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

[Tim K]

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> wrote:

Hi,

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/ (examples/psk31_tx.grc)

Receive: https://github.com/tkuester/gr-psk31/ (examples/psk31_rx.grc)

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: http://www.megafileupload.com/7sm9/psk31_tx.grc 

Transmit Image: http://pasteboard.co/giNm3kNzC.png or http://www.megafileupload.com/7smc/psk31_tx-audiocard.png

Receive Graph: http://www.megafileupload.com/7sma/psk31_rx.grc

Receive Image: http://pasteboard.co/giOlxtWUf.png or http://www.megafileupload.com/7smb/psk31_rx-audiocard.png

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 (multi_tx.grc)

Receive:  https://github.com/argilo/sdr-examples (tutorial/6_psk.grc)

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: http://www.megafileupload.com/7smi/psk31_tx-attempt2.grc

Transmit Image: http://pasteboard.co/giOMGNqD9.png or http://www.megafileupload.com/7sme/psk31_tx-attempt2.png

Receive Graph: http://www.megafileupload.com/7smh/6_psk-hackrf.grc

Receive Image: http://pasteboard.co/giPflR4TI.png or http://www.megafileupload.com/7smf/6_psk_hackrf.png

For the receive, I just left radio rx part in and replaced the decoder parts with decoding logic from https://github.com/tkuester/gr-psk31/ (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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