ERP or actual transmitter power?

[AlexWRXZ642]

I have just thought of something:

Most of our mobile's output 5W from the radio itself. Usually they come with a high gain antenna, thus making the ERP of HT's greater than 5W, possibly closer to 10 watts.

even the radios are FCC approved for GMRS.

E.g the Wouxun 935G, comes with a 2.5dB gain antenna according to buytwowayradios.

However, the KG-805F(RS) is 2W ERP, with 1 watt out of the radio to a 3dB gain antenna. Also FCC approved.

We all know the limit for mobiles and bases is 50W, but is that ERP or actual Transmitter power in to the antenna?

if my antenna has gain, is this technically not allowed since the ERP will exceed 50W? It seems that HT's are allowed more than 5W ERP, but what about mobiles and bases?

If you have a 50W radio, you probably run a 2-6dB gain antenna. So what is the deal? This is pretty confusing to me. Thoughts?

[Sshannon]

27 minutes ago, AlexWRXZ642 said:

I have just thought of something:

Most of our mobile's output 5W from the radio itself. Usually they come with a high gain antenna, thus making the ERP of HT's greater than 5W, possibly closer to 10 watts.

even the radios are FCC approved for GMRS.

E.g the Wouxun 935G, comes with a 2.5dB gain antenna according to buytwowayradios.

However, the KG-805F(RS) is 2W ERP, with 1 watt out of the radio to a 3dB gain antenna. Also FCC approved.

We all know the limit for mobiles and bases is 50W, but is that ERP or actual Transmitter power in to the antenna?

if my antenna has gain, is this technically not allowed since the ERP will exceed 50W? It seems that HT's are allowed more than 5W ERP, but what about mobiles and bases?

If you have a 50W radio, you probably run a 2-6dB gain antenna. So what is the deal? This is pretty confusing to me. Thoughts?

It depends. You have to check the regulations for the frequency you’re curious about. Some frequencies are limited by ERP and some are simply measured power at the output. 
Unless otherwise specified, handheld radios are limited the same as mobile radios. 
 

§ 95.1767 GMRS transmitting power limits.

This section contains transmitting power limits for GMRS stations. The maximum transmitting power depends on which channels are being used and the type of station. 

(a) 462/467 MHz main channels. The limits in this paragraph apply to stations transmitting on any of the 462 MHz main channels or any of the 467 MHz main channels. Each GMRS transmitter type must be capable of operating within the allowable power range. GMRS licensees are responsible for ensuring that their GMRS stations operate in compliance with these limits. 

(1) The transmitter output power of mobile, repeater and base stations must not exceed 50 Watts. 

(2) The transmitter output power of fixed stations must not exceed 15 Watts. 

(b) 462 MHz interstitial channels. The effective radiated power (ERP) of mobile, hand-held portable and base stations transmitting on the 462 MHz interstitial channels must not exceed 5 Watts. 

(c) 467 MHz interstitial channels. The effective radiated power (ERP) of hand-held portable units transmitting on the 467 MHz interstitial channels must not exceed 0.5 Watt. Each GMRS transmitter type capable of transmitting on these channels must be designed such that the ERP does not exceed 0.5 Watt. 

[MarkInTampa]

1 hour ago, Sshannon said:

 

(1) The transmitter output power of mobile, repeater and base stations must not exceed 50 Watts. 

(2) The transmitter output power of fixed stations must not exceed 15 Watts. 

 

Stupid question, what is the difference between a base station and a fixed station? 

[UncleYoda]

12 minutes ago, markskjerve said:

Stupid question, what is the difference between a base station and a fixed station? 

Base station, which is well understood by HAMs, is setup at a fixed location (typically antenna on pole, tower or tree).  Fixed station is some mysterious type (not used in HAM) named but not properly defined in the GMRS regs (definition given is not valid) that no one can explain including FCC.

[Sshannon]

2 hours ago, markskjerve said:

Stupid question, what is the difference between a base station and a fixed station? 

The requirements are clear. A base station is allowed to talk to other base stations or mobile or portable stations. 
A fixed station may only communicate with other fixed stations. 
Both are stations in a fixed location. 
What hangs people up is that they cannot imagine how they would use them within those constraints. 
One other thing that I think is interesting (apparently I have no life) is that fixed stations may transmit on the 467 MHz main frequencies, but only up to 15 watts outpu. Base stations may not transmit on the 467 MHz main frequencies, but they can transmit up to 50 watts on the 462 MHz main frequencies. 
There’s a very long and contentious thread that’s probably named “What’s a Fixed Station?”

[OffRoaderX]

The official and unambiguous answer is: The FCC, based on their public record of enforcements clearly does not care, so why would I (or anyone with a life) care?

 

[WRQC527]

29 minutes ago, OffRoaderX said:

why would I (or anyone with a life) care?

 

 "It's easy to become confused by these questions. Before we take action we need to talk about this some more at another time."

~ Ten Bears, Dances with Wolves

[WRKC935]

The only place in the rules where ERP is even mentioned is specifically posted above regarding the 467Mhz iinterstitial channels.

So a GAIN antenna can NOT be used with a .5 watt radio on those specific frequencies.

And since you grasp the concept of gain and such.  Most fail to realize that while we are limited to 50 watts of output at the transmitter there is zero height limitation on a GMRS base station or repeater antenna.  You can go as high as you want and can afford to.    Here is the reason this fact is significant.  Broadcast and LMR (commercial) radio are in fact height limited.  And the reason is a realized gain due to height.  That gain is about 6dB for every time you double your antenna height.  So if you have a repeater at your home and it's on a 20 foot roof peak.  You stand up a 320 foot tower next to your house and park the antenna up there.  Cable loss not considered. You have a perceived gain of 24dB.  Putting that into perspective.  To put out the same signal at 20 feet would require feeding the antenna 12800 watts.  Again, not considering cable loss.

Go from a 3dBi gain antenna on the roof to a 6dBi gain antenna on the tower in the process and it's now 25600 watts. 

Antenna height, to a point is the most important thing to have with a radio system of any type if you want it to have good coverage.

And antenna gain, both from design and height equally effect both your receive and transmit, where increasing power output only increases the distance you can be heard.  It does nothing for your ability to hear others.

 

 

[Sshannon]

10 minutes ago, WRKC935 said:

The only place in the rules where ERP is even mentioned is specifically posted above regarding the 467Mhz iinterstitial channels.

So a GAIN antenna can NOT be used with a .5 watt radio on those specific frequencies.

And since you grasp the concept of gain and such.  Most fail to realize that while we are limited to 50 watts of output at the transmitter there is zero height limitation on a GMRS base station or repeater antenna.  You can go as high as you want and can afford to.    Here is the reason this fact is significant.  Broadcast and LMR (commercial) radio are in fact height limited.  And the reason is a realized gain due to height.  That gain is about 6dB for every time you double your antenna height.  So if you have a repeater at your home and it's on a 20 foot roof peak.  You stand up a 320 foot tower next to your house and park the antenna up there.  Cable loss not considered. You have a perceived gain of 24dB.  Putting that into perspective.  To put out the same signal at 20 feet would require feeding the antenna 12800 watts.  Again, not considering cable loss.

Go from a 3dBi gain antenna on the roof to a 6dBi gain antenna on the tower in the process and it's now 25600 watts. 

Antenna height, to a point is the most important thing to have with a radio system of any type if you want it to have good coverage.

And antenna gain, both from design and height equally effect both your receive and transmit, where increasing power output only increases the distance you can be heard.  It does nothing for your ability to hear others.

 

 

Well, all antennas in the Personal Radio Services, which includes GMRS, are subject to the following:

95.317. Registration of antenna structures that may constitute a menace to air navigation.

(a) Each antenna structure used for a Personal Radio Service station is subject to the antenna structure rules set forth in part 17 of this chapter. In particular, the owner of an antenna structure that is more than 60.96 m (200 ft) in height above ground level (see § 17.7 of this chapter for specific criteria) may be required to notify the FAA and register the antenna structure with the FCC. 

(b) Further, stations located on or near a military or public-use airport with an antenna structure that is more than 6.10 meters (20 feet) high may have to obey additional restrictions. The highest point of the antenna must not exceed one meter above the airport elevation for every hundred meters of distance from the nearest point of the nearest airport runway. Differences in ground elevation between the antenna and the airport runway may complicate this formula. For stations near an airport, see http://appsint.fcc.gov/UlsApp/AsrSearch/towairSearch.jsp to figure the maximum allowable height of the antenna. Consult part 17 of the FCC's Rules for more information (47 CFR part 17). 

[WRKC935]

7 hours ago, Sshannon said:

Well, all antennas in the Personal Radio Services, which includes GMRS, are subject to the following:

95.317. Registration of antenna structures that may constitute a menace to air navigation.

(a) Each antenna structure used for a Personal Radio Service station is subject to the antenna structure rules set forth in part 17 of this chapter. In particular, the owner of an antenna structure that is more than 60.96 m (200 ft) in height above ground level (see § 17.7 of this chapter for specific criteria) may be required to notify the FAA and register the antenna structure with the FCC. 

(b) Further, stations located on or near a military or public-use airport with an antenna structure that is more than 6.10 meters (20 feet) high may have to obey additional restrictions. The highest point of the antenna must not exceed one meter above the airport elevation for every hundred meters of distance from the nearest point of the nearest airport runway. Differences in ground elevation between the antenna and the airport runway may complicate this formula. For stations near an airport, see http://appsint.fcc.gov/UlsApp/AsrSearch/towairSearch.jsp to figure the maximum allowable height of the antenna. Consult part 17 of the FCC's Rules for more information (47 CFR part 17). 

Yes, this is correct.  But if you either have the structure already, permission to install on a tower owned by others, or have deep enough pockets to stand up a tower there is no limit to the height of a GMRS antenna.  On LMR, the coordination body / FCC limits ERP, power out and height to maintain coverage only extends to your licensed operating area.  Yes, we are limited to 50 watts out on power.  But we have no ERP restriction outside the 467Mhz channels that are limited to .5 watt ERP.

And while the FCC has the requirements in place for obstruction marking (tower lights) in their regulations, it's the FAA that sets these standards.

[UncleYoda]

1 hour ago, WRKC935 said:

 [..] to stand up a tower there is no limit to the height of a GMRS antenna.  [...]  But we have no ERP restriction outside the 467Mhz channels that are limited to .5 watt ERP.

You're still stating both of those wrong.  Putting up a tower is subject to the height restrictions.  And the ERP applies to the 462 MHz interstitial frequencies at 5.0 W too.

[WRKC935]

5 hours ago, UncleYoda said:

You're still stating both of those wrong.  Putting up a tower is subject to the height restrictions.  And the ERP applies to the 462 MHz interstitial frequencies at 5.0 W too.

So me in the part 95 regulations where it says you can't place an antenna above X height.  It's NOT there... anywhere.  What you can build for a tower is going to be limited by your location with regard to airports, flight paths and other factors.  And yes, getting the proper permitting for a 1000 foot tower may not may not be possible in a specific location.  You may be limited to 20 feet and be required to have obstruction lighting on it even at that height if you are right off the end of a runway.  But that is still not a GMRS SPECIFIC height restriction.  It's a general restriction that would apply to any tower including one for a TV antenna.  

[Sshannon]

Because of the general restrictions on antenna structure heights (which by definition includes the antenna itself) no additional restrictions are needed for GMRS. That’s completely different from your original comment:

“Most fail to realize that while we are limited to 50 watts ofoutput at the transmitter there is zero height limitation on a GMRS base station or repeater antenna.  You can go as high as you want and can afford to.”

[WRQC527]

I heard two guys one day arguing about how tall a tower was. I told them to lay it down and measure it. They said we don't care how long it is, we want to know how high it is.

[WRKC935]

On 8/25/2023 at 2:43 PM, Sshannon said:

Because of the general restrictions on antenna structure heights (which by definition includes the antenna itself) no additional restrictions are needed for GMRS. That’s completely different from your original comment:

“Most fail to realize that while we are limited to 50 watts ofoutput at the transmitter there is zero height limitation on a GMRS base station or repeater antenna.  You can go as high as you want and can afford to.”

I see how if you want to split hairs here that it applies. 

What I am saying is that if I go down to the local TV station that has two UHF MSF5000's repeaters sitting on a deck at 750 feet. Yes, they are there I have worked on them.  If I get permission from them to go up  there and reprogram one for a GMRS frequency, lower the power to 50 watts (100 watt stations) then I am completely legal as far as the FCC is concerned.  Now that's not going to happen since they use those repeaters.  But, the FCC regulations regarding GMRS don't have any restriction on me doing it.  That's the point I was trying to make. 

[WRQC527]

8 minutes ago, WRKC935 said:

if you want to split hairs

Every so often someone nails the essence of mygmrs.

[Lscott]

On 8/25/2023 at 2:44 PM, WRQC527 said:

heard two guys one day arguing about how tall a tower was.

As a practical mater it can be done using a long tape measure and a stick like a broom handle. A bit of high school geometry applied will give the answer without having to take down the tower. Look in the back of the book for the solution.

[WRKC935]

10 hours ago, Lscott said:

As a practical mater it can be done using a long tape measure and a stick like a broom handle. A bit of high school geometry applied will give the answer without having to take down the tower. Look in the back of the book for the solution.

You know they make a tool for that.

 

[Lscott]

2 hours ago, WRKC935 said:

You know they make a tool for that.

 

The method is based on “similar triangles”. It’s one of the first things one learns in an elementary geometry class. No special tools required other than a bright sunny day to get a good shadow on the ground of the tower and short stick.

example:

http://4.bp.blogspot.com/-HoYTwic-P-w/U1yOwu2z9RI/AAAAAAAAifw/_wnynMunKx4/w1200-h630-p-nu/picture2.jpg

[Sshannon]

On 8/25/2023 at 12:44 PM, WRQC527 said:

I heard two guys one day arguing about how tall a tower was. I told them to lay it down and measure it. They said we don't care how long it is, we want to know how high it is.

 

19 hours ago, Lscott said:

As a practical mater it can be done using a long tape measure and a stick like a broom handle. A bit of high school geometry applied will give the answer without having to take down the tower. Look in the back of the book for the solution.

It was a joke.  

[BoxCar]

D'Oh

[WRQC527]

**DISCLAIMER** The following is a joke. It is meant to incite some combination of laughter, giggles, groans, emoticons, other jokes, or assorted other reactions. Or maybe no reaction. 

A high-gain mobile amateur radio antenna and a high-gain mobile GMRS antenna got married. The ceremony was pretty boring, but the reception was really good.

[Lscott]

3 hours ago, Sshannon said:

 

It was a joke.  

I got that part. I just wanted to point out it was rather easy to measure using a simple technique. I would guess there's likely someone who really wants to know how it could be done. For example there are old TV antenna towers free for the taking provided the interested party does the removal. It would be nice to see if it’s really worth it when a minimum tower height is a target.

[Blaise]

9 hours ago, Sshannon said:

 

It was a joke.  

They *don't* make a tool for that...

[WRKC935]

10 hours ago, Lscott said:

I got that part. I just wanted to point out it was rather easy to measure using a simple technique. I would guess there's likely someone who really wants to know how it could be done. For example there are old TV antenna towers free for the taking provided the interested party does the removal. It would be nice to see if it’s really worth it when a minimum tower height is a target.

Oh I can't afford free towers.  Especially big broadcast towers.  What you end up finding out is the towers typically will not pass a structural analysis and can't be used unless extensive reinforcement is done to them, if it's possible at all.  When the power that be (local building inspectors) ask for the results, you don't be a permit to stand the thing back up.

 

And that says nothing of the cost of dismantling a standing tower, transporting it and erecting in at a new location.

I personally went through this with a Rohn 80 that was only 10 years old at the time.   While it would still pass analysis, the concrete alone to put it back up was going to cost me 15K.  With a total cost of about 50K to get the thing standing.  I didn't have enough land to do it either, which of course is a concern. 

Point is if a tower that costs tens or even hundred of thousands to erect is FREE, free is TOO expensive for most.