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JT65-HF. Presented by Al Mecozzi WA8LBZ. IN THE BEGINNING THERE WAS WSJT. BACKGROUND Joe Taylor, K1JT, developed a suite of open-source programs designed for weak-signal digital communication by amateur radio. The programs are WSJT, MAP65, WSPR and SimJT.
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JT65-HF Presented by Al Mecozzi WA8LBZ
IN THE BEGINNING THERE WAS WSJT
BACKGROUND Joe Taylor, K1JT, developed a suite of open-source programs designed for weak-signal digital communication by amateur radio. The programs are WSJT, MAP65, WSPR and SimJT. All four of these ready-to-run Windows programs are free and can be down loaded at http://www.physics. princeton.edu/pulsar/K1JT/index.html. Installation files for Linux are available for WSJT and WSPR. All you need to use these programs is a SSB transceiver, personal computer with a sound card and an interface between the two.
The MAP65 program implements a wideband, polarization-matching receiver for JT65 signals. It works together with Linrad (by SM5BSZ) and dual-polarization RF hardware to receive and decode all detectable JT65 signals in a 90 kHz passband, matching the linear polarization angle of each one and producing a band map of decoded callsigns sorted by frequency. Its principal application is EME on the VHF and UHF bands.
The MAP65-IQ program is a single-polarization version designed to work with the SDR-14, SDR-IQ, Perseus and other SDR receivers. It has all features of MAP65 except the polarization matching capability, and it supports the JT65A, B, and C sub-modes.
The WSPR program (pronounced "whisper") stands for "Weak Signal Propagation Reporter." This program is designed for sending and receiving low-power transmissions to test propagation paths on the MF and HF bands. Users with internet access can watch results in real time at WSPRnet. Version 2.11 of WSPR includes FMT, a package of command-line utilities that can help you make highly accurate frequency measurements without expensive laboratory equipment.
The WSPR program implements a protocol designed for probing potential propagation paths with low-power transmissions. Normal transmissions carry a station's callsign, Maidenhead grid locator, and transmitter power in dBm. The program can decode signals with S/N as low as -28 dB in a 2500 Hz bandwidth. Stations with internet access can automatically upload their reception reports to a central database called WSPRnet, which includes a mapping facility.
The SimJT program generates JT65 and CW test signals with a user-specified signal-to-noise ratio. It is useful for testing the JT65 decoder and the relative capabilities of these two modes.
The WSJT program ("Weak Signal Communication, by K1JT") offers specific digital protocols optimized for meteor scatter, ionospheric scatter, and EME (moon bounce) at VHF/UHF, as well as HF skywave propagation. The program can decode fraction-of-a-second signals reflected from ionized meteor trails and steady signals 10 dB below the audible threshold.
The WSJT program facilitates basic digital communication using protocols explicitly optimized for a number of different propagation modes. * FSK441 for meteor scatter * JT6M for ionospheric scatter * JT65 for EME at VHF/UHF, and for HF skywave propagation * JT2, JT4, WSPR: experimental modes
Of the all the modes and sub modes mentioned earlier, the focus of this program is on the JT65 mode. JT65 is a digital protocol intended for amateur radio communication with extremely weak signals. It was designed to optimize Earth to Moon to Earth (EME) contacts on the VHF bands, and conforms efficiently to the established standards and procedures for such QSO's. JT65 includes error-correcting features that make it very robust, even with signals much too weak to be heard.
The JT65 protocol uses 65-tone frequency shift keying with constant-amplitude waveforms and no phase discontinuities. This type of modulation is much more efficient than on-off keying, especially when combined with an optimal coding scheme. In addition, it is much more tolerant of frequency instabilities than phase shift keying.
A huge variety of efficient error correcting codes are known and understood mathematically. Among the best know are the Reed Solomon codes. These codes are used to produce the extremely low error rates characteristic of modern CD-ROM's and hard disks. JT65 uses the Reed Solomon code RS(63,12), which encodes each 72-bit user message into 63 six bit “channel symbols” for transmission. Every codeword in this code differs from every other one in at least 52 places, which, in a nutshell, is why the codes is so powerful. Even at very low SNR, distinct sequences are very unlikely to be confused with another.
JT65 does not transmit messages character by character, as done in Morse code. Instead whole messages are translated into unique strings of 72 bits, and from those into sequences of 63 six bit symbols. These symbols are transmitted over a radio channel; some arrive intact, while others are corrupted by noise. If enough of the symbols are correct the full 72-bit compressed message can be recovered exactly.
The decoded bits are then translated back into the human-readable message that was sent. The coding scheme and robust Forward Error Correction (FEC) assure that messages are never received in fragments. Message components cannot be mistaken for one another. The first usable version of JT65 was finished in November of 2003.
But wait a minute, if the WSJT program can do all those different weak signal modes, including JT65, why are we talking about JT65-HF? Good question. It turns out that the WSJT program, as good as it is at doing the job it was designed to do, it is difficult to set up and complicated to operate.
JT65-HF Now comes Joe Large W4CQZ. He developed the JT65-HF program. JT65-HF is based on code from the WSJT Project and would not be possible without the efforts of Joe Taylor K1JT and others within the WSJT development group. JT65-HF is not part of the WSJT project. Any questions or issues with JT65-HF should not be addressed to The WSJT Development Group, they will have no idea what you are asking about.
NOW LET'S TAKE A LOOK AT THE JT65-HF PROGRAM
Before beginning the basic setup instructions for JT65-HF, there are some basic concepts that apply to the JT65 protocol. First and most important is that of time synchronization. You can not successfully have a JT65 QSO without close synchronization of your computer's time with UTC time. Period. End of discussion.
If you have internet access there is NO EXCUSE for not having a properly synchronized clock. Free solutions to this issue are readily available. Many use D4; http://www.thinkman.com/dimension4/ Do not assume your PC's clock is stable. Many have highly inaccurate clocks that gain/lose time at a substantial rate.
Considerations for transmitting JT65. JT65 is indeed an FSK mode in that it transmits distinct single tones from a tone set of 65 values. But. JT65 is NOT TRANSMITTED using FSK. It uses AFSK and this is a critical distinction. Avoid ALC action if possible with an AFSK signal. Much like any other audio input to an SSB transmitter JT65 can generate a poor signal if over driven.
JT65 is a weak signal mode. Its primary purpose is to facilitate EME (Earth to Moon to Earth) communications. For use on HF you need to re-think your power levels. Often a few milliwatts will do amazing things. Some situations call for much higher power levels, but in day to day HF usage, 10 to 20 watts is probably enough, if not too much.
Your Callsign is a required input. Your Callsign must be entered before TX functions will be enabled. JT65-HF does not support calls with either a suffix or prefix at this time. Your callsign must contain only the letters A … Z and digits 0 … 9. Any other characters will result in the input box being cleared and a warning message issued.
Your Maidenhead Grid Square is a required input. You may enter either a 4 or 6 characters. If you do not know your Maidenhead Grid Square you will need to find someone who can help you with finding this information.
The Sound Input Device and Sound Output Device are required inputs. The default value for sound input device and sound output device are often correct, but you should confirm this.
If you want to transmit, a PTT Port is a required input. If you have used another digital mode program and successfully configured PTT by serial port, you should have no difficulty in doing so with JT65-HF. You may enter either a number (like 1 or 10 or 120) or a fully specified device string (like COM1 or COM10 or COM120). If you use VOX to control your rig leave the PTT Port set to its default value of NONE. PTT via rig control or PTT via Parallel Port are not supported.
Once you have set the PTT Port you can click the “Test PTT” button to quickly toggle your transceiver from RX to TX to RX. No tone will be generated for the test, it simply toggles the PTT line for about 1/10th second. Warning: Some systems have shown issue with the PTT routines where the TX will come up but not return to RX. In some cases where PTT errors occur you will need to check the box for “Use Alternate PTT Method”. In most cases PTT works well with the default or alternate method.
