Agilent 53181a with built-in 3GHz support?

[hp3310a]

Hi all,

  I'm contemplating purchasing a 53181a frequency counter and the unit I'm looking at is somehow special. Unlike the others I have seen so far it seems to come with built-in 3GHz capabilities. The screen filter print in the top-left corner says "AGILENT 53181a 3GHz", see for yourself:



I'm puzzled as I can't find any mention in the documentation such a model exists. No mention in the comparison paper from Keysight about the differences between 53131a, 53132a and 53181a and their successors (https://www.keysight.com/us/en/assets/7018-06688/data-sheets/5967-6039.pdf). Like other 53181a, this unit has only one channel with a BNC connector at the front (none on the back).  I thought the high-frequency optional inputs come with non-BNC connectors? What's going on?

[TERRA Operative]

The 3GHz input is BNC, the higher frequencies use N connectors, this optional input is always located in the top right of the front panel (unless rear inputs are used) where your picture shows a blanking plug.

I wonder if that unit has had the 3GHz input removed, or if the display window was replaced?

In any case, without the 3GHz input connector in the upper right corner, I'd not count on it being a 3GHz capable model at all. I've seen exactly 0 literature (including in the official schematics) that the main boards are capable of anything much over 225MHz.



[EDIT] Ok, I just checked the service manual, and the unit in your photo has definitely had the factory fitted 3GHz option removed at some point.
In the parts list on page 5-8, Option 030 shows parts for the option itself (the 3GHz PCB, a cable, and some screws) but also a display window marked as 3GHz applicable to the 53181A only.

https://www.keysight.com/us/en/assets/9018-01065/service-manuals/9018-01065.pdf?success=true

So, if you buy it, don't pay any premium for the 3GHz capability as it ain't there. But if you can score it for a standard 53181A price, you can get reproduction 3GHz options on ebay for a reasonable-ish price to add back in.

[hp3310a]

Thanks for digging into this, I found a picture of such a unit (once you know what you are looking for, it pops up everywhere) as sold new https://assets.tequipment.net/assets/1/26/DimLarge/53181a_image_1.jpg

Definitely missing on "my" unit, I'll ask the vendor what is up with that. The unit is relatively young (2007) and looks very lightly used.

Thanks again!

[Kean]

Some options like 030 (3GHz) on the 53181A may be installed with just the front or rear CH2 connector, or sometimes both front and rear connectors.

I'm not sure how exactly you get to specify what you want, but it is mentioned in the datasheet.  Do a search on the words "front" and "rear" - https://www.keysight.com/us/en/assets/7018-06688/data-sheets/5967-6039.pdf