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Some experiments with SDR.


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#1 hhm0

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Posted 03 January 2014 - 12:25 AM

After reading the awesome post @

http://s4gru.com/ind...creen-part-one/
, I decided to do some stuff with my LG-D820, RTL-SDR(w/E4000,and a 1-paper-clip antenna).

 

Using the calculations mentioned in that post, I tuned to the 18xx frequency, and to the 19xx, based on the info from 1x engineering. I saw a wider signal than I was expecting, but soon found that the 1900 band uses 5MHz allocations, and not 1.25 as 800 does.

 

I have been getting eHRPD w/EVDO, and occasionaly 1x, so did not need to check LTE.

 

I made a call, checked for new email, and streamed video, as testing.

 

However, according to that post, 18xx is uplink (phone to tower) and 1900 is downlink (tower to phone). This was what the looking around showed me. However, I only saw traffic on the uplink (a lot, proportional to the actions being performed (email checking makes a bit of activity, and watching streaming video makes much more, for longer). However, on the downlink frequency, no discernable activity showed. Is this because my paper clip antenna will not pick up the towers anyway, or is this my device doing secret stuff? :-D Or is an alternate downlink frequency being used, or is my device rebroadcasting traffic (for the NSA :-D), or maybe for traffic alleviation via mesh network

:-D?

 

Attached is the screen of SDR app!

 

Enjoy! :-)

Attached Thumbnails

  • 2014-01-03-015754_1280x800_scrot.png


#2 dbsynergy

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Posted 03 January 2014 - 01:42 AM

It's probably that the paperclip can't hear the tower very well. Those cheap SDR's don't have very good receive sensitivity. Since your phone is probably very close to the SDR, it will show a very strong signal, and depending on how your signal is on your phone, it could be broadcasting something like 5 watts of power. 

 

I've been having some fun with my RTL-SDR and I'm considering getting a more expensive Ettus Research SDR to experiment with. I actually hooked my SDR up to my big ham radio antenna in my back yard and I can hear AM broadcasts from the other side of the world. Those things are a lot of fun.



#3 WiWavelength

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Posted 03 January 2014 - 05:32 AM

If the handset is sitting right next to the paperclip antenna, the uplink RSSI is probably around 0 dBm, while the downlink RSSI is probably in the neighborhood of -90 dBm.

 

AJ



#4 hhm0

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Posted 04 January 2014 - 10:45 PM

Thanks for the info, everyone!

 

Makes sense. (and as far as I know the RTL-SDR does not use beamforming techniques for SDMA receiving out-of-the-box :-D)

 

But anyway, it is pretty awesome seeing my device radio-waving!

 

I don't have an amatuer radio antenna, since I don't have an amateur radio license (at least not yet)!



#5 kg4icg

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Posted 05 January 2014 - 04:27 PM

Most Hams build there antennas for the higher bands. You do not need a license to listen and you can find the info on the net. In the order of a high gain directional antenna will work best.
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#6 hhm0

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Posted 21 January 2014 - 09:36 PM

Antenna input is attached to coaxial cable which goes to somewhere outside (hopefully roof antenna, hard to work outside in the winter coldness to verify this!).

 

1x800 voice call, uplink (signal changes based on voice, full volume -> full signal):

800up.png

 

1x800 voice call, downlink (in order to see any change in signal, had to hold the device within a few inches of the SDR device. Signal may be some kind of subtraction/difference or something.):

800down.png

 

Bonus...

EV-DO data 1900 downlink:

1900down.png






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