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Re: [Discuss-gnuradio] PSK31 (from audio to radio)

From: Ron Economos
Subject: Re: [Discuss-gnuradio] PSK31 (from audio to radio)
Date: Wed, 14 Sep 2016 03:51:34 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

I have an alternative flow graph. It's based on the multi_tx.grc flow graph in https://github.com/argilo/sdr-examples. The osmocom Sink is set up for a bladeRF, so be sure to change that for hackRF. The message in the Vector Source block in "This is W6RZ testing." with a trailing line feed.



On 09/13/2016 11:11 PM, Cinaed Simson wrote:
On 09/10/2016 05:19 PM, pen tester wrote:
Thanks Cinaed for your response.

For everything up to the multiply on the TX side - this is actually from
a working example that TXs using an audio card [1]. So just for a proof
of concept I would like to leave that as-is and just append on TX over
Osmocom Sink. Happy to look at simplifying later, just wanted to get POC
for PSK31 over radio for now on the transmit and receive.

Also thanks for spotting my Freq mistake too.

My plan now is to use the fldigi app for testing the rx side while I try
and make the rx side work - just figuring out how to write to a wav file
sink that is accepted by fldigi too... and trying to find some TX examples.

[1] https://github.com/tkuester/gr-psk31/
<https://github.com/tkuester/gr-psk31/> (examples/psk31_tx.grc)

The output of the psk31_tx.grc example doesn't appear to be either BPSK
or QPSK - both which should have a constant envelope  - or at least
approximately constant.

Instead, the output looks like a beat signal of 2 signals close in
frequency - resulting in an envelope varying in amplitude.

I'm presuming psk31 implies BPSK with a low baud rate - 31 symbols per

I may be missing something.

On 10 September 2016 at 11:40, pen tester <address@hidden
<mailto:address@hidden>> wrote:

        Still playing around and I have a question about the value which
     should go in the Polyphase Resampler on the tx side please. Any
     advice on the AM rx too would be helpful :-)


       * Simply trying make the working PSK31 audio tx to tx over HackRF
         instead using [1] and updates from Tim's response
       * Screenshot: http://pasteboard.co/1dLjHxMAU.png


       * Simply trying to make the working PSK31 audio rx work using a
         RTLSDR instead based on [2]
       * The first line is an attempt to take in the AM signal and just
         pass it on to [2]
       * For the AM rx, I used [3] as a guide
       * Screenshot: http://pasteboard.co/1dLZWV9mv.png

     [1] https://github.com/tkuester/gr-psk31/
     <https://github.com/tkuester/gr-psk31/> (examples/psk31_tx.grc)
     [2] https://github.com/tkuester/gr-psk31/
     <https://github.com/tkuester/gr-psk31/> (examples/psk31_rx.grc)
     [3] https://www.csun.edu/~skatz/katzpage/sdr_project/sdr/grc_tutorial3.pdf

     On 6 September 2016 at 05:49, pen tester <address@hidden
     <mailto:address@hidden>> wrote:

            Yes, your graphs are really useful :-) Thank you for
         responding in such detail!

            Here is what I am up to:

         Transmit side:

           * I made your changes to your transmit graph [1]
           * All the changes were fine but I was confused about the use
             of the Polyphase Resampler as I could not get the values to
             work without underflows when executing i.e. "UUUU..."
           * So instead (this is probably wrong) I tried using a Rational
             Resampler with an Interpolation of 1e6 and a Decimation of 48e3.
           * Updated version: http://pasteboard.co/hmyGOGTE4.png
           * Either way, the tx graph looks healthier - just need some
             advice on the resampler perhaps?

         Receive side:

           * I am using the start of this receive graph [2] as it was
             using radio rx already
           * and just modifying the demod portion to be more like your rx
           * Updated version: http://pasteboard.co/hmzrMBAIi.png
           * I also need advice from anyone who could point in the right
             direction on the AM rx side please?

         [1] https://github.com/tkuester/gr-psk31/
         <https://github.com/tkuester/gr-psk31/> (examples/psk31_tx.grc)
         [2] https://github.com/argilo/sdr-examples
         <https://github.com/argilo/sdr-examples> (tutorial/6_psk.grc)
         [3] https://github.com/tkuester/gr-psk31/
         <https://github.com/tkuester/gr-psk31/> (examples/psk31_rx.grc)

         On 4 September 2016 at 12:33, Tim K <address@hidden
         <mailto:address@hidden>> wrote:

             Hey hey!

             Glad to see someone using this. (And that it's apparently
             still working! Goodness... I need to clean this up...)

             I'm giving advice freehand right now, as I don't have my
             radios with me to test this. There are definitely more
             elegant ways for this solution, this is just the quickest I
             could think of without reverse engineering what I wrote
             forever ago.

             Since this is AM, I think you'll only need the Real port on
             your "Float to Complex" block. You can attach the "Null
             Source" to the Imaginary port. Do a quick check to make sure
             the real signal's not exceeding +/- 1... you might want to
             attenuate it to +/- 0.7 for now, someone else should comment.

             As far as the transmit side goes, I'd leave everything up to
             the "Multiply" block untouched. Consider that your "audio
             input" to the radio. After that...
              - Multiply Const (set to 0.7 for safety)
              - Polyphase Resampler (float/float) set to (1e6 / 48e3) -
             This gets your sample rate up to radio speeds
              - Float to Complex (in the Real port, Null Source to the
             Imag port) - This makes your signal "complex AM"
              - Send the Complex stream into your Osmocom Sink (set to
             1e6 sps) - And transmit!

             If I remember correctly, some radios don't like working at
             non-integer sample rates. (The hackRF may be ok though...)

             Play gently with your TX gain until you can see it on
             another radio. (IIRC the HackRF is simplex... perhaps an
             RTL?) Use AM to demodulate.

             I've been meaning to do a write up on this for a while. If I
             ever get around to it, I'll make sure to CC you.

             - Tim

             On Fri, Sep 2, 2016 at 11:55 PM, pen tester
             <address@hidden <mailto:address@hidden>> wrote:

                 I am trying to get a simple working example of PSk31
                 working (transmitting with a hackrf and receiving with a
                 rtlsdr dongle). Here is what I have so far.

                 Working PSK31 tx and rx with a sound card
                 Transmit: https://github.com/tkuester/gr-psk31/
                 Receive: https://github.com/tkuester/gr-psk31/

                 These work great for sending a PSK31 message over audio
                 card and receiving with the audio card.

                 I just slightly modified them to take input from the
                 "Audio Source" block instead of a "Wav File Source" to
                 use the sound card directly:

                 Transmit Graph:
                 Transmit Image: http://pasteboard.co/giNm3kNzC.png
                 <http://pasteboard.co/giNm3kNzC.png> or

                 Receive Graph:
                 Receive Image: http://pasteboard.co/giOlxtWUf.png
                 <http://pasteboard.co/giOlxtWUf.png> or

                 Turning up the audio a little and tuning to 2003 approx
                 on the rx graph results in reception of the sent message
                 "Hello World!"

                 Reference version for using hackrf instead of sound card
                 Next, I wanted to modify these to audio versions to work
                 over Radio using a HackRF and RTLSDR dongle.

                 These graphs seems very useful but I couldn't get it
                 working end to end for some reason.

                 Transmit: https://github.com/argilo/sdr-examples
                 <https://github.com/argilo/sdr-examples> (multi_tx.grc)
                 Receive:  https://github.com/argilo/sdr-examples

                 I made some changes to the freq to be in range for
                 RTLSDR .e.g changed freq from 441e6 in ref graph,
                 changed to 841e6.

                 My merged attempt
                 The attempt I am currently trying to get working is
                 based on the audio soundcard flies for the transmit:

                 Transmit: Using  audio tx (psk31_tx_attempt2): where I
                 just replaced the audio sink with the Osmocom sink (not
                 sure what else is needed here for transmission over hackrf)

                 Transmit Graph:
                 Transmit Image: http://pasteboard.co/giOMGNqD9.png
                 <http://pasteboard.co/giOMGNqD9.png> or

                 Receive Graph:
                 Receive Image: http://pasteboard.co/giPflR4TI.png
                 <http://pasteboard.co/giPflR4TI.png> or

                 For the receive, I just left radio rx part in and
                 replaced the decoder parts with decoding logic from
                 (examples/psk31_rx.grc). I made other minor changes such
                 as freq and sample rates.

                 My question
                 So in summary, just looking for a little guidance on my
                 merged attempt to get psk31 out over a hackrf and
                 received using a RTLSDR. Any advice for a learner would
                 be great :-)


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