2017 May

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May 02

23:52 UT Kjell got Ant 5 back in the field, with the notch filters installed. When the 3C84 calibration occurred, I found the Ant 5 delays needed adjustment, so I did that, although it will not appear in the data until the solar day ends. The adjustment was only 0.5 ns. Some others were tweaked by 0.1 ns as well. In order to evaluate the new Ant 5 FEM, I need to first measure and set the DCM attenuations in the < 2.5 GHz bands, so that as we tune to those bands we do not saturate the ADCs. My first attempt to do that failed for some reason, but I will attempt it again this evening.

May 04

04:35 UT I finally had a chance to check the performance of Ant 5, only to find that it looks just like the other antennas. Looking into it further, I discovered that Kjell had put the notch filter in without taking the 2.5 GHz filter out! It is also in the wrong place. It needs to be between the first (Miteq) LNA and the second amplifier/first variable attenuator. Instead, he had put it between the two attenuators, leaving the 2.5 GHz filter in place. I emailed him to fix it, but I believe he is on a short vacation until next week, so nothing will happen until he returns, just before we all arrive at OVRO on May 12.

May 05

03:49 UT Kjell switched the position of the notch filters, and removed the 2.5 GHz filters in Ant 5, so I had a chance to really evaluate it. However, I find that the power is huge in both channels, requiring at least 10 dB more attenuation. Then the DCM power attenuation setting becomes too low for most bands. I am not very happy with it, but I do need to think more carefully and make sure I am making the correct interpretation. I will work on it over the weekend.

May 10

04:35 UT I took some packet capture data on bands 1, 2 and 3, and I find that the signal is not really very high on those bands. I verified by looking at the ADC levels. I then tuned to band 35 (which is 600-1000 MHz, aka band 0), and Wow!, the ADC signal was off the charts! I set the attenuation appropriately to allow me to capture some data, and could see that most of the band is filled with strong RFI. Therefore, it is very clear that what is happening is that the RF is being swamped by the <1 GHz part of the band, and is NOT the fault of the notch filter itself. So we need to add a 1 GHz HP filter (or possibly we can get the notch filters changed to cut off 1 GHz). Anyway, we will experiment when we are at OVRO next week.

May 11

03:16 UT Kjell found some 1.1 GHz HP filters and installed them in the Ant 5 FEM. I am happy to say that the FEM is performing just fine now. There is a lot of RFI in those bands 1-3, so it is not a panacea, but it will give us additional good science bands interspersed with bad science bands. I am somewhat encouraged that we could proceed with this conversion and get us our full 1-18 GHz range back! I have started a two-src.scd schedule with pcal_hi-all.fsq (will not sample the lower bands).

03:27 UT Actually, I thought better of it, and decided to modify pcal_lo-all.fsq, which was doing bands 4,5,6,7,8,9,10,11,12,12. Now it will do 2,4,5,6,7,8,9,10,11,12, so I added band 2 to the mix. Oops, that is dumb, because band 2 has the top end blanked by the notch filter. I will change to 1,4,5,6,7,8,9,10,11,12, and so will do band 1. Anyway, it is on the hi receiver right now. It will go to the lo receiver at 03:54 UT, and start the first scan with band 1 at 03:56 UT. I am not actually sure if the science bands are correctly defined for band 1, but we'll see. I am running 3C273-hilo.scd, which alternates between hi and lo receivers on 3C273 every half hour or so.