User guide

MS-DMT Guide v1.04

Released 05-30-2014

The sound device characteristics will determine its usefulness as a PC Sound Device Modem for

use with the software due to the complex 110A waveform and its constant 2400 baud symbol

rate, decoding 110A and similar waveforms planned to be supported by the software. An

accurate and stable sample rate is critical for accurate Digital Signal Processing (DSP).

Differences in sample clocks between stations, thermal clock drift and latency will lead to

decoding errors and loss of synchronization. Never have any external PC Sound Device Modem

resting on top of equipments that heat and or cool and never have them in direct sun light, a

stable thermal environment means less drift.

The following categories of sound device solutions will support different maximum reliable data

rate operation with the range the specified channel conditions performance requirements of the

standards as follows:

 On-the-Board sound device chipsets can often provide reliable support of 75bps to

600bps for 110A class waveform data rates at most due to noise floor and deterministic

phase jitter. Interfaces and cabling between the PC and radio are often susceptible to RF

interference and are also often sources of EMI. In addition their sample clocks are often

poor as to accuracy which is very noticeable at the lower data rates, especially 75bps. If

using an On-the-Board device and it is the only sound device in the PC, then System

Sounds MUST be disabled, which is SOP for all such device use in MARS digital comms

and an absolute requirement with this tool.

 Plug-In (e.g. PCI card, PCMCIA CardBus Type II) sound devices can support 75bps to

600bps and often 1200bps for 110A class waveform data rates reliably. In some cases

2400bps may be found reliable. These devices have somewhat less noise and phase

jitter than on-the-board devices. Interfaces and cabling between the PC and radio are

often susceptible to RF interference and are often sources of EMI.

 Outboard sound devices (e.g. USB port (without built in hub) and IEEE 1394 (FireWire)

sound devices) offer the lower noise and lower phase jitter than most internal devices.

However USB devices do suffer from additional USB port latency issues. Be sure the USB

sound device is on its own PC USB port, never go through a hub. Use a high speed USB

2.0 or higher port (USB 3.0 and eSATA/USB combo ports) and using short, double

shielded USB cables also reduce any USB audio latency. According to Listen Inc., Firewire

audio devices appear to have a problem with computers that use NEC or Agere Firewire

chipsets, where Texas Instruments chipsets are preferred and Toshiba chipsets are

found to work well. Radio communications interfaces with sound devices and the

manufacturers cabling (e.g. US Navigator, Signalink-USB) designed specifically for use