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Author Topic: GMRS ANTENNA RULES  (Read 722 times)

K7MPZ

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GMRS ANTENNA RULES
« on: January 14, 2020, 06:01:36 PM »

I was just told, in no uncertain terms, that I was not to use my 18" gmrs antenna when I was using any of the shared channels. My radio is a licensed gmrs/frs ht, and it lowers power where required. I have been reading all the documents on changes to power and channels that I can find, and have never, ever, read anything related to antenna restrictions. I really do not want to swap a decent antenna back to a rubber-ducky. Is there any document anyone can tell me about that may have led the very smart emmcom instructor to tell me to ditch my antenna? This 'rule' was even included in bold letters in the class handout.
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Dale Fiorillo
Sequim, Wa
K7MPZ

KC0MYW

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Re: GMRS ANTENNA RULES
« Reply #1 on: January 14, 2020, 09:51:23 PM »

Here is the applicable part of the 'Code of Federal Regulations' that addresses FRS Radios:

47 CFR Part 95 Subpart B

The part that deals specifically with the antennas is here:

Section 95.587B

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K7MPZ

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Re: GMRS ANTENNA RULES
« Reply #2 on: January 14, 2020, 10:29:03 PM »

I read all of that, and nothing pertained to a gmrs handheld  using the shared frs channels. I would think that if there were any restrictions on a gmrs/frs hh they would be in the gmrs rules. An frs hh cannot remove its antenna.
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Dale Fiorillo
Sequim, Wa
K7MPZ

W9IQ

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Re: GMRS ANTENNA RULES
« Reply #3 on: January 15, 2020, 03:15:34 AM »

The applicable regulation is 95.1767(2)(c). It restricts a GMRS station on the FRS interstitial frequencies to 0.5 watts ERP.

Assuming that you have a certified radio in which the antenna connection has not been modified, then connecting it to another antenna would require an evaluation of the output power of the radio and the gain of the antenna system to determine if it complies with the regulations.

Since all of this requires some engineering expertise, your instructor is essentially on the right path when addressing "laypersons".

- Glenn W9IQ
« Last Edit: January 15, 2020, 03:32:28 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K7MPZ

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Re: GMRS ANTENNA RULES
« Reply #4 on: January 15, 2020, 11:36:21 AM »

Ah, but Glenn, I do not use the interstitial frequencies, I use ch 5. I found only one rule relative to a hh gmrs unit. It is 95.1787, on page 33, it says the antenna must be a non-removable integral type, but this is for transmitting digital data !! What's your take on that?
Dale
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Dale Fiorillo
Sequim, Wa
K7MPZ

W9IQ

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Re: GMRS ANTENNA RULES
« Reply #5 on: January 15, 2020, 12:04:28 PM »

Ah but then you do, Dale. Channel 5 is 462.6625 MHz. This is an interstitial channel as defined by 95.1763(b). The antenna/power allowance for this interstitial group is different than that I previously cited. 97.1767(b) limits the GMRS ERP in this case to 5 watts. It is worth noting that this is different than a GMRS certified radio which is limited to 2 watts ERP per 95.567.

So you are still stuck with having to compute your ERP with your antenna of choice if it is not the stock antenna that came with the radio. And you probably won't convince your instructor of how right you are once you have done that.

Regarding your other question, 95.1787 lays down requirements for the manufacturers that wish to have product certified as GMRS data transmitters. This does not directly affect you as the licensee/user. Due to other regulations, you are not allowed to modify permanently attached antennas, for example.

Note that these requirements for certification change from time to time. Unless the regulations specifically disallow you to use a transmitter certified under older regulations, you may continue to use it. So for example, if in the past a manufacturer could have a detachable antenna for certification but now they cannot for new certifications, you could continue to use the old version as a licensee since there is nothing in the regulations prohibiting you from doing so.

- Glenn W9IQ
« Last Edit: January 15, 2020, 12:25:28 PM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K7MPZ

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Re: GMRS ANTENNA RULES
« Reply #6 on: January 15, 2020, 12:17:18 PM »

Oops, I thought the interstitial frequencies were between the channelized frequencies. I stand corrected, or sit, as it is to windy here to stand.
Moving on, you stated the erp on ch5 was 5watts, and my gmrs automatically lowers to 2watts. Even with the better antenna I wouldn't there would be a 3watt increase in erp?
Dale
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Dale Fiorillo
Sequim, Wa
K7MPZ

W9IQ

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Re: GMRS ANTENNA RULES
« Reply #7 on: January 15, 2020, 12:52:56 PM »

It may pay to review what ERP means within the context of FCC regulations (and more generally). It begins with the definiton of EIRP:

PEIRP=PXMT * GANT

     where PXMT is the output power of the transmitter and GANT is the linear (unitless) gain of the antenna system compared to an isotropic antenna.

Then ERP is defined as:

PERP=PEIRP/1.64

So if your transmitter is putting out 2 watts and you are allowed an ERP of 5 watts, then your linear antenna system gain can be no more than 4.1 over an isotropic antenna - equivalently 6.13 dBi or 3.98 dBd.

You could consult the antenna data sheet to determine their claimed gain. Likely this will be an overstated number which would put you on the "safe" side. It would probably serve as a reasonable legal defense as well - not that the FCC is running around looking to bust minor GMRS ERP violations.

For manufacturers certifying transmitters, electric field strength measurements would typically be used to confirm that it is within the ERP limit. But I have seen certified transmitters where the lab simply asserts that the antenna has X dB gain against a measured power output.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KI4SDY

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Re: GMRS ANTENNA RULES
« Reply #8 on: April 12, 2020, 06:26:30 AM »

Repeatedly, through history the FCC has created radio services with limited use, power and antenna regulations. While this is done with the primary intent to protect the users and other radio services from interference, often the result is diminished performance and use of the service. Crippling a radio service from the beginning does nothing to promote it's use. After implementation, the FCC should review their regulations and the result on each service annually. They should ask the public for input regarding the rules and what changes they would value. Any good manager would do this.

When government dictates down to the public, the results are usually less than wonderful. Regulations created with public input are better received and usually result in workable solutions. Although the FCC asks for public input in most situations. From what I have seen over the decades is that they ignore what the public wants and they do what they had in mind to begin with. That is why we have users on here now trying to get good performance from their GMRS equipment, while jumping through hoops to avoid violations. Sad!
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K7MPZ

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Re: GMRS ANTENNA RULES
« Reply #9 on: April 12, 2020, 07:26:41 AM »

Amen! The whole service is a stupid mess, with many users trying to provide a public service, and probably more looking for any way to break the rules. You probably remember how the cb went crazy!  If you read the requested rule changes from the manufacturers you can see some outlandish stuff.  Sorta off topic, but have you ever seen an frs radio that has had its little fixed antenna modded? 
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Dale Fiorillo
Sequim, Wa
K7MPZ

KB8VUL

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Re: GMRS ANTENNA RULES
« Reply #10 on: April 18, 2020, 06:53:39 AM »

So I get the idea of the low power FRS frequencies and the antenna thing.  My thought would be to figure out what those frequencies were and then NOT use them.
A bigger question would be what is the max height of a GMRS repeater antenna? 
It's obvious that antenna height on a repeater has a huge effect on it's coverage footprint.  But is there a set regulation for maximum height?
I know there is som debate on ham radio antenna height being limited to 200 feet.  But that is more a regulation of the tower and the requirement to have FAA approved obstruction lighting on it, not a mandate for maximum tower height.
Is GMRS the same way or is there a limit?
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K7MPZ

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Re: GMRS ANTENNA RULES
« Reply #11 on: April 23, 2020, 09:22:14 AM »

I don't have much choice on what frequencies are used, they were established years ago for the CERT radios, little $10 junkers.  There are rules for the repeater antennas, but I didn't spend anytime reading them, sorry, but Google will tell you.  I don't understand your last question.
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Dale Fiorillo
Sequim, Wa
K7MPZ

W9IQ

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Re: GMRS ANTENNA RULES
« Reply #12 on: April 23, 2020, 10:00:16 AM »

GMRS small base stations and small control stations are limited to a 20 foot antenna height above the building, tree or ground to which they are attached. The height limitation is definitive of the class of station. To exceed this height limitation, you need to make an application to the FCC on form 605. It is then no longer considered a "small" station.

A GMRS repeater has no antenna height restriction other than the usual FAA and FCC requirements.

- Glenn W9IQ

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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

AD0AR

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Re: GMRS ANTENNA RULES
« Reply #13 on: April 23, 2020, 04:59:24 PM »

So if I live on top of a mountain, as long as the antenna is no taller than 20 feet above the structure it is attached  to, it's legal?
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W9IQ

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Re: GMRS ANTENNA RULES
« Reply #14 on: April 23, 2020, 05:04:44 PM »

Yes.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.
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