[evlatests] T302 Linearity Test

[Paul Harden]

Bob Hayward wrote:
> If the non-linearity is somehow coming from the LO used in the T302 
> leaking into the T304 and compressing the first RF amplifier, then 
> switching in the Solar 20 dB Attenuator wouldn't affect the strength of 
> the LO birdy (since the Solar Attenuator is in front of the T302 mixer). 

The T302 is an upconverter using high-side LO injection.  For C-band, 
the LO is in the order of 16 GHz or higher.  All T302s received 
extensive bench testing to ensure they were compliant to specifications. 
  Test data sheets exist on each T302 module build.

The amount of LO power and birdies was one of the things tested on each 
IF.  I believe the specs were LO leakage in the IF must be at least 40dB 
below the LO power, and -70dBm minimum on the IF outputs.  The average 
IF output power was around -35dBm.  I do not recall ever having a 
problem with achieving the LO leakage/spurious specs.  There was almost 
scarcely a hint of the LO in the IF outputs.  That was measured with the 
8-12 GHz IF filters on the T302 output (even though further downstream 
in the system).  It seems to cause compression problems in the T304 
amplifiers, the LO leakage would have to be tens of dB above the nominal 
-35 or -40 dBm IF power.

Still, it may be a good idea to look at the C-band inputs to the T304 to 
ensure nothing has changed, or we don't have LO leaking in from some 
other source (bad cable or something).

Eric Chavez, who now takes care of the T302s, can better answer what 
these power levels are.

Paul Harden