My 8924C Radio Test Set must have sensed the presence of the 8920B downstairs. It's gone in a huff and won't turn on :-(
4 Philips and 32 Torx fasteners later and I've got the PSU out. Nothing on the +15V standby output so a definite PSU fault.

It was working fine last time I used it. I'm guessing a start-up resistor has gone high resistance. Another 17 screws and I'll have the lid off the PSU.

Updates as it happens.

Good evening gentlemen,

Thank you all for your contributions to this thread, and for your encouragements!

I already spend quite some time digging in the cal data structure. I think I begin to understand how they are used by the equipment, at least for part of them, most in the Rx/SA path. As you may guess, there is still a lot of work to do: this began this as a rainy winter project, continued as a shity spring projet but that was put on hold by a sunny summer!!! I'll continue this work when time permits, that is not in the short term...

With regard to spectrum analyzer calibration and measurement accuracy, as you know, HP8920 architecture is modular: i.e. each module (Input atten, input section, 1st miser, receiver, measurement, SA, etc.) are I beleived all calibrated separatelly and their calibration data is brought into the equipment either using a memory card (as confirmed here by some of you) or for some assemblies by some onboard eeprom.

If this assumption is correct, Spectrum Analyzer module is only one piece of the puzzle, and at the end of the day, overall measurement accuracy will depend on cal accuracy of all modules in the analyzer path (Atten/RF Input/1st mixer/ Part of Receiver). If any module calibration is not right, the result will not be right and tweaking SA module cal may not be the right thing to do... I still need to think a bit more about how to manage this the best...

Regards,

Jeff

ik0ibi added folder HP8920 CRT module manuals

Hi CrazyFin, Your asks are welcome !

Using the Jeff's software, I attached two "full calibration data" (not only from s.a.)
from two different 8920 sets of mine,?just some post before in this thread.
Let Jeff decide if can be useful open a Folder in Files section,
dedicated only to calibration data dump.

My last post about epson card calibration data,?
is a sort of advice,
because I think that is very difficult that,?
from 1990 to our days,?
calibration card owner? cyclically changed batteries,
and if yes using the right procedure.
Looking at my pics, error 85 means unformatted card,
battery was low and all data lost, even card format.

There is no calibration service for 8920 in Italy, neither from agilent/keysight.
Shipping and custom charges to send Amtronix can be even more expensive then Sweden HP.

The only hope we have is the Jeff's work !

Ciao !
Angelo

Hi @Angelo / ik0ibi

I did not fully understand if you attached the cal data file in your post or into the files section?

@Jeff and all others looking on how to calibrate the spectrum analyzer module. Here is an older post in HP Agilent Keysight group here at groups.io that confirms the fact that the SA module was built buy a third party supplier and that they supplied the module with an EPSON card containing the cal factors for each SA module:
/g/HP-Agilent-Keysight-equipment/message/4886

I think the original software that was able to do full calibration (and which was used by HP back in time) was running on HP Rocky Mountain Basic?
I do now that Amtronix does calibration of the spectrum analyzer modules but I have not found any similar firm here in Europe that can do it.?

I contacted HP / Agilent / Keysight here in Stockholm, Sweden and they wanted 1200 USD for a full calibration that would fix the SA module as well... :-(

Hi Finn, Hi Jeff,
this in attachment is an Epson card, that I bought some times ago from an honest vendor on Ebay USA.
Should contain S.A. calibration data to download in 8920.
Of course serial number does not match my s.a. card, but data could be closer than.
This card type is a 128Kbyte RAM card, so is absolutely necessary to keep the battery fresh.
Predictably, the battery was low and data lost...
Thanks God, the vendor was honest, understood the problem and offered a prompt remboursement.
Vy"73 de ik0ibi
Angelo
Rome, Italy?
??

Roberto Barrios has very good page where he has documented his LCD-conversion on his HP 8920A:

@Jeff:

First of all: Thank you very much for your hard work on creating that program that can download the calibration factors for the spectrum analyzer module in HP 8920A:s!!
I currently do not own a HP 8920A but I had one that I (unfortunately) sold in August previous year. I will hopefully be able to find one to buy within few months and the I will contribute here on this forum with the cal factors from my unit.

It had the exact same problem with spectrum analyzer being approx 3 to 4 dB too low and I did A LOT of research on how to calibrate the spectrum analyzer module in the HP 8920A.
I was in contact with Amtronix and many other specialists on the HP 8920A and they all confirmed that the spectrum analyzer module in HP 8920A was made by a third party supplier and requires a special program to calibrate. Calibration factors are then exported to the EPSON card and then uploaded to the spectrum analyzer module.

So when you buy a spectrum analyzer module it SHOULD normally come with an EPSON card that contains its calibration factors. Look for example at Amtronix webpage where you get a spectrum analyzer with its corresponding calibration data on an EPSON card:


I just wish that some ex-HP employee would be able to shed some light on all the different calibration factors and the calibration procedure for the spectrum analyzer module in HP 8920A. Anyway, I really think that with your cool program Jeff, we in the community now will be able to start figuring out how to calibrate the spectrum analyzer modules ourselves.

I believe you all have seen the Component Level Schematics that can be found in the files section? If not, I have downloaded my CLIP for the 8920-series from this link


I am still looking to buy a HP 8920A but I haven't yet found one with the options that I am looking for (I need for example one with 100W input as one of the options and I do not want one with the electrical input assembly since that will make the low frequency range to be 30MHz instead of 400kHz which is for the mechanical input assembly).

I am also hosting it on my website at ? case sensitive.

Hi,

Not really.

Cal data is stored in EEPROM and this program is only there to get to this cal data (if you are curious about how it looks...).

If I'm correct Lithium battery on 8920A is only there for RTC and battery backuped RAM that is used to save equipment user settings, user IBASIC programs etc.

Regards,

Jeff.

RFI-EMI-GUY added folder HP8920 Instructional Video

I got into this thread late. Is this program something useful for backing up my 8920B before replacing the lithium Ion memory battery?

just happened to be looking at the CLIP ....there are only two MMIC's in that that like an MSA-0486 IIRC.

Would just replace both and see what happens.

The 8920? CLIP may be in the files area ....at least it used to be

Wow, that really is counter-intuitive but it now makes sense.? Thanks for the detailed explanation about the signaling paths.?

?

I’m inclined to leave well enough alone for now, then perhaps at a later time I’ll ship it off to Amtronix for a full cal with the new output module.?

?

Paul

The way that the 8920 generates the low frequency is somewhat counter intuitive.

There are three paths in the Outpur Assembly

The synthesizer runs from 500-1ghz? ?so that range is just straight amplification for path 1 and the 500 -1G range
Path 2 uses a? /2 divider on the Synthesizer so you get 250 -500 Mhz range?

Path 3 which is what you are having problems with? mixes the synthesizer with 1Ghz? to get the .4 to 250 range
For a 1 Mhz? output you have 999 Mhz mixing with 1Ghz.
The higher the output frequency needed the lower the Synthesizer frequency needed.

This is the more complex of the three but at least at this point you know your 1Ghz and Synthesizer? signals are correct going into the assembly??

You can use a 9 Pin D extender which gets you everything but the RF signals? ...usually use some small coax and RS-232?Male and female pins to extend those as needed for the inputs.

You should have an external Spectrum Analyzer? ....without that I wouldn't bother.

It is better to fix the original module to maintain the calibration

The replacement Output Module arrived and the 8920A now passes all self tests.? Thanks to all for their assistance.

If i can figure how to crack open the Output Module, I may try to find the culprit.? Because it failed at 1 MHz and was on the lower edge of acceptance at 10 MHz, is it reasonable to first suspect a capacitive coupling problem???

Paul, W9AC

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