can we expect from a HF propagation model ?
among the many ionospheric effects altering radio waves
propagation and that should be taken into account. Doc IRPG.
and specification of amateur programs (III)
can be expect now from amateur programs ? Light propagation prediction programs
like Ham CAP, G4ILO's HFProp and alike have been designed to make
the use of VOACAP easy for hams. They should not be compared bit-to-bit with a
complex engine like VOACAP, Proppy or the old WinCAP Wizard 3.
first applications will never ask you to enter "Man-made noise in -dBW at 3 MHz in the 1 Hz
bandwidth" or "the multiplier to adjust the predicted critical
frequency of the Es layer", nor will they suggest that you choose between the
CCIR.013 and SAMPLE.022 antennas. These small applications present prediction parameters using
the terms accepted in the Amateur Radio, and assign correct defaults to the
ones that should not be adjusted in ham applications. The main purpose of these
light ionospheric models is to let the operator see at a glance the trends
of propagation while he/she is on the air - with a minimal distraction from
the transceiver. They are useful, and many amateurs keep these program running
on their computer screen whenever they do DX'ing, and they help them a lot.
all these programs, from the simplest to the most complex can be grouped in two
VOACAP-based programs showing a prediction accuracy potentially equivalent, and
respecting "VOACAP rules"
Non-VOACAP based programs that provide an overview of
propagation conditions. They are based on the simplified models and their
accuracy is inherently lower than that of the programs in the first group, ProLab Pro
being probably an exception.
most important in all these applications are not the
number of parameters that they claim to use but the accuracy of their
predictions. Idem for their user interface : some are
on-the-air operations oriented while others are research-oriented programs.
Not all analysis and prediction programs are
thus the same. Without knowing anything in this matter, we can already foresee several
features, source of potential inaccuracies, weaknesses, gaps or bugs that will
be disappointing, annoying or irritating, and will lead you at the end to select
another product better designed, more accurate, complete or user-friendly.
least five major features belong to the requisit, what other call the
specification of any modeling program, and especially an amateur propagation
prediction program :
the reference model
the graphic user interface or GUI
the exchange of data
the available resources
it is not itself the reference model, but you probably don't run the
master application on the supercomputer, Hi!, like any modeling
program, a propagation analysis and prediction program is based on a
reference ionospheric model. As we just told these down-sized
versions of the reference model can be more of less complete,
flexible, and thus provide a more of less accuracy.
used are the key arguments to take into account when selecting a
product. At the limit, hundreds of parameters injected in
approximate algorithms will never give you an accurate prediction
(hopefully they are tricks to improve results). If a publisher uses
a well-known model, performing and recent, it will not hesitate to
speak about it to attract customers. If nowhere on his website or in
the product specification there is mention of a model or a method
based on scientific studies, you can already conclude that the
product uses probably approximations and will never give you
accurate predictions. At best such a product uses median values, old
but efficient algorithms known to provide general forecasts,
overviews, but they are unable to give you an accurate forecast for
a specific day, and even less at short-term. Its forecasts show 50%
of confidence, in other words a 50-50 reliability; they can be exact
today and false tomorrow, all the art to interpret statistical
you wish to get accurate forecasts, a flexible and powerful product,
do always select either a VOACAP-based application or an advanced
model using real-time data and a down-sized version of IRI-2001 and
,when they will be available, a down-sized version of the International
Geomagnetic Reference Field (IGRF)
without to forget to take into account weather conditions (for the
top band propagation).
prediction programs differ also from each others by the quality of
the graphic user interface, what you see on the main screen, in its
message boxes, its scrolling menus or when displaying a
ionospheric map (GIM) prepared by the université
de Berne (this type of chart seems no more available online).
GUI depends on each publisher and sometimes on the operating system.
At first sight it is a minor detail without relation with the
reliability and accuracy of the forecast. However this interface is the only way
that you have to communicate with the model; this is through its
screens that you feed it and receive outputs. So, when you request
the program to display a coverage prediction around a target
location or at the earth scale for example, the screen resolution
comes into play. When you click somewhere in the chart to display an
additional chart or figures, subroutines must be able to locate your
cursor with accuracy on the chart or on the map and then provide an
answer with all required accuracy.
GUI must also response quickly to your requests and without bug.
Here all is a matter of design and development, for short of
know-how. Some applications are written in elementary languages,
sequential or procedurals (GWBasic, Fortran, etc) while others use
object-oriented language (3GL, etc). Some use much resources, others
are supported by a technical team contrary to many freeware, but not
all, that are provided as one states "as it, without warranty, expressed or implied,
made by the publisher as to the accuracy, suitability and functioning
of the program and related material".
last, be aware that no product is never perfect. In the worst case,
here is a real-life example. A well-know publisher has quoted in his
product specification "supported by Mac OS, Windows
98/NT/2000/XP", except that he visibly not tested the basic
functions of the program under Windows XP. Indeed, what to conclude
when bugs occur at first run on the main propagation map and when
the download function is almost inop... This is unacceptable and
such advertising are misleading.
take care when buying a new propagation program putting in light a
new GUI or features. Download always first the demo when available
and check on the FAQ or on the Internet (eHam, forum, etc) if other
users are satisfied of this product because, unfortunately, it seems
that no publisher will never tell you all the true for marketing
on the reference model, the program must be able to output a result, a forecast in form of
tables, report, charts or maps, static, dynamic or animated.
many programs are still using outmoded menuing or provide
practically the same interface as the engine that drive their
forecast, and designed more then ten years ago when the graphic
interface was in infancy and still seldom used. To believe that
imagination and originality are no more the interest of publishers...
last, outputs should be flexible, using various type charts or
reports, custom layout, etc. The program must also include a printing option, a small function that some applications forgot.
Hopefully at the time of printscreens, OLE and other DDE this
problem can sometimes be bypassed but its omission it is definitely not a clear
and complete design.
exchange of data
complete application is flexible what means that it should be able to fit
also to external needs and change for example its layout or data format
on request. But first af all a well programmed application and
complete must be able to export its data or outputs in other
formats. In addition it should be able to receive external inputs
through batch user files, macros and other shell mode.
imagine well that very few programs support all these functions. In
fact I don't know any supporting simultaneously more than three of these
features, excepting those running of supercomputers. We start thus
from a wrong side, but don't go way, the situation is not as
desperated as it looks to.
addition, the design and the GUI are strongly depending on the
available resources, I mean the power of the
computer running the application. To get
quickly a forecast that means to use one or more fast
CPUs able to process many operations in a single second, have
at disposal a large amount of memory to handle many
processes, functions and variables simultaneoulsy, and extended and
fast mass storage disk space (hard disk of high capacity and fast
access) to install the application and exchange exeternal data.
Hopefully I can already to tell you that any Pentium or faster
computer is today capable to support most of these functions. Some
free and low cost elementary programs run even on AT machines but
you can probably no more find these ancestors, Hi !
forecast for each variable
buying a propagation program, we expect to get good results,
a return on investment, Hi ! But after all what has been
told about specifications of such programs, and after have used
myself several of them intensively during months, you gave already
understand that I have to refute or at
least temper your good a priori about the performance
of these applications because not all is perfect.
2005, this multi-node NEC
SX-5 was among the most powerful supercomputers in the
Some models are equipped with 512 CPUs in parallel and are
able to process up to 400 billions operations per seconds (4
TFLOPS). Their mass storage extents on several tens of cubic
meters ! Most are used to simulate complex processes like
the atmosphere or other large-scale systems. Five years
later the model SX-9 is 200 times faster.
we told, a least two constraints are inherent to ionospheric models to
get an accurate forecast : the computer resources to handle many
parameters and algorithms or functions used.
we shortly explained what resources are require to use such
programs, let's imagine that you own a powerful computer (at least Pentium
II) or that you can use the one of your institution. Remain the question of the
accuracy and the reliability of the prediction. An accurate
program, able to give you a forecast with the highest
reliability or a high degree of confidence means that the
model don't only trust in statistic values but considers a
great number of on-line variables, many functions and many
sub-models processing specific varaibles, parameters and processes. At
the limit, this program must be able to ouput a forecast for
each variable and interactions between each of them as well.
But hopefully amateurs don't request such a level of power
and content also with a much lower reliability, often close
this, can a program running on a personal computer provides
similar results than a forecast calculated on a
supercomputer like the NEC
multi-node SX-5 displayed at left ?
Asking the question is already to answer it. Of course both
systems are "hops" apart and any down-sized
ionospheric model is by definition a lighter version of the
master, less complex and thus providing more limited
predictions or less accurate in both space and time. But
sometimes small means also powerful, isn't it ?... Yes, it
talk amateur radio
[amateur programs are powerful] means that in average this
is... not the case. But before answering to this question
and to explain why this is not always the case, we are going
first to answer to another one to set the frame of our
are not many questions that an amateur radio asks about propagation. A
propagation prediction program has to answer to two questions depending
on whether the amateur is a DX chaser or a contester :
For the DXer the question is straightforward : what will be best
time and the best frequency to work such a DX country?
For the contester, this is the contrary : he or she would like to know what
band to use and at what time to get the largest coverage, worldwide.
For some DX-peditions working with a large team the world map can be
divided in several sectors (e.g. per continent). In this case the
coverage will be more limited.
As we are not medium, simulation programs will provides us the answer to these
questions. But as we introduced, many factors can affect the propagation
conditions. What are they and how are they gathered in these programs ? We have
explained that sun and geomagnetic conditions as well as the
operators' working conditions represent the essential factors to
take into account. Both groups are thus divided in several subsets,
each being constituted of several data to set correctly if you want
an accurate prediction.
The most used
As we explained about ionospheric
perturbations, HF propagation uses primarily sky waves that reflect on or in
the ionosphere. Therefore ionospheric conditions
are extremely important to get an accurate propagation estimation. The density
and altitude of ionospheric layers are variable up to change from hour-to-hour
and even in less than a quart of an hour. In addition, each band shows its
proper behaviour and might be suddenly closed although it was open one hour ago
or that the adjacent band is still open.
Most of the time this change in
the propagation conditions are directed by the sun activity and in a lesser
extend by the fluctuations of the geomagnetic field. Or said in other words, at
some occasions, depending on the activity and the position of the sun (and thus
the time of the day and the season) the propagation medium - the ionosphere - simply doesn't support
any more transmissions. To avoid to be confronted to such problems, propagation
program permit you to calculate in a few seconds the best time and frequency to
increase your chances to make a good QSO at long distance.
that the propagation question does not occurs at short distance where other
factors intervene to permit of deny a communication circuit. First there is the
gray line map and the sun position that you have to follow along the day to be
able to work such or such countries located in the sunlight, then to this area
you have to substract the skip distance that depends directly on the working
frequency. Do not try for example to work a station located 500 km away on the
20 or 15m band. Even if that station works with 1 kW he has all chance to arrive
on your antenna too weakly to be heard. That could however work if your signal
is emitted vertically in using for example an antenna place close to the ground
(2-5m high) that will display a main lobe close to 90° with the ground. But
don't forget that in this case your sky waves have also more chances
to cross the ionospheric layers without reflection... Add to this
effect the Pseudo-Brewster Angle (PBA) that produce an attenuation
of your signal over poor grounds. As you
see many parameters can interfere with the theoretical propagation that
forecasts an opening of a closed band to some countries.
confirms already that an accurate propagation prediction program must
incorporate the circuit specifications like your antenna specifications (power,
gain, height, takeoff angle, etc), the expected signal-to-noise ratio and the ground properties
(dielectric constant, conductivity) in addition to the latest solar and
In this matter, what are parameters the most used in these programs ? In a model like VOACAP (signal
model) or CCIR (atmosphere noise model the next input parameters are
environment (date, time of day, required S/N ratio and reliability, ...)
Transmit terminal (mode, power, coupler loss, ...)
Transmit antenna (frequency, antenna gain, main lobe heading, band range, takeoff angle, ...)
- Receive terminal
(mode, signal sensitivity, atmospheric noise, man-made noise, ...)
Receive antenna (frequency, bandwidth, gain, main lobe heading, band range, takeoff angle, ...)/font>
(conductivity, dielectric constant, Pseudo-Brewster Angle, ...)
- Solar conditions (smoothed sunspot number or
average solar flux)
addition some products add :
Geomagnetic conditions (horizontal and vertical components, Ap, Kp, Q-days
these parameters differ from the ones used by your current application, tell you
that you have maybe forgotten something in selecting your program. As we have just
seen, examining the propagation channel alone without considering terminals (TX and RX)
and sometimes objects in-between will not reflect properly your working
conditions and thus the prediction will be affected with a large biais factor.
To get an accurate prediction suited to your working conditions, it is important to consider the
entire end-to-end system, including not only the Sun and geomagnetic conditions but also your antenna
specifications and the ground surrounding your transmitter (and if possible the
receiver). This is using all these parameters that a model like VOACAP is able to
simulate correctly the propagation between two stations or more exactly, to give
very good results under "ordinary" working conditions :
not too close to the top band, not too close to the polar caps and
preferably using an antenna polarized the same way as magnetic field
at the concerned latitude.... I know, that represents already many
exceptions. But as we told earlier, nothing is never perfect...
The poor prediction
capabilities of small programs is obvious in many amateurs products. The
antenna properties for example are often ignored although they are emphasized in a model
like VOACAP. Antenna modeling is not taken into account without reason. As you
know its radiation pattern and pick up efficiency vary from location to location,
from the heigth above ground and near obstructions. To get a model as close as
possible to the reality it must also consider with the same importance parameters
like the local ground conductivity, the dielectric constant, and optionally terrain variation factors.
These parameters are mandatory
to establish a good propagation estimation chart, whether you work with only one circuit
(from your station to a remote one) or operate a large network of circuits (this
latter concerning first broadcasts).
Beside these parameters, the
most important factor to consider is the status of the propagation medium itself
that displays the most large variations. It must be know that HF propagation losses can
reach 60 dB. In the field that represents the equivalent of changing your output
power by a 6-factor ! In other words in the most complete programs, a bad setup will
change your band from open to closed !
The other parameters have less
impact on your signal. In increasing for example your ouput power from 100 W to
1 kW, you add only 10 dB more along your path. And quasi nonebody excepting a
handful of professionals use highly directive HF arrays that exceed 20 dB.
of a VOACAP model