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

[Paul Demorest]

This data set also has phase-binned WIDAR data, the autocorrelations 
from this can be used to look at these switched power signals vs 
frequency on a finer scale than the Pdif (which is 1 number per 
subband).  It looks like the P-band cal signal is not totally smooth vs 
freq near 3 GHz, and has some lumpiness on ~10--20 MHz scales.  A 
possibility is that there is nothing special/broken about ea03.. it may 
just happen to have a big spike in the band I was looking at, and 
looking over a wider freq range would show similar features in some of 
the apparently "good" antennas as well.  If this is useful info it could 
be tested fairly easily sometime.

-Paul

On 2016-06-20 09:12, Wes Grammer wrote:
> 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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