		As a point of interest.

In Europe it is both legal and common practice to change tx xtals, this is both a boon and a pain as you can not be sure from one day to the next what freq. someone is using.

I guess Synthersisers will make this easier and even more common therefore good Tx freq control becomes even more imperitive.

MPX PROFI systems with "Channel check" will not allow the tx to transmit any RF if it detects the frequency is in use - I think this should be the norm for all new Tx's especially synthersised units.

(in reply to flyboy11)
       Post #: 12

changing tx crystals - 4/8/2003 9:48:19 PM   
Pete the Geek


 

Posts: 21
Joined: 3/3/2003
From: Russellville, AR
Status: offline 		I imagine this is common place as alot of us newbs don't know this information. I seriously doubt the effects of changing out a transmitter crystal on this frequency will cause major cataclysmic events....sorry, I just can't believe that LOL. It works for the English

(in reply to flyboy11)
       Post #: 13

changing tx crystals - 4/8/2003 10:54:21 PM   
Jim Schwagle



Posts: 561
Joined: 12/23/2002
From: Canyon Country, CA, USA
Status: offline 		It's not that your plane will crash because of the crystal change. Other, primary users, are spaced between our channels. They're much closer to you frequency-wise than another RC'er. If your swap puts you a little off and an RC crane drops a pallet on someone you're going to get a visit from the FCC, and lots of lawyers and if enough people do this the rest of us will lose the 72MHz band because the FCC doesn't give a rip about the Hobby industry. We're secondary users, not the primary users and the radio makers must swear on a bible that the radios won't cause interference on the primary users channels. We won't if we follow the rules. Oh yeah, swap a transmitter crystal and forget your AMA coverage, or your homeowners either. Do something illegal and all coverage bets are off.

By the way, it is my understanding that the British and other European RC'ers have their own dedicated band, that's why they can swap crystals. We don't.

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       Post #: 14

changing tx crystals - 4/9/2003 12:57:08 AM   
strato911



Posts: 1479
Joined: 9/17/2002
From: Winnipeg, MB, CANADA
Status: offline 		[QUOTE]Originally posted by Jim Schwagle
Oh yeah, swap a transmitter crystal and forget your AMA coverage, or your homeowners either. Do something illegal and all coverage bets are off.[/QUOTE]And boy are those fines steep! quote from FCC:
quote:

§ 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.)



_____________________________

I try to learn from other people's mistakes...
I won't live long enough to make them all myself.

(in reply to flyboy11)
       Post #: 15

changing tx crystals - 4/9/2003 6:10:23 AM