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| Noise on 2mm array roughly 2Hz/sqrt(Hz) for most pixels (assuming decorrelation works, as is usually the case). Noise on 1mm on the other hand is around 20Hz/sqrt(Hz). | Noise on 2mm array roughly 2Hz/sqrt(Hz) for most pixels (assuming decorrelation works, as is usually the case). |
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| Concerning the 1mm array, less nice. S/N is in that case, checked on Uranus, 50Jy, and Mars, 130Jy, seems 80-100mJy/sqrt(Hz), but without correcting for tau. So I'd say (Alessandro) it's not more than 2 times worse than usual. We'll see tomorrow. We're waiting for Andrea with the new mixers. Could be that the amplifiers we added to boost I and Q on the up-converting side add some noise. | Concerning the 1mm array, a bit less nice. Noise is roughly 20Hz/sqrt(Hz) .. say between 10 and 20 in good weather. Signal on Uranus (50Jy) is 5000-10000 Hz. Thus S/N say between 500 if you're pessimistic and 1000 if you're optimistic. That means 50-100mJy/sqrt(Hz) per pixel. Same thing seen on Mars (in that case, due to very low elevation, we applied a correction very approximative). S/N is in that case, checked on Uranus, 50Jy, and Mars, 130Jy, seems 80-100mJy/sqrt(Hz), but without correcting for tau. So I'd say (Alessandro) it's not more than 2 times worse than usual. We'll see tomorrow. We're waiting for Andrea with the new mixers. Could be that the amplifiers we added to boost I and Q on the up-converting side add some noise. |
Daily reports
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Contents
Thursday 8 November 2012
Alessandro and Martino driving from Grenoble to Granada with the electronic equipment (NIKEL et al.)
Friday 9 November 2012
Cryocooler started. Unfortunately the 3He pumps makes very strong vibrations in the cabin possibly affecting GISMO observations; that was not a problem as long as the weather was to bad for observations, but the forecast was good for the night, so we stopped the pump in the evening. Hopefully the pump is not mandatory for the 1st phase of the cooling process.
Saturday 10/11
The NIKA cooldown is not suffering from the pump stop. The inner parts of the cryostat are also cooling down in some way. At mid afternoon the cryostat is below 8K. However we can start the dilution only if the 3He pump is switched on. If the weather degrades again so much that the observations with GISMO are not possible any more we will switch on the pump, otherwise we have to wait until Tuesday.
Alain and Juan have been testing the NIKA software remotely, sneaking the Elvin messages from the GISMO observations.
Sunday 11/11
Snow; GISMO can't observe, so we turned on the 3He pump in the morning to proceed with the cooling process. The 3He-4He dilution started in the afternoon. ~250 mK near midnight.
Monday 12/11
Martino and Alessandro reached the telescope this morning. The cryostat is cooling down slowly but with no apparent problems. Temperature is 180mK at 1pm roughly. Expected to reach 100mK overnight. The plan in case we have to switch off the 3He pump and reduce vibrations on GISMO is to stop injecting (close eV3), stop the pump and open eV10 leaving the mixture to slowly (we hope as slowly as possible) go back in the reserve.
Tuesday 13/11
De-installation of the GISMO electronics, cryogens, installation of the NIKA electroncis, laser alignment, switch on everything. In the evening, NIKA is cold, start to look at the behaviour of the resonances. Problem: impossible to see the 1mm array ! Work till 3am to investigate the problem, make hypotheses and tests.
Wednesday 14/11
We feared the feed line was broken on the 1mm array or something else that necessitate to warm up and open the cryostat to fix the problem. We organised an emergency trip for Andrea to bring spare arrays, amplifiers, mixers, etc. In the mean time Martino found the problem: something must be broken in the IQ mixer; it delivers a 4GHz harmonics >10000 time stronger than the tones ! We could use a low pass filter so that everything higher than the band of the tones (which is 2 to 2.5 GHz) is cut, or better, we could change the mixer. In both cases it won't be necessary to open the cryostat (ouf !). Until the spares arrive we can still get the resonances of the 1mm array by reducing the power on the LO. Not great but good enough to see the resonances.
Our first hours on the sky were a bit tedious. Test various observing scripts, many little things to change in the various software, to handle, merge and format the data correctly. We gave back the telscope 2.5 hours in advance of the schedule so that Juan Penalver can do an unscheduled pointing cession with EMIR, we have enough data anyway to work and be ready for tomorrow.
Thursday 15/11
Changed other things on the 1mm (e.g. added an old isolator at input to further kill the 2nd LO harmonics). Way better that yesterday (barely seeing Mars !), but not yet optimal (noise at meast 2-3 times worse than expected. But usable. Found 90 reasonable pixels. 126 pixels on the 2mm.
Started observations at 17h. Still not possible to do the pointing model.
Noise on 2mm array roughly 2Hz/sqrt(Hz) for most pixels (assuming decorrelation works, as is usually the case). Signal on Neptune (6.5Jy at 2mm) was around 600Hz, so S/N is roughly 300. If we trust that is 20mJy/sqrt(Hz) per pixel on 2mm. This is further confirmed on Uranus (18Jy at 2mm), for which the signal is around 2kHz. The cosmetics also does look nor bad. Out of 126 pixels, by eye, I'd say 2 thirds are good.
Concerning the 1mm array, a bit less nice. Noise is roughly 20Hz/sqrt(Hz) .. say between 10 and 20 in good weather. Signal on Uranus (50Jy) is 5000-10000 Hz. Thus S/N say between 500 if you're pessimistic and 1000 if you're optimistic. That means 50-100mJy/sqrt(Hz) per pixel. Same thing seen on Mars (in that case, due to very low elevation, we applied a correction very approximative). S/N is in that case, checked on Uranus, 50Jy, and Mars, 130Jy, seems 80-100mJy/sqrt(Hz), but without correcting for tau. So I'd say (Alessandro) it's not more than 2 times worse than usual. We'll see tomorrow. We're waiting for Andrea with the new mixers. Could be that the amplifiers we added to boost I and Q on the up-converting side add some noise.