EAST AFRICAN
REPORT
BY CHRIS
GREENWAY
ARTICLE FROM COMMUNICATION - EDITION 149 - APRIL 1987
------------------------------------------------------------------------------------------------------------------------------
To understand propagation on the Tropical Bands it is useful to know something of the properties of the D-layer of the ionosphere. This layer only exists during daylight and has different effects on three parts of the radio spectrum.
1. Frequencies below about 3 MHz (including the LF and MF bands) are completely absorbed by the D-layer. Thus skywave propagation on these frequencies normally only takes place during darkness (when there is no D-layer) or in the period around dawn and dusk (when the D-layer is weak). The only circumstances in which skywave propagation can take place during the middle of the day is during winter in the high latitudes, when the sun’s rays are weak and hitting the ionosphere at a shallow angle. This explains why mediumwave DXing is possible throughout the day in northern Scandinavia during the winter.
2. Frequencies above about 9 MHz (the exact frequency varies with latitude and season) pass through the D-layer unaffected (except during Sudden Ionospheric Disturbances - SID’s) and are reflected back to earth by the F-layer, which lies above the D-layer.
3. Signals between about 3 and 9 MHz (including Tropical Bands) are absorbed by the D-layer if they strike it at a shallow angle, such as is necessary for long distance propagation. However, if they strike it at an acute angle, close to the vertical, they will pass through it and be reflected by the F-layer. It is this principle which allows stations to use these frequencies during the day to cover areas up to a few hundred miles from the transmitter (i.e. beyond the groundwave range of mediumwave transmissions).
In Europe many stations use the 6 and 7 MHz bands during the daytime on this basis. Radio Luxembourg on 6090 kHz and relays of West German domestic services on 6005, 6030, 6085, 6190 and 7265 kHz are good examples.
On the lower frequencies, below 6 MHz, the angle the signals hit the D-layer, and hence the distance they cover, becomes very critical. In southern England, for example, daytime reception of the Austrian scouting station on 5035 kHz (about 800 miles distant) is normally possible. However, reception of 5057 kHz Tirana (about 1,200 miles away) is not possible until dusk approaches.
Here in Nairobi, this propagational characteristic means that for most of the daylight hours the only stations audible on the tropical bands are those in neighbouring countries of Burundi, Rwanda, Tanzania, Uganda, eastern Zaire, as well as Kenya itself.
In a future report I hope to talk further about listening in East Africa on the tropical bands as well as reception on other bands. In the meantime, it may be interesting for members in Europe to see what stations are audible here on the 90 metre band during the evening.
3200 Fuzhou, China (audible before TWR sign-on)
3200 TWR Swaziland (not 3205 as per WRTH)
3204.5 RRI Bandung ( Indonesians fade-in shortly before networked news at 1500)
3205 AIR Lucknow
3210 Maputo, Mozambique (// 4866)
3215 SABC Radio Oranje/Radio Orion
3220 CPBS Beijing (1st Programme // 9064)
3230 Radio RSA (Portuguese 1900-2000)
3230 Radio Nepal (// 5005)
3231.5 Antananarivo, Madagascar (French programme with short English news bulletin
just before 1800, sign-off at 2000)
3235 AIR Gauhati
3249.8 RRI Banjarmasin
3264.8 RRI Bengkulu
3270 SWABC (1st Programme)
3270 Radio Beijing
3276.7 RRI Jakarta
3277 Radio Kashmir (relays AIR English news at 1530)
3279 Beira, Mozambique
3287.5 Antananarivo, Madagascar (Malagasy programme, sign-on at 1515 to sign-off at
1900 - sometimes later)
3290 CPBS Beijing (2nd Programme // 6890)
3295 SWABC (2nd Programme)
3295 AIR Delhi
3300 Bujumbura, Burundi (// 6140 also audible in daytime)
3305.7 Zimbabwe BC (Radio 2)
3315 AIR Bhopal
3320 SABC Radio Suid Afrika/Radio Orion
3330 Kigali, Rwanda (// 6055 also audible in daytime)
3330.8 Moroni, Comoros (normally swamped by Kigali)
3347.4 Radio Zambia (General Service)
3355 AIR Kurseong
3356 Radio Botswana (// 4820)
3365 AIR Delhi
3366 GBC-2, Accra (this is the only West African audible on this band)
3370 Beira, Mozambique
3375 AIR Gauhati
3380.8 MBC, Blantyre
3390.1 Radio Candip, Bunia, Eastern Zaire (also audible in daytime on // 5066)
3395.7 Zimbabwe BC (Radio 1)
(c) Copyright British DX Club
