Before conducting a field test, it’s beneficial to test the constituent parts of the radar. Since this is an HF radar, using a higher frequency where it’s easier to build antennas to test with targets smaller and closer than the ionosphere can be expedient. In general the three essential functions of a radar are:
- time synchronization: ability to send/receive with accurate absolute time–here provided by GPS into the GPIO and FPGA.
- transmit: ability to send a signal at a desired RF frequency and bandwidth, with accurate timing
- receive: ability to receive a signal at a desired RF frequency and bandwidth, with accurate timing
1. Timing test
2. Transmit/receive test
This test requires the GPS-GPIO timing working first
The antennas can be build from wooden dowels with solid wire attached. The dowels are about $1 each from Home Depot. The test is run in the 38-50 MHz license free range since this fits within the Red Pitaya maximum frequency while using shorter/smaller antennas.
3. Monostatic radar test
As for test #2, the radar waveforms should be suitable to detect range and Doppler. If there are problems with the monostatic test, or if it’s desired to simulate the ionosphere “on-air”, a transponder can be used.
3a. Indoor test
Can the radar detect Doppler indoors or through the window? Is the window metallized, blocking radio/radar signals? Range measurements indoors will have extreme clutter and suffer from small lab size relative to radar wavelength. It may be possible to use an MTI algorithm to distinguish moving objects from the background.
3b. outdoor test
Taking the radar outside, can it detect range/Doppler of people and cars/trucks? Can it measure the range of individual buildings?
These algorithms are more for ground-based testing, we intend to use more advanced algorithms for ionospheric sensing.
- FMCW homodyne radar except using the 40 MHz band instead of 2.4 GHz like I did.
- Doppler radar, where you deliberately don’t get much range information, just Doppler (velocity) like the earliest radars.
- forward scatter–just for testing, not for ionosphere