AUSTRALIAN SHORTWAVE JOURNAL

AUSTRALIAN SHORTWAVE RADIO JOURNAL

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Monday, December 13, 2010

Splendid propagation from Asia in mid-afternoon on 9 MHz and 11 MHz

Despite the continuing very low level of solar activity, there is a lot of
shortpath action in our mid afternoons from Asia, and particularly
China, on 9 MHz and 11 MHz.

These are some selected entries, as intercepted on December 12, 2010, from
one of my favourite field monitoring sites on South Hill, Warrandyte State
Park, 20 km east of central Melbourne.

9635 VIETNAM VOV nat network 0400
9685 CHINA CNR5 Chinese 0415
9730 BURMA BBC Rangoon dialects 0415
9750 MALAYSIA VOM-Kajang huge signal Malay 0430
9810 CHINA CNR2 Chinese 0400
9850 VIETNAM VOV nat net 0430
9870 INDIA AIR Hindi to 0435*
9875 VIETNAM VOV dialects network *0400
11685 CHINA CNR11 Tibetan 0430
11720 VIETNAM VON nat net 0400
11770 CHINA PBS Xinjiang Urumqi Chinese 0430
11835 CHINA CNR2 0430
11915 CHINA CNR2 0430
12045 CHINA CNR1 0415
12055 CHINA CNR1 0430

Notes about the E and F Layers

The E layer is the middle ionospheric layer, 90 km to 120 km above the
surface of the Earth. Ionization is due to soft X-ray (1-10 nm) and far
ultraviolet (UV) solar radiation ionization of molecular oxygen (O2).

Normally, at oblique incidence, this layer can only reflect radio waves
having frequencies lower
than about 10 MHz and may contribute a bit to absorption on frequencies
above. However during intense Sporadic E events the Es layer can reflect
frequencies up to 50 MHz and higher.The vertical structure of the E layer is
primarily determined by the competing effects of ionization and
recombination.

At night the E layer rapidly disappears because the primary
source of ionization is no longer present. After sunset an increase in the
height of the E layer maximum increases the range to which radio waves can
travel by reflection from the layer.

This region is also known as the Kennelly-Heaviside Layer or simply the
Heaviside layer. Its existence was predicted in 1902 independently and
almost simultaneously by the American electrical engineer Arthur Edwin
Kennelly (1861-1939) and the British physicist Oliver Heaviside (1850-1925).
However, it was not until 1924 that its existence was detected by Edward V.
Appleton.

The upper limit of hop length is set by the height and curvature of the
ionosphere. The maximum hop lengths for E layer propagation are about 1800
km (3200 km for F layer).

The Asian propagation discussed here is via various multi-hop and
multi-layer modes, such as 2E, 2F, 3E or 3F.

The Specialised Asian Daytime Mode appears in ouir summer, for all-daylight
propagation across our noon period, on 6 MHz and 7 MHz, via F(Es)F mode,
with reflection off the topside of the Sporadic E layer.

Great Circle Distances from Melbourne to various Asian destinations include:

Malaysia (Kajang) 6070 km
Thailand (Udon) 7360 km
Vietnam (Hanoi) 7700 km
Burma (Rangoon) 7930 km
India (Delhi) 10063 km

I am waiting for the first Daytime Midday Mode to materialize this summer!

Regards from Melbourne!

Bob Padula

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