What is this cable?

[rcc147]

Looking for help with a mystery cable. Please see pics.

I have an old cable running from the roof into the apartment. On the roof was a 'VHF Matching Box (75 [Unknown symbol] > 300 [same symbol])' that used to connect to one end of the cable. The box has a coaxial connector on the other end of the it. The cable is flat with two wires in it.

Any idea what this was used for? If it was connected to an OTA antenna, could I hook it up for that purpose again?

Thank you.

 

[CowboyDren]

It's called a balun or a 75-ohm to 300-ohm transformer. Usually they're attached with screws to the antenna's feed lines, so that you can use regular coax cable to carry the signal.

Looks like you need a new one, and to figure out where it used to attach to the antenna. You can get one at any hardware store, usually for less than $4.

 

[HIFI]

that is a converter used to hook up a 300ohm line to a cable ready tv or a coax line to an older tv that only had the 300ohm connection. yes it will work on the antenna but probably won't get much unless you have a digital tuner at this point

 

[rcc147]

Thanks for the comments. I connected the box to my tv and the mystery cable, the result was 15 very good quality OTA channels on my tv, including some HD. Very pleased, especially as the other end isn't connected to an antenna, just lying on the roof.

 

[CowboyDren]

Thanks for the comments. I connected the box to my tv and the mystery cable, the result was 15 very good quality OTA channels on my tv, including some HD. Very pleased, especially as the other end isn't connected to an antenna, just lying on the roof.

That's...impressive. If you can do that with no antenna at all, put a $10 set of rabbit ears with a 7.5" hoop up on the roof, and see what happens next...

 

[TV_View]

That's amazing that you get all of those channels with something that small. I get 7 channels and require a big attena to get them.

 

[Houston]

rcc,

15 channels is pretty good, but, given your location, you probably have a LOT more available to you.

If you'll post your ZipCode, we can look up your Chart, and see if you can improve on that number.

Or, if you'd rather do it yourself, you can follow these...
LookUp & Posting Instructions for finding your Free Local TV Channels

Have a good Day !
S.W.

 

[Bouncy64]

Tha little wierd looking thing was correctly identified as a matching balun, or matching transformer, it "transforms", the 300ohm feed from the two(2) connectors on your antenna to 75 ohm feed, that way you can use 75 ohm coastandard tv/cable coax), instead of having to use 300 ohm 2 wire feed line all the way from the antenna, using "standoffs", as there was no sheilding really with the 300 ohm 2 wire feed line and you used to have to use standoffs with it all the way down the tower continuing into the house and connected to the older 2 wire feeds on the back of the older style tv's, if you did not use stand-offs you would lose alot of signal coming from the antenna.

If you were to get a new matching tranformer, an outdoor one, which comes with a weather boot, to aid keeping the water out of your 75 ohm coax, once 75 ohm tv/cable coax gets water in it, it degrades and will turn the sheilding and center conductor green, and you loose alot of signal.

Once you install an antenna, you will have much better picture quality and many more channels, the higher you get an antenna, and the least amount of obstructions the better they perform, presently with mine, and mine has a signal amplifier I can receive approx. 35+ channels perfectly, some from as far as 100 miles away (antenna sits on a fifty(50) foot tower) from Buffalo(US), Erie Pennsylvania(US), Ohio(US), Toronto(ONT.), Hamilton(Ont.), Kitchener(Ont.), Paris(Ont.), London(ont.) etc, I am located on the north shore of Lake Erie, near what is refered to as Long Point, Ont.

So as you can see, a properly set-up outdoor antenna blows an indoor,(rabbit ears, or an attic antenna), out of the water so to speak, simply because there is much less obstructions, be it house wiring, heating/cooling duct work or anything else that can interfere with signal reception.

So yeah, an outdoor antenna will help you out greatly.

Those services, in my opinion, that list what channels you can get from whatever zip or postal code can be rather decieving, and do not take into account the use of an amplifier, which can aid greatly in the reception of either non existant channels or weak ones to the point that they are recieved perfectly. With tv amplifiers it is a matter of db gain that can make the difference, the more gain the better.

 

[harshness]

2 wire feed line

The term you were looking for is "twin-lead".

Twin-lead - Wikipedia, the free encyclopedia

 

[Jim5506]

The word balun is a contraction of the phrase balanced-unbalanced, it converts a balanced 300 ohm twin lead line to an unbalanced 75 ohm cable.

 

[roashru]

I dont know about everyone else I love 300 ohm wire. I use it mostly to make folded dipole antennas for broadcast TV.

rcc147, that wire is the old TV signal transmission line before coax.

 

[dodge]

I dont know about everyone else I love 300 ohm wire. I use it mostly to make folded dipole antennas for broadcast TV.

rcc147, that wire is the old TV signal transmission line before coax.

300 ohm twinlead makes a nice antenna for 2 meter ham radio as well, as for tv I think it sucks!!!

 

[roashru]

300 ohm twinlead makes a nice antenna for 2 meter ham radio as well, as for tv I think it sucks!!!

A folded dipole antenna made from 300 ohm wire dose have its limitations but its CHEAP!. I normally make 7 feet across and 2 feet down in the middle. More suited for UHF analog VHF is clear with sometimes noticeable herringbone diagonal lines. With the new digital broadcast TV the made folded diploe antenna seems to help reduce signal multipath.

If interested, For some reason a minimum of 1.5 feet 300 ohm wire down the center is required for the antenna to work. 3 foot or more to a transformer is best.

 

[Jim5506]

Good quality 300 ohm twinlead is BETTER that RG-6, the problem with it is that it is attacked by UV and deteriorates after a couple of years and must be replaced.

You can splice 300 ohm twin lead without ever cutting it, just lay two pieces along side each other of 6 ft or so and wrap them in black electrical tape, works great.

 

[Splicer]

Those services, in my opinion, that list what channels you can get from whatever zip or postal code can be rather decieving, and do not take into account the use of an amplifier, which can aid greatly in the reception of either non existant channels or weak ones to the point that they are recieved perfectly.

I'm sorry, but this is just not true. An amplifier has absoutely NOTHING to do with reception of a signal what-so-ever. Reception of the signal is the job of the antenna itself. The amp;ifier can only amplify the signal.

Example: Point an antenna away from the transmission towers. If there is no reception of signals from the tower, an amplifier will not help at all. If reception from the tower is weak, an amplifier can increase what signal is being received to a usable level.

And an amplifier, even the best one ever made, along with the most expensive and best antenna made, will ever 'create' a channel that is "non-existant". Non existant means there is no channel.

I understand you are trying to help, but you need to understand how things work a little better first. Lots of info here, pretty much everything needed to know, so you would be well advised to take some time and go through the forum(s) and do some searches to get the knowledge.

With tv amplifiers it is a matter of db gain that can make the difference, the more gain the better.

This is not really factual. With TV amplifiers, the noise level moreso than the gain (dB) is what makes the difference of the amplifiers effectiveness. As a rule of thumb, the higher the gain, the more noise that will be introduced. Also, there is such a thing as too much gain. Too much gain will cause as many issues as too little gain can. And this is before even taking the noise level into consideration.

If you were to get a new matching tranformer, an outdoor one, which comes with a weather boot, to aid keeping the water out of your 75 ohm coax, once 75 ohm tv/cable coax gets water in it, it degrades and will turn the sheilding and center conductor green, and you loose alot of signal.

The problem using a "weather boot" is they generally cause more problems than prevent. The boots, designed to keep water out, generally hold the water in. And it is to keep the water out of the fittings more than the cable itself. But the only thing that will turn green is the center conductor and that is only if its a solid copper center conductor. Copper clad steel rusts. The braid will corrode and turn white for non copper braid, and for copper braid, it will of course turn green. But you are correct on one point. The signal is dramatically impeded.

 

[rcc147]

Thank you to everyone who responded to my question. I learned a lot and was impressed with the quality (and quantity) of responses.

Will definitely hook up to an antenna and get some more channels!

 

[roashru]

Good quality 300 ohm twinlead is BETTER that RG-6, the problem with it is that it is attacked by UV and deteriorates after a couple of years and must be replaced.

You can splice 300 ohm twin lead without ever cutting it, just lay two pieces along side each other of 6 ft or so and wrap them in black electrical tape, works great.

The newer 300 ohm wire is tough it has a white foam core and is ultra low loss. I still sometimes use the cheap stuff but it still will dry rot.