Dipoles and a bit about loops

 I use both a halfway dipole cut for 15 meters and a dipole cut for the CW end of 40 meters for 15 meters. 

The dipole gives about 7 or 8 dBi gain broadside.The 40 meter dipole gives maybe  a bit more gain but in four narrow directions. If I did not need an antenna for 40 meters I would just as soon have two 15 meter dipoles at right angles.  I did something similar this year on 10 meters. I ended up with three dipoles, one NE/SW, one E/W and one N/S on a three position remote switch.  Sometimes switching gave me one or two S-unit increase with the right antenna. Peak gain was from EZNEC was almost 8 dBi and the minimum gain at any point was never more than 3 dB down from that with one of the three antennas and that was only at precisely two compass points. I have had large Yagis on ten metersand switching between these three dipoles felt like instantly swinging a Yagi! A dipole is a really good antenna if high and broadside to the desired direction. It is the nulls on any antenna that really hurt.The null off the end of a good dipole can be two or more S-units. Some longer wires have more nulls. I think nulls are bad and want to avoid having them if possible.


one note about loops. A Quad loop is never going to be more than two in phase dipoles spaced at 1/4 wavelength with their ends bent down to touch. Two in phase dipoles stacked at 0.6 wavelengths might give almost 5 dB gain over one dipole but with stacked dipoles at 1/4 wave the gain drops to about 1 dB. The Quad loop is definitely no more than that and I think usually a bit less. Other loops are going to be even worse than that.  

Comments

Post a Comment

Popular posts from this blog

Some basic antenna info

  Antenna thoughts August 2025 If one knows the basics of antennas then it becomes easy to choose what antenna is best for you. There is no one “best” antenna. There are very good antennas of course but even a very good antenna is not going to be right for all uses. I will discuss some antenna basics here and give some “rule of thumb” guidelines on how to think about antennas.  The halfwave dipole can be considered the basic building block of antennas. I think understanding the dipole is the key to understanding antennas. Also for antennas we need to think in terms of wavelength, not feet or meters.  For example a dipole 1/2 wavelength long and 1/2 wavelength high above ground is an excellent antenna. It has a gain of about 8dBi off the broadsides. It has a slight reduction in signal strength off the two ends. It’s peak radiation ( off the sides) is centered at about 30 degrees. The actual radiation is rather broad from about 15 to 45 degrees and gradually drops off above...
Read more

Half Square Antennas

 I have had half square antennas on 80, 40 and 20 meters. In all cases the top wire (spacing) was one-half  wave length long on the band I built it for. The half square is not a multiband antenna. My results were that the 80 meter antenna was the best antenna I ever had ( except maybe my full size 4 element 20 meter monobander)! The top wire was at about 60 feet or so. On 40 meters the Half Square antenna worked but not nearly as well as my 40 meter dipole in that it seemed to have the same gain in Europe but a more narrow pattern resulting in deeper nulls of the side than the dipole which was at about 35 feet. On 20 meters any full size (halfwave) dipole or end fed is hands down at least an S unit better if it is a halfwave (32 feet) or more high! I model a lot with EZNEC and the EZNEC results were almost exactly what I saw in practice. Any dipole or halfwave wire will have a gain of about 8 dBi if anywhere near a halfwave high. Any vertical over real earth will have maybe 0 ...
Read more

RADIATION FROM ANTENNAS

Image
 Radiation from Antennas Evaluating radiation from antennas is not widely understood. My intention is to attempt to simplify this misunderstood concept. I will use the term wire but it could actually be any conductor normally used in antenna construction . I will also use the term amp or ampere to be current flow.  Radiation from a piece of wire (antenna) is simply proportional to the amount of current flowing in that wire. It is also proportional to the length of that wire. If the wire length is measured in feet and the current in amperes we can do some comparisons.  I will start very basic to introduce what may be a new concept to many. First of all , if one amp of current flows in a piece of wire one foot long that will result in less radiation than if we have one amp flowing in a wire two feet long. I think that is easy to understand. We have a term for current flowing in a wire. That is feet-amperes . If you take the length of the wire and multiply it by the amount...
Read more