You remember this stuff, right? Two wires with a fat piece of plastic between them. Bare wire or lugs at the end. If you’re old enough to remember knobs on TVs, you’ve probably seen your share of it. No one uses that 300 ohm flat antenna wire anymore, though. Did you ever wonder why?
Here’s the simple answer: coaxial cable is better. Coaxial cable is much more resistant to interference. It’s more durable, too. Not that the old flat wire is unsafe or anything — if you’re using it now there’s no reason to stop. If you’re wiring a new antenna though, you’ll find that the connection you get from that antenna is always coax.
Which leads us to the question, if coax is so much better, why did anyone ever use twin-lead cable at all? It’s cheaper to make, and it does actually perform better over long distances than coax if there isn’t any interference. The big reason though, is impedance. Impedance is that hard-to-explain characteristic of wire that represents how much a circuit opposes the introduction of current into it. One way of imagining it is to think of a clogged pipe, and how much the clog in the pipe stops the water from flowing. (That’s not technically accurate but it gives you some idea.)
Whether or not you can wrap your head around impedance, the point here is that twin-lead wire is much more similar in impedance to the antenna itself. You don’t need a transformer to go from the antenna to the wire. With coax, you do. That’s one more part that was hard to make in the old days, and expensive too.
Today, we don’t have to worry much about the cost of a matching transformer that converts a signal from 300 ohms to 75 ohms (which is what coax uses.) So, we’re free to use coax cable and enjoy its superior shielding and freedom from interference. It’s a little more expensive, but not enough to make a huge difference.
Actually twinlead is far superior to coax.
Twinlead has MUCH lower loss and is the exact impedance of the antenna so it doesn’t require lossy baluns to convert down to 75 ohms.
…….
And interference was also never an issue, that’s simply a modern myth.
……..
The ONLY reason coax became popular is because it was easier to work with so it became more popular.
……
More popular doesn’t mean better.
……..
Every antenna made today is still a 300 ohm antenna.
…….
The only thing companies did was add a lossy balun to it to convert the impedance to 75 ohms.
I did antenna installs and repair for years in the 60’s – 70’s – 80’s, Coax (RG59 & RG6) are superior to 300 ohm cable, that’s why you don’t see it used any more. True it is very low loss under ideal conditions, but try using 300 ohm wire next to aluminum or steel siding, try putting it under ground, under an metal window frame, or run it horizontally on the side of a house that is located next to a radio transmitter tower. Every stand off that is used to hold the 300 ohm cable messes with your signal because of inductance & capacitance and if spaced at the right distance between each other could suck out some or all of you signal. If it was that good. then why don’t the cable company’s use it to wire up towns with.
If you have to much signal loss in the feed line from your antenna to your TV with coax, then you are border line reception and need an low noise hi gain antenna amplifier.
300 ohm transmission line is superior to coax in terms of signal loss. However, it has to be installed properly on standoffs to keep it clear of other objects. It should have a twist to it , about 1 twist every 18-24 inches to help reduce interference pickup. It should go though a sleeve when it passes through a wall. Rain and snow on the transmission like also increase loss, so the line should be ran in places where they will not get buried in snow. I grew up in a deep fringe reception area, and running the low loss line was worth the extra effort.
One other problem with the typical 300-Ohm balanced transmission line is that dirt on the dielectric also increases losses. Back in the 1950s, there were companies which marketed a 300-Ohm ladder line which had bare wires kept separate by little lucite spreaders. Dirt and water weren’t as much of a problem with this form of Ladder Line than it was with the solid plastic webbing between the relatively inexpensive 300-Ohm twin-lead.
Some companies offered a shielded version of the twin lead as well, somewhat more loss than the unshielded variety, and shielding wasn’t really needed because of the common-mode rejection gained by putting a 180-degree per foot twist into the line. The twist did two things, it improved the common mode rejection, basically making it self shielding (Remember, the letters “UTP” in Cat-6UTP computer LAN wire stand for “Unshielded Twisted Pair”. Most of the noise reduction in microphone cables comes from common mode rejection, not the shield. The twist in the antenna transmission line also cut down on the wind whipping the TV antenna lead-in causing damage to the wire and the customers’ nerves.
Coaxial cable has the advantage off being able to be taped or zip-tied directly to the metallic antenna mast, thereby cutting down on installation costs and, when properly terminated immunity to additional losses due to schmutz on the cable’s outer surface. There can be a problem with coax being poorly terminated and water migration between the dielectric and the shield, however this can be mitigated by doing the job right and sealing the connections with something other than cheap electrical tape, or my answer…I installed direct burial flooded RG-6 from the antennas to the inside of my house. Even a nick in the outer jacket of the cable won’t be an opening for water ingress and cable damage.
I remain,
The Old Soldering Gunslinger
Thank you for all that information I had heard the same thing. I will however be using twin lead for a nearly lossless antenna stacking project. I’ll be using it to gang four antennas. In this case the runs will be very short and they’ll be covered with PVC tubing
Absolute hogwash. Twin-lead, or balanced line is superior to coax in every way except for performance under wet conditions. Its characteristic impedance of 300 or 450 ohms is a reasonable compromise between the very low and very high impedances presented by the antenna at different frequencies, minimizing mismatch losses. It has FAR less loss when dry. It is about 1/4 the cost. The warnings about being close to other objects are seldom a problem in real life – if kept away from metal objects, that’s the main consideration. It is self-shielding, in that while the signal is equal but opposite in each wire, interference affects each conductor equally, and cancels itself. This is not true of coax, which picks up interference on the outside of its shield and takes it directly to your TV. The main reason many people use coax today is because they assume newer and more expensive technology ‘must be better’, whether or not that’s true.