Digital HF Prediction Tool Help

Function
Input map
Input fields

Which T index?
Outputs
Feedback

Function

Predict the reliability and other features of digital HF radio transmission or reception.

The reliability of a radio system is defined as the probability of achieving a specified system performance (eg, minimum required signal-to-noise ratio) under a specified set of conditions (eg, time, date, solar activity level, transmitter power, etc.).

Reliability can be expressed as one of four types, depending on the number of frequencies involved and whether multimode interference is considered:

Basic Circuit Reliability (BCR): only single-frequency transmission is used and the possibility of multimode interference is ignored.
Basic Reception Reliability (BRR): multi-frequency transmission is used and the possibility of multimode interference is ignored.
Overall Circuit Reliability (OCR): only single-frequency transmission is used and the possibility of multimode interference is included.
Overall Reception Reliability (ORR): multi-frequency transmission is used and the possibility of multimode interference is included.

Input map

The white/black areas on the map represent the day/night sectors of the Earth's ionosphere, at a height of 200km. HF circuits that cross the day sector are more likely to be disrupted by shortwave fadeouts, associated with solar flare activity.

The horizontal gray bars on the map represent the approximate locations of the day/night terminators, at an ionospheric height of 200km. The ability of the ionosphere to support HF circuits changes rapidly near a day/night terminator.

The large red dot on the map represents the approximate location on the Earth where the Sun is directly overhead at the current (computer) time on the specified date of the prediction.

Note: If the Sun appears to be in the wrong place, the applet probably has the wrong time. You can check what universal time the applet thinks it is by looking in the Java Console (if enabled on your browser). Look under Tools/Sun Java Console. The date and time are loaded on applet start, so if you want to update the solar position you will need to reload the applet.

You can select a small or large map (centered either at 0 or 180 degree) from the drop-down list at the left of the first row of panel buttons.

If the map's scroll bars do not appear properly, pass the mouse pointer over the "Help" or "webmaster" hotlink at the very bottom of the display. (You may need to scroll down the applet window.)

If you move the map's scroll bars, the white/gray/black areas of the map might not be refreshed properly until you move the mouse cursor back onto the map, or minimise and maximise the applet window.

Input fields

The information to be entered is as follows.

Type of prediction (Base-to-Area or Base-to-Base)
Base type
Base name and location
Communication area (if Base-to-Area) or Second base name and location (if Base-to-Base)
Transmitter power
Environmental noise density at the receiver site on 3MHz
Receiver bandwidth
Required signal-to-noise ratio (SNR) for the specified receiver bandwidth
Date
Solar activity level as measured by the IPS T index
Minimum probability of ionospheric support
Minimum antenna elevation angle (Note: only isotropic antennas allowed at present)
Limits for multimode interference to occur:
- maximum signal-to-interference ratio (SNR margin)
- minimum relative delay time window
- minimum frequency shift window
Frequency set

Type of prediction

The type of prediction must be selected first. The default is Base-to-Area. If a single circuit Base-to-Base prediction is desired, press the drop-down menu next to "Prediction Type" on the input GUI and select "Base-to-Base".

Base type

The base type can be either a transmitting ("Tx") or a receiving ("Rx") station. This is specified by pressing the drop-down menu to the right of the "Base Station" box on the input GUI and selecting either "Tx" or Rx".

Base name and location

The base name and location can be entered in either of two ways:

If you know the geographical name of the base station location, press the "Base Locator" button and, in the new locator window that opens up, left-click inside the box next to "Name" and enter the first three or four characters of the name (case insensitive). Press the "Search" button to reveal the full name and geographic coordinates. If the name and coordinates are incorrect, press the "Clear" button and try again with a more characters in the name field.

When the correct name and coordinates show up, left-click the "Load Base" button to enter that place as the base for the prediction and to close the locator window. The base name will appear in the box next to "Base Station" on the input GUI and its name, coordinates and type will appear just below the map region. Also, the base type (either "Tx" or "Rx") will appear at the base station location on the input GUI map.

The locator window can be dismissed also by either of the following methods:
- left-click the "X" button at the top right of the Base Locator window
- right-click at the top of the Base Locator window and select "X Close"
- press the "Base Locator" button again
If the name of the base station does not show up at all in the locator window, because it is not in the terminal database, use the following second method for entering the base details.
Alternatively, left-click anywhere on the map image. The corresponding latitude and longitude at the mouse location will be entered as the base name and coordinates for the prediction. (Note that, as the mouse cursor is moved over the map area, the geographic coordinates of its location are displayed just above the top of the map.) You can then manually change the name for the base in the "Base Station" box or leave the name as coordinates.

For a Base-to-Base prediction, the name and location of the second base station can be set by either of the above two methods. The base type for the second base station will be set automatically to that opposite to the type for the first station and displayed on the input GUI map. Also, the shorter great-circle path between the two base stations will be displayed by a green curve between the two station markers.

Communication area

For a Base-to-Area prediction, the communication area of coverage is specified by drawing a green box on the map image. This is done by left-clicking and dragging the area box on the map image in any direction. Note that the coordinates of the end corner of the box are displayed just above the top of the map. Also, as you are dragging the mouse, the colour of the box is initially pink if you are in the day sector, but becomes all green when the mouse is released.

Transmitter power

The transmitter power is specified by manually entering the value in units of kilowatts (0.001 to 1000 kW).

Receiver site noise density

The receiver site noise density can be specified from the drop-down menu in the second row of buttons/data items. Select either one of the four standard noise categories ("Remote", Rural", "Residential", "City"), or select "User" and manually enter a value in the adjacent box for the site noise, measured in units of dBW/Hz at 3MHz (-204.0 to 0.0 dBW/Hz). Alternatively, the receiver site noise can be ignored altogether by selecting "Ignore", which effectively sets the noise floor at -204.0 dBW/Hz.

Receiver bandwidth

The receiver bandwidth is specified by manually entering the value in units of hertz (1.0 to 99999.9 Hz).

Required SNR

The required SNR for the specified receiver bandwidth is specified by manually entering the value in units of dB (-99.9 to 99.9 dB).

Warning: What is required here is an SNR value for the specified Rx bandwidth. This must be a dB value, not the SNR density (dB/Hz).

Date and T index

The default date is the current date. If you change this, you must select also an appropriate T index for the new date. T indices can be entered either manually in the "T index" box (-100 to 300, whole integers only) or automatically from the pull-down menu ("Tmonth", "Tday", "Taus", "Tnh", "Tsh", "Tnz", "Tant"), the menu choice being dependent on the application (see below).

Minimum probability of ionospheric support

The minimum probability of ionospheric support is specified by manually entering the value as a percentage probability (0.1 to 99.0%). For a "worst case" scenario, a high value should be chosen (eg, 90%), whereas for a "best case" scenario, a low value should be chosen (eg, 10%). 50% would represent a "typical" case.

Minimum antenna elevation angle

The minimum antenna elevation angle is specified by manually entering the value in units of degrees above the horizontal (0.0 to 90.0 degrees). A "typical" value is 5 degrees for "good" ground conditions or 10 degrees for "poor" ground or obstructions.

Limits for multipath interference

The limits for multipath interference to occur are specified by manually entering the values for:

maximum SNR margin, in units of dB (0.1 to 100.0 dB)
minimum relative delay window, in units of milliseconds (0.1 to 100.0 ms)
minimum frequency shift window, in units of hertz (0.1 to 100.0 Hz)

For multimode interference to occur at a particular time on a particular circuit, there must be at least two ionospheric propagation modes open for that time and circuit, with the difference in the SNR values (SNR margin) between the dominant mode (mode with the highest SNR) and a sub-dominant mode being less than or equal to the specified SNR margin value and with their arrival times at the receiver being separated by at least the specified delay value and their frequency shift from the receiver's tuned frequency being at least the specified frequency shift limit.

Frequency set

If you select "Amateur" from the pull-down frequency menu at the end of the fourth row of buttons/data items, the amateur frequency set is loaded. If you select "Arbitrary", the default arbitrary frequency set is loaded.

Delete or alter any unwanted frequencies and/or add other frequencies (maximum of 10), in units of whole Megahertz (0.001 to 30.000 MHz).

Other buttons

Select the SetTBM button to open up a new window, which allows the setting of parameters to be used in generating output display charts of either Throughput, Bit Error Rate or Modulation.

Throughput is the rate at which data "symbols" can be received accurately (also known as the baud rate) and is expressed in the unit of "baud" or symbols per second. Typical values range from 300 to 3200 baud.

Bit Error Rate (BER) is a measure of the likelihood of receiving data bits incorrectly and is expressed in units of parts per million (ppm), i.e., "the number of data bits received incorrectly per million transmitted bits". Typical values range from 1 to 1000 ppm.

Modulation is the blocking of data bits into quantised data symbols or "waveforms", which are transmitted over an analogue "channel" as either pulses or "tones" of standardised amplitude and/or phase shift and/or frequency shift. Typical values range from 2 to 6 bits per symbol (bps). Larger values of modulation result in higher "fidelity" in the received message.

These three parameters (Throughput, BER and Modulation) are interrelated - changing the value of one of these parameters usually changes the values of the other two parameters. The SetTBM button allows you to set three pairs of values for two of these parameters to be used to generated three charts of the third parameter.
Select the LoadTBM button to accept the specified pairs of TBM parameter values and to close the TBM window.
Select the Do Prediction button to perform the prediction. If some input data is missing or any of the input parameters are outside their valid range, the prediction will not proceed and an error message will be displayed in red below the map, indicating the problem or the valid range for the faulty parameter and the current value. Enter a valid value for that parameter and press the Do Prediction button again.
Select the Clear button to clear all the settings.
Select the Reset button to reset all the settings to the initial default settings.

Which T index?

The T index defines the state of the ionosphere for the prediction. This value depends on a number of factors, including phase of the solar cycle and how disturbed the ionosphere is currently.

The following is a menu of the T index "flavours", from which to choose:

T index	Description	Application
Tmonth	Monthly observed or forecast global T index	Past or future date
Tday	Daily forecast T index(Southern Hemisphere)	Daily average
Taus	Real-time Australian region T index	Now
Tnh	Real-time Northern Hemisphere T index	Now
Tsh	Real-time Southern Hemisphere T index	Now
Tnz	Real-time New Zealand T index	Now
Tant	Real-time Antarctic region T index	Now

Notes

For backwards-looking predictions for past dates, or for longer term (quiet) planning predictions, use the observed or predicted monthly global T index (Tmonth), which follows the long-term solar cycle trends.
The daily forecast T index (Tday) is issued each morning (23:30UT) by the Australian Space Forecast Centre and should be used for the Southern Hemisphere region (particularly during disturbed conditions).
Ionospheric conditions are partially determined by seasonal effects, which can result in differences between Northern and Southern Hemisphere T indices.
For real-time communications, use the relevant real-time index for your hemisphere or region.
If communicating from one hemisphere/region to another during a disturbed period, use the lower of the two indices.

The tool starts up with the monthly predicted global T value. If you select one of the other T index "flavours" and a value of -999 appears, this indicates that the selected daily or real-time T index is not available currently. In such a case, either select Tmonth or manually enter what you consider to be a reasonable value between -100 (deepest possible solar minimum) and 300 (highest possible solar maximum).

Outputs

The prediction output is displayed in either a new browser window or a new tab, depending on your browser settings. The output is preceded by a summary of the input data.

Base-to-Base prediction

For a Base-to-Base prediction, the output is presented below the input summary in a table that lists the following parameters for each UT hour:

Each of the frequencies in the specified frequency set.
REL = Most RELiable frequency (highest OCR - see below).
DOM = DOMinant frequency (highest signal-to-noise ratio (SNR)).
BRR = Basic Reception Reliability (ignoring interference) for the whole frequency set.
ORR = Overall Reception Reliability (including interference) for the whole frequency set.
BCR = Basic Circuit Reliability for an individual frequency.
OCR = Overall Circuit Reliability for an individual frequency.
SSM = Strongest Signal Mode (ionospheric mode with highest SNR on a given frequency).
SIM = Strongest Interfering Mode (ionospheric mode, other than the SSM, with lowest Signal-to-Interference ratio, relative to the SSM, on a given frequency).
THR1/2/3 = Maximum Throughput (symbols per second) for three specified pairs of Bit Error Rate (BER) and Modulation values.
BER1/2/3 = Minimum BER (parts per million) for three specified pairs of Throughput and Modulation values.
MOD1/2/3 = Maximum Modulation (bits per symbol) for three specified pairs of BER and Throughput values.

Notes

If, at a particular hour, the ionosphere does not support any of the frequencies for the specified circuit, then the symbol ".." is placed in the entries in all of the columns and rows for that hour.
If on a particular frequency there is a dominant mode, but no interfering mode falls within the specified multipath tolerances, then the symbol ".." is placed in just the SIM row for that frequency.
If on a particular frequency the BCR is non-zero, but the OCR is 0.0%, then the symbol ".." is placed in all the THR/BER/MOD rows for that frequency.
If on a particular frequency the SIM is an equatorial scatter mode, this is represented by the symbol "SS".

Saving output

To save the tabulated data, left-click on the "click here to save this output." hotlink at the bottom of the table. A "File Download" window will open and ask you to open or save an ASCII text file called B2B_ZZZZZ.txt, where "ZZZZZ" is a random ID number. Click the "Save" button. Another window will open, allowing you to specify where the file is to be place. You can also change the name of the file if you wish. Click the "Save" button. When the download is completed, click the "Close" button.

Base-to-Area prediction

For a Base-to-Area prediction, the output is accessed by left-clicking on the hotlink that appears below the input summary, usually within one minute. The output consists of six sets of charts for each UT hour, displaying information on one of the following.

Information type	Description
Maximum Reliability (REL)	A set of three, colour-coded, area plots of either BCR, OCR and BCR-OCR or BRR, ORR and BRR-ORR.
Most Reliable Frequency and Mode (RMI)	A set of three, colour-coded, area plots of the most reliable frequency (highest OCR); the strongest signal mode on that frequency; and the strongest interfering mode (if any) on that frequency.
Dominant Frequency and Mode (DMI)	A set of three, colour-coded, area plots of the dominant frequency (highest SNR); the strongest signal mode on that frequency; and the strongest interfering mode (if any) on that frequency.
Maximum Throughput (THR)	a set of three, colour-coded, area plots of Throughput for the three specified pairs of BER and Modulation values, on the most reliable frequency for any specific location.
Minimum Bit Error Rate (BER)	A set of three, colour-coded, area plots of Bit Error Rate for the three specified pairs of Throughput and Modulation values, on the most reliable frequency for any specific location.
Maximum Modulation (MOD)	A set of three, colour-coded, area plots of Modulation for the three specified pairs of BER and Throughput values, on the most reliable frequency for any specific location.
Summary (SUM)	A set of four, colour-coded charts that show the variation in the overall coverage for: A minimum level of reliability (Basic, Overall and Reduction due to multipath interference) - top left chart A minimum level of throughput for three combinations of modulation and BER tolerance - top right chart A maximum BER for three combinations of throughput and modulation - bottom left chart A minimum level of modulation for three combinations of throughput and BER tolerance - bottom right chart. Overall coverage is defined as the percentage of the Region of Interest (ROI) where the specified Grade of Service (GOS) is achieved, on the most reliable frequency for any given location. The GOS criteria are listed at the bottom of each set of charts. Data are shown for three ranges in the ROI: Up to a certain distance (D km) from the base station (solid lines); Up to twice that distance (2D km) from the base station (dotted lines); The total ROI (dashed lines).

For convenience in estimating coverage, all but the SUM sets of charts also display curves of constant range from the base station.

Initially the REL charts for 00UT are displayed. To access the output for another UT hour, left-click on that hour at the top of the display. Alternatively, left-click the "Next" or "Previous" hotlink to display the next or previous hour, respectively. To view the RMI, DMI, THR, BER, MOD or SUM charts, left-click on that parameter's hotlink on the second line of the display.

Saving output

To save the output charts for only the currently displayed UT hour, left-click on "the displayed UT hour as a PNG file" hotlink on the third line of the display. The current display will be downloaded into a PNG-formatted image file, called XXXYY_ZZZZZ.png, where "XXX" is either REL, RMI, DMI, THR, BER, MOD or SUM, corresponding to the current display; "YY" is the UT hour of the display; and ZZZZZ" is a random ID number;

To save the current output display for all 24 UT hours, left-click on the "all UT hours as a zip archive of 24 PNG files" hotlink on the third line of the display. The current display will be downloaded into 24 PNG-formatted image files, one for each UT hour, archived into a zip file called XXX_ZZZZZ.zip, where "XXX" is either REL, RMI, DMI, THR, BER, MOD or SUM, corresponding to the current display; and "ZZZZZ" is a random ID number

A "File Download" window will open and ask you to open or save the individual PNG or zip file. Click the "Save" button. Another window will open, allowing you to specify where the file is to be place. You can also change the name of the file if you wish. Click the "Save" button. When the download is completed, click the "Close" button.

Request for feedback

This tool is still under development and is based on theoretical models (particularly section 10 and the Appendix of Rec. ITU-R P.533-11), developed from actual measurements of radiowave propagation modes. We now feel the need for some user feedback to make it more user-friendly, so your comments would be greatly appreciated. Please send an email with your comments to webmaster@ips.gov.au.