Ok Mike, thanks.
BTW, What you see again and again are the slightly inappropriately selected versions of the compensation capacitors.
I can only explain it to myself that this is either due to a lack of knowledge of the requirements or a lack of available crafting budget.
High stability and low loss (low relative permittivity) is required because the value of the compensation capacitor has a significant influence on the relevant characteristics of the impedance coupler.
Suitable capacitor types are therefore:
- (Silver) Mica
- Ceramic Class 1 C0G (NP0)
Electric strength requirements
The required electric strength depends on the voltage across the primary winding of the coupler. With a transmission power of 100 W over the system impedance of 50 ohms, a voltage of slightly less than 90 V would build up.
Suitable electric strengths (with plenty of reserve for unexpected cases…) are therefore:
- 250 V for transmission powers up to approx. 50 W.
- 500 V for transmission powers up to approx. 150 W
And yes, the connection wires of the compensation capacitor should be as short as possible (i.e. no longer than about 5 mm if possible).