[evlatests] Widened L-band tuning for VLA antennas

[Rob Long]

Hi all,

      4010 MHz is the highest legal and calibrated freq. on the L6.

Rob

Dan Mertely wrote:
> Even if you can get the L6 to lock above 3990, the
> F4 has an input filter on the L6 input of 3750/630, which
> eliminates the use of 4090.  -Mert
> 
> 
> Ken Sowinski wrote:
>> 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.
>>
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