IFLO compression by the FAA 1350/1330 Mhz radar using lbw,lbn


lband wide circular polarization.
lband wide linear polarization.
lband narrow circular polarization.

     The compression of iflo/ lband receivers (lband wide , lband narrow) was measured on 29apr03. The setup was:

Three set of measurements were done
  1. lband wide circular polarization, (hybrid in).
  2. lband wide linear polarization, (hybrid out).
  3. lband narrow.
    The power levels were adjusted to have -40 dbm upstairs and -52 dbm downstairs (these were the values on the power meters, the actual values are 20 db more do to the coupler). With -52 dbm downstairs, the fiber optics can not provide enough power to saturate the downstairs iflo (see power levels in the downstairs iflo). So any saturation must be occurring upstairs.

   Data was taken for 100 seconds. There were 8+ complete rotations of the radar in this time (12 second rotation period). The 1415 Mhz samples were normalized to (sample/median(power) - 1)  where the median power was compute over the 100 seconds.

    The 1350 Mhz data was searched for the peaks when the radar was pointing at the observatory. These ipps (the 95 samples) were then plotted. The 1350 data was normalized to full scale while the 1415 Mhz data was normalized to medianTsys -1 (so the radar 1350 scale and the 1415 Mhz scale are not the same).  Each data set has two pages:

lband wide circular polarization.

The compression went to about 80% (-7 db) with polA a little worse than polB.

lband wide linear polarization.

The compression went to about 80% (-7 db)  with polA a little worse than polB

lband narrow circular polarization.

The compression went to about 80% (-7 db)  with polA a little worse than polB. One ipp (the dark red) had  a large 1350 value and small 1415 value for the entire 95 usecs.
Except for the one ipp of lbn, all of the compression recovered within the pulse duration (5 usecs). You can see the double bumps in the  faa radar (this is the 1350 then 1330 pulses spaced by 6 usecs). The compression actually starts to recover  during the 1 usec between the 1350 and 1330 pulses.


  1. The IFLO (connected to either lband system) is being driven into saturation by the 1330,1350 faa radar pulses when they point at the observatory (once every 12 seconds). The compression goes to 80% (-7 db). It is important to realize that it is the IFLO (first mixer stage) and not the dewar/postamp package that is being driven into saturation. The mixer chassis has about 40 db of gain and its amplifiers have the same dynamic range as those that precede it in the postamps of the lband receivers.
  2. The system recovers rapidly from the compression (within the 2 usecs of our time constant)
  3. There was one unexplained ipp (95 usecs) when the radar was high all the time and the 1415 Mhz was low. It did  not repeat.
processing: x101/030429/dofaa.pro