Small comments to the great .grc examples
Brumi-2021 opened this issue · 3 comments
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)
(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 ,
b-) Regarding the modulation index level of each part , If I understood correctly , current grc is using 26% for (L+R) and (L-R),
(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% .
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 !!!
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?
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 ?