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Re: Linear link budgets



----- Original Message ----- 
From: "Grant Hodgson" <grant@ghengineering.co.uk>
To: <amsat-bb@amsat.org>
Sent: Friday, January 05, 2007 11:35 AM
Subject: [amsat-bb] Linear link budgets


> However, if 2 equal level CW signals were being transmitted, then the 
> Peak Envelope Power of these 2 signals would be 6dB higher than each of 
> the signals individually.  This is because the voltages of each of the 2 
> CW signals have to be added together, giving a peak signal with double 
> the voltage of each signal, which is 4 times the power or a 6dB increase.
> 
> regards
> 
> Grant  G8UBN

Hi Grant, G8UBN

I aegree.
As you remember AO40 had a U band uplink in 70 cm and another L band
uplink in 23 cm and both where operating at the same time in certain part 
of the orbit.

Using my spectrum analyser connected to 144 MHz IF of my 2400 MHz
downconverter it was possible for me to observe what you stated using the
following procedure:

Uplink a CW carrier in 70 cm and get a reference level on spectrum analyzer
at 2 dB/division for better definition and than switch off 70 cm

Uplink a CW carrier in 23 cm and adjust the output power to get the same
reference level on the same frequency.

Uplink again the carrier in 70 cm while carefully adjusting the frequency 
and possibly the phase until the reference level on spectrum analyzer rised
exactly by 6 dB or 4 time in power because the voltages of each of the 2
CW carriers 70 cm and 23 cm where added togheter in the transponder IF
giving a signal with double the voltage of each signal wich is 4 time in
power or a 6 dB increase as you stated.

Now if the transponder was linear to get a 6 dB increase uplinking in 70 cm
alone or in 23 cm alone it would require a 4 time increase in uplink power
or in 70 cm or in 23 cm from the ground station.

On the contrary uplinking at the same time in U band and L band on the same
frequency less than 4 time increase in uplink power (summing U band and 
L band power ) was necessary to get a 6 dB increase from the mode 
S transponder.

Switching from CW to SSB and carefully adjusting the frequency on 70 cm
or 23 cm for the minimum distortion or warbling it was possible to get a
6 dB increase in downlink with less than 4 time increase of EIRP from the
ground because probably one of the two receivers on transponder was more
sensitive of the other one or because the satellite antenna gain on L band
was greater than the antenna gain on 70 cm    

Best 73" de

i8CVS Domenico 










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