Calibration drift?

Discussion in 'Wireless & RF Design' started by magneto259, May 15, 2009.

  1. magneto259

    Thread Starter New Member

    May 15, 2009
    5
    0
    Hello all I'm having a problem at work we can't figure out. I build and just recently started performance testing our antennas. We have a indoor antenna range for testing with our equipment inside of it. Heres the problem thats been getting worse in the last few weeks. When we shoot a horn to horn calibration with our low band horns and begin testing we get data that claims some of our antennas are below the spec at 500 mhz but when I test previously known good antennas it will sometimes give us a failed test. After a few runs I can run a new calibration and see that the gain at 500 mhz has dropped a few db from the previous baseline calibration. Currently we don't run a amplifier off of our pna that generates the signal because removing the amp cured our drifting problem for a few weeks. After the problems started again we tried the amp again to boost the signal on the receiving end as well as configuring it to boost up the source horn. But it didn't help the problem. We have checked cabling, attenuators and just about anything else in the signal path. Our current signal generator is a Agilent E8362B and we use Orbit antenna software to get our performance data. Oh and yes I do let the equipment warm up for about 2 hours before and calibrations or testing. But the drifting ocurrs anyway. Any suggestions or help would be graciously appreciated. Thanks in advance!!!!
     
  2. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    What equipment do you use at the receiving end?
     
  3. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Can you verify that the source is not the cause of the drift? Maybe you saw the drift before when the amplifier was on the source side because the drift was also amplified.
     
  4. magneto259

    Thread Starter New Member

    May 15, 2009
    5
    0
    In our current setup we use a horn to receive then it goes to the pna which our pc is hooked up to capture the data for calibrations. We just remove the receive horn and put up a antenna holding fixture to test the individual antennas. Since we have been fooling around with it we have used the amplifier to boost the receiving signal back to the pna. This is the setup we have always used til the drifting occured. It went away when the amp was cut out of the equation. But now it does it either way.

    Do you mean source as in the signal generator? If so the only way i currently know how to the quick and dirty way is to just swap out the pna since it is what generates our signal. If you mean the horn itself I could try to find another one to use. They are alittle hard to find around the shop.

    Thanks for the responses!
     
  5. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    Sorry, I didn't know the E8362B was an analyser. I just looked at it on the web.
     
  6. magneto259

    Thread Starter New Member

    May 15, 2009
    5
    0
    No sweat man. I'm starting to think that maybe the signal generator is going bad or something there abouts.

    Thanks for the reply.
     
  7. Tesla23

    Active Member

    May 10, 2009
    318
    67
    If you have time, run a test over the weekend but remove the range, just run a cable (and a few attenuators) between the antenna test points. Before you do this, measure the attenuation of each section. If this drifts, (and a few dB is a lot), then re-measure the attenuation of each section to try to localise the fault.

    If the hard-wired test passes then the problem may be in the range (or test antennas).
     
  8. magneto259

    Thread Starter New Member

    May 15, 2009
    5
    0
    Well I won't be able to till Monday morning i'm off til then. But i'll give it a shot. Thanks for the reply!
     
  9. magneto259

    Thread Starter New Member

    May 15, 2009
    5
    0
    Hello all I got to work and we are going to try to swap out our source horn with a freshly calibrated one and see what happens. I'll post back the results. Thanks again everyone!
     
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