11
The answer from a theoretical purist is probably, "No," because your diagram specifies zero radiation outside of the disk. Practically speaking, there will always be some radiation above and below the disk and the shape of the disk will not be as perfect as you describe.
A well known solution that approaches your requirements comprises multiple ...
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 ...
6
Achieving such a sharp radiation pattern is difficult. There are many effects that can can cause the radiation pattern of an antenna to be less "sharp". Some of them can be fixed through engineering, such as by manufacturing components to tighter tolerances. Others are unavoidable physical limits. In the best case, diffraction will limit the ...
6
140 miles is too far away on 20m for groundwave propagation and the "skip" zone or first hop distance, given 20m's general DX capabilities, is much longer than 140 miles. So, I wouldn't expect to hear it "without issue". However, when you're tuned to 14.100, you should be able to copy other beacons in the rotation, if your antenna works.
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 ...
5
Rather than just answer your question, I'll show you how to answer it yourself.
VOACAP is a good tool for all kinds of HF propagation questions. Entering your location and the location of the beacon into the point-to-point predictions tool, with parameters set to CW, 100 W, dipoles at 33 feet, and "Residential" noise, clicking on "Prop Charts&...
4
What you are describing is not "antenna phase" but impedance. An antenna, like many two-terminal devices, is a load that can be described by an impedance. It can be purely resistive (like a resistor), meaning current and voltage are in phase. Or it can be reactive (like a capacitor or inductor) with current and voltage being 90 degrees out of phase....
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 ...
4
antenna that have disk like lobes
The pattern of an antenna is never going to be disk-shaped (because the directivity is angle-dependent, not limited to a volume).
But: an omnidirectional antenna (in azimuth) with a very high directive gain in elevation approximates what you want.
A simple vertical stack of vertical half-wavelength dipoles, driven in ...
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 ...
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 ...
2
Magnetic loops do not need a choke more than other kinds of antennas but I recommend you have one anyway especially if you will have coax running through your house. The reason to have a choke with a magloop is to reduce rf receive noise which can be picked up by the coax from local rf noise sources in your house. This is also valid for other types of ...
2
Well, what you describe is the phase of a complex current. That's not inherently the same thing as the phase of an electromagnetic wave! But it's the basics of all electrical theory, so it's necessary you understand it, so you've got a good basic education there.
So, sorry to drop more theory on you:
In free space propagation, there's no current, and no ...
2
I'm going to disagree with Marcus and say that you can probably get this to work, for some relaxed definition of "work".
The detector you've drawn has poor selectivity, meaning it will detect quite a lot of stuff besides the intended signal. The inductor and capacitor provide some amount of filtering, but not nearly as good as you'd get in any ...
2
Well, your GPIO will need a defined voltage level and a couple of µA of drive strength, so completely "passive" is probably not really possible.
Now, you'll need the following:
Antenna
potentially, amplification here
Filtering
potentially, amplification here
Rectification
Thresholding
GPIO activation
For antenna choices, see Texas Instrument'...
1
There's no such thing as a "magnetic" and an "electric" wave. Only electromagnetic waves propagate – that's at the very basis of wave theory, so 1. is definitely wrong, and 2. would need rephrased to "will it produce an electromagnetic wave", and the answer to that is "yes!", otherwise it would not be an antenna.
So, ...
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 ...
1
"EFHW" means end-fed half-wave. It is by definition a half-wavelength long, so it is not short. And it's fed at the end, so it can't be a loop, which has no ends. I wouldn't say it's a very good choice for a space-limited application.
There are loop antennas too, and any wire antenna can be bent or curved, though that may make it a very different ...
1
Some antenna designs use multiple parallel elements like this. For example, fan dipoles. Or, as you can see the Butternet HF9V has a couple parallel wires hanging off it in the upper half:
These extra elements add additional resonant modes to the antenna, which is what makes these antennas multi-band. In a fan dipole, if the elements are kept some distance ...
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 ...
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 (...
1
I have been astonished by the receive-only performance of the Shared-Apex Loop Array (SALA) that I have used at a friend's contest station:
Unlike a beverage, which I believe will run out of gas at 20 meters, the SALA works well from 160 through 20. The SALA also takes up a lot less room than a beverage and erecting an orthogonal pair allows the receive ...
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 ...
1
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
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 ...
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