Electronics > Repair
INSTEK spectrum analyzer GSP-827 -6 dBm down than the real value
G4JMO:
Thanks Fraser. Yes, you're absolutely right, 2GHz is making things hard for myself. The reason for the choice of frequency is that I'm without a sig gen that goes below this at the moment. My Giga-tronics 6100 only goes down to 2GHz. Anyway, all seems good. I guess you're right, it could have been a poor interstage capacitor joint...who knows!
Regards
Andrew
G4JMO:
...having warmed up for an hour, the calibration signal is now showing 0.6dB error :)
G4JMO:
A further development!
I left the unit running for several hours. On checking the -30dBm 100MHz internal calibration level, it now showed -36dBm !! :palm:
I tuned the unit off and immediately back on, switched the cal signal on and.......-30.6dBm!
I should have checked the external 2GHz signal too but I switched it off too quickly!
I'll leave it running again and see if it changes and if it does, check internal and external sources.
Fraser:
Please advise what equipment you are using to RF measure levels.
Grateful if you will confirm that you have tested the level of the calibration output port and ensured that it is stable in amplitude.
Maybe a quick restart from scratch.
Choose a confirmed accurate output signal source. Test the spectrum analyser by viewing the RF source and noting the measured level on different attenuator and IF filter settings. Leave the unit to warm up over several hours and repeat tests exactly as before (including the level of RF source). Compare notes. If an offset is present, switch off SA, restart it and carry out tests again. Note readings Now switch off SA and leave it to cool down for several hours. Switch on and repeat tests.
Using such a test protocol will give us a firm baseline against which to offer advice.
As a side note, most SA's carry out a power on self test diagnostic that also checks the signal path and levels in the IF chain. Not sure whether you unit does this ?
Aurora
G4JMO:
There is no calibration output port to be able to externally verify the unit's calibration signal level.
External source from my Gigatronics 6100 is being validated on an HP8565A spectrum analyzer.
Since my last post 40 mins ago and restarting the unit, the internal calibration is unchanged at -30.5dBm. The unit has been on continuously for at least 3 hours now, apart from the few seconds to restart it.
I've just realised in my previous tests I could have stolen the 100MHz calibration signal from my 8565 instead of using the 2GHz source. Oh well!
If I don't see the reduction again in the next 2 hours, I'll let it cool off for a few hours and then restart from cold and log the amplitude of an external cal signal from my 8565A, which I know is stable, removing one of the variables.
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