hi all,
during the calibration of the 8481D power sensor using the attenuator and the 436A power meter; the reference of 1uW could not be adjusted using the "cal adjust" knob on the power meter, it read 0.5 uW max. the power meter is fine, since i checked it using a calibrated power sensor and it does give 1uW reference fine.
the question is: is it possible to adjust the power sensor or at least debug it to see where to find the fault? the manual for the sensor does not give in depth maintenance info. where can i find replacement parts if i was to do the dirty work to repair the sensor assuming parts are available.
too long but, any help or resources is appreciated.
thanks in advance :-D
Assalamu 'Alaikum,
First of all, I won't open it up unless your lab as the capablities to repair sensors. Secondly, I'll try connecting it to a sig gen to see if it even reads. Sounds like to me it could be blown. Hope this helps!
Allahu Akbar Barakallah :-D
wa alaikum alsalam,
well it reads fine but the readings are out of range. the problem is that the reference 1uW is reading 0.5 uW so everything is out. the maintenance manual with the sensor is weak, no details. do you have detailed maintenance for it ? well i dont think it i'll bother fixing it if i dont have detailed resource with component pn and specs, cuz they have customized FETs for the auto zero portion of its circuit, i dont think i'll be able to replace those. I just feel that there should be something to adjust it somehow, but there isnt. too bad.
thanks bro :-D
Hold on, you mean 1mW ref, right? :? :?
i think that is a typo. Your reference with a sensor should be @ 1mW.
8481D-slap it on your meter, set cal factor% knob to the ref cal factor on the sensor, usually 98/99/100 or so. Punch the zero button and while the zero led is lit you should have +/- 1 or 2 counts and the nW indicator will also be lit. Push in your power ref button and adjust the cal adj pot for a reading of 1.000 uW.
If it doesn't work odds are the cartridge is blown, replace it or the whole bulkhead.
IMO
No, it is 1 uW on the 8481D. It is the newer version of the 8484A, low power sensor (-70 dBm to -20 dBm).
Someone at some point over powered the sensor, possibly by not calibrating with the 30 dB attenuator attached. If so, you use to be able to order and replace the bulkhead (semiconductor device in the front end). Now, the cost of the bulkhead probably exceeds the cost of a good, used replacement. If you company has issues with ordering WHOLE equipment, ask the vendor to call it a "8481D repair kit" on the purchase order.
BUT - check the reference attenuator first. Many morons think this precision 50 MHz reference attenuator is a handy way of measuring their 10 watt radio output - 10 watts - 30 dB equals 10 mW right? I believe this attenuator is suppose to be 30 +/- 0.015 dB. Sounds like yours may be reading 33 dB or so.
well the reference is 1uW because you have to attach a 30dB attenuator that comes with the 8481D to reduce the power coming into it, since the range is -70 dBm to -20 dBm ---> with the attenuator it becomes -40 dBm to +10 dBm, were the reference becomes 1uW for the sensor.
the attenuator is within limits. I dont think the bulkhead is bad, because the sensor gives me output on all frequency ranges, but its not within specs. I am going to try and change the autozero circuit and see what happens.
So what happened? :?
well, we couldn't do much to fix it. the bulk head is fine, but the components that the sensor is made of is all costumized for its circuitry to get accurate measurements and cannot be replaced easily.
when all cards failed, I just oredred a new pair of sensors :wink:
my advice is, if the bulk head is bad, then just replace it and sensor will work. other than that dont worry about it, its not worth fixing.
here is the key to checking power meters if you suspect a PM fault. hook up the power meter calibrator! power sensors are blown up as much by techs troubleshooting Power meters as they are by users. hook up a sensor to the ref out with the ref on and hit the zero button and its bye bye to around 1300 dollars. this is also true with the low power sensors 8481d, 8484 that are standardized with out the ref attenuator installed.