Wednesday, October 5, 2011

Welcome to the JT65A Digital Mode for High Frequency Weak Signal Communications.

Welcome to the JT65A Digital Mode for High Frequency Weak Signal Communications.

Introduction to a weak-signal digital mode

Have you ever wondered how much of the noise you hear on the HF bands is actually comprised of signals too weak to be copied? JT65A is a weak-signal digital mode that allows you to pull great DX out from under the noise on the high frequency spectrum. The JT65A communications protocol was conceived and first implemented by Joe Taylor, K1JT. Joe, a Professor Emeritus of physics at Princeton University, shares a Nobel Prize with Russell Alan Hulse (ex-WB2LAV) for the discovery of the first pulsar in a binary system as well as the first confirmation of the existence of gravitational radiation in the amount and with the properties first predicted by Albert Einstein. Joe has contributed to the amateur radio community in much the same way, changing the playing field for weak-signal operation.

JT65A is actually a "sub-mode" of Joe's original JT65 protocol, which he designed to optimize EME contacts on the HF and VHF bands. JT65 includes error-correcting features that make it very robust, even with signals much too weak to be heard. It was later realized that this protocol, with some adaptation, would also be very usable for terrestrial HF communications.

This is a WEAK-SIGNAL digital mode! - You should not run much power, at all. Many amateur radio operators have worked the world with a simple dipole antenna and 20 watts. Some have done it with less power. You simply should NOT be running 100 watts, UNLESS YOU ABSOLUTELY HAVE TO! By running at 100 or greater power, you MAY cause intense interference to all of the other stations on the same frequency, countering any possible benefit of using this mode! DO NOT RUN HIGH POWER UNLESS YOU KNOW FOR CERTAIN THAT YOU CANNOT COMPLETE THE TWO-WAY CONTACT WITHOUT LOWER POWER! USE ONLY THE POWER NECESSARY TO COMPLETE THE CONTACT! The method suggested is to start all calls with lower power, and only increase the power if you must. Most operators start with 5 to 20 watts. They only increase the power if no contact is made!

It is true that on some bands, under certain propagation conditions, the contact can only be accomplished with 100 watts of power. However, it is also true that under many conditions on most HF bands, it is often demonstrated that lower power has been sufficient to accomplish amazing results. THIS MODE IS DESIGNED FOR WEAK-SIGNAL DETECTION AND SUCCESSFUL TWO-WAY COMMUNICATION!

How much power do you really need to transmit, with JT65A? Here is a calculator to help you figure that out, based on the reports you receive from other JT65A stations.

Here is a list of common JT65A frequencies:

Freq kHz / Sideband / Note

 28076.0 / USB
 24920.0 / USB * note 3 *
 21076.0 / USB
 18102.0 / USB
 14076.0 / USB
 10139.0 / USB * see note 1,2 *
  7036.0 / USB   (International)
  7039.0 / USB   (Typically Europe)
  7076.0 / USB   (USA)
  3576.0 / USB
  1838.0 / USB
  1805.0 / USB
* Note 1 * Do not use 10145-10150kHz because JT65A is NOT COMPATIBLE with PSK31, MFSK, or RTTY and the other fast time-sharing modes such as PACTOR, ALE, PSKmail, and APRS.

* Note 2 * It is becoming a standard practice on 30m to actually use 101378 kHz as the window frequency (USB), to play 'nice' with WSPR stations. This, of course, is an issue with certain countries/regions where digital operation is not allowed below 10140 kHz. However, most JT65A appears to be shifting to 101378 for a window (dial) frequency. This issue with the frequency problem between IARU regions needs to be resolved. I will update this when new information is available.

- NOTE 3: Per discussion amongst the JT65A crowd on the reflectors: There is discussion about moving the 12-meter window frequency, USB to 24927. THIS IS A PENDING ISSUE: Those amateur radio operations in Region 3 must operate at 24920 to 24929. Discussion is currently underway to resolve an issue with using 24920 KHz (PSK-31 since 1999). I will update this list as soon as a new concensus is reached. (last updated October 1, 2011)

Special Two-Part Article Published in CQ Amateur Radio Magazine

David Witkowski (W6DTW) and Tomas Hood (NW7US) co-authored a two-part article that was published in CQ Amateur Radio Magazine in October and Novemember 2010 that explored JT65A and the JT65-HF Software. You may download the two PDF files, below.

Download links:

Part 1 - JT65A and JT65-HF Software
Part 2 - JT65A and JT65-HF Software

Installing the JT65-HF Software

The JT65-HF software installation package is found at Execute the installation file, after you download the most recent version (at the time I write this, the latest version was 1.0.6; the installation file is named, 'setupJT65-HF-1060'). If you receive a Security Warning box, be sure to 'allow' the installation to proceed. Follow the 'Setup - JT65-HF' installation wizard prompts (accepting the License Agreement, and all defaults), until the software is fully installed.

After installation is complete, start JT65-HF and click on 'Station Setup'. The 'Configuration' dialog appears, defaulting to the first tab, 'Station Setup'. Be sure to configure each setting and field with the appropriate information (callsign, Grid Square, and so forth). When these fields are properly completed, click on the second tab, 'RB/PSK Reporter/Rig Control'. This tab allows you to select from several rig control options, including Ham Radio Delux software (which must be running if you select this option). Also on this tab are the options to report stations 'decoded' by JT65-HF to the PSK Reporter web server, and the reverse beacon server.

Example map: see if NW7US has been on JT65A mode using JT65-HF software within the last 3 hours (mapped on PSKReporter/Google Maps)

When you have configured your station settings and operating preferences, click the 'Save Settings and Close Window' button.


The JT65 protocol makes use of compression to pack as much info into the period as possible, but even with compression the maximum of 13 characters can be sent in a random-text message. Supported characters are limited to 0-9, A-Z (caps only), space, and some punctuation. This is NOT a rag-chewing mode!

Supported characters:


(Note: space is between Z and +)
A standard JT65 QSO contains everything necessary for a valid QSO: callsigns, grid squares, and signal reports. The standard QSO requires 6 periods (i.e. 6 minutes) and proceeds like this:

CQ K1JT FN20     (First station calls CQ)
K1JT W6DTW CM97  (A second station answers CQ w/ grid square)
W6DTW K1JT -18   (CQ station sends signal report)
K1JT W6DTW R-16  (Answering station sends "R" + sig report)
W6DTW K1JT RRR   (RRR indicates that the R+signal was received OK)
K1JT W6DTW 73    (RRR was received OK)
W6DTW K1JT 73    (The end of the QSO, K1JT signs '73')
You may have noticed that some of these messages contain more than 13 characters. This is because the JT65 protocol uses a few clever tricks to increase the data compression efficiency, but only if the message is written in a standard pattern, such as those shown above. The 13 character per message limit applies only to random text. Some JT65A ops have taken to using their 73 sequence to offer info on their setup, so it's not uncommon to see "K1JT W6DTW 73" replaced with "VERT25W W6DTW" (indicating 25W on a vertical) or "DPL10W W6DTW" (indicating 10 watts on a dipole). Sometimes when people are having trouble you will see messages such as "CHECK CLOCK" or "NO COPY QRZ?" The use of "TU7" (short for "thank you and 73") has been gaining popularity.

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