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So I'm curious as to why UHF and VHF require larger antennas. My parent's house was about 100 miles from the WTC and the antenna was massive. People in the city

So I'm curious as to why UHF and VHF require larger antennas. My parent's house was about 100 miles from the WTC and the antenna was massive. People in the city though used smaller sized ones.

h2odragon 4y ago
VHF requires larger antennas than UHF. most of the reason bigger TV antennas were a thing was the "bigger is better" illusion. They make fancy stacks of elements and pt "+28 Dbi" numbers on the box but at any specific frequency those could be outperformed by a simple single cut wire. (they weren't utter horseshit: considered across the whole band they could be better for being bigger, but thats a technical and theoretical "win") There are places where "more metal harvests more signal" in antenna design, but they're little dots on a broad map, not where you'd expect them to be. Herringbone antennas at WiFi freqs are fun.
- ryanianian 4y ago
  The single cut wire will only be better at its resonant frequency. The TV antennas are designed to cover their entire bands.
- sgtnoodle 4y ago
  Yagi arrays are a real thing, and they do take up a lot of space.
pcl 4y ago
UHF and VHF (that is, Ultra High Frequency and Very High Frequency) are the 3GHz-300MHz range and the 300MHz-30MHz range, respectively. That translates to a 10cm-1m wavelength for UHF and 1m-10m for VHF. Minimal effective antenna size for a basic wire antenna is 1/4 the wavelength, so you end up with big antennas for low frequency / large wavelength. https://udel.edu/~mm/ham/randomWire/ https://udel.edu/~mm/ham/randomWire/
- derstander 4y ago
  Note that different organizations use the same terms for slightly different bands. In the IEEE nomenclature for radar, UHF is 300MHz to 1GHz. 3GHz is solidly within S-Band. And L-Band is in between them.
xen2xen1 4y ago
Every frequency has a wavelength, as in a literal length of wave, which means a literal length of perfectly sized antenna. There's a formula. The right size for FM (100mhz) antenna is something like 4 or 5 feet, but for wifi (2.4ghz), it's the size of a water molecule. That is not an accident, as the FCC did not lease 2.4 out permanently since water absorbs it, hence we can just plop an unregulated router/AP in our house. This paragraph is probably vague and generalized, and possibly wrong-ish towards the end, but close enough to aid general understanding.
- lolc 4y ago
  Fluid water absorbs it very well, but the wavelength for 2.4 GHz is 0.125 m.
  - usrusr 4y ago
    “length of a water molecule (at an accuracy of 1 ft)"
  - galangalalgol 4y ago
    Yeah antennas need to resonate, not just absorb. A litre of water wouldn't be a very good antenna at 2.4, but it would warm up due to absorption if it is a trong signal. A vhf antenna might make a terrible antenna at 2.4 as well, but it would also warm up in a strong enough signal. Don't belive me? Shove one in a microwave (please don't really).
Spooky23 4y ago
You brought back a fun memory. When my family moved upstate, about 125 miles north of the city, my dad was determined to watch the yankee games on channel 11, and my grandfather wanted to see his Mets. He special ordered a massive antenna at Radio Shack. This thing disassembled was the full length of an old full size Chevy station wagon, I’m guessing 12 feet in the box and a bit longer assembled. Dad and grandpa mounted the thing to a pole that was also quite high attached to a device that would rotate the antenna. When it was time for a game, you had to rotate the antenna to hit a specific gap in the mountains, which varied for different channels. Good times.
sgtnoodle 4y ago
People closer to the transmitter receive enough raw signal power that they can get away with a really insensitive antenna. Farther away, the antenna needs to be more optimal to pick up enough signal to be usable. It's not that the giant antenna is magically better, it's that the smaller antennas are mediocre.

So I'm curious as to why UHF and VHF require larger antennas. My parent's house was about 100 miles from the WTC and the antenna was massive. People in the city though used smaller sized ones.

h2odragon 4y ago

VHF requires larger antennas than UHF. most of the reason bigger TV antennas were a thing was the "bigger is better" illusion. They make fancy stacks of elements and pt "+28 Dbi" numbers on the box but at any specific frequency those could be outperformed by a simple single cut wire. (they weren't utter horseshit: considered across the whole band they could be better for being bigger, but thats a technical and theoretical "win") There are places where "more metal harvests more signal" in antenna design, but they're little dots on a broad map, not where you'd expect them to be. Herringbone antennas at WiFi freqs are fun.

ryanianian 4y ago
The single cut wire will only be better at its resonant frequency. The TV antennas are designed to cover their entire bands.
sgtnoodle 4y ago
Yagi arrays are a real thing, and they do take up a lot of space.

pcl 4y ago

UHF and VHF (that is, Ultra High Frequency and Very High Frequency) are the 3GHz-300MHz range and the 300MHz-30MHz range, respectively. That translates to a 10cm-1m wavelength for UHF and 1m-10m for VHF. Minimal effective antenna size for a basic wire antenna is 1/4 the wavelength, so you end up with big antennas for low frequency / large wavelength. https://udel.edu/~mm/ham/randomWire/ https://udel.edu/~mm/ham/randomWire/

derstander 4y ago
Note that different organizations use the same terms for slightly different bands. In the IEEE nomenclature for radar, UHF is 300MHz to 1GHz. 3GHz is solidly within S-Band. And L-Band is in between them.

xen2xen1 4y ago

Every frequency has a wavelength, as in a literal length of wave, which means a literal length of perfectly sized antenna. There's a formula. The right size for FM (100mhz) antenna is something like 4 or 5 feet, but for wifi (2.4ghz), it's the size of a water molecule. That is not an accident, as the FCC did not lease 2.4 out permanently since water absorbs it, hence we can just plop an unregulated router/AP in our house. This paragraph is probably vague and generalized, and possibly wrong-ish towards the end, but close enough to aid general understanding.

lolc 4y ago
Fluid water absorbs it very well, but the wavelength for 2.4 GHz is 0.125 m.
- usrusr 4y ago
  “length of a water molecule (at an accuracy of 1 ft)"
- galangalalgol 4y ago
  Yeah antennas need to resonate, not just absorb. A litre of water wouldn't be a very good antenna at 2.4, but it would warm up due to absorption if it is a trong signal. A vhf antenna might make a terrible antenna at 2.4 as well, but it would also warm up in a strong enough signal. Don't belive me? Shove one in a microwave (please don't really).

Spooky23 4y ago

You brought back a fun memory. When my family moved upstate, about 125 miles north of the city, my dad was determined to watch the yankee games on channel 11, and my grandfather wanted to see his Mets. He special ordered a massive antenna at Radio Shack. This thing disassembled was the full length of an old full size Chevy station wagon, I’m guessing 12 feet in the box and a bit longer assembled. Dad and grandpa mounted the thing to a pole that was also quite high attached to a device that would rotate the antenna. When it was time for a game, you had to rotate the antenna to hit a specific gap in the mountains, which varied for different channels. Good times.

sgtnoodle 4y ago

People closer to the transmitter receive enough raw signal power that they can get away with a really insensitive antenna. Farther away, the antenna needs to be more optimal to pick up enough signal to be usable. It's not that the giant antenna is magically better, it's that the smaller antennas are mediocre.