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348 posts

Ultimate Geek


# 20905 9-Apr-2008 18:23
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I currently have the main cable from uhf vhf diplexed and going into the lounge to the sky box, the rf out from sky box goes to 4 way f splitter the to all the tv's. The PC is on the other side of the house at the end at approx 30m of RG6 with a wall plate (all f connected) The PC has pefect DVB-T reception in the lounge on unsplit cable and on short length of split cable but when it is in the normal location reception is stuttery (signal level repoted as fine in MP). It seems the combination of long cable and the splitter is adding just enough noise to the picture to cause problems. Also the prime reception on pre split cable is alot better than on even a short length of split cable. So it seems i need some form of amplifier.

What is reccommended for this situation??
I was looking at one of these

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  # 122395 9-Apr-2008 19:57
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Typically greater than 4way splits an amplfier is required, obviously add a long run and you can tip the scales. The Kingray SA162/4 amps I have found to be good value, place the amp directly after the Sky box to avoid overloading that, ie dont put the amp on the input to the sky boxs.

Cyril



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  # 122400 9-Apr-2008 20:22
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Will this overload the signal on the 2 tv's with less than 2m cable runs to them? Do they need attenuators?

 
 
 
 


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  # 122405 9-Apr-2008 20:35
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Most likely, you should have posted that minor detail/I should have asked. Purhaps a better way to manage it is replace the 4way with at 2way and then the 4way so to only amplifiy the long feed.

Normally amplifiers are introduced in controlled manners, and earlier in a chain so to maintain better C/N ratios, however in this type of application and using domestic amplifiers its a more hit and miss afair.

Cyril



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  # 122426 9-Apr-2008 21:16
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 Given that a 4 way amp and a 2 way are pretty much the same cost, i may aswell get the 4 way amplifier as there are currently 2 long runs of cable in the house and it is possible that there will be more in the future. I could take an output from the 4 way splitter into the 4 way amp then just use the amp for the long runs and the splitter for the short runs.



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  # 123629 15-Apr-2008 11:12
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I have received the amplifier now and set it up yesterday, as a test i plugged everything into it to see if it would make the close tvs get worse reception. It didnt make any difference to the VHF channels and marginally improved prime reception. However i still get the exact same problem at the pc with Jitter quite often at least every 30 seconds. Basically it has made no noticable difference whatsoever to the pc reception. I can't help feeling the amplification has been nulified by the bad weather and high wind. On a clear day it might be good enough. I will later test to see if the unsplit cable with be able to power the tv card in the bad weather.

I cannot accept that i won't be able to get freeview HD in bad weather though. What else can i do, obviously i am just on the recpetion fringe for DVB-T works in good weather but not bad. But then again i cant tell that its just the amplifer not doing anything or not working correctly.

Any help appreciated, i am beggining to get frustrated now and running out of ideas.

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  # 123634 15-Apr-2008 11:37
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I'd be inclined to put a two way splitter fairly close to the aerial. Those tv's that work fine without an amplifier work of one feed of the splitter.  Take the other output from the splitter and feed into the amplifier.  This means you're getting a good signal to amplify and should work for longer legs of cable.  Adjustable amplifiers allow you to get the right signal boost ratio for your setup.

If it really is not working, you could also look at splitting off the UHF before the diplexer too, in case you're getting a bit of loss there.  Each splitter, diplexer and cable length decreases the strength/purity of the initial signal. 

Is your longer length running past any power cables/interferance etc which make this problem specific to this length of cable etc?

Good luck.  
Jackson.




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  # 123641 15-Apr-2008 12:41
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Thanks for that, that is very good advice i will try some of those things when the weather improves and see if i can fix it. The only problem with taking the UHF only feed is that the diplexer is built into the balun of the UHF aerial so im not sure how i would do that. I might need a new balun that doesnt include a diplexer and then take just the UHF and VHF cables down into the lounge separately, then probably just amplify the UHF signal, that should reduce and interference of losses.

As for the specific cable it runs along the outside walls of the house for 90% of the run so wouldn't be near any power cables but there is a small section under the house where it may run accross a power cable or even parallel to one for a bit, i will check and fix it up if that is the case. Thanks for reminding me about that.

 
 
 
 




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  # 123670 15-Apr-2008 14:29
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I have tested it with just the aerial cable plugged straight into amplifier without the sky box. Still the same issue, so it seems splitting it near to the aerial and taking one to the amp and one to the other tvs isnt going to help.



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  # 123676 15-Apr-2008 14:50
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Just checked the run of cable and found it was running next to a power cable for about 3-4 metres. Re routed it elsewhere but the problem is exactly the same no noticable difference whatsoever



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  # 123995 16-Apr-2008 12:01
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Here is where i am up to:

When the PC is plugged into a cable in the lounge (Split and Unamplified)  the picture is perfect, used it all last night and watched Boston Legal HD. (Even in the bad weather)
When it goes back to the room on the other side of the house reception goes back to jittery ( amplified or unamplified or even joined straight to aerial main cable).

There is obviously something funny going on with the cable to the room. I have checked the routing and can't see and tight bends or running next to other cables. Perhaps there is a cable running parallel to it inside the wall (the cable is clipped to outside wall of house). Will try unclipping the cable all the way along and just let it hand in the air where i no there is no interference.

Perhaps the amplifier is not doing anything at all, it may be faulty, difficult to check though.

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  # 124008 16-Apr-2008 12:34
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Are you able to bypass the splitter temporarily and patch the antenna straight over the 30m run.  If that works then your cable is probably okay.

This is based on 30M of RG-6 being roughly 6dB of loss and a 4-way split being about the same.

How long is the run from the roof to the sky box?  If that is significant, you may be better off with a masthead diplexer/UHF amp combo.



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  # 124012 16-Apr-2008 12:41
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I have tried the main aerial cable joined straight to the 30m cable and still the same problem
Also tried the main aerial cable plugged straight into the amplifier and then just the 30m plugged in (The amp states: Gain 12db @ 44mhz, 16db @860mhz) not sure what frequency DVB-T is running at.

Perhaps a masthead amp may be the only thing left if there is nothing wrong with the cable.

EDIT:
Oh yea and the cable from aerial to sky box is about 15m long max, not particularly long just from the roof down the outside wall and into the lounge.

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  # 124090 16-Apr-2008 15:33
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I wonder if you have an earth loop that causing the problem, can I suggest you get a long mains lead if you have one, power all the gear in the troubled room via that from the good room, ensure nothing is connected in multple places that include VHF/UHF antenna connections etc etc, ie you want everything to have one earth and thats in the good rooms powerpoint.

Cyril



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Ultimate Geek


  # 124092 16-Apr-2008 15:40
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If looking for a Masthead Amplifier what should i be looking for?
There are a few on trademe but not sure which is the best.

Also how do i attatch a better quality balun to the aerial (The current one is a balun and diplexer together, but it is quite a poor quality one looks pretty shoddy and is a saddle and clamp one). The current one is attatched to the metal pole of the aerial with a screw and also is attacthed to a loop of metal that goes between the reflector at the back and the last element (not sure what this does, if i replace it this part will go aswell, is it doing anything useful?)




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Ultimate Geek


  # 124093 16-Apr-2008 15:50
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So what you are saying is that is should plug the computer etc into a long extension cable then to the same point as the amplifier in the lounge. What do you mean by no connections in the UHF/VHF cable? I have a wallplate in the troubled room.

Another thing i was considering is taking a split close to the UHF aerial on the roof and diplexing that with the Sat dish signal to my room, this bypasses the troubled cable (which can still work for RF out Sky TV) and is a shorter run and is split much closer to the aerial. How much noise am i adding by diplexing the UHF/VHF signal with the SAT signal (does this negate the benefit?)

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