intro to JT65-HF

In case you’ve never seen it before, let’s explore a seemingly-little-known digital mode called JT65-HF.  In some ways, it is very similar to other digital modes such as PSK31, but it some ways, it is very much different.

First, the similarities.  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.  None of that will be new to you if you’ve ever done digital before.

It is also a low-power mode, even more so than PSK31.  On the upper HF bands, you’ll often run 5W-10W or so.  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.  Some JT65-HF users are committed to 5W max, period.  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.  In most cases, 10W will be sufficient.  This is an extremely efficient weak-signal mode.

Just like PSK31, you’ll also want to watch the ALC meter on the rig to keep from overdriving the signal.  This isn’t quite as critical on JT65-HF as it is on PSK31, but it is still important.  There should be zero ALC for these modes – if you see some, turn down the sound card volume/output until ALC readings disappear.

OK, fine, that’s the stuff you already knew.  So what’s so different about JT65-HF?

First, your favorite software doesn’t do this mode.  It’s not in FLDIGI or HRD/DM780 or MixW or anything else like that.  You need special software.  (Have no fear, it’s free!)  There are technically two choices, though in reality there’s only one good choice for the new user.  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.  What you really want to get (trust me on this) is JT65-HF.  The current version is 1.0.7, and can be found at the link listed at the end.  Installation is pretty easy, and requires only limited configuration.

Second, and the thing that is most unique about JT65-HF, are the QSO procedures.  It is not a transmit-at-will or send-whatever-you-want mode.  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).  And here you thought a 140-character tweet on Twitter was short!

The sequence of a contact depends on the computer clock being very accurate.  We’re not talking within 30 seconds here.  2 seconds off is barely acceptable.  1 second off is usually OK.  In reality, you’ll want it to be less than 0.5 seconds off.  What that means for you is that the built-in Windows clock sync probably won’t be sufficient.  You need to get good clock sync software.  The most popular one is D4 (Dimension 4);  Meinberg is the other major choice (links below).  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.  Either of them will keep your clock accurate to within a few hundredths of a second.

So now that your clock is good, you’re ready to decode some signals.  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.  If you’re receiving a signal, it should look something like this waterfall:

This is very similar to waterfalls for other digital modes.  Across the top is the offset in Hertz – note the 2kHz width.  From top to bottom is time, most recent on top.  The thin red lines delineate minutes.  Where you see two thin red lines close to each other means I was transmitting most of that minute.  In the current minute (at the top) there is a modestly-weak signal at nearly -500Hz, and a strong one at about +40Hz.  If you go back several minutes, you might see the very weak signal at -150Hz and another at about -730Hz.  Those very weak signals could very well have been decoded.  The “sync” tones at the left of the 175Hz signal are transmitted more than the others, so they tend to show up the best.

JT65-HF is done 60 seconds at a time.  For 48 seconds, a station will transmit, and then there are 12 seconds of silence.  Then in the next minute, the other station transmits for 48 seconds, followed by (you guessed it) 12 seconds of silence.  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.  Near the end of the 12 seconds, the receiving station decides if he wants to answer a CQ, or proceed to the next step of an in-progress QSO.

OK, time for the description of how a QSO works.  I’m going to call CQ, and W1AW will decide to answer me.

I click on the Call CQ button and Enable TX.  At the 00 second mark (of either the even or odd minute, depending on which I chose), I will send CQ N0RQ EM13 .  (This is what is generated by the program, and as you’ll see, both grids and a signal report are exchanged.)  My xmit will last for 48 seconds, and in the following minute, I’ll wait to see if I get a response.
W1AW sees my signal, decodes it, and decides to answer, so he’ll double-click the decoded line which will make the software start sending at the 00 second mark of the next minute.  He will send N0RQ W1AW FN31 .  When I see that and decode it, I’ll proceed to the next step (either by double-clicking on that decoded line, or by clicking on the Answer Caller button), which will make me send W1AW N0RQ -06 . “06” is the signal strength in dB, automatically filled in by the program, and will range from -01 (extremely strong) to -25 or so (extremely weak).  After that, W1AW will send N0RQ W1AW R-13 , meaning “roger, your signal is” -13 or whatever.  My response to that is W1AW N0RQ RRR , and then he’ll send N0RQ W1AW 73 (or some freeform “73”-type text), and the final step is for me to send W1AW N0RQ 73 (or perhaps something like TU HQ! 73 or 5W DIPOLE 73).

To see it a bit more clearly, it would look like this:

CQ N0RQ EM13                                 (I CQ)

N0RQ W1AW FN31         (he answers with his grid)

W1AW N0RQ -06                             (I send signal report)

N0RQ W1AW R-13           (he sends Roger and my signal report)

W1AW N0RQ RRR                            (I acknowledge receipt of his report)

N0RQ W1AW 73               (he sends a standard or freeform 73)

10W DIPOLE 73                                 (I send a freeform or standard 73 – contact is over)

Key note: only proceed to the next step if you heard that the other station proceeded to his next step – otherwise, repeat the step you’re on until you hear him proceed.  The buttons in the JT65-HF software show the natural progress of a contact – the first row of buttons if you’re doing the CQ, and the second row of buttons if you’re answering a CQ.

That’s it in a nutshell.  When you actually see the JT65-HF screen and watch a couple of QSOs, it will make a lot more sense.  As you can see, a single contact takes 7 minutes or more.

JT65-HF is so labeled because it sends 65 tones spread out over 175Hz. The “JT” part comes from the original creator of this type of mode, Joe Taylor, K1JT, the 1993 winner of the Nobel Prize in physics, and the author of the excellent HSMS and EME software known as WSJT.

JT65-HF is written by W6CQZ, and is an extremely efficient weak-signal mode – it is possible to decode signals you simply cannot hear in audio and can even barely see on the waterfall display.  You’ll probably love it or hate it – if you’re a ragchewer, you might hate it – but many of us have found it to be addictively fun!  Even with my modest remote station in the central US and low power, I’ve worked guys all over Europe and in other countries as well.

For logging, the mode in your log should say JT65 (though technically, the mode is JT65A).  A good majority of JT65-HF users are LOTW participants, making QSLing easy.  The software has a built-in logging function, which creates a standard .adif file, which can easily be imported into your favorite logging software.

Before concluding, it is certainly worth mentioning a very useful add-on product called JT-Alert by VK3AMA.  It is distinct from JT65-HF, but works closely with it.  It looks at the decodes made by JT65-HF and then displays info and makes sounds when it detects things like CQ, or your callsign being sent by someone (such as an answer to your CQ), or a wanted state.  It can also detect that you’ve worked someone before on the band you’re on and optionally ignore any alert that may have been generated.  It is a helpful tool that is worth installing.

Here are those links I promised:  download the latest software and .pdf setup/operations doc   JT-Alert add-on software with visual and audio alerts  “cluster”-type spots for JT65-HF and other digital modes  JT65-HF group discussions (on Google groups)  D4 time sync  Meinberg time sync

Although I’ve gone into a modest level of detail with this article, there are setup options and some operating procedures that were not covered.  I highly suggest reading the excellent setup manual/documentation.  The JT65-HF group discussions are also very useful, with a great set of friendly and helpful folks participating.

Go forth and have fun on JT65-HF!

73, Dave NØRQ

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