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Motorola Quantar PA output question

Posted: Thu May 12, 2011 7:15 pm
by fixanythingman72
I just got a UHF R2 110watt Quantar. We are co-ordinated for 100W, we heard that when these PAs are run near full output they can be prone to failure. Does anyone have any experience with this? Should we run at 100w output?

Re: Motorola Quantar PA output question

Posted: Fri May 13, 2011 12:06 pm
by N4DES
I have Quantars in 800 that run a constant data (control channel) 24/7/365 at 100 watts and they rarely fail.
They are a workhorse and probably rated for 3x what they actually deliver. I wouldn't worry about your UHF at all at 100 watts.

If your really concerned you can turn it down to 80 or 90 watts. No one in the field will see a difference in performance.

Re: Motorola Quantar PA output question

Posted: Fri May 13, 2011 12:55 pm
by Astro Spectra
Don't forget to factor your antenna gain and feeder loss in setting your transmitter power to meet the EIRP limit.

Re: Motorola Quantar PA output question

Posted: Fri May 13, 2011 12:57 pm
by escomm
Just make sure you don't have the early model power supplies with the crap transistors or the silver chassis that flakes all over the damn place.

Re: Motorola Quantar PA output question

Posted: Fri May 13, 2011 4:12 pm
by Bill_G
My experience is the UHF run and run for years at full power, but fail if run greater than 3db down (half).

Re: Motorola Quantar PA output question

Posted: Fri May 13, 2011 6:22 pm
by techtonics
I have seen quantars at 120 watts with no issues at all

Re: Motorola Quantar PA output question

Posted: Mon May 16, 2011 9:19 am
by fineshot1
I guess i'm gonna be the one to inject clouds in the coffee.

We have 6 UHF TBand sites to cover our county(Moto SZ). Each site has 12 UHF R4 Quantars.

Total of 72 R4 Quantars.

On average we replace about 1 or 2 PA's a month and they are all set at about or just below 100W output.

Maybe its a TBand thing, not sure.

We also have some UHF R3 Quantars but they are so new I can't yet compare as we have had no PA's fail yet.

We also have some VHF R2 Quantars and they have been around for about 6 years now with no failures at all.

Re: Motorola Quantar PA output question

Posted: Tue May 17, 2011 6:14 am
by 515
A system I had been involved with has a total of 12 UHF R1 Quantars all transmitting the Astro Modem data continuously. They are the 125 watt PA's, but the power was set around 30 watts on these links to reduce the amount of heat generated in the comm shelters. As far as I know, there have been no PA failures on those UHF links that have been in service for over 2 years now. They are all in climate controlled comm shelters, for what that's worth. I'm sure if those PA's were dropping like flies, I would have heard about it.

I've also heard from someone involved in a large statewide 800 MHz P25 system that most of their PA failures were on the voice channels, as opposed to the control channels which transmit 24/7. On this particular system, they don't normally rotate the control channels, so those PA's transmit for years at a time. It might have something to do with how the control channel PA just comes up to temp and stays there, where the voice channel PA's are constantly heat cycling...

Re: Motorola Quantar PA output question

Posted: Tue May 17, 2011 12:47 pm
by d119
fineshot1 wrote:I guess i'm gonna be the one to inject clouds in the coffee.

We have 6 UHF TBand sites to cover our county(Moto SZ). Each site has 12 UHF R4 Quantars.

Total of 72 R4 Quantars.

On average we replace about 1 or 2 PA's a month and they are all set at about or just below 100W output.

Maybe its a TBand thing, not sure.

We also have some UHF R3 Quantars but they are so new I can't yet compare as we have had no PA's fail yet.

We also have some VHF R2 Quantars and they have been around for about 6 years now with no failures at all.


It may just be a T-Band thing. I maintain several Quantars in different bands - VHF, UHF, UHF-T and 800MHz. I replace PA's on the T-Band units FAR more frequently than any other.