Rf tranmitter and receiver to mesure phase shift

[theone_in_themoon]

I need to implement a speedgun with microcontroller..... i need to know abt what kind of transmitter and receiver can i use to measure the phase shift b/w the original and reflected signal. so that i can measure the speed of the object from that phase shift (doppler's effect)

plz suggest the name of some easily available ... and appropriate for my project ..... transmitters and receivers.
Thankyou

 

[flyhigh]

Transmiter path - oscillator-amplifier-antena.
Receiver path antena- LNA - mixer. LO of the mixer is transmit oscillator. The IF otput from the mixer is proportional to Dopler shift.

That is the principle of simplest CW-Dopler speed meter you can get. The thing to consider is leaking of transmiter to receiver input - this should be very large unless you will always get speed of 0 (Tx signal will be strong on both inputs of a mixer).

flyhigh

 

[harkonnen]

What you want to make is a Doppler Radar which is basically a homodye (direct-conversion) receiver.

You transmit a carrier signal and receive the reflected signal.
When using a single Antenna you have a directional coupler between the power amplifier (transmitter) and the antenna.
The reflected carrier signal that comes back doppler-shifted goes through the coupler instead back to the power amp. That signal can be mixed with the transmit signal. This means that twice the doppler shift frequency will be present at the output of the mixer.

However, keep in mind that the parasitic leakage of the transmit signal to the mixer is not neglectible. This creates a DC offset.

 

[theone_in_themoon]

thankyou very much for your helps..... but i would be even more grateful if you could tell me exactly what kinda hardware.... with its IC name ... or specification should i use...im not that good at these things

 

[mr_ghz]

Hi theone_in_themoon

I guess that building own microwave designs wouldn't be your thing... Isn't it? So I recommend to use a so called 'gunn-source'. This includes a GUNN-diode in a cavity for creating a radar-frequency of 10GHz or 24GHz. The signal is coupled to a waveguide. You can attach a horn antenna to this waveguide, so the signal is sent in freeair. The antenna determines also the covered area (detection area).
The reflected signal is received from the same gunn-source and demodulated in a schottky-diode. What you get at the output is the IF-signal (doppler-signal) in the range of some Hz to kHz (depending on the object's speed).
Look at this page for an example of such gunn-sources: **broken link removed**
I'm sure you will find cheaper ones when searching google.

Bye

 

[theone_in_themoon]

thankyou very much for ur guaidance mr_ghz.......i was also thinking that making my own radar kinda thing would very very difficult.....im grateful that you told me a better way....

plz also tell me where can i get these Gunn-diodes...and for how much price........and ifyou could tell me some link or url for cicuit diagrams .... or HOW ACTULLY TO INTERFACE ....THIS DIODE WITH ANTENNAS .... i would certainly be very thankful ... indeed

take carez....

 

[mr_ghz]

Hi theone_in_themoon

Look at the URL I gave in my last post. There you can buy such modules (including the necessary gunn-diode). The sell also horn-antennas that can be attached directly to these modules.
I would suggest you to use a K-Band module (means a working-frequency of 24GHz). They have a higher frequency-output for the doppler-signals.
What you additional need: You have to amplify the output of the schottky-diode with a OP-amplifier about 500-5000 times. Use two inverting or non-inverting amplifiers and make a lowpass filter at some kHz. Don't forget the input impedance at the schottky-diode: it should be about 1000 ohms. The output of the amps can be fed to an A/D converter. But first connect an oscilloscope and look at the signals, this will help.
On the RF side you need to attach an antenna (the modules even work without, but you have to bundle the radar-waves to one direction, so you need one). The larger the antenna, the smaller the beam and the bigger the range. If you need this system to measure the speed of cars and you use a 'standard' hornantenna with about 5cm length, you can reach detection-distance up to 50 meters.

Bye