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High Frequency (HF) System Engineering

ACE-HF PROPAGATION PREDICTION PROGRAM — OVERVIEW

The following is an overview of the three principal departments of the software.

1. The Network Screen is the principal Frequency Management tool, and displays circuit status at each frequency and for 24 times-of-day. The frequency manager may employ such screens to determine best frequencies for each circuit and for the network as a whole, and may also determine predicted circuit quality. The Circuit Dwell Time Chart shows either predicted Reliability or SNR values for all times-of-day and all frequencies for a selected circuit, and permits the frequency manager to build a frequency plan by selecting best frequencies for the day. The Situational Awareness Screen appears when the software opens, illustrating the current status of each circuit in a defined network. Using that screen, the system operator may quickly evaluate the network’s current status.

2. The Circuit Analysis Screen shows predictions to simulate any defined circuit. The default example shows a graph of SNR vs. time-of-day for a circuit from Seattle to Chicago. Similar graphs compare the effectiveness of different frequencies, and all may be animated through their ranges. The user may plot a number of parameters, including Reliability, Required Power Gain, Signal Strength, Elevation Angle, and Throughput Rate (for digital signaling modes). MUF, Best Frequency, and Summary Charts may also be displayed to better understand each circuit’s effectiveness.

3. Animated area coverage displays may be created for any transmit location. The maps may be
animated by frequency, time-of-day or smoothed sunspot number, and may be displayed by the included MOVIE program at any speed. Coverage at median SNR levels or for any selected Reliability value may be created. The default example displays 40-m coverage from the ARRL ham station W1AW in terms of required power gain. The red area shows the coverage gained by increasing transmitter power or antenna gain by 10 dB. The green area shows the effect of decreasing system gain by 10 dB. The animated coverage displays quickly show a station’s effectiveness and are an important HF propagation-teaching tool.

OBJECTIVES

The main purpose of ACE-HF is to predict the effectiveness of operating large HF networks under a wide variety of environmental conditions. ACE-HF may be used for system design and planning, where the objective is to predict future performance as different designs are perfected. More frequently, the software is used as a Frequency Management tool where the objective is to optimize current network performance. See section 4 of the Network Frequency Management tutorial for guidelines on Frequency Management.

All HF networks have a common need: to find the best frequency for each circuit’s operation, and to assure that the network provides dependable communications. HF skywave propagation is highly dependent on time-of-day, and a frequency that provided good connectivity during local daylight hours may be unsuitable for evening operation. Thus, it is important to create a frequency plan that optimizes 24-hour operations.

ACE-HF provides many tools for the network frequency manager. The principal aids are the Frequency Management charts that evaluate network circuit integrity. Predictions for up to 72 network circuits may be made for 24 hours and ten frequencies, and these predictions are presented in tables designed for easy selection of best frequencies. In a few minutes, a frequency plan can be created for each network circuit and for the network as a whole, the latter facilitating all-call operation.

Accurate system simulation is the key to optimized operation, whether the goal is to design a new HF system or to manage frequencies within an existing network. ACE-HF Network provides many tools for quickly defining each circuit and for then visualizing the effectiveness of those definitions. These tools include:

• Input Screens that permit the precise definition of station locations, power levels, antenna types, gains and azimuth settings. Existing antenna models may be selected from an extensive collection, or the user may specify unique models made for the station. Users may define station locations with a large location database, or may quickly define a new network circuit by simply pulling a dot on the map.
• Exclusive to ACE-HF, ACE animated coverage maps are the keys to understanding HF effectiveness. Essential for overall system planning, these maps include moving day-night terminators (graylines) and yield great insight as one watches station coverage expand and contract as time-of-day changes. Coverage map movies are often used as a primary training tool for new HF operators.
• Once coverage effectiveness is understood, detailed circuit predictions may be visualized using the Circuit Analysis Screen. Charts of SNR and many other parameters are automatically graphed vs. time-of-day or frequency, and charts of MUF, Best Frequency and SNR/Reliability Summaries are available. Perhaps most useful is the pop-up menu that permits the analyst to see within seconds the effect of changing reliability and other system parameters, or even a different antenna.
• For routine network operation, the frequency manager will depend on the ACE-HF frequency management screens. These permit the user to quickly define up to 72 circuits, automatically run predictions for each circuit in both directions, and present the results on tables of predicted SNR and Reliability levels for each frequency and time-of-day. The predictions may be viewed on several charts:
• Circuit Charts show four groups of 18 circuits and can be animated by time-of-day. Reliability or SNR data for bi-directional or one-way circuit operation may be selected and best frequencies are highlighted by color. The optimum frequency range of the entire network is also shown, thus identifying frequency channels that fail to support propagation during a specified time range.
• The Circuit Dwell Time Chart presents the data for each circuit in a frequency vs. time-of-day format, and these charts are used to create frequency plans that select the best frequencies while minimizing the need to change frequency too often.
• Network Dwell Time Charts are similar and permit frequency planning for the network as a whole.

To make a frequency plan, the user simply clicks and drags the mouse cursor over the best frequencies to be selected. Controls are provided for selecting only certain network circuits in case multiple plans are needed for different network areas.