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Old Apr 28, 2005, 09:39 AM
Rev. Dr. Moses P. Lester
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Joined Feb 2005
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yet another newbie radio freq question

i gathered, from the searches i did, that topics very close to this one have been covered a hundred times before, but i had a very hard time understanding the conclusions from them. (mainly because the answers i saw were confusing and just didn't seem logical to me)

here's my situation and question, specifically:
i've started scratch building a few r/c boats. in the past i had built a couple airplanes, and from back in those days, i have an old but decent transmitter. (airtronics vanguard vg6dr 6 channel FM on 72mhz)
is it possible and legal to buy and use new crystals and receivers which would work with this transmitter on the 75mhz surface bands for my boats?

while searching for answers to this question, i came upon info that suggested that it might be illegal to do this. i had a very hard time believing this, because i could think of no sound legal argument for FCC regulations being that way. what purpose would it serve, other than to please corporate lobbyists from futaba who want me to buy more radios? also, i noticed in my TX and RX that the crystals plug in and out quite easily, as if they were designed to be switched. but i guess if it is against the regs, then it is against the regs, and my bitching won't change things. i just wanted to get clarification on that point.

so am i stuck buying a couple hundred dollars in redundant radio gear for every boat i build, if i want more than just a cheap 2 channel AM radio controlling it?
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Old Apr 28, 2005, 09:49 AM
KC8WPF
CG Bob's Avatar
Euclid, Ohio, United States
Joined Sep 2004
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Quote:
is it possible and legal to buy and use new crystals and receivers which would work with this transmitter on the 75mhz surface bands for my boats?
Yes, but the radio system has to be sent to a factory repair center to be retuned from 72 MHz to 75 MHz.
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Old Apr 28, 2005, 09:58 AM
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Guelph, ON
Joined Sep 2004
1,846 Posts
Hi moses,

I think, depending on just how old your transmitter is, it may not be legal anymore. Somewhere around 12-15 years ago, "narrow band" TX/RX became mandatory.

Other than that, several people have sent their air gear in to be retuned to surface frequency. I seem to remember the $40 as a cost, but I could be wrong there. It is not simply a matter of popping in new crystals, apparently .

If you do invest in a $$ surface radio, you can switch between crystals for that frequency, ie five boats=five RXs with different crystals, swap TX crystal to run different boat.

I'm by no means an expert, but until someone else comes along and posts more specific details (CGBob is always great with tons of detail), this should be a decent starting point.

Ray

hehe: Cross post
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Old Apr 28, 2005, 10:16 AM
KC8WPF
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Euclid, Ohio, United States
Joined Sep 2004
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From the U.S. Code of Federal Regulations (U.S. Federal law), is this section by the FCC:

"Sec. 95.645 Control accessibility.

(a) No control, switch or other type of adjustment which, when
manipulated, can result in a violation of the rules shall be accessible
from the transmitter operating panel or from exterior of the transmitter
enclosure.
(b) An R/C transmitter which incorporates plug-in frequency
determining modules which are changed by the user must be certificated
with the modules. Each module must contain all of the frequency
determining circuitry including the oscillator. Plug-in crystals are not considered modules and must not be accessible to the user."

The various R/C manufacturers cite this regulation in their literature. Based on the law, you CAN NOT change the crystals in the transmitter. In reality, lots of people do change the transmitter crystals quite frequently - the important thing is to stay within the band range (75 MHz, 72 MHz low, or 72 MHz high). The FCC is really too busy prosecuting (or persecuting) the various networks for "shock" TV and radio; and cracking down on false "MAYDAY" calls to chase after the R/C hobbyist.
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Old Apr 28, 2005, 10:22 AM
Rev. Dr. Moses P. Lester
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Joined Feb 2005
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Quote:
Originally Posted by RGinCanada
Other than that, several people have sent their air gear in to be retuned to surface frequency. I seem to remember the $40 as a cost, but I could be wrong there. It is not simply a matter of popping in new crystals, apparently
ouch, that's not was i was hoping. was hoping that i could just switch crystals if i felt like flying a plane or sailing a boat on any given day.
my radio was bought in the early 90s, if i remember, so it was right around that law-change time you mentioned. not sure of the exact date.

Quote:
Originally Posted by RGinCanada
If you do invest in a $$ surface radio, you can switch between crystals for that frequency, ie five boats=five RXs with different crystals, swap TX crystal to run different boat.
that helps somewhat, though.

Quote:
Originally Posted by CG Bob
The various R/C manufacturers cite this regulation in their literature. Based on the law, you CAN NOT change the crystals in the transmitter. In reality, lots of people do change the transmitter crystals quite frequently - the important thing is to stay within the band range (75 MHz, 72 MHz low, or 72 MHz high). The FCC is really too busy prosecuting (or persecuting) the various networks for "shock" TV and radio; and cracking down on false "MAYDAY" calls to chase after the R/C hobbyist.
heh yeah, i fail to see how i could present a hazard to anyone or anything by changing the frequency my models run on, within the assigned model bands. i wouldn't even be misusing it so far as to be running a boat on the aircraft bands.

thanks for the help, guys.
and thank you, howard stern and janet jackson, for taking the heat off me!
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Old Apr 28, 2005, 11:29 AM
KC8WPF
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Euclid, Ohio, United States
Joined Sep 2004
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One other option is to get your Amatuer Radio (HAM) license. You can then operate any type of R/C model on 50 MHz. The down side is that most of the R/C gear on 50 MHz is 8 or more channels.
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Last edited by CG Bob; Apr 28, 2005 at 11:36 AM.
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Old Apr 28, 2005, 08:34 PM
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United States, OR, Beavercreek
Joined Jan 2004
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The radios went to narrow banding in 1991, a radio from that era would have a gold sticker located (most of the time) on the back of the transmitter if the radio has been narrow banded.

I've got quite a few radios from the early 90's and before, and almost all of them have the gold sticker on the back, the radios that arenít stickered I don't use.
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