ntsc signal spikes

Question

ntsc signal spikes

Closed this issue 3 months ago · 9 comments

not sure if it's the hacktv-gui or the hacktv software, but when making ntsc signals, i save signal as float file, when i play it back in gnuradio, i see spikes in the i and q signals. at the sync pulses, i see it go from 1 to -1 in short blips.
hard to explain, i sent the iq file to bladerf and see the spectrum flash , not sure if the i or q signal is getting clipped when the file was being generated. any insights ? thanks

Answer 1 · 2024-09-17T21:42:56.000Z

Can you share the hacktv command line that produces the IQ file?

Answer 2 · 2024-09-18T16:03:35.000Z

-o /home/drsdr/Music/tviqfile.dat -t float -m m -s 13500000 -filter /home/drsdr/downloads/video.mp4

Answer 3 · 2024-09-18T16:25:35.000Z

I'm not able to reproduce it here, the syncs are not overflowing the output.
Are you doing any signal processing in gnuradio that might be introducing them?

Also can you tell which version of hacktv you are using? Newer versions have the --version argument.

Answer 4 · 2024-09-18T18:46:33.000Z

ok thanks, i am just using the gnuradio file source and feeding that into a qt gui sink block, as for hacktv , i just followed the getting started guide for linux, and it told me to apt get install hacktv .
perhaps i'll try building hacktv from src folder and see if issue goes away, thanks for looking into it. cheers

Answer 5 · 2024-09-18T21:41:57.000Z

Ah, yeah that might be an older version. I tweaked the levels of ntsc/m earlier in the year: 40c0aa6

Answer 6 · 2024-09-19T13:47:29.000Z

also can you provide me the complete steps to build the project? do i have to do gitclone commands in the terminal before the cd src and make ?

Answer 7 · 2024-09-19T23:21:58.000Z

You can git clone, or download the source in a zip: https://github.com/fsphil/hacktv/archive/refs/heads/master.zip

There's some notes in the README to build it, it's quite simple. Hardest part is installing the dependencies.

Answer 8 · 2024-09-23T16:46:46.000Z

i compiled the src folder, and now the ntsc spikes are gone.
when will the : apt get install hacktv , have the latest src ?
the hacktv in the dragonos build seems to have the old hacktv as well.
anyway compiling the latest src fixed the issue, thanks again.

Answer 9 · 2024-09-24T14:18:02.000Z

Good to hear it's working.
Unknown on the package update, I don't really do releases so it's up to the packager. It would do no harm to send them a message.