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0

They're the same, but the second one is better :) It's more intuitive to separate the diameter and the spacing, and it's clearer that the whole thing is unitless. Be aware that this only holds for a narrow range of diameters and spacings.


1

A more general answer... Antennas have a number of characteristics critical to their performance, including but not limited to gain, radiation pattern, impedance, and sometimes efficiency and polarization. These performance characteristics are all tied to frequency. When designing an antenna, these characteristics can be graphed vs. frequency and there ...


6

It means the range of frequencies in which the antenna is designed to operate. Operated outside that range, the antenna may not meet its specifications. This particular antenna is a telescopic whip, a kind of monopole antenna. Such antennas are typically 1/4 wavelength long. It is advertised for 300 to 1100 MHz, and it's length can be adjusted from 24.5 cm ...


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I understand people like to use coax for antenna experiments but in this case I don't think its a good choice. That outer loop diameter is too small for 40 meters and it is a wire when it really needs to be a tube. What I would suggest is making this thing again but using copper tubing for the outer loop and simple insulated wire for the inner loop(inner ...


1

Well this is rather simple and in reality you dont need to ensure the far end is open, you can leave your antenna attached and it will still work just fine if all you are trying to do is determine the length of your feedline. Before I get into the explanation let me share a video I did years ago demonstrating the exact setup you are trying to do using a ...


3

There are many properties of an antenna that could be optimized: Maximum gain Beam width Front-to-back ratio Feedpoint impedance SWR bandwidth Robustness to manufacturing variation Typical designs aim for "pretty good" in all of these parameters. Optimizing for one parameter exclusively will typically come at the detriment of others, and result ...


1

The driven element length is chosen to give the right impedance for your matching network. There's no rule about it being longer or shorter than anything. The directors(s) are always shorter than the reflector(s) because their self impedance, combined with their spacing, is important in establishing the correct currents on each element. (of course I mean ...


5

I suspect your results are an artifact of your optimization methodology. I simulated the design described in the link with NEC2 using the EZNEC front-end. For reference, EZNEC calculates the gain as 13.03-dBi in free space with 2-mm diameter elements (the link doesn't specify element diameter). I believe this is close enough to your model's gain of 13.6-dBi ...


0

In my situation, do I have to use the second formula to find near-field reactive region boundary? The choice between the two equations you provide is determined by if the antenna is "electromagnetically short", so it isn't about if it is "very short" from a human's perspective of short, but rather how its length compares to the ...


1

Question 1 : Do the EM waves travel by creating disturbances in the air particles such as compression and rarefaction? The answer is no. Electromagnetic propagation is not dependent on air, unlike sound waves. It can travel in free space. That being said, electrically or magnetically charged air particles, and Earth's magnetosphere can alter the trajectory (...


3

Question 2 & 3 not fully answered... You probably actually are within line of sight of the FM transmitter. Broadcast transmitter antennas are typically placed on high towers specifically so that more people will be within line of sight of the tower. Of course, you may not actually be able to "see" the tower because of atmospheric attenuation ...


1

This problem is very easy to model with any MOM tool, like EZNEC. E and H fields can be calculated using Near Field grid. Even better, exact power transfer from Tx to Rx antenna can be modeled. Modeling should include both Tx and Rx antenna, including Rx antenna termination resistance. Ratio of transmitted power and dissipation on Rx termination resistor ...


4

Radio waves (such as broadcast AM and FM) can travel through a vacuum (thus do not require air). They are electro-magnetic (or EM) waves, the same as light waves (from the sun and stars, etc.), that can travel through space, but at a vastly lower frequency. The radius these EM waves can travel (unless blocked or absorbed) is the radius of the universe; but ...


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In the J146/440 antenna, on the right: For 2m, the leftmost and rightmost element form the J-pole, and the center element is too short to matter very much. (It probably adds some inductance, which could explain why the left element seems a little shorter than it should be for 2m). For 70cm, the center and leftmost element form the J-pole, and the rightmost ...


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