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Re: taps for a Raised Cosine function

From: Fabian Schwartau
Subject: Re: taps for a Raised Cosine function
Date: Tue, 10 Aug 2021 21:01:15 +0200
User-agent: K-9 Mail for Android

Hi Kristoff,
You can just put an additional RRC in front of it or you can calculate the tabs by folding die tabs of the RRC with themself. There is probably a numpy function to do that. Have not tested any of that, but both ways should do the trick.


Am 10. August 2021 20:44:05 MESZ schrieb Kristoff <kristoff@skypro.be>:
Hi all,

I am playing around with PSK demodulation, now doing a small project
trying to decode the slow-speed PSK data on the 198 KHz carrier of BBC
radio 4.

The specs are here:

According the document (page 2 of the document, page 8 of the PDF), the
system uses a shaping-filter of cos(pi * f * Td / 4).
(with Td = 50)

If I am correct, this is in fact a raised-cosine filter with beta = 1.

So the document seems to specify a raised-cosine filter, both on the
transmit and receive side; so not a ROOT raised-cosine as is used in
most PSK systems.

How do I create the filter-taps for the Polyphase clock sync block for a
raised-cosine filter?

I found a function firdes.root_raised_cosine, but no firdes.raised_cosine?

Is there a way to easily convert the taps of a RRC filter to those of a
RC filter? (RC = RRC^2, so square the value of all taps?)

Any other ideas?
- put an additional RRC low-pass filter in front of the Polyphase
clock-sync block?
- use firdes.pm_remez() ?

Thanks in advance,


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