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 Post subject: TX RX
PostPosted: Mon Apr 01, 2013 2:12 pm 
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Joined: Mon Apr 01, 2013 2:04 pm
Posts: 1
Hi friends..I have a gpr with 300mhz dipol antennas and 100mhz dipol antennas in same unit. I would like to know that what is distance between tx and rx with 300 mhz antennas and 100 mhz antennas please?


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 Post subject: Re: TX RX
PostPosted: Mon Apr 01, 2013 6:04 pm 
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Joined: Tue Mar 26, 2013 7:51 am
Posts: 12
Hello, ozanmeklih.
I work with GPR "Loza" using dipole antennas. It all depends on how deep you want to explore?. The approach of the antennas will be well resolved first 5 meters and the distance between the antennas will be more probing depth but the loss in resolution. When working with GPR "Loza" between such antennas must be at least 50 cm

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 Post subject: Re: TX RX
PostPosted: Mon Apr 01, 2013 6:57 pm 
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Joined: Fri Apr 17, 2009 7:52 am
Posts: 379
Location: Boden, Sweden
Hi ozanmeklih,
A good rule of thumb is to keep 1/4 of the wavelength in the material between the TX and RX.
But, there are exceptions and ways to make this shorter. None the less, it is a good starting
point, dipole antennas do have lots of ringing and close proximity of the TX and RX can actually
make this even worse. That's why some manufacturers have such large antennas to reduce this
effect, but this is something you need to test with your equipment.
Georadarinfo, you are mistaken, the distance between the TX and RX bear no influence whatsoever
on penetration depth if the travel time through the media is not bigger than the penetration depth
of the device. GPR doesn't work the same way as resistivity probes where that distance does
have a major impact, this is a common mistake from geophysicists that didn't have much exposure to
GPR, but lots of experience with resistivity methods .
On a completely another plane, the distance between the TX and RX will indeed add lots of clutter to the top
part of the data making difficult to see shallow objects, perhaps that's what you meant. But, it is
a design task of any antenna designer to reduce as much as possible this effect to obtain better data,
this sometimes is called "top resolution".
Finally 50cm between the TX and RX for a 300MHz sounds excessive and unnecessary, for a 100MHz on the
other hand it sounds a little bit too little unless working on a heavily saturated media. You see "loza" or not
the EM propagates through the media according to the laws of physics not manufacturers ;)
When it comes to GPR it is important to explain the "why" not only the "what".
Regards,

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Sweden
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 Post subject: Re: TX RX
PostPosted: Mon Apr 01, 2013 10:18 pm 
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Joined: Tue Mar 26, 2013 7:51 am
Posts: 12
Hi GeoAdmin,
My advice is from the field of practice. From the practice of dipole antennas GPR "Loza".
We all know that in practice, the theory does not always confirmed
Regards

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 Post subject: Re: TX RX
PostPosted: Tue Apr 02, 2013 6:29 pm 
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Joined: Fri Apr 17, 2009 7:52 am
Posts: 379
Location: Boden, Sweden
Hi Georadarinfo,
Yes, that's correct, it is your very personal experience on your very particular piece of hardware.
It is however, my personal experience that most antennas I have tried, and I have tried a lot
from virtually all manufacturers, do work the way I explained, not in theory, but in practice.
That is very easy to test if you get the opportunity of trying other devices.
Facts, this forum is about facts and facts only, for advertising and selling there is a separate
section, I strongly suggest you to use that channel.
Regards,

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Reinaldo Alvarez Cabrera
Geoscanners AB
Sweden
http://www.geoscanners.com


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