How many coax cables can come off an aerial?

[SUNRAY]

A large proportion of the signal will be reflected off the mismatch and will be lost.

SO WHAT?

Perhaps less than a quarter of the signal will be available at each TV.

Oh now I have to think about this for a nano second... I think you said you are an expert with 25 years of experience... Yes?

 

[SUNRAY]

They are not silly, wrong, or ignorant.

They are in my opinion and many others on here.

Read up on impedance matching and consequences of mismatches.

I fully understand the consequences.

You are clearly a typical sparks

No. No. No. I try to avoid sparks in my work. No I try to do the job properly, my work doesnt spark.

, good at what you do, and think you can also

DO is the word you seem to have missed here

specialised tasks such aerial installs

Installs? do you mean installation or possibly installations?

. Leave that to the experts who understand it.

Yes I can pick you up on you poor wordsmith work too.

You have absolutely no idea what my experiences are and for that matter I have no idea what yours are. I certainly know you keep bleating on about electrical matters and getting those wrong, now you tell me you are a TV speciallist with 25 years experience and now you're quoting incorrect loss figures.

 

[ericmark]

If your connecting up a transceiver and banging 300 watt into the aerial then clearly it must be right, but on receive only it really does not matter, aerials are very odd things at the best of times, I have spent many a happy hour building aerials loved the HB9CV and the slim jim, but this is TV, and a pair of simple resistors found in a B&Q splitter is often good enough.

I remember setting out a long wire to get BBC World Services, and had arranged a 2 meter chat with local farmer, only to find I was locked in, so used the meter and the SWR was not too bad, so used a long wire for a 2 meter chat, no way should it have worked, but it did.

So cutting a slim jim and selotape to window using 300Ω feeder is fine if it works, seem to remember around 9 inches for TV frequency. I have used a bit of 300Ω feeder with 30 watt taped to flat window to talk around the world with packet radio from Hong Kong, so if it works great.

OK if I was doing it as a job you want it to work first time so you use an active pre-amp and proper net works, but @SUNRAY is right, try simple first.

 

[ericmark]

Oh and qualifications if it matters, RAE and Degree in electrical and electronic engineering, licensed as a VP8, VR2, and GW7.

 

[SUNRAY]

If your connecting up a transceiver and banging 300 watt into the aerial then clearly it must be right, but on receive only it really does not matter, aerials are very odd things at the best of times, I have spent many a happy hour building aerials loved the HB9CV and the slim jim, but this is TV, and a pair of simple resistors found in a B&Q splitter is often good enough.

I remember setting out a long wire to get BBC World Services, and had arranged a 2 meter chat with local farmer, only to find I was locked in, so used the meter and the SWR was not too bad, so used a long wire for a 2 meter chat, no way should it have worked, but it did.

So cutting a slim jim and selotape to window using 300Ω feeder is fine if it works, seem to remember around 9 inches for TV frequency. I have used a bit of 300Ω feeder with 30 watt taped to flat window to talk around the world with packet radio from Hong Kong, so if it works great.

OK if I was doing it as a job you want it to work first time so you use an active pre-amp and proper net works, but @SUNRAY is right, try simple first.

Oh and qualifications if it matters, RAE and Degree in electrical and electronic engineering, licensed as a VP8, VR2, and GW7.

Oh I'm not questiong you Eric. Thanks for the sensible statement.

 

[winston1]

Another bloody stupid comment.
I know what he means.
sxturbo knows what he means.
Everybody else knows what he means.

That is everbody except one... guess who that stupid one is.

Please stick to the facts without picking on a little spelling mistake, especially one as common as this one.

I know what he meant as well. But if you never correct errors no one will learn. It was NOT a spelling mistake, it was the use of the wrong word (the upper case A gave it away.

 

[winston1]

SO WHAT?

If a large proportion of the signal is lost surely even you can see that could lead to not enough left.

 

[EFLImpudence]

Perhaps the OP had just been reading Shakespeare or watching a cartoon and not doing his washing.

 

[SUNRAY]

If a large proportion of the signal is lost surely even you can see that could lead to not enough left.

What large proportion are you referring to?

Yes I can see that if the signal level is low then adding a second device could take it below a useful level BUT, actually it's a bigger BUT needed, if the signal is that low in the first place then in all likelyhood it's probably not good enough to run one device properly.

What I can see is a very good example in an earlier post referring to too much signal.

What I can see is I currently have a splitter in my installation with a loss of 11dB to each and every device connected to it. (For those who are unfamiliar with deciBels 11dB is an attenuation to approximately 25% of voltage or 10% of power or 2 S points[in very rounded figures]).

What I can see is my neighbour has a wallwart (from USA so not likely to be plugged into mains) plugged into his PVR aerial socket. I suppose Winston is now going to say it's not impedance matched and will not work.

 

[ericmark]

When a mistake can result in wrong advice, then it needs a query, but when you know without question what is meant, then it is rather a pointless exercise, 220 volt, 230 volt, 240 volt and low voltage in most posts mean the same, but I tend to write low voltage (230) just in case, and I still call the unit inside a shaver socket an isolating transformer even though I know technically it does not transform anything.

Dyslexia rules KO.

 

[winston1]

If your connecting up a transceiver and banging 300 watt into the aerial then clearly it must be right, but on receive only it really does not matter, aerials are very odd things at the best of times, I have spent many a happy hour building aerials loved the HB9CV and the slim jim, but this is TV, and a pair of simple resistors found in a B&Q splitter is often good enough.

I remember setting out a long wire to get BBC World Services, and had arranged a 2 meter chat with local farmer, only to find I was locked in, so used the meter and the SWR was not too bad, so used a long wire for a 2 meter chat, no way should it have worked, but it did.

So cutting a slim jim and selotape to window using 300Ω feeder is fine if it works, seem to remember around 9 inches for TV frequency. I have used a bit of 300Ω feeder with 30 watt taped to flat window to talk around the world with packet radio from Hong Kong, so if it works great.

OK if I was doing it as a job you want it to work first time so you use an active pre-amp and proper net works, but @SUNRAY is right, try simple first.

Of course with transmitting it is essential to match everything. Lots of power reflected back to the tx can do a lot of damage.

I would hope the B&Q splitter has 3 resistors, not 2. But anyway such splitters are lossy, just over 6dB rather than just over 3dB for a properly designed one. Perhaps more important a properly designed one has about 25dB discrimination from one output to he other whereas with 3 resistors it is 6dB. This is important to prevent spurious signals generated in one TV from affecting the other.

But at the end of the day TV aerial installations should be done properly, not bodged. There are lots of posts on various forums of people getting poor Freeview reception, almost all of which are due to poor aerial installations.

 

[winston1]

I still call the unit inside a shaver socket an isolating transformer even though I know technically it does not transform anything.

All the ones I have seen transform one output to 110/120v.

 

[JohnW2]

Of course with transmitting it is essential to match everything. Lots of power reflected back to the tx can do a lot of damage.

Very true, but totally irrelevant to this thread.

But at the end of the day TV aerial installations should be done properly, not bodged.

As has been said, when there is absolutely no 'safety' issue, nor any possibility of anything being 'damaged', there is nothing wrong with 'bodges' which work satisfactorily. Even if they don't carry on 'working satisfactorily' for ever (and, in context, I don't really see what would/could change over time), one can re-address the issue if/when that situation arises.

A poorly-functioning or non-functioning TV is, after all, not going to be life-threatening, a 'fire risk' etc. !

 

[winston1]

As has been said, when there is absolutely no 'safety' issue, nor any possibility of anything being 'damaged', there is nothing wrong with 'bodges' which work satisfactorily.

Sorry I disagree. Have you no pride in your work?

Even if they don't carry on 'working satisfactorily' for ever (and, in context, I don't really see what would/could change over time),

In the context of the original question and the possibility of lots of signal loss due to a mismatch, it could well show up next time transmitter maintenance is carried out and it goes on half power working.

one can re-address the issue if/when that situation arises.

I'd be pretty annoyed if I had paid for an installation and then had to pay again to put it right due to former bodging.

 

[SUNRAY]

Additionally I has occurred to me that one of the ports on my splitter is adapted from F to BNC to PL269 then 20metres of RG58 then converted to BNC then tee piece and one branch ~ 1m RG58 BNC to BNC and converted to Belling lee, the other branch ~8m of RG62 BNC to choc bloc and a short tail of some random coax to Belling Lee. I hate to think what that lot does to impedance matching or loss.