Want to replace old flat tv cable with better coax.

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jg wrote:

Is the antenna 40-ft high from the ground or roof top? How do you get up to it? With an antenna that high you want to do it right the first time. I strongly suggest getting a new antenna with a good UHF front-end and a rotator to fine tune the aiming. An antenna amplifier would be a good investment too. I would use coax because it's stronger and more durable than twinlead. This will minimize the possibility of a broken downlead, requiring you to go back up to the antenna. Be very careful with this project. Have a helper close by and look out for power lines that might come in contact with the antenna and mast. Good luck.
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In that particular area, you have to be very careful using an antenna amplifier, especially if you are talking about a pre-amp mounted at the antenna. Only a professional will know which amp will work in that area. Some of the Sacramento signals are so strong on UHF that the pre-amp can do more harm than good. Remember, doubling a weak signal will help, but also doubling that very strong signal can put that signal all over the dial. I had a pre-amp in a large directional antenna in Sacramento and had to have it removed. I couldn't get ANY distant channel as all the locals wiped them out. Using a weak amp MIGHT help in this case. You CAN NOT improve the signal-to-noise ratio at the antenna. What you hope to achieve is to keep as much of that signal as possible. In other words, to reduce the lead losses. But ALL pre-amps/amps introduce some noise. You can't get a better signal that what you are getting at the antenna, no matter what you do.
You might check with dealers in your area. But I have an idea that if you replaced your lead to just ONE coax cable from antenna to tv, you'd see a major improvement in reception from San Francisco and/or Modesto.
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On 10 Feb 2006 09:58:17 -0800, snipped-for-privacy@aol.com wrote:

All I have is a RS amplified antenna in the attic -- the amplifer is in the antenna -- and I love it because I'm in Baltimore and I can get all the DC stations**. Rarely but sometimes, the signal is too strong with Baltimore stations, so I have an A-B swtich that disconnects the entire antenna if I want. Then I just use the one foot piece of co-ax from the VCR to the A-B swtich, and even that little signal is more than enough when I'm tuned to any station that overloads when using the amplified antenna.
I suppose I could have gotten a variable reducer, or an amp with variable amplification, and sought the best compromise value, but this was simpler, and lets me use maximum for the DC stations. For example, for a few months channel 9 was weak. Then it got to be fine and about the same time channel 7 got weak. Now they're both fine, but I want to keep amplification at its max for the hardware I bought.
**BTW, this is better than cable because cable doesn't have DC stations. Often there is a sports game or even a non-sports show on tv in Baltimore while DC is carrying the regular weekly show.
Also, once when I was watching Law and Order on two tv's at the same time (fiddling with one of them) I saw that the last minute of the show, the part after the last commercial, was shown on the DC channel, but on the Baltimore channel, they put in another commercial. Very distressing. The earlier part of the show they had been totally synchronized. Channel 11 in Baltimore basically cheated everyone out of that last minute or 30 seconds, which resolved some of the plot issues. Now I watch channel 4 in DC more often.
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40 ft. from ground. Getting to it is fairly easy. I just get on the rooftop, take a couple of nuts out and bring the antenna down towards me. I did it in the past. Thanx for your suggestions.
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If you want a really detailed list, www.fcc.gov has database search pages for various services. I can't remember the exact URL, but go to the FCC site, then the pages for the "Media Bureau" and then there'll be links to television and other broadcast databases.
When you find the query page, you feed it your latitude and longitude in Degrees/Minutes/Seconds and feed it a radius distance in miles (or kilometers?) and it will come back with a list of every TV station (analog an digital), repeater, and station under construction, with a distance and degree heading.
Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
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Close, but no cigar.
http://www.fcc.gov/mb/video/tvq.html
The site I saw about 3 years ago, actually mapped out (mapquest style) all the towers within any given radious.
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jg wrote:

I don't think Univision shows cartoons anymore.
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You can't expect good reception by mixing the two kinds of cable. Use one or the other. Coax is preferred. You get less ghosts with coax, and most likely better signal. Depending on your directions, an antenna rotor may benefit you. That way you can point it toward SanFrancisco or your local towers.
BTW: Coax is easier to install. You dont need all those standoffs and stuff.
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jg wrote:

Hi, Twin lead also has better quality foam ones not the skinny twirly kind. Coiling up extra coax is not a good idea it can act like RF choke and could lower signal level. Tony
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Coiling up extra coax wil not make it like a RF choke and will not lower the signal level. As long as the coil diameter is large enough that the center conductor does not cut into the iner insulation and short to the shield, nothing on the outside of the coax will affect the strength of the signal. The signal is carried on the inside of the outer shield. Coil up all the extra you want. One thing that will affect the signal is if you have way too much coiled up (like 20 or more feet) is the extra loss in the length of coax. YOu will get the same ammount of loss if it is coiled or just ran in a line.
If you are transmitting , coiling up the coax may have a benifit as it will act as a choke and keep the transmitted rf that is coupled from the antenna from getting back to the transmitter. Discussion on this is beyond the TV application and not needed here.
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On Sun, 12 Feb 2006 13:25:44 GMT, "Ralph Mowery"

You sound like you know what you're talking about, but one thing gets me. Here you say it will act as a choke and at the start of the previous paragraph you say it won't. Why does transmission have a different result from reception, or is there some other difference?

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I have been a ham radio operator for over 30 years and at one time held a first class phone license that was good for the comercial radio repair.
When receiving the signal comes from the antenna it comes down on the outside of the inner wire and the inside of the outer sheild. Unlike Direct current which uses all the wire area, as the frequency goes up, the signal only uses part of the area. That is a copper tube can carry just as much signal as a solid wire the same diameter. Large coax (usually called hardline) is often made this way. There is nothing useful on the outside of the shield of the coax. In otherwords everything from the receiving antenna is on the inside of the coax and coiling it up has no effect .
When transmiting it is possiable that some of the signal from the antenna will couple or be introduced on the outside of the coax. This unwanted signal will come back down the coax on the outside of the shield and can cause problems with the transmitter and other electronics in the house. If the coax is wound in a coil it may choke off this unwanted signal. The coil is usually placed outside the house .
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You seem to know a lot. Here's a question, if my mast is well grounded (buried a few feet) do I still need to ground the coax before it enters the house? The way I see it, the mast will dissipate any charge on the antenna? Yes?
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jg wrote:

Not sure who you are addressing, but the shield of the coax does need to be grounded before entering the house. This is regardless of whether the antenna mast is grounded, but it should be. I would run a copper ground wire, at least 12-gauge, from a clamp on the antenna mast to a good copper clad ground rod. Connect the shield of the coax to this ground wire too. You can use a coax grounding 'block' to make the shield connection to the ground wire. This block is the kind that cable TV companies use to ground their coax before it enters the house. You can buy one at Radio Shack or hardware stores with coax parts.
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I try not to give advice on lightning protection. For about 25 years I had a tower up about 40 feet and never took a hit of any kind. The tower was not very well grounded and there were about 6 coax cables from various ham antennas coming into the radio room. None were grounded . There was also a wire about 130 feet long split in the middle and coax comming into the radio room. It was up about 30 feet and not grounded in any way. Only damage I ever took was a couple of telephones over the phone line. The installation was done by the phone company and I never looked at it to see how well it was done. Others I have know had well grounded systems and still had their equipment wiped out by lightning.
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jg wrote:

When moisture gets into flat cable (300-ohm twinlead) it degrades the signal. If the insulation is cracked and the wires are exposed, it should be replaced all the way to the antenna. Don't use cheap twinlead. The good kind has foam insulaton under the plastic outer insulation. Connect the new twinlead just like the old one at the antenna. Clean the antenna terminals with some electrical cleaner spray and a plastic scrub pad. It might be better to replace the terminal screws, nuts and washers with new ones made of brass or stainless steel. This may require cutting and/or drilling the old screws off. They usually get corroded on an old antenna.
Currently I just have it directly wired to

If you decide to continue using twinlead to the antenna, you should install an impedance matching transformer where the twinlead connects to the existing coax. (See next paragraph below.) Twinlead has less signal loss than coax so it's preferred in reception areas where signal strengths are low. This may not apply in your case. Coax has greater signal loss than twinlead but better immunity to noise reception from home appliances. This is a consideration when deciding which kind of antenna lead wire to use. If coax is used all the way from the antenna to the TV it might require an antenna amplifier to make up for the signal loss in the coax. The amplifier is installed on the antenna mast. The power supply for the amp' is located near the TV.

If you want to connect 75-ohm coax to a TV antenna which only has two screw terminals for twinlead, you'll need an impedance matching transformer. This is the kind which is used on the back of older TV's that have antenna screw terminals instead of a female coax connector. The matching transformer has a coax connector on one end and two wires (pigtails) on the other. The pigtails would be attached to the two terminals on the antenna and the coax goes to the female connector on the matching transformer. You should use a transformer made for outdoor use. You can buy one at Radio Shack or home improvement stores that have a TV hardware department. The labeling will say that it's made for connecting coax to a TV antenna which has screw terminals.

Matching transformers for TV use are not expensive, so it's not worth the effort to make one. It's also not easy to make one that works well at TV frequencies, especially UHF. Proper impedance matching between antenna and lead wire is important for getting the best signal quality to the TV.

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While you are at it, you may wish to replace the antenna as well. If you do be sure to get one with good UHF reception. Once the US switches to digital TV, I believe in 2009, all TV signals will be in the UHF band.

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That's not true. VHF High Band and UHF.
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JG,
I agree with everyone here that coax is better but so far noone has mentioned there are two types of coax, 50 ohm and 75 ohm. Make sure that you use the 75 ohm coax. 50 ohm is generally used for communications and you can't tell the difference between the two by the size or thickness of the coax. You can tell by the number stamped on the coax, eg. RG75U, etc.
J
jg wrote:

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On Thu, 09 Feb 2006 17:35:10 -0500, Joey

Yes, this is correct. Most hardware stores only carry the 75 ohm RG75U these days. The 50 ohm was popular in the 70's and 80's during the CB radio craze, but is seldom used these days except by amateur radio people and the few that still use CB. In fact Radio Shack no longer carries the 50 ohm cable in bulk. I wanted a piece for my scanner and they only had pre-made cables, and not the lengths even close to what I needed. I finally chopped a piece off an old CB antenna and soldered on my own ends.
Geeezzzz, I'm having a brain fart.... Is that RG50U.... ???? Don't sound right.... The older I get the more my memory fades !!!
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