Two way radio comms

Non model specific questions

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m-l_johnny
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Two way radio comms

Post by m-l_johnny » Thu Nov 01, 2018 11:31 am

Been doing some browsing around overland (wheeling with a destination) forums. I'm seeing FRS/ GMRS radio systems being used.
Since I'm a numbskull when it comes to non-mechanical things, can someone (Cowboy?) give me the quick and dirty on a few questions? Not sure I've understood everything I've read on the interwebs. My eyes tend to roll back into my head when I start reading about all the different frequencies.

FRS is Family Radio System. Essentially the short range walkie-talkies?
GMRS: General Mobile Radio System. Requires a license from the FCC, no test like HAM license, though. Am I correct in understanding that the range is typically farther than CB?
What are the benefits/ cons of using GMRS over CB? I did read something about GMRS is a cleaner sound on receiving end.
Are CB antennas compatible with GMRS?
Is GMRS tuned the same way, or need to be tuned, with the same meter?

Thanks!
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Re: Two way radio comms

Post by Cowboy » Fri Nov 02, 2018 3:21 pm

Man, this is a subject I haven't talked about in a long time...how you doing Johnny?
m-l_johnny wrote:
Thu Nov 01, 2018 11:31 am
FRS is Family Radio System. Essentially the short range walkie-talkies?
Pretty much, they are normally 1/2 watt, which will get a range of around 1-2 miles depending on terrain.
GMRS: General Mobile Radio System. Requires a license from the FCC, no test like HAM license, though. Am I correct in understanding that the range is typically farther than CB?
That all depends on how much power is applied... :lol: . Handheld FRS/GMRS radios don't really have a 35 mile range, because they usually transmit 1/2 watt on the FRS channels and 1-2 watts on the GMRS channels. There are dedicated GRMS radios that transmit more power, up to 50 watts IIRC? At 50 watts it would definitely outperform a regular commercially available CB radio that we have been using for decades.
What are the benefits/ cons of using GMRS over CB? I did read something about GMRS is a cleaner sound on receiving end.
The big difference is the way the radios "talk" to each other. CB radios operate in the High Frequency (HF) spectrum around 27mhz, that's a wavelength of a tick over 35 feet. Keep in mind, that is one full wavelength, we don't use a full wavelenght antenna, we use 1/2 or 1/4 wavelength antennas for most applications, you only need half of the sine wave. Which is why the old steel whip CB antennas were 108 inches long, that is 1/4 wavelength of 27mhz. The new "fiberglass" whips we use now are still "electrically" 108" long, they are just wound up as a coil inside the fiberglass.

FRS/GMS radios operate Ultra High Frequency (UHF) spectrum at 462-467mhz, that's a wavelength of smidgen over 2 feet. The other differences are the way they throw that energy through the air, kind of like AM radio stations vs FM radio stations...to put it in a way that might be easier to visualize for you. AM low frequency signals carry a long way at low power, but it's noisy and unclear. FM has to use much more power to transmit the same distance but it is very clear. Part of why that works is because of the separation between the channels, CB radio uses 40 channels in a span of less than 1mhz; FRS/GMRS radios use 22 (as the standard) channels spread over 5mhz, that 5mhz is further chopped up with privacy codes, I don't remember exactly how those work, I think it's done digitally as pseudo encryption.
Are CB antennas compatible with GMRS?
CB antennas and GMRS antennas are different animals, because they are drastically different wavelengths, being HF vs UHF. I do not know if they make a hybrid antenna that to work with both signals...do they make CB/GMRS combo radios? I actually don't know the answer to that question.
Is GMRS tuned the same way, or need to be tuned, with the same meter?
I don't have any experience with dedicated (manufactured specifically as) GMRS antennas, but I would not expect them to be tune-able, the UHF antennas we use in the military and commercial world are either manufactured for an exact frequency or they are for a frequency range; I would expect GMRS antennas to be the later, in that they are built to optimize the 462-467mhz range. Which would also work at half or double that frequency, but the efficiency diminishes the farther you go into the harmonics, i.e. x2, x4, x8, x16 times the frequency (same going the other way, 1/2, 1/4, 1/8, 1/16).

Hopefully I've helped a little, and not actually caused more confusion.

Here's an article I found with a quick search of the interwebs, to me it reads at a pretty easy to understand level, not that that is a bad thing...especially for your's truly.
https://midlandusa.com/gmrs-or-frs-radio-how-to-choose/
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Re: Two way radio comms

Post by m-l_johnny » Fri Nov 02, 2018 4:30 pm

Thanks Cowboy!

That does help. It's been too long since I've done any wheeling, I presume most still use CB on the trail.

If I ever start doing any trips with overlanding groups, I'll probably end up adding another radio.
Hi. I'm Johnny.... And I'm a Jeep addict....

'76 CJ7 money pit of fun.
pics here

I am not Jonny Throttle.

Yes, I really am as stupid as I look.

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