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



At 02:22 PM 11/7/2005 -0600, RANSOM, KENNETH G. (JSC-OC) (BAR) wrote:

>  Pat,
>Could you expand on this comment?
>
>"May I recommend for the future that satellite designers use VHF or lower
>frequency downlinks instead of UHF and above so it is easier to receive
>without the higher path loss. "
>
>I'm trying to decide if you are wanting less Doppler all the way around by
>moving every thing to lower frequencies (A/v or V/a) or if you would rather
>have less Doppler on the receive and have to deal with it on the transmit
...


Hi Kenneth,

Pat is referring to the lower free-space path loss on 2m.


Let's say someone launches a new LEO satellite with 1 watt
of output power and a 0 dB gain transmit antenna. On the
ground you listem for it with a quarter-wave vertical.

If the satellite uses 2m on the downlink, the received
signal level will be nearly 10 dB higher than if it used
70cm for the downlink.

So, mode B satellites like VO-52 tend to be much easier to
hear than similar mode J satellites when you are using
omni antennas to receive them.

On your uplink side, you need 10dB more EIRP but this tends to
be no problem as even QRP rigs have more than enough power
for the uplink.

73,
Tony AA2TX
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