[evlatests] Widened L-band tuning for VLA antennas

[Dan Mertely]

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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