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QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

This forum is for discussions regarding System Infrastructure and Related Equipment. This includes but is not limited to repeaters, base stations, consoles, voters, Voice over IP, system design and implementation, and other related topics.

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alexreyes
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QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby alexreyes » Tue Jan 31, 2012 3:30 am

I recently bought a 2nd hand Quantar VHF 125W R2 from a friend. It was tuned down to 20W upon looking at the codeplug via RSS. I tried to set it up @100W but when I keyed the repeater after re setting the configuration, PA Fail lights up. I reduced the power output to 50W and the same thing happen. I thought of trying it at 40W and so I did. It worked fine and well at 40W. Anyway I programmed the repeater at 146.xxxTX and 152.000RX. Could someone assist and help me in making it work at least at the 100W mark or maybe 125W as the unit is the 125W variant? Any help/advise will be greatly appreciated. Thanks and more power...

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d119
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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby d119 » Tue Jan 31, 2012 9:31 am

Does the station have an AC HIGH or AC LOW power supply in it? It may be that your power supply cannot give the PA what it needs if you have a mismatch of PA and power supply...

You need to go into the RSS and do a "Validate Configuration" and see if the validation passes, then tell us what you've really got in there.

WB6DGN
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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby WB6DGN » Wed Feb 01, 2012 6:52 pm

A 125w, 900 Mc. VHF Quantar???

desperado
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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby desperado » Sun Feb 05, 2012 6:10 pm

It almost sounds like you cooked the circulator or the internal SWR sensor. Turning these 125 watt PA's down to less than half their total rated power level is asking for trouble.
For one thing, the input drive I believe remains constant on the exciter, meaning that the PA needs to burn off the power as heat in the PA. Turn the thing up to normal operating spec and see if it will work correctly. If it does, quit being cheap and if you need a low power unit, either buy a low power unit, or buy a proper inline attenuator and connect it up. Bird sells any number of attenuators that are 3,6,9..... db and rated clear up into the thousands of watts. Then you can run the station at it's accepted power level and have the needed power going to the antenna.
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xmo
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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby xmo » Sun Feb 05, 2012 7:19 pm

The power output specification for the 125 Watt Quantar is 25 to 125 Watts, so setting it to any value within that range is running the station at its accepted power level.

That said, you could be right about there being a circulator or sensor issue - also it would pay to be sure that the connected load is 50 ohms. If the station is running into a less than optimum duplexer or antenna or the wattmeter being used or any of the cables have issues - then the station may simply be protecting itself.

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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby alexreyes » Wed Feb 22, 2012 6:48 am

Thanks for all your advises. I appreciate very much. Anyway, I attached a bird power meter on the TX line and glad that it kicks solid 125 watts at 30 Watts TX Power Out programmed at the channel information Advanced Tab. Basing from the Power Output reflected at the Bird Power Meter, I surmised that the 30 watts typed at the Transmit Power Out box/slot in the Channel Information Advanced tab is only the "driver" as my friend suggested. That is why whenever I program it at 50 Watts and up - the PA FAIL lights up - am I right to say its because it "overdrives"? How can I see to it that the real power output(125 Watts or any other value) be reflected at the Transmit Power Out box/slot in the Channel Information Advanced Tab? Last question if I may is the Exiter/PA Cooling Fans/Blower. Does it have settings? i.e. automatic/continous/on/off? I haven't seen it working unlike the Power Supply cooling fan that works well upon Power on. Thank you again.

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escomm
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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby escomm » Tue Feb 28, 2012 8:17 pm

When was the last time you ran a PA alignment on the station?

alexreyes
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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby alexreyes » Fri Mar 02, 2012 4:56 am

sir escomm I havent done any PA alignment yet. the reason why is that I dont have the Quantar service manual. I am afraid I might screw it up. I am planning to do it anyway. but first I have to get as much info as many as possible on how to run a PA alignment. Can you please share what you know? Also on the PA/Exciter cooling fan if you have any idea. thank you.

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escomm
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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby escomm » Fri Mar 02, 2012 8:50 am

Don't think you need the manual to calibrate the PA, just a watt meter and the RSS, everything should be able to be done from the service screen. The procedure is detailed within the RSS. Has been a while but IIRC you hit the button to initiate the calibration, record the reading from the watt meter in the RSS, repeat a couple of times until the station is putting out the proper power. In any event I think the bottom line is that everything you need is in the RSS.

alexreyes
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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby alexreyes » Mon Mar 05, 2012 5:17 am

copy sir escomm. thank you very much. I'll let you know once I am done with the PA alignment. My last question deals with the PA/Exciter cooling fans. Do they have setting adjustment? or can you set them at say: AUTOMATIC, CONTINUOUS, ON or OFF? My friend says it is thermo-controlled, which means that it will only be powered on once it has reached the programmed heat signature. I haven't tried long modulation aboard my Quantar. I am just wondering why up to now I haven't seen them work unlike the non Onan power supply cooling fan that powers on upon main power switch on. Any idea or suggestion or advise pls?

Will
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Re: QUANTAR VHF 125W PA FAIL AT 50W BUT OK AT 40W

Postby Will » Fri Apr 13, 2012 6:37 pm

Yes the fan in the Onan power supply is temperature controlled by a TD5 integrated temperature sensor. Comes on at about 100 degrees heatsink temperature. The fan also has a tachometer output that the Station Control looks at to see if the fan is running.
There have been a lot of failures with the fan in some power supplies. Check in Important Quantar part numbers.


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