You simply need to connect the audio output of your radio to your Mac’s audio input (this is thejack on the back, usually with a little microphone icon). A few models come with audio input cords, most don’t. Also, some models expect an actual microphone to be connected, and require a small adapter (usually included) to allow direct audio to be connected.
Also, you probably want to tap the audio from your radio’s headphone or external speaker jack, rather than a line level or “Record” output, which may be too low in amplitude.
Basic Operation...
The large buttons on the left side of the Signal Window select the mode of operation - CW, RTTY, FAX, etc. or one of the signal tuning aids.
The smaller buttons on the right hand side select various options for each mode, things like the baud rate, inversion, etc. As they are mode specific, the number of buttons and their use changes as you change decoding mode.
Two windows are displayed. One [usually] shows the audio input, so you can adjust tuning and volume levels. The other is the display of the decoded text or image. There are no provisions to print the text or image, although this will come in time.
The following sections describe operation for each mode. Please take the time to read the sections for the modes you’re interested in decoding.
One general tip - watch the audio volume levels. If the audio volume is too high, the audio can be clipped, which will cause lots of errors (garbage) to be displayed while decoding. So, if the decoding doesn’t seem to be working very well, try turning the volume on your radio down before you try turning it up!
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Morse Code
Morse Code
The audio from your radio is displayed in the Signal Window in an amplitude vs time basis. The audio is sampled in one half second chunks, which is evident in the update of this window. Four lines are also displayed - two horizontal and two vertical.
The two horizontal lines are the thresholds for detecting a signal. The ambient noise level should be below the bottom line, the code signal should be above the upper line. The more separation between the two, the better. Adjust your radio's volume and tuning accordingly. The program's audio filter is centered for 750 Hz. When receiving CW, your radio’s AGC should of course be turned off.
The two vertical lines move to show where new data is being placed, and where data is being read. There is a buffer in the area between the two lines. If the speed of the received code is too slow, so that dashes (or even dots) exceed the width of this buffer, you may have decoding problems.
Several buttons are available in this mode. The seven three allow you to select the receive speed, either 5, 7, 10, 13, 16, 20, 26, or 34 wpm. The next button (with the question mark '?') allows you to have the program automatically select the speed, based on previous audio captured. The program defaults to 13 wpm.
The button with the red X clears the speed buffer. This should be used when you've tuned in a new station, or the station has changed speed, or a lot of noise/static was received. Use this button if the program seems to select erroneous speeds.
The last button (Auto) sets the auto-speed mode, where Multimode will periodically check the received speed, and make the necessary changes.
There is a text window where the decoded text is displayed. You will notice a slight delay between when each character is received, and when it is actually displayed. This is normal. Presently, a character isn't displayed until the next one is received, which means that the last character of a message may never get printed; this will be fixed.
The spectrum display mode is very handy to use when trying to tune in a station.
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Weather Fax
Weather Fax
6. Fax Mode:
Fax mode is commonly used to decode weather maps, this is also referred to as HFFAX mode. It is also possible to decode pictures directly from weather satellites. Since this two modes use different modulation methods, it is necessary to select which mode should be decoded. Two buttons, called HF and SAT, select the mode. Satellite mode has recently been added, so I would be interested in reports of how well this mode works.
Next, the correct speed must be selected. The speed is measured in lines per minute (LPM), and possible selections are 60, 90, 120, 240 LPM. For HFFAX, 120 LPM is almost always used, and for satellites, 240 is always used.
Finally, you may select whether to display gray scale, or line mode (black and white). Gray scale should be used for satellite images (which are also sent via HFFAX stations) and other images where shades of gray are sent. Line mode is useful when weather maps are sent that have no shading information. It is possible to display these in gray mode, but improper tuning and noise may affect the picture quality. In these cases, line mode provides a better image quality.
There is also an AUTO mode, this attempts to use the phasing and start/stop tones sent by HFFAX stations to properly synchronize to the fax signal. This mode has just been added, and may still need some work, but please give it a try.
To assist in correctly tuning in a fax station, a tuning display is available, located in the information window near the buttons. This displays a spectrum of the received signal. Two small tick marks appear on the bottom of this display, the one on the left represents the audio tone for black, the one on the right for white. A typical fax consists mostly of white. So, you can quickly tune in the station by aligning the peak tone (representing white) to the right mark. If the fax also contains a lot of black, you’ll see a second (usually shorter) peak over the left mark.
When you start decoding in fax mode, a window (titled Fax Window appropriately enough) appears, showing the decoded fax document in real time. Proper tuning of your receiver is necessary to correctly decode and view the fax. If the image appears negative (white on black) try changing from USB to LSB or vice-versa. I've found that you need to very carefully tune the radio, to achieve proper reception. Note that proper tuning for FAX decoding may NOT mean tuning your radio to the actual frequency of the station, some offset may be necessary.
Chances are, when you start to decode a fax, you won't be correctly aligned in the horizontal direction. Pressing the << or >> button (located in the lower left corner of the fax display window) will slightly shift the decoding to the left or the right.
If you find that the picture is slanted, then the Timing Delta in the General window of the Preferences will have to be adjusted. This can be done manually, or with the Calibration mode. If you wish to do it manually, then here’s the procedure: If you find that vertical lines slant to the left as they go down, then the Timing Delta must be made more negative. If vertical lines slant to the right as they go down, then the Timing Delta must be made more positive.
When you reach the bottom of the window, no new image information is displayed. You can click the clear button to clear the display, and start decoding new information at top of the display..
It is possible to scroll around the fax window using the scroll bars. The fax window size may also be changed to suit your display. It may be possible to screw up alignment on a slower computer by moving around too much, this was a problem with the 680x0 version. (presumably because too much time is spent sloshing pixels around).
Please note that if insufficient memory is available, the maximum number of shades displayed will be decreased, with only black and white possible as the worst case. Less memory than that will probably cause a crash!
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RTTY
RTTY
Baudot is the standard mode for transmitting teletype ofver shortwave radio. It uses a 5 bit code, which only allows for 32 symbol total, obviously not enough for all the letters, digits, and punctuation. Therefore, two special characters may be transmitted - letters shift (LTRS) and figures shift (FIGS). These two modes determine which character will actually be printed when a 5 bit symbol is received.
Tuning:
While in the Spectrum Display mode, tune your radio so that two spikes are visible, representing the mark and space tones. You want to mark tone (the lower frequency) to be centered as close to 1900 Hz as possible. Then take a note of the frequency of the space tone. The difference in frequency between the mark and space tones is referred to as the shift.
Go to the Baudot mode, and select the correct shift frequency (the 170, 250, 450, 600, 850 buttons). Select the closest shift if the station’s shift is not exactly one of the available values.
When properly tuned, the mark/space tones are represented by black and white pulses. Gray means the audio tone is neither a mark or space. If you see gray mixed in (or all gray), then either the station isn’t properly tuned in, or the shift isn’t correct.
Select the combination of speed and polarity (Normal or Inverted) for proper display of decoded text.
The various buttons in the Signal Window perform the following operations:
The 170, 250, 450, 600, 850 buttons select the shift frequency.
The 45, 50, 56, 75, 100, and 150 buttons select the baud rate.
The N button selects Normal shift, the I button selects Inverted shift.
The ABC button acts as an LTRS shift, and will return the program to letters mode, from figures mode. Very useful if a burst of noise shifts the program into numbers mode.
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SITOR-A
SITOR-A
SITOR-A mode sounds very distinctive, with a chirping sound. In this mode, three characters are transmitted at a time. The receiving station then sends one character back, indicating whether or not the three characters were correctly received. If not, they are re-transmitted. Each cycle takes 450 milliseconds, so you hear two “chirps” per second.
You will notice two types of chirps are heard, one longer than the other. The longer chirp is the data, the shorter chirp is the acknowledgement from the receiving station. Often, you may only be able to hear one of the stations from your location. You must be able to hear the longer chirp to decode data.
The BAD or OK lamp will flash as each packet is received. This can help in properly tuning in the station. Only SITOR-A is supported at this time, Mode for SITOR-B (FEC) will eventually be added. When you can only hear the receiving station transmitting the ACK/NAK symbols (a shorter chirp sound), the OK lamp will flash BLUE, to indicate that something is being received, although it cannot be decoded.
You'll notice that three colors are displayed in the signal window - black, white, and gray. The black and white colors represent valid mark/space tones being received, the gray means neither tone is present. Normally you'll see a burst of white/black bits, surrounded by gray. When you first tune in a SITOR-A station, it may take MultiMode a few seconds to properly synchronize on the signal.
The spectrum display mode is very handy to use when trying to tune in a station.
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SITOR-B FEC
SITOR-B FEC
This mode can be used to monitor FEC and NAVTEX transmissions at 100 baud.
NAVTEX transmissions may be found on 518 kHz.
There are three indicators, marked PHASE, BAD, and OK.
The PHASE indicator will light up blue when phasing signals are being received. These are typically sent at the beginning and end of transmissions, and during transmissions as filler.
The BAD OK indicator will light up red when garbled or invalid characters are being received.
The OK indicator will light up green when valid characters are being received.
When first tuning in a station, the BAD indicator will light up, until the reception is synchronized with the transmission. It may also light up during reception, if the lock on the signal is lost.
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ACARS
ACARS
ACARS is the acronym for Aircraft Communications Addressing and Reporting
System. It is a data transmission between airplanes and ground stations. The purpose is to handle many types of traffic that would normally be done by voice in the past. ACARS transmissions are on VHF. The following frequencies are commonly used:
129.125 MHz
130.025 MHz
130.450 MHz
131.475 Mhz
131.550 MHz
As with all other VHF-Aeronautical transmissions, AM mode is used. Most scanners automatically change to AM mode when tuning the 108-136 MHz aircraft band, but you may want to verify your scanner does this.
The transmissions sound like data bursts ranging from about 0.2 second to 1 second in length. Due to the high altitude of aircraft, transmissions from aircraft may be monitored for several hundred miles. Those living close to airports may also hear the ground transmissions sent to aircraft.
Tuning in ACARS transmissions is fairly easy - just select ACARS mode and adjust the radio’s volume for proper decoding. Please note - it is very important to have the squelch of your radio completely off, that is, so you always hear the background static. The squelch action of any radio is too slow, and you’ll miss the packet!
You will find that many transmissions are garbled or not decoded. This is a very difficult mode to demodulate without external hardware, so good reception quality and strong signals are required.
MultiMode displays the transmitted packet, and parses out some of the information, such as the plane’s wing number, flight number, etc. It does not attempt to parse out other specific information in the text portion of the packet, which is displayed on the second line. A timestamp is also displayed on the first line.
Here is an example of a received ACARS transmission:
.N227AA 5Z 2 [13 Sep 97 20:57:06]
5651 AA0742 OS LGA /ALT00000122
N227AA is the aircraft registration, note the leading periods, to force it to 7 characters.
5Z is the message type
2 is the downlink block identifier
[13 Sep 97 20:56:51] is the date and time, added by MultiMode
5651 is the message sequence, minutes and seconds past the hour
AA0742 is the carrier and flight number (American Airlines flight 742)
OS LGA /ALT00000122 is the text message sent, for those modes which include a message
There is an LED type indicator under called PACKET in the Signal Window which lights up green when a good ACARS packet is received, and red if a packet is received but it is bad. In addition, statistics are displayed for the number of good and bad packets received, along with the percentage of good packets. This is useful for adjusting your radio setup, obviously you want to maximize the percentage of packets which are good.
You may create a file called ACARS.LST, which is a listing of plane registration numbers, along with text that you may enter. This file is read in when MultiMode first starts up, and must be located in the same folder as the MultiMode application. When a packet is decoded, the plane registration number is compared to the registration numbers of the planes in the ACARS.LST file. If a match is found, the text from that line of the file is displayed after the timestamp. You may use this file to display text or comments about each aircraft.
An example of the file format follows below:
.N814US This is plane number 1
.N320US This is plane number 2
.NIM5AA This is plane number 3
.N781NC This is plane number 4
.N609AA This is plane number 5
Note that the first 7 characters of each line are the plane registration number, followed by a space. The rest of the line contains the text to be displayed. Leading periods are required to force the registration number to be seven characters long.
If you are not interested in using the ACARS.LST file, you may simply remove it from the MultiMode folder.
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Calibration
Calibration
This mode is used to calibrate MultiMode to the particular timing of your computer. Each computer runs at a slightly different speed, which means that the audio sampling may not be exactly the correct value. Any error in sampling will cause FAX and SSTV images to be skewed and distorted. You only need to calibrate MultiMode once for your machine, the calibration is saved in your MultiMode preferences file.
The easiest way to calibrate is to tune into WWV or WWVH, the standard time stations, which transmit on 2.5, 5, 10, 15, and 20 MHz. (Users outside of North America can use whatever time stations are audible in their region)
This mode draws a new horizontal line on the screen every second. The second pips from the time station should be displayed as a black dot on each line. There may also be some extraneous small dots due to noise or other audio. These black dots should start to form a vertical line. If the computer’s timing is correct, this line should be perfectly vertical. (There are a series of gray vertical lines spaced across the page to help you determine if the black line is indeed vertical)
If the line is slanted one way or the other, you should use the + and - keys on your keyboard to adjust the timing offset, which is displayed as the Delta in the calibration window. Each press of the + or - key will increment or decrement Delta by 0.1. Holding down the option key while you press + or - will increment or decrement by 1.0, to speed things up.
After finding the correct Delta for your machine, select Preferences from the Edit menu. In the box for Timing Delta, under General settings, there should be a number equal to the Delta from the Signal Window. Click the OK button, and the Delta will be saved in your preferences file, so that it is automatically loaded the next time you use MultiMode.
You may want to record the Delta for your machine, so that in case you should lose your Preferences file, you can simply re-enter it, rather than going through the calibration procedure again.
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Registering MultiMode
Registering MultiMode
MultiMode is shareware. Please read the enclosed documentation for complete details on how to register your copy, and receive a License file.
By registering your copy of MultiMode, you’ll help support my efforts to develop newer versions, which will further increase the number of modes which can be monitored, and the features available. I’d like to be able to continue developing new versions of MultiMode, so that we Mac users won’t be forced to abandon the Macintosh for the wintel platform.
