GMRS Repater Power Output

[caerickson]

I'm in the process of installing a new GMRS repeater. I'm using a Motorola GR 1225 repeater rated at 45 Watts Maximum output to the Duplexer.

I have checked FCC Part 95 and I'm confused whether GMRS is Wideband or Narrowband and section 95.135 (Maximum Authorized Transmitting Power) states that no station may transmit with more than 50 Watts output, but subsection D states that a Fixed Station must not transmit with no more than 15 Watts output power. I called the FCC and they couldn't answer my questions about the output power and whether it should be narrow banded.

Can anyone give me some clarification?

 

[12dbsinad]

Wideband is allowed.

50 watts out of repeater.

Speaking of watts, I WOULDN'T run that GR at 45 watts... you will cook it.

 

[RFI-EMI-GUY]

Amazing that the FCC could not answer those questions . I concur the rules permit 50W and wide-band. wide band is the good stuff, don't let anyone tell you otherwise!

 

[n1das]

I concur with the 50W maximum transmitter power output. You might want to turn the repeater's power output down to no more than about 25W to prevent it from cooking itself and to keep it bulletproof reliable.

Regarding bandwidths, you can use either wide or narrow bandwidth mode on the GMRS primary channels. There is nothing in the rules restricting you to using one or the other. Whichever bandwidth you choose to use is up to you.

One thing to consider is the FRS problem with wide bandwidth operation on a GMRS repeater. When using wide bandwidth on the repeater, local FRS activity on the upper FRS channels adjacent to (12.5kHz above and below) the repeater input can get into the repeater. When the FRS activity happens to use same CTCSS/PL tone that the repeater uses, the repeater can get keyed up and you'll hear very distorted scraps of chatter from the FRS activity. I've witnessed this on several occasions and I've heard repeater users yelling at them to stop and of course the FRS users never hear them (LOL). I've witnessed GMRS repeaters getting hammered for hours from kids screaming into their FRS radios and playing call tones. It's also happened to one of my GMRS repeaters that was running wide bandwidth at the time. Switching my repeater from wide to narrow bandwidth mode completely solved the problem.

I run narrow bandwidth mode in my commercial gear on all GMRS channels, like the 22-channel GMRS/FRS bubblepacks already do. All of my adjacent channel splatter problems from local bubblepack users 12.5kHz away from whatever GMRS primary channel I'm using went away as soon as I made the switch from wide to narrow. A few simple programming changes was all that was required. My GMRS repeaters benefited too after switching them from wide to narrow mode.

Good luck.

 

[cmdrwill]

Speaking of watts, I WOULDN'T run that GR at 45 watts... you will cook it.

Depends IF the PA has been 'fixed'. And IF you changed out the fan to a better one and have it blowing out.
You have to get rid of the heat. cool air in hot air OUT.
Most of the ones we see have so much dust and dirt in them they would burn up at 5 watts.

 

[jeepsandradios]

I wouldn't push a GR1225 over 25 watts if its a 45 watt radio. Even the new PA (I have 3) will burn up after continuous use.Besides after the duplexer (a good one) you will not notice a difference in the power levels in real life.

 

[n1das]

I wouldn't push a GR1225 over 25 watts if its a 45 watt radio. Even the new PA (I have 3) will burn up after continuous use.Besides after the duplexer (a good one) you will not notice a difference in the power levels in real life.

What kb2ztx said. High powered mobiles really aren't built for repeater service without turning them down.

The stresses from repeated thermal cycling due to being keyed on long enough to heat up and then cool down afterwards will take it out in no time at all. I've read about PA failures in MOTOTRBO Capacity Plus trunking systems where the repeaters used for the voice/data channels frequently failed while the control channel practically never failed. All were transmitting at rated output. The control channel was always transmitting 24/7/365 whereas the voice/data channels were on the air only when there was traffic on the system. Accumulated stress from repeated thermal cycling of the voice channel repeaters was found to lead to more frequent PA failures. I'm thinking of the XPR8300 and XPR8400 series MOTOTRBO repeaters.

Bottom line is don't push a GR1225 over 25W if it's a 45W radio when used as the transmitter for a repeater. You need to factor in a large enough de-rating factor for transmitter specs when used for repeater service.

Good luck.

 

[N4GIX]

I'm thinking of the XPR8300 and XPR8400 series MOTOTRBO repeaters.

This can and does happen even on non-trunked repeaters. At least three have failed here in Indiana over the past year. The worst part on these is that the PA is non-repairable. It has to be replaced and they are starting to be hard to source these days.

As a result, all XPR8300 and XPR8400 are recommended to be turned down to ~25 watts...

 

[radioman2001]

For repeater power out what is being missed here it that the transmitter should legally not exceed 50 watts RF power out at the antenna. Whats not being taken into consideration is you can increase ERP or Effective Radiated Power with the use of gain antennas. I see no specific rule that defines the output power with ERP for repeaters, so you can effectively put out 350 watts ERP with a good commercial gain base antenna. Using that method you can take your 45 watt repeater and turn down the power to say 25 watts save you transmitter and still get more ERP and even better receive reception on the system with a gain antenna.

 

[lmrtek]

Mobile radios are generally designed for 20% duty cycle so in ham use or other long winded rag chew service you will be lucky to run them at 1/4 their output in continuous duty without modifications

 

[SCPD]

Caerickson, I doubt seriously you are operating your repeater as a Fixed station. It is considered a Base, and you are operating in the Mobile Service.... I know, believe me: it is confusing !- but you can use the 50 watts..... your repeater is a "Base", not a "Fixed" station (unless you are operating under unusual conditions- in which case you already know this..... )
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Good luck with your new repeater--- run it Wide Band, it will sound much better; its legal for GMRS... and if you can swing it, put up that 30Db gain antenna (I am kidding, of course!) and radiate that 500KW signal- perfectly legal too.... but don't burn things up!


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..............................................CF