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50 ohm inputs for Siglent SDS1104X-E

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joeqsmith:

--- Quote from: David Hess on January 04, 2024, 05:02:48 pm ---...
The 519 was a special case where the oscilloscope deflection plates were driven directly without a vertical amplifier, and Tektronix even had a variation of the GR-874 connector with a smaller center connector which was 125 ohms for it.
...

--- End quote ---

Indeed it was special as it appears to be Tektronix's first GHz BW product.  I take it your first comment wasn't actually about their first GHz products but something much later.


--- Quote ---When Tektronix first started making 1 GHz oscilloscopes, ...
--- End quote ---

No matter.  It all very old tech and not anything relevant today.   Even my 4GHz 80's LeCroy is in that category but it does use a standard 50 ohm input w/ SMA. 

David Hess:

--- Quote from: joeqsmith on January 05, 2024, 01:25:24 am ---
--- Quote from: David Hess on January 04, 2024, 05:02:48 pm ---When Tektronix first started making 1 GHz oscilloscopes, ...
--- End quote ---

No matter.  It all very old tech and not anything relevant today.   Even my 4GHz 80's LeCroy is in that category but it does use a standard 50 ohm input w/ SMA.
--- End quote ---

It came up with the 7A29 1 GHz vertical amplifier in the 7104 1 GHz mainframe.  The amplifier was designed with a BNC input and Tektronix found out that commercially available BNCs were not actually 50 ohms, so they made their own which was.

I doubt SMA connectors had this problem, but I wonder if TNC or N connectors did.

It is relevant today if you are expecting BNC connectors to be 50 ohms.

joeqsmith:

--- Quote from: David Hess on January 05, 2024, 02:46:19 am ---..
It is relevant today if you are expecting BNC connectors to be 50 ohms.
..

--- End quote ---

I thought the discussion was about low end scopes with no internal 50 ohm termination.  The dominant error will be the scope's front end, not the connector.  Still, for the interconnect, while my 80's LeCroy used SMAs, the one from 2000 uses a their own interface.  No BNCs.   

But I am sure people who work in this are understand that even bent coax will cause a mismatch. 
https://www.eevblog.com/forum/rf-microwave/is-is-possible-to-repair-a-hairline-crack-in-semi-rigid-coax/msg4896009/#msg4896009

***

--- Quote from: David Hess on January 05, 2024, 02:46:19 am ---... I doubt SMA connectors had this problem, but I wonder if TNC or N connectors did. ...

--- End quote ---

All connectors have their limitations, including SMAs.  I have a few 3.5mm connectors at home.  These are similar to an SMA but are an airline.  The following article talks about the history.  It includes a plot comparing the SWR for combinations for 3.5mm and SMA interconnects. 
 
https://www.gore.com/sites/default/files/2016-06/Intermateability-SMA-Connectors.pdf

I wouldn't be at all surprised to find some of these connectors costing more than the scopes we are talking about in this thread.   

backyard_cnc:
The main focus of my need for these is 50ohm work under 50mhz and besides with a 200mhz BW on the scope I’m hardly concerned about how this device might perform at such high frequencies!

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