3 ms·

Yes, for a definition of "low-bandwidth" that you'll probably find disappointing. The WSJT digital modes are capable of long-range communication at well below t

Yes, for a definition of "low-bandwidth" that you'll probably find disappointing. The WSJT digital modes are capable of long-range communication at well below the noise floor, but we're talking about single-digit bits per second in typical use. https://www.physics.princeton.edu/pulsar/K1JT/ https://www.physics.princeton.edu/pulsar/K1JT/

pmoriarty 7y ago
What about short, rare bursts of high bandwidth transmissions from a mobile platform? Depending on how creative one was about the locations and operation times of the transmitter, I'd expect it'd be pretty difficult to find.
- superkuh 7y ago
  Those transmissions won't go more than the next slight rise in the ground or valley. High data rate requires line of sight which requires height above terrain which requires either money or rare luck.
  - pmoriarty 7y ago
    "High data rate requires line of sight which requires height above terrain which requires either money or rare luck." What about a transmitter temporarily sent aloft on a balloon, model rocket, or drone, then making its brief high-bandwidth transmission and then parachuting or landing, being retrieved by its operator who then disappears until the next transmission from another location? It might even be disposable, and potentially either deliberately sink itself in to an ocean or other difficult to access place, and/or self-destruct to make recovery and forensics more difficult.
  - ac29 7y ago
    > High data rate requires line of sight This isnt true. High data rate requires large channel size, which is certainly more commonly found in >1GHz portions of radio spectrum that require line of sight. But, a 10MHz channel is just as fast at 400MHz as it is a 4GHz. HDTV doesnt require line of sight to gets tens of megabits on VHF/UHF channels.
    - superkuh 7y ago
      In what legal jurisdiction can you use a 10 MHz bandwidth channel under <30 MHz (where you actually get ionospheric bounce (sometimes))? And even worse than the answer to that (nowhere) is that in the USA the data rate limit is actually in terms of symbol rate, not bandwidth used, to a mere 300 baud for the bands that have regular non-line of sight propagation.
      - ac29 7y ago
        > In what legal jurisdiction can you use a 10 MHz bandwidth channel under <30 MHz (where you actually get ionospheric bounce (sometimes))? I never implied you could? Its certainly possible in VHF/UHF, though (for licencees). > And even worse than the answer to that (nowhere) is that in the USA the data rate limit is actually in terms of symbol rate, not bandwidth used Sure, but those limits only apply for HF and longer-wavelength frequencies. You're welcome to do 256QAM in the microwave range, for example.
        superkuh 7y ago
        > Its certainly possible in VHF/UHF, though (for licencees). >You're welcome to do 256QAM in the microwave range, for example. Which gets back to line of sight propagation (tropo is not common) and everything I said in my first post. I've tried the home to car omnidirectional link thing on 902-928 MHz. All that matters is line of sight. I tried a 25w bidirectional amp (ham general license) and that didn't help. I tried bringing the ubiquiti transceivers w/broadband hamnet firmware all the way down to QPSK modulation and the narrowest channel I could. I even tried using narrowband 56k telemetry dongles. I customed designed and built my own microstrip based filters for the front ends. The only thing that really helps, and it's not enough, is height above terrain. When I go park my car on the hills outside of town megabits are possible. But the slightest hill or valley losing LOS kills it.

pmoriarty 7y ago

What about short, rare bursts of high bandwidth transmissions from a mobile platform? Depending on how creative one was about the locations and operation times of the transmitter, I'd expect it'd be pretty difficult to find.

superkuh 7y ago
Those transmissions won't go more than the next slight rise in the ground or valley. High data rate requires line of sight which requires height above terrain which requires either money or rare luck.
- pmoriarty 7y ago
  "High data rate requires line of sight which requires height above terrain which requires either money or rare luck." What about a transmitter temporarily sent aloft on a balloon, model rocket, or drone, then making its brief high-bandwidth transmission and then parachuting or landing, being retrieved by its operator who then disappears until the next transmission from another location? It might even be disposable, and potentially either deliberately sink itself in to an ocean or other difficult to access place, and/or self-destruct to make recovery and forensics more difficult.
- ac29 7y ago
  > High data rate requires line of sight This isnt true. High data rate requires large channel size, which is certainly more commonly found in >1GHz portions of radio spectrum that require line of sight. But, a 10MHz channel is just as fast at 400MHz as it is a 4GHz. HDTV doesnt require line of sight to gets tens of megabits on VHF/UHF channels.
  - superkuh 7y ago
    In what legal jurisdiction can you use a 10 MHz bandwidth channel under <30 MHz (where you actually get ionospheric bounce (sometimes))? And even worse than the answer to that (nowhere) is that in the USA the data rate limit is actually in terms of symbol rate, not bandwidth used, to a mere 300 baud for the bands that have regular non-line of sight propagation.
    - ac29 7y ago
      > In what legal jurisdiction can you use a 10 MHz bandwidth channel under <30 MHz (where you actually get ionospheric bounce (sometimes))? I never implied you could? Its certainly possible in VHF/UHF, though (for licencees). > And even worse than the answer to that (nowhere) is that in the USA the data rate limit is actually in terms of symbol rate, not bandwidth used Sure, but those limits only apply for HF and longer-wavelength frequencies. You're welcome to do 256QAM in the microwave range, for example.
      - superkuh 7y ago
        > Its certainly possible in VHF/UHF, though (for licencees). >You're welcome to do 256QAM in the microwave range, for example. Which gets back to line of sight propagation (tropo is not common) and everything I said in my first post. I've tried the home to car omnidirectional link thing on 902-928 MHz. All that matters is line of sight. I tried a 25w bidirectional amp (ham general license) and that didn't help. I tried bringing the ubiquiti transceivers w/broadband hamnet firmware all the way down to QPSK modulation and the narrowest channel I could. I even tried using narrowband 56k telemetry dongles. I customed designed and built my own microstrip based filters for the front ends. The only thing that really helps, and it's not enough, is height above terrain. When I go park my car on the hills outside of town megabits are possible. But the slightest hill or valley losing LOS kills it.