"Mobile Amateur (Doppler) Rain Radar" Project

Is it possible to make your own Doppler rain radar? Yes, I think so but nobody did it until yet. It is my target to build a mobile amateur rain radar for 10.4 GHz under 2000 Euro. 3 cm rain scatter is very similar and OE5VRL (Rudi) gave me some ideas with his rain scatter detector http://www.dl6nci.de/oe5vrl.htm

The Doppler effect, named after Austrian physicist Christian Andreas Doppler who proposed it in 1842, is the change in frequency of a wave for an observer moving relative to the source of the wave.
Christian Doppler was born in my city Salzburg and his Doppler effect is part of my life as physicist and ham radio amateur.

                

1. Time schedule & status

- March 2010 : Start of  project
- June 2010 : Make my radio license
                            * finished with my call OE2IGL
- Summer 2010 : Finishing system concept and calculations
                            * finished (see system overview)
- Summer 2010 : Finishing prototype computer and µ-controller software
                            * first tests with PIC32 and C-compiler finished
                            * computer software "dBZ calculation" with USB (via RS232) connection finished
                            * computer software "Radar visualisation" finished
- Spring 2011 : Finishing feed/dish/receiver & software
                            * homemade 10.4 GHz feed finished
                            * prime focus dish mounting on tripod finished
                            * µ-controller software with high speed ADC (0.5 MSps), USB connection, LCD display finished
                            * RSSI circuit, impedance converter finished
- Summer 2011 : Finishing transmitter/feed/dish/receiver without azimuth rotor
                            * µ-controller software with 12 bit HH-12 encoder, call sign generator
                            * modified SAT LNB downconverter
                            * mounting head and rotor concept finished in more detail
- Summer 2012 : Finishing Rain Radar system with azimuth rotor
                          * azimuth rotor with worm gear, H-bridge and HH-12 encoder finished
                          * µ-controller software finished
                          * bought 10.4 GHz transmitter and setup of transmitter/feed/downconverter/reveiver
- Summer 2013 : Option Dual Polarisation Radar and Doppler Radar
- Winter 2013 : Option with additional elevation rotor

2. System overview




3. Technical details

Frequency                     :       10.402 GHz, vertical polarisation
Dish diameter                :          0.97 m
Dish gain                       :          39.0 dBi
Dish beam width            :            2.0 °
Dish rotation                  :               2 per minute
Stepper resolution          :           0.9 °
Time per step                 :            75 msec
Echo time                       :              2 msec
Pulse                              :         8.88 µsec
Effective radiated power :           40 dBi
Sensitivity                       :             3 mm/h at 100 km




4. Details

10.2 - 10.8 GHz circulator:

- Isolation: 30 dB
- VSWR: 1.12
- Insertion loss: 0.35 dB




 Homemade 10.4 GHz conical feed (wave guide)

- Copper tube with inner diameter D: 20 mm
- VSWR adjustment by moveable back wall
- Wave guide formula:

        1 / Lamda₀² = 1 / Lamda_c² + / Lamda_g²
        
        Lamda_c = 1.706 x D
        Lamda₀ = 28.81 mm (10.4 GHz)
        
        -> Lamda_g = 54 mm

- Wave guide drawing:



I use this feed to transmit and receive signals in combination with a circulator. Therefore return loss must be as low as possible (< -30dB). After first measurements of return loss and adjusting back wall with the screw I got around -20dB. Then I adjusted the length from the open end to the pin to 54mm (1x Lamda_g). Now the retrun loss is better than -45dB.




- for prime focus dish with f / D = 0.36



   

- Corrugated horn feed (part of a standard sat tv LNB) for standard offset dish with f / D = 0.67






Downconverter 10.402 GHz -> 652 MHz

Some microwavers made good experience with standard satellite LNB's. They have low noise figure, high gain and are very cheap. So I will try such a modified LNB.

 

 




Receiver with RSSI (received signal strength indicator) output IC (e.g. UBC3000XLT scanner)




or AR8600 scanner with 10.7 MHz I.F. output and external RSSI (NE614) + impedance converter (TLC272)





PIC32 µController (Ethernet/USB Starter Kit)




with I/O expansion board and LCD display




Sampling pulses every 2.22µsec and echo time up to 2ms

   


Mounting head for azimuth and elevation





Prime focus dish

  





DC motor with encoder for azimuth

12V worm gear motor with additional worm gear to get only 2 rpm.
Torque is approx. 100 Nm.
HH-12 Encoder has a resolution of 12 bit and an accuracy of approx. 0.2°.

   

DC linear motor for elevation (0 to 90° degrees)





5. Austrian microwave meeting 2011

OE2JOM, OE5VRL, OE3WOG








HOME