How long can a TV extension cable be?

[MM]

Right, the new LCD TV has arrived and I've set it up in the kitchen. Found 77 digital TV channels, 35 Radio, 22 Data/Other (what ever those are).

**It also found 14 analogue channels**, which astonished me. I had always assumed a digital TV can only receive digital signals. I've switched through BBC One, Two, ITV, Channel 4 and Five, no problem. Five gives the best picture (reception).

Initially, I tried setting up the TV in the living room, the one place where the picture was grainy on the analogue portable. The LCD TV said "weak or no signal".

So there's definitely a problem there. To cease with the guess-work I have measured the actual length of the cable from the amplifier to the wall plate: 13 metres +/- 20cm

The length to the kitchen wall plate is a lot shorter. I haven't measured it, but it'll be about 6m

MM

[tony sayer]

In article , MM scribeth thus

Nope.. Our new Sony receives analogue and digital expect that round these parts analogue is off the air from the 13th but it still has its uses for a couple of analogue security cams that are in the distribution system:)...

[John Williamson]

Which proves you have a cable related fault. Or, as an outside chance, a fault on the distribution amplifier. But you've tried swapping the connections round at the amplifier end?

Which, with undamaged cable and a decent joint at each end will make sod all difference. If one had been 50 metres and the other a couple of metres, maybe you'd see a difference you could show with a meter.

[MM]

Yes. No diff.

You mean, the 13 metre distance should be fine, yes? (I mean, to the living room wall plate.)

Does it make a difference that there is another unconnected aerial cable in the same conduit? What they did on constructing the house is plan for a satellite dish in case the buyer might eventually want one, so they left a lengthy coil of aerial cable (presumably the CT100 that has been referred to in this thread) in the corner in the living room. This is routed up though the same conduit in which the said 13m length of cable from the loft-mounted amplifier is routed. I just wondered if there mightn't be some sort of interference between the two cables, the "loose" unconnected roll and the one connected to the wall plate.

Note that this "spare" roll of cable is taken up into the loft through the conduit and then there is another generous length of it lying around for any future satellite dish installer to make use of.

MM

[tony sayer]

In article , MM scribeth thus

Umm ... you are on the -right- cable aren't you?..

Has happened...

[MM]

The spare roll (for the provison of a satellite dish) is not connected to anything. Just routed down the same conduit to the living room, terminating in said spare roll (which one doesn't really notice as it's tucked behind the TV table).

What I could try is a 15m length of CT100 to which I could fit the appropriate connectors, one end for the amp in the loft, the other to the TV (or buy a ready-made cable). Then I could string out the 15m and see whether the TV complains then of a weak signal.

I'd pull the cables out of the conduit if I could, but they are really tight in there. Why the bloody hell the builder couldn't have used two separate conduits, beats me. Would have added minimal cost to the overall cost of building, and they didn't stint elsewhere. Generally, the house is a quality build, compared to some other modern, new houses I've seen. Very small local builder.

MM

[Dave Liquorice]

Quite frequently but earlier everything was working well after the cable in the loft was rerouted but it was then fiddled with again and is now broke again. I suspect a break/kink in the cable somewhere. As there is a spare length just switch over to that.

[MM]

Ah, well, I suppose I could do that, but it would negate the provision by the builder for a satellite dish later on. However (thinking aloud...), why should I bother myself about what the next owner, whenever that might be, wants or doesn't want. Until your suggestion above, I had kind of looked at that spare roll of cable as sacrosanct!

MM

[fred]

In article , MM writes

If installed by the builder then don't get your hopes up that it's decent stuff.

Strip the sheath on a bit at the end of a spare and/or on the reel and compare with the pics here to be sure:

[tony sayer]

In article , MM scribeth thus

Yes but the right cable is connected .. sure of that?..

Yes good idea..

Quite .. maybe there're crushed can cause all manner of odd problems..

[Terry Casey]

Something that it doesn't seem easy to find data on - but there is a graph on the Vishay data sheet at

indicates that reactance versus resistance for a 0.35W 75 ohm carbon film resistor is virtually unity up to 1GHz!

[Ian Jackson]

In message , Terry Casey writes

Indeed.

While cracked carbon resistors potentially are likely to have the lowest inductance, they are neither high tolerance no high stability. Surprisingly, some spiral cut metal film resistors don't seem to have excessive inductance. That said, I recall an impromptu production-line change to a certain type of resistor (Electrosil, I believe) causing serious problems at as low as 200MHz.

I suppose that today's tiddly chip resistors are too small to have much inductance . Mind you, I'm surprised they are big enough to have any resistance!

As for making good terminations, even though the resistor has some inductance, the secret is to space the resistor at the right distance above a groundplane. This adds capacitance, distributed along the length of the resistor. In effect, the inductive resistor becomes part of a transmission line, and a good wideband match can be maintained to the cut-off frequency.

[Terry Casey]

Strange!

I clicked the link in your reply and it instantly downloaded a third copy of the file!

(The second copy is from where I checked the link in my previous post ...!)

[Ian Jackson]

In message , Terry Casey writes

It's nearly an hour later, and I've tried it again. Eventually, my computer decided there was a PDF to download, which I did. [Still got the blank screen, though!] I see that the Vishay resistors are high quality carbon film, which explains their good RF characteristics.

[MM]

I had another brainwave a few minutes ago. Is there a wireless way of connecting the aerial amplifier to the TV?

MM

[John Rumm]

Not realistically.

[The Natural Philosopher]

well yes and no.

And realistically, BUT its complex.

You could have a selection of tuner dongles couple to a computer that would relay live video streams over a wifi link to computers geared to receive them..

Or to could build your own relay station, and downconvert the TV bands into lower channel numbers ( to prevent instability) and re-radiate into your location..

But a bit of cable does seem a lot simpler.

[MM]

I thought there were these gadgets advertised whereby you could watch a program anywhere in the house?

MM

[John Rumm]

That's a "video sender". They can transmit a single channel of baseband video (i.e. 0 - 6MHz, not the 450 - 950MHz of UHF RF from the aerial). So you could take the AV out from a VCR for example, and send it to a remote TV using one of these. That is not what you want to do however - you want the full RF band.

[MM]

Okay, I'll shut up now! ;)

MM