[amsat-bb] AO-51 S Downlink

Clare Fowler lcfowler at magma.ca
Sun Sep 17 20:09:40 PDT 2006

In addition to pointing the antenna directly at the
satellite and determining the offset of the downconverter
frequency there is a third large variable in being able
to receive mode S.

I have received full quieting signals with a 6 1/2 turn helix
when AO-51 is above approximately 35 degrees

This evening I tried a QSO with Dave G1OCN when we
both had a max elevation of 5 degrees. I could hear him
and myself for over a 3 minute period but he did not 
hear himself or me.

I was receiving with a 1.2 meter dish which has about
14 db +/- more gain than the 6 1/2 turn helix. 
With the dish the AO-51 downlink signal is +10 db over
S9 when the elevation is above about 15 degrees.
The AO-51 signal at 4 degrees elavation was S5 +/-
QSB. This is again a difference of about 14 db. (S meter
checked with a signal source and step attenuator)

This 10 to 15 db loss in signal level at very low elevation
can be partially attributed to increased range but primarily
due to the off pointing angle of the S band antenna on AO-51

Farther measurements would likely show considerable
variations in the S band downlink signal level relative to
elevation and azimuth.

Clare VE3NPC
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