[evlatests] L301 Settings at L-Band

[Jim Jackson]

All,

I just realized from Barry's message about L-Band LO frequencies that - 
despite repeated warnings from Rob, Terry and myself - you all are still 
using 12160 MHz as the LO input to the T302 at L-Band. This is a completely 
unsuitable LO frequency for this module due to the 7.5-12.5 GHz filter 
located at the input of the T304. 12160 MHz leaks through the mixer in the 
T302 and enters the T304 completely un-attenuated, then mixes with the two 
LO's in it and makes birdies in the 1-2GHz signal fed to the 
digitizers.  Based on measurements in the lab and the specs of the T304 
input filter, an L301 setting of 12928 MHz is the lowest we would 
recommend,  13184 MHz would be better.

We've been telling people this since the L-Band receiver and first early 
T302 prototype were put into Antenna 13.  Please don't bother us with any 
further complaints about EVLA performance at L-band until this is changed 
in the software, observation scripts and anywhere else it needs to be changed.

Jim


At 12:41 PM 3/13/2006, Barry Clark wrote:
>L301 frequencies were both 12160,
>L302-2 frequency was 13706.25
>
> > From rperley at aoc.nrao.edu  Mon Mar 13 11:40:27 2006
> > Date: Mon, 13 Mar 2006 11:40:23 -0700
> > From: Rick Perley <rperley at aoc.nrao.edu>
> > To: Barry Clark <bclark at aoc.nrao.edu>, Bryan Butler <bbutler at aoc.nrao.edu>
> > CC: Jim Jackson <jjackson at aoc.nrao.edu>
> > Subject: L-Band Freq.
> >
> >     Memory was right:
> >
> >     1340 MHz, BW = 12.5 MHz.
> >
> >     For this frequency, Ant. 14 did not give any fringes on IFs B and D.
> >
> >     Rick
> >