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<title>MFSKpix</title></head>
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<h2 style="text-align: center;">MFSK</h2>
<br><big><font style="font-family: serif;" face="Verdana, Arial, Helvetica" size="-1"><big>MFSK16 and MFSK8 are
multi-frequency shift keyed (MFSK) modes with low symbol rate. A single
carrier of constant amplitude is stepped (between 16 or 32 tone
frequencies respectively) in a constant phase manner. As a result, no
unwanted sidebands are generated, and no special amplifier linearity
requirements are necessary. The tones selected are set by the
transmitted (4 or 5 bit) bit pattern and a gray-code table.
<br><br style="font-family: serif;"></big></font></big>
<font face="Verdana, Arial, Helvetica" size="-1"><big><span style="font-family: serif;">The mode has full-time Forward Error Correction, so it is very robust. Tuning must be very accurate, and the software
will not tolerate differences between transmit and receive frequency. The mode was
designed for long path HF DX, and due to its great sensitivity is one of the best for long distance QSOs and skeds. MFSK8
has improved sensitivity, but is very difficult to tune, and suffers more from Doppler. It is useful as the band fades out.</span></big></font><br><br>MFSK-32
and MFSK-64 are high baud rate and wide bandwidth modes designed for
use on VHF and UHF. These are very useful for send large
documents or files when some transmission errors are can be tolerated.<br><br>This is an example of properly tuned MFSK16 signal with a s/n of approximately 9 dB.<br><br><div style="text-align: center;"><img style="width: 735px; height: 104px;" alt="" src="images/mfsk-9db.png"><br><br><div style="text-align: left;">The same signal viewed with the waterfall expanded to the x2 factor.<br><br><div style="text-align: center;"><img style="width: 160px; height: 102px;" alt="" src="images/mfsk-9db-x2.png"></div></div></div><h3>MFSK Picture Mode</h3>Fldigi can send and receive images using all MFSK baud rates.
When operating with other modem programs you should limit sending
pictures to the MFSK-16 baud rate. The program
can send and receive MFSK images in both
black and white and in 24 bit color. The transmisssion mode for MFSKpic is similar to FAX.<br>
<br>
Reception of an MFSKpic transmission is fully automatic. The
MFSKpic transmission has a preamble sent which will be visible on the
text screen. The preamble reads as "Pic:WWWxHHH;" or
"Pic:WWWxHHHC;" for b/w or color respectively. The WWW and HHH
are numbers specifying the width and height of the picture in pixels.<br>
<br>
The successful reception of a MFSKpic is highly dependent on s/n
conditions. The data is transmitted as an FM modulated signal and
is subject to burst and phase noise on the transmission path. It
can provide excellent photo transmission on a really good path.<br>
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<td><img style="width: 210px; height: 212px; float: left;" alt="" src="images/mfskpix-bee.jpg" hspace="10"></td>
<td>This
is an example of a photo received on a bench test. The received
image is an exact replica of the transmitted image. The color
depth is a full 24 bits.<br>
<br>
Images should be carefully selected for size before beginning a
transmission. To calculate the transmit time for an image use the
following formula:<br>
<br>
Time(sec) = W * H / 1000 for black and white<br>
<br>
Time(sec) = W * H * 3 / 1000 for color<br>
<br>
where the W and H are the dimensions of the photo in pixels. A
200 x 200 image will take 120 seconds to transmit in color and 40
seconds to transmit in b/w. The symbol rate for this mode is 1000
data bytes per second. The color image consists of 3 bytes; red,
blue and green for each pixel.</td>
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<td><img style="width: 208px; height: 283px; float: left;" alt="" src="images/k0og.jpg" hspace="10"></td>
<td>This
is an example of a picture received live on 80 meters (thanks K0OG) </td>
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<br>
Received images are saved in the default folder
$HOME/.fldigi/images (Linux) or <defaultpath>/fldigi.files/images
(Windows).<br>
<h3>Transmitting an Image
</h3>
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<td style="text-align: center;"><img style="width: 300px; height: 210px;" alt="" src="images/Xmt-Pix.jpg"></td>
<td>You can only transmit an image while in the MFSK-16 mode. The
image can be prepared for transmission while in the receive mode.
Right click in the transmit text box and select "Send Image"
from the popup menu. This will open up the transmit image dialog which
will be blank to start.<br>
<br>
Press the "Load" button and a file selection dialog will allow you to
select a suitable image for transmit. The file selection dialog
also has a preview capability so you will see what the image looks like.<br><br>You may also open a window manager file browser and drag and drop an image to the center part of the <span style="font-style: italic;">Send image</span> dialog.<br><br>The "X1" button is a three-way toggle that allows you to transmit an image file in<br>X1 - normal and compatible with other modem programs<br>X2 - double speed, and<br>X4 - quadruple speed. X2 and X4 are fldigi specific image modes.</td>
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<td><img style="width: 300px; height: 210px;" alt="" src="images/Xmt-Pix1.jpg" hspace="10"></td>
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The Send image dialog after the image was drag and dropped onto the dialog.<br><br>
The properties box said this image was 120 x 119 24 bit
color.
So it should take 42.8 seconds to transmit in
full color. You can send a color or a b/w image in either color
mode or b/w mode. If you transmit a color image in b/w the
program will convert the image before transmiting. If you
transmit a b/w image as full color you are in effect transmitting
redundant information, but it can be done. I selected the
"XmtClr" button for a trial run. Pressing either the "XmtClr" or "XmtGry" will put the program and
the transceiver into the transmit mode if it was in the receive mode.
The image is cleared and then repainted as the transmission
proceeds. You see the same image progression that the receiving
station should see. The main display also displays the %
completion on the status bar. Hold the mouse over either the
XmtClr or the XmtGry button and the tooltip will tell you the transmit
time for this image.<br><br>
You may abort the transmission at any time by pressing the "Abort Xmt"
button. That will return you to the text mode for MFSK. You
will then have to toggle the T/R button if you want to return to
receive.</td>
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<td style="text-align: center;"><img style="width: 154px; height: 180px;" alt="" src="images/Xmt-Pix3.jpg" hspace="10"></td>
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The receiving program decodes the "Pic:110x119C;" as a color picture
110 wide by 119 high. Here is shown being received on a computer
running Vista Home Premium.<br>
<br><br>
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<td><img style="width: 357px; height: 117px;" alt="" src="images/Xmt-Pix4.jpg" hspace="10"></td>
<td>This is what the waterfall will look like during the reception of an MFSK-16 image.<br>
<br>
The
actual spectrum signature will vary with the image bytes being
transmitted. The waterfall scale is in the x4 mode and the above
photo was being transmitted in 24 bit color for this screenshot.
The waterfall clearly shows that the image transmission is within
the bandwidth occupied by MFSK-16.</td>
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<h3>Picture with a slant</h3>If either the send, receive or both ends
of the transmission are using an uncalibrated sound card whose sampling
rate is not an exact multiple of 8000 Hz the resulting picture at the
receive end will appear slanted. The degree of slant is directly
related to the accumulation of the frequency error at both ends of the
transfer. Stations wishing to send and receive MFSKpic's should
calibrate their sound card. The <a href="DigiWWV.html">WWV calibration mode</a> is used to measure and set the parts per million (ppm) correction factor for the sound card.<br><br>Your
sound system may be fully corrected, but the sending station may have
an uncorrected sound card. You can usually correct for small
errors in the following way. After the full picture is received
move the mouse to bottom left or right corner of the slanted images
(the corner that clearly visible). Then left click on that
corner. The program will correct for the slant. The
correction will not be perfect but it may help to make the image more
viewable.<br><br><div style="text-align: center;"><a style="font-weight: bold;" href="index.html">Contents</a><br>
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