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Quantro low power from FPA

Posted: Wed Sep 23, 2009 4:39 pm
by dacndar
Hello All,

I have a 900 MHZ Quantro with TTF1242B DPA and TTF1212B FPA. This combo is rated at 150 watts. I am only getting 80 watts out of the FPA. When I go into the power output/wattmeter calibration in CPS I get a "overdrive message" and PA fail if I try to increase the power above 100 watts. I then check the power output of the FPA and see that I am getting 60 watts minimum out. In the process of playing around I decided to disconnect the FPA forward power sensor (green wire). When I do this I get almost 150 watts out of the FPA so I think there may be a problem in the power control circuit? One other thing that may or may not have any bearing on this issue. I notice the reflected power is .196 volts as observed on the CPS metering screen. This voltage is the same even if I disconnect the reverse power sensor or I ground the reverse power input to the Quantro. And when I use an external power supply to see if the voltage would track, it only toggles between .196 and 0 volts, unlike the forward power input that does track an external voltage.

If I were to use only the DPA anyone know of a way to trick the Q into thinking the FPA is still connected? You can do this with the MSF5000 by supplying a voltage equivalent to what the forward power sensor would put out at normal power. I have tried this on the Q but doesn't seem to work.

Any input would be appreciated.


Re: Quantro low power from FPA

Posted: Wed Sep 23, 2009 10:50 pm
by W6JK
The Nucleus II rigs I've been working on have a watt meter calibration process you have to go through before you can properly set the output power. It could be that something like what you're seeing could result if this step is skipped. It could also be that your gear is completely different. I never seen one of those. :)


Re: Quantro low power from FPA

Posted: Sat Oct 31, 2009 5:20 pm
by com501
These units are VERY sensitive to reflected power. What is your connection from the FPA to your load? It should be minimum 1/2" superflex. We have had issues with the smaller cables providing just enough power issues that the units would not calibrate correctly.

Secondly, I am assuming you are running a dual isolator on the output that is tuned correctly and has a properly sized load attached to handle the full tx output.
What would be the harm in just running the unit with the power control disabled? Are you using it in the ham band?

Bob emailed me, and I will dig out the service bulletins and do a search on MOL next week and see what I can come up with.

Re: Quantro low power from FPA

Posted: Sat Oct 31, 2009 9:36 pm
by dacndar
Thanks for the response com501. On the bench, the output cable that is integral to the FPA was connected to a wattmeter and 200 watt load load was on other side of wattmeter when I calibrated the power output. Yes, also dual output tuned circulator and appropriate load. Even tried calibrating without circulator. In the metering screen of the RSS the reverse power displays at .196 volts all the time, even with the reverse power lead disconnected or when not in transmit. I suspect that this is what is causing the drive to be reduced to the DPA and thus not achieving full power out of the FPA. Is the A/D conversion for forward/reverse power done in the exciter or the IPA? I even used an external power supply to the reverse power input to see if the voltage would track. It does not. At around .5 volts input the the value jumps to .306 but these are the only two values I ever see for reverse power voltage value. On the other hand the forward power input does track an external voltage input. I suspect a bad A/D or buffer amp but I don't have another exciter to prove this theory.

I have no problem disabling the power control. This is for ham band. I just haven't figured out how to do it. I can't find anywhere in the software to do this except in PA test and that is only temporary. But even in PA test I cant get full power unless I disconnect the forward power lead. Then I get 165 watts. If you know how to disable power control in normal operation that would be the ticket.


Re: Quantro low power from FPA

Posted: Sat Oct 31, 2009 10:02 pm
by com501
What is the exact model number of your unit, if you have it, and I will pull the appropriate manuals off of MOL and see what I can find for you.

If your email can accept a fairly large attachment (50-60megs) I will send you the pdf of the manual if I can get it.

If not, I can get it to Bob and he can get it to you that way.

Re: Quantro low power from FPA

Posted: Sun Nov 01, 2009 8:11 am
by dacndar
I should be able to receive large files. The model number is T5365A. That is the only info on the back of the frame other than serial number. The RSS does not display model only serial number AFAIK.