RF backscatter module

I need to find a better way to switch the two impedances. So I will try with a MOSFET, and also another model of pin diode, but new this time to avoid any problem.

When I will receive them, I will be able to first test with a VNA that I have a consistent impedance switching, and then I will start to make a frequency generator and do the first RF backscatter experiments.

Then I will be able to choose the best uC suited for this task. When I receive the parts, I will post again.

Today I built a quick pcb with a pine diode and an SMA connector. The pin diode switch between a sort and an open circuit.

The pine diode I used was not the best choice, but the only I already have in my pile of junk. I tested it with my VNA, to metter the impedance change.

It's a big fail. My two impedances are near the same ... the impedance doesn't change from a short...

Maybe this IC was damaged, because it was unsoldered on junk, maybe also I heated it too mutch, or even it's because I missed to add a DC blocking capacitor.

So basically, when reflecting a signal, there is two images, one F=SwitchingFreq+CarrierFreq and one F=SwitchingFreq-CarrierFreq

Maybe I will try to filter one of the image with a stub filter in the future (but losses might be a problem).

The short term goal to test this module, is to use it as a ham radio beacon. So it will only need to send the same centence in CW.

The differents steps to archive this goal will be :

• Experiments with backscatter
  • Selecting a pin diode or a mosfet
  • What frequency is the best ?
  • How mucth power is needed ? What are the best "natural" source of RF power ?
• Microcontroller
  • What peripherials are the best to drive the backscatter part efficiently ?
  • How low power ?