Products > Test Equipment
Conversion of 500MHz TDS744A to 1GHz TDS784A
<< < (3/24) > >>
nctnico:
The sensitivity for low signals isn't great. If you look at the specs of the TDS784A you'll see it struggles to get to 1GHz.
Jay_Diddy_B:

--- Quote from: Ivan7enych on December 16, 2014, 08:11:10 am ---
--- Quote from: Jay_Diddy_B on December 15, 2014, 02:26:41 am ---So I carefully removed these capacitors and saved them so I could put them back.

After removing the capacitors you have to run the Signal Path Compensation (SPC).

--- End quote ---

Thank you for this investigation!

I have no old GPIB board now. What do you think, if I simply remove 4 capacitors without running Signal Path Compensation, will it make some problems?

--- End quote ---

You don't need any external equipment to run the SPC. It is built into the scope. Go to the Utility menu, select CAL, run the SPC. The SPC takes about 5 minutes.

I initially calibrated channels 1 & 2 using the field adjustment software, which requires the GPIB Card and compared them to channels 3 & 4 which I did not calibrate. There was very little difference with my scope.

The calibration is only as good as the signal generator used for the calibration. The Agilent E4425B that I used is very good.

It takes about 40 minutes per channel to perform the HF CAL.

Regards,

Jay_Diddy_B
Ivan7enych:
For now I'm quite happy with the modded tds754->784, it allows me to see 1.2GHz output from antenna and to use it as a simple spectrometer, see ouput frequency and power. RF output from selfmade cloverleaf antenna is put directly to 50ohm terminated oscilloscope input.

Model type resistor has been removed, capacitors on every channel removed, field calibration hasn't been done yet.
Jay_Diddy_B:
Hi Ivan7enych and the group,

The modification seems to work well !!

I am waiting on the delivery of a Fluke 6061A RF generator that I ordered from eBay so that I can automate the adjustment process.

Regards,

Jay_Diddy_B

szhebo:

--- Quote from: dxl on December 15, 2014, 08:39:02 pm ---Hi,

i can confirm the modification. I have a TDS754D, which i upgraded to TDS784D by changing the ID resistors. However, the calibration failed, because freqency response was out of spec (1 GHz was low by ~-4 to -5dB). After removing the capacitors, the calibration runs now flawlessly, and the Field Adjustment software
says it passed calibration.

:D

Regards

--- End quote ---

Hi dxl?


I also have a TDS754D, and want to upgrade it to TDS784D, but the schematic is different from the TDS744A, I tried to find TDS784D acquisition board photos on the web, but failed.


Could you please tell me how to change the ID resistors of TDS754D, from R52 to R57, which on should be removed and which one should be added/Keeped?


And for the signal path I found two capacitors across each signal leads, one is C781/C782/C783/C784, another is C740/C741/C742/C743, and the second one with two 3.3K resistors in series across the signal leads. My question is if two capacitors(C781/C782/C783/C784+C740/C741/C742/C743) of each path need to be removed or only the previous one(C781/C782/C783/C784) need to be removed?


Looking forward to your reply!


Many thanks!


Regards,


szebo


Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod