3 ms·

How much ambient power is typically available in different environments? I skimmed the article but didn't catch any clear information. Also, if I collect ambie

by mmooss 2y ago

How much ambient power is typically available in different environments? I skimmed the article but didn't catch any clear information. Also, if I collect ambient wifi power, for example, instead of reflecting wifi - to whatever extent I do that - I create a sort of black hole. How does that affect availability of the wifi signal for its intended use?

genewitch 2y ago
RF is cube root I believe - nope, inverse square law, sorry - from an isotropic radiator. So 1000mW from your wlan AP is very quickly 10mW, at 10 meters. Lightning exists and that's on the scale of 64gigawatts of energy, I have a differential lightning detector that can "hear" lightning roughly the entire hemisphere. I had to make the antennas. Blitz system blue. Clear channel broadcast stations (the FCC term, not the company 'ClearChannel') must output 10KW - 50KW no more and no less. If you're within a dozen or two miles of one that is beam-formed, you can pick it up with basically any semiconductor, a wire, and a speaker. Like, a resistor will work. edit: I can probably do a demonstration video with a VNA/antenna analyzer and an HT radio, if such a thing doesn't exist. But the "voltages" that radios can detect can go as low as, well, i'll quote one of my radios specs: > Sensitivity: -140.0 dBm (0.02 µV / 50 ohms at 15MHz) MDS Typ. at 500Hz bandwidth in HF > Sensitivity: -141.5 dBm MDS Typ. at 500 Hz bandwidth in FM Broadcast Band (64 – 118 MHz) > Sensitivity: -141.0 dBm MDS Typ. at 500 Hz bandwidth in VHF Aviation Band (118 – 260 MHz) i was only able to test that radio to -136dBm or so. I forget why, i think the service monitor i was using was really old and probably needed some new caps and a decent interior cleaning. But the radio specs claim it can detect 2 hundredths of a microvolt in specific circumstances (like detecting a very faint beacon signal)
clysm 2y ago
You create an RF shadow, not a black hole.
- genewitch 2y ago
  Broadcast AM stations sometimes have to pay other towers in the area to install a special ground match unit on their tower legs, that makes the non-broadcast tower "invisible" - otherwise there'd be a null in that direction. Like a cardioid shape.

by mmooss 2y ago

genewitch 2y ago

RF is cube root I believe - nope, inverse square law, sorry - from an isotropic radiator. So 1000mW from your wlan AP is very quickly 10mW, at 10 meters. Lightning exists and that's on the scale of 64gigawatts of energy, I have a differential lightning detector that can "hear" lightning roughly the entire hemisphere. I had to make the antennas. Blitz system blue. Clear channel broadcast stations (the FCC term, not the company 'ClearChannel') must output 10KW - 50KW no more and no less. If you're within a dozen or two miles of one that is beam-formed, you can pick it up with basically any semiconductor, a wire, and a speaker. Like, a resistor will work. edit: I can probably do a demonstration video with a VNA/antenna analyzer and an HT radio, if such a thing doesn't exist. But the "voltages" that radios can detect can go as low as, well, i'll quote one of my radios specs: > Sensitivity: -140.0 dBm (0.02 µV / 50 ohms at 15MHz) MDS Typ. at 500Hz bandwidth in HF > Sensitivity: -141.5 dBm MDS Typ. at 500 Hz bandwidth in FM Broadcast Band (64 – 118 MHz) > Sensitivity: -141.0 dBm MDS Typ. at 500 Hz bandwidth in VHF Aviation Band (118 – 260 MHz) i was only able to test that radio to -136dBm or so. I forget why, i think the service monitor i was using was really old and probably needed some new caps and a decent interior cleaning. But the radio specs claim it can detect 2 hundredths of a microvolt in specific circumstances (like detecting a very faint beacon signal)

clysm 2y ago

You create an RF shadow, not a black hole.

genewitch 2y ago
Broadcast AM stations sometimes have to pay other towers in the area to install a special ground match unit on their tower legs, that makes the non-broadcast tower "invisible" - otherwise there'd be a null in that direction. Like a cardioid shape.