[evlatests] Widened L-band tuning for VLA antennas

[Ken Sowinski]

On Fri, 9 Nov 2007, Rick Perley wrote:

>    1) The previously-reported incoherency between the VLA and EVLA is
> now known to be due to the executor's (mistaken) belief that the L6
> synthesizers cannot bet set above 3090 MHz.   Hence, the VLA antenna
> were fringing nicely at another (unrequested) frequency.  My earlier
> tests (on antennas 5 and 10), taken under Modcomp control ( which
> apparently suffered no such misconceptions) clearly show that 4010 MHz
> is a legal and working frequency.  Ken is currently checking the
> documentation to determine what the upper limit is.

The executor thinks that 4010 is the highest legal L6 frequency.
For a 50 MHz BW observation that covers 1810 to 1860.  In gneral:
L6   F_sky range
4010 1810 to 1860
4040 1840 to 1890
4060 1860 to 1910
4090 1880 to 1930

The LO setting algorithm in the executor will want to choose
4040 over 4010 when the band center is above 1835 or so, but
fails because of the builtin limit of 4010.

Clearly, from past experience,  most L6s can tune higher than 4010,
but we are on the falling shoulder of the C band IF response and
losing sensitivity quickly.

1.  We should find out whether most L6s can tune to 4040 or 4060.
2.  I will have to convince myself that raising the L6 tuning
     range will not have any unwanted side effects at other bands.