Author Topic: E4407B measures low above 3 GHz  (Read 1009 times)

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Offline mbielmanTopic starter

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E4407B measures low above 3 GHz
« on: May 03, 2023, 09:43:00 pm »
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 quick
test 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
 

Offline mbielmanTopic starter

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Re: E4407B measures low above 3 GHz
« Reply #1 on: May 04, 2023, 12:05:29 am »
Added attachment!
(didn't take last time)
 

Offline Aiy

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Re: E4407B measures low above 3 GHz
« Reply #2 on: May 04, 2023, 08:04:32 pm »
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 reply
https://www.eevblog.com/forum/testgear/esa-instrument-adjustments/msg4245055/#msg4245055

If 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
 

Offline mbielmanTopic starter

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Re: E4407B measures low above 3 GHz
« Reply #3 on: May 04, 2023, 08:46:22 pm »
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 tuning
is NOT my problem. Amplitude above 3 GHz measure about 8 dB low up to 26 GHz.

regards
 

Offline Aiy

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Re: E4407B measures low above 3 GHz
« Reply #4 on: May 04, 2023, 08:55:59 pm »
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
 

Offline mbielmanTopic starter

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Re: E4407B measures low above 3 GHz
« Reply #5 on: May 04, 2023, 09:05:15 pm »
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!
 

Offline mbielmanTopic starter

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Re: E4407B measures low above 3 GHz
« Reply #6 on: May 13, 2023, 03:38:27 pm »
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_new

    To 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
 

Offline mbielmanTopic starter

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Re: E4407B measures low above 3 GHz
« Reply #7 on: May 13, 2023, 05:17:22 pm »
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
 

Offline mbielmanTopic starter

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Re: E4407B measures low above 3 GHz
« Reply #8 on: May 13, 2023, 07:23:17 pm »
I think maybe I have it! From my software:

****************************
Current A0 =  -217.54764938
Current A1 =  2.14350725259e-06
Current A2 =  -4.45896207651e-19
Current A3 =  1.80807374179e-29
****************************

*******************************
New A0 =  -219.85466512
New A1 =  2.14359154241e-06
New A2 =  -4.490327566e-19
New A3 =  1.89406947545e-29
********************************

This looks about right.
 


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