First Let's go way back, almost 200 years ago. A German scientist named George Ohm proposed that electric current equals Voltage divided by Resistance.
An example would be if you connected a wire across the positive and negative terminals of a battery you will have some resistance. If you doubled the length of that wire and reconnected it, you would have double the resistance and only half the current would flow through it. George Ohm's scientific colleagues in Germany thought this was complete nonsense in 1827. However by 1841 George was awarded medals of scientific achievement, and his law was recognized as fact.
In 1831 British scientist Michael Faraday thought that magnets might produce electricity. He placed a coil of wires around a magnet and it produced electric current. He also found that if two coils of wire were wound around an iron ring, connecting or disconnecting one coil to a battery produced current in the other coil ! This is the basic principle of the Transformer.
In 1832 US scientist Joseph Henry discovered something unusual. He called this Inductance. He noticed that when magnets with coils around them tended to maintain their current even when conditions change. he discovered this by disconnecting an magnet with a coil around it from a battery and still watched the spark travel from the disconnected wire to the battery at some distance, and it had the same current ! He called this lengthening of the electricity to complete the circuit Inductance.
In the next 5 years the advances in electro-magnetism and electricity advanced rapidly, until only 5 years later in 1837 Samuel Morse and more importantly Alfred Vail who actually built the first telegraph key was invented. The telegraph key has looked pretty much the same since.
What about Capacitors and Capacitance?
Well they actually go back 100 years or more before George Ohm! In fact Ben Franklin and Ewald George von Kleist (Germany) in 1745 discovered that electric current (like lightning) could be stored in jars called Leyden Jars. Named after a Dutch city.These were filled with water. These were called condensors at the time, gradually became known as Capacitors, as the storage of electricity became known as Capacitance.
If you wanna go really nuts with this stuff, the Ancient Greeks were already rubbing pieces of amber together to create electric sparks. In fact the word amber in Greek is called Elektron, and is this is the origin of the English word Electricity
Whew.....Okay got that out of the way!
What does this have to do with Inductance, Capacitance, Reactance and Ohm's?
Your antenna is the device that converts electric currents into electromagnetic waves and vice versa.
It can be considered a “resistive-inductive-capacitive device”. The antenna is the conductor above ground serving as a pathway running down to your transceiver circuitry. The antenna system is the most important feature of your radio operation & one that you can greatly optimize. Although most hams don't pay that much attention to it. They think in terms of amplifiers and radios, neither of which contribute to what you can hear or talk to very much.Your Antenna and how well it works as a “resistive-inductive-capacitive device” determines who you can talk to and how efficient your transceiver will be in recieving signals and the noise associated with it. It all begins and ends at the antenna. Your transceiver is just changing the electricity back into readable signals for you. But you bring Garbage in from the antenna you will get Garbage out of the transceiver. Pay MOST attention to your Antenna it determines what your whole entire ham radio experience will be like for the rest of your amateur radio days.
IMPEDANCE........... is the resistance to alternating current flow by an antenna system. Also known as "Z".
Impedance involves the resistivity of the “wire or coax ” and the two forms of signal transformation and changes caused by various Capacitance and Inductance (these changes are known as Reactance). We want to adjust the Impedance so that it best “matches” our antenna to our feed line to our transceiver and if these are all adjusted to an optimal point, we will achieve maximum efficiency in sending & receiving signals. Admittedly the resistance to the wire whether it be coax or something else as a feeder cannot be changed or adjusted, we are in fact adjusting antenna to match the resistance or Ohm's of the wire.
Here is the basics of what you need to know without going into annoying theory.
INDUCTANCE or Inductive Reactance....... if our antenna is a bit longer than optimal for a given
frequency, you have too much Inductance or Inductive Reactance.
CAPACITANCE or Capacitive Reactance..... if our antenna is a bit shorter than optimal for a given
frequency, you have too much Capacitance or Capacitive Reactance.
We achieve resonance in our antenna by shortening or lengthening the antenna.
or by employing devices like “tuners or baluns or gamma matches, etc ” to bring about the
best balance to cause all Reactance to cancel out, leaving only the Ohm Resistance of the coax or wire feeder.
The antenna then is said to be resonant. Simple Huh?
SWR is a measurement of how well your feeder wire or coax and your antenna is matched to efficiently handle RF energy generated by your transciever. 50 Ω is what you want. A perfect match will have a SWR of 1:1. This means that theoretically, 100% of our transmission energy is being fed to the antenna and none is being reflected back because of a Impedance mismatch. Impedance unfortunately is affected by things around your antenna, such as other conductive materials, like any metal, masts, wires and the actual antenna height above the ground. As well as the ground itself. So rarely do you get a perfect match, all the time on all frequencys.
The SWR has nothing to do with how good your antenna is. You can have great SWR on many bands and frequencys, it probably means you have a Crappy antenna. The SWR value by itself should be regarded as an indicator of how well you may have your whole antenna system matched to your radio at that frequency. Nothing else. Great SWR does NOT mean great antenna.
Ever heard this: "ladder line has low loss" put a tuner in the shack, run "low-loss" ladder line up to a dipole of whatever length, WALLA a low-loss multiband antenna, easy to build, and cheap. How many times have you heard that on 80 meters.
It is has been mentioned many times in the ham radio community that ladder line, window line, etc. has lower losses per foot than say LMR400 or similar, particularly on HF frequencies. However is this really true? Ladder line is frequently used in VHF and UHF installations, where the Loss IS certainly lower than average coax. But if this true for HF as well? Since coax has thicker conductors than ladder line you would assume that coax would win the less loss per foot contest hands down wouldn't you?
Turns out that is not the whole story, and here's where things get complex (I'm sorry). Let's go to the higher end of the HF frequency (where coax losses are highest) 10 meters or 30 mhz where a lot of coax and ladder line are measured. According to DX Engineering 100 feet of 300 ohm ladder line has a loss of .67 and 100 feet of LMR 400 has a loss of .7 Basically the same. And thats at the highest end of the HF spectrum where the coax loss is the highest, at all bands lower coax will win this argument easily.
How can ladder line even equal the loss of coax even though it has thinner conductors with less copper? It's the same reason power lines run at high voltages for long-distance distribution: Higher impedance means for a given power less current and more voltage. Less current means less loss (resistance).
Power equals the current multiplied by the voltage of the line. IE:
If you took 100 volts and 1 amp it would equal 100 watts. If you had 1 volt and 100 amps it would also equal 100 watts. The ratio of volts to amperes is the line impedance! We are back at Ohm's Law in the first section of this page.
Resistive losses are the square of current, times resistance. This means higher impedance means more volts per amp, which means less amps are necessary for a given power, which means less loss. So ladder line's higher impedance is good for carrying high power 300, 450, 600 ohms means less amperage is used, which means lower loss. So far so good for ladder line affectionados! And also you said 300 ohm twin lead.. You say. "Not the stuff I will buy .......450 Ohm true ladder line for me! Then I will definitely have lower loss than coax! "
Not so fast: The issue is the standing waves set up alternating nodes of high current, and high voltage. They are spaced a 1/4 wavelength apart, repeating every 1/2 wavelength. As explained above, a higher voltage is associated with lower loss, and conversely higher current with higher loss. What does this mean? The ladder line's feedline's physical length is dictated by your distance from your antenna usually and its electrical length varies with frequency, and the load impedance varies by frequency too. At any particular frequency, the standing waves may fall in a way that reduces loss or increases it.
Lets take a typical example on 20 meters, and WHY you never hear of super stations or just about anybody else with serious antennas using ladder line on this band.
450 Ohm ladder line at 14 mhz has a loss of .25 db nice, however the SWR is now 9-1 !!! There are complicated formulas involving reflection coefficients online, but if you do the complicated math it comes out that a 9-1 loss assuming NO LOSS through the TUNER (which is absurd) the db loss is actually over 1 db, where as straight coax assuming a 1-1 SWR match would be .4 db !
The 450 ohm ladder line has more loss than LMR-400. More often than not, LMR-400 will outperform this 450 ohm ladder line if used to feed a 50 ohm load without a matching device. Yes there is even better 600 Ohm ladder line...but now the cost difference is not there. So what's the point.
How would you fix this, well as mentioned above: The issue is the standing waves set up alternating nodes of high current, and high voltage. They are spaced a 1/4 wavelength apart, repeating every 1/2 wavelength. SO you could try to cut the ladder line or lengthen it and after much trial and error to find the node of high voltage and low current, and then on that EXACT frequency you will have the lowest loss that you could get with ladder line, HOWEVER you still have a 9-1 SWR ! Either way in the end you'd probably still have more loss than if you ran coax.
Factor into it that, once ladder line gets wet the SWR becomes multiples higher and very inconsistent, It even doesn't work well in higher winds ( I know twist it...yea okay ), If it freezes its totally useless. This also assumes that you kept it away from any metals and there are no sudden sharp turns in it. Also assumes that your tuner is a magic tuner with no loss and that it isn't grounded, because that adds a whole nother bunch of variables you don't want.
Have you asked yourself yet....." is this cheaper stuff called ladder line really worth the trouble"
Ok, so is Ladder Line totally useless: No
If you only have some room for one antenna in your backyard and your wire, whether it's a random loop or a random length wire and you want to cover all the bands. Let's say 160-10 or 80-10 meters then you don't really have much choice do you? If you went with coax and a balun, chances are you will not be able to get a reasonable swr on all the frequencies you would like. Enter the ladder line to the rescue. Sort of.
If you are able to keep the ladder line away from any metals, do not make any sharp turns to it, and USE 600 Ohm wide spaced ladder line, and can bring it into your shack where it terminates either directly on the back of your tuner, or through a balun to convert the last leg to coax, you can do it.
You will have to have a tuner that can tune a coat hanger to work on 160 meters and get 50 ohms to make it work. Meaning get yourself a good manual tuner. You will have to tune each band you plan on transmitting on everytime. But yes it can work. Do not use 300 or cheap 450 ohm line, this is what most amateurs use and why they have alot of issues with the weather, wind , RF, and many other problems too many to list with ladder line.
Me personally I like multiple antennas, each resonant on whatever bands they are designed for, and fed with coax and a balun if needed. In fact I don't even use a tuner, on my antenna farm and for various commercially produced antennas that I have tested for manufacturers. Nor do I use a tuner for all my personal antennas that I have made. This would included dozens of cubical quads, dozens of yagi's and plently of loops and other wire configurations.
But yes it can work.
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