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2

Engineer999. While it might seem like a good idea to connect your antenna to the building ground wire, my experience has been that for those vertical antennas which are designed to operate without radials it makes little or no difference what the ground is connected to. You also should consider that if you are in a multi-tenanted building where you aren't ...


2

It may be great, it may not... that's definitely an empirical question due to the many factors: how much of the xmit current on the ground leg will be parallel and next to your vertical? this could cause destructive interference and make the antenna pattern more directional. are there other currents on the ground that will make their way into your antenna ...


2

A null is a state where parts of a system are in nearly perfect balance. A lobe represents a state where they are maximally unbalanced. If a system is balanced, even a small change can make it quite obviously imbalanced. By contrast, if a system is maximally unbalanced, a much larger change would be required to make the system be noticeably less ...


8

To increase an antenna's gain, the elements of the antenna must be arranged such that they interfere constructively in the intended direction, and destructively in every other direction. This is possible because varying the distance to an element varies the phase of the wave, so in some positions the phase difference is such that the waves interfere ...


2

As @glen_geek points out in his answer, "getting to zero" is pretty definitive. If you'll accept "very narrow lobes" as an acceptable interpretation of "sharp lobes" then I'd add: Antenna systems can achieve a very narrow beam-width with some of the following techniques: an array of elements as in a yagi-uda an array of arrays ...


8

Its all in the nature of nulls: Two signal sources (same frequency) can possibly subtract exactly producing a very deep null. Two signal sources (same frequency) can only add constructively to double amplitude, at best. Or, if you wish, imagine a sinusoidal wave whose average value is 1.0, and whose peak is also 1.0. I've chosen a frequency of 1 Hz, but ...


0

For your required distance of 10-20 ft, you might consider first testing a dummy load. An antenna approaching any kind of efficiency will be larger than the space you're looking to cover. And any antenna that is portable will closely approximate a dummy load... So try a few wire wound resistors and see what happens. Will be interesting to see what your ...


5

That is a great idea. In fact antennas of this design are quite common, and you probably have a much smaller antenna of similar construction on your Wi-Fi router: Effectively, the lower dipole element, which is a tube, forms a "bazooka" or "sleeve" balun. See also W8JI's description of sleeve baluns. I'll let you follow the links for ...


0

If a feedline isn't centered in a balanced antenna's near field, it can couple into the EM near field, pick up induced currents, and thus distort the pattern. If you feed the feedline into a quarter wave length pipe segment of a half wave dipole, the end exit of that pipe will be a very high voltage node at resonance that can capacitively couple to the feed ...


-1

An electrically resonant circuit or object would be very difficult or extremely large at those low frequencies (possibly county, country, or planet sized). But mechanically resonant generation of a 1 Hz alternating EM field might be easy. You can accelerate either a charged object, or a magnet in some cyclic or periodic fashion. Note that according to ...


5

The wavelength at 1 Hz is several times greater than the circumference of the Earth. At these frequencies, one arguably can't even have an "antenna" for terrestrial communication, since any two such antennas would be so close together they would be more like two plates of a capacitor or two windings of an inductor than an antenna. 1 Hz isn't even ...


6

From some research, beam antennas only seem to come as monoband antennas. Not true — actually 20/15/10m tri-band beams are very popular. Multi-band yagis come in two basic flavors. Trapped. Works on the same principle as a trap vertical to alter the effective electrical length of the elements at different frequencies, except there are way more elements to ...


0

Dipoles are resonant on odd harmonics of their fundamental frequency. So a dipole resonant on 20 meters, or 14 MHz, is also resonant on 14×3 = 42 MHz, 14×5 = 70 MHz, and so on. 10 meters is (approximately) an even harmonic of 20 meters, so this does not work. At the even harmonics you get zero reactance in the feedpoint impedance, but the resistance is very ...


4

Engineer999. The driven element of a yagi antenna is normally a half wave dipole, and it's true that a dipole antenna is resonant on multiple harmonically related frequencies. An ideal 10 m long dipole for example is resonant on 15 MHz, 30 MHz, 60 MHz, 120 MHz etc. However the distances between the elements along the boom of a yagi required to provide ...


1

A resonant 20 meter monoband Yagi will not work on 10 meters. Have you considered a 3-band 10-15-20 Tri-bander? It is a beam, and definitely not a monobander. There are also smaller tri-band directional beams, such as the Hexbeam.


2

If you feed a wire antenna at its center with open wire or balanced line, where the length of the antenna may or may not be designed to be resonant on any operating frequency, then the result is usually called a doublet antenna. A doublet’s length is usually chosen so that it isn’t anti-resonant (a full wavelength, etc.) on any of the desired operating ...


1

I think this is the wrong question. You ask does antenna X exist, but what you really should be asking is Given this configuration, can it be made resonant with a good SWR. Random wire antennas exist. All you need to make anything work is a good antenna tuner. Of course, this doesn't guarantee efficiency, radiation pattern, or that it radiates at all. ...


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