debojitacharjee
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How the loop and dipole antennas are integrated?
- Thread starter debojitacharjee
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Typically with a diplexer but old designs from the 50s through 70s may just have them in parallel.
debojitacharjee
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But why a single loop antenna works for UHF?
It works good enough over the entire UHF range by itself.
debojitacharjee
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Do you know how to calculate the loop size and turns of a simple loop antenna?
Ubbe
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Full Wave Loop Antenna Calculator
Use this online calculator to determine the length of a full-wave loop antenna from the frequency. Both metric and English units of measurement are supported. Quarter-wave matching section lengths are also calculated.
www.66pacific.com
/Ubbe
debojitacharjee
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This formula is not much useful because loop in feet doesn't say whether it's the length of the wire or the diameter of the loop?
This loop is not also using a variable capacitor.
Ubbe
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Most loops doesn't use a capacitor. I have a loop that covers from 500Khz to 30MHz and doesn't use a variable capacitor.
It's always the length of the loop that are measured, not its diameter, as you can form it circular, square or a triangle, whatever you like.
/Ubbe
It's always the length of the loop that are measured, not its diameter, as you can form it circular, square or a triangle, whatever you like.
/Ubbe
Whenever I've seen loop antennas being discussed, the relevant parameter is length of the wire. Since a loop antenna can be a circle, an oval, a square, a rectangle, a rhombus, a diamond, a triangle, etc., the "diameter" is not usually considered. If the loop antenna is built as a circle, the calculated length would be the circumference.
debojitacharjee
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But why then on most loop antenna calculators, the number of turns are counted?
I'm not the antenna expert that some folks on here are, but I think that you add turns in order to make the antenna a manageable size when trying to receive the AM broadcast band (530-1700 kHz in the U.S.).
Using the calculator that you linked to, a single-turn loop antenna would have to be 40 or more feet in diameter in order to receive the AM broadcast band. At higher frequencies, such as the FM broadcast band (88-108 MHz in the U.S.), a single-turn loop antenna would be much smaller.
Using the calculator that you linked to, a single-turn loop antenna would have to be 40 or more feet in diameter in order to receive the AM broadcast band. At higher frequencies, such as the FM broadcast band (88-108 MHz in the U.S.), a single-turn loop antenna would be much smaller.
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Not a separate capacitor, but the capacitance of the loop itself is a factor and has to be included in any calculations even if indirectly. As we know, the resonance frequency is both the result of the that capacitance, from the loop itself and any added capacitor, and the inductance of the coil. And the statement the diameter is not relevant is false--as length, diameter, number of turns are dependent on each other, you can write the formula different ways; and the sensitivity of the loop depends on the area which is a function of the shape. Regarding the last statement, consider if you ran the the loop halfway one direction and then back next to itself. I worked with a physicist who was once employed to design antennas and would point this out often. A more complete formula is at VK3CPU Magnetic Loop Antenna Calculator
Ubbe
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Like a folded dipole, but curved? I've seen those type of antennas.
/Ubbe
debojitacharjee
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That's a magnetic loop antenna calc. I need a simple loop calc?
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Magnetic loop is just another name for a small loop relative to the wavelength. You are certainly talking about such.
paulears
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In one of your multiple topics you asked how a folded dipole could possibly work? Well a loop antenna is a sort of opened up folded dipole, but being a circle, polarisation is less critical. However - all these things have very low efficiency, so only work on string signals.
You also mentioned magnetic loop antennas, and these are MUCH more complicated to understand, and despite your comment about VHF, more applicable to HF operation. They tend to be multi turns of wire too - often ships would use these and they would be often rotatable, so they could swing and be directional. They tended to not have gain in a practical sense, but they were quite deaf at the sides, so you could take bearings.
You also mentioned magnetic loop antennas, and these are MUCH more complicated to understand, and despite your comment about VHF, more applicable to HF operation. They tend to be multi turns of wire too - often ships would use these and they would be often rotatable, so they could swing and be directional. They tended to not have gain in a practical sense, but they were quite deaf at the sides, so you could take bearings.
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