NCDXF Beacons -

The defaults for a fresh install are set for an NCDXF Beacon type prediction. You may need to adjust the antenna gains to more closely match your station. In the case of beacon predictions you are the "receive" station as the circuit is "reversed". See the Reversed-Circuit Receiver section.

Big-Gun Station -

These default antennas and transmit power, 1500 watts, are of course for a "big gun" type station.

The philosophy is something like "it is better to know that a circuit is at least usable and a path exists than see none and not even try". With this in mind, we establish a minimum "circuit" gain for two frequency ranges. In this context "circuit gain" refers to the total gain for both transmit and receive antennas. Of course everyone should adjust these to his or her station.

Using an Isotrope type antenna and these gains simulates a high dipole on 30/40/80 meters: 3.5 to 13.0 MHz = 9 dBi (receive) + 3 dBi (transmit) = +12 dBi circuit gain.

Using an Isotrope type antenna and these gains simulates 3-element Yagis at both receiver and transmitter: 14 to 30 MHz = 9 dBi (receive) + 15 dBi (transmit) = +24 dBi circuit gain.

This odd mixture of gains, or compromise, is used because VOACAP allows only one receive antenna but up to four transmit antennas. Thus the compromise on 9 dBi for receive and the rather high transmit antenna gain achieve our desired "circuit" gains. These gains are very near what the QST propagation charts used.

For the purpose of HF propagation prediction and amateur radio, it appears difficult to "improve" on the use of Isotrope antennas with appropriate gains, by substituting antenna models. The Isotrope antenna avoids "holes" in the predicted data caused by nulls in the patterns of "real antennas". It should be noted that the default "minimum take-off angle" (Minimum Angle, found in Circuit-Configuration Manager on System page) should be at least 3 when using the Isotrope type antenna for predictions.

Please do note these power and gain values are not reasonable for use in creating NCDXF beacon system predictions. An alternate antenna "group" is provided for predicting beacon system propagation.

If you wish to customize the antennas to more closely match your station please read the sections HFAnt and External Antennas.