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Use of FRS / GMRS Radios in Backcountry

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Use of FRS / GMRS Radios in Backcountry

Postby Ranboze » Thu Nov 30, 2006 8:54 pm

I am by no means on expert on this subject, but I've been hanging out with some radio experts and have changed how I use radios based on the knowledge my friends have imparted to me.

My main point is in regards to the use of "subchannels", eg channel 8 sub 2. "Sub" is short for "subaudible tone" (not "sub-channel") that's transmitted on your signal. Radios set to a specific "sub" (usually numbered 1 to 38 ) block out all incoming signals on the same CH except those using the same "sub." Radios set to "sub" 0 (no tone) will hear all signals (with any or no "sub") on the same CH.

People using the same channel but different SUB (other than 0) won't hear each other. Nice right? That's what you want, right? Well... if you're in a big box store, or Disneyland, or the county fair the SUB is nice because you won't hear everyone else on the same CH.

An important fact, though, is that you will be able to hear ONLY someone on the same CH and SUB.

So, let's say Mary, Dave and I are out in the woods and have our FRS or GMRS radios set to CH 9 sub 7. Then, let's say, I become separated from my group. I start radioing them, but they turned their radios off, or some such thing. Anyone on CH 9 sub 0 OR CH 9 sub 7 can hear me. So, I put out a distress call. If someone on CH9 sub 0 hear's me and tries to respond, I can not hear that caller... I can hear ONLY someone transmitting on CH 9 sub 7. With up to 38 subaudible tones per channel, the likelihood of someone else being on the same CH and sub is pretty small.

Subchannels provide for convenient private conversations in big public areas, but can be more harmful than good in remote areas if the radio is being used as a potential tool for safety.

I never knew this stuff, and always fell victim to the the "privacy channel" gimmick without understanding the ramifications of it.

Cliff notes:
If I have a radio is tuned to CH 9 sub 7:
Only those on [CH 9 sub 7] -OR- [CH 9 w/NO sub] will hear me.
I will hear ONLY others using CH 9 sub 7. I can not hear someone on CH 9 w/NO sub.
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Postby krudler » Thu Nov 30, 2006 9:22 pm

I'm not doubting you, but does this mean that if me and my friend are skiing on Mammoth Mtn and using radios on Channel 9 sub 7, anyone on channel 9 w/no sub will hear our whole conversation? Wouldnt that kind of defeat half the point of the "sub channels" in the first place? Very interesting indeed.
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Postby Shawn » Thu Nov 30, 2006 9:26 pm

Ranboze -

That's a very nice explanation of a topic few choose to understand.

Pardon me if I pile on with a little history of the "sub" business.

Many years ago during the early days of two-way FM radio communicating without interference wasn't much of an issue. When the two-way radio business became popular, various agencies would interfere with each other by virtue of being on the same radio frequency but in similar regions (e.g. Fresno and Bakersfield) and unintentionally hear the other guys signals. The issue becam worse as radio repeaters became common place on mountain tops - extending the reach of the two way radio communication.

Thus commercial radio manufacturers, like Motorola and General Electric created a scheme to silence the interference using a "Continuous Tone-Coded Squelch System" (CTCSS). Motorola called there's Private Line (PL) and GE named theirs Channel Guard (CG).

Over the course of time, 37 standard sub-audible tones accepted for use in the commercial two-way radio business. The range roughly from 67.0 hertz to 254.0 hertz. As your post suggests, the sub-audible tone is injected onto the transmitted signal. On the receive side, the speaker is only opened when the selected tone is "heard" and decoded.

As an aside, my house is at about 1,100 ASL in a rural area among vineyards but there is a highway nearby. WHen I listen to the FRS channels from here its a nice blend of spanish grape picking and people driving thru talking about how far is it to McDonalds. :D

Shawn (aka WB6JWB)

PS. Guess I posted the same time Krudler did; the short answer is "yes".
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Postby Ranboze » Thu Nov 30, 2006 10:07 pm

Nice history Shawn. And yep Krudler... if you and your buddy are shredding it up on Mammoth while chatting on CH 9 sub 7, everyone on CH 9 no sub (within range) can hear you.
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Postby Randonnee » Mon Dec 04, 2006 7:38 am

Great description Shawn.

Krudler: as Ranboz says you are right in the assumption that others can listen in. However, this does not defeat the purpose of the system, as it is not intended to keep your converstaions private. The purpose it to allow many users on the frequency without disrupting the other users.

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Postby krudler » Mon Dec 04, 2006 8:53 am

I see I see....thanks, this is very interesting and makes perfect sense....good stuff to know!
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Postby dave54 » Tue Dec 19, 2006 1:44 pm

On a semi-related side note...

Has anyone actually gotten a license to use the GMRS frequencies? I know the federal regulations require it, but no one I know ever bothered to get one, and the FCC apparently doesn't care about intermittent unlicensed GMRS use in the backcountry.
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Postby Ranboze » Tue Dec 19, 2006 7:12 pm

I have only an FRS radio, which does not require a license. However, if I did have a GRMS radio, not sure if I'd get the license... because of the very reason you mentioned. I use the radio primarily in the backcountry and am not making any $$$ off its use. However, you may find the following interesting:
~~~~~~~~~~~~~~~

The FCC has notified several entities -- including two trucking companies and a balloon festival sponsor -- regarding the alleged use of Amateur Radio frequencies by unlicensed individuals. Special Counsel in the FCC Spectrum Enforcement Division Riley Hollingsworth advised all of the parties that unlicensed use of radio equipment not only can interfere with licensed users but violates federal law and could lead to fines of up to $10,000...
"Information before the Commission indicates that at the 2005 International Balloon Fiesta held in Albuquerque, there were numerous balloonists using Amateur Radio Service and General Mobile Radio Service (GMRS) radio transmitting equipment without licenses," Hollingsworth wrote Paul Smith, the event's executive director on August 23. "Both services require a license from the Commission."

Hollingsworth told Smith that while the FCC encourages all balloonists to use communication equipment of some kind, he'd like the Balloon Fiesta to advise those participating in this year's event October 6-15 that unlicensed operation is illegal. He invited Smith to post the Advisory Notice on the event's Web site.

The Commission also contacted two trucking firms regarding alleged unlicensed transmissions from tractor-trailer rigs on 10 meters earlier this year. Hollingsworth sent a Warning Notice to Cardinal Express of Concord, North Carolina, on August 28, and Melton Truck Lines of Tulsa, Oklahoma, on August 30. The FCC cited information indicating that a Cardinal Express rig on Interstate 85 in North Carolina was the source of radio transmissions on 28.085 MHz on August 2. Hollingsworth told Melton Truck Lines that the FCC had information that one of its rigs, also on Interstate 85 in North Carolina, transmitted on 28.085 MHz on June 11.

Hollingsworth warned the trucking firms that, in addition to fines and other enforcement sanctions, operating transmitting equipment without a license could land drivers in jail and lead to seizure of radio equipment. He indicated this week that both trucking firms and their drivers have contacted him in response to the warning notices and are cooperating with the FCC.

The FCC sent a third Warning Notice to Parker Contracting of Panama City, Florida, on August 21 citing allegations that the contractor's employees have been operating unlicensed radio transmitting equipment on 145.020 MHz and interfering with licensed users. Hollingsworth said the contractor promptly contacted the Commission to report it had collected the Amateur Radio transceivers and was applying for a business license.

On August 18, the FCC wrote Neva Poovey of Newton, North Carolina, citing information indicating that she or someone in her residence had been operating radio equipment that caused interference on 10 and 12 meters. Hollingsworth noted that FCC records did not indicate a license authorizing transmissions on those bands had been granted to anyone at Poovey's address. Poovey's husband Michael responded to tell Hollingsworth he was testing "a huge mobile linear" with another individual in his driveway. A nearby radio amateur complained to the Commission after hearing the transmissions on the two amateur bands.

A Technician class licensee in Puerto Rico -- Joaquin Diaz Fontanel, WP3BH, of Humaco -- was the target of a Warning Notice sent August 28 regarding alleged operation on 7.080 MHz, a frequency not available to Technician class operators.

"Such operation may reflect adversely on your qualifications to retain and Amateur Radio license," Hollingsworth warned.

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GMRS radios

Postby Mike McGuire » Fri Jan 19, 2007 10:35 pm

Wiki has articles on GMRS and FRS radios http://en.wikipedia.org/wiki/GMRS http://en.wikipedia.org/wiki/Family_Radio_Service
It seems that channels 1 through 7 of FRS are the same as 9 through 15 of GMRS. All other channels of both services are incompatible. However according to the GMRS article
Recently, hybrid FRS/GMRS consumer radios have been introduced that have 22 channels, instead of the 14 channels associated with FRS. On this type of radio, only channels 8-14 are strictly license-free FRS channels: Transmitting on all channels above channel 14 requires a license, and transmitting on the shared FRS/GMRS channels 1-7 also requires a license if, as is the usual case, the effective radiated power of the radio is greater than 500 milliwatts (1/2 watt). It is the responsibility of the radio user to read and understand all applicable rules and regulations regarding GMRS.
I don't think we'll find FCC enforcers wandering round the backcountry with field strength meters to catch you radiating above your licensed power level even if you stick to just FRS channels. The question in my mind is what power level these hybrids actually run at on the FRS channels. I will have to try it some time when I am marginal on getting through on an FRS channel by shifting to one of the GRMS only channels.

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Postby dave54 » Sat Jan 20, 2007 6:02 pm

The 'recently' in that quoted article is relative. I have had my Motorola T5500 radios with both FRS and GMRS for 3 years. We nearly always use ch 21 or 22 because we have never heard any other traffic on those channels. But then again we almost exclusively use them in remote areas.

The above noted incidents in earlier post involve commercial users, higher power transmitters, or use near urban areas. It is understandable the FCC clamped down on those users. The FCC seems to be intentionally ignoring backcountry use of off-the-shelf radios, giving a tacit approval of unlicensed use in that situation.
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GMRS radios

Postby Mike McGuire » Sat Jan 20, 2007 6:23 pm

Actually last time I went shopping, I couldn't find a purely FRS radio. I think they quit making them in favor of the hybrids.

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