ROS User's Guide 2.0 (English).pdf
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User's Guide v2.0
15 April 2010
Copyright
©
2009, 2010
by
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.
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SSB transceiver connected to an antenna.
•
PC with Windows™ Operating System.
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A minimum 600MHz CPU with 128MB RAM.
•
Monitor with resolution 1024x768 or 1024x600
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16 bit Sound Card.
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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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