Alan,

By sweeping the frequency of the doppler unit, I can produce a beat
frequency proportional to the target's distance. (In my case about
200Hz/meter). It takes 6.6ns for a signal to go one meter and then bounce
back.

I can vary the frequency by modulating the supply voltage to the
gunnplexer. For 10GHz gunnplexers, the voltage sensitivity is on the order
of 10MHz/Volt (aka. 10kHz per mV). I estimate my 24GHz unit will have a
similar voltage sensitivity.

In my design, I will modulate the supply voltage to the gunnplexer to
produce a frequency ramp of 3Mhz over a 100us span. (Sawtooth wave at
~6kHz, 3kV/second, 10MHz/V*3kV/s=3D30GHz/s=3D3Mhz/100us)  If a target is
located 5 meters away then after 33ns (6.6ns*5=3D33ns) the signal bounces
back into the receiver and is mixed the the new frequency being emitted.
Because the frequency is ramping at a rate of 30GHz/second, after 33ns the
difference between emitted and received frequencies is 990Hz. My design has
an ARM microcontroller that will perform a FFT to measure the frequency to
compute either the speed or distance. I don't intend to do both at the same
time.

I certainly will have to perform calibration for distance measurements,
it's a crude method. But I will be happy just to get within 10% of the
actual distance.

On Sun, May 8, 2016 at 10:58 AM, <alan.b.pearce@stfc.ac.uk> wrote:

> > You only need a homodyne for speed.  If you can ramp the voltage quickl=
y
> > enough then you can get distance.  You cant have speed and distance at
> the
> > same time.
>
> To get distance I thought you needed pulsed transmissions and timed the
> delay of the return pulse, but the gunnplexor modules only provided
> continuous carrier - which is ideal for burglar alarms and the like.
>
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Jason White
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