Friday, June 29, 2007

Oven Controlled Crystal Oscillator MCOCXOW

I looked for crystal controlled COs. Here is one data sheet from Golledge. Excellent stability, we do not know the price. It is their featured product, from price and availability point of view.

AIPS : initial calib idea

Initial Calibration steps in AIPS

  1. INDXR
  2. First clip source for arbitrarily high points (100 KJy), due to correlator errors. (CLIPM)

  3. SETJY to set fluxes of prim calib sources in SU table
  4. CALIB on prim calib to find antenna solutions, SN tab 1
  5. CALIB on second calib : SN tab 2
  6. GETJY to calculate second calib fluxes to second calib (using SN and SU tables)
  7. CLCAL apply second calib source calibration to target sources: CL tab 2

Now, one is free to excise interference. once one has cleaned all the data, return to step 4 above to redo the calibration process (after deleting all SN and CL tables generated above).

Thursday, June 28, 2007

Is our PM senile?

One of Gandhi's letter goes on sale somewhere in the world, and some concerned 'Gandhians' wake up and write to the PM. Our ever-ready prime-minister orders Ministry of External Affairs to intervene to 'acquire' the letter from the Christie's.

Now, either those Gandhians have no better work to do than asking my poor country to pay up 10,000 pounds for a stupid piece of paper. Or PM has gone senile to provide so much of attention to some old, half-dead people. Or, perhaps I have too much time to ponder over such matter.

BUT, NO! It's my fu***ng tax money, and some oldies are looting it. They, by virtue of their age, do not pay any tax, if I remember correctly.

Update: India may serve a notice to Christie's, looks like the Law department has nothing much to do either. There are so many legal reforms pending, all we think of is one piece of paper...

fruitful day!

things done:

  1. AIPS processing tutorial by Chiranjeevi, it has given a new perspective about GMRT interference removal and calibration.

  2. ms for SAX 1808 paper is ready for desh's view.

  3. there has been tons of discussion about radio telescope.

    • the 2-bit samples from 4 elements could combined in one byte per sample rate.

    • Cross-correlations of each two-element pairs (total 6 pairs, called 'baselines') can be done for N delays. Resultant array of N correlations can be passed over to FFT, resulting in amplitudes and phases for N/2 spectral channels. (This job can be simplified by using tabulated results for all 8-byte combinations).

    • The value N above is decided by delta-u and delta-v that we can have, using 1/imsize for our map (possibly 1/60 deg).

    • We need to keep computing such cross-correlations over a large time, integrating amplitude and phases over a large time (about 8 seconds or so).

    • These integrated amp and phases are the output (dynamic spectrum) of an effective software correlator.

Wednesday, June 27, 2007

BITS Goa Radio Telescope

when i spoke about our plans for hardware for our radio telescope, there was some feedback from my supervisor (Deshpande, RRI). he was of the opinion, that

  1. our telescope was a fantastic idea, and could eventually do international science using 4 element dipoles. we have to plan and execute it well, of course.

  2. in the beginning, we could make images using 2 antennas only, with Mandar and Aniket's data acquisition cards. this means, as soon as we demonstrate 2-slit interferometer, we can think of maps in the second semester.

  3. we should think of using 2 bits and less bandwidth. eventually, we will have 4 element dipoles. so, we will have to store 4x2 = 8 bits = 1 byte at nyquist rate. if we opt for smaller bandwidth (0.25 MHz), we could be saving 0.5 MBytes per second on the disk, with each byte being a sample each from 4 elements.

  4. In the immediate plans:

  5. we should converge using "Mini Circuits" ICs for our RF components. See their website

  6. also, for LO stability, either

    a) opt for GPS receiver, and use its 10 MHz signal for LO

    b) use a "oven controlled crystal oscillator"

    the second option is better for us for now. we will continue to explore the second option for better eventual stability of frequency signal. for better mapping, we need our sampler and LO to be really stable.

Wednesday, June 06, 2007


I read the book Freakonomics. The book entertains and just gleams economic incentives in many daily issues (of largely American life). However, the best thing was the data about education gleamed from US schools, the incentives for cheating in high-stake exams. Thinking on that line, here are a few questions that arose in my mind:

  1. What is the incentive for a student to join a school? Or, in other words, can we convince every parent and child to take education seriously, think long term, invest time and money in it?

  2. What is the incentive for a bank or financial company to fund a student for his schooling? Can a micro-finance company find some benefits in spreading basic education in rural areas?

  3. What is the reason that students sleep in my class? Or what incentive do they have in listening to me and to work harder on the course material?

  4. What is the incentive that I keep myself in education? What would make me stop and move away from Goa?

The last one is a serious question too!