# Category: Feed line length calculator

## Feed line length calculator

Voodoonris / 18.02.2021

QRZ Forums. I kept hearing about how balanced feedline works well to feed a dipole. So today I took down my 75 ohm coax and replaced it with ' of ohm twinlead. Well it works OK, but not as good as the coax worked.

With the balanced feedline it seems very narrow banded. It seems like a waste, it took a lot of time to run it through my attic making sure to keep it away from all the metal ductwork, copper pipe, and wires. Before I take it down, is there anything I should check for?

If I can't get it to work well with this dipole, how well do you think it would work for feeding a M Zep? I'm thinking the impedance at the end of the Zep should be higher than the impedance at the center of my 80M dipole. The feedpoint impedance of anything is based on its design vs. A "double Zepp" is kind of a made-up antenna used by hams and is a full-wave center-fed antenna fed by balanced line. An "extended double Zepp" is usually a center-fed doublet with each side about 0.

Everything except the original "Zepp" is a made-up design by hams attempting to make stuff work better, or match matter, or extend frequency of operation. The "original Zepp" is a very old design actually used on Zeppelins, thus the name. Like the Hindenberg, they can blow up. Any doublet can be fed with balanced line, and how well they work is entirely up to the way they're installed, the way the feedline is routed, and how good the antenna tuner is.

Remember unless the line is matched to the load like a Ohm antenna fed with Ohm balanced linein all other cases the line transforms the impedance and what the transmitter sees has almost nothing to do with the actual antenna impedance. Smith Charts are wonderful things. I guess some software should be on my wish list huh? You guys aren't creating the charts by doing the math on a calculator and plotting on paper are you?

I don't seem to remember the Smith Chart from school, but school was over 30 years ago. I've spent the last 30 years working on and designing electrical, mechanical, hydraulic, and pneumatic equipment.

How to Determine Coaxial Cable Length Correctly for Your Antenna?

I haven't worked with RF or really any frequency above maybe Hz in years and years. I know of the Smith Chart, but my understanding of them is very basic, and only to read them. I would really have to go back and study in order to be able to create a Smith Chart.

Are you using an external antenna tuner? KH6AQNov 16, Doublets work well, mine works well on forty where it is a full wavelength. I feed it with just over a quarter wave peace of ladder line at forty meters.Search other ham radio sites with Ham Radio Search. The input impedance of a transmission line is often needed. Much experience is required just to guess what it might be. This program accurately calculates it Balanced Lines 4 Balanced, Twin-Conductor Transmission Lines, 20Hz to 1GHz This program analyses the performance of a variety of balanced lines from lines with very wide-spaced, large-diameter, bare conductors for power distribution, via HF ladder-line antenna feeders, to figure-of-8 and oval plastic-insulated types.

There are also the various overhead open-wire and paper-insulated underground forms of construction used in telephone and digital networks. At the UHF end of the spectrum there are receiver input tuned lines 1 or 2 inches long. Large diameter tubes are used as tank circuits in high power VHF transmitters Also see these earlier versions of this program: Balanced Lines 1 Balanced-Pair, Open-Wire, Transmission Lines, 16Hz-1Gz This form of transmission line has been in use since the earliest days of the electric telegraph.

When the telephone was invented a long-distance network of low attenuation, balanced pair, overhead lines was already in existence. There was a rapid world-wide telephone expansion. Simultaneously the distribution of electric power within towns and into the countryside began using lines of the same type. They are still widely used. This program will investigate behaviour of lines at power frequencies.

To specify the line the only dimensions required are conductor diameters and length. Shapes and sizes of insulators and spacers are incorporated indirectly via the resulting impedance Zo and velocity VF Balun Transformers Toroidally-Wound Transmission Line Transformers with 1-to-4 Impedance Ratio The analysis applies to bi-filar wound transformers having an impedance step-up ratio of 1-to The low impedance winding is always unbalanced to ground. The high impedance winding may be unbalanced, or balanced with grounded centre-tap.

The winding consists of two insulated wires laid alongside each other to form a short balanced-pair transmission line. The twin line is wound round the ferrite core and becomes an RF choke insofar as longitudinal currents are concerned Series L and shunt C are distributed along their length. The inductance due to a coil winding is added to the inductance of a solid cylinder of the same diameter and length of the coil.

The distributed capacitance of the coil is the same as that of the solid cylinder provided the turns are not spaced too wide apart. L and C can be estimated mathematically from coil dimensions The two wires together form a single-conductor choke, simultaneously behaving as a two-wire balanced transmission line.

The choking action allows two different circuits to be connected together via the line without regard to the grounding arrangements of either. At one end of the balun can be an unbalanced circuit with one terminal grounded. At the other end the circuit can be floating relative to ground or it can be held firmly balanced against ground Coax Choke Self-Resonant Frequency of Single-Layer Solenoid Coils Coils have a distributed self-capacitance equivalent to a lumped capacitance connected between its ends.

Consequently, all coils have a parallel resonant frequency. At resonance there's a very high impedance between the ends of the coil. A common application is use of a coil as a resonant RF choke Performance is computed in terms of reflection coefficients, VSWR and actual transmission efficiency. The line's matched loss is displayed for comparisonForgot Password?

The feed line also called the transmission line is the RF power conduit between your radio and your antenna. All the energy you generate travels to the antenna through the feed line. By the same token, all the signals picked up by your antenna must reach your radio through the same feed line. To complicate matters, all feed lines are not created equal. The amount of loss at any frequency will vary considerably from one type of feed line to another.

The most common type of feed line is coaxial cableor simply coax. There is also insulating material between the center conductor and the shield. This material can be hard plastic, foam plastic or even air.

A popular type of feed line for HF use is ladder line. In fact, at HF frequencies it is the most common feed line for random-length dipoles and other antenna designs. Ladder line consists of nothing more than two wires in parallel separated by insulating material. Just remember that the higher the decibel number, the greater the loss.

Feed lines also have a characteristic impedance value measured in ohms. Coaxial cable commonly used for Amateur Radio has an impedance of 50 ohms while ladder line impedances can vary from to ohms. Amateur Radio transceivers are designed to work with an impedance of 50 ohms, so you must use 50 ohm coax, or find a way to convert the to ohm impedance of ladder line to 50 ohms.

## Doretta Smith

If you are using an antenna that is designed to deliver a ohm impedance, it is best to use a coaxial feed line to provide a ohm antenna system impedance for your transceiver. The other approach is to use a device called an antenna tuner to transform the impedance of the antenna system to 50 ohms for your radio without physically adjusting the antenna at all. An antenna tuner is a kind of adjustable impedance transformer.

Some tuners operate manually; you twist the knobs until the SWR meter shows a SWR, or something reasonably close to it. Other tuners are automatic and do all the adjustments for you. Taking the antenna tuner approach is not a good idea when you are using coaxial cable under high greater than SWR conditions.

The tuner may provide the 50 ohm match to your radio, but the mismatch and high SWR still exists between the antenna tuner and the antenna! This translates to high losses in the coaxial cable. At HF frequencies, the loss in ladder line is so low, you can still see good results even when the SWR is horrendous. So which type of feed line should you use at your station? Fortunately, the answer is simple: You want the feed line that has the lowest loss at the highest frequency you want to operate.

As you probably guessed, low-loss feed lines are more expensive. A little planning and common sense goes a long way when it comes to selecting feed line. As long as the SWR is low, the loss will be acceptable. However, if you have an antenna that is feet from your radio and you are operating at, say, MHz, RG would be an extraordinarily bad choice!

For base stations in particular, always buy the lowest-loss coax you can afford. For instance, feet of LMR is overkill quality for a station that only operates on the meter band. Find A Class Use our class locator to find a class offered in your local area. Learn More.N8YX on Sun Aug 11, pm. N9XR on Thu Oct 17, pm. JuanLargo on Sun Dec 01, am. N9XR on Mon Dec 02, pm. JuanLargo on Tue Dec 03, pm. N9XR on Tue Dec 03, pm. N9XR on Wed Dec 04, pm.

Sponsored content. The place for Ham Radio Operators to relax and have a good time. The use of ladder line to feed half wave dipoles for multi-band use is preferred due to low transmission line losses due to high SWR's, much better than coax. The limitation is ladder line lengths, not cut in multiples of half wave lengths of the bands used. Since we do not live in free air space, the constant used is Then, use the same formula for the other bands, such as 29 Mhz, Then there are the other odd bands.

For a given half-wave antenna fed with one wavelength of ohm line at frequency F, what does the impedance at the transmitter end of the circuit do as F is increased or decreased?

What happens to the system impedance when F is halved or doubled? Under what circumstances will the transmission line itself start to radiate?

I was interrupted and have not gotten back to this. I have developed a program that determines best ladder line lengths for multi-band use with ladder line and a dipole. Thanks for the links, Paul. This topic is massively misunderstood by many. I am always trying to learn more.

On Figure 1, there are two resistances shown on the cartoon. The loss resistance appears to refer to the transmission line losses. Another large loss is the ground losses in verticals. Where does that resistance fit in the schematic here? In a way, these losses are radiation resistances as they are resistances at the lumped impedance antenna input. On EZNEC, it appears to increase the resistance when the vertical is lower to the ground AND the resistance is higher when the ground conductivity is higher.

This does not seem to be intuitive. There is no way that I see this to be the case. If we rework their schematic to show a lossless signal source and source resistance as above, we would see a signal reflected from the antenna heading to the transceiver. If the transmitter section is working right, the signal will see a 50 ohm resistor running to ground.

Does the signal bounce back and forth over and over again? Yes it does indeed, but this signal is seeing your radio and a portion of it is being dissipated back into the radio.

## Beer Line Length Calculator

They antenna tuners do not change the SWR on the line, or the loss it produces. What can we do to reduce the loss? N8YX wrote: For a given half-wave antenna fed with one wavelength of ohm line at frequency F, what does the impedance at the transmitter end of the circuit do as F is increased or decreased? If the ladder line is balanced, it doesn't radiate RF.There are many different types of microstrip patch antennas, and many of them can be found in the MicrowaveTools Antenna A-Z database.

All the equations for determining the size and impedance of an inset fed patch antenna are at the end of this post. Matlab scripts are provided. A well designed patch antenna can have a peak gain between 6 and 8dBi, and as such it is considered to have a directional pattern click to rotate 3D image below which is linearly polarized along the width of the patch.

The rectangular patch is one of the more common types of patch antennas. This antenna is designed using a rectangular piece of electric conductor situated above a ground plane. The rectangular piece of copper measures long. Note that the wavelength depends on the material situated between the ground plane and the patch; meaning when air is between the patch and ground, the length of the rectangle electric conductor is of the free-space wavelength.

If the antenna is loaded with different dielectrics, the length of the antenna decreases as the dielectric constant increases. The natural input impedance of a patch antenna dependent on where within the patch the feed is located. If the feed is located closer to the edge of the patch the input impedance will be high, if the feed is located closer to the center of the patch the impedance will be low.

Below is the standard input impedance of an inset fed patch antenna at 2. This type of antenna is inherently a high Q antenna, meaning that this antenna is relatively narrow banded. There are many different ways to feed a patch antenna, the inset fed patch antenna is fed via a microstrip feed line connected to a specific point within the patch.

Through varying the location of where the microstrip connects to the patch antenna the measured input impedance can be controlled. The Microstrip patch antenna is a little different than many antennas, as the structure itself does not radiate, but rather the edge gaps between the patch and the ground plane. This can be visualized below. The areas where the patch radiates from are shown below.

The patch antenna radiates from the side in which it is fed and the opposite side. This creates a skew in the pattern, causing the boresight of the antenna not being located exactly normal to the planar surface of the patch antenna.Tune Around! Matching Problems using a tuner and high impedance feedline.

Most matching problems occur when the antenna system presents an extremely high impedance to the tuner. An antenna system should be considered everything from the tuner to the tip of the antenna. High impedance feedline is usually considered that which has over ohms impedance.

Common high impedance feedlines are ohms, ohms and s ohm in impedance. When the antenna impedance is much lower than the feedline impedance, an odd quarter-wavelength feedline converts the low antenna impedance to a very high impedance at the tuner. A similar problem occurs if the antenna has an extremely high impedance and the transmission line is a multiple of a half-wavelength.

The half-wavelength line repeats the very high antenna impedance at the tuner.

Incorrect feedline and antenna lengths can make an antenna system very difficult or impossible to tune. This problem often occurs on 80 meters if an odd quarter-wave 60 to 70 foot open wire line is used to feed a half-wave to foot dipole. The odd quarter-wave line transforms the dipole's low impedance to over three thousand ohms at the tuner.

The line inverts or teeter-totters the antenna impedance. A problem also occurs on 40 meters with this 80 meter antenna example above.

The feedline is now a multiple of a half-wave 60 to 70 foot and connects to a full-wave high impedance antenna to foot. The half-wave line repeats the high antenna impedance at the tuner. The antenna system looks like several thousand ohms at the tuner on 40 meters. The following suggestions will reduce the difficulty in matching an antenna with a tuner:. Never center feed a half-wave multi-band antenna with a high impedance feedline that is close to an odd multiple of a quarter-wave long.

Never center feed a full-wave antenna with any feedline close to a multiple of a halfwave long. Never try to load a G5RV or center fed dipole on a band below the half-wave design frequency. If you want to operate an 80 meter antenna on meters, feed either or both conductors as a longwire against the station ground. Suggested lengths for high impedance feedline on dipole type antennas Good lengths are green shaded area in the chart below. Some trimming or adding of line may be necessary to accommodate higher bands.

Here are 2 examples:. You have a dipole and you want to make it into a multibander using a tuner. You would use either, or feet according to the chart above. On meters, an 80 or 40 meter antenna fed the normal way will be extremely reactive with only a few ohms of feedpoint resistance. Trying to load an 80 meter or higher frequency antenna on meters can be a disaster for both your signal and the tuner.

The best way to operate with an 80 or 40 meter antenna is to load either or both feedline wires in parallel as a longwire. The antenna will act like a "T" antenna worked against the station ground.

### Beer Line Length Calculator

Source: MFJ Enterprises as printed in most of their tuner manuals.The modern common Windom antenna is not an original single-wire fed Windom, but rather an off-center-fed or "OCF" two wire feed dipole. In other words an meter Windom feet long would have one leg This would be The antenna could be scaled for other bands.

There is one caution with this. The large offset means the balun must be particularly good current balun on the lowest frequency bands, and the terminal best able to stand the highest voltage to earth should be on the shortest antenna side. Nearly all baluns are not symmetrical in voltage to ground capability for both terminals. Loren G. Windom, ex- W8GZ, was instrumental in the development of the Windom antenna. Loren lived in Reynoldsburg, Ohio. Loren was originally 8ZO from Columbus, Ohio in His call is now reissued.

### Coax Loss Calculator

Windom's original idea was off-center feeding a horizontal antenna to present a feedpoint impedance of ohms. This is close to the surge impedance of a single-wire feed line, allowing an inexpensive single conductor to be used as a feed line. In theory, with suitable selection of the feedpoint tap point and antenna length, a reasonable match should occur on multiple harmonically related bands.

The Achilles heel of the original single wire Windom is the single-wire feeder. It has no "return conductor" or shield, so the single-wire feeder:. Later generation of the Windom are more correctly called off-center-fed dipoles or in abbreviated form, OCF dipole antennas. Some people might take issue with using the word "dipole" because the antenna has more than two opposing polarities along the length, but in my opinion it is perfectly fine. Physics does have two-pole "dipoles" that are rigidly described as suchbut not in the context of antennas.