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Forums › Freeview (DVB-T/DVB-S) › Variation in UHF Freeview signal


45 posts

Geek


Topic # 94063 5-Dec-2011 14:56
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Hi All,

I am in Nelson (Marybank) and have put a new UHF aerial on the roof. I have aligned it to Mt Campbell (Google Earth bearing +22degrees magnetic variation) and have great signal strength and quality (85-90%) during good weather. When it rains though, the signal drops off and the picture become unwatchable.

It seems strange that there is such a variation in signal strength. Any ideas where I should start first?

Cheers,
Chris

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  Reply # 554080 5-Dec-2011 15:13
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Sounds like you are just on the edge of a good signal, and rain is enough to kill the signal.

I am assuming your aerial is aligned vertically,

Ideally you would stick a field strength meter on and see what actual signal you are getting, and go from there, but if you dont have access to one ( or someone with one) one solution is probably a powered masthead amp.

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  Reply # 554087 5-Dec-2011 15:24
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That does sound like alot more rain fade than normal. Are there a lot of trees close to your house (between you and the hill)? Even then I wouldn't expect that to make much difference at UHF frequncies. I presume you have checked that the terminal/balun box on the antenna is sealed?

 
 
 
 




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  Reply # 554089 5-Dec-2011 15:28
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Thanks for the reply. I'll start with getting up on the roof tonight and changing it from horizontal to vertical and see how it goes from there.

Is the cable likely to make a difference? Pulling new cable is a nightmare at our place so I have just used the old cable from the vhf aerial?

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  Reply # 554096 5-Dec-2011 15:39
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cep32: Hi All,

I am in Nelson (Marybank) and have put a new UHF aerial on the roof. I have aligned it to Mt Campbell (Google Earth bearing +22degrees magnetic variation) and have great signal strength and quality (85-90%) during good weather. When it rains though, the signal drops off and the picture become unwatchable.

It seems strange that there is such a variation in signal strength. Any ideas where I should start first?

Cheers,
Chris

Did you replace the co-ax as well with RG6?
What are you using, TV or STB?
Sounds like the rain is killing your signal. With that signal strength it's most likely water in the coax or bad connection somewhere getting wet. What's the signal/quality when wet? 85% is starting to get down towards drop out level at times.
I set up a Sony EX720 in a weak signal area and 45 - 65 was about the choppy dropout level.
Sounds like you used a compass to align? Can you not see the Transmitter directly from the roof?
Moving the antenna a few degrees either way can make a difference with weak signals.

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  Reply # 554099 5-Dec-2011 15:42
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cep32: Thanks for the reply. I'll start with getting up on the roof tonight and changing it from horizontal to vertical and see how it goes from there.

Is the cable likely to make a difference? Pulling new cable is a nightmare at our place so I have just used the old cable from the vhf aerial?


Well if you have the wrong polarity your losing about 22db to start. Changing to the correct polarity will probably do the trick.
New quad shield rg6 cable will definitely be an improvement over old cable for VHF.



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Geek


  Reply # 554122 5-Dec-2011 16:15
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Thanks. Looks like I have some work to do this week.

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  Reply # 554138 5-Dec-2011 16:48
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cep32: Thanks. Looks like I have some work to do this week.


I suspect as the others said above you just have to make sure you have the aerial with the correct polarity.
Thats probably 90% of the issue.

This page:
http://www.freeviewshop.co.nz/digital-terrestrial-i-8.html

is one of the few useful freeview references I know of. Funnily they dont have anything like that on the Freeview website (feel free to prove me wrong)

This line is important (for you):

Mt Campbell Nelson     Vertical

So just make sure you have the aerial  | instead of --

If that doesnt fix it then you could be busy this week.

Fingers crossed for you and be careful on the roof!





Nothing is impossible for the man who doesn't have to do it himself - A. H. Weiler

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Master Geek


  Reply # 554213 5-Dec-2011 19:38
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Mt Campbell, Motueka is Vertical. Kaka Hill Nelson is Horizontal. So once you turned your antenna over all should be clear.



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Geek


  Reply # 554649 6-Dec-2011 19:09
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Thanks all for the advice. I changed it to vertical last night. It has been pouring down all day and is still and the picture is crystal clear.

Solved I say. In fact is there any way that I can label this "solved in the heading?

Cheers,
Chris

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