RF backscatter module

Description

The goal of this project is to build a small very low power RF transmitter. It will reflect RF ambient power to transmit data.

This module can be able used to operate during a very long period of time in harsh environment, like space or high mountain. It's also a way to use the RF fog of our city to do something useful.

The RF Energy can be provided by harvesting a strong signal already present, or by using a highly directional antenna pointed to the sensor and a power amplifier.

It works the same way as RFID, but the range will be higher, a few kilometers.

The module will be a small pcb of 1cmx2cm with castellated holes on the side. It will have one onboard microcontroller, and one RF input/output. The controller will have most of it io/pins wired to the castellated holes, to be able to acquire directly data from external sensors or computer.

Project Logs

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The next test
Julien • 07/12/2018 at 09:06 • 0 comments

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.
First test
Julien • 07/11/2018 at 11:37 • 0 comments

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.
How it works
Julien • 07/10/2018 at 20:48 • 0 comments

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 plan
Julien • 06/24/2018 at 21:25 • 0 comments
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 ?