Rg58

[Mack]

i have some rg58 antenna wire, is that any good for the TV

[president_ltd]

i have some rg58 antenna wire, is that any good for the TV

not really, wrong impedence.

in theory one could use some balums at each end to correct that, but reality is that its a lot of work to go to.

any modern antenna cabling is quad shielded RG6.

that quad shielding is important these days with DVB.

[rrobor]

Its 50 ohm instead of 75 ohm. It would do in good signal areas, but is it worth it. If you are fitting cable through walls etc get the best. It may cost an extra $10 on the run but done correctly thats it you never need to redo it. Always remember signal strength is dropping as more houses go up so it will only get worse.

[Mack]

it's only going throuh a tin wall, it's for the shed and the shed has it's own antenna

[murray44]

The 'theory' says don't do it but common sense says give it a try, it will probably work. If you have problems go and buy some RG59 (or similar).

You can't hurt anything.

[rrobor]

Done for a shed its fine, you may loose 2 or 3 DB, 3DB is half signal but in reality if you could just see snow on the picture you would just notice the difference.

[president_ltd]

in the world of digital TV its just as likely to not work at all.

[murray44]

in the world of digital TV its just as likely to not work at all.

I don't want to start a whole new debate here, but you actually don't need as strong a signal with digital as you do with analog.

A slightly weak analog signal may show up as 'snow' but the digital signal is 'rebuilt' by the receiver so any noise is ignored.

[president_ltd]

I don't want to start a whole new debate here, but you actually don't need as strong a signal with digital as you do with analog.

A slightly weak analog signal may show up as 'snow' but the digital signal is 'rebuilt' by the receiver so any noise is ignored.

yes and no.

1. signal strength.

the 'ghosting' (analog) or higher bit-error-rate (BER) (digital) of an impedence mismatch (e.g. using 75 ohm cable rather than 50 ohm) is caused by the impedence mismatch causing signal reflections back to the transmitter.. because of the time it takes for the signal to 'reflect' you get ghosting (analog) or BER (digital).

you also get some signal cancellations at some frequencies which often results in scenarios like "i can't tune in to SBS" or "i can't tune into TEN".


2. impedence mismatch on digital tv

besides the above (higher BER, too much that are UNCorrectable wlll cause blockyness and glitches in mpeg2 stream), you also get a much poorer S/N ratio. you also have significantly more loss over the cable than quad shielded - but whether that is a problem does depend to some extent on the length of the cable.



not wating to get into an argument, but there are many things misunderstood about correct cable types. using the wrong cable may work short-term - may even work longer-term - or may be totally useless today and require one to go put the correct cable on right now.

but if you were doing it 'right' on the basis of not wanting to ever revisit it, one would be using correct cable (RG6 quad shielded) w/ low-loss connectors (F type) and provided the antenna is up to it, that will be futureproof as far as when analog is turned off if not being used for digital today.

[murray44]

yes and no.

1. signal strength.

the 'ghosting' (analog) or higher bit-error-rate (BER) (digital) of an impedence mismatch (e.g. using 75 ohm cable rather than 50 ohm) is caused by the impedence mismatch causing signal reflections back to the transmitter.. because of the time it takes for the signal to 'reflect' you get ghosting (analog) or BER (digital).

you also get some signal cancellations at some frequencies which often results in scenarios like "i can't tune in to SBS" or "i can't tune into TEN"..

High BER can be caused by many things but not necessarily impedance mismatch. I've run hundreds of BERT over the years, lots of them have been with 'bodged up' cables and you can still run clean BER.

Impedance mismatch does cause reflections but this causes power loss on the transmission line.

Ghosting is not caused by reflections on the transmission line, typical ghosting is caused by multipath transmission between transmitter and receiver. Multipathing occurs when you receive the signal direct from the TXer and then receive a second signal which, for example, has bounced off something nearby i.e. steel bridge, local hills etc. It's the delay between these 2 signals that causes the problem.


2. impedence mismatch on digital tv

besides the above (higher BER, too much that are UNCorrectable wlll cause blockyness and glitches in mpeg2 stream), you also get a much poorer S/N ratio. you also have significantly more loss over the cable than quad shielded - but whether that is a problem does depend to some extent on the length of the cable.



not wating to get into an argument, but there are many things misunderstood about correct cable types. using the wrong cable may work short-term - may even work longer-term - or may be totally useless today and require one to go put the correct cable on right now.

but if you were doing it 'right' on the basis of not wanting to ever revisit it, one would be using correct cable (RG6 quad shielded) w/ low-loss connectors (F type) and provided the antenna is up to it, that will be futureproof as far as when analog is turned off if not being used for digital today.

That's why I suggested trying the wrong cable, it may work fine and you won't hurt anything. :)

[rrobor]

Cripes the guy is fitting an antenna to his shed. Chances are that the 50ohm will be better than cheap 75 ohm . You are also getting strung out about impedance and forgetting 75ohm is an average not an absolute as being Australian you have to remember the four and twenty Pii. Ghosting as Murray says is multipath signals IE as the crow flies then a bounce off the neighbours tin roof etc.
It aint going to be a castastrophy if it doesnt work and Ill bet if he is in a reasonable area it will.

[murray44]

:iagree:

[president_ltd]

Ghosting as Murray says is multipath signals IE as the crow flies then a bounce off the neighbours tin roof etc.

'multipathing' is one cause of ghosting, the other is impedence mismatch.


anyway, nuff said i think the horse is well and truly flogged.

[rrobor]

You know it annoys me when someone tries to have the last word with a statement like that. If you believe that then quite frankly I dont care. I dont, and I doubt if you know the impedance of that cable at UHF. The cable from memory is computer stuff , So at lower frequency has impedance of 50 ohm what is it on UHF. Anyways I dont care if you believe this causes ghosting and as enough has been said I think its time to move on.

[president_ltd]

we wouldn't want you eating another hat now would we rrobor?

[chrisp]

In practice I agree - try whatever cable you have and hope for the best - what have you got to lose other than a bit of time.

However, I can be a pedantic bastard at times and I do wish to point out that any impedance mismatching will cause reflections which may cause problems.

Have a read up on TDR techniques - a way of determining cable problems. see Time-domain reflectometer - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Time_domain_reflectometer)

[murray44]

Chrisp,

I don't think anyone disagrees that impedance mismatch WILL cause reflections and COULD cause possible problems.

At this point, I think Mack has hooked up a bit of RG58 (a bit of coat hanger wire for an aerial) and is happily watching telly. hahaha

[watson]

Or he just got bored....and installed a beer fridge in his shed instead :rotfl:

[Mack]

Murray is close, the tv worked reasonably well with a indoor antenna. i bought a outside antenna from a garage sale and they gave me this roll of cable for free.

All hooked up with rg58 picture is perfect on all stations, thanks

[rrobor]

See that, didnt eat my hat last time and she'es apples this time, how good is that.

[president_ltd]

there ain't no beenie on your avatar, i figure that means one ate said hat. :)

[watson]

Mack has got his answers..his telly works...shame about the beer fridge.
So that's all she wrote.