... here's a "which bands & modes would you use?" exercise, good for discussion here:
https://brushbeater.wordpress.com/2017/02/05/keypounder-sends/
Will try and post some answers soon.
Spoiler alert: here come my answers. May not be the right ones, they’re certainly incomplete, but here goes.
Q1:
What frequency segment and time will you select to minimize DF likelihood and maximize the chance that HQ will acknowledge it? What will your alternate(s) frequencies be, and under what circumstance will you use them?After playing with
http://www.voacap.com's point-to-point predictions for a bit (result plot below) I'm going with 40m @ 0830z as primary. The reasons for this are (1) it's in the dead of night so we're less likely to be seen, and (2) the message being passed was received just after dark, and this is the soonest window. For secondary, I'll go with 17m @ 2200z. Both of these are centered on the red-est, most probable checkers on this plot:
Could've also gone with 20m @ 2230z, but it's a lot easier to get a 40m antenna to tune on 17m than on 20. BTW, this was done with the model input set to 100w CW (about equal to 20w PSK31), with dipoles strung at 50’.
Q2:
What antenna(s) systems will you use for transmitting this message? How high will they be placed? How will you orient and erect them and take them down to minimize possibility of observation? Explain in detail, including specifics of antenna and transmission line.Slightly long 40m dipole, strung at 50' on some of those 50'+ trees described in the problem statement. A day ahead of time, tarred bank line (thin, almost invisible) is set up over two suitable tree limbs. Nothing too conspicuous there, just guys out slingshotting rocks and twine up in there air. Dipole broadside bearing is about 315deg, eyeballing it on a map. Close enough. Decent coax fed (say LMR240, but RG58 would be fine too), with an ugly balun up at the feed point. Cut a little long, it'll need a little bit of tuner to get to the target frequency on 40m, and definitely some tuner to get up to 17m. (get an auto-tuner, they're faster) Main thing is that we're not screwing around with trying to get a dipole perfectly resonant on 40m – just cut that sucker 5% long, hang it, hit the "tune" button, and go.
Also with four helpers, when sending's done it's easy to pull down the wire and bank line, stuff it all a bag, and get out of Dodge.
Honestly, I’d’ve preferred to run a single vertical wire antenna from a tree limb. It’d be a lot simpler. Just couldn’t get the receive level up enough without running an amp, or relying on the receive station to have a mega-beam. Also, a dipole has at least some beam pattern, so that’d cut down on the direction finding and detection. I really wouldn’t want to run a vertical wire with extra power.
Q3:
What mode will you use for transmitting the message? If digital, which specific mode and why?BPSK31 @ 20w. It's robust and packs the most punch of any of the common digital modes, doesn't require an external amp. Also, it's fast enough to send 125 random characters in < 50 seconds, leaving open the possibility of re-transmission within the 2 minute time window. As modeled with voacap, that's about the minimum that'll reliably get through. If the receiving station has a beam to give some gain, I'd maybe want to back off on the power a corresponding amount to cut down on detection. Or conversely, maybe keep the send power the same and use the extra receive gain to improve reception.
Q4:
Before you leave for Venezuela, you will be given an opportunity to study data available through NOAA on radio propagation. Which ionosonde stations will you study, and why?No idea on this one. I'd just look at the usual ham space weather sites and postpone transmission a day or so if conditions are unusually bad.
Q5:
What will your cover story be if you are stopped by Venezuelan security forces?Um, we're like on a DXpedition. See, fat guys in Hawaiian shirts. ...? Well it explains the radio gear. NGO studying cropland soil leaching? Dunno, this one would depend a lot more on local conditions not given in the problem, or maybe other factors that I don't understand.
ps: Looking over at Brushbeater to see if the solution from somebody who actually knows about this stuff had been posted yet, they're still floundering around with partial answers. So... discussion?
