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bastibl / gr-rds

FM RDS/TMC Transceiver
http://en.wikipedia.org/wiki/Radio_Data_System
GNU General Public License v3.0
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Small comments to the great .grc examples #72

Closed Brumi-2021 closed 1 year ago

Brumi-2021 commented 1 year ago

Hello thanks a lot for sharing that gr-rds and FM stereo ( rx / tx) . Great job, it is the perfect reference that I was searching, and also it works with version gnuradio 3.10.6 !

Just let me add small comments to your examples, for your consideration , (1) rds_rx.grc Regarding that deemphasis block , as I am in EUR, I would just add this comment , Tau : Time constant in seconds (75us in US, 50us in EUR) image

(2) rds_tx.grc Here in that transmitter example , I would just add two comments ,

a-) I think it is missing to add in audio baseband , the two symetrical pre-emphasis filters , image

b-) Regarding the modulation index level of each part , If I understood correctly , current grc is using 26% for (L+R) and (L-R), image (but not sure if this is the right FM stereo specs)

Then , based on that , my understanding is that in FM STEREO transmission,
(L+R) baseband , and (L-R ) double sideband suppressed carrier (DSBSC) sub-channel , could be each one 42,5%,
Pilot Tone 19Khz 10% , and RDS BPSK around 5% .

image

In that sense , I think we can increase that 0.26 to 0.425 , if I am not wrong .

Feel free to close or modify that issue , if it is not completely correct,

Cheers, and thanks for your great contribution to gnuradio community !!!

bastibl commented 1 year ago

Thank you very much for the issue and for the detailed comments. This sounds very reasonable to me. Would you mind opening a PR to incorporate these changes?

Brumi-2021 commented 1 year ago

Ok , thanks , I will try to submit the related small PR to update accordingly those two GRC examples .

BTW , two more small comments , in the current RDS receiver , I do not see two correct dots in the decoded BPSK constellation, I saw just an horizontal line , maybe it is my set up problem . And regarding the transmitter , I tried several different receivers . The stereo separation works very good , but I always can hear some very small residual background audio noise there in both channels , not sure where it comes from , pending to investigate it . I tried to increase the RF signal but not related. Anyone had same issue ?

bastibl commented 1 year ago

Closed with https://github.com/bastibl/gr-rds/pull/73