During those 12 seconds, the computer is very busy decoding everything it can in the 2kHz segment and displaying the results in the decode window. Then in the next minute, the other station transmits for 48 seconds, followed by (you guessed it) 12 seconds of silence. For 48 seconds, a station will transmit, and then there are 12 seconds of silence. The "sync" tones at the left of the 175Hz signal are transmitted more than the others, so they tend to show up the best. Those very weak signals could very well have been decoded. If you go back several minutes, you might see the very weak signal at -150Hz and another at about -730Hz. In the current minute (at the top) there is a modestly-weak signal at nearly -500Hz, and a strong one at about +40Hz. Where you see two thin red lines close to each other means I was transmitting most of that minute. From top to bottom is time, most recent on top. Across the top is the offset in Hertz - note the 2kHz width. This is very similar to waterfalls for other digital modes. If you're receiving a signal, it should look something like this waterfall:
Start the software and tune your rig to 20m (USB dial freq 14076) or 40m (USB dial freq 7076), or pick one of the other bands, but make sure to pick a standard JT65-HF freq (1838, 3576, ~10138, 18102, 21076, 24920, 28076 kHz) and make sure it is USB. So now that your clock is good, you're ready to decode some signals. Either of them will keep your clock accurate to within a few hundredths of a second. If you're running Win7 or Vista, look at Meinberg first, but D4 will work if you run it as Admin and in XP compatibility mode. The most popular one is D4 (Dimension 4) Meinberg is the other major choice (links below). You need to get good clock sync software.
What that means for you is that the built-in Windows clock sync probably won't be sufficient. In reality, you'll want it to be less than 0.5 seconds off.
We're not talking within 30 seconds here. The sequence of a contact depends on the computer clock being very accurate. And here you thought a 140-character tweet on Twitter was short!
It is highly structured (similar to FSK441 or ISCAT on VHF) and because the maximum number of characters you can send in freeform is 13 (that's right, thirteen). It is not a transmit-at-will or send-whatever-you-want mode. Second, and the thing that is most unique about JT65-HF, are the QSO procedures. Installation is pretty easy, and requires only limited configuration. The current version is 1.0.7, and can be found at the link listed at the end. What you really want to get (trust me on this) is JT65-HF.
You could use WSJT v9, which is THE choice for VHF/UHF high-speed meteor scatter (HSMS), as one of its modes is JT65A (JT65-HF), but this is not the wise choice for HF because it doesn't help with QSO procedures on HF. (Have no fear, it's free!) There are technically two choices, though in reality there's only one good choice for the new user. It's not in FLDIGI or HRD/DM780 or MixW or anything else like that. So what's so different about JT65-HF?įirst, your favorite software doesn't do this mode. OK, fine, that's the stuff you already knew. There should be zero ALC for these modes - if you see some, turn down the sound card volume/output until ALC readings disappear. This isn't quite as critical on JT65-HF as it is on PSK31, but it is still important. Just like PSK31, you'll also want to watch the ALC meter on the rig to keep from overdriving the signal. This is an extremely efficient weak-signal mode. It is important not to crank up the power too much because it will make it hard or impossible for others to hear weaker signals, just like on PSK31. Some JT65-HF users are committed to 5W max, period. On the lower bands, 5W-10W will often do the trick, but for DX you might well crank it up to 30W-40W if really needed. On the upper HF bands, you'll often run 5W-10W or so. It is also a low-power mode, even more so than PSK31. None of that will be new to you if you've ever done digital before. The equipment required is the same as other digital modes, that is, the rig, the antenna, the computer with software, and a sound card interface. In some ways, it is very similar to other digital modes such as PSK31, but it some ways, it is very much different.įirst, the similarities.
In case you've never seen it before, let's explore a seemingly-little-known digital mode called JT65-HF.