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.