GPR - project

[Seeker]

Hi everybody,
too many people asked about GPR-schematic ,but it is too new field and there are only unusable schematics .
I begin a development of easy-to-make and PC-based GPR .It will be open project and everyone can assist with ideas, check up the assembly or develop the software.
My vision for GPR is : small output power, in 0,9-3GHz band, narrow beam antenas and use some bionics design.

[aft_72005]

Hi Seeker
OK, good idea.
Please upload at the first system circuit or diagram.

[Seeker]

Hi I send blockdiagram , but I wll exlain it later (after 4 hours )

[Seeker]

Ok aft_72005,
I think first check the principle of work of GPR in free air , and then select the best frequency by test on ground in band 0,9-3GHz.
Generator is modulated from controller with sinusoidal signal where frequency will increase and decrease.After amplification up to 0,5W signal will be rediate by helicalantena, left rotation. When signal reflect from obstacle polarization will change to right rotation and will be received from second helicalantena with right rotation. In mixer come two signals from first and second antena. In result we get frequency proportional of distance(delay of signal) to obstacle and amplitude proportional of reflection quality.
Controller direct the modulation frequency by spesial principle, where only one frequency is proportional to all depths in one mesurment cycle.There we use narrow band filter.Amplifier have volume control to avoid outband signals.Detector can be sinhro to avoid delay of integration circuit.
In basic variant indication can be 40 LED for depth(for 4 m depth , step 0,1m) with brightness proportional of strength of signal and audio for threshold.
In second variant I think add wheel and PC for indication and drawing of pictures.

That's all. It is simply.
So, what you think?

[Leto]

GPR for ALL

Hello Seeker...
thank you for last input... I think it's a GREAT project.

Attached is another very simple design; almost finished by UIUC students.

[Seeker]

Hi Leto,
I read attached file. Yes, our project something like this , but I want to avoid DSP and mathematics, and all expensive parts. The idea in our project I take from nature, some animals use linear frequency scaning to compute distance and position of target. The helical antena have many advantages to another types and rotating polarization give us 20dB attenuation between TX and RX signals in straight reception.
First mast to describe algoritm of modulation, proportional of scaning depth.
The transmiter mast make bursts with step-change or continuously linear-change frequency for one cycle of measuring.This cycle mast contain all discretes (steps) of depth and corresponding duration to format the output signal.Our aim is to obtain synonymity of got signal after mixing.

OK, the theme is too large for one message, I will proceed tomorow, now I will go to sleep.

Best regards

[aft_72005]

Hi seeker
I study principle of your GPR , its good and seem
As practical .
Low frequency in this band have better response and
Penetrating in The ground .
Best regards .

[Seeker]

Hi aft-72005,
The ground is not homogeneous structure. The different stratifications have different absorptions, reflections and speeds of frequences.It is important to know if ground is dry or wet .The water have absorption of 2480MHz and pass at 3100MHz .The our aim is to find flat place in 900-3000MHz band of amplitude-frequency characteristic of penetrate of ground, which is 200MHz wide for most types of ground. Actually for 4m depth no matter what is attenuation of signal,but we need resolution and I think 2480MHz is good for initial checks.

Best regards

[aft_72005]

Hi Seeker

Thanks, what resolution we can obtain with 2480 MHZ ?

For example may be see small stone or nugget in 4m deep.
Best regards .

[Seeker]

I think all > 1/4 wave in ground, but it is in function of mixer dinamic range and amplifier.I think, we mast make schematic now.
What is your GMT+? Call me by ICQ.

[aft_72005]

Hi Seeker

Thanks ,

My time is a proximally GMT+3.5 hour , and prefer communicating by
Email or this forum . because telephone connection
Expensive in my country .
See you later.
Best regards.

[Leto]

Hello Seeker.

I agree with ~12cm band to be right frequency for start.. and great for finding caves, architecture,.. also bar-led display is good for testing but because of lateral echoes would be not so usefull on field.
Helical antennas comes in small sizes compared to wavelengths so the system would be also very compact. Is your electronics sistem also adaptable for higher frequencies (higher resolution, lower range)? For uses like probing walls, etc.. As I know such antennas are rather poor radiators..but I guess there is no problem with this range.

[Seeker]

Hi aft_72005,
ofcourse I don't think call to anybody by phone too! The forum is good place to exchange ideas, but I would like to synchronize my shedule to anothers. ICQ is fast way to give signal for attendance.

Anyway,I proseed the exlanation essentiality of GPR.
The controller direct the TX frequency in series of steps,where one measurement cycle consist 256 frequency steps with variable duration and Ftx-Frx = constant for any particular step and depth.Every one step will give us information for determinate depth. If we choose this intermediate frequency equal to narrow band filter , we will received pulses long as current step, with amplitude equal of reflection of layer or object.

In descrabed principle of work, we will avoid DSP for Furrie-analysis and all marsh-lands of mathematics.I think, this is critical point for more amateur GPR projects.
The schematic will not be simple , but will be linear and with minimum SHF elements.

[Seeker]

Hi Leto,
I think lateral echoes not problem in our case more then in another GPR systems.The antennas will be not only one .Actually , there will be one TX antena and 4 RX antenas. The RX antenas will be connected together, in step ,sum up signals. All signals which are no in step will be decrease.The resolution is define by wavelenght , but in ground speed of EMfield is lower then in air.Range is define by modulation and absorptions of ground.

[aft_72005]

Hi Seeker
Another method used in the matter ,sending impulse .
Please study pdf file which send to your email
becase i can not upload here , which better ?
What is your GMT ?
Best regards.