Using ComTekk Multi Decoder


1. Running MultiDecoder

2. GUI Controls

3. Setup Window

4. Windows Mixer

5. Calibration

6. Log File

7. Log Viewer



1. Running ComTekk Multi Decoder

First-time users must enter their user registration information to enable the software. This will be sent via email after purchase is made. Due to it's nature, there is no free trial period available.

Once ComTekk Multi Decoder has been successfully installed, you may simply double-click the MultiDecoder desktop icon or Click the Windows Start menu, then Programs, choose the ComTekk folder, then MultiDecoder.

To control MultiDecoder:

  1. To run the program, click the desktop icon or go to Start->Programs->ComTekk->Multi Decoder .
  2. The top dot-matrix display indicates the current program status. A green "Ready" shows the decoder is running and listening for tones. VU meter indicates the presence of audio.
  3. Click the "POWER" button or "X" button in the upper-right corner of the window to close the application completely.

Continue on to Section 2 below for detailed description of the buttons and screens.




2. The MultiDecoder User Interface




1. POWER - Close / Exit the program

2. Hold - Stops the decoder and freezes the current display(s), allowing time to write down frequencies before another tone-out is decoded.

3. Clear - Clears the display(s)

4. Replay - If enabled, this button will replay the last recorded tone-out. WAV recording must be enabled in Settings. Button will be enabled after the first recording is complete.

5. Stop - Stops playback.

6. Tones: Standard/Measured - Frequencies may be displayed as Standard or Measured. Click appropriate button to select. See Decoder Settings for more info. When using Standard mode and a non-standard tone is detected, it will be displayed in RED. Measured mode will display the actual frequency as decoded, which may be slightly different from the standard tone. This mode is useful when troubleshooting or trying to determine non-standard tones.

7. Squelch - sets the relative signal level detection threshold, so background noise or weak signals can be rejected. The default setting should work for most applications.

8. Setup - Opens the program Settings window (preferences).

9. Help - Opens the User Manual (this file)

10. About -Opens the program information screen, and Product Registration.

11. View Log - Opens the current log file for viewing using the Windows default viewer. CSV Log File must be enabled in Settings.


1. VU Meter - Analog meter display gives an easy-to-read indication of relative audio input level. This is handy for setting receiver and software volume controls. The level should be somewhere in the mid-range when radio traffic is being received.
If there is no indication on the VU meter, it is likely the wrong input is selected, or level is too low. See Setup section below.

2. Mode Display - The top-most dot-matrix display gives the current program status, such as "Ready", "Calibrating", "Decoding".

3. Data Displays - The two lower dot-matrix displays on the left give the tone frequencies decoded and calibration details. Control these with the "Hold" and "Clear" buttons. The bottom display is for the 2nd tone.

4. Status Bar - Located at the very bottom of the program window, gives additional information such as file names, recording & logging status, etc.

5. REC - Audio recording indicator, glows red while recording is active.

6. CTCSS - When detected, indicates the sub-audible tone frequency.

7. DTMF - Displays decoded DTMF digits.

8. DCS - Displays decoded Digital Code Squelch if detected. Requires a receiver with discriminator (unfiltered) output - It is not possible to decode DCS from the audio/speaker output on most scanners! Google search "discriminator tap" for more information.




3. Settings Window


Audio Tab :

1. Audio Input Device - Select the input (recording) device [Windows Vista/7], or sound card [XP, NT, 2000, 98] to be used as the audio source. Click the button at right to modify this setting

2. Mixer - Opens the Windows Recording Control [XP, NT, 2000, 98], or Recording Device properties [Vista/7] to set the default recording device and input level.

3. Pre-recording buffer - Use this feature to start recording audio BEFORE tones are decoded. When set to zero, recording will start immediatly after tones are decoded.

4. Lockout long tones - Any tone frequencies entered here will be displayed, but not logged or recorded. This is handy for filtering out CW (Morse Code) ID's and certain other unwanted tones.. Separate multiple entries with a space and/or comma.

5. Close - Closes the Settings Window. All settings are saved when program is exited.



Decoder Tab:

1. 2-Tone Trigger Time up/down - Sets the minimum tone duration to be decoded. Enables filtering of unwanted short duration tones, such as voice, ANI or FSK signals.

The most common 2-tone format is 1.0 seconds for the 1st tone, and 3.0 seconds for the 2nd tone. A trigger time of 600 mS is ideal for this format. If using a scanning radio, set the unit on MANUAL. When in SCAN mode, the first part of a transmission is often cut off, preventing the decoder from capturing the first tone.

2. Min. Decode Frequency - Any tones below this frequency (such as CTCSS) will be ignored by the 2-tone decoder. CTCSS tones will always be displayed in the appropriate box.

3. Single-Tone Trigger Time up/down - Sets the minimum tone duration to be decoded [in seconds]. Single-tone alerts are typically 5-8 seconds in duration.

4. Use Standard Tone Set - When using the 2-tone decoder in Standard mode, the decoder will select the nearest standard tone frequencies from the selected Tone Set. Motorola (Quick-Call II) is by far the most common. Also available are Plectron and Reach/Zetron.

5. Noise Detection - Improves tone detection by ignoring voice and other signals with a high noise level. If your are having difficulty decoding tones on a weak noisy channel, try disabling this feature.

6. DTMF Enable - Enable/disable DTMF decoding.

7. Min. digit ON - Minimum DTMF digit duration in milli-seconds. Shorter tones will be ignored. DTMF ANI (unit ID) tones are usually 40-60mS in duration.

8. Max. string duration - this is a timer that serves several functions: a) tells the program when it's ok to start a new string (clears the display); b) Logs the DTMF string (sequence) if DTMF logging enabled; c) Activates the relay control if enabled; and d) starts audio recording if enabled (below).

If display is being cleared in the middle of a DTMF string, the setting is too short. If new DTMF digits are being added to the previously received string, the setting is too long. The default setting is 5 seconds. An ANI string is usually less than 1 second long.

9. Restore Defaults - resets decoder duration times to recommended settings.

Logging Tab:

Dispatch Logging:

1. CSV Log File - Name of the log file, stored in "Comma-Separated Values" format, which is compatible with Microsoft Excel, and others. Click the checkbox to enable or disable logging.

2. Log/WAV Folder - Destination folder where log files and audio recordings will be stored. A dedicated folder is highly recommended. To change this folder, uncheck then check the CSV Log File box.

3. Log DTMF strings - When checked and logging enabled, DTMF codes will be saved to the log file.

4. Min. DTMF string size - Determines minimum number of DTMF digits that will be considered a valid string. Most ANI strings for example, are at least 3 digits. If minimum is not met within Min. string duration time (see #8 above), the digits will not be logged and relay will not be activated.

5. Log CTCSS/DCS with tones - When checked and logging enabled, CTCSS tone frequencies will be saved to the log file whenever a valid 1-tone, 2-tone or DTMF string is decoded and logged.

6. Log ALL CTCSS / DCS - This option will force logging of any analog or digital squelch codes received.

NOTE: DCS decoding requires a receiver with discriminator (unfiltered) output - It is not possible to decode DCS from the audio/speaker output on most scanners! Google search "discriminator tap" for more information.



1. WAV Recording - When box is checked, enables audio recording of decoded radio calls. WAV files will be stored in the Log/WAV Folder selected above.

2. Record Time - Duration of audio recording [in seconds], starts immediately after the last tone is decoded, or in the case of DTMF, after Max. string duration time (see Decoder tab above).

3. Delay between recordings - Prevents recording duplicate or repeated tone-outs, which are often sent twice as a policy.

4. Record on DTMF - Activates recording whenever a valid DTMF string is received (see Decoder description above for more).



Calibration Tab:

1. Auto-Calibrate - Calibration is not required, and in most cases not necessary. This step need only be performed once, unless you change to a different sound card. See calibration section below.

2. Cal Factor - Resulting time-base correction multiplier after calibration is complete. A value of 1.0 is default, uncalibrated.

3. Reset - Returns calibration to the default uncalibrated state.



Relay Control Tab:

This feature may be used to activate a light, bell, door or other electrical device whenever ANY tones are decoded. It may also used in conjuction with ComTekk Radio Interface to act as a repeater, retransmitting audio when a tone-out is decoded.

An external serial (RS-232) or USB relay adaptor is required to utilize this feature.

1. Control Port - feature is enabled when a valid serial port is selected (COM1 ~ COM64 supported). If selected port is not available, drop-down will return to the <OFF> position.

2. Control Pin - Select DTR (pin-4) or RTS (pin-7) control pin.

RS-232 pins
Standard DB-9 serial connections as seen on the back of a computer

3. Active State - determines whether the pin's voltage when activated by the decoder. Select High for positive voltage (+) or Low for negative (-).

4. Hold Time - the time in seconds that the serial pin will remain active. If set to 10 seconds and relay is connected to a bell, the bell will ring for 10 seconds every time tones are successfully decoded.

5. Test button - Click and hold to cause selected serial port/pin to be activated. Release mouse button to deactivate.

6. Activate on DTMF - When checked, the relay will activate after a DTMF string has been received, delayed by Max. string length Decoder setting. Relay will still be activated on any single or 2-tone signal as well.


NOTE: Always use an isolated external circuit to protect computer from possible damage.




4. Windows Mixer Controls


Windows Volume Control (Output): [Windows 95, 98, NT, XP, 2000, ME] - scroll down for 7/Vista.

This screen controls the sound card OUTPUTS and will generally have no effect on the decoder, since it uses the sound card INPUTS, which are controlled by the Recording Control (see next section below).

Windows Playback Control


Windows Vista/7 playback [output] settings, accessible from Windows Control Panel


Click "Properties" then select the "Levels" tab for output mixer controls. Again, these controls will have NO effect on the decoder's operation:



The Windows Recording Control [Windows 95, 98, NT, XP, 2000, ME] - affects sound device INPUTS, such as LINE , AUX, Wave, or Microphone. Vista users, scroll down.

To access Recording controls, click the Mixer button in the Settings window, or with a double-click on the speaker icon in your system tray. Select "Options" from the menu, then "Properties." Click the "Recording" radio button. Be sure the appropriate input item is checked. Settings will be saved on closing this window.

It is very important to have the correct input device enabled, otherwise the decoder will not function.

Windows Recording Control


For Windows Vista/7 users, click the Mixer button in the Settings window. Line In is selected in the example below.



Click "Properties" then select the "Levels" tab for Line In level control. This sets the audio level sent to the Tone Decoder. Adjust this level while there is activity on the receiver. Monitor the decoder's VU meter, and set for a mid-range indication.


Additionally, the program may be given exclusive control of the selected device by checking the box below. This prevents the user from accidentally changing settings for this device. While not required, this option may be helpful in some situations.



5. Calibration


NOTE: Calibration is NOT required, but may improve results in some cases

Computer sound cards vary greatly in quality and design. They have their own time-base which controls the A/D and D/A sampling rate, which in turn directly affects the frequency. The calibration routine allows for compensation for timebase error, thus allowing more accurate frequency decoding.

ComTekk MultiDecoder includes auto-calibration, which does not require any specialized equipment. However, a FULL-DUPLEX sound card is required. This means the card has the ability to play and record simultaneously. Virtually all modern sound cards are full duplex.

NOTE: Calibration need only be performed once for a particular sound card.



1. Loop the sound card OUTPUT back to its INPUT. Three different ways to do this are presented below:

Cable loopback method
Option1: [above] Use a 1/8" stereo cable to connect
Line/Speaker OUT to Line/Aux/Mic IN.


Option 2: Click the "Vol" button to open the Windows Recording Control. Select the "Wave Out Mix" (or similar) checkbox to create an internal loopback. Not all sound card drivers have this option. If available, it negates the need for an external connection.


Option 3: Audio pickup - If you have a microphone connected to (or internal to) your computer, Click the "Vol" button to open the Windows Recording Control. Select the "Microphone" checkbox to enable the MIC input. Place the microphone directly in front of a computer speaker so it will pick up the sound from the tone generator. Take care not to get it too close which will generate feedback, voiding the calibration.


2. Once the loopback is established using one of the methods described above, Click the "Calibrate" button to begin.

Calibration Screen

If using speakers and loopback is working, you should hear a very short tone. The Status will change to "Calibrated" and the frequency and calibration factor will be displayed. The VU meter will indicate relative INPUT level. It may be necessary to adjust input or output levels, or the microphone position if using Option 3 for loopback.

The measured frequency should be somewhere close to 1,000 Hz. If it is closer to 2,000 Hz, the volume and/or input level is most likely too high.

If the calibration tone was not detected, this will be indicated on the "Status" line. Make adjustments and click "Calibrate" to try again. It may be necessary to attempt a different loopback method if you can't get it to work after several tries.

6. Log File

To enable the text log feature, click the "Log File" checkbox. The Open File dialog will pop up - select a new file name and folder, OR select an existing file to append a previous log. You will be prompted whether to append the file.

To stop/disable logging, just click to un-check the "Log File" checkbox. For convenience, the last folder used is saved upon closing the program.

The log file is a text file, saved in .CSV (Comma Separated Value) format, which can easily be viewed and edited with Microsoft Excel, or any text editor, such as Notepad or WordPad. This program includes a built-in viewer and audio player for convenience (see next section below).

Tip: If you don't have MS Excel, CSView is available as a free download.

Each decoded tone or pair is saved with a date, time, and tone frequencies in Hertz (Hz). If logging single-tone entries, the "Tone2" field will contain a zero "0" value. The last field contains the WAV file name/path if audio recording has been enabled. DTMF strings will be save as "DTMF" in the Tone1 field, and the actual digit string in the Tone2 field.

To view the log file while running MultiDecoder, simply click the "View Log" button.



7. Log Viewer

To view the current log file, click the View Log button on the main screen. If log file is not found, a file open dialog will appear which will allow you to browse to open the desired file. The file name and path will be displayed at the bottom of the LogView window.

Log entries with an associated WAV file will be displayed in the last (right) column. Double-click on the entry row to play the audio file.

Use the HOME and END keys to navigate to beginning and end of log view. Use arrow keys or scroll bar / mouse wheel to move up/down.

The decoder will continue to function while the viewer is open. Use the Refresh button to reload the log file and list any new entries.