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 Post subject: Re: Certification
PostPosted: Tue Sep 28, 2010 1:40 pm 
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Joined: Wed Sep 08, 2010 8:50 am
Posts: 8
Hi Admin,

i read the document about Antenna-Bandwith. The Author defined the Center frequency as a difference between the upper limit und lower limit of bandwith (at -10dB) divided by 2.

So that means when we have 187 MHz lower limit and 477 MHz upper limit, we should have
(477-187)MHz /2 = 290 MHz/2 = 145 MHz Center Frequency as its defined by the equation, right?

please refer to this Link below. Here ist the Center Frequency 332 MHz (show Table 2).

http://geoscanners.com/pdf/antcomp.pdf

When i calculate this like below, i get the right Fc :

(upper limit + lower limit) / 2
(187 + 477) MHz / 2 = 662 MHz / 2 = 332 MHz as definded in Link above?

So, what is now right. difference between upper- and lower limit or sum of them divided by 2?

best regards
Araz


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 Post subject: Re: Certification
PostPosted: Tue Sep 28, 2010 1:56 pm 
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Joined: Fri Apr 17, 2009 7:52 am
Posts: 379
Location: Boden, Sweden
Hi Araz,
You are absolutely right, in the text it says "Center frequency as a difference between the upper limit and lower limit of bandwidth (at -10dB) divided by 2".
Whereas it should say "Center frequency as a difference between the upper limit und lower limit of bandwidth (at -10dB) divided by 2 plus the lower limit of bandwidth.

Fc = (Fh - Fl)/2 + Fl = (477- 187)/2 +187 = 332MHz

it is very interesting that you put it in a different way:

Fc = (Fh + Fl)/2 = (477 + 187)/2 = 332MHz

It is not as intuitive to understand as the longer version of the formula, but definitely much easier to calculate!
Which is of course correct Fc = (Fh - Fl)/2 + Fl = Fh/2 -Fl/2 +Fl = (Fh - Fl + 2Fl)/2 = (Fh + Fl)/2 !

Either way the correct center frequency is the frequency that is in the center of the bandwidth.
This doesn't necessarily means the peak frequency though.
I'll fix the pdf as soon as I can, thanks for reading and trying to understand.
My very best regards,

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


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 Post subject: Re: Certification
PostPosted: Tue Sep 28, 2010 2:39 pm 
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Joined: Fri Apr 17, 2009 7:52 am
Posts: 379
Location: Boden, Sweden
Hi Araz,
PDF fixed now! This pdf has been downloaded 5088 times, it is a pity that only now this has been discovered.
Regards,

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


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 Post subject: Re: Certification
PostPosted: Tue Sep 28, 2010 4:53 pm 
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Joined: Wed Sep 08, 2010 8:50 am
Posts: 8
Hi Admin,

thank you very much for your help. I find also thats pity. but you have fixed it now and every one can calculate or understand Fc right.
maybe I'll need an 400 MHz Antenna, because i'll get an used TRX and i want to test this system. can you tell me if your Company have an used or new (inexpensive) 400 MHz Antenna? :)

best regards


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 Post subject: Re: Certification
PostPosted: Wed Sep 29, 2010 6:12 pm 
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Joined: Fri Apr 17, 2009 7:52 am
Posts: 379
Location: Boden, Sweden
Hi Araz,
Antenna manufacturers usually design and build their antennas to target a specific system. This means that you cannot buy an antenna from Geoscanners and plug it into a Mala Geoscience radar system. There are a few companies that have compatible antennas among different gpr systems, for instance most antennas from Geoscanners AB can be safely run with GSSI or IDS systems. Our radar systems also can run GSSI or IDS antennas as well. As said before, the TX and RX electronics are more often than not already included with the antenna, so there is no need to purchase them separately.
We do have a "400" MHz antenna, it is called GCB-400 and we can sell you only new ones, but I need to insist on the fact that you need a GPR system to run those.
For questions regarding sales, quotations etc I would like you to send me a PM.
My best regards,

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


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 Post subject: Re: Certification
PostPosted: Wed Sep 29, 2010 7:09 pm 
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Joined: Wed Sep 08, 2010 8:50 am
Posts: 8
Hi Admin,

what is crucial for the antenna?

i thought only the following properties are necessary

Feed Point impedance
Transmitted Pulse Amplitude
Transmitted Pulse Width
Receiver Sensitivity
Pulse Repetition Frequency
Scan Rate
Range
Filter
Gain Points

I have no idea which kind of TRX i'll get it, because my University want to buy it.
i'd like to test it to get more Infos about this technology.

could you please sent me the Datasheet of GCB-400, i'll just compare this with the TRX-Datatsheet (as soon as i get).

with best regards


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 Post subject: Re: Certification
PostPosted: Thu Sep 30, 2010 7:02 am 
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Site Admin

Joined: Fri Apr 17, 2009 7:52 am
Posts: 379
Location: Boden, Sweden
Hi Araz,
Actually all parameters are important. A major gpr manufacturer has a very good slogan "The difference is the data" and I couldn't agree more with that. The major thing when comparing systems/antennas are not the parameters, but the quality of the data these systems/antennas provide.
My best regards,

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


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