4 ms·

For someone not well versed with the terminology, can someone please tell what kind of bitrate this can provide? In bytes per second.

shakna 1y ago
It's not even a byte per second. The latency of the distances involved mean you're looking at around two seconds per round trip, plus a little extra because of the fuzziness of radio in space and absolutely everything that can distort it. There's a lot of math that goes into selecting the right bit-width for the signal, which I ain't doing here and now [0], but most 24dB things tend to be 32bit for reasons. The arrays here are a bit more, but probably fit that kind of channel. Assuming 32bit and 30dBi, you'd be sending at roughly 20-30MHz, and receiving at about 1kHz. (Less if you hit bad weather.) So... 1 bit per second. Not byte. Bit. [0] https://www.spaceacademy.net.au/spacelink/spcomcalc.htm https://www.spaceacademy.net.au/spacelink/spcomcalc.htm
- whatsupdog 1y ago
  Thank you so much. Are these rough calculations based on the smallest (quad), mini or the large array?
  - shakna 1y ago
    That was for the large array, assuming you were bouncing from you to moon and back again. Point-to-point on the Earth would actually be semi-decent, as another comment pointed out.
- radiorickky 1y ago
  No, if you do the math it's about 40 bytes per second (300bps) for Earth-Moon-Earth using their 240-antenna array.
  - shakna 1y ago
    Care to share the math, if you've done it? It's 1.3 to 1.6 seconds each way to the moon, by radio link. JPL's much, much, much bigger arrays can only achieve 64kbps.
    - ant6n 1y ago
      I dont get it, How does latency affect bandwidth here?
      - shakna 1y ago
        Because we're not stationary, and nor is the moon. Latency means greater dispersion, and lower successful return rates.
        but-vaccum 1y ago
        Latency itself doesn't mean squat. Throw a pair of trancievers into deep space and no relative motion and all bitrate limiting factors (dispersion, multipath, doppler shift- I'm sure there's more) disappear besides SNR/inverse square and retransmission. Going beyond intuition- secondary reasoning says since GSO bandwidth & bitrate is acceptable for TV and sat phones by the hundred. Tercheriary is we have/had a few hundred bps from Voyager II and that's a might bit further out than the moon, and it was called out that using an 80meter dish it could be pushed to a little over 1kbps- which means at some point inverse square becomes the only non-neglegiable factor. So please, explain with something besides repeatedly saying "latency." Even if I'm wrong, they're strong enough counters to deserve more than a single word.
        shakna 1y ago
        ... I'd love to see, this particular project, "throw a pair" of tranceivers into deep space.
    - deleted 1y ago
      [deleted]
- shevy-java 1y ago
  Ok so ... moon is slow going.
- djexjms 1y ago
  This is obviously incorrect. Latency is not the same as bandwidth. EME hobbyists will bounce voice signals off the moon.
drmpeg 1y ago
A lightly coded (13/15 LDPC) 256QAM OFDM signal at 40 MHz wide could do 250 Mbps. Or 31.25 million bytes per second if you prefer. This would be for a point to point terrestrial link. OFDM probably wouldn't work for EME (at any power level).

shakna 1y ago

It's not even a byte per second. The latency of the distances involved mean you're looking at around two seconds per round trip, plus a little extra because of the fuzziness of radio in space and absolutely everything that can distort it. There's a lot of math that goes into selecting the right bit-width for the signal, which I ain't doing here and now [0], but most 24dB things tend to be 32bit for reasons. The arrays here are a bit more, but probably fit that kind of channel. Assuming 32bit and 30dBi, you'd be sending at roughly 20-30MHz, and receiving at about 1kHz. (Less if you hit bad weather.) So... 1 bit per second. Not byte. Bit. [0] https://www.spaceacademy.net.au/spacelink/spcomcalc.htm https://www.spaceacademy.net.au/spacelink/spcomcalc.htm

whatsupdog 1y ago
Thank you so much. Are these rough calculations based on the smallest (quad), mini or the large array?
- shakna 1y ago
  That was for the large array, assuming you were bouncing from you to moon and back again. Point-to-point on the Earth would actually be semi-decent, as another comment pointed out.
radiorickky 1y ago
No, if you do the math it's about 40 bytes per second (300bps) for Earth-Moon-Earth using their 240-antenna array.
- shakna 1y ago
  Care to share the math, if you've done it? It's 1.3 to 1.6 seconds each way to the moon, by radio link. JPL's much, much, much bigger arrays can only achieve 64kbps.
  - ant6n 1y ago
    I dont get it, How does latency affect bandwidth here?
    - shakna 1y ago
      Because we're not stationary, and nor is the moon. Latency means greater dispersion, and lower successful return rates.
      - but-vaccum 1y ago
        Latency itself doesn't mean squat. Throw a pair of trancievers into deep space and no relative motion and all bitrate limiting factors (dispersion, multipath, doppler shift- I'm sure there's more) disappear besides SNR/inverse square and retransmission. Going beyond intuition- secondary reasoning says since GSO bandwidth & bitrate is acceptable for TV and sat phones by the hundred. Tercheriary is we have/had a few hundred bps from Voyager II and that's a might bit further out than the moon, and it was called out that using an 80meter dish it could be pushed to a little over 1kbps- which means at some point inverse square becomes the only non-neglegiable factor. So please, explain with something besides repeatedly saying "latency." Even if I'm wrong, they're strong enough counters to deserve more than a single word.
        shakna 1y ago
        ... I'd love to see, this particular project, "throw a pair" of tranceivers into deep space.
  - deleted 1y ago
    [deleted]
shevy-java 1y ago
Ok so ... moon is slow going.
djexjms 1y ago
This is obviously incorrect. Latency is not the same as bandwidth. EME hobbyists will bounce voice signals off the moon.

drmpeg 1y ago

A lightly coded (13/15 LDPC) 256QAM OFDM signal at 40 MHz wide could do 250 Mbps. Or 31.25 million bytes per second if you prefer. This would be for a point to point terrestrial link. OFDM probably wouldn't work for EME (at any power level).