Added an active GPS antenna to the RTL 4000 tuner/spectrum analyzer

Added an active GPS antenna to the RTL 4000 tuner/spectrum analyzer. Got a little active GPS antenna from ebay (item 150748428125) only 6 $, and made a little 'T' section to power it, while connected to the 4000 DVB-T tuner:

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That is just a LM317 to create a voltage of 4.75 V here:

active 10p GPS -0-------||-------0- E4000 DVB-T stick connected to PC USB antenna | with xpsa spectrum analyzer software SMA ) LM317 ) _____________ | | | | +4.75

+9V top + 15V ----- |in adj out|----------------- | |_____________| | | === | [ ] 220 | | 1u | | | /// ------------| === iu | | | [ ] 6k8 [ ] 680 /// | [1] | /// /// [1] could not find a 560 Ohm SMD

LM317 is a bit overkill, it is mounted on the back of the minuscule PCB. Could not find any 78L05.. Thing is powered from a very small wallwart.

There is considerable extra gain from this active GPS module, and the long cable allows to find a quiet place, far from GHz processor whisper.

So now I get a lot of very interesting GPS spectra, and I can record the IQ signal.

There does not seem to me an impedance mismatch (was my worry).

Reply to
Jan Panteltje
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You need to mark the all important RF choke and there's a typing error. I'm surprised that that you were able to see GPS spectra at

-130dBm.

connected to PC USB

spectrum analyzer software

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

On a sunny day (Thu, 28 Feb 2013 11:58:21 -0800) it happened Jeff Liebermann wrote in :

Yes, I is perhaps .3 uH, or 3.3 uH, did not have my glasses on, both will be faily high impedance, maybe you can see the color code in teh picture ;-)

My way of working is: grab in the bin and make a circuit that works with what I get: THAT is engineering. This guy has it:

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\ :-) We should be happy with people like him. An 'astronaut farmer'.

stick connected to PC USB

spectrum analyzer software

Reply to
Jan Panteltje

I have an active GPS antenna with 30dB gain that can handle LNBF voltages. You can see the GPS signal on the satellite type L band spectrum analyzer.

I got it for timing use. These GPSDOs are quite deaf for some reason, so you need really high gain antennas.

The Trimble timing antennas are at least 30dB.

Reply to
miso

PS, for signal etc, see this link:

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I am not that far yet with processing, but I can record the GPS IQ signal, for example: rtl_sdr -f 1575420000 -g 40 -s 2728000 out.dat

The amplitde of the spectrum changes in big ways during the day it seems.

PS recording 'astronaut farmer' in HD worked, this Dennis Tito is a very inspiring guy, while listening to his 90 minutes press conference:

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I realized I had my timers set for ZDF, while the transmission was on ARD, alias Das_erste, middle of the night change timers, it worked, after editing out stuff about 9 GB HD content left...

Reply to
Jan Panteltje

On a sunny day (Fri, 01 Mar 2013 14:02:15 GMT) it happened Jan Panteltje wrote in :

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OK: Recoding the GPS band as IQ signals to a file out14.dat: nice -n -19 rtl_sdr -f 1575420000 -g 0 -s 2728000 out14.dat Found 1 device(s): 0: Generic, RTL2832U, SN: 77771111153705700

Using device 0: Generic RTL2832U (e.g. hama nano) Found Elonics E4000 tuner Exact sample rate is: 2728000.137308 Hz Tuned to 1575420000 Hz.

And the result when processing the IQ signals with the mathlab (octave in Linux) routines from the link in the above site:

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gives:

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There is only a very weak signal here today, the normal GPS module hardly sees one sat: gpspc -d /dev/ttyUSB0 Panteltje (c) gpspc-0.8 for EM-411 GPS receiver board No previous position known pdop 0.0 hdop 0.0 vdop 0.0 satellites used 0 satellites in view 12 id 10 elevation 74 azimuth 177 snr 0 id 7 elevation 68 azimuth 125 snr 13 id 4 elevation 18 azimuth 201 snr 0 id 8 elevation 48 azimuth 180 snr 0 id 5 elevation 40 azimuth 298 snr 0 id 2 elevation 36 azimuth 243 snr 0 id 13 elevation 36 azimuth 75 snr 0 id 16 elevation 16 azimuth 34 snr 0 id 23 elevation 13 azimuth 81 snr 0 id 26 elevation 13 azimuth 259 snr 0 id 29 elevation 6 azimuth 318 snr 0 id 30 elevation 0 azimuth 13 snr 0

I have made several runs, with 2 different RTL tuners...

Does not make much sense, sat 4 and sat 29 are low at the horizon...

7 and 8 OK...

Need to try again later.

But at least it is all working :)

Reply to
Jan Panteltje

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