New answers tagged

1

I don't understand the parameters of your equations. But ignoring the equations and answering the text of the question: beam forming depends on frequency and phase. If the phase of the output of two beam forming elements is equal and opposite at the angles and frequency of measurement, the received output power output from that 2 element array is zero. If ...


3

This is a harder question to answer than you think for a number of reasons. I'll start off with the ideal answer: The Diamond RH-771 claims that it has 2.15 dBi gain at 70cm (or 0 dBd). Most rubber ducks are significantly worse than quarter wave antennas, and often exhibit negative gain. A short antenna like the SRH-701 has no gain (or -2.15 dBd). The ...


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 ...


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 ...


-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.


1

If you are using copper wire, 14 gauge is about as small as you want to get. Be aware, however, that if you hang a long copper wire that thin, it will stretch. This is not a big deal as long as you don't care about its length for antenna purposes. If you use something like copper clad steel, you can go as low as 16 or 18 gauge and it will still support its ...


3

First check your local regulations. Some specify the minimum gauge for wire antennas. For example NEC Article 810 specifies a minimum of 14 AWG for wire receive antennas. For temporary antennas such a POTA activation using a smaller gauge would be acceptable. I've also know hams to ignore the local regulations. If transmitting check that is can handle the ...


2

"RF ground" usually means "something that is at the same potential as the soil". This is important because if you have a wire (such as your feedline, for example) which is not at ground potential, then there exists a non-zero electromagnetic field between that wire and the soil. That means the feedline is radiating/receiving, which is ...


0

RF will flow through the outermost layer of tin, in either tinned copper braid or tinned copper wire. Thus, very little current will actually flow through the highly conductive copper in the center. The conductivity of copper is much better than tin. Tin is only 17% compared to copper at 100%. Will you notice a difference? The only way to tell is with two ...


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. ...


1

For HF (e.g., 3MHz), the skin depth effect is <50 x 10^-6 m even for aluminum, and it is thiner for higher frequencies, so braid should be fine. The bandwidth of the J-pole is affected by the diameter of the radiating element. The band is wider at higher frequencies, so to cover the 2m amateur band, you need about the diameter of rg58 shield. HF bands, ...


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