JT65-HF -- an 'Odd' but Fun Digital Mode
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
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
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.
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
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.
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
VK2LGW QF57 .
(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 VK2LGW
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
VK2LGW -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 VK2LGW
W1AW R-13 ,
meaning “roger, your signal is” -13 or whatever. My
response to that is W1AW
VK2LGW RRR ,
and then he’ll send VK2LGW
W1AW 73 (or
some freeform “73”-type text), and the final step is for
me to send W1AW
VK2LGW 73 (or
perhaps something like TU
HQ! 73 or 5W
see it a bit more clearly, it would look like this:
W1AW FN31 (he answers with his grid)
W1AW VK2LGW -06 (I send signal
W1AW R-13 (he sends Roger and my signal
W1AW VK2LGW RRR (I acknowledge
receipt of his report)
W1AW 73 (he sends a standard or
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
station using low power, I’ve worked guys all over
Europe U.S.A. Asia 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 and eQSL 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
WSJT-X running with
JT-Alert by VK2AMA
Here are some links:
download the latest software and .pdf setup/operations
add-on software with visual and audio alerts
http://hamspots.net/wsjt/ “cluster”-type spots for
JT65-HF and other digital modes
group discussions (on Google groups)
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.