Unexpected success in signal integrity. - Page 1
Forum section: electronics / general

author: vlad777
author_rank: Frequent Contributor
timestamp: November 01, 2021, 09:06:45 pm
content: Unexpected success in signal integrity.I have/had a problem that, when my computer is on, it's interference drowns out the tv signal.(I don't have, and can't install ground, I only have phase and neutral.)I tried to put a ferite on the hdmi cable, but it didn't have an effect.(Assuming that hdmi cable is shielded.)(When the pc is off , tv works normally)So I tried to wind up a wire around the hdmi cable and connect it to the oscilloscope, inan attempt to see the interference from pc.Surprisingly, tv started to work and didn't drop out.So how long and how many windings should my wire be; also should I put a resistor accross athis coil, to dissipate the interference signal energy, and what should be the resistance?I assume that the interference is mostly from smps, so 40-150kHz.Many thanks.PS Sorry for the spelling errors , spellcheck doesn't seem to work

author: RJSV
author_rank: Super Contributor
timestamp: November 02, 2021, 12:30:03 am
content: Fascinating, Vlad !My first thoughts go to SHIPS and how they have to 'make an artificial ground'. I will do some WEB search on that. I think also you could benefit from an RF Sniffer: some little hand-held crystal rectified with 12 inch dipole antenna. That helps get specific with spots on that cable.Of course the TV itself seems to be the best trouble point detector.I will do some thinking / WEB searches and try to respond (later).Great subject.

author: Brumby
author_rank: Unknown
timestamp: November 02, 2021, 12:51:05 am
content: If you have something in place that is working, I'd leave it alone!! Seriously, why spend time chasing down a path that is not going to make things any better?What I would suggest is that you keep monitoring and see if your "fix" keeps working - and only start playing around if you find occasions where it doesn't.As for what you should do (if it does show less than optimal results)..... My first piece of advice is to take note of exactly what you have done (number of turns, turn spacing, location on cable, etc.) so you can re-create that again ... then experiment.

author: vlad777
author_rank: Frequent Contributor
timestamp: November 02, 2021, 02:07:54 am
content: You know these TVs have "signal quality" metrics. This still drops periodicaly but the picture is ok.So there is something to improve on.Also what kind of coupling is this? The shild of the hdmi cable is (one winding) of one coil going through the center of another coil.I have never learned anything about this arrangement. It reminds me of homopolar motor (also a mistery to me).I have already seen this interference in another scenario where automated led light would kill the tv signal.So SMPS work on tens of kHz but may ring in 100MHz range, what do you think?

author: RJSV
author_rank: Super Contributor
timestamp: November 02, 2021, 02:28:23 am
content: Is this TV receiving NTSC type air transmission?Does your area use a digital transmission format ?And do you use an old school type Picture Tube? That can put out 50 Hz and some 100 hz.I'd like to see any crude schetch : what happens with the 'ground' terminal, on the scope probe ? Just hanging, or did you connect the Scope probe ground to the (far) end of that winding.As to the power supply, I've seen often a big ferrite bead can go round the output lead, as well as some big capacitor. Sometimes a tiny, 10 pf type cap has the speed needed, to load down an rf 'hash' noise.With some CRT related interference, even your screen content, in itself, can vary the noise levels (a bit).

author: vlad777
author_rank: Frequent Contributor
timestamp: November 02, 2021, 02:41:49 am
content: Digital DVB-T2 led 43" TV.

author: RJSV
author_rank: Super Contributor
timestamp: November 02, 2021, 03:14:43 am
content: I see some DTV signal quality products, for a few bucks; but that might be similar to your TV having signal strength read out. Possibly change the results you are observing: re-arrange the room, giving some distance between.Your 'coil secondary' needs two connections, (I think)although there is always capacitative coupling, everywhere to everywhere, I suppose that's enough to have current flow down the winding.It's just that (we) look to BOTH ends of a coil / transformer, when evaluating a circuit.Wouldn't take long, to also try just two values of a load resistor, like 330 ohms, and also try 10 k ohms.

author: vlad777
author_rank: Frequent Contributor
timestamp: November 03, 2021, 09:23:04 pm
content: This wire thing I did, works perfectly until I turn off the TV. (I don't touch the wire or antenna.)Then the TV will not work until I move the whire like you would do when adjusting antenna.So I wonder does the TV tuner has some functionality to adjust to the channel(air) ?Old 56k modems had the ability adjust to the wire whith:probing, ranging, equalizer, echo canceller training.How are these methods called in TV industry?

author: wraper
author_rank: Unknown
timestamp: November 03, 2021, 09:35:16 pm
content: Your HDMI cable probably is a substandard piece of garbage and you should replace it with a better cable.

author: vlad777
author_rank: Frequent Contributor
timestamp: November 03, 2021, 09:36:29 pm
content: 5$ hama cablehttps://en.wikipedia.org/wiki/Hama_(company)

author: wraper
author_rank: Unknown
timestamp: November 03, 2021, 09:42:09 pm
content: Hama should be fine I guess but $5 for it is a bit suspicious. Try changing display resolution or refresh rate.