Digital TV Reception - Radio Frequency Interference - Transformers / Dimmer Switch

soflahe · 08-11-2005, 11:15

I recently had 8 small downlighters installed in my living room. The lights are on a dimmer switch and use step-down transformers (4 I think). If the lights are off there is no problem and if the lights are fully on there is no problem. However, at a certain point in the power spectrum the (digital) television reception is adversely affected.

The ntl cable is dual screen coax and it runs up one wall, across the ceiling (where the lights are installed) and down the opposite wall where it meets the TV. If I run a cable across the floor there is no problem.

I expect that the problem is being caused by either the dimmer switch or by one or a combination of the transformers.

I would be very interested to learn if anyone else has had similar experiences or if anyone has any suggestions or recomendations.

Thanks!

SMHarman · 08-11-2005, 11:25

Are the LV transformers dimmable?
Does the dimmer switch support dimming of LV transformers?
How close are the transformers to the coax when in the ceiling void?

Stu038 · 08-11-2005, 11:58

When you say DTV is affected is that all channels or just some, also does the STB connect to your TV via scart or coax?

soflahe · 08-11-2005, 12:10

Are the LV transformers dimmable?

I don't know but I expect that they are. We previously had 6 identical downlighters in the same room which also functioned with a dimmer switch. We never had a problem. However, in the old configuration there werew less transformers and the cable ran along the floor and not across the ceiling.

Does the dimmer switch support dimming of LV transformers?

I don't know but I expect that it does.

How close are the transformers to the coax when in the ceiling void?

I imagine that at least one of the transformers is within 1 metre of the cable but I don't know for sure. I'm not entirely sure how many transformers there are nor do I know their exact location.

I currently think that the fault may be due to (1) the location of the cable with respect to the nearest transformer or (2) the incremental number of transformers in the ceiling. However, might it be the switch? If it is the switch that can be easily solved.
__________________

All channels are affected. However, some are worse than others.
The STB connects to the TV via a SCART.

Stu038 · 08-11-2005, 12:41

That's a lot of nasty wide band interference there if its affecting all channels.

I'm guessing that the reason your having to route the cable this way is to avoid door frames etc..? If that is definitely the route you want the cabling to go then your only real option is to get service out to have a play, ntl do use a quad shielded cable as well as the standard RG59 (but only in black) which may help your situation, the problem is that the majority of the service techs won't know anything about it as its primarily used within the Headends and Hubsites.

I would suggest that you give faults a ring and ask for a visit, then when the service tech arrives explain things to him and politely suggest that he tries some 59 HEC and connectors that his supervisors should be able to get from Headend or Local Access networks. May take a few visits and there's no guarantee that it'll fix the problem but its worth a try.

soflahe · 08-11-2005, 13:47

You are absoloutly right about the cable routing. However, the cable was rerouted by my electrician and not by ntl. If past experience is anything to go by I expect that ntl are unlikely to help me with recabling. I think that rerouting regular cable beneath the skirting boards should solve the problem.

SMHarman · 08-11-2005, 14:16

It sounds like some poor lighting hardware, by comparison I have 8 100W LV transformers in my roof void, each attached to a single 50W bulb, all attached to one dimmer.
The CATV cable runs through there and by electrician did a cowboy job on this and put standard TV ariel coax in, instead of Sat.CATV coax so has braided shield only.
No interference though.
What has changed to cause this, the lighting or the cable routing, or both.

altis · 08-11-2005, 15:42

Quote:

Originally Posted by soflahe

... the cable was rerouted by my electrician and not by ntl ...

I wonder what cable he/she used...

soflahe · 08-11-2005, 16:04

The cable was standard (?) dual screen.

Unfortunately there are a number of changes hence the difficulty in isolating the exact cause of the problem.

1. Originally there were 6 lights attached to 6 (?) transformers. There are now 8 lights attached to 8 (?) transformers. There are an incremental 2 lights and 2 transformers (I am asuming 1 transformer per light).

2. The original cable was dual screen and ran across the floor. The new cable runs up and across the room through the ceiling void. Accordingly, the cable is now closer to both the lights and to the transformers.

3. There is a new dimmer switch (although the old dimmer switch functioned perfectly).

4. There is a new wall mounted junction box (although the old one functioned perfectly).

Something is receiving the radio interference - I justy don't know what it is.

I am hoping that simply trying a different brand of dimmer may solve the problem. Alternatively, the junction box may be causing the problem. I am hoping that I don't have to reroute the cable (beneath the skirting boards) but I expect that this will be necessary.

SMHarman · 08-11-2005, 16:07

MK Dimmers for this are very good, make sure you get the right load rating, sounds like you would need a 400W LV dimmer.

soflahe · 15-11-2005, 07:43

Many thanks to all for their help and suggestions. Just a quick note to close the loop on this.

It turned out that the wall mounted junction box was causing the difficulty. I'm not sure of the source of the interferecne but it was the junction box which was receiving it. Replacing the box (with an older version) solved the problem and saved me quite a deal of bother.