[evlatests] P band, 4 band and power levels

[Charles Kutz]

With ~ 57dB of gain in the 4-Band, adding 15 dB of attenuation at the 
output will have little effect on the noise figure.

nf=nf1+(nf2-1)/gain1

The 15dB attenuator is based on the observed difference between the peak 
of the 4-Band signal and the peak of the P-Band signal.

That said, we intend to arrive at the optimal solution empirically.


Chuck Kutz



Paul Harden wrote:
> 
> Barry Clark wrote:
>> But 15 dB sounds too much - it will decrease the headroom 
>> available to the P band.
> 
> In the 4/P Converter, the 4- and P-band signals are combined just prior 
> to the mixer.  Attenuating the 4-band signal would not affect the P-band 
> power to the mixer.  The mixer is the limiting device that determines 
> overall gain headroom.  At present, the higher power at 4-band causes 
> the mixers to go into gain compression about 10 dB before P-band.
> 
> It would seem that by attenuating the input power at 4-band *only*, this 
> would improve the 4-band headroom and leaves the P-band headroom as it 
> is (about 36dB).  The 4-band attenuation would equalize the two bands to 
> about the same power level, and the same headroom.
> 
> I agree that 15dB sounds too much and could start interfering with the 
> noise figure.
> 
> Paul H.
> 
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