Beginner

GNU Radio
1

Hello list,

First of all, thanks for the great tool.

I am a newbie, just started to play with gnuradio.

For the start, I’d like to implement some simple, low bit rate
modem.

I don’t have any particular hardware, so I’d use the sound card of my
computer, and hook up my HF radio.

So for the start I thought I download a PSK31 modem, but I couldn’t find
one. I am 100% sure that this has been done before. Could you please
give me
pointers to such projects?

The final project would be a GMSK receiver of telemetry data from a high
altitude balloon.

Thank you very much for your help.

73 de HA5OGL

–
Levente Kovacs
CTO, CSO

2

I have not seen a whole PSK31 modem implemented.

Looks like there is a decoder here:

and here:

I experimented with an encoder here:

It would be allot more work writing the GUI front end than the actual GR
portion of the modem; probably why it has not been done.

Thanks,
Lou
KD4HSO

Levente Kovacs wrote

I don’t have any particular hardware, so I’d use the sound card of my
Thank you very much for your help.

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3

On Sun, 31 Aug 2014 10:13:08 -0700 (PDT)
madengr [email protected] wrote:

I have not seen a whole PSK31 modem implemented.

Looks like there is a decoder here:
GitHub - bitglue/gr-psk31: GNU Radio blocks for PSK31 groking

and here:
GNURadio PSK31 Decoder, Part 1 | SDR Adventure

Thenks, I’ll look into it later.

I experimented with an encoder here:
PSK31 GNU Radio Simple Transmitter - YouTube

Yes, I saw that.

It would be allot more work writing the GUI front end than the actual
GR portion of the modem; probably why it has not been done.

My initial thought is that I feed the decoded bits to a TCP sink, and I
write
a GUI in C, that listens on that particular TCP port. Unix socket would
be
nicer, but I can’t find a unix domain socket sink/source.

Is there any other way to get data and feed to other C application?

73! de HA5OGL

–
Levente Kovacs
CTO, CSO

4

ZeroMQ has just been implemented in GR:

If you check out the latest GR from Github you’ll see the blocks in GRC.
I
have not tried it. Here is more info:

http://gnuradio.org/redmine/versions/42

I was playing around with receiving data from the GR flow into Python
via
message queues. They do work, and I was able to empty the queues more
than
fast enough for 31 bps. However I have read the functionality will be
deprecated. There is a good write up here:

http://ha5kfu.sch.bme.hu/fft_test

and here:

Thanks,
Lou
KD4HSO

Levente Kovacs wrote

–
Levente Kovacs
CTO, CSO
http://levente.logonex.eu

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5

Regarding doing it in C; everything seems to be mostly there to do it in
Python as a native GR application.

  1. A QT-GUI text input box would be needed to buffer-up the transmit
    text as
    it is typed, convert to varicode then drop the bytes into the transmit
    stream, interrupting the continuous 01010101… The modulation is
    simple.

  2. The RX signal processing may be able to use the PSK receiver, then a
    custom block would have to be written for the varidecoder, maybe dumping
    the
    text as messages, or to stdout.

  3. The latest QT frequency sink has a click to tune functionality,
    generating a frequency message, and the frequency translating FIR filter
    has
    a tuning message input. What I don’t know is if the PSK receiver has
    wide
    enough carrier recovery for point-and-click tuning, given 31 bps and a 2
    kHz
    channel bandwidth. I suppose some experimentation is in order.

Anyway, I think 50% of it is there already to do it all in GR.

Thanks,
Lou
KD4HSO

Levente Kovacs wrote

My initial thought is that I feed the decoded bits to a TCP sink, and I
write
a GUI in C, that listens on that particular TCP port. Unix socket would be
nicer, but I can’t find a unix domain socket sink/source.

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