MUF Forecasts

Long-range forecasts several months ahead, such as those pub- lished in QST and other journals, provide only the most general form of prediction. A series of 30 charts, similar to Fig 21.23, forecast average propagation for a one-month period over specific paths each month on the ARRL Web site. The charts assume a single average solar flux value for the entire period. Early editions of The ARRL Operating Manual included a similar series of such charts for three representative sunspot values and a variety of paths.

The uppermost curve shows the highest frequency that will be propagated on at least 10% of the days. The given values might be

exceeded considerably on a few rare days. On at least half the days, propagation will be possible as high as the middle curve. Propagation will exceed the lowest curve on at least 90% of the days. The MUF on any particular day cannot be determined from the charts, but the calculated time of the MUF is reliable.

Short-range forecasts a few days ahead still depend on predic- tions of solar radiation and geomagnetic indices, but the previous 27-day history and current conditions improve these estimates con-siderably. Daily forecasts are even more reliable, as they are based on measurements of solar and geomagnetic activity no more than a few hours old. Forecasts can be made at home using one of several popular programs for the personal computer, including CAPMan, IONCAP, IONSOUND, MINIMUF and MINIPROP

PLUS. These are described in more detail in the accompanying sidebar.

Fig 21.23—Propagation predic- tion chart for East Coast to Europe that appeared in QST for December 1994. An average 2800- MHz (10.7-cm) solar flux of 82 was assumed for the mid-Decem- ber to mid-January period. On 10% of these days, the highest frequency propagated was pre- dicted at least as high as the uppermost curve (the Highest Possible Frequency, or HPF, approximately 21 MHz), and for 50% of the days as high as the middle curve, the MUF. The broken lines show the Lowest Usable Frequency (LUF) for a 1500-W CW transmitter.

MUF Prediction on the Home Computer

Like predicting the weather, predicting propagation—even with the best computer software avail- able—is not an exact science. The processes occurring as a signal is propagated from one point on the Earth to another are enormously complicated and subject to an incredible number of variables. Experience and a knowledge of propagation conditions (as related to solar activity) are needed when you actually get on the air to check out the bands. Keep in mind, too, that ordinary computer pro- grams are written mainly to calculate propagation for great-circle paths via the F layer. Scatter, skew- path, auroral and other such propagation modes may provide contacts when computer predictions indicate no contacts are possible.

Brief information about prediction programs for the IBM PC and compatible computers follows. The programs can be divided roughly into two categories. The first includes programs best suited for quick, on-the-fly predictions. Programs such as MINIMUF, IONSOUND or MINIPROP are excellent tools for assessing what bands are likely to be open in the near future, usually using recent propaga- tion indices broadcast on WWV as data input—to see, for example, whether 21 MHz is likely to be open tomorrow morning on the path from Kansas City to Berlin, given a solar flux averaging 95 over the last several days.

The second category includes programs designed for long-term analysis and station planning. These programs require more investment in computer hardware, and will often take a considerable period of time to do their complex calculations. Most long-term planning programs benefit greatly from the use of a math coprocessor, although most of them will run, even if slowly, without a math coprocessor in the system. ASAPS, IONCAP and CAPMan typify this category of heavy-duty propa- gation programs. Table 21.7 summarizes the features and attributes of these programs. Each pro- gram is copyrighted unless otherwise indicated.

ASAPS V2.2

ASAPS, for Advanced Stand-Alone Prediction System, was developed in Australia. It rivals IONCAP (see below) in its analysis capability but performs calculations in significantly less time. It is also interactive with the user; transmit power levels, antennas and other parameters may be changed and the new results viewed almost instantly without further menu entries. Available from: IPS Radio and Space Services.

l0N€AP, Version PC.27; €APMan, Version 3.0

IONCAP, short for Ionospheric Communications Analysis and Prediction, was written by an agency of the US government. This program is considered by many amateurs and professionals alike as the most comprehensive and best HF prediction program available. The program has been under devel- opment for almost 30 years, and was ported to PCs from a mainframe environment. IONCAP offers no menu; rather, an ASCII input file containing instructions and data must be prepared for program execution. CAPMan is a “user-friendly” version of IONCAP that has been tailored for ham use.

IONCAP is available from: National Technical Information Service. CAPMan is available from Kanga- roo Tabor Software.

l0NS0UND HDX, l0NS0UND, l0NS0UND PR0

There are now three versions of IONSOUND, at price levels from $15 to $75. The low-end IONSOUND HDX program is tailored specifically for the locations shown in the propagation forecast on ARRLWeb. It provides calculated data that one would not expect from a program of its price class. Its bigger brothers, of course, provide more features—IONSOUND PRO is the top of the line model. Graphs present mode chirp plots (frequency versus delay time versus intensity), much as an ionsonde oblique-incidence sounder might produce. For each path calculation, the user must first answer several screens of questions, such as noise environment at the terminal points, receiver bandwidth, required S/N ratio, order of layer modes and so on. Available from Skywave Technologies.

MlNlMUF, Version 3.5

Written in BASIC, this was the first prediction program to become available for use on home com- puters. The program was published in Dec 1982 QST (R. B. Rose, “MINIMUF, A Simplified MUF- Prediction Program for Microcomputers,” pp 36-38). This is public-domain software that has been

customized by many subsequent software writers. The core algorithm’s accuracy suffers outside the range from 250 to 6000 miles. MINIMUF calculations do not consider the E region, further limiting its accuracy.

MlNlPR0P PLUS, Version 2.0

MINIPROP has undergone several revisions since it first appeared. It was written primarily for the amateur community, and has an excellent user interface, with great graphics. In addition to the cus- tomary propagation data, it provides sunrise-sunset and gray-line information, along with a world map showing either long- or short-path propagation graphically. MINIPROP PLUS also produces a unique “DX Compass” showing the MUF in 12 azimuth directions for a given time of day. Available from Sheldon C. Shallon, W6EL.

Application Tips

Because of the lag in F-layer response to a rapid increase in solar activity, it is best to use either a 5, 15 or 90-day running average of the 2800-MHz (10.7-cm) solar flux for prediction calculations. The type of application determines which is best. The 5-day mean is a short-term dynamic input; the 90- day mean is appropriate for long-term planning. The ultimate test, of course, of a prediction program is to get on the air and listen to the signals arriving from the part of the world you just modeled!

Table 21.7

Features and Attributes of Propagation Prediction Programs

“Review data” indicates ability to review previous program display screens. Price classes are for early 1999 and subject to change.

†Available on the World Wide Web at: http://elbert.its.bldrdoc.gov/hf.html

+Shipping and handling extra.