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Say the deck is stacked.

I'm out in the country with an all-band QRP home-brew rig, and an active antenna. Or say ship-wrecked and marooned on that desert island. The battery only has enough juice for say 1-min Tx, and 30-min Rx. The Sun is at the bottom of cycle so conditions may be bad.

I need to get that priority message out.

How do I find out what bands are open?

P.S.

Just a quick note to the comments about the scenario being totally unrealistic. An amateur radio expedition from VU was caught unawares when that Boxing Day tsunami hit the Andaman Island chain in the Indian Ocean. Unlike a team that goes out after the event, when the expedition went out they didn't know what they were going to have to handle.

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  • $\begingroup$ If you set your conditions such that there's no way to check, then all you can do is guess. $\endgroup$ – Phil Frost - W8II Jul 22 '14 at 12:46
  • $\begingroup$ Also, what do you mean by "active antenna"? You mean the kind that has a preamplifier built in? I don't think those are usually designed for transmitting, so your priority message may never get out. $\endgroup$ – Phil Frost - W8II Jul 22 '14 at 12:49
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    $\begingroup$ The question in the title is not the one in the actual body of the question ... "how to find out what[sic] bands are open" is to check in all manner of places. I would start with the Cluster, for example. But the body of the question asks how you can guess which bands are open - which is a whole different thing. $\endgroup$ – Scott Earle Jul 23 '14 at 1:46
  • $\begingroup$ @PhilFrost I've widened the stack some; got rid of the active antenna reference. $\endgroup$ – VU2NHW Jul 23 '14 at 12:12
  • $\begingroup$ By "open", do you mean "in use" so someone will hear you? Until I read all of the question, I would have assumed that "open" meant not in use so that you had a clear frequency to transmit on, to be free from interference. $\endgroup$ – YetAnotherRandomUser Jun 27 '18 at 0:02
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If you are stuck on an island and have only enough battery for one minute of transmitting, the important thing isn't that propagation is good, but that someone hears you.

Use your 30 minutes of receive time to find an area of some band that is very busy, with very many very strong signals. By reciprocity, the better you can hear them, the better they can hear you, and having many people on frequency increases your odds.

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If the deck is stacked, then the best bet is to play the odds. Evenings, check 20 Meters & below. Days, check 20 Meters & above.

You can scan for beacons on 20, 10 and 6M to be alerted to band openings. But if you were truly on a desert island with one shot, I would head for 20M band when the terminator is rolling by, and hope for the best.

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Try WSPRNet. It shows real time data of number of WSPR beacons on all ham bands. http://wsprnet.org/drupal/wsprnet/map

You can also use WSPR to listen and see what can be heard or even make beacon to see who can hear you.

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Since you have set the conditions so that there is no way to actually check (think: cluster, solar reports, propagation alerts - all on the internet) then you are stuck with guessing.

If it's day time try 20m or 15m. If it's night, 40m and 80m. Around dawn or dusk, try 40m and 20m.

Be aware that these will likely get you contacts quite a long way away though! The person you spoke to might be literally half way round the world, and not be much help to you.

Sometimes you don't want the propagation to be TOO good!

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    $\begingroup$ If you are out in the country, you might be better off on 80m during the day - all people you could contact would be within a few hundred km (or miles). Mind you - on 75m in the US, you might find your battery has run flat before one of them stops talking! $\endgroup$ – Scott Earle Jul 23 '14 at 1:53
  • $\begingroup$ I'd hope not to operate a voice-mode - rather be hoping to work Axx, or an F1 mode if in distress. But that could probably make another question - Should I use a digital (Axx/Fxx) mode if declaring a priority ? $\endgroup$ – VU2NHW Aug 4 '14 at 10:34

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