Re: taps for a Raised Cosine function

[Fabian Schwartau]

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.

Fabian

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:
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.