NO3M

Amateur Radio

New 630m QSO distance world record set by VK4YB and NO3M

On October 14, 2019, at 1032z, VK4YB and NO3M completed a distance record setting QSO on the 630M band using JT9. This QSO was the culmination of two years of effort around every equinox since September 2017. Hopes were wearing thin as we were moving away from the recent equinox (Sept 23). Even when the path may have been open over the past 3 weeks, either end would be plagued with QRN. While the particular opening that facilitated this QSO was not as comparably strong as others in the past, something special was obviously at play.

The distance is 9307.5 mi (14979.0 km), increasing the previous record distance of 8351.9 mi (13441.0 km) set by VK4YB and K5DNL by almost 1000 mi.

Below is the screenshot provided by VK4YB:

 

(click image to enlarge)

630m Auto Tuner

This project is based on prior auto tuner work by Ralph, W5GJV. However, instead of a Foster-Seely type phase discriminator like Ralph used, I chose to use a double balanced mixer (DBM) phase detector with the voltage sample shifted approximately 90 degrees. Doing so shifts the DC output (IF port) indicating the phase error so that there are not two zero crossing points within the useful phase error range, but rather one zero crossing within a +/- 90 deg range, with 0VDC corresponding to a 0 deg phase error.

The phase detector is based on one used by M0BMU in his tuning indicator circuit. The control circuitry is similar to W5GJV’s, but with some changes as needed to deal with the single ended phase detector output, required DC amplification, etc.

I created a short (16 min) video demonstrating the automatic tuner on 630 meters:

73 Eric

JT9-2 Linux script

The executable program by ON7T for the JT slow modes only runs on Windows platforms and crashed when attempting to run it under WINE.  Below is a PHP script that will run on Linux to handle the receive side of things.  External applications needed:

arecord, sox, jt9 (part of wsjtx)

No sound device was specified when invoking arecord, this assumes one is using PulseAudio and selects the appropriate sound device from the PulseAudio volume control application.

 

<?php 

$f = "decoded.txt"; 
$wav = "jt9-2.wav"; 
$wav_tmp = "jt9-2_tmp.wav"; 
file_put_contents($f, ""); 

while (true){ 

  do { 
    usleep (200); 
  } while ( !((int)date("s") == 0 && ((int)date("i")) % 2 == 0) );

  $timestamp = str_pad(date("Hi"), 4, "0", STR_PAD_LEFT); 
  //$slot = intdiv(date("i") % 4,2); // PHP 7 
  $slot = (int)((date("i") % 4)/2); 
  printf("Time: %sz %d\n",$timestamp,$slot); 
  exec ("arecord -c 1 -r 12000 -f S16_LE -d 105 ".$wav." 2>&1 >/dev/null");
  exec ("sox ".$wav." ".$wav_tmp." speed 2.0 2>&1 >/dev/null");
  exec ("jt9 -9 -d 3 -S 300 ".$wav_tmp." 2>&1 >/dev/null");
  $decodes = file_get_contents($f);
  echo $decodes;
  file_put_contents($f, "");
  unlink($wav);
  unlink($wav_tmp);
}

?>

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