TV antemnna problem

I have a TV antenna as a back up to my dish. I believe the head end unit of the antenna amplifier is defective. It is on the antenna.The twin lead from the antenna connection goes in one end and the coax goes on the other. The coax then goes to a plug in unit in the house which is connected to the TV. Is this unit on the antenna a special device or is it nothing more than a standard converter from 250 ohm twin lead to 75 ohm coax? If so, that will save me buying a whole new amplifier. Thanks DS
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on
What makes you think it is defective? What is the " plug in unit in the house"? It has to have some sort of identification.
It could be an amplifier up there with a power supply down below or the unit below might be the amp and the part on the antenna is just a 300 ohm twin lead to 75 ohm cable transformer. But if your signal has deteriorated and you have an amplifier you really have to find out where it is. The transformers themselves rarely go bad, but the connections out in the weather may have corroded. Tell us what you have.
Charlie
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and
a
unit
candy bar. There is no power going to it. The only wires are the twin lead at one end and the coax at the other. (If it's an amplifier, it would need a power lead, no?) The other unit is a box , maybe a little bigger than a cigarette box, which plugs into the wall in the house. The coax from the antenna goes on one connection and a coax cord to the TV set goes on the other. There is a gain control on it and an FM signal trap. This would seem to be the actual amplifier. It's a Radio Shack product. I believe the top unit is defective because I may have broken something in getting the old coax connector loose. I'm just wondering what will happen if I merely replace the top unit with a 250 to 75 ohm transformer. Thanks. ds
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R.Smyth wrote:

Not necessarily. From what you say below, it sounds like the plug-in unit would likely be feeding a DC voltage up the coax to power the amplifier up at the antenna. Same principal the cable company uses, actually. There is 60 VDC on the big feeder cables to power the amps and line extenders. It gets trapped out at the tap units where your house connects.

Maybe nothing, but likely improved if you broke the center conductor loose in the coax connector. Yes, you can replace it with a 75-300 Matching Transformer. Your downfeed cable should already have an F connector on it, and the other end you can srip the twin lead on both the antenna wire and the "lugs" end of the 75-300 MT, twist wires and electrical tape to secure. Soldering wouldn't hurt but isn't necessary. Get rid of the plug in wall box down below, a female-female F connector "Barrel" will tie those two cable ends together.
HTH.
--
The real Tom Pendergast [ So if you meet me, have some courtesy,
aka I-zheet M'drurz [ have some sympathy, and some taste.
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First, it does seem that the unit on the antenna is only a twin lead to coax transformer and the amplifier is down near the tv. If you think you broke something at the transformer while getting the coax connector loose then it is very likely that what broke is the short piece of the inner conductor of the cable. If this is true, you would be well advised to replace the cable with a preassembled cable that has the connectors already in place. It is possible to just cut the cable and attach a new connector. But given your inexperience with this sort of stuff it is unlikely that you can accomplish this so that you have a weatherproof connection. It is one thing to hack together a fitting to use inside the house, but making a weather resistant connection is not as forgiving. If the cable that you have is a commercially assembled one you could just reverse it and put the end that had been in the house in the air and then put a new connector on the end that is now indoors. Or as someone else has suggested replace both the transformer and the cable. It won't hurt anything and will likely help.
Charlie
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The Radio Shack device IS an amplifier. These things are generally poorly made, and tend to fail, I've gone through a few of them in the past 10 years.. Fix the other problem first, then see if you really need the amplifier.
The device at the top is most likely just a 75-300 ohm balun. You can replace that, but probably need to replace the F connector on the coax.
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J Kelly wrote:

Sorry, I disagree with that part. If he was fighting to get the end off, it's much more likely that he would've broken the "panel mount" female F connetor loose. It's pretty hard to break the male connector on a piece of cable, short of running it over or otherwise mutilating it.
--
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aka I-zheet M'drurz [ have some sympathy, and some taste.
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wrote:

Not if it wasn't installed correctly to begin with. I meant that the balun needs replaced, and probably the coax connector also. I didn't word that well...
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Does the plug in unit at the TV also plug into a wall socket? If not you do not have an amplifier. You have a impedance, balance to unbalanced transformer.
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I would buy an inexpensive 300 ohm to 75 ohn transformer and a piece of 75 ohm coax cable. Unhook the twin lead at the antenna and hook it into the new transformer. Hook the new coax into the other end of the new transformer and run it right to your TV. You have to bypass BOTH the amplifier (at the antenna) AND the power supply (plugged in at the back of your set).
If that fixes your problem, you could either replace the amplifier, or, it may in fact be a "good enough" signal, especially since you say it is only a back-up.
John
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