[evlatests] P-Band Status

[Ken Sowinski]

Some comments on Rick's report to help in repair.

On Mon, 26 Nov 2007, Rick Perley wrote:

>    a) Antenna 13 is claimed to be outfitted at P-band, but provides no
> fringes at all.  Its Tsys values are also completely corrupted.

Not working at all.  The T304 input converters are ramped
all the way up, so it looks like there is lots of out of
band noise being fed to the downconverters.  Chuck is
looking at the sampler spectra.


>    b) Antenna 21's fringes are low by at least an order of magnitude on
> all IFs.  Tsys is shown as relatively normal, so the problem is in the
> signal path.

The polarizations are swapped.


>    c) Antenna 11's fringes are low by a factor of about 2.5, on all
> IFs.    Tsys is normal, so again, we are losing signal.

Crossed hand and parallel hand correlations are all the same, so
it looks like a broken dipole or hybrid.


>    d) Antenna 26C is weak by a factor of about 2.5, and Tsys is
> elevated by about a factor of 1.5 -- close enough to suggest this is the
> cause.
>    e) Antenna 26D gives no discernible fringes, and a bandpass
> indicating no signal.  Its Tsys reads 1800K (!), and is erratic.

TP in 26C is erratic.  If the ALC is set when the power is
low, performance suffers when the power is high.  Interference
or a HW problem?  BD don't seem to work at all there seems to be
little in band power; I've no idea why.


>    f) Antenna 28C and 28D (LCP) fringes are low by a factor of about
> 5.  Again, Tsys is normal.

Looks OK today.


>    g) Antenna 7D is weak by a factor of 3.3, and an elevated Tsys (500K).

Still bad.


>    h)  Antenna 24B gives no fringes, and the bandpass is just noise.
> (The other IFs are fine, however).

Looks OK today.


>    Delays:
>
>    There are a number of significant delay errors, as listed below.
> The IF order is (A, B, C, D), in nsec.   The value is to be added to
> that which was used in the observation.
>
>    14:  0, -50, -20, -60
>    17:  0, -40, 0, -40
>    18:  -20, 0, -40, -50
>    23:  -20, -40, 0, -50
>    24:  +250, nofrg, +40, -40      **** Note delay error in IF 'A' ***
           ^^^^
Only this was fixed.

>    26: -30, 0, 0, nofrg.