[evla-sw-discuss] The T303 converter

[Ken Sowinski]

I suggest alternatives to Barry's suggested rules for using the T303.
The changes are informed by the tuning restrictions imposed on the
first LO in the Ka band receiver and, perhaps, misunderstandings on
my part.

K and Q bands are treated as Barry proposed for K band:
If all the requested bandwidth is within a 4 GHz block
    select the straight through path for both IFs, giving both IFs in USB
Else if the AC band is at higher frequency than BD
    AC uses straight through in USB, BD converts by L301-2 giving LSB
Else
    Error - cannot be tuned


Tuning for Ka band is complicated because the first LO is limited to
44 to 49 GHz.  With this limited range if any part of the requested
bandwidth lies below 32 GHz the conversion path of the T303 must be
used and that IF must be placed in the BD IF pair.  AC must lie
entirely above 32 GHz.  So:

If all the requested bandwith lies above 32 GHz
    use the rules for K and Q bands
Else if only BD extends below 32 GHz
    AC uses straight through is USB, BD converts by L301-2 giving LSB
Else
    Error - cannot be tuned


I would simplify Ku band:
AC uses conversion by L301-1, BD by L301-2; both LSB


Warning:  Though it should always work, I have not explicitly verified
that L302s can be set to get all the desired bandwidth through the
downconverter in all these cases.