Topband: Radio Arcala, HFTA, elevation angles

[k9la at frontier.com]

More comments.
Radio Arcala – My only experience with them is in CQ WW CW a couple years ago. There was another OH up that a way running a vertically polarized antenna (I don't remember at the moment if it was a vertical or a 4-Square). This other OH had a stronger signal than Radio Arcala for the several times I checked. Note that this is not an extensive comparison. As a side comment, when Radio Arcala announced this project, I expressed my concern to them – but by then it was too late. Regardless of the results, we're going to learn something (as GM3POI pointed out).
HFTA – Those 1.8 MHz elevation angles likely came from IONCAP/VOACAP as the program does give results below 2 MHz. The real issue is there is very little (if any) validation data on 160m.
Elevation angles on 160m – I believe useful elevation angles on 160m fall into three categories. With the nighttime E region critical frequency around 0.35 to 0.5 MHz, elevation angles below about 10 degrees are refracted by the E region (in other words, E hops). The importance of these extremely low angle E hops is not well understood. Higher angles can result in ducting at night as long as the electron density valley above the E region peak is well formed. My guess for these angles (from ray tracing work with Proplab Pro) is something like 10 to 20 degrees. Above 20 degrees, the wave passes through the E region and is not refracted enough to get into the duct – so we get F hops. Please realize this is a very general summary, as “stuff” happens.
160m differences – When considering propagation on any band, one has to consider refraction, absorption, and polarization. With refraction by a given electron density profile inversely proportional to the square of the frequency, 160m is bent the most and results in shorter hops. Due to 160m being close to the electron gyro-frequency (one of N0AX's favorite words), absorption is more than on our HF bands. This results in shorter hops with more loss. In fact, the extraordinary wave (one of two characteristic waves that propagate thru the ionosphere) is usually considered out of the picture on 160m due to significantly more absorption than the ordinary wave. And again due to 160m being close to the electron gyro-frequency, polarization tends towards highly elliptical as compared to circular polarization on our HF bands. And vertical polarization couples the most energy into the ordinary wave at the high latitudes.
Carl K9LA