2
\$\begingroup\$

I'm building a simple Greinacher based RF Power meter for the PMR band i.e 446MHz. I intend it to work as a confirmation device and not something really acurate.

The circuit is quite simple: Greinacher schematic

The led is for visual control if the system works well.

I have obtained the Following routing (without the LED): Routing picture

From left to right: I have the input SMA, with a transmission line adapted to 50Ohms. Which goes into the C1 capacitor, then in the diodes, and then in the C3 capacitor.

Is it relevant to consider the trace between C1 and D1 and between D1 and C3 as transmission lines? They are short L < 4mm, for a wavelength of around 70cm. For the moment I have used the embedded calculator in kicad to find the dimensions of the transmission line used : enter image description here

\$\endgroup\$
2
  • \$\begingroup\$ I suppose, you will be connecting an antenna? That's why you are willing to keep everything matched to 50Ohms ? It may be a subject for another question but you might want to make something to smoothly convert the wide line to the width of the first capacitor. \$\endgroup\$ – Arnaud May 28 at 22:01
  • 2
    \$\begingroup\$ You are right, I intend to use it to measure without precision the power emitted by a device. And I will be connecting this small board to a dipole antenna. That's a great suggestion I didn't thought of that ! \$\endgroup\$ – Lucas Vivi May 28 at 22:09
1
\$\begingroup\$

I made a bit of research and to be considered as a transmission line you would need at least Lambda/10. This is at this point that we consider that along the line you don't have the same voltage. This is also true for power lines!

This at your frequency give a length of at least 6.7cm which you are well below.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.