Turn it down on JT65

It’s been 3.5 years since I wrote this post and I’m not sure the information in it holds up anymore, as I was a very new ham when I wrote it and I was still learning. As with many things in ham radio, the obvious solution isn’t always the right one. I’d defer to Jarrad’s comment below as a good clarifier. — KK4DSD

Check out those alligators swimming on the right side of my waterfall!

I wasn’t having much luck making phone contacts tonight, so I tuned over to the popular JT65 frequencies and heard a lot of activity. I switched off my QRO rig and fired up the FT-817, running on battery power, as it wasn’t connected to my station power supply at the moment.

On 40 meters, I started CQing with 2.5 watts and had a station in Ohio respond immediately. He had a nice signal, -7, and came back to me with a -8 report.

I reasoned that if I was that loud on a stateside contact at 2.5 watts, I could go with much less power and conserve my battery. So I dialed the 817’s power back to its lowest setting — half a watt. I CQed again and a station from Illinois responded, giving me a -11 signal report, well within range of a copyable signal for JT65.

I CQed once again and a Quebec station 1,000 miles away came back with a -12 signal report. Again, a very good signal for this mode.

I decided to try my luck on 20 meters and see if I could score any DX. I CQed repeatedly, but never had any takers, then I noticed several VERY loud signals in the waterfall. One of the stations had a booming -3 signal and he was basically quieting the entire frequency on transmit. Then another signal came crashing in, and the weaker signals not wiped out by the -3 station, were certainly wiped out by the second loud station.

Folks, JT65 is a weak signal mode. Five watts is considered high power for JT65. I have no way of proving it, but I suspect stations are raising their power levels a good bit. One thing’s for certain, if you are full-quieting the frequency, you’re using too much power. You’re stepping on everyone else on frequency who is trying to operate in a proper manner. And by the way, check your ALC, because some of you gators are causing splatter comparable to the best death scenes from Italian horror films circa 1980.

I enjoy JT65 because it lets me make QSOs on a very small amount of power. I have a high level of success with the mode, as long as folks play nice and keep the power down to a considerate level.

And if you don’t believe me, check out the JT65 Power Calculator, one of the best tools I’ve come across concerning this mode. (Edit: It looks like the power calculator has been down for at least several days. I hope it comes back to life, as it’s a very nice tool.)

Is there even a reason to use JT65 for casual QSOs if you have higher levels of power to burn? If I had more power, I’d run PSK or RTTY, because frankly the “Russian ice cream truck” sound of JT65 isn’t THAT fun to listen to. I use it because it lets me make contacts with my low power, not because I enjoy a 6-minute macro-based QSO with no real interaction.

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8 thoughts on “Turn it down on JT65

  1. I suspect you could be right about this.. It is quite possible that some op’s are using much more than QRP power. I did a search on this and found your article because I am having to crank up my power more and more to get a response. I’m running a 170 foot doublet that’s up 65 feet. The signals come in strong here, and I’m only using a Yaesu FT-857D for my digital work -(not noted as having the best receiver in the world, I’m sure) but the sigs boom in nevertheless. The problem can’t be my antenna.. especially since I have worked the world with QRP CW with this same antenna. So why can’t I be heard? Probably because I’m running less power than most. Or perhaps, some op’s have terrible receivers and don’t have things set up properly.

    • I haven’t been on the JT modes in quite a while, but it seems they have exploded in popularity in the past few years, and I suppose with popularity comes more operators who aren’t familiar with the origins of the mode as one for weak signals and lower power.

      I really enjoyed the JT modes but I think I prefer the fast pace of CW nowadays.

      But there are always going to be ops who overdrive ALC, or forget to turn down their power down after operating on RTTY, etc. You can hardly go onto 14.070 without seeing splatter, too much power, grimy signals, etc.!

  2. “Weak Signal” is not analogous to “Low Power”.

    As you found out, 500 mw can be a very strong signal… and likewise, even 500 Watts could be a weak signal when working DX or during times of poor propagation.

    Over-driving the AF stage of the transceiver is much greater sin than running more than 5 Watts…

    A decent SDR Receiver with pre-distortion technology putting out 100 Watts would easily outperform your FT-817 at 5 watts in terms of IMD (<-50 IMD for the SDR, ~ -30 for the FT-817).

    In the above example, the 100 Watt SDR would produce 7dB less interference than a 5 Watt output 817… You could even drive an amp to 400 watts with such a setup and still cause less harm than the 817…

    The point is, dirty signals wipe out JT65 waterfalls, not power. Sure, you shouldn't run more power than you have too, but as you've found out 5 Watts can be more than enough and times, and likewise, even 500 Watts could be a 'weak signal' under the right circumstances.

    • Thanks for the clarification. As with so many things in amateur radio, the most obvious explanation isn’t always the right one. When I wrote this post years back, I thought I was observing an overuse of power, but perhaps I wasn’t!

      • I hope you didn’t feel I jumped on you Andrew! Its a pretty common misconception that power = wiped out waterfalls on digital modes when the truth of the matter is distortion is the problem.

        I’m not so much concerned with how much power anyone runs, but in my books a clean signal is mandatory. It doesn’t matter whether you’re a QRPp guy or a QRO guy; transmitting a clean signal should be one of the common decencies of Ham radio.

        Occasionally I come across JT65 signals, that whist weak on their primary, decode multiple times in JT65. The operator at the other end is likely overdriving something (probably the AF stage) somewhere in their transmitter that I can successfully decode their distortion products!

        When this happens, the decodes arising from distortion are usually around 12 dB lower than the main trace… that’s absolutely tremendous distortion if you think about it!

        73,

        Jarrad

  3. I’ve been doing a bit of testing, and it looks like the popular program JT65-HF does have a bit of problems DISPLAYING other signals in the presence of a strong (not necessarily high powered, perhaps just close) station. It can indeed look ‘wiped out’, as I confirmed with a friend who lives 2km away with just 5 Watts on 20m.

    There is one caveat however, despite not showing other stations due to my strong signal, my friend was able to successfully decode other stations.

    The software I use, WSJT-X v 1.6 had no such issues when my friend transmitted, even though he was a -01.

    Therefore, I’d recommend that if you have trouble visualizing (but not decoding) other stations in the presence of a strong station, try using WSJT-X. Not only does it not seem to suffer the ‘display wipe out’ issue, it also is more modern and includes support for JT9.

    Thanks again for the post Andrew, was good to explore some of the issues that surround operating JT65 🙂

    • Thanks Jarrad, that’s an interesting test, and likely the effect I thought I was experiencing when I originally wrote this post. I was sort of comparing it to a SSB pile-up situation in which the loudest voice in the pile can step on the weakest signal, making it harder to hear. As you’ve informed me, this may not be logical thinking on the JT modes.

      I too have changed to WSJT-X!

  4. I am not far from the ocean. Using a hex beam at 45 feet fed with 75′ of LMR400 with a pretty elaborate ground system. The rig is a Kenwood TS-590SG. For the life of me, whenever I call a station even those that I am copying with a -5 or -6 else always gets there first with a -1 or -2. Usually use 5-10 watts but even with 20 watts I don’t stand a chance. I an SSB pileup and the amp on I will usually get in with 2 or 3 calls but no luck on JT65.

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