[evlatests] EVLA state, April 20th.

[Ken Sowinski]

On Fri, 21 Apr 2006, Vivek Dhawan wrote:

> Antenna 13:
>
> 2. There is a 10-sec sawtooth in the phase (all IF's), of
>   magnitude 3degrees per GHz, i.e. <5deg or absent at L-band,
>   120 degrees at Q-band.

We have seen evidence of this before and it is
likely caused by misprogramming the chirp rate
register of the DDS.  An error in the data sheet
caused us to set the "ramp rate" register to twice
the required value causing the fringe frequency
rate of change to be half the required value.
This produces a maximum phase offset of about
2 degrees/GHz in 10 seconds for antenna 13; reasonably
consistent with Vivek's observation.  I will talk to
Pete about the reqired change to the L302 MIB.  Now
is a good time to fix this because we are in the
midst of redoing the L302 anyway.