Vertical antenna null skirt

Thermal noise is low as the resistor. Yes , but loads loop is based on reflected wave and the one direction current dissipate on a 1K resistor gives you the front back and the other direction the current see a Balun. Again it is not a loop with high current and high Q or a tunned loop, it is very broad band the BW is over 10 MHz. It is extremely easy to get a 50 ohm NF of 0. Unfortunately, at 1. I did this same experiment with the multiple paralleled BF's over 15 years ago and was limited by flicker noise, which is unspecified, YMMV.

Maybe you had better devices than I did. Here I agree, I was luck , I was not expecting 43 db gain. Latest page update: 25 Sept added refs 3J, 3K, 3L.

This page is a collection of short vertical antennas that I built over the years, for the 80 mtr band. I am not interested in local QSOs, so I'd like my antenna to have a radiation pattern with a relatively small takeoff angle. Radiation straight up is to be minimized. A tall order indeed! The radiating element of a vertical monopole antenna is basically half of a dipole. The missing leg of the dipole has to be replaced by something else, for the monopole to "push against".

This typically takes the form of one or more radials. Let's take a monopole radiator that is short with respect to the desire operating frequency. To make it resonant at that frequency, some form of loading is required.

By the way: resonant operation is not a requirement - it just makes coupling to a feedline easier. One standard solution is "inductive loading": placing a loading coil somewhere between the feedpoint at the bottom of the monopole and the tip of that monopole. The current-distribution along the radiator is such that the current is highest at the feedpoint.

Placing a loading coil here, requires the smallest inductance. The current-distribution tapers off, from maximum at the feedpoint to zero at the tip of the radiator element. So, as the loading coil is placed farther away from the feedpoint, a larger inductance is required. At the tip of the radiator, the current is zero. This would require an infinitely large inductance. See the diagram below.

The placement of the coils does affect the shape of the current distribution, but does not change the fact that it is maximum at the feedpoint and zero at the tip. Base-loading i. Also, coil placed at the based of the antenna may be more easily accessible.

So why not always use base-loading? This is primarily driven by coil losses, hence, efficiency of the antenna. The coil losses basically depend on the current, coil dimensions, material, construction, and core. Note that the efficiency-vs-placement curves are fairly flat over a relatively large range around the mid-point.

Note that this tends to shift towards the tip of the monopole when "capacitive hat" loading is added. Despite the above recommendations, the short verticals on this page are all base-loaded, and with just one or three short radials.

Primarily for construction reasons, and because I converted some of them from center-loaded dipole experiments. Short dipoles for the lower bands 40 mtrs and below do not perform well for DX when installed horizontally at low height: significant ground losses, and a high radiation takeoff angle.

Take half a loaded dipole, add a single elevated radial and you have a loaded L-antenna ref. In general, discussions about loading of dipole antennas e. For my short 80 mtr mid -loaded verticals, see this page. My short 80 mtr linearly -loaded vertical is on this page.

My short 80 mtr end-hat -loaded verticals are on this page. Over several decades, Barry Booth W9UCW and a group of fellow hams, have done an incredible amount of well-documented and systematic, repeated tests to assess the performance of various configurations and installations of short , loaded antennas. In particular concerning the use of high vs. General summary of the conclusions of these two articles:.

For the vertical radiator, I re-used aluminum tubing from a dipole experiment. It is 2. I had already tapped a standard M6x1 thread into the tube ends. From my available materials, I chose tubing with 32 mm OD 1. A 2 m 6 ft section of PVC tubing with an OD of 40 mm 1,6" will serve as "mast", stuck into a heavy cast-iron umbrella stand.

I glued a to mm PVC adapter piece to the bottom end of the coil core. This way, the antenna can simply be stuck onto the top of the mast. I installed a BNC jack towards the bottom end of the coil core, and a banana jack next to it.

The latter is connected to the ground solder-lip of the BNC jack. The radial wire is plugged into it. The bottom end wire of the coil is soldered to the center conductor of the BNC jack. Note that the to PVC adapter piece is not glued onto the core - at least not until the number of wire turns of the coil has been adjusted for the desired resonance frequency! A 32 mm female-to-female coupler sleeve is glued to the top end of the core.

It receives a 32 mm insert for a screw-on end-cap. An M6x25 bolt is installed into this end-cap, with washers and a lock-nut. The radiator is screwed onto the bolt, and is easily removable.

As a "counterpoise", I use a simple 7 m 22 ft radial made of "zip cord" household hook-up wire. It is strung horizontally, from the bottom end of the coil core. No particular reason for using 7 m, it is just the length of wire that I had on hand. Also, I cannot fit much more than that on my terrace in a straight line. Note that a small number e. See ref In my case, the antenna and the radial are 2 m 6 ft above the terrace floor. According to loaded-dipole calculators such as ref.

Coil calculators e. Note that "Harry's Law of Coils" always applies. I have measured quite a number of "close-wound" loading coils that I made. With my personal coil winding technique, I obtain a close-wound turn spacing of about 0. For an indoor antenna, the foil antenna works rather well. It can out perform a vertical and pull in the weak ones with ease. I think you'll find it one of the most inexpensive antennas you can build yourself.

The discone has no gain to speak of, yet can provide the user with a range of ten times the design frequency for reception and transmissions. This means that a discone designed at MHz will work fine up to 1. Hiding the discone outside may prove to be quite a feat. Unlike most antennas, the discone has a large skirt and is tall to boot. Its shape can draw attention. If you can place the antenna outside, it will give you excellent coverage over its range.

Inside, the discone works well minus the attenuation caused by the building it's in. There are many Discones available on the market if you choose not to build one. Building one can be fun if you take the time and lay everything out ahead of time. There are a couple items I would like to point out about discones. Design parameters are easy. This gives the user the closest impedance ohms.

Thus a skirt element length is: 0. A SO chassis connector can be fit into the cut-off funnel end and the top-hat soldered to the centre pin of the SO Insulating spacers can be used to strengthen the gap. I've used a brass screw that was soldered between the centre pin and the top-hat, but you can use anything that you can solder. Wire beams indoor For many of us, the antenna is the biggest problem. Radio fans have to contend with neighbours and the XYL in order to pursue their hobby.

The wire beam is unrolled and suspended in the direction required for operation. After the operation is complete, the wire beam is rolled up and stored for the next time. This type of beam is excellent for 10m and up to 1. You may be able to set up a wire beam for frequencies below 10m if you have the space to do so.

This antenna is also excellent for suspension in an attic. A simple model is shown below: R DE D -- -- -- -- -- -- Aside from the elements, the rest of the configuration is non-conductive. The wooden dowels are not required if suspension is taught.

You can see that variations of this set-up can be incorporated to accommodate most any frequency from 10 to 1.