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GR1225 Repeater

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#1
If the FCC License says you're authorized to transmit at 35 watts, what should a GR1225 repeater be set at for UHF? I've been told that programming it at 22-25 watts while using a Motorola "station master" approximately 12db gain base antenna is the equivalent of having the repeater programmed at 35 watts. Also told that if the repeater was programmed for 35+ watts, the amplifier would need frequent replacement. Looking for some clarification.
 
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#2
It could probably handle intermittent duty at around 45 watts, but if it's going to be a ham machine, or a repeater with constant use, backing it down to 25-30 watts wouldn't hurt it.

And yes, the 12db antenna will effect your ERP. Does your license mention anything about ERP or just transmitter power in general?
 
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#3
You really need to pay attention to both the transmitter power out AND the EPR authorizations on the license. What does the license say? A 12 db gain antenna? Well, assume 25 watts out, and 2 db feedline loss, you'd have a 250 watt ERP. 25 watts applied directly to the 12 db gain antenna without feedline loss would be about 400 watts ERP, not 35. That repeater is rated at 25 watts continuous duty, and 45-50 watts out for a 50% duty cycle. With that much antenna gain, it can be real easy to run afoul of ERP limitations on a license.
 
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#4
I'd say the use the repeater gets is as much as a suburban/rural(ish) type of police department or maybe even a school bus company. Has its peak moments, but it's not constant radio traffic like a busy Friday night in a descent size city.

I just looked up the license via FCC online database and there is no Maximum ERP listed.
Output power listed is 30. The antenna was just hooked up to a watt meter and it registered at 40 watts, whatever that may mean in terms to what we're discussing. With the GR1225 repeater the meter registered roughly 22-25 watts when it was activated.
 
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#5
WSGSD said:
I'd say the use the repeater gets is as much as a suburban/rural(ish) type of police department or maybe even a school bus company. Has its peak moments, but it's not constant radio traffic like a busy Friday night in a descent size city.

I just looked up the license via FCC online database and there is no Maximum ERP listed.
Output power listed is 30. The antenna was just hooked up to a watt meter and it registered at 40 watts, whatever that may mean in terms to what we're discussing. With the GR1225 repeater the meter registered roughly 22-25 watts when it was activated.
Sometimes the ERP is listed on the coordination paperwork filed at the time of the license application, but it doesn't end up on the actual license.

Your next paragraph about the antenna registering at 40 watts makes no sense whatsoever. In answer to your original question, I'd run it at a level that it's happy under continuous duty.
 
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#6
Regarding the 40 watts....I wasn't paying close attention when it was done, but a tech hooked the antenna up to a watt meter to ensure it was operating to standards. When this was done, I think it was connected to an ICOM mobile in his truck. The radio was keyed up and the meter read a solid 40 watts. I saw the needle in person. The tech said the antenna was just fine. The original FCC license dates back to 1982 and I'd have to do some serious digging to see if the original paperwork exists to see if a ERP was listed. In the meantime I may have the vendor give the repeater's wattage a slight increase so it's closer to the licensed 30.

In regards to your suggestion of running it at whatever it's happy at, how would I know if it wasn't happy where the programming should be knocked back?
 
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#7
WSGSD said:
Regarding the 40 watts....I wasn't paying close attention when it was done, but a tech hooked the antenna up to a watt meter to ensure it was operating to standards. When this was done, I think it was connected to an ICOM mobile in his truck.
Ok. That 40 watts has nothing to do with the antenna, but if he checked reflected power, he would have been looking for less than 10% reflected power. 40 watts forward, 4 watts reflected would be acceptable. What you missed was the reflected power reading, which is what matters when it's the antenna that's being tested.

WSGSD said:
In regards to your suggestion of running it at whatever it's happy at, how would I know if it wasn't happy where the programming should be knocked back?
By "happy", I mean it's rated continuous duty power, as specified in the manual. That's where it doesn't fail, or run excessively hot. Trying to squeeze an extra 20% of power out of it could shorten it's life by 80%, and you'd never notice an increase in range. Have your tech set it to the level required for continuous duty operation, and the chances of it failing because of over use are greatly diminished.
 
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#8
Thanks for the info. The radio vendor wasn't overly proactive regarding my idea on upping the wattage. I've used info I've obtained from this forum in discussions with my radio vendor & they look at me odd like, "where did you learn about that?" The end result has always been positive. I'll have to take his word on what the continuous duty setting is or I'll have to hunt for the manual. He'll be coming back to finish the job, I'll discuss the antenna and repeater and hope for the best.
 
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