How Does That Work?

securespark · 10 Jan 2021

I have a single TV aerial with a co-ax that drops down to the lounge. Going out from the lounge is a co-ax running to an aerial amp. in the garage.
The two leads in the lounge are joined together by a co-ax connector that plugs into the lounge TV.

Running out from the garage amp. is a co-ax feed to a TV in the den.

Also in the lounge is a drop lead to a di-pole.

We are re-arranging the lounge, so I was looking to re-route the aerial cables.

Sadly, the labels applied 22 years ago have dropped off, so I have no idea which is which.

But I digress!

Having disconnected the two co-ax cables from the connector that was plugged into the back of the lounge TV, I expected the picture to the den TV to drop out.

But it didn't. It only dropped out when I killed the supply to the aerial amp. in the garage.

Moreover, all three leads in the lounge give a perfect picture.....

So, how can a length of disconnected co-ax with a TV at either end and an aerial amp. in the middle give a perfect picture on both TVs?

1974stephen · 10 Jan 2021

Is it that really nasty £6/100m cheap coax from the wholesalers with about three strands of copper screen and no foil, the type electricians tend to use who don't know better? If so, that could be acting as the aerial itself if you're in a high gain area with near a powerful transmitter. I'm near the Sutton Coldfield transmitter and it's common for an old metal coathanger to give a decent picture!

securespark · 10 Jan 2021

I'd say it was fairly decent standard, but it is not screened.

Certainly, the strands are plentiful.

It is 22 years old if that makes a difference either way!

JohnW2 · 10 Jan 2021

1974stephen said:
Is it that really nasty £6/100m cheap coax from the wholesalers with about three strands of copper screen and no foil, the type electricians tend to use who don't know better?

... or perhaps the type people tend to use when they know (perhaps better than those promoting more expensive products) that nothing more expensive is necessary in the area (and with the cable length) they are working?

Kind Regards, John

securespark · 10 Jan 2021

Just done another test.

Disconnected the lengths of co-ax from the aerial amp.

Connected the length of co-ax that runs from the lounge to the aerial amp into the lounge TV.

Still working.

JohnW2 · 11 Jan 2021

securespark said:
Just done another test. Disconnected the lengths of co-ax from the aerial amp. Connected the length of co-ax that runs from the lounge to the aerial amp into the lounge TV. Still working.

Try a 'coat hanger' (or equivalent) !

I'm within line-of-sight to the local repeater mast, and virtually anything plugged into the aerial socket of a TV will get a (non-pixelated) picture!

Kind Regards, John

333rocky333 · 11 Jan 2021

Similar to how a coathanger used to do the job I suppose , dont you remember back in the days when you were allowed radios on site, you would just wrap a bit of cable round the broken off ariel and tag on to something metal, think it was all Medium Wave then.
I was always told them amps are waste of time, if you have crap signal to start then it just boosts the same crap signal, not sure how true that is, far better to initially pay more for a decent arial.
Or stick a second one by the den, I got one from screwfix and stuck it in the loft about 20 quid and its fine, cheaper than paying someone to climb up to chimney

333rocky333 · 11 Jan 2021

If its a freeview tv you may lose some channels, round here London Live is weak, my chimney Arial got broke by pigeons sitting on it, it got worse and worse and i used to miss ends of programs, thus i had to get a new one

JohnW2 · 11 Jan 2021

333rocky333 said:
I was always told them amps are waste of time, if you have crap signal to start then it just boosts the same crap signal, not sure how true that is, far better to initially pay more for a decent arial.

I think that it's all down-to 'signal-to-noise ratio'. If you start with a noisy signal, then an amplifier will certainly amplify the noise, as well as the signal - but if the signal is 'weak but fairly clean', an amplifier is more likely to be of value.

Kind Regards, John

333rocky333 · 11 Jan 2021

JohnW2 said:
I think that it's all down-to 'signal-to-noise ratio'. If you start with a noisy signal, then an amplifier will certainly amplify the noise, as well as the signal - but if the signal is 'weak but fairly clean', an amplifier is more likely to be of value.

Kind Regards, John

How do you define a noisy signal, I assume a weak signal is when the thing freezes and pixilates

333rocky333 · 11 Jan 2021

Also @JohnW2 what sort of load are them amps, what sort of cost to run a year, I assume not much

JohnW2 · 11 Jan 2021

333rocky333 said:
How do you define a noisy signal, I assume a weak signal is when the thing freezes and pixilates

Yes, a weak signal can do that, but so can a stronger but 'noiser' signal.

It was easier in the good-old days of analogue TV - a noisy signal then produced an obviously 'noisy' picture ('snowstorm' etc.), whereas a weak signal could result in no usable (or stationary!) picture at all, particularly if it was too weak to synch one of both of the timebases!

Kind Regards, John

JohnW2 · 11 Jan 2021

333rocky333 said:
Also @JohnW2 what sort of load are them amps, what sort of cost to run a year, I assume not much

As you imply, pretty trivial (running costs) I would have thought, particularly newer ones.

Kind Regards, John

securespark · 11 Jan 2021

JohnW2 · 11 Jan 2021

securespark said:
.... 12V 25 mA ....

Well, if that is remotely like a fair indication of how much power it actually 'draws' from the 230V supply, then that 0.3W (i.e. 3,333 hours for 1kWh) suggests that I probably wasn't far off when I suggested that the running costs would be "trivial"

Kind Regards, John

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How Does That Work?

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