3 ms·

In nearly all cases, the lower the baud rate, the lower the bandwidth. You can come up with sufficiently pathological cases but indeed it’s the bandwidth that s

by gaze 3y ago

In nearly all cases, the lower the baud rate, the lower the bandwidth. You can come up with sufficiently pathological cases but indeed it’s the bandwidth that should be limited. EDIT: you should look at the shanon-Hartley limit. The bandwidth is proportional to the symbol rate.

Animats 3y ago
> In nearly all cases, the lower the baud rate, the lower the bandwidth. You can come up with sufficiently pathological cases but indeed it’s the bandwidth that should be limited. This is not the case for classical frequency-shift amateur radioteletype. This sends two tones on single sideband, at 2125 Hz or 2295 Hz. So it uses up about 2.3KHz of bandwidth no matter how low the baud rate goes. 45.45 baud is classic mechanical Teletype speed, so the bandwidth is about 50x the data rate in that mode. You can do FSK up to maybe 600 baud; you need a few cycles to detect the tone frequency with classical filters. 300 is a traditional limit. Beyond that antique technology, you need a modulation scheme less than half a century old.
- Johnythree 3y ago
  Your "2.3KHz of bandwidth" is caused by using a wide SSB filter to send a relatively narrow shift of 170Hz. You equally could have used a narrower filter.
  - Animats 3y ago
    Pre-single-sideband suppressed carrier systems used an AM carrier, so there really were two audio tones. It's also possible to send FSK over FM, which was often done on VHF where there's more room. Before everything went digital, this sort of thing tended to involve a chain of analog processing stages.
    - Johnythree 3y ago
      Hams sometimes used Audio Frequency Shift tones modulated on to an AM carrier as a temporary way of getting on air with an old style AM transmitter. Which of course meant two sets of sidebands (eg four in total) and a excessively wide signal.. But any of the better quality transmitters (Ham, Commercial or military) used pure FSK directly.

by gaze 3y ago

Animats 3y ago

> In nearly all cases, the lower the baud rate, the lower the bandwidth. You can come up with sufficiently pathological cases but indeed it’s the bandwidth that should be limited. This is not the case for classical frequency-shift amateur radioteletype. This sends two tones on single sideband, at 2125 Hz or 2295 Hz. So it uses up about 2.3KHz of bandwidth no matter how low the baud rate goes. 45.45 baud is classic mechanical Teletype speed, so the bandwidth is about 50x the data rate in that mode. You can do FSK up to maybe 600 baud; you need a few cycles to detect the tone frequency with classical filters. 300 is a traditional limit. Beyond that antique technology, you need a modulation scheme less than half a century old.

Johnythree 3y ago
Your "2.3KHz of bandwidth" is caused by using a wide SSB filter to send a relatively narrow shift of 170Hz. You equally could have used a narrower filter.
- Animats 3y ago
  Pre-single-sideband suppressed carrier systems used an AM carrier, so there really were two audio tones. It's also possible to send FSK over FM, which was often done on VHF where there's more room. Before everything went digital, this sort of thing tended to involve a chain of analog processing stages.
  - Johnythree 3y ago
    Hams sometimes used Audio Frequency Shift tones modulated on to an AM carrier as a temporary way of getting on air with an old style AM transmitter. Which of course meant two sets of sidebands (eg four in total) and a excessively wide signal.. But any of the better quality transmitters (Ham, Commercial or military) used pure FSK directly.