TV antenna


  #1  
Old 07-16-03, 09:34 AM
broketruch
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Question TV antenna

I have Two sets in my home connected on same line in from antenna, this is fed using 75Ohm coax into a spitter then terminating at each TV set. The problem is poor reseption from once good. My wife had a tech. person advise us to change the fead wire and it should correct the problem. My question to you is; will Having two 75OHM coax wire coming from antenna work better than splitting the signel at the TV set? I've read the Q. & A. at the start of this, but I would like some input before I lay out my money.
 
  #2  
Old 07-17-03, 01:37 AM
threesheds
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I don't think you should run two leads from the antenna. This would be more or less the same as dividing the signal without a splitter but just up at the signal source rather than a bit lower down the cable. You'd find that one TV could affect the other when changing channels. Signal levels could vary. Just a general imbalance altogether.

Your technician may have meant that you change your cable to a low-loss type perhaps. Being the man on the spot and able to see your problems, he could be right.

As well as that, there's a few ways you could approach this. It amounts to a bit of a book unfortunately:

If you are using a proper splitter then that is the correct way to do the job. Since splitting the signal is causing noticeable signal loss though you could use a powered splitter/amplifier. This amplifies the signal enough to overcome the fact that the signal is being divided between 2 TVs.

If you already have the signal split using one of these, there is something else that could be causing poor quality pictures:

Some splitter/amplfiers give a good bit of signal boost. They come with different amounts of it. If your one gives a high level of amplification it can overload the front end (tuner) of the TV. If this happens you can end up with a snowy picture, or an effect that's known as cross-modulation. This shows as lines on the picture and, on dark scenes, you may be able to see movement in the background.

Signal overload can be checked for by pulling the coax plug from the back of the TV and holding it just the mereset fraction away from the socket. If the picture looks better doing that than when the plug is pushed in properly then it's likely that you have too much signal.

This can be inexpensively overcome with the use of attenuators. A three, or maybe a six, Db attenuator would be the thing to ask for.

If the signal is weak because of the split and you don't have any amplification of any sort, another approach could be to amplify the signal before it gets to the splitter. If this is done, the amplifier should be as close to the antenna as possible. An outdoor masthead one is best. You can try using an indoor one if you can get it within a few feet of the antenna (maybe if the lead runs into the loft). However, it was a long time before I trusted a powered amplifier to run constantly in the loft. I'm now pretty sure they are as safe as anything else but, even so, I was careful to mount my amplifier where it would do no harm if it did overheat. Over cautious maybe but better safe than sorry.

One final way (phew!) is to fix another antenna to the same pole and run a lead to the second TV.

On balance I usually favour the powered splitter/amplifier. It's easier to set up than anything else but be aware of the 'too much signal' effects you can get with them.

Have a word with your local tech about these options and see what he says.
 
  #3  
Old 07-18-03, 01:45 AM
fatcatdj
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TV antenna? What year is this posted? Anyways, the splitter/amp is the way to go. My cheap cousin refuses cable or sat tv yet still complained about
reception with a colour tv antenna & 2 sets. The splitter-amp did the trick.
He's finally looking into buying a VCR, since you can now pick one up for $69.00, but feels that it might just be a fad.
 
  #4  
Old 07-22-03, 08:13 PM
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fatcatdj,

I'm ROFL,

I think your cousin is right. VCR's are just about on their way out!
And to think my first vcr was $1050, and my first blank tape was $16.95!!!!!!!!!! (1981).

fred
 
  #5  
Old 07-23-03, 01:34 PM
threesheds
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There's been a bit of a swing back to antenna's (please, can I call them aerials? ) in UK lately. Lots of people are on cable and satellite TV but there's also a service called 'Freeview' gaining popularity.

We have 5 basic analogue channels and there is pretty much blanket coverage of these by way of repeaters up and down the country. Freeview takes advantage of this and uses a technology that enables many digital channels to be carried on the old analogue signals, which of course are picked up by the rooftop aerials that people have been using for years.

This is bad news for the Government who want to see analogue transmissions come to an end (I think they want the frequencies back). They have said that analogue transmissions will continue until something like 80% of the population have switched to cable/satellite digital.

There's not too much chance of that happening now that people are cottoning onto the fact that digital channels can be viewed for free by buying a box for about £80-00 ($100?) that plugs into the ordinary old aerial. So, far from the aerial becoming redundant, it is gaining ground again.

Some parts of the country are still a bit patchy for coverage though. A fairly strong analogue signal is needed if the digital picture is not going to freeze or pixelate once in a while.

Unfortunately one area where the signal is less than ideal is just where I live, so I have to pay for cable TV
 
  #6  
Old 07-24-03, 02:50 PM
Teratum
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Broketruch:

Have you checked the connection between the antenna and the coax? The fact that it was once good and now bad on both TV's indicated problem in the area before the signal gets into the splitter.
It can be just a simple broken wires or loose connection between the coax and the antenna arrays.

If it was once good without any amplify, adding an amplify will not fix the problem. Besides 2 TV's set from one antenna is not too much of increasing the load or attenuated the signal. Per high freq. transmission theory, if the impedance is matched, the 75 ohms parallel with another 75 ohms through a splitter, still give overall 75 ohm impedamce. There is some very small Cu loss in the process, but should not be significant unless your receiving signal starts off very low.
 
  #7  
Old 07-24-03, 07:43 PM
broketruch
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Thumbs up solusion

Thank you TERATAM this was the problem. The fact my wife wanted the unsightly wire to be hidden promted me to check all possible connections . the problem however was not obvious, it was at the antenni on the tower.Looking was not enouph I had to feal all the connections, but did find the wire not to make a good contact. Thanks to all who made a reply.
 
 

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