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Re: Satellite modes (Was - Hamsat or VO-52 Modes)



At 11:55 PM 11/7/2005 +0000, John B. Stephensen wrote:

>There is not an improvement using omnidirectional antennas below 2 meters as
>the noise level increases with decreasing frequency at 6 dB per octave.
>Galactic noise levels intecept the earth-bound thermal noise level at about
>200 MHz. Thus the 70 cm band is at a disadvantage if the antenna pattern
>includes the horizon.
>
>If the antenna points away from earth the antenna size is constant with
>frequency as the gain increases at the same rate as path loss. The only
>issue is then pointing accuracy.
>
>73,
>
>John
>KD6OZH

Hi John and Trevor,

Yes! Although the free-space path loss decreases, you do
not get an improvement going to 10 meters because the noise
increases so much. Anyone who remembers RS-12/13 mode T might
recall how it was better than mode A.

As an aside, this is why there is virtually no difference
between mode B and mode J if you are using highly directional
antennas. The background noise is much lower on 70cm.

73,
Tony AA2TX
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