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Repeater output power


taco6513
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The maximum power for GMRS is 50 watts. The repeater is 50 watts out of the duplexer or out of the radio before the duplexer? I need code and verse please.

Since a duplexer is neither required, nor even mentioned in the regulations, it is 50 watts out of the xmtr antenna connector.

 

§ 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.

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What part of “The transmitter output power of [a]... ...repeater... ...must not exceed 50 Watts” is not clear? There is no mention of a duplexer because one is not specifically required to have a useable repeater. You could just use two antennas with sufficient separation. BTW, the power loss in a good quality UHF duplexer would be under 0.5db.

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So it's a matter of how you read it?

 

 

What part of “The transmitter output power of [a]... ...repeater... ...must not exceed 50 Watts” is not clear?

 

 

That's what I was thinking too.  "Transmitter" is a very specific piece of hardware. Not really an 'open to interpretation' kind of statement.

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  • 3 years later...

What confuses me is you can have 50 watts out of back of radio but when u run say 500 feet of coax say (LMR400) your power would only be about 20-25 watts to antenna.so how do repeaters over come power loss in the system?

I would love to know the true answer to this.

Because it would be better the 50 watts is going into antenna since that is the last component of system before signal goes into air.

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6 minutes ago, WRQJ277 said:

...u run say 500 feet of coax say (LMR400) your power would only be about 20-25 watts to antenna.so how do repeaters over come power loss in the system?

1) Better coax with less loss

2) Shorter run of coax

C) Another amp, contrary to what the rules say

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5 minutes ago, WRQJ277 said:

What confuses me is you can have 50 watts out of back of radio but when u run say 500 feet of coax say (LMR400) your power would only be about 20-25 watts to antenna.so how do repeaters over come power loss in the system?

I would love to know the true answer to this.

Because it would be better the 50 watts is going into antenna since that is the last component of system before signal goes into air.

Oversimplified, two big factors:

  • Height- being above everything else will give them great line of sight. Height is might, as they say.
  • Antenna gain (and resulting ERP, or effective radiated power). Repeater antennas generally waste a lot less energy upwards, focusing on out and down. Where your average mobile antenna is 3 db gain (may even be dbi, which equates to more like 1dbd), where some repeater antennas are more like 9dbd.
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59 minutes ago, WRQJ277 said:

What confuses me is you can have 50 watts out of back of radio but when u run say 500 feet of coax say (LMR400) your power would only be about 20-25 watts to antenna.so how do repeaters over come power loss in the system?

I would love to know the true answer to this.

Because it would be better the 50 watts is going into antenna since that is the last component of system before signal goes into air.

When you are up at 1500 AGL, often times the entire repeater is cabinet mounted that high on the tower, with a very short coax run.

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Uh... 500' of LMR on uhf is about 15db of loss. You'd have about no power at the end. 3db is a cut in half of power.

A good repeater will use good cable. I just optimized an antenna and repeaters this week that is 275 high. Cable is 1 5/8 with a loss of .445. Sweeps show 1.2db of loss. 50 watts leaving duplexes with 8.1 db of gain. Thats basically a 7db gain in the system. 

The difference between public safety and critical infrastructure like this vs a hobby is money. Very few on this site would pay the cost of parts let alone tower crews cranes and such. 

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5 hours ago, gortex2 said:

The difference between public safety and critical infrastructure like this vs a hobby is money. Very few on this site would pay the cost of parts let alone tower crews cranes and such. 

 

Last climber I hired was $200 and hour from the second he got out of his truck until he pulled out of the driveway.  It doesn't seem too expensive until you get to the point where he is just standing there waiting for you to finish your work between climbs.

 

A friend of mine has a 300' commercial tower that hosts several cellular carriers, the county police and all of his amateur and GMRS gear.  Cost him well over $1M to get it installed.  He was charged $60K just to have the land certified that it's not historically significant nor has any specially spiritual/ritual significance for Native Americans.

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10 hours ago, marcspaz said:

 

Last climber I hired was $200 and hour from the second he got out of his truck until he pulled out of the driveway.  It doesn't seem too expensive until you get to the point where he is just standing there waiting for you to finish your work between climbs.

 

A friend of mine has a 300' commercial tower that hosts several cellular carriers, the county police and all of his amateur and GMRS gear.  Cost him well over $1M to get it installed.  He was charged $60K just to have the land certified that it's not historically significant nor has any specially spiritual/ritual significance for Native Americans.

Just wondering, is your friend making back a decent amount of that cost from the fees being paid by the cell carriers and the county police? Or would recovering that cost take ultimately too long to realize?

Warren, WRPC505 / WQ1C

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1 hour ago, WRPC505 said:

Just wondering, is your friend making back a decent amount of that cost from the fees being paid by the cell carriers and the county police? Or would recovering that cost take ultimately too long to realize?

Warren, WRPC505 / WQ1C

 

He made his money back in just a few years.  He is letting the county use it for free, but the other companies are paying over $30k a month, collectively. 

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7 hours ago, marcspaz said:

He made his money back in just a few years.  He is letting the county use it for free, but the other companies are paying over $30k a month, collectively. 

I think this is a business I need to look into....

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7 hours ago, Blaise said:

I think this is a business I need to look into....

 

There is a lot more to commercial towers than just getting it in the air.  If you have working capital, it could be a good thing. Just remember there is risk. 

 

Two recommendations I would offer is this... if you're going to a bank or venture capitalist, you need a solid business plan that looks like its going to work, and a backout plan to still make money if it doesn't. 

 

The other is, talk to potential customers. Tell them what you're planning and ask them what their needs are in order for them to consider doing business with you in the future.

 

By doing this, the County emergency services office was able to help my friend get through obstacles that stopped the process, because the County said it served the greater public good. He had no idea they would be an ally until he talked to the Emergency Coordinator. 

 

Good luck! I hope you succeed! 

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There are companies that aggressively search for "open" areas lacking coverage that also have the ability to have a tower placed there. Those companies are responsible for 90%+ of all new tower site builds. They have lawyers at their disposal, zoning specialists, and years of experience building out sites.

They also have relationships with wireless carriers, and know that they're likely going to have 1 or more carriers as tenants on the site before the first shovel hits the ground.

That's the kind of business plan you should have before you go spending hundreds of thousands (or more) to put up a tower.

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  • 2 weeks later...

Honestly, if you need the actual FCC regulation on the matter, then look it up on the FCC web site.  If you are smart enough to get logged into this web site, you are smart enough to look it up. 

The regulation is pretty cut and dried, 50 watts out of the radio transmitter, amplifier or whatever the source is.  That's the on paper FCC rule.

Reality. If you are running a hybrid combiner network feeding three repeaters into one antenna, your losses in that combiner network will exceed 6dB.  So if you are running 100 watts into the combiner, you are STILL only getting 25 watts out to the antenna feed line and then you have the loss of that line to contend with as well. 

My system is putting 18 to 20 watts out of the building. 

Feed line is 300 feet, and .817dB per 100 feet.  So that's .817 X 3 or 2.451dB.  Plus the .5dB loss per connector on the cable, the .5dB loss for the surge suppressor...

Am I gonna tell you that I am pushing past the 50 watt maximum at the station, of course not.  My station is completely legal. 

 

But lets have a different discussion. 

Lets talk about 12dB sinad, capture and minimum signal required to hold open squelch.

The average MTR2000 will open squelch with a PL at about -120.5 to -122dBm.  And requires about -118to -119.5dBm for a 12 dB sinad.

That's a signal change of a very scratchy signal to a fully copyable signal with background static.  For a full quieting signal you need to increase your input signal from -120 to about -105dBm. So about 15dB of increase.  So what is that in terms of watts? specifically the power change. 

If you are running a 10 watt radio, and you are generating a signal level of -120 at the repeater input, to make that signal -105 would mean you increased your signal to 80 watts to achieve that -105dBm signal level. 

 

SO, does a 50 watt radio make a big difference over a 10 watt radio?  It does, but not as much as you think.

With my silly little 18 watts I talk 37 miles in some directions.

Because antenna HEIGHT and gain is FAR more important than what your watt meter says your power out is.

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46 minutes ago, WRKC935 said:

Because antenna HEIGHT and gain is FAR more important than what your watt meter says your power out is.

 

QFT.

 

I have witnessed first hand, a well placed high gain antenna running 100w out, significantly outperform a poor antenna at low elevation and 1,000w+.

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Not sure where you all get your coax loss figures but they are way off. 

https://www.qsl.net/co8tw/Coax_Calculator.htm

Any considerable length of general purpose coax (LMR-400 and down) is very lossy in the UHF and up spectrum. Heck loss with bonafide hardline gets to be pretty bad at long lengths depending on the size

As a wise old Elmer once said your transmission line should cost more than your radio and antenna combined. Now in his time they didn't have the ability to separate the amp deck from the radio head. But still putting your amp deck 400' in the air on the tower isn't exactly feasible to being cost effective. Maybe it is if you live in a lightning free area and if you do I would love to see a picture of a real unicorn. Now on towers I know they use isolation to keep the equipment safe. But at home at least 80% dont. At home many use long runs of whatever coax they can afford. Ive seen countless YT vids of folks using trucker special. And it works because its just enough signal to hit 2 or 3 local repeaters. Yay the radio gets out!! But does it really? Most everyone goes by what repeater they hit. Try Simplex. You will find it doesn't go too far. Unless a repeater is well over the horizon a couple watts will hit it. But weather can wreck havoc on that. And if you have a 40-50 watt radio on high hitting your antenna thru lossy coax you might only be getting 3 or 4 watts out of your antenna. Yep antenna gain will help but again in this spectrum a flock of birds can block signals. You want to keep that coax/hardline at home as short a possible. If youre going for a repeater it doesn't need too be a mile in the air. The repeater is already there. That's why many an HT can hit them. 

Anyhow as usual I drifted off subject. Check your coax calculations. They are much worse than you think. Dont forget to factor frequency and swr. Do nite that oddly RG8 is better on UHF than 213. Velocity factor? That's not 8x but big old RG8. As for reference my antenna is 23ft in the air. I use a 21' foot LMR-400 Coax run. I can hit Repeaters on UHF from 65 miles away. I am on a hill. Not the highest point around but south and east of me is all downhill. To the north is a valley where the city is that lets me bypass it and cover small towns north up to 60 miles UHF and 100+ miles VHF. West Im blocked by my faraday cage built house(no I didn't build it) that even on 2nd floor an HT wont work standing in the windows.(I think the guy who built this house lined his hats with foil). The local GMRS repeater is 4 miles away and a 2m and 440 repeater is 2 miles and cant hit them inside. At first set-up I had my 8Watts HT, 65ft. of RG8X and a Tram 1480 antenna. I could hit tepeaters up to 25 miles on UHF. When I got the Yaesu 50watt radio I gained about 5 miles total. But once I shortened coax to a single run off 21' of LMR400 and moved amp deck just inside garage my ranger increased dramatically. Plus reception of Simplex stations increased 50fold. I have Simplexed 45miles on UHF.

So my point is: Double check your coax loss. You will find its more than you think. Secondly build your base system, unless you are doing your own repeater, to do Simplex. Doing this will give you more repeaters to choose from. Unless you live in a deep valley short good coax is the way to go. 

Buzz

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5 hours ago, WRQK455 said:

Not sure where you all get your coax loss figures but they are way off. 

 

Can't speak for everyone, but I get my coax loss information from the manufacturer of the cable I use in any given application. Pretty solid source.

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The best way to know your cable loss is to measure it. Not always practical when you're stringing 150 ft or more of hardline directly from the spool onto a tower, but for most of the GMRS mortals, it's in a coil with terminations installed prior to us heaving it up onto a pole/tower/rooftop. If you know the input power, and can measure the output at the other end before it is hoisted and connected to the antenna, then you can calculate/know your own losses easily enough.

I say that because while the manufacturers do tend to post numbers grounded in reality, the various distributors can get a little creative when it comes to their claims. Rounding up, rounding down, convenient lapses in stated lengths (oops, it was 1.5 dB per 50 ft, not 100 ft.) can all make a difference. I've seen some knockoff brand RG400 jumper cable assemblies that had nearly 3 dB of loss in a 5 ft. jumper. It should have been less than 1 dB even including the connectors.

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