Re: taps for a Raised Cosine function

A raised cosine is also known as a Hann window.

https://www.gnuradio.org/doc/doxygen/classgr_1_1fft_1_1window.html#a599d7e9625d6cc77203a8b877c4911e2a0099ec5d7a2ab5d7a7f3fd7f7835c72a

Example usage: https://github.com/bitglue/gr-radioteletype/blob/3a00e28a2c83b45e9252da41802dcbe30decc49a/python/radioteletype/filters.py#L161-L170

On Tue, Aug 10, 2021 at 12:46 PM Kristoff <kristoff@skypro.be> wrote:

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:
http://downloads.bbc.co.uk/rd/pubs/reports/1984-19.pdf

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.
https://en.wikipedia.org/wiki/Raised-cosine_filter

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.

Question:|
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,


Kr.