This repository contains 3D CAD models, pcb designs, and RF simulation files for a drone-based antenna calibrator entitled Precision Radio Instrument for Antenna Measurements (PRIAM). Its chief application is towards 21-cm cosmology and low-frequency radio instruments. The entire drone-based experiment is represented in the following block diagram:
Tip
- A complete Gitbook guide can be found here:
https://krishnamakhija.gitbook.io/priam/ - The repo containing the ROS and SDR code along with the flight path generator can be found here.
Two drones have been developed, one with a Flamewheel F450 frame and one with a Tarot T960 frame.
A scaled down drone for experimentation and testing. This was used for testing the custom ROS nodes, RTK performance, and new versions of the flight stack. This was also used to evaluate potential features and upgrades such as RPM-based gyro filtering, and system model verification.
- Flamewheel F450 frame,
- DJI 2312E 960 KV motors,
- DJI 9450 propellers,
- APD 80A F-Series 80F3[X] ESC,
- Pixhawk 2.1 CubeOrange,
- Drotek F9P-based RTK GPS,
- Maxbotix MB1242 SONAR,
- FrSky X8R radio,
- 915 MHz SiK telemetry,
- 4S 4500 mAh Li-Po battery.
- ODROID XU4 single-board computer
The actual experiment will be carried out on a larger drone capable of bearing the entire payload. It will be capable of extremely precise magnitude and phase measurements of an antenna-under-test (AUT) using a custom-developed autonomous calibration routine. Here are some of its hardware specifications:
- Tarot T960 frame,
- APD 80A F-Series 80F3[X] ESC,
- Tarot 5008 High Power Brushless Motor (340kv),
- Tarot 1855 props,
- 12Ah battery -- about 35-40 mins of endurance expected,
- 12 kgs of total weight capacity,
- Retractable landing gear,
- Drotek F9P-based RTK GPS,
- Pixhawk 2.4.8 flight controller,
- 915 MHz SiK telemetry,
- 2.4 GHz X8R radio,
- Maxbotix MB1242 SONAR.
- Raspberry Pi 4B payload computer with UPS and separate battery,
- Ettus B205-mini software-defined radio (70 MHz - 6 GHz),
- Custom RF circuitry: RF switch, and dual-pol balun,
- Dual-polarization, half-wavelength, telescopic, crossed-dipoles (70 MHz - 1 GHz),
- High accuracy frequency reference (phase payload)
Complete CAD models and further details are to be found in the CAD Files folder. That folder also contains drawings and Inventor files for custom parts for both drones.
In addition, several RF modules have been designed.
Two switches have been designed:
- A simple switch to enable X- and Y- polarization calibration (left) and
- A network of RF switches to enable X-, Y- and circular-polarized calibration (right).
There is also a dual-pol vertically oriented balun included in this repository.
Microwave Office (MWO), Eagle, and Fusion360 files of these components are included in the RF Related folder. Details of each are in nested README.md files.
NOTE: Several sub-assemblies and parts in the 3D models have been obtained from GrabCAD. None of the work in this repo is towards commercialization or monetary profit. However, credit is due to the creators of those files anyway.