Using the
AudioMEPT QRSS Controller

Introduction

AudioMEPT is a Windows program designed to generate audio for a Manned Experimental Propagation Transmission (MEPT) or other QRSS application. It can also be used as a general-purpose timed announcement, for any suitable application which requires the same message to be sent at exact 10 minute intervals. AudioMEPT includes the ability to control a transmitter PTT circuit via a PC COM port or equivalent USB adaptor in the conventional manner.

AudioMEPT is different to previous applications (such as the ZL2AFP VMEPT Tool) in that:

• It uses a fixed and accurate message frame time (10 minutes).
• It enables message start to be synchronised to an exact minute and second.
• It easily facilitates mixed-mode messages such as WSPR and MT-Hell.
• it will send audio files in .WAV, .WMA or .MP3 format.

Using an exact and repeatable 10 minute message frame allows:

• Messages to be placed accurately on spectrograms and internet grabbers, in both time and frequency domains (grabbers typically have a 10 minute refresh time)
• Facilitates 'stacking' of multiple images for signal enhancement and noise reduction
• The use of mixed messages, such as WSPR and QRSS, including Multi-Tone Hellschreiber
• Easy synchronisation to UTC via UTP and the PC clock

AudioMEPT has a very simple user interface with just a few controls.

Screen-shot of AudioMEPT while transmitting

In the above screen-shot you can see all there is to the program. At the top is the menu (described below), and below that the name of the file currently loaded for transmit, or being transmitted.

Just below that is a progress bar 10 minutes long. It is blank during Standby, and starts incrementing when the transmission starts. It will stop somewhere less than the full length if you set the STOP time to be less than 10 minutes. When the transmission completes the progress bar is again cleared.

At the bottom left three settings are displayed: the selected COM Port for PTT control, the Start Time, and the Stop Time.

At the bottom right two parameters are displayed: the current status (Transmit, Receive or Standby) and the current time (as read from the PC clock).

File/New Pattern brings up a dialog which allows you to choose the audio file to be transmitted. Any appropriate .WAV, .MP3 or .WMA file can be used. Audio files in .WAV formet are best made with the the "MEPT Controller V1.08" program. Files can be converted to other formats using a sound editor such as Audigy.

File/COM Port allows you to select which COM Port (may be a physical port or a USB - Serial adaptor) is used for PTT. This is the same arrangement used by many radio programs.

File/Quit saves the current settings (file, port, start and stop times), then closes the program. Next time you start the program it will fire up loaded and ready for action.

TX/RX/Start forces the transmission to start NOW (irrespective of time sequence) so you can make adjustments to the transmitter etc.

TX/RX/Stop forces any transmission to stop immediately. This is useful if something goes wrong, or to stop after you've completed testing. The next transmission will occur at the next set time.

Timer/Start Allows you to set the start time of the next and subsequent transmissions.

Timer/Stop Allows you to set the finish time of the current and subsequent transmissions.

Explanation:
The timer knows only about unit minutes and seconds. It will start every 10 minutes. If (for example) you set the start time to "X0:30", it will start transmission at hh:00:30, hh:10:30, hh:20:30 etc (hh represents any hour). Hours and tens of minutes are ignored. You can set a start time later than the stop time: this simply means the transmission starts late in the 10 minute cycle and finishes early in the next one. For example Start = "X8:00" and Stop = "X2:00" means that a four minute long transmission starts at eight minutes into the 10 minute frame.

Try not to confuse the immediate TX/RX Start/Stop commands with the Timer Start/Stop commands - they have quite different functions.

Help/Help Brings up this Help file.

Help/About Shows the program version information and a copyright message.

1. Run the program. Set the COM port, and select a suitable .WAV file (you could test with the file provided, but not with the transmitter enabled).
2. Select TX/RX/Start to check that the COM Port PTT operates the rig. Use the Windows sound applet controls to set the transmitter audio (and power) level.
3. Select TX/RX/Stop when your tests are completed.
4. Use Timer/Start and set an appropriate start time.
5. Use Timer/Stop and set an appropriate stop time. Check the properties of the file you have selected in order to know its duration: i.e. how much time to allow for the file to be completely transmitted. (Windows Media Player can tell you this). Allow a few seconds extra and then add this value to the Start Time to arrive at a suitable Stop time. Ignore the tens of minutes in the result.
6. Check that the transmission starts and stops at the times you've set, and that the message has not been truncated unintentionally. You're now in business!

This process has been considerably simplified since the ZL2AFP MEPT Controller program included the facility to render visual patterns into .WAV files directly. See the Making Waves" page for details.

Mixed Mode with WSPR

The secret here is to place the WSPR segment first. That way the critical timing requirement (± 1 second) of WSPR is best preserved. The easiest way to do this is make two separate .WAV files, a WSPR one (explained below) and a QRSS one (as described above). Then use a sound editing program such as Audacity to add the QRSS file to the end of the WSPR file. In order for the two to appear in the appropriate segments of the band, for example QRSS at 10140.050 kHz, and WSPR at 10140.200, you need to place the transmitter frequency and the pitch of the audio files appropriately. If say you have the transmitter (USB suppressed carrier or dial) frequency on 10138.700 kHz, the QRSS audio pitch for 10140.050 kHz will need to be 10140.050 - 10138.700 = 1.350 kHz.

The easiest way to generate the WSPR .WAV file is simply to record your own 'transmission' from the WSPR software. You could use two computers, two sound cards and a cable between them, or the 'Stereo Mix' option to record using the Windows Soundrec applet. Preferably record (or convert to) 8 bit mono with 49 kbps sampling rate, in order to make attaching the files easier. When you combine the files, ensure that there is a minimum of quiet time at the start of the file, in order to preserve correct timing. If later you find the WSPR transmission starts a little early or late (assuming your PC time is accurate), simply adjust the quiet time slightly at the start of the file, again using your sound editor.

The default band-centre audio frequency for WSPR is 1500 Hz, which is why the above example works well. With the same dial frequency of 10138.700 kHz, an audio pitch of 1.500 kHz gives the expected transmission frequency of 10138.700 + 1.500 = 10140.200 kHz.

A similar arrangement will work for other bands (often with the same .WAV file), as the separation between QRSS and WSPR transmissions on many bands is the same. If joining the files is too difficult for you, start with recording the WSPR segment, and when that has finished, simply play the QRSS file through Media Player, and have Soundrec continue to record it on the same file.