[evlatests] T301 and T302 headroom

[Terry Cotter]

The 4P converter does not meet the Headroom spec as called out in the 
project book. The project book spec is 45 dB from 1 dB compression. The 
spec it is meeting as measured from the converters built is 38 dB. The 
45 dB spec is what Paul measured on a previous converter and I believe 
was an error since the converter was oscillating. The question is what 
do we need. I asked Chuck what the headroom is of the receiver but he 
could not tell me. I believe the problem can be fixed by moving some of 
the gain to after the mixer and adding gain to the power detector 
circuit. The headroom of the Baseband converter is 30 dB. All of these 
converters will have to be retrofitted in the future with the solar 
attenuators.


The LSC converter also does not meet the headroom spec in the project 
book. Its specification is a little more complicated since three 
different receivers are involved. The L-band spec is 44 dB and it is 
meeting about 35 dB. The S-band spec is 41 dB and it is meeting about 33 
dB. The C-band spec is 39 dB and it is meeting about 31 dB. The headroom 
specs are for noise power and the measurements are being made with a CW 
signal. There will be some difference with the measured headroom when 
noise in injected. There is also some confusion as to the RF input 
level. The headroom of the L-band receiver is specified to be 40 dB, the 
S-band 38 dB, and the C-band 33 dB. Again the headroom of the Baseband 
converter is 30 dB.