Freeview Signal

  Chud55 18:58 14 Mar 2009

My freeview signal is completely fine. I have it built into my Samsung LCDTV and the model is LE19R8. Anyway i get all the channels etc. But i recently got a PC in my room. And now I use my TV as the computer's Monitor by using a VGA Cable. Now everytime I put on the TV I loose freeview signal to most channels....about 5 Channels have still got Signal. The rest are usually glitchy and laggy or dont have signal at all. I first thought it might be the VGA cable that might of been interrupting the freeview signal. But I was wrong. So I switched my PC off and the signal was fine. Switched the PC back on signal was bad. So obviously its the PC. Also wierdly one solution was changing the plug that the PC used. But after half an hour the signal would be low again. Does anyone have a solution to this? Or does anyone else get this problem?

  Stuartli 19:15 14 Mar 2009

If your TV is being used in monitor mode, then presumably it can't be used as a TV as well (unless, perhaps, you have a PIP feature).

  Chud55 19:21 14 Mar 2009

Well yes it can be used in TV Mode. I just change the channel. When i want to watch TV when im on the PC or playing the 360 I just change the channel. And then change it back to PC or Xbox after. I think you misunderstood I dont want to use it as a PC and TV at the same time. I just change Channels anyway. Its not the VGA cable that affects the freeview its the PC. When ever its on the freeview signal is low. When ever its off the Signal for Freeview is brilliant.

  Fruit Bat /\0/\ 19:48 14 Mar 2009

Sounds as if your PC is giving out electromagnetic interference.

  johnnyrocker 20:12 14 Mar 2009

does your pc have a tv card?


  Chud55 20:51 14 Mar 2009

No....Im not running the Freeview from the TV. Im using it on the TV itself.

  octal 07:51 15 Mar 2009

As Fruit Bat /\0/\ says it sounds like it's interference from the power supply in the computer. So many of those power supplies are rubbish, especially the older type, because they were imported and don't comply with the current standards for emissions on electro magnetic compatibility. The reason you are getting a signal on 5 channels is probably that the signal which carries those channels is sufficiently strong enough to override the interference, whereas the other channels are not.

It will be a difficult one to solve, because trying to track where the interference is getting into, it could be getting down the leads that come from the computer to the TV. Do you still get the interference if you disconnect the lead that goes from the computer to the TV?

  Stuartli 10:50 15 Mar 2009

Are the five channels that can be picked up BB1, BBC2, ITV1, Channel 4 and 5?

If so, it would appear to indicate that the TV's analogue tuner is being employed (digital signal transmissions are currently at a very low level compared to analogue until each region has been switched to full digital).

  Chud55 11:51 15 Mar 2009

Yes I still get interference when I disconnect the lead that goes from my PC to my TV. I thought that was the problem because I did disconnect it at a time and the signal was fine. But about half an hour later the signal went low again. So it must be the PC itself that actually interfering with the signal. No the channels are not BBC1,BBC2, ITV1, Channel 4 and Channel 5. The Channels that do work are E4+1, Dave, Dave Ja Vu, ITV2+1, Channel 5....There are a few other that do work but I never watch them. It really depends on the day aswell. I mean sometimes BBC1, BBC2, Channel 5 and ITV1 will work like today. But on some days they dont work. Well ITV1 doesent work today. I just want to resolve the problem. Would a Freeview booster work?

  Stuartli 12:51 15 Mar 2009

That scenario indicates you might need a new aerial (wideband type); using an aerial booster on a poor signal isn't the answer.

As for the sometimes missing ITV channels, these are transmitted in a different form to the rest of the stations (QAM64 rather than QAM16); they tend to require a good signal from the TV aerial.

You can find out plenty about Freeview, transmitters etc from:

click here

Info on connecting TV and other equipment:

click here

This website also has a lot of information about transmitters etc (some of it is aimed at the trade).

  skeletal 13:14 15 Mar 2009

I’m with octal on this one. It does seem as though the PC is emitting radio frequency interference (RFI). It is most likely to be the power supply, but there are other things it could be. One interesting point is that some “dodgy” manufacturers declare that their equipment passed all the regulations when it hasn’t. They are breaking the law, but they rely on the fact that so few people could figure out interference problems they will never be caught out!

Remember that freeview channels, for a given frequency, are spread throughout the tuning spectrum, so Ch1, Ch6, 18 27 etc etc, could all be on the same frequency and get wiped out, but 2, 5, 17, 28 are on another and work. Note I’ve made the numbers up, but you can get the info somewhere if you want! (Just as I was about to post I saw Stuarli’s post, his links may give more info.)

The problem may change day by day because the signals can be so weak that many outside conditions (e.g. rain) can further weaken them at which point the local interference “wins” and all is lost.

To find a cure may be difficult; experienced radio frequency (RF) engineers devote their lives to this sort of problem.

The interference may get into the TV in several ways:
Through signal cables;
Power leads;
Directly as an RF signal;
A combination of all the above.

It looks like you have eliminated the signal cable between the PC and TV but you still have a lot to do!

I started to write a series of tests, but it quickly became too complex so I thought of something else you could try. It is to attach a ferrite core to the power lead of your PC. Fix the core at the PC end of the cable. Try:

click here

It won’t break the bank and could help. It will only do so if a lot of the interference is coming down the mains lead; if it is being directly radiated from the PC itself, it won’t be so good.

If you try any TV signal boosting methods (I mostly agree with Stuartli), place the booster as near the aerial as possible, not behind the TV where it will boost the interference and signal together.


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