R1 = 470R and R2 = 10k, gives a 450 ohm parallel combination. This is required for the 10:1 divider into a 50 ohm input.
C1 = 220pF to 2.2nF, C0G/NPO dielectric, 50V
This AC couples the signal from the probe into the measuring instrument. Many spectrum analysers have a 0VDC requirement on their RF input.
The actual value isn’t too important at the frequencies we are interested in.
Edge mount RF connectors
The 1.6mm thick PCB is designed to take SMA edge mount female connectors to connect to an SMA-SMA RF cable.
These connectors are available from a wide range of sources but most readily and cheaply from eBay
You can solder a coaxial cable onto the pads at the expense of ease of swapping the connection between probes.
Metal pin for contact probe
For the contact probe pin we recommend using a male pin header from a 2.54mm pitch connector strip and filing the end to sharp point with a metal file.
These parts are available from all major component distributors and from eBay again.
We also recommend securing this in place with a generous blob of 2-part epoxy adhesive to provide some additional mechanical strength.
Ferrite cores for current transformer adaptor
The current transformer adaptor was designed to use the excellent Wurth Elektronik 742715x series of ferrite cores which are available in different sizes.
If you do get one, tie the two-pronged plastic unlocking key to the probe with a bit of string so that you don’t lose it!
An M3 screw and nut will secure the core to the board, but again a blob of two-part epoxy adhesive or some hot melt glue will do the trick.
Experiment with the number of turns but we generally use between 5 and 10 as a starting point.