Agilent PXA N9030A 26.5GHz SA repair and flattness calibration issues - Page 1
Forum section: electronics / testgear

author: GHzLab00
author_rank: Newbie
timestamp: June 26, 2025, 11:22:08 pm
content: Hello everyone, I'm new here.Let me introduce myself a bit before starting with my problem description:I'm an engineering student and my main studies focuses on analog, RF and power electronics. I'm an electronic test equipment enthusiast since 2015 when I got my first instruments as a present from a professor. They were an hp 181A oscilloscope and a Wavetek 185 function generator and they both had issues. I needed them to build and debug a solid-state Tesla coil I was planning to play with at the time, and the only way was to fix them beforehand. I managed to do it in my summer school pause with the help of the precious service manual informations and a cheap hardware store multimeter. That was a very good training experience that made me fall in love with the test equipment world. In the following years I started searching and exchanging for newer and better-quality test equipment to build up my personal laboratory. And here comes the present, where the newer test equipment’s, previously useful, service manuals does not exist anymore, and everything has lots of firmware and software abstraction levels. That is not what I’m familiar with!1. The bargainRecently I had a nice score from a local dealer that did make a big step-up for my lab: an Agilent N9030A 26.5GHz spectrum analyzer that I got broken for “cheap”. The problem was in the RF path since the spectrum was fine from LF up to 3GHz but passed the low band the signal was drowned in the noise.2. The testsInjecting a signal directly after the preselector filter did make some larger peaks appear on the screen but, obviously, they had the incorrect magnitude, and many spectral images were present. Excluding other parts like the high-low band switch or the attenuators, that they tested fine by themselves, the only possible culprit was the preselector filter. Unlike other older hp/Agilent SA the YTF is a standalone almost passive (just the driving coil and the heater) module without any converting stage like the famous RYTHM modules that are well known to age badly. Knowing that this part was almost impossible to fix and probably also unobtanium for a reasonable price, my first idea was to replace it with another YTF I had laying around modifying the driving coil circuit.3. The findJust out of curiosity, some days later I did try to measure the original preselector response with my VNA to check how far off the center frequency was and that’s where I discovered that the driving coil was open. I recognised that the coil assembly was very similar (actually, they’re the same) to the one of the previously mentioned RYTHM modules and, fortunately, I had one with a dead converter section laying around. I managed to swap them as fast as possible as not to introduce any dust or debris inside because I didn’t have a clean room on hand!4. Some hopeI tested the filter, and voilà, it was working again, I was very excited, so I tried to mount it back on the spectrum analyzer mainframe and… well, in the high band I had a huge power measurement error with respect to the actual input signal. I did run the YTF alignment process, but I recovered only a couple of dBs at best; that was strange since the signal at 15GHz had a measured loss that was inside the service manual specs (6.5dB).5. The patchReading the manual, I discovered that there was a special function in the spectrum analyzer that let you introduce a gain correction value for antenna measurements. This function needed only a properly formatted CSV file with a look up table of some frequency-loss points and with that it was possible to change the flatness response. My idea was to perform a level calibration using a sweep generator, a power splitter and a power sensor like it is done in real laboratories and apply this correction layer.6. The calibrationI wrote an automated program on Matlab that let you collect the measurements from the N9030A spectrum analyzer and the 8485A+E4419B power meter increasing the frequency of the sweep generator at discrete steps of 50MHz. Since the SA is connected to one port of the splitter and the power sensor is connected to the other one, I had that the total measurement error between the two ports was just the difference of the readings in dBm (neglecting mismatches and splitter ports power balance that should be way lower than SA specs).7. The resultsFrom my measurements I got a plot of the losses response over frequency that are attached below and the beloved CSV file that let me recover, at least partially, the operation of the instrument. I imported the file into the SA and the results are somewhat good (check the attached picture). The drawbacks of this methods are:- The constats applies only in the spectrum view and some measurements are not accounted for- Every time I turn the analyzer off and on, I must recall the file or apply a user defined presetTherefore, this is not the optimal solution and so I searched for a way to make it work. I tried asking to some calibration laboratories in the area if they had the knowledge or capabilities to perform such adjustments but without any luck. Then I tried asking the manufacturer, but prices were quite high and nevertheless they did not provide their services to private customers like me. The original calibration software exists, it is under license, but it would be somewhat affordable If it didn’t required tons of specific instrument models that I don’t possess to perform the adjustment (and the private customer problem still holds).8. My doubtsDigging in the hard disk content I think I found the CAL constant files in the "AlignDataStorage" directory, and I've tried to understand its content without any luck (It's a windows SQL server database file if I understand it correctly). My questions are: does anyone knows how these database file works? If it’s possible in any way to access the constants and change them in order to get the proper level measurements? Is there another way to change the flatness calibration constants? I need to account for the YTF centering in any way or the two points self-alignment is sufficient?Any other suggestions or help will be very much appreciated!Here are the alignement files I fount in my unit if you want to take a look:https://drive.google.com/drive/folders/1CziHI9hg0vGIToOqFds12eHA9U9xerLI?usp=sharingThank you very much and Happy measurements!Edit: I had to fix image dimensions and add the files link.