I'm building a probe for a Boonton 92EA meter. I found a schematic and pictures here.
Page down to the SMD PCB and see the pictures and a schematic just above pictures. See the parts used under, THE UPDATED REV.B BOONTON PROBE CONTAINS: I have duplicated the parts and made a PCB.
(wherein, the problems may lie)
Here is a picture of the disassembled probe showing the board.
The back side has a ground plane the extends from output connector to the 1000pf capacitors that connect to ground, but no further. I soldered the PCB top ground and bottom foils to the case through the holes in the case. (ok, the copper pipe) I'll install heatshrink to insulate and beautify! Here's a picture with tip, ground lead and heatshrink.
My probe is flat to somewhere between 1 MHz and 2 MHz. Worst case on one range was 2% low, most ranges were with less than 1% of my scope reading. (yes, I converted Vpp to RMS) Yes, I know the scope is not a great reference, but if it's close to my scope, it is close enough to calibrate. (I hope) Some of the higher frequency loss may be in my measurement method. I'll take another stab at it tonight. I just realized my scope has an internal 50 ohm termination. My new plan is to install a BNC T on the scope input. Connect the sig gen to one side of the T and My probe to the other side of the T. At this time I have a frequency generator that will go to 10Mhz. :-( But, I'll get 10MHz working and find someone with better equipment to test further.
The Boonton Probe is supposed to work to 1.2GHz. Manual suggests a 3% error 100MHz to 1GHz and 7% 1.0GHz to 1.2GHz I don't know if I can duplicate those spec's on my kitchen table, but with your help I want to make the probe work to as high a frequency as possible. I want to make it good enough that it would be possible to send a probe and meter somewhere for calibration. As you can see I have wires to reverse the polarity going to the output connector If needed I can redo the PCB to make the crossover like Boonton did and connect the output connector directly to the PCB. Better, I may just reverse the orientation of the BAT62. Originally I was going hardwire the cable to the Probe and thought, I'll just connect the cable properly and eliminate the crossover. Plans changed when I decided cutting a Boonton cable in half made it to short. (I wanted two probes from one cable)
So, looking at the pictures: Do you see any problems with my PCB layout to cause HF loss? Do you see any problems with the probe tip or housing? The complete probe is 1/2 inch OD and about 6 inches long.
Thanks, Mikek PS. Hope I didn't leave anything out for Phil to bitch about! :-) Naw, I probably did.