3 Aerials problem

C

Captain Beer

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#1
Ok, here is the problem, I need to put up three aerials to recive all the channels I want. I have made some pictures to try show what my problem is. I can't put all 3 on the one pole, there are trees in the way of the local tower and it doesn't get any picture up there, so I have put it on the front of the house.

I tried plugging both feeds into a Y splitter but ended up with a very bad picture. I have found a combiner that can do UHFx2 and VHFx1. Only problem is where to but the combiner? The Grid and the other aerials are about 20m away from eachother.

Please edit my picture and show me what to do.

http://img.photobucket.com/albums/v725/whoiswarren/Aerials1.jpg

http://img.photobucket.com/albums/v725/whoiswarren/Aerials2.jpg

Cheers

P.S. I live in South Africa and we still have analogue tv on VHF.
 
rolfw

rolfw

Believe it when I see it Admin.
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#2
What are the frequencies/channel numbers of the channels from the three transmitters?
 
C

Captain Beer

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#3
The far one is:

61 - SABC3
57 - etv
10 - SABC1
7 - SABC2

Local:

MNet - 67
SABC3 - 64
 
C

Captain Beer

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#4
Anyone have some advice? Have to do it this weekend if I can :cool:
 
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spiney

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#5
Well, it's very difficult trying to give advice, from a different broadcasting setup in another country, but .....

It's best to use wideband metal block "satellite" combiners (in reverse) that work over 5-2400 MHz - even though you're only on terrestrial frequencies - rather than the cheaper and much worse "Y" type plastic splitters.

This assumes that:

1) Your reception on each aerial is adequate to start with, ie you're within range of - and using the correct aerial for - each wanted transmitter.

2) There isn't cross-interference between unwanted channels on the different aerials, which might manifest as various "patterns" over the wanted channels (I'm assuming entirely analogue broadcasting!). When combining several aerials, this is a common problem, even in the UK with UHF only tv transmitters!
If so, then you might need to fit frequency filters individually to the separate aerials, depending on what problems might be encountered. For example, you might have to fit different frequency bandpass filters separately to the VHF and UHF aerials.

But, the combiner is still the 1st step, you won't know what else might need doing until you've 1st tried that!

Obviously, any local help and advice you can find would be most useful!

And sorry, no idea who your best local supplier might be!

(For info on such splitters, see links near bottom of my Freeview aerials guide, in our FAQs section. Most of that is about UK digital terrestrial, so doesn't apply here!).
 
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Captain Beer

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#6
Awesome stuff. Thanks :)
 
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spiney

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#7
Dunno about "awesome", but can't guarantee anything!

Combining tv aerials is fraught, there's always the possibility of wanted and unwanted signals "combining" to give various patterning effects. So, I'm promising nothing.

In general, combining passively is much better than using amplifiers, at least there's that.

Having a tv aerials switch would avoid any such problems - at the cost of some inconvenience - but I can't recall ever seeing one, only satellite dish versions!
 
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spiney

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#8
Oops ......

Sorry, there's something i didn't say, because it seemed obvious, but might not be .....

In my Freeview guide, aerials from 1 transmitter are combined to get a stronger signal (for digital tv to work). In which case, as mentioned, the cable lengths from aerials to combiner (reverse splitter) must be the SAME length. However, for aerials pointing at different transmitters, this restriction does not apply, and then cables to the aerials can be any length!

Also, when looking at wideband splitter specs, these will mention signal loss, which increases with number of output ports. But, when used in reverse as combiners, these loss figures no longer apply. The expected loss for using any wideband splitter in reverse as a combiner would be about 2dB, which is negligable.
 
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