[evlatests] P-band switched power observed at S-band

[Wes Grammer]

The noise diode has a specified bandwidth of 1000 MHz, so I would expect 
if you had noise leakage at S-band, you'd certainly see a lot more at 
L-band. Also, given the LBRs are nominally all the same, one wouldn't 
expect ea03 to be that different from the others, unless something is 
broken in the cal path.

If the cal coupler was installed backwards on one or both channels, most 
of the cal power will be radiating out of the dipole, rather than 
injected into the front end. Depending on the range of adjustment 
allowed and the directivity of the coupler, this might have gone 
unnoticed when it was built. Or alternatively, if the isolated port 
termination on one of the coupler is broken or missing, a lot more power 
will be dumped into the dipole. Since the LBR has linear polarization, 
the excess power may be seen in both channels on the cryogenic receiver.

It would be easy to swap this receiver out, and check it in the lab.


On 6/17/2016 5:42 PM, Vivek Dhawan wrote:
> Based on Paul's list, I looked at Pdif vs. antenna at P band.
> Turns out ea01 has zero Pdif at P band, which explains why it
> is so good at not leaking into S band. But ea10, 11, 18, at
> the bottom of Paul's list, are really good, they have normal
> P-band cals and do not leak. We should figure out what is
> different between one of these and ea03, the worst.
>
> Looking at the block diagram (maybe not correct) a 500MHz low-
> pass filter on the output of the P-band noise diode, before it
> is injected into the P band receiver, might fix it.
>
>>>>> > >  Cheers,
>>>>> >  Paul
>>>>> > >  ----
>>>>> > >  P/S Pdif ratios
>>>>> > >  Ant    IF-A   IF-B   IF-C   IF-D
>>>>> >  ea03*  0.758  0.763  1.355  1.350
>>>>> >  ea07   0.503  0.492  0.512  0.506
>>>>> >  ea09*  0.416  0.422  0.292  0.286
>>>>> >  ea15   0.400  0.400  0.282  0.295
>>>>> >  ea25   0.247  0.299  0.015 -0.014
>>>>> >  ea21   0.244  0.248  0.457  0.498
>>>>> >  ea26   0.151  0.158  0.125  0.116
>>>>> >  ea12*  0.136  0.133  0.494  0.474
>>>>> >  ea05*  0.119  0.122  0.077  0.074
>>>>> >  ea14*  0.112  0.116  0.147  0.146
>>>>> >  ea28   0.097  0.102  0.065  0.065
>>>>> >  ea23*  0.086  0.087  0.167  0.179
>>>>> >  ea04   0.074  0.077  0.061  0.057
>>>>> >  ea16   0.072  0.072  0.073  0.070
>>>>> >  ea13*  0.065  0.057  0.029  0.030
>>>>> >  ea24   0.061  0.060  0.060  0.060
>>>>> >  ea27*  0.054  0.054  0.057  0.059
>>>>> >  ea17   0.050  0.048  0.069  0.050
>>>>> >  ea06*  0.044  0.044  0.049  0.049
>>>>> >  ea22   0.039  0.036  0.054  0.063
>>>>> >  ea20   0.038  0.037  0.048  0.051
>>>>> >  ea19*  0.023  0.024  0.008  0.008
>>>>> >  ea18*  0.002  0.001  0.006  0.006
>>>>> >  ea01* -0.000 -0.000 -0.000 -0.000
>>>>> >  ea10* -0.001 -0.000  0.004  0.004
>>>>> >  ea11* -0.008 -0.007 -0.021 -0.021
>>>>> > >
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