E4407B measures low above 3 GHz - Page 1
Forum section: electronics / testgear

author: mbielman
author_rank: Contributor
timestamp: May 03, 2023, 09:43:00 pm
content: Discovered an issue w/my SA while testing a repaired ESG (E4437B). There is a slight dip at 1.7 GHz but above 3 GHz the amplitude is low by as much as 8 dB.I read through this post (https://www.eevblog.com/forum/testgear/esa-instrument-adjustments/) but I do not think a mistuned YTM is the issue. (if I do the quicktest as suggested I see no change)I contacted a calibration lab and they don't think it's a cal issue. They want to replace parts instead!Looking through the TME docs it sure looks like some adjustments would help but no direct solution as of yet.Also I do not have another SA w/range above 3 GHz, so I cannot do tests outlined in the service manual. :-(See attached.Anyone have a poor man's way of performing a tune up on these?Mark

author: mbielman
author_rank: Contributor
timestamp: May 04, 2023, 12:05:29 am
content: Added attachment!(didn't take last time)

author: Aiy
author_rank: Regular Contributor
timestamp: May 04, 2023, 08:04:32 pm
content: Hi there,You can have a look over here:https://www.eevblog.com/forum/testgear/esa-instrument-adjustments/I had problems with my E4407B as well. Look at 6th replyhttps://www.eevblog.com/forum/testgear/esa-instrument-adjustments/msg4245055/#msg4245055If you can get OK signal through using the quick procedure, you have a shot at fixing it using the rest I describe there.Best regards

author: mbielman
author_rank: Contributor
timestamp: May 04, 2023, 08:46:22 pm
content: Hello. Yes, I found your post and read it carefully. As I pointed out, I did the quick procedure you describe and saw no change in amplitude. My guess is that the YTM tuningis NOT my problem. Amplitude above 3 GHz measure about 8 dB low up to 26 GHz.regards

author: Aiy
author_rank: Regular Contributor
timestamp: May 04, 2023, 08:55:59 pm
content: Oh, sorry. I did not read your post thoroughly enough, sorry about that. I saw your post over at the HP/Agilent/Keysight group also.Can it be a stuck input attenuator? If you vary the input attenuator, does a peak marker change value?Best regards

author: mbielman
author_rank: Contributor
timestamp: May 04, 2023, 09:05:15 pm
content: No worries. Yes, I tried that. Really no change until I get to about 60 or 65 dB attenuation, but at that point, the signal is barely above the noise floor. I have NOT tried bypassing the attenuator yet.thanks!

author: mbielman
author_rank: Contributor
timestamp: May 13, 2023, 03:38:27 pm
content: Aiy,I tried your method for tuning the YTF but I'm apparently missing something. From your post:With the YTF offset frequencies in hand, the next step is to evaluate the DAC polynomial with:DAC(input_frequencies + YTF_offset_frequencies) = DAC_setting_newTo get the new polynomial, do a polynomial fit using the DAC_setting_new and the input_frequencies arrays.So let's say at 4GHz, the offset is 400kHz. Then the pair for the polynomial fit is (4,000,000,000 , 4,000,400,000.).Is that correct???Mark

author: mbielman
author_rank: Contributor
timestamp: May 13, 2023, 05:17:22 pm
content: Well that's clearly not right!Perhaps you mean evaluate the original polynomial (original coefficients) with (input_frequency + offset_frequency)When I do that and do a poly fit on those values, I get the exact same coefficients.I suspect that my E4407B is tuned fairly well as it is, so perhaps that is why I get the same results.My offsets vary from -1.8MHz to +18MHz (at 26GHz) and I see little if any change in amplitude.I've been trying to automate this procedure and the GPIB part is easy. It's the math that is not right!Mark

author: mbielman
author_rank: Contributor
timestamp: May 13, 2023, 07:23:17 pm
content: I think maybe I have it! From my software:****************************Current A0 = -217.54764938Current A1 = 2.14350725259e-06Current A2 = -4.45896207651e-19Current A3 = 1.80807374179e-29***********************************************************New A0 = -219.85466512New A1 = 2.14359154241e-06New A2 = -4.490327566e-19New A3 = 1.89406947545e-29********************************This looks about right.