3 ms·

huh? Am I mis-reading/understanding the units? 80m bands are common, and I guess I've heard people talk about 160m. This is 2200m? 2.2km? What would the a

huh? Am I mis-reading/understanding the units? 80m bands are common, and I guess I've heard people talk about 160m. This is 2200m? 2.2km? What would the antenna look like? a quarter-wave dipole? haha Is this the kind of thing subs would use to communicate, for example?

segfaultbuserr 7y ago
> This is 2200m? 2.2km? Yes, it's 136 kHz. The NIST transmits the 70 kW WWVB time signal at 60 kHz (5000-meter) in order to inform you the standard time in UTC from atomic clocks. It was extremely useful before GPS, less useful today, but it still serves a hundred thousands of radio clocks, NTP time servers or so. In the beginning of radio, even lower frequencies were used. The Grimeton Radio Station (callsign SAQ) in Sweden uses 17.2 kHz, or 17441-meter. The oscillator of the radio is not an electronic oscillator like a crystal, but an extremely fast AC generator with moving parts rotating at one million RPM, invented before vacuum tubes and subsequent establishment of "electronic engineering". This radio station still operates today for celebrations, and it can be heard by amateur radio operators worldwide with their homemade equipment (a computer soundcard can be the radio receiver, 17.2 kHz is audio frequency). * https://en.wikipedia.org/wiki/Grimeton_Radio_Station https://en.wikipedia.org/wiki/Grimeton_Radio_Station > haha Is this the kind of thing subs would use to communicate, for example? You greatly underestimated subs ;-) 136 kHz is Low Frequency. Submarines use Very Low Frequency (something like SAQ's frequency), or Extremely Low Frequency, as low as 100 Hz, not a typo, it's hertz. > What would the antenna look like? Every wire is an antenna, you don't really need a "real" antenna to get the radiation out or pick up the signal. At low frequencies, the antenna is always inefficient, and one just needs to accept this fact and gets used to it. Usually the antenna is built to be as large as practical, but not larger. If you are the military, you can build a multi-kilometer antenna, but if you are an amateur, it would be as large as your rooftop or backyard can fit, not larger, then you build an impedance matching network to make it usable (but it doesn't improve the efficiency of the antenna itself), and you put as much power as possible into the antenna. Finally, receiving a large station is easy, when they transmit tens of thousands of watts, a small and inefficient random-wire antenna can pick up the signal from, e.g. WWVB or SAQ. It's how nuclear submarines receive one-way communication from the command & control. Receiving a 1-watt amateur signal (legal limit for 2200 meters) is much more difficult. The article says, > home-built single FET 200 W class E amplifier, a 90-foot top-loaded vertical antenna, this gives me no more than 0.5 W EIRP, probably less. 200-watt in, 0.5-watt EIRP out, the antenna efficiency is 0.25%. And it's a transatlantic communication from U.S. to Great Britain without gigantic military antenna and about 0.5-watt of radiated power, I think you can now understand the technical achievement here.

segfaultbuserr 7y ago

> This is 2200m? 2.2km? Yes, it's 136 kHz. The NIST transmits the 70 kW WWVB time signal at 60 kHz (5000-meter) in order to inform you the standard time in UTC from atomic clocks. It was extremely useful before GPS, less useful today, but it still serves a hundred thousands of radio clocks, NTP time servers or so. In the beginning of radio, even lower frequencies were used. The Grimeton Radio Station (callsign SAQ) in Sweden uses 17.2 kHz, or 17441-meter. The oscillator of the radio is not an electronic oscillator like a crystal, but an extremely fast AC generator with moving parts rotating at one million RPM, invented before vacuum tubes and subsequent establishment of "electronic engineering". This radio station still operates today for celebrations, and it can be heard by amateur radio operators worldwide with their homemade equipment (a computer soundcard can be the radio receiver, 17.2 kHz is audio frequency). * https://en.wikipedia.org/wiki/Grimeton_Radio_Station https://en.wikipedia.org/wiki/Grimeton_Radio_Station > haha Is this the kind of thing subs would use to communicate, for example? You greatly underestimated subs ;-) 136 kHz is Low Frequency. Submarines use Very Low Frequency (something like SAQ's frequency), or Extremely Low Frequency, as low as 100 Hz, not a typo, it's hertz. > What would the antenna look like? Every wire is an antenna, you don't really need a "real" antenna to get the radiation out or pick up the signal. At low frequencies, the antenna is always inefficient, and one just needs to accept this fact and gets used to it. Usually the antenna is built to be as large as practical, but not larger. If you are the military, you can build a multi-kilometer antenna, but if you are an amateur, it would be as large as your rooftop or backyard can fit, not larger, then you build an impedance matching network to make it usable (but it doesn't improve the efficiency of the antenna itself), and you put as much power as possible into the antenna. Finally, receiving a large station is easy, when they transmit tens of thousands of watts, a small and inefficient random-wire antenna can pick up the signal from, e.g. WWVB or SAQ. It's how nuclear submarines receive one-way communication from the command & control. Receiving a 1-watt amateur signal (legal limit for 2200 meters) is much more difficult. The article says, > home-built single FET 200 W class E amplifier, a 90-foot top-loaded vertical antenna, this gives me no more than 0.5 W EIRP, probably less. 200-watt in, 0.5-watt EIRP out, the antenna efficiency is 0.25%. And it's a transatlantic communication from U.S. to Great Britain without gigantic military antenna and about 0.5-watt of radiated power, I think you can now understand the technical achievement here.