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If we could get a few HF stations on Mars, what would the propagation look like? Thought shamelessly copied from this blog.

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  • $\begingroup$ Aw drat, you stole my question! space.stackexchange.com/questions/2570/… $\endgroup$ – a CVn Oct 29 '13 at 16:19
  • $\begingroup$ LOL. I wasn't even thinking of that, I've wanted to ask this question here for about 2 months, if not longer. $\endgroup$ – PearsonArtPhoto Oct 29 '13 at 16:25
  • $\begingroup$ I second Michael; that was on me list too! $\endgroup$ – VU2NHW Oct 29 '13 at 20:29
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According to NASA TP 2000 209756, particularly section 2.5, it shouldn't be too different from similar propagation on Earth during daytime, except we'd need significantly lower frequencies than we are used to for similar results. According to that report,

The Martian dayside ionosphere at solar maximum has a peak density similar to that of the Earth nightside ionosphere at solar minimum. (...) Even though the Martian ionospheric peak density and TEC [total vertical electron content] are lower than in the Earth’s ionosphere, we can still use them for ionospheric communication.

According to table 2-2, Usable Critical Frequency and Hop Distance for Various Launch Angles, and assuming I'm reading the data correctly, around 4 MHz would be about the upper bound for near-range communications (NVIS to almost-NVIS), and by the time you get a take-off angle of 60° this climbs to a whopping 8 MHz and a single hop distance of 400-450 km. (The table says 433 km.)

If you want to penetrate the ionosphere, section 2.6 Summary and Recommendations says to use a frequency above 450 MHz. Nighttime communications beyond those offered by line of sight are tricky:

[T]he nightside ionosphere has some limitations for global communication because of its low usable frequency and very unstable conditions.

The report specifies a critical frequency of 0.6 MHz during solar minimum night time. That isn't impossible to work with (it was at one time considered "high frequency") but it takes a lot more than a "rubber duck" antenna on a handheld radio to produce useful results and bandwidth is highly limited, so nighttime ionospheric communications on Mars would be extremely limited at best. (You'd probably buffer up data for transmission after sunrise and focus your efforts on a higher frequency, near the boundary between what we consider MF and HF around 2-4 MHz in order to achieve reasonable antenna sizes as well as reliable communications even during solar minima.)

If you can manage a take-off angle in the 75° range, the maximum usable frequency climbs to a whopping 15.5 MHz, says table 2-2. At those frequencies, it should be possible to pack quite a bit of data into a transmission.

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  • $\begingroup$ Wouldn't all that rust lying around drastically reduce range? $\endgroup$ – VU2NHW Oct 29 '13 at 20:38
  • $\begingroup$ @VU2NHW That should be covered by Does iron ore in the ground affect my signal?, but particularly if you get the antenna high enough off the ground to start approaching near-horizontal take-off angles, I personally doubt it'd be an issue. But of course, I've been wrong before! $\endgroup$ – a CVn Oct 30 '13 at 8:12
  • $\begingroup$ To quote Charles Shultz who drew Peanuts: I once thought I was wrong but it turned out I was mistaken. $\endgroup$ – SDsolar Jun 1 '17 at 8:00
  • $\begingroup$ They seem to be using the complementary definition of "launch angle" compared to what hams do... e.g. your notes for 60° take-off angle apply to what we call 30°, and the info for 75° is what we call 15°. A 15° take-off angle is what DXers are usually trying for anyway, and given that, apparently 20m is usable in the daytime. Very much like earth at solar minimum :) $\endgroup$ – hobbs - KC2G Jul 7 at 15:18
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I just read the ionospheric sounding data obtained from MARSIS and it looks like Top Band (160 meters) would work great. Moreover: zero atmospheric noise (no thunderstorms).

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