This is a reproduction of the 3GHz input option (Option 030) to suit the HP 53131A, 53132A and 53181A Universal counters.

Assembly is straightforward SMD stuff. Just be sure to get the ribbon cable assembled correctly as shown in the photos.

(Image of the PCB is of an earlier version without the prescaler bias trimpot, all else is identical)

I suggest mounting the resistors in the signal path upside down to help improve high frequency response. It might not make a huge difference, but it can't hurt.

The MB510-PF prescaler chip is the only 'obsolete' part that can't be sourced from Digikey/Mouser/etc.

It can be sourced from Aliexpress or ebay etc. The ones I purchased were salvaged parts, but they worked.

For the BNC connector, I sourced a cable with panel mount female BNC to female SMB connectors with approximately 15cm length from ebay.

(Make sure to buy one that has the mounting nut that screws from the FRONT of the BNC, NOT the rear!)

This is the exact listing (You can mesage the seller and ask for custom lengths and quantities):

https://www.ebay.com/itm/181252444696

If the above link stops working:

https://www.ebay.com/sch/i.html?_nkw=bnc+smb+cable+RG316+bulkhead

To set the prescaler bias trimpot:

• With the completed PCB fully installed, insert a trimmer screwdriver through the hole in the side of the unit and rotate the trimpot fully clockwise.
• With no input applied to the input jacks, turn the unit on and select the optional channel.
• Slowly rotate the trimpot counter-clockwise until the random counts stop. The counts will slow down as you approach the optimum value so be patient and wait a bit between adjustments to ensure the counts stop for a reasonable length of time (say half a minute or so)
• The final setting is a tradeoff between input sensitivity at higher frequencies and having a display that doesn't randomly count. The less it randomly counts the less sensitive it is, especially above 2.5GHz or so.
• Done!