Ambitious cheap GPR ideas, not even a pre-project....

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Ambitious cheap GPR ideas, not even a pre-project....

Post by Externet » Sat Jan 12, 2008 10:36 pm

Hi all. A lunatic one...
GPR is ground penetrating radar. You transmit into the soil, read a bounced signal, like an echosounder. Not much more.
A useable wavelenght is 2 metres, and I have a some 2m very bored marine radios that would be happy to see some activity.
They are 25 Watts, sort of low power for the task, but useable too for not very deep use.

A flat antenna ... lide06.gif
could be dragged trough the soil surface, a car battery could provide the juice, hitting only a burst every metre traveled could be enough, the whole contraption towed on a 'radioflyer' cart....

But how to capture the receiver return ?
If the burst is tone modulated and Rx fast enough, could it work ?
How to visualize the return?
An echosounder/fishfinder display would be neat to adapt, but unsure how...

Miguel :eek:
- Abolish the deciBel ! -

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Post by bodgy » Sun Jan 13, 2008 1:23 am

Wouldn't it be VLF that needs to be used, or am I thinking of caving?
On a clear disk you can seek forever.

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Post by dyarker » Sun Jan 13, 2008 5:17 am says VHF/UHF. So 2M should be okay for some soil types.

Speed of light about 1 foot per nanosecond, to get a resolution of tenths of of foot you'd need to measure 100 picosecond intervals. That would be a 10GHz clock, and some damn fast logic (not 74HCT). As 10GHz is kinda rediculous, GPR must use a different method. I don't know. Maybe phase shift of modulation frequency instead counting time between transmit pulse end and bounced pulse end.

Good luck with this one!
Dale Y

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Re: Ambitious cheap GPR ideas, not even a pre-project....

Post by sparkle » Sun Jan 13, 2008 12:42 pm

Externet wrote:... the whole contraption towed on a 'radioflyer' cart....
See page 3 of :grin:

There are many patents and publications on this subject, but US patent 3,806,795 is a good starting point. Transient waveforms have their advantages, but it is possible to probe with a continuous unmodulated sine wave at a single frequency, receive reflections using another spiral antenna with the opposite circular polarization, determine amplitude and phase of the reflection, then change frequencies as needed to resolve range ambiguity for determining the first major reflection's range. Networks analyzers with inverse fourier transform math function can thus sweep a transmission line and do the equivalent of time domain reflectometry, displaying discontinuity locations vs distance along the line.

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