Murray Greenman ZL1BPU
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 differs from previous applications (such as the ZL2AFP VMEPT Tool) in that:
Using an exact and repeatable 10 minute message frame allows:
- 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.
- 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, essential for WSPR
ZL1BPU and ZL2AFP AudioMEPT V0.00.
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, 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).
This is the most complicated part of the whole business, but fortunately you need only do it occasionally, and it can be straightforward if you follow the instructions in the Help file. There are two methods: an older method based on reverse FFT by Marcus DF6NM, and a recent Windows program by Con ZL2AFP. The purpose is of course to make an audio file which portrays an image of the text you wish to send.
Making Waves Instructions for making .WAV audio patterns
ZL2AFP MEPT Controller Windows MEPT Controller and .WAV file maker.
This is the preferred (and simpler) method of making .WAV files. It will not make a pattern with two or more concurrent tones. This makes life a lot easier for the transmitter.
DF6NM's Chirppix DOS executable by Marcus DF6NM.
Here's an example using the older Chirppix method. This is the 'source' .BMP image:
Source pattern file example (x2 and rotated)
Chirppix was then used to make a WAV file. If you make a .WAV file from the example 2T_dual.bmp, this should be the result:
2T_dual.wav, an AudioMEPT ready .WAV file example
This is what the transmission of this file looks like on ARGO in 3 second slow mode:
ARGO screen-shot of the example
Compare this picture with the original graphic just above! This is truly a WYSIWYG (what-you-see-is-what-you-get) application! Both methods described are WYSIWYG, and both will generate multiple power levels. Chirppix can however also generate more than one tone at a time, although impressive linearity will be required of the transmitter if you choose to do this.
Note: The five 'power stripes' clearly show at different levels of brightness. The first two are hard to tell apart due to AGC action in ARGO, but if your transmitter is suitably linear, they will be in accurate 6dB steps. The 'power stripes' are very useful in assessing signal strength on grabbers and other spectrograms.