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Discuss RTL-SDR and cheap software defined radio
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PostPosted: Tue Sep 19, 2017 3:38 pm 
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Hello,

I've just received a GPS patch antenna from Aliexpress. What do I need to take out of the antenna to use it for inmarsat? The inside of my antenna doesn't look the same as the one on the rtl-sdr.com website. I can't see the bandpass filter.
Thanks for your help.
Regards,
James


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File comment: Inside of the GPS patch antenna
1505835297603512660670.jpg
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PostPosted: Wed Sep 20, 2017 9:35 am 
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Well this isn't a very clear image it's far too blurry.

Can you post a link to the GPS antenna that you bought?


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PostPosted: Wed Sep 20, 2017 2:37 pm 
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Hello,

Thanks for answering.
https://m.fr.aliexpress.com/s/item/32788800179.html

I managed to receive a few GPS satellites (but not enough to locate me), so I know that the antenna works. I'm using the rtl-sdr v3 to power it. I can't see any strong signals in sdr#. I haven't tried with an extra LNA. What else can I do to get a better reception?
Thanks again for your help,
James


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PostPosted: Thu Sep 21, 2017 6:28 am 
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These antennas are designed to be used sitting on the metal roof of a car, so try to get a large piece of metal for it to sit on. That will improve the reception.

I'm not too sure on where your filter is, have a look in between the two amps, it should be on of the components. Unless it's maybe just not implemented, or implemented with discrete components instead.


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PostPosted: Thu Sep 21, 2017 9:32 pm 
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I don't know much about electronics, but I can't see the bandpass filter. The inside of my antenna isn't the same as the one on page 196 of the RTL-SDR guide book.
I tried the antenna on an oven tray in my back yard (a small yard with walls all around it). I managed to get 3 SMALL bars in rtknavi, not enough to get a position. it's a bit disappointing...
Would the Outernet antenna perform a lot better (the $ 25 one) ? would I need an extra LNA or is the integrate LNA enough ?
As I haven't got mutch outdoor space, I'm looking for something I can use inside, near a window.
Apart from GPS, Inmarsat and Outernet, what other interesting things can we do with the Outernet antenna and a RTL-SDR dongle ?
Thanks again for your help.


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PostPosted: Sun Sep 24, 2017 12:06 am 
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James_from_France wrote:
I don't know much about electronics, but I can't see the bandpass filter. The inside of my antenna isn't the same as the one on page 196 of the RTL-SDR guide book.
I tried the antenna on an oven tray in my back yard (a small yard with walls all around it). I managed to get 3 SMALL bars in rtknavi, not enough to get a position. it's a bit disappointing...
Would the Outernet antenna perform a lot better (the $ 25 one) ? would I need an extra LNA or is the integrate LNA enough ?
As I haven't got mutch outdoor space, I'm looking for something I can use inside, near a window.
Apart from GPS, Inmarsat and Outernet, what other interesting things can we do with the Outernet antenna and a RTL-SDR dongle ?
Thanks again for your help.


It's possible that the antenna you have has a different (cheaper) design. If you upload a clearer image it might be possible to see what it's doing. But if you're looking at using it for GPS, then you don't need to remove any filters.

You need a decent clear view of the sky for GPS to work, it won't work if only a small portion of the sky is visible. Also, with the GPS antenna, are you remembering to power it using the bias tee? Always remember that you need to turn the bias tee on first.

The Outernet active antenna is very good, but it's limited in frequency to 1525 – 1559 MHz, and GPS is at 1575 MHz. You'll get Inmarsat and Outernet, but not GPS. With that antenna you could also get AERO, but IMO L-band AERO is not that interesting.

If you get an antenna that can go a bit higher, you might be able to get Iridium signals at 1.6 GHz.


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PostPosted: Mon Sep 25, 2017 6:32 am 
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Not all the GPS antennas have a saw filter that can be removed. Some use a very narrow band ic like MAX2659 without saw filter.
This image is useless because not clear. Posting full size images is good if you can read the names of the ICs.


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PostPosted: Wed Sep 27, 2017 8:58 am 
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Hello again,

The components are so small that I won't manage to remove them. I'm not very good at using soldering irons.
I'm not really interested in GPS signals, I just wanted to try the antenna.
I would like to try to receive and decode inmarsat messages from ships. I've tried using the rtl-sdr for pocsag, noaa satellites, tracking planes,... Now, I would like to try something else.
A nother question : on the raspberry pi, what's the difference between installing the drivers with sudo apt-get install rtl-sdr and the git clone method?
Thanks again for your help.
Regards,
James


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PostPosted: Wed Sep 27, 2017 12:02 pm 
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Not much. With apt-get you might get an older version of the drivers though depending on what Linux release version you're on.

Using git lets you get the latest version, or if you want 'unofficial' drivers that have been modified. e.g. keenerds drivers.


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