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Still trying to understand power output regulations

Blaise

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Blaise Community Regular

Blaise

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I've read 'til my head aches, but still can't find an answer.  Can someone set me straight?

I'm trying to spec a base-station, and I'm looking at the '50 Watt' requirement.  As near as I can tell, virtually none of the commercially available GMRS transmitters really output 50 watts.  It's usually somewhere between 45 and 48, from what I see.  But even if they *did*, antenna cable and connector losses seem like they're going to eat a minimum of 10% of your power, even over fairly short runs, so really, there's no hope of ever transmitting anywhere *near* the 50 watt limit, and realistically you'll be closer to 40 watts.

Now I realize that transmission power is less important to range in this band than antenna placement, gain, etc., but all other variables being equal, if I'm not mistaken, transmitting with 25% more power is going to get you as much as 11% more range and 25% more coverage area.  That's a lot more than nothing!

Is this just a loss GMRS operators accept, or is there more to it?  Are folks using amps to bump their unit's output power up over 50 watts to make up for losses?  Is there a trick to this that I'm missing?

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SteveShannon Grand Master

SteveShannon

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6 minutes ago, Blaise said:

I've read 'til my head aches, but still can't find an answer.  Can someone set me straight?

I'm trying to spec a base-station, and I'm looking at the '50 Watt' requirement.  As near as I can tell, virtually none of the commercially available GMRS transmitters really output 50 watts.  It's usually somewhere between 45 and 48, from what I see.  But even if they *did*, antenna cable and connector losses seem like they're going to eat a minimum of 10% of your power, even over fairly short runs, so really, there's no hope of ever transmitting anywhere *near* the 50 watt limit, and realistically you'll be closer to 40 watts.

Now I realize that transmission power is less important to range in this band than antenna placement, gain, etc., but all other variables being equal, if I'm not mistaken, transmitting with 25% more power is going to get you at least 11% more range and 25% more coverage area.  That's a lot more than nothing!

Is this just a loss GMRS operators accept, or is there more to it?  Are folks using amps to bump their unit's output power up over 50 watts to make up for losses?  Is there a trick to this that I'm missing?

We just accept it. I doubt that it really amounts to 11% greater range unless you’re transmitting to space. Remember it’s line of sight. 

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Blaise Community Regular

Blaise

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20 minutes ago, Borage257 said:

Antenna height and low loss cable matter more than watts*. 

Yes, I thought I made it clear I understood that by starting with "Now I realize that transmission power is less important to range in this band than antenna placement, gain, etc., but..."

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marcspaz Veteran

marcspaz

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eh... this is a tricky subject because people see a huge difference in numbers of watts, but lose sight of the fact that those numbers have minimal impact on the real range and intelligibility of your signal. 

 

Bottom line is more power is not the answer. So we just deal with it... accept it... and try to get than antenna as high as possible.

 

I ran a real world test with a radio that has 46w actual output and LMR400 cable (one of the more common in GMRS base installs).  At the end of a 100 foot run, I measured 24 watts.  My range was about 8.5 miles.  At 8 miles away, my son said he heard me fine and he had a 4 s-unit reading on the mobile radio.  In that half mile to 8.5, I disappeared. 

 

I put my amp on and ran 350 watts out. which netted me 182 watts at the input of the antenna.  That was an increase in power of over 700%.  At the 8 mile mark, my son said I was at 5 s-units (measurable, but not significant), but he still completely lost me about 1,000 feet further away than with 46 watts... not eve a 1/4 mile increase.

 

On an offroad trip, I was on top of a 4,400'+ plateau, using the same 46w radio, and was able to talk to someone 168 miles away.  I could hear the other station about 7 s-units.

 

And of course there is satellite communications, were the repeaters have about 1/4 watt and sound fantastic here on earth, 200+ miles away.

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KAF6045 Experienced

KAF6045

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4 hours ago, Blaise said:

I'm trying to spec a base-station, and I'm looking at the '50 Watt' requirement.  As near as I can tell, virtually none of the commercially available GMRS transmitters really output 50 watts.  It's usually somewhere between 45 and 48, from what I see.  But even if they *did*, antenna cable and connector losses seem like they're going to eat a minimum of 10% of your power, even over fairly short runs, so really, there's no hope of ever transmitting anywhere *near* the 50 watt limit, and realistically you'll be closer to 40 watts.

The regulation is 50W maximum OUTPUT TO THE ANTENNA. No amplifiers beyond that... (I suppose one could use a 10-15W mobile as the station, with a 5dB or so  amplifier mounted on the antenna mast with only a short 1-3ft coax between it and the antenna (6dB with 15W in would be 60W out, illegal! Depending on losses it might take a 6-7dB gain)

4 hours ago, Blaise said:

Is this just a loss GMRS operators accept, or is there more to it?  Are folks using amps to bump their unit's output power up over 50 watts to make up for losses?  Is there a trick to this that I'm missing?

You use a high-gain antenna. An antenna with 6dBd gain (ie: 6 dB gain compared to a half-wave dipole... about 8.2dBi -- gain relative to the theoretical "isotropic" antenna [a perfect spherical pattern]) receiving, after coax and connector losses, about 40W will emit an EFFECTIVE radiated power (ERP) equivalent to 160W (3dB -> 2x, so 2x2 time 40). That is, the strongest point in the beam pattern will be equivalent to a half-wave dipole fed with an actual 160W.

The beam pattern will be fairly thin stretching toward the horizon. Don't expect much coverage above or below the antenna (if the antenna is on a tall tower on a tall mountain you may need to find a variation of phased segments designed to "steer" the pattern downward to reach the intended area of coverage)

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MichaelLAX Veteran

MichaelLAX

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Nicely Done!

Geoffrey also ran, unsuccessfully as Governor of Michigan and was Kevorkian's defense lawyer as "Doctor Death" and his brother Doug, was a leader of The Knack, a one-hit wonder from 1980, who wrote and sang about his passion over his later girlfriend, a 17 year old high school student in "My Sharona" and whom is now a very successful real estate agent in LA.  RIP Doug a couple of years ago.

In 1979 a Hit Song Made This Future L.A. Real Estate Agent a Pop Culture Icon

Doug Fieger dies at 57; leader of the L.A. band the Knack sang ‘My Sharona’

Screen Shot 2022-09-29 at 7.43.23 AM.png

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