Using JT65 On The HF Bands

JT65HF Main Window

JT65HF Main Window

Many of our readers have probably heard about Joe Taylor’s (K1JT) WSJT family of protocols. These protocols were originally developed for Earth-Moon-Earth (EME) or Moon-bounce (via the JT65 variations), Meteor Scatter (via the FSK441 and JT6M variations), Tropo and other very-weak signal communications applications.

All of the WSJT family of protocols and their associated software applications make use of some very sophisticated signal processing techniques to enable communications in extremely weak signal environments. For example, JT65B which is used for EME communications on the 2m band enables communications from the earth to the moon and back using the moon as a (very-poor) reflector. These paths can have 250 dB of loss or more! The JT65 protocol provides about a 10 dB advantage over CW in terms of signal to noise margin on a given path. To help you understand this, using the JT65 protocol to make a contact can provide the equivalent of upgrading the two CW stations using 100W rigs on both ends of a QSO to include a 1 KW amplifier. To understand how the WSJT protocols accomplish this, you can read Joe’s contribution on EME and WSJT that is part of the 2010 ARRL Handbook here.

Joe Taylor’s software is open source and his WSJT family of protocols have been adapted to many applications including their use on the HF bands as well as for Reverse Beacon applications (a.k.a. WSPR). One of these adaptations uses the JT65A variant of the WSJT protocols on the HF bands. This is packaged as part of the JT65HF software from J. C. Large, W6CQZ.

JT65HF can be used to make QSOs on the HF bands at very lower power over long distances using marginal antennas. JT65 QSOs are very simple and only provide the minimum of information exchange to confirm a QSO. The typical sequence (this example has me answering a CQ call from JI1CPN):

  1. CQ JI1CPN PM95         (PM95 is JI1CPN’s grid square, giving his approximate location)
  2. JI1CPN AB1OC FN42  (I respond to the CQ with my call sign and grid square)
  3. AB1OC JI1CPN -12      (JT65HF measures my signal strength for JI1CPN and uses it in his report back to me)
  4. JI1CPN AB1OC R-10   (I give JI1CPN his signal report)
  5. AB1OC JI1CPN RRR   (JI1CPN confirms the we have a good QSO)
  6. TU73 4OVR4 5W         (I confirm the QSO and tell him about my setup)
  7. TU GUY CU 73             (He sends 73 – this is optional)

This is all there is to a JT65HF QSO. The 73 message can be changed to use a limited amount of custom text but that’s it. Each step of a QSO starts at the exact beginning of a minute and takes exactly one minute to complete with 50 seconds used for the transmission of the step and 10 seconds left for the op on the other end to ready a response for transmission. JT65HF automates this sequence so its pretty easy to work through a QSO. If one of the transmissions does not get through to the other end, the other op sends nothing and the sending station repeats the same transmission again until its received correctly. Also note that there is a standard frequency on each HF band where most JT65HF QSOs take place.

Anyone who has setup their station to operate using digital modes already has almost everything needed to use JT65HF. The first additional thing that you need to do is install a precise clock synchronization client on your PC. JT65’s detection algorithms require the transmitting and receiving computers to be synchronized with a fraction of a second. If your PC’s clock is not properly synchronized, you will not get good performance from the decoding software or it may not decode at all. Note that the windows built-in time setting feature IS NOT ACCURATE ENOUGH and you will need to disable it.  You will need a more precise synchronization client which uses the NTP protocol – I suggest the NTP Demon for Windows from Meinberg. Once your clock synchronization is taken care of you will need to download the JT65HF software, install it on your PC (Windows or widows via a virtual environment on the mac, Linux, etc.) and setup the program. There are two simple setup steps.

JT65HF Station Setup

JT65HF Station Setup

The first is your station setup. Here you set your call sign, grid square, and your sound card port. The JT65HF documentation explains how to setup and use the program in detail. One option that you also might set is “Send CW ID with 73…”. This will send your call sign in CW at the end of a QSO for ID purposes.

JT65HF Rig Control/PTT Setup

JT65HF Rig Control/PTT Setup

The other options that you need to set are for Rig Control and PTT. You can use Ham Radio Deluxe, DXLab CommanderOmniRig or the COM port connected to your radio’s CAT interface for these functions.

I think the best way to understand how this all works is to see an actual QSO. The video above shows a JT65HF QSO that I made on 15m with JI1CPN in Japan. I made this contact using only 5w. The video begins with JI1CPN calling CQ. The tones that you hear at the start are his CQ call. I respond to his CQ (note that you can hear my tones but the waterfall does not change while I am transmitting). We then proceed through a JT65 QSO as I outlined it above. Note that I send a custom text message to him at the end giving some information on my antennas and the power level that I used to during the QSO. The video is about 5 minutes long which is the typical amount of time that a JT65HF QSO takes.

I hope that you have found this article interesting and that you might give JT65HF a try. JT65HF is also useful to get on a band where you antennas may not be ideal. There is a pretty good JT65HF community on 160m and its fun to use it to work some DX on this and other HF bands!

Fred (AB1OC)

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