ROS User's Guide 2.0 (English).pdf

User's Guide v2.0

15 April 2010

José Alberto Nieto Ros

nietoros@hotmail.com

Translated to English by Al Gallo VK4LOW

Introduction

ROS is a keyboard-to-keyboard digital communications software whose purpose is

to optimise HF, Moon Bounce or Meteor Scatter communications. It uses a very

simple human interface made up of two operation modes: ROS HF and ROS EME.

ROSHF. The HF (3-30Mz) communications systems achieve their transmissions

trans-horizon using the ionosphere as a natural reflector to produce a global

coverage in one or several skips. It's important to take into account the HF channel

characteristics to understand the solution adopted in the ROS HF system. On the

one hand, in HF a multipath effect is produced (the signal is reflected in several

layers of the ionosphere), and o the other hand the channel suffers a time change

(the ionosphere is a natural, dynamic medium, highly dependent on solar activity).

This justifies why the crisscrossing plays such an important role in the conventional

systems and why the long delays have been accepted as unavoidable in these

applications.

• The multipath effect involves temporal dispersion of the transmitted energy

and represents an interference phenomenon between symbols, which

makes the channel's equalization process a very complex and critical task

within the receiver, limiting the system's functions.

• The channel's temporal variability entails complete signal fadings perceived

by the radio amateur as connection loss.

• In conventional systems, the crisscrossing breaks the error bursts produced

by the combined effect of both factors, helping the decoding process to

function adequately. For this to be effective, these crisscrossings must be

very large, creating considerable delays in the system.

The alternative developed for ROS HF is based on the CDMA type modulation.

This isn't actually “Spread Spectrum” because the 3khz HF standard channel is

maintained, but rather the transmission of crisscrossed symbols along the full

available bandwidth, crisscrossing the symbols along the time as well. This allows

dealing with an adverse channel situation when some frequencies cancel or

disappear. In this case the symbols can be recovered through a suitable

information reconstruction procedure.

ROS HF has three symbol baud rates: 16, 8 and 1.The last one is most suitable to

detect extremely weak signals in HF.

The coding system is popularly known as convolutional code R=1/2, K=7 NASA

Standard.

Another innovation of this software is that it can automatically detect transmissions

at 16, 8 and 1 baud indiscriminately, allowing the change of symbol rate according

to propagation conditions and without the need to previously inform our contact.

ROS EME is a mode designed for Moon Bounce communications. The

communication channel in this modality is quite different from that of HF, and the

frequency diversity systems don't provide any significant advantage. That's why

the modulation system used is the classic 16-tone MFSK. To ensure a better

orthogonality the tones have been separated by 4Hz, a more than sufficient

amount, to achieve a 64Hz bandwidth.

The slender bandwidth required by this modulation allows us to perform automatic

frequency scanning of up to ±1300Hz, very useful to detect Doppler shift when

working Moon Bounce on 70cm.

The symbol rate is 1 baud, being a mode that also decodes in real time, allowing

the asynchronous Moon Bounce communication as well. It can decode signals of

up to –35dBs over noise AWGN.

In addition, ROS EME uses an initial synchronism sequence that allows detecting

the received signal's Doppler shift and subsequently starting to decode in real time.

ROS HF, as well as ROS EME use as FEC the popular convolutional code R=1/2,

K=7 NASA Standard.

This software sends automatically reports to the operators who include their email

address in any of their messages. The reports include reception conditions and

information about the receiving station. More details on this manual.

Hardware and Software requirements.

• SSB transceiver connected to an antenna.

• PC with Windows™ Operating System.

• A minimum 600MHz CPU with 128MB RAM.

• Monitor with resolution 1024x768 or 1024x600

• 16 bit Sound Card.

• Interface to toggle the transmitting station's PTT.

Installation

Before opening ROS for the first time it's necessary to execute the file install.exe.

The latest ROS version can be downloaded from http://rosmodem.wordpress.com/

Main window:

Operation protocols

There are two operation protocols in the ROS mode; one for 16 and 8 baud and

the other for 1 baud.

Protocol for 16 and 8 baud

In this case the nomenclature is similar to other digital modes such as PSK31,

MFSK, RTTY, etc. Most of the buttons will appear familiar.

We will highlight some innovations:

This button inserts your email address between the two special

characters “<” and “>”. This way, all the operators who are listening will send an

automatic reception report to the email address you inserted in the message.

The report includes the message such as it has been received, with data related to

the operator who has copied the signal's telemetry.

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