How long can a TV extension cable be?

[MM]

Ah, good to know, thanks!

MM

[MM]

Thanks for the above and previously. What might I have to do when the new telly arrives next week? It's a Samsung LCD with Freeview (not Freeview HD).

By the way, I already have a Freeview USB stick connected to the PC. This is connected to exactly the same wall plate that feeds the analogue TV, if I had one in the computer room. The Freeview reception is excellent and I can receive a large number of TV and radio channels. This little gizmos has been absolutely fantastic and cost about 20 quid from Amazon about two years ago.

So, the aerial + amplifier appears fine for receiving Freeview already.

MM

[Richard Russell]

Not true. Apart from the attenuation caused, you're completely ignoring the importance of matching the characteristic impedance of the cable to its load. Adding a 'tiny capacitance' in series will wreck this matching, resulting in reflections. These may be visible as ghosting/ringing (on an analogue signal) or cause deep notches in the frequency response (affecting both analogue and digital reception).

That may well be true, but it doesn't alter the importance of correct matching.

Richard.

[Ian Jackson]

In message , BartC writes

You're just asking for trouble!

I feel quite sick!

If you can't (or can't be bothered to) solder the coax solid inner conductor into the pin, instead of 'crimping' it with a pair of side cutters or pliers, I reckon it's better first to put a slight 'kink' the inner conductor at about 5mm from the end. The kink should be made sufficient to make it quite difficult to push the conductor into the pin. Not only does it give you a reliable, relatively permanent contact, but it has the additional advantage that the plug can later be removed, and re-used!

[MM]

The amplifier is plugged into the mains. They fitted a 13A socket in the loft near the amp just for that purpose.

I've now seen that the FULL output socket on the amp is supposed to have a terminator if nothing is connected to it. According to the user guide I downloaded, the installer is supposed to fit this. He didn't.

Can one get a terminator from Wilkinson, or do I have to order one online?

(Dunno what the effect is of not having the terminator present.)

MM

[MM]

Nope!

Everything you and others said about a suspected dodgy connection or broken wire must be true, since this morning I moved the cable some small distance (still left it lying on top of the insulation, i.e. not routed along the joists) and now the picture is back to being grainy.

I moved the TV to another room in case the signal this morning (from the transmitter) is weaker, but no, reception in the kitchen is as good as ever (i.e. excellent).

I've been up and down the step-ladder numerous times, with the TV in the hall on an extension cable from the wall plate, and up in the loft I've jiggled like crazy, but the picture doesn't improve. Dunno whether it helps the diagnosis, but when I say grainy, don't get the idea that the picture is unwatchable. It is still watchable, but it is NOT as clear and as sharp as in any of the other rooms.

But last night it WAS excellent, even in the living room, so it must have been pure fluke the way I first un-routed the cable and left it lying.

Dunno what to try now. I checked the plug where it goes into the amp and it looks all right. Same with the wall plate, I've got it off the wall and it's dangling there, but the connection seems well-made.

MM

[John Williamson]

Typical of either damaged cable or a bad connection. Disassemble the plug and wall plate and re-make the connections properly, and if that doesn't cure it, you *could* get a proper aerial cable tester and find out where the cable fault is, or you could just replace and re-run the cable properly.

If it's the polythene and air insulated type, once the insulation gets kinked, it can cause problems later. Foam insulated isn't so bad, but damage can still linger. Foil shield is, IME, more fragile, too, and can be a right pig to terminate correctly.

[Bill]

In message , MM writes

Only if you want to be a perfectionist, you will be OK without it. I have put anylisers on the output of distribution amps and looked at the levels with and without having the main, and unused, outputs terminated, there is a measurable difference but not enough to cause the problem you described.

[The Natural Philosopher]

depends on how buffered it is: can cause cable resonances if its all been done with attenuative pads.

But if it DID briefly work WITHOUT the pad, that aint the problem....

[Bill]

In message , BartC writes

A description of how to fit them is here:-

a job is worth doing then it is worth doing properly!! :-)

[tony sayer]

In article , MM scribeth thus

Was the plug soldered properly?. Was the cable kinked at all anywhere?..

[tony sayer]

In article , BartC scribeth thus

Sorry but thats not very good practice or science come to that. If in the RF I work in we had unsoldered joints there would be fires and smoke;!..

[Terry Casey]

Unlikely!

A terminator is just a 75 ohm resistor. 'F' type terminators are available but, if your amp uses 'Belling' style connectors (like an ordinary aerial plug/socket on a TV, find a local shop that sells components - or go to Maplin

- and buy a 75 ohm resistor (the old fashioned kind with wire connections) and a plug. (If you can't get a 75 ohm resistor, 82 ohms is acceptable.)

Fit the resistor inside the plug between the centre pin and the body. If you have a soldering iron, it is easiest to solder the wire onto the cable clamp - as well as the centre pin, of course - but otherwise you will have to devise your own method of trappimg it between the clamp and the body. This will vary slightly from one plug manufacturer to another.

This will NOT fix your current problem, though - but it might fix other problems with you DTV reception that you aren't even aware of at the moment!

[tony sayer]

In article , Terry Casey scribeth thus

Yeah!, Wilkinson's do couplers;)...

[Bill]

In message , tony sayer writes

A few years back I stripped out a rack that had contained Band 3 bases. One of the N to N leads I re-used was O/C when I took a plug apart the pin had never been soldered. There were a number of black arc burns on the inner copper. I often wondered how many faults they had had reported that they never found!

[Alan]

In message , Terry Casey wrote

Or fit a F type 75 ohm termination to a F to a Belling Lee converter

A few quid for the lot from Ebay.

[Alan]

In message , MM wrote

If you are going to replace a small section, say the bit in the loft to the point where it goes into the conduit then use F plus and a barrel connector (female to female addaptor) for the join. Example showing the idea:

[BartC]

The signal from a TV aerial is at microscopic power levels. And I do tend to bend the inner core of the coax to make sure it makes contact inside the hollow pin of the plug.

But if it doesn't, doesn't it just form a tiny capacitor? (And I wouldn't be surprised if the first thing the signal encountered inside the TV was an actual 10pf or 100pf series capacitor.)

[Ian Jackson]

In message , Alan writes

If you're not 'into' electronics, that's by far the easiest way to do it.

I've been in the electronics industry since the 1960s and, surprisingly, I've never come across any commercial Belling Lee 75 ohm terminations. In contrast, F terminations are everywhere. [I presume that that is because they are used on professional equipment in the cable TV industry.] I've always had to make my own B&Ls, or do as suggested above.

[The Natural Philosopher]

10pf is a fair bit more than a wire inside a hollow pin.

And the FIRST thing is generally a 75ohm load, actually.

If the cable is separated from that, you can get nasty cable resonances. Especially on LONG cables........