Re: [Discuss-gnuradio] BPSK31 Adventures

[Martin Braun (CEL)]

Hi Iain,

On Sun, Jul 15, 2012 at 08:13:13PM +0100, Iain Young, G7III wrote:
> Inspired by Javier and Martin's recent posts on DPSK, I thought I would
> resurrect my (Amateur Radio )(B) PSK31 transceiver implemented in GRC.

Nice!

> I set the number of constellation points to 2 (for BPSK), set the
> differential encoding to "No", and set the samples/symbol to the
> equivalent value in the MPSK Receiver block.
> 
> There I come across a problem. What to set Excess BW, Frequency BW,
> Timing BW, and Grey code to. I have looked at Tom's page on the
> Frequency BW, but am afraid I don't grok that side of things at all
> well.

Grey code doesn't matter for BPSK, so ignore that. The frequency and
timing loop BW's depend on how quickly you want to acquire freq/timing
synch, but don't worry about these, either--if you don't know what they
exactly do, just use the defaults (I think something around 2\pi/100?)
and play around with these values.

The 'excess BW' is the rolloff factor of the root-raised cosine filter.

> Is there a way to work out what those value should be from the working
> values of the MPSK Receiver block ?

It depends on your app.

> Attached is a flowgraph (both .png and .grc) Both the MPSK Receiver
> chain, and the PSK Demod chain eventually output to a file sink for
> doing the varicode decoding.
> 
> 
> Two quick further questions on the PSK Demod block (which actually
> uses the Gerneric Demod block to do most of the dirty work):
> 
> 1) Can someone confirm if I need to use the packed to unpacked block
> that I'm using ? I've seen notes that the output is indeed packed (hence
> the unpacker being in the flowgraph), but also other places saying it's
> already unpacked ? Or is it just the DxPSK block that has the unpacked
> output ?

PSK Demod packs all bits of 1 sym per byte. As you're using BPSK, you
don't need to unpack. You'll have 1 bit per byte.

> 2) Do I need to use AGC before it ? Again I came across some places
> that say it's already in there, but couldn't see any evidence. Is it
> just the DxPSK block that incorporates the AGC block ?

It's not in there, but for PSK31, you might not need it, as all the info
is in the phase anyway.

MB

-- 
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

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