SatSig topic:

AMC 12 installation in East Africa

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Mar 1^st, 2007 at 11:57am

Dear all, am installing a 2.4 m dish in mombassa ( Kenya)and will be pointing to AMC 12. after calculating my Azimuth and and Elevation, i realized my Elevation is very very low. i had -18 deg after subtracting the offset. Can any body advice...

Mar 1^st, 2007 at 4:51pm

If you try very low elevation angles you may find the bottom back edge of the dish hits the mounting post.

You can solve this by turning the entire dish upside down. The feed arm will be at the top and the feed high up, looking down, so you will need a ladder to access the BUC/LNA/feed. Take great care.

Think: When the front face of the dish is vertical the beam elevation angle is either the offset angle (in the normal case) or the beam elavation angle is minus the offset angle and down into the ground (in the dish upside down case). In the upside down case, tilt the dish backwards by the offset angle and the beam elevation will then be zero, i.e. towards the horizon. Then tilt it back a further 5 deg, for example, to set the beam elevation to a wanted 5 deg.

Best regards, Eric.

Mar 3^rd, 2007 at 3:53pm

Thanks!!!

Mar 3^rd, 2007 at 5:20pm

Here is a picture illustrating the the pointing of an upside down dish.

Note that satellite operation below 10 deg elevation angle is not advised for Ku band (10-14 GHz) or below 5 deg for C band (4-6 GHz). The path length through rain is long and you suffer more rain attenuation and noise increase, also you observe tropospheric scintillation where the signal goes up and down all the time like the twinkling of a star near the horizon.

The upside down configuration with the beam elevation set to zero is useful for terrestrial point to point applications, such as long range WiFi connection. In such a case you need a feed that works at the relevent WiFi frequency. In some case a WiFi dongle mounted at the feed point is reported to work well.

Best regard, Eric.