[amsat-bb] 435 AO-40 uplink

[Charles Suckling <charles.suckling@xxxxxxxxxxxx>]

Hasan

Based on lots of observations (ie watching the level of the beacon) , Mode 
L uplinks have to be very strong indeed  before there is any significant 
"robbing" of downlink power.  At such times the mode L agc will be in the 
5-10dB region.  Unless the stations you can hear using Mode L are causing 
this level of agc, it seems more likely that U uplinks are being affected 
more by the agc on Mode U than by what Mode L stations are doing.   While 
the Mode L  generated downlink signals are still some dB short of the 
beacon, I don't think they will be stealing enough power to be easily 
observable on other downlink signals.  More likely, they will be making it 
more difficult for lower erp Mode L stations by activating the agc.

With AO-40 now at longer ranges, the L receiver agc does not often come off 
the 0.74dB "endstop" even with the "big guns" operating.  The U receiver, 
on the other hand, shows much greater variations.

A mode L station with a constant erp will therefore achieve a more 
consistent downlink level relative to the beacon than will be the case on 
Mode U.

This posting is not meant to condone or encourage excessive power on Mode 
L.  It is a wonderful uplink facility, which suffers less QSB under high 
squint conditions, and very consistent downlink signals.  I agree that it 
is a shame that a very few stations seem to be abusing 
it.    Operationally, there may be the need for greater care with uplink 
erp, as the amount of erp needed varies quite significantly with squint 
angle (perhaps more so than Mode U).  Thus there is a need to back-off 
uplink power from say 20 degree squint to 6 deg squint.

73

Charlie G3WDG





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