On my raspberry 3B+ cpu load is around 50% (SDR and drift correction running)
Beiträge von DL3DCW
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The described raspberry with touch display works not only as a stand alone SDR receiver for NB downlink, it also takes the drift correction and control the TX chain. First, a Yaesu FT817 transceiver (connection via CAT) and a Kuhne MKU2424 Up converter (connection via RS232) will be used for the uplink.
So only a mouse click on a free frequency or a CQ call in the waterfall is needed and the TX automatically adjusts to the appropriate uplink frequency. Additionally there are some useful functions/tools planned.
If the raspberry solution works well in practical operation and the software is more user friendly i will provide a memory card image and a manual / circuit board as soon as possible. But please be a little bit patient. Its only my hobby
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Until now i have no problems with the two SDR sticks in my raspberry setup. Everything works fine. And "drift free". I am very happy with this solution
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At the moment everything looks very good. I'm excited.
As long as the rx signal drifts by a few kHz (see main waterfall), the demodulated audio signal only drifts by a few hertz. And all that with so little effort.
Only one additional SDR stick and a small software tool is required. All on one raspberry. Not more. Perfect.
If everything works fine i will create a sd card image for raspberry pi (like HAMServerPi). That makes it a little bit easier.
Alternatively everyone can create his own solution for other systems by using/modificating the files/sources from sd card image. And makes it better then i can do
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I love my raspberry and raspbian/linux. Because i'm only a hobbyist. Everything is a little bit easier. At least for me
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I only put the idea (not initial from me) of software drift correction in my raspberry setup and hope to make something a little bit easier. For me and for all of us. Thanks to you and thanks to all. That's the spirit of amateur radio
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Since the described software drift controller is tested in my raspberry setup it continues here (for a better overview):
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Testing software drift controller on second SDR stick ...
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But be careful, i have learned as soon as you say "this works better than GPSDO" then you start a witchhunt and a lot of OMs declare you "insane"...
For me the described solution seems to be working fine. Specialiy on my little raspberry station setup. Thats all i need. Keep it simple
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Do you now use SvxLink on the second stick to listen to the correction signal?
I only use a (modified) devcal utility from SvxLink package for calculating drift offset on second SDR stick.
If i get GQRX working with rtl_tcp server then i only need one SDR stick for all. In the moment GQRX crashes if i want to use rtl_tcp.
But with second SDR stick it is a nice workaround. I can live with that if i am not able to solve the problem with GQRX and rtl_tcp.
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First "quick-and-dirty" software drift controller on raspberry with GQRX works!
I only use a second SDR stick (0,5ppm) on the same computer and a homemade software tool. No additional hardware is required. The tool can lock to any (unmodulated) satellite signal (e.g. engineering beacon). With the SDR software can be work as usual. There a no disturbing clicks etc. in the demodulated audio.
Now I have to do some fine tunings and tests. Also everything have to be much more user friendly. Because in the moment it is really a quick-and-dirty solution
On the screenshot below you can see the drifting signal in the main waterfall. Demodulated audio is very stable (only a few Hz deviation) over long time.
Image 1: Software drift controller and GQRX on raspberry pi
Image 2: "Drift free" satellite receiver
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However, a second SDR is required if the frequency ranges are far apart. But if we can use the AMSAT beacons as reference signals this will be not a problem.
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Duplicating the I/Q data and use it for both (drift correction tool and SDR software) sounds very good. This avoids the disadvantages of using two sdr sticks. We are getting closer and closer to the goal
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Found the command line tool "devcal" from SvxLink package. It can determine the deviation from a reference frequency.
Devcal and Gqrx works with two SDR sticks in parallel on my raspberry. But there is still something to do.
Not perfekt and only for first tests. But maybe this is how a solution can look like ...
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As a quick-and-dirty solution i imagine a simple tool which directly accesses a second sdr stick, determines the deviation from the reference frequency and send the correction data via the remote interface to gqrx.
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Someday a clever person will programm a SDR software that is capable of locking on a signal (in the bandwith of a RTL-SDR) and on a second (following) demodulator you can listen to SSB. That would be the nicest and easiest solution
Full ack. This will be a fine solution. Now we have to find this clever person
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I did some short test with Gqrx remote interface: Setting LNB LO take no effects to rx frequency. Only the displayed rx frequency changes. Setting new rx frequency via remote interface works fine.
If there is a drift so we can set the new rx frequency at first and then set the new LNB LO frequency.
I could not hear any (disturbing) clicks during changing the rx frequency. For SSB/CW i think this will be ok.
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In Gqrx remote interface there is also a command for get/set the LNB LO frequency. I think this will be very useful for software drift controlling.
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But would be work with any other SW which is capable of changing the frequency from an external source. I use the mouse scrollwheel in my setup.
In the Gqrx SDR-Software there is an interface (remote control) for readout and set the frequency via tcp connection.
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Confirming very strong signal on 10.489,675 MHz. Wow!
