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DC coupled 2.7 GHz Active Probe Project - Now Available!

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hpw:

--- Quote from: joeqsmith on May 27, 2024, 03:21:12 pm ---A similar setup using a PECL driver but with a 10MHz fundamental.   C1/M1 is directly looking at the output of the PECL driver through the waveguide and about 6" of coax.   Consider this is still not what the actual signal looks like as we just added a fair bit of capacitance which is dampening that fast edge.     

C2/M2 is the Lasmux probe   
C3/M3 is the PP002A/AP-1M probe/buffer
C4/M4 is the HFP3500

I took the data zoomed out a ways to better show the noise and settling times.   Then zoomed in, aligning the edges.

--- End quote ---

IMHO, you have a noise & a sine signal on your C2/M2 is the Lasmux probe ... as an interval of about 17..18ns as about 60MHz.
Just switch on your WM FFT Spectrum analyzer. In addition I use an 4..8x AVG to get ride of the WM 8bit ADC noise.

One about overshoots: I used none differnetal and differential probes AB034 and did get ride of the ground connections as asymmetric added additional overshoots  :--.  In addition I love the AP034 pin header connection, as getting 2 free hands to tune at the gear. Also 2 hands free even two or more AP034 used O;)

IMHO, may an option to use the Bodnar fast pulse :D

lasmux:

--- Quote from: hpw on May 28, 2024, 09:47:41 am ---IMHO, you have a noise & a sine signal on your C2/M2 is the Lasmux probe ... as an interval of about 17..18ns as about 60MHz.
--- End quote ---
Yes I thought that also. Maybe some noise pickup from some other radiating piece of equipment?

joeqsmith:

--- Quote ---So say reduce R2 to say 100k, and reduce R3 to 2k.
--- End quote ---
I can't answer what your target application was or why you chose the parameters you did.  For digital, the 1M DCR isn't really important. 


--- Quote from: hpw on May 28, 2024, 09:47:41 am ---...
One about overshoots: I used none differnetal and differential probes AB034 and did get ride of the ground connections as asymmetric added additional overshoots  :--.  In addition I love the AP034 pin header connection, as getting 2 free hands to tune at the gear. Also 2 hands free even two or more AP034 used O;)

IMHO, may an option to use the Bodnar fast pulse :D

--- End quote ---

I have not shown how my differential probes compare but could if you would like to see them.   

During review, I used a antique Tektronix pulse head with SJL's GigaWave 6400 oscilloscope.   
https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg5284957/#msg5284957

As for the noise it is certainly possible it is coming from an external source.  We have various radio/TV and other stations in the area.   Keep in mind that all probes are exposed to the same environment and I do not normally make measurements at home in a screen room.   :-DD    Attached images show spectrum from 1 to 10MHz with the Lasmux probe attached.  The ground and tip were shorted together with some wirewrap wire.  Probe was allowed to float in the air so no other electrical connections were made except the cable to the spectrum analyzer.   

 


joeqsmith:
Probe wrapped in foil appears to knock out the low frequency.   

lasmux:
The 60MHz low frequency? It's not shown on your plots that only go up to 10MHz.

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