GMRS small base station

[BJ_NORTON]

So I was talking with a ham about GMRS today and he was saying how GMRS is too limited because you can only run 5 watts ERP. I was thinking to myself that GMRS is allowed 50 watts unless you are operating on one of the few interstitial channels shared with FRS, then the 5 watt ERP rule comes into effect.

So, I went home and looked at the GMRS page on the FCC's website, and under the heading of Operating a General Mobile Radio service (GMRS) system, they say "A GMRS system consists of station operators, a mobile station (often comprised of several mobile units) and sometimes one or more land stations. A small base station is one that has an antenna no more than 20 feet above the ground or above the tree on which it is mounted and transmits with no more than 5 watts ERP."


Ok, that's fine but what is the difference between a small base station, and any other type of GMRS station? Rule 95.135 clearly states a maximum of 50 wattsis allowed, and then defines 3 more power limits:

[FONT=verdana, geneva, lucida, lucida grande, arial, helvetica, sans-serif]95.135 Transmitter power limits. [/FONT]
[FONT=verdana, geneva, lucida, lucida grande, arial, helvetica, sans-serif](a) No station may transmit with more than 50 watts output power. [/FONT]
[FONT=verdana, geneva, lucida, lucida grande, arial, helvetica, sans-serif](b) [Reserved.] [/FONT]
[FONT=verdana, geneva, lucida, lucida grande, arial, helvetica, sans-serif](c) A small control station at a point north of Line A or east of Line C must transmit with no more than 5 watts ERP. [/FONT]
[FONT=verdana, geneva, lucida, lucida grande, arial, helvetica, sans-serif](d) A fixed station must transmit with no more than 15 watts output power. [/FONT]
[FONT=verdana, geneva, lucida, lucida grande, arial, helvetica, sans-serif](e) A small base station must transmit with no more than 5 watts ERP.[/FONT]

​

So when is a GMRS station allowed 50 watts?Does this mean a home base station can only use 5 watts ERP, or 15 watts PEP, or the full 50 watts?


I'm so confused






Thanks for any help!

 

[evfd1625]

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I believe repeaters and mobile are the only stations that can transmit 50 watts.

 

[Rt169Radio]

Really? I thought that it was handhelds that could do only up to 5 watts, mobiles 10/15/20 watts, and base stations could do 50 watts?

 

[nd5y]

Part 95 spells out the different types of stations and power levels allowed.
eCFR — Code of Federal Regulations

 

[Rt169Radio]

Part 95 spells out the different types of stations and power levels allowed.
eCFR — Code of Federal Regulations

Well that's good to know.

 

[quarterwave]

I think some of the language is leftovers from when you had be specific on where your station was. A "Base" and a "Repeater" are essentially the same on the output side...its on the technical criteria of how and what they receive and what they do with it. They are 50 watts max.

Where the "Small" (base or control) comes in is these are not considered permanent stations, and as in some part 90 rules, did not require coordination when installed as part of a properly licensed system. They more or less counted as mobiles.

When I first licensed in GMRS, I had to choose a frequency for my repeater and give coordinates, HAAT, etc for it. Rules update....now you don't...pick one....roll on.

 

[BJ_NORTON]

ok, I did some more looking around today and found an old yahoo groups posting about small base stations and the thread turned to power levels there too. I think it pretty much agrees with what quarterwave said, that is that there are some leftover rules that never got removed from previous rules where you had to pick a channel and list specific locations:

There used to be a GMRS-specific definition for fixed stations. It
defined a station that transmitted from one specific geographic point
as identified on the license, to another specific geographic point as
identified on the license. A fixed station could not communicate with
any other class of station. It was strictly limited to point-to-
point. They were also not permitted within a 75-mile radius of large
urban areas. The 15 watt power limit, along with a limitation that
you could only use a directional antenna, existed for fixed stations
between 75 and 100 miles of a large urban area. There is a link to
the older, pre-ULS rules on the PRSG website where you can find
further information.

and I think the small base station rule still applies for using a base station on the 7 interstitial frequencies; the height and power requirements seem to be meant to keep a high power base station from obliterating anyone within 25 miles on that FRS frequency. So I think I'm going back to being comfortable running a GM300 at 40 watts as my base station, and only using the interstitials on my HTs.

 

[KB7MIB]

Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2338; U; en) Presto/2.8.119 320X240 LG VN530)

Full power base radios, at least in the past, had to meet stricter frequency tolerances than mobile's and HT's. A small base/control station allowed you to connect your mobile/HT radio to a base antenna that is no more than 60' above the ground, or 20' above the building or tree (tree? really? who mounts more than a wire antenna in a tree? I never understood that part.), and operate on the regular channels at normal power output, and the 7 interstital (FRS-shared) channels at up to 5 watts ERP, without having to meet the stricter frequency tolerance rules of an actual base radio. A full power base and/or control station with a taller antenna is still allowed.

 

[k8zgw]

control station

The rule was intended to bring GMRS in line with Business band, with reference
to a "small base station" or "control station" that is intended to work a repeater from "home".
In most cases no more then 5 watts into a 20 foot high antenna should be all that is needed.
Where you could work simplex thirty or forty miles between two radio's running
15 watts ( or so) to an antenna at 60 feet ( I know this works, we do it all the time.)

These rules have/had nothing to do with FRS, they were in place long before some
idiot even thought about FRS.

Don

 

[BJ_NORTON]

The rule was intended to bring GMRS in line with Business band, with reference
to a "small base station" or "control station" that is intended to work a repeater from "home".
In most cases no more then 5 watts into a 20 foot high antenna should be all that is needed.
Where you could work simplex thirty or forty miles between two radio's running
15 watts ( or so) to an antenna at 60 feet ( I know this works, we do it all the time.)

These rules have/had nothing to do with FRS, they were in place long before some
idiot even thought about FRS.

Don

So any thoughts about legal power levels for a home base station today? Should I reprogram for 15 watts? and why the vague power limits to begin with?

 

[k8zgw]

IF it's not broke, don't fix it

I'm just quoting "rules", I think it has to do with how you use it.
IF you are using it to talk thru your, or a local repeater, 5 watts should be plenty.
IF you are using it for SIMPLEX OPERATION on the repeater OUTPUT frequencies,
I see no reason why you can't run 50 watts ( I run 15 to 25 for simplex)
The reason for the "vague power limits", because you should use the lowest power
that will get the job done. Right now, I have a 5 watt and a 30 watt gmrs repeater(s)
as well as my 440 machine, which runs about 20 watts out of the duplexer,
to a 6 DB antenna at 120 feet, with 5 watt handheld coverage at about 7 to 10 mile
radius of the repeater ( 3 miles to the south, because of hill and I don't know how far north
because I don't have a boat) :~)

Don

 

[KB7MIB]

Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2338; U; en) Presto/2.8.119 320X240 LG VN530)

On the interstital channels (the 7 that are shared with the FRS) you can't exceed 5 watts ERP. To determine the power output you need to set your radio to, take a power level out of your radio, mulitply it by the gain rating of your antenna, and subtract the loss of your coax, and by playing with the power output level, you'll come up with the power output you can use to meet or stay under the 5 watt ERP limit on those channels. (For example, 5 watts out into a 3dB gain antenna, fed with coax that has a 3dB loss will give you 5 watts ERP. Obviously, you need accurate antenna gain and coax loss numbers for your specific installation.)
On the 8 regular channels (550, 575, 600 etc), use the minimum power level necessary to achieve and maintain reliable communications. This can be up to 50 watts out of the radio, with no ERP limit. If 5 watts works, use it. If you need 15 or 45 or somewhere inbetween to achieve the coverage you need/want, then that's what you need.

 

[KB7MIB]

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Deleted double post, sorry.

 

[Rt169Radio]

Who knew that GMRS was so complicated.

 

[BJ_NORTON]

On the 8 regular channels (550, 575, 600 etc), use the minimum power level necessary to achieve and maintain reliable communications. This can be up to 50 watts out of the radio, with no ERP limit. If 5 watts works, use it. If you need 15 or 45 or somewhere in between to achieve the coverage you need/want, then that's what you need.

I agree you should use the minimum power necessary, unfortunately I don't have the ability to easily change power levels. I'm using a Motorola GM300 mobile that a friend programmed for me. I don't have a computer old enough to program mobiles from that era. It took him 6 weeks to program this rig and get it back to me, so I'm not super excited about taking it back to turn down the power if I don't have a legal obligation to do so. If I decide there are a few other channels I want changed I'll have the power turned down then.

I only operate on the interstitial FRS freqs on my HTs, so I'm not too concerned about exceeding power levels there, I think they only put out 4 watts into an inefficient radiator...

Anyway, I had no idea the a "simple" GMRS license could be so complicated! Its been quite the learning process!

 

[k8zgw]

GM300

Your GM300 is either a 25 or 45 watt radio,
Don't sweat the "small stuff" just use it on the repeater
frequencies.

Don

 

[KB7MIB]

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Yea, if the power output isn't easily adjustable, leave it as is. No harm there

 

[gewecke]

Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2338; U; en) Presto/2.8.119 320X240 LG VN530)

Yea, if the power output isn't easily adjustable, leave it as is. No harm there

True, after all what harm is another 20-30 watts out right... :roll:

73,
n9zas