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R: AO-40 ordering antennas, downconverters




----- Original Message -----
From: AA2AE <aa2ae@optonline.net>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, July 23, 2002 11:51 PM
Subject: [amsat-bb] AO-40 ordering antennas, downconverters


> Group
>
> The Transystem downconverter with 37db gain and 1db NF seems to compare
well
> with the SSB Electronics UEK 3000 converter and it's a lot cheaper.
>
> Any comments on this set-up and antenna alignment/mounting tips welcomed.
>
> Thanks for all your help.
>
> 73, Tony - AA2AE
>

Hi Tony AA2AE,

Transystem downconverter NF=1 dB

SSB Electronics UEK 3000 NF=0.6 dB

How much improves the signal to noise ratio (S/N) switching from an overall
1 dB NF to an overall 0.6 dB NF with the same antenna ?

NF= 1 dB ; Noise factor F=1.259 ;Equivalent noise temperature =75 kelvin

NF= 0.6 dB ; Noise factor F= 1.148 ;Equivalent noise temperature = 42 kelvin

Suppose that the cold sky temperature + temperature due to spillover is 10
kelvin

With Transystem the overall T= 75+10=85 kelvin
With UEK3000  the overall     T= 42+10=52 kelvin

Less noise using UEK3000 = 10 log     (52/85) = -2.13 dB
                                                             10

or 2.13 dB improvement in signal to noise ratio using UEK 3000
against Transystem

So Transystem seams not to compare well with UEK 3000 because the
S/N ratio improvement in dB is much more than the difference in dB
between the NF of the above converters particularly when the cold
sky temperature added to that due to spillover is very low.

An improvement of  S/N=2.13 dB make the difference when squint angle
is very high and signals to be received are very weak because to be received
with a 3 dB best signal to noise ratio it is necessary to double the uplink
power.

I hope this help a bit

73" de i8CVS Domenico

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