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JT65-HF -- an 'Odd' but Fun Digital Mode

from Dave Dunbar, N0RQ on December 8, 2014
View comments about this article!

"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 04/06/2011

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:


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

Member Comments:
This article has expired. No more comments may be added.
JT65-HF -- an 'Odd' but Fun Digital Mode  
by KC9YTJ on December 8, 2014 Mail this to a friend!
Good older article, but it should have been updated to reflect more recent advancements in the JT area -- for instance, WSJT-X, which addresses the "doesn't help with QSO procedures on HF" issue, and the subsequent development of JT9, which is an even cooler mode.
RE: JT65-HF -- an 'Odd' but Fun Digital Mode  
by W0BTU on December 8, 2014 Mail this to a friend!
" it should have been updated to reflect more recent advancements in the JT area -- for instance, WSJT-X, which addresses the "doesn't help with QSO procedures on HF" issue, and the subsequent development of JT9, which is an even cooler mode."

I fully and emphatically agree. The JT-65 segments are going to quickly get too crowded. JT-9 is not only superior, but it takes up far less space!


"WSJT-X implements JT9, a new mode designed especially for the LF, MF, and HF bands, as well as the popular mode JT65. Both modes were designed for making reliable, confirmed QSOs under extreme weak-signal conditions. They use nearly identical message structure and source encoding. JT65 was designed for EME (“moonbounce”) on the VHF/UHF bands and has also proved very effective for worldwide QRP communication at HF; in contrast, JT9 is optimized for HF and lower frequencies. JT9 is about 2 dB more sensitive than JT65A while using less than 10% of the bandwidth. With either mode, world-wide QSOs are possible with power levels of a few watts and compromise antennas. A 2 kHz slice of spectrum is essentially full when occupied by ten JT65 signals. As many as 100 JT9 signals can fit into the same space, without overlap.

"WSJT-X offers a "bi-lingual" operating mode in which you can transmit and receive JT65 and JT9 signals, switching between modes automatically as needed. Displayed bandwidth can be as large as 5 kHz. If your receiver has as upper-sideband filter at least 4 kHz wide, you can have all the typical JT65 and JT9 activity on screen at once, available for making QSOs with a click of the mouse. Even with standard SSB-width IF filters, switching between JT65 and JT9 modes is quick and convenient."
More fun than before  
by WB4M on December 8, 2014 Mail this to a friend!
Since this article was written, there have been improvements to JT-65 and also the addition of JT-9. There are now more programs that run JT-65 and now there is JT-Alert that helps track needed/worked states, countries, etc. I've managed to earn WAS on both JT-65 and JT-9, pretty close to DXCC on JT-65. It's not really a QSO mode, but wonderful for QRP. I know some think it is boring but no worse than a macro-exchange QSO on PSK.
RE: More fun than before  
by W8QZ on December 8, 2014 Mail this to a friend!
One other SW package that DOES include JT-65 is MultiPSK (my personal favorite, and a package that is regularly updated).
RE: More fun than before  
by KD8MJR on December 8, 2014 Mail this to a friend!
Very nicer article. When was it originally posted?
I assume late 1990 early 2000's.
JT65-HF -- an 'Odd' but Fun Digital Mode  
by KD2EOM on December 8, 2014 Mail this to a friend!
Without JT65 I never would've earned my Worked All Sates award. It was able to reach the close states (less than 300 miles away) via ground wave on 20/15 meters when nothing else would work. Now that the solar cycle is ending it might come in handy.
RE: More fun than before  
by N4NLQ on December 8, 2014 Mail this to a friend!
"Very nicer article. When was it originally posted?
I assume late 1990 early 2000's."

This article was originally published on: 04/06/2011.

Allan - N4NLQ
JT65-HF -- an 'Odd' but Fun Digital Mode  
by AH7I on December 9, 2014 Mail this to a friend!
Thanks for reminder and instigation to move this ahead in the project queue. 73, bob ah7i
RE: More fun than before  
by KD8MJR on December 9, 2014 Mail this to a friend!
"This article was originally published on: 04/06/2011."

Thanks Allan. I thought it was older because he mentioned windows XP. Re reading it I realize he was talking about XP comparability mode.
JT9 - Another Fun Digital Mode  
by K3VAT on December 9, 2014 Mail this to a friend!
I'd like to endorse W0BTU's comments on JT9 and the WSJT X package. Sometimes when band condx are good, dozens of JT65 stations can be found on their respective frequencies. This can lead to QRM and difficulty making the Q. Many JT9 signals can fit into the same bandwidth as a JT65 signal. Additionally, I find that JT9 signals are often stronger, even with the same station switching between modes. I encourage the use of JT9, especially on the lowbands (160M, 80M and even on 40M). Great DX can be had with these digital modes even on very modest power. Check out QRZ.Com, my page (K3VAT) for more info.
73, Rich, K3VAT
RE: JT9 - Another Fun Digital Mode  
by HAMMYGUY on December 11, 2014 Mail this to a friend!
This type of mode appeals to many. It's kind of nice to have a computer to talk with others instead of dealing with the aspects of voice. Voice tends to bring out the stage fright in ham radio.

Yeah the QSO's are canned, but the weak signal aspects of this mode allows for very late DX in most bands. Well after the SSB and CW signals are gone, JT65 keeps picking them out of the noise floor.

I just learned of JT65 a short time ago. It's been a a blast having a new mode catch my interest so much.
RE: JT9 - Another Fun Digital Mode  
by K5UNX on December 11, 2014 Mail this to a friend!
Got JT65 working yesterday using WSJT-X. I like it, but it won't take over as my #1 preferred mode. I'll definitely keep at it.
JT65-HF -- an 'Odd' but Fun Digital Mode  
by KW4JA on December 12, 2014 Mail this to a friend!
WSJT-X works better with my xp pentium computer. It decodes all signals before the top of the minute unlike JT-65HF which only does it with a much faster computer.

JT65-HF -- an 'Odd' but Fun Digital Mode  
by KW4JA on December 12, 2014 Mail this to a friend!
JT-9 is superior to JT-65 in all respects except most dx don't use it except a few Euros. It can be the best mode but it's useless if no one uses it.
Heck, I still run MFSK-16, which is about ten times better than psk-31 for dx.

JT65 and PSK31 are like Miley Cyrus and Kim Kardashian. JT9 and MFSK16 are like Pavoratti and Sarah Brightman. Guess which modes are used most?
RE: JT65-HF -- an 'Odd' but Fun Digital Mode  
by WO7R on December 13, 2014 Mail this to a friend!
JT9's day is coming. When people see the advantage, it will become more popular. It will just take time.

As the older software is replaced by newer, everyone is going to have it and then it will be easy to "just try out". That is almost certainly not true today. So today we have what are often called "network effects" working against it. That is, everyone has JT65, fewer have JT9 so even fewer use it JT9 because JT65 is just so much more popular.

Hams are a conservative bunch on the whole; we tend not to replace things just because we can. When JT9 is in everyone's toolbox and the sunspots turn down, it will begin to see its day.
JT65-HF -- an 'Odd' but Fun Digital Mode  
by ON6AB on December 27, 2014 Mail this to a friend!
JT65 has finished. It became the victim of its own popularity. Bands are overcrowded with people working each other with S9+ signals. A weak signal mode??
90% of all JT65 contacts can be made using cw. Faster and easier. JT65 was fun, it is not anymore...
JT65-HF -- an 'Odd' but Fun Digital Mode  
by WU7B on January 8, 2015 Mail this to a friend!
I have a problem with my JT-65 HF. I get reverse images on my 20mtr waterfall. Therefore I don't get any contacts. Also, now can not see the waterfall on any frequency, just occasional dots where the image is suppose to be. I deleted the old version and reinstalled and still get the same results.
JT65-HF -- an 'Odd' but Fun Digital Mode  
by WU7B on January 8, 2015 Mail this to a friend!
I would have posted in a users group. but the users group seems not to exist.Ben
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