From ajk@astro.uni.torun.pl Wed Mar 23 19:57:59 2005 From: "Andrzej Kus" To: "Peter Wilkinson" , "Stuart Lowe" , "Neil Roddis" , "Danielle. A. Kettle " , "Ian Browne" , "M Birkinshaw" Cc: , "Roman Feiler" Subject: URGENT: OCRA-p problems solved !!!!! Date: Wed, 23 Mar 2005 20:58:32 +0100 Dear OCRA Friends, Finally I have the VERY GOOD NEWS to all of you OCRA-p works again with perfect stability and full sensitivity !!! Late afternoon tests and measurements reveal that one of our 5 cm LNA generated variable interferences which were radiated via its horn to subreflector and were seen reflected by OCRA receiver. The fault was discovered accidentally by unplugging all power supply units one by one at situation where we had high level of noise (rms=2 mV) on OCRA double difference. We did this such tests in the past but apparently this LNA doesn't oscillate all the time. It starts and stops at fixed antenna elevations (!?). Most probably with variable amplitude, frequency. This was absolutely curious behaviour, which could not have been easy spotted or deduced. Took us about 6 month to discover ! Uff what a relief ! To make the story short the current situation is as follow: 1. No sign of any amplitude jumps (to level of rms) in power outputs, single and double difference at all tested elevation range 90-40 deg. 2. Tsys for A1, A2, B1, B2 are 41, 39, 41, 39 K at zenith distance z=23 deg 3. RMS for 1 sec integration around 10 micro Volts 4. Cal 3.3 mV 5. 3C147 found immediately, no problem with pointing 6. Flux at 30 GHz for 3C147 2.324 Jy gives 0.55 mV/Jy for single horn and doubles for two horns (positive and then negative response), the effective sensitivity is about 18 mJy (1 sec integration) for one horn. Thus for two horns we get around 9 (sometimes less ~5 mJy). At the moment the weather is not perfect and warm front is about to pass. 7. It looks like we switched the output cables from video amps to DAQ card which resulted in change of A and B in the data. Thus cal is now present in A channel. Please do not be worried about this. At the moment the weather data are being collected for Stuart at Zenith and various orientation of horns against wind direction. He will get the data in the morning. Tomorrow morning we will turn the receiver round by -180 deg toy get it into the initial position as we like to have exactly the same pointing corrections for positive beam. I think that we can restart serious observations and some of you can come for astronomical measurements after Easter. I attach screen shot file showing measurements on 3C147 and CAL just to prove above news. So I am very happy man today and will celebrate the success with glass of good wine at home. Gienek and others will have it at the Observatory tonight. With best wishes and see you tomorrow at the telecon. Andrzej