SUMMARY OF THE PROBLEM  (For more details about the hardware see my first log)

I build a (DIY) prototype of a 800-1600MHz FMCW GPR and I am not that happy with the results yet.

There could be many causes but I would like to start by getting your opinion on the performance of the front-end. If that is not ok, there is no point at continuing with more complicated stuff like antenna's.

THE MEASUREMENT

I attached a good coax cable + a series of attenuators between antenna input and output.

This way I should get an idea of the sensitivity of the device and if it is working.

Coax properties  (measured with calibrated VNA) :  800MHz : -0.5 dB , 1600Mhz : -1.1 dB, 20ns delay (TDR measurement) , length 5 meter.

Attenuators  I used 10dB and 20dB inline attenuators ( see image). I increased the attenuation from 60dB to 110dB and the measured voltages behave exactly as expected ( 20dB attenuator -> voltage 10x lower). So confirms there are no measurement errors or stray signals leaking in.

 A scan measurements with 80dB (4x20dB) attenuation between TX and RX input

A scan ( with hardware high pass / differentiator enabled).

The frequency is about what I would expect :

with a 20ns delay and a 800MHz/1ms sweep I expect a  beat frequency of 20ns * 800MHz / 1ms = 16KHz. And there are about 16 cycles. Note : the FFT uses zero padding that is why the FFT peaks at 4x higher value.

A scan measurements with 110dB (4x20dB+2x10dB) attenuation between TX and RX input
Amplifier gain is set higher to maximize signal.

What I would like to learn from experienced builders :

• Is this front-end performance OK ?  Do you need extra measurements to say ?
• Would you expect a higher sensitivity ? Or a cleaner sine wave ?
• Any other test you could suggest to learn more ?