Overall, I'd try out the original design for sure but stay away from the design sold by the ebay auction seen above.
Damn now might have to actually solder cable to it for finding out
Paid no attention to details, was cheap and was ordering SWR bridge anyway from same dude (because it was also cheap). If turns out crap... what you gonna do - cant always win with these ultra cheap momentary mood purchases...
BTW, about return path, he says on one of pics:
"Do not forget to solder the ground wire somewhere on the ground surface of the probe..."Edit: Fired it up with temporary connections - electrically works. Found some info in russian space:
Long Word doc, mostly in russian, with lots of schematics and this:
Rough translation of important stuff:
- input capacitance approx 0.7pF formed by C1-C3
- input resistance 10Mohm
- gate shift voltage is created by resistive divider R2-R3 and supplied thru R1=10Mohm
- input capacitance of BF998 is approx 2.1pF, because of that probe voltage will be 3x lower than actual voltage on DUT
- R4 must be matched to used cable impedance
- probe works from
100kHz to 1GHz, with max error of 2.5dB- on
>1GHz frequencies error significantly rises- transistor gate and C1-C3 must not be placed on grounded plane or in shielded enclosure to avoid forming capacitance
- input wires max 10cm in length
- C1 feed wire must be at distance from PCB
(ground plane?) and enclosure (shield)