[amsat-bb] SQUINT vs Performance Profile from AO-40

["Colin Hurst" <hurst_cj@xxxxxxxxxx>]

All,
With the prospect of the S band transponder being switched
on again in the coming weeks, I would like to share we you
some preliminary results that I have obtained from evaluating
my station performance against squint.
The nitty gritty of how I obtained these results will in due course
be written up as an article which I will ask Paul to out on the 
Amsat site.
The database from which this information has been compiled
covers 40 Orbits, 27,000 CRC'd A blocks and countless non
CRC'd blocks. It has not been a 5 minute exercise.
To appreciate this information I suggest you plot the data
below on a sheet of graph paper or if you have a copy of MS
Office (or other) chart it using MS Excel (select smooth line).
The important thing to remember that this is a PERFORMANCE
PROFILE as viewed at the qth of VK5HI. 
The objective was to qualify downlink performance versus squint 
angle. The info below is a "smoothed" curve for reception of
the S2 Middle Beacon. 
Although based on telemetry sampling the profile should equally
apply to the transponder. I would like to think that it will help to
avoid some of the levels of frustration noted on the BB by fellow 
amateurs, coming to grips with the "practicalities" of using AO-40.

Current S2 downlink reception equipment is
750 mm solid aluminium dish.
3 turn helical feed, 7.3 degree pitch spacing.
0.7 dB NF / 38 dB preamplifier (DB6NT)
Converter SSB UEK-13 
or AIDC-3733 (with k5gna Murata PCB)
Telemetry capture with G3RUH Modem with P3T (W4SM)
and AO40Rcv (AE4JY) running in parallel. Primarily using
AO40Rcv for auto up/down keying of 736R frequency control.

Best regards,
Colin VK5HI

VK5HI S2 Downlink Performance Profile
Squint    dB
0           0.0
5           0.0
10         0.0
15       -0.5
20       -1.5
25       -3.5
30       -6.0
35       -12.0
40       -24.0
45       -30.0
50       -27.0
55       -22.0
60       -16.0
65       -16.0
70       -22.0
75       -29.0
80       -35.0
85       -38.0
90       -40.0


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