开云体育

So, for fun I thought I'd make my own version of the 3GHz 53132-68003 Channel 3 option for my 53132A Universal Counter.
I am able to source divide-by-128 prescaler chips here in Japan (I'm using a UPB1506GV by NEC) and the rest of the parts are available on Digikey and Mouser etc.


I went with a coplanar microstrip at almost 50 ohms for the entirety of the signal path, and instead of the obsolete original MSA-0986 amplifiers, I am using two BGA420 amplifiers for a total of roughly 26dB of gain at 1.8GHz, down to 18dB at 3GHz. I wonder if I should add another amp stage?



I mostly replicated the HP design, but the original diodes are also obsolete so I went with RB876WTL, they have a slightly higher Vr than the originals used by HP (HSMS-8202) at 5V rather than 4V, but their Ct is 0.58pF compared to the 0.26pF of the originals.
How much of an effect will this capacitance have and is there a better diode to use here? Also what sort of maximum capacitance should I aim for for a working frequency just above 3GHz? (I'm still learning these design details...)



Here are links to the schematics and board layout so far, also 3D renders of the front and rear of the board too:





For reference, here is the relevant pages from the HP 53132A CLIP:


Any help, advice, pointers, heckling, etc would be greatly appreciated.
I'll release the design files once I'm done, and as I am making 10 of these, I'll have 9 to sell once the design is all characterised and tested for anyone interested.



Thanks!
Jared