Electronics > Repair

Cal Error in HP E4418B

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I am fairly new to the HP E4418B power meter + sensor business.
I repaired one E4418B that didn't show anything on the display, so far so good.
I purchased a used HP 8484A power sensor with a cable which is supposedly good (but not tested by the seller, good source he claims).

Now when I connect the HP 8484A power sensor to the power meter it detect is and measures around -70dBm. I can zero but I cannot calibrate it, the power meter gives Cal Error when I try.

Now, when I repaired the E4418B I removed the backup RAM battery so it defaulted to E4418A, and I am still waiting on a USB-GPIO adaptor to correct this.
When I turn on the reference source the power meter measures -37dBm, so it's definitely doing something. I measured the S11 roughly and it shows below -10dB return loss at least up to 3GHz. I have also measured the reference source on my scope and sure enough it gives 50MHz with stable output.

I don't have another power meter and I don't have another power sensor to swap out so I am not sure which is broken. Is there anything else I can try to narrow down where the fault lies?


The 8484A only measures up to -20 dBm, so it can't be calibrated by connecting it directly to the 0 dBm reference on the power meter. The sensor would have originally been sold with an 11708A 30 dB reference attenuator, which should be used for the calibration.

Here's the operating manual for more detail: https://www.keysight.com/gb/en/assets/9018-05414/user-manuals/9018-05414.pdf

Sorry, I didn't mention that I do in fact have a HP 11708A between the power meter and the calibration port.

Ahh OK.

Depending on how rough your S11 measurement was, that might indicate a problem with the sensor if it's not much below -10 dB, power sensors generally should have very good return loss. My 8484A measures below -30 dB up to around 6 GHz, and below -20 dB to 9 GHz. I have a blown 8482A and that measures around -10 to -15 dB.

Stepping back a bit on this, there are really 4 things I think that can cause this issue:

* 8484A sensor
* 11708A attenuator
* E4418B reference output
* E4418B meter itself
Out of all of these, the most likely is that the 8484A sensor itself is actually broken - I have generally seen that unless you pay a couple of hundred dollars for the sensor and buy from someone who says it is working and offers a refund then you're going to be buying a dead sensor.

Now, that said, the manual for the 8481A does provide a very basic way for you to determine if it is the meter or the sensor - This will at least help you get in the rough area for where things might be wrong.

When you measured the reference output, as long as it was somewhere near the 50MHz 0dBm then the calibration process should work. Measuring the 11708A might be harder given what you have but if you can measure S11 then you should have the equipment available to confirm that the attenuator is 20dB near 50MHz, again as long as it is somewhere near that then the process should work even if the actual numbers are highly uncertain.



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