ZL2AFP Controller for Visual MEPT

Installation and Help Information
by
Murray Greenman ZL1BPU
July 2008

Introduction

ZL2AFP Vmept.exe is a very simple application which uses the PC sound card to generate Visual Manned Experimental Propagation Transmissions (V-MEPT). It is used in conjunction with a specially designed sound file (.WAV file), that you make yourself, and provides transmitter control in addition to generating the sound for the transmitter.

Since it can be used at the same time as a Spectrogram receiver program such as ARGO, the periodic transmissions generated by Vmept.exe allow you to transmit and receive alternately and thus actively participate in the 'QRSS Knights' V-MEPT community.

Download

ZL2AFP Vmept Tool (26kb)

Installation

Simply unzip the archive into a suitable folder on your computer. It contains just three small files, the executable, a script and an example file. If you intent to use DF6NM's Chirppix program to generate your .WAV files, it's a good idea to place those programs in the same folder.

Create a shortcut to the Vmept.exe executable, and drag it onto the desktop for easy use.

Setting Up

This procedure describes how to use DF6NM's Chirppix to generate single-tone narrow-band audio files suitable for transmission of V-MEPT signals on HF using an SSB transceiver.

  1. Download and install DF6NM's Chirppix in the same folder as Vmept.exe.

  2. Using a graphics editor (Paint, Paintshop Pro etc), create a small .BMP bitmap file containing the image you wish to transmit. An example - shown below four times real size - is included in the archive. Notice that the transmitting direction of the picture is from left to right, but Chirppix works from bottom to top, so when you are done, you must rotate the picture clockwise. Also, the pattern is white on black. Every dot that's not black will be transmitted. You can transmit more than one frequency at a time, but for this application the technique isn't recommended, as it requires very high transmitter linearity and each carrier must share the available power. This way of making messages is the ultimate in WYSIWIG - the picture you create is exactly what the other guy will see on ARGO!


    Image example x4, before rotation

    The image should be preferably no higher than 16 pixels, and certainly no higher than the bandwidth actually used. It need not be wider (longer) than the message, and any spare space will be wasted with the transmitter on and idle. The example picture is 16 pixels high and 124 pixels wide, and takes about 160 seconds to transmit.


    From the VK6DI 'grabber' on 30m - what you see really is what you get!

    In this design (intended for HF using ARGO 3-sec mode) the pixels represent about 1Hz spacing (i.e. dots 10 pixels apart are 10Hz apart), and each takes just under one second to transmit. For text, follow the example and space the dots vertically every second pixel. Use only five dots for the height of the characters, or they will slope to the right excessively. For DFSK space the dots and dashes apart by four or five pixels. The bottom of the picture represents the lowest audio tone, and the nominal design frequency when generating the .WAV file.

    You can send just about any mode you like, such as OOK Morse, FSK, CASTLE, DFSK etc - in the example Sequential MT-Hell is followed by diagonal stripes. Note that each of the stripes is at a different power level - mid grey (R,G,B=128,128,128) represents -6dB, darker grey (R,G,B=64,64,64) represents -12dB and so on. You can use at least six power level steps. You may need to experiment for some time to make the perfect picture.

  3. Rotate the image 90 to the right. Save the image in your working folder as a .BMP file (for example 'mypic.BMP') with 256 grey levels. Open a DOS command window from the Start Menu (START/RUN and type in 'COMMAND'). Change directory to the working folder. Then run the MAKEWAVE script. The procedure is as follows:
    CD\RADIO\VMEPT	(or whatever)
    MAKEWAVE mypic.bmp 1000
    
    where '1000' or whatever you choose is the lowest transmit audio frequency in Hz. You should then find a file 'mypic.WAV' in the same folder. That's all there is to it!

Operation

Run ARGO and set up for reception on the band of choice.

Set the transceiver to the desired frequency (you may need to fool with this a little, as the band used for VMEPT is very small and you must fit between other stations). It is easiest (with a digital transceiver) to store the frequency (say 10139.000kHz) in a memory and fine tune the operating frequency by 'tuning' the value used when you 'compile' the message with MAKEWAVE. For example if you use 1020Hz, and the transceiver memory set to 10139.000kHz, on USB the lowest signal frequency transmitted would be 10140.020kHz. You absolutely MUST use a very stable and accurate transceiver!

Start Vmept.exe. Enter the WAV file name in the top box (or browse for your file). Enter a time (seconds) in the box below. This will be the repeat period, and needs to be greater than the time taken to send the message (this will be worked out by the program and displayed as the default time). 10 or 15 minutes (600 or 900 seconds) are suitable.

Select the COM port to use to control PTT on the transceiver. It works fine with a USB serial adaptor as well as conventional serial ports.

Finally, press 'Start' to start transmitting the message. The PTT will activate the transmitter and a second later the message will start coming from the sound card. A TRANSMITTING status message appears at the bottom right of the window. As normal, you will need to set the sound card audio level for an appropriate transmitter power.

Once the program is running, the message time will count down. When the message has completed, PTT will be released, the message 'IDLE' is shown again, and the count down will continue (perhaps while you watch for signals with ARGO) until it reaches zero and the process repeats.

The 'Stop' button stops the transmission process; the 'Cancel' button closes the program.

Hint:
If you set 5, 10 or 15 minutes as the message repeat period, and start the program on a 'round' minute (xx:30 UTC for example) the message will repeat in a tidy and predictable manner for days on end.


Copyright Con Wassilieff and Murray Greenman 2008. All rights reserved.