Amplitude Modulation - Single Sideband Radios in V+

V+ Visual Programming SystemUsing the latest features of VCOMM+, AM SSB (Amplitude Modulated Single Sideband) is now significantly more realistic than previously possible.  Most military HF radios use AM SSB for the modulation scheme.  Tuning these radios to receive a signal when the exact transmitting frequency is not known requires some practice since the incoming signal is garbled as you tune across the incoming frequency.  This is caused by the nature of the modulation, but manifests itself as the equivalent of pitch shifting the incoming signal as well as a number of other anomalies.

The new AM SSB feature in VCOMM+ coupled with SimPhonics V+ software enables the user to create realistic SSB DIS/HLA radios.  This is made possible using DirectX and Windows XP, allowing the incoming audio stream to be pitch shifted in real-time and mixed with a sine wave along with other effects before the stream is sent to the SMx or other sound card channel.

AM SSB Effects Simulation

SSB is simulated as a modulated version of the original received signal.  First, the amplitude of the modulation is determined by using the transmitted frequency and transmitted bandwidth to verify the receiving radio is within the bandwidth. If the receiving radio is tuned within the transmitted bandwidth, an appropriate attenuation factor will be calculated based on the 3dB bandwidth parameter sent by the transmitter. If the receiver is tuned outside the bandwidth, no signal will be received.



The SSB.wav audio clip is an actual recording of SimPhonics new SSB DIS/HLA radio tuned slightly off frequency.

Double click SSB.wav to listen to the WAV file.

AM SSB effects are available in V+ Build 210 or higher

When the receiver is tuned within the transmitter bandwidth, the model then calculates the frequency difference between the transmitter and the receiver.  If both frequencies are the same (difference = 0), then the signal will be heard in its original form (un-modulated).  If there is a frequency difference, the received signal will be modulated by a sine wave whose frequency is equal to the difference between the transmitter and receiver tuned frequencies.

Enabling AM SSB simulation

AM SSB effects are available in V+ build numbers 210 or greater.  (VCOMM+ software builds 100 and higher)  The AM SSB effects are only available on radios that were created with a system type of SYS_GENERIC. For both the transmitting and receiving radios, the modulation must be set as follows:

  • MM_AMPLITUDE (enum value = 1)

  • AM_LSB (enum value = 6),

  • or AM_SSB_FULL (enum value = 7),

  • or AM_SSB_REDUC (enum value = 8),

  • or AM_USB (enum value = 9)

Assume a transmitting radio is set to:

  • Tuned Frequency = 2.6 MHz

  • Bandwidth = 1 KHz

  • Major Modulation = 1 (MM_AMPLITUDE)

  • Detail Modulation = 7 (AM_SSB_FULL)

and a similar receiving radio is set to:

  • Tuned Frequency = 2.6002 MHz

  • Bandwidth = 1 KHz

  • Major Modulation = 1 (MM_AMPLITUDE)

  • Detail Modulation = 7 (AM_SSB_FULL)

The resulting received audio signal will be modulated by a 200Hz sine wave resulting in a pitch-shifted, garbled signal. The received audio will also be slightly attenuated due to the fact that the tuned frequency is not in the center of the pass band.

The following V+ screen shot shows a SSB radio setup for generic use, using either an off-the–shelf sound card, or SimPhonics SMx system. 


Note the object in the top right corner.  This is the object that sets up the additional modulation parameters for the radio that distinguishes it from a standard generic DIS/HLA radio.

This sample worksheet can be downloaded from SimPhonics web site at:

Listening to the Tuning Effect

Using two computers running Windows XP or Windows 2000 and a suitable sound card on both machines (or use SimPhonics SMx system) set up this worksheet mentioned above on both computers.  Use the constant on the R PTT input pin as shown below for Push-To-Talk.  (You can connect this to hardware via one of SimPhonics I/O devices)  Tune one computer’s radio 100 Hz or so from the other, and listen to the effect.  This tuning effect works in real-time as you tune through the incoming signal.



Native Platform

I/O Devices

OS Compatibilities

Windows NT, 98-2000 & XP compatibilities


Amplitude Modulation

single sideband radios in V+


documents, software, V+ and WAV files

Sample V+ Designs

learn how V+ designs are used in a Beech 1900D simulator



related topics

learn more about V+ and related products



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