LBN SEFD across the reciever band

14may02

The source B0831+17 was tracked rise to set with the lbn system doing 1 minute on off position switching. The receiver is circularly polarized but rapidly moves to linear polarization over a 100 Mhz. The source is < .6% polarized (from the nvss data). The frequency bands used were:

band	frequencies
#1	1150,1200,1290,1415
#2	1340,1415,1500,1560

Frequency band 1 was used rise to 14 degrees za and then the program began alternating between band 1 and band 2. The SEFD was computed for each measurment using chris salters fit to the source flux. A 6.25 Mhz bandwidth was recorded. The radar blanker was not used (so the point at 1340 Mhz may have been affected). The plots shows the SEFD vs frequency and zenith angle. The figures are:

Fig 1 shows the SEFD vs frequency with pol A black and pol B red. The vertical range is the za dependence. 1200 and 1560 Mhz sefd are definitely worse.
Fig 2 plots the SEFD vs za by frequency. The top plot is pol A and the bottom plot is pol B. Each color is a different frequency.
Fig 3 is the ratio of the SEFD to the SEFD at 1415 Mhz. The upper plot is pol A and the lower plot is pol B. Larger numbers mean worse performance.
Fig 4 plots the ratio SEFD POLA/SEFD POLB vs frequency. Pol A is worse than polB by 10 to 20% over the useable range of the receiver. The bump at 1340 Mhz may be from the FAA radars at 1330,1350 affecting 1 polarization more than the other.

Conclusions:

The SEFD for lbn stays below 4 at low za for 1260 to 1530 Mhz.
Polarization A SEFD is 10 to 20% worse than pol B. The daily system temperatures measured using the cals at 1415 Mhz give TsysA=30 and TsysB=26. The difference 4./26 is 15% and agrees with the SEFD ratio at 1415 Mhz. So the discrepancy is being caused by the difference in Tsys and not the gain (it also means that the calratio at 1415 is probably correct).

processing: x101/020514/doit.pro

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