Notes to myself

apr 2003

     Notes to refresh what's left of my memory (or: "an attempt to postpone the losing battle with entropy").

Signal processing:

    going from continuous to discrete fourier transform
    polyphase filterbanks.
    gaussian width after convolving 2 gaussians.
    Jon Hagen's acf-> spectra memo (.pdf)
    rms voltages needed for 2,3,4, and 5 bit sampling.
   Radar decoding.
    clipping a sine wave

Creating harmonics (how strong the various freq terms are)
Harmonics created when clipping a sine wave.
Side band harmonics do not always move farther out than at the fundamental.
Problems using a 90 deg hybrid to convert linear to circular (lbw example)
properities of a gaussian
properteis of sin(x)/x

Computing Trcvr.
Telescope gain 
Beamwidth, near/far field transition
satellite orbits: velocity,angular velocity, period vs radius
sun,moon separation during 21aug17 eclipse

Idl use of color

Using idl to process ao spectral line data

List of cpu compute servers at AO.
Disc locations by cpu
Backing up of monitor data.
bitfield storage format. converting big endian to little endian.
Ao Network Info

Suppose you have a tone of  Amplitude A and frequency w and a side band of amplitude B  and frequency (w+delta)
                  (Aexp(iwt)+Bexp(i(w+delta)*t)2= AAexp(i2wt)+ ABexp(i(2wt +delta)) + BB*exp(i(2w+2delta)t)

rms voltages needed for 2,3,4, and 5 bit sampling.  (top)

        The optimum voltage levels for 2, 3, , and 5 bit sampling were computed using the threshold levels from fred schwab. To compute the rmsVolts I just took PktoPkVolts/Nlevels * sigmaLevels. This ignores the problem of whether or not the levels are centered on 0 volts or not.
Rms Volts vs Nbits
Nbits level threhsold
(in sigmas)
Sigma (1./level)
(in levels)
rms (Volts) assuming
2V PkToPk A/D
rms (Volts) Assuming
5V PkToPk A/D (ri)
2 .99568 1.004 0.502 1.255
3 .58601 1.706 0.427 1.067
4 .33520 2.983 0.373 0.932
5 .18814 5.315 0.332 0.830

Compute Trcvr.  (top)

    The receiver temperature is computed using a hot and cold load at the input. let: If we measure the output power ratio on load1 and load2:
y=(Tamp + alpha*Tomt + (1-gamma^2)(1-alfa)T2)/(Tamp + alpha*Tomt + (1-gamma^2)(1-alpha)T1)
Solving for Tamp gives:
Tamp(1-Y)=Y(alpha*Tomt + (1-alpha)(1-gamma^2)*T1) - (alpha*Tomt + (1-alpha)(1-gamma^2)T2)
Tamp= (1-alpha)(1-gamma^2)*(T2-Y*T1)/(Y-1) - alpha*Tomt
If you assume that alpha,gamma are equal to zero, then you will get a Tamp that is higher than it really is.

Telescope gain  (top)

k - boltzman's constant
K - deg Kelvin
Jy - Jansky
m - meters
w = watts
J   - Joules
Hz- hertz
Ae - effective area of telescope
G  - gain
T   - Tsys
k: Boltsmans' Constant
1.38e-23 Joule/degK
-228.6 db/degK
-198.6 dbm/degK
convert TempK to energy Joules
Jy: Jansky
1e-26 W/(m^2*Hz)
-260  db/(m^2*Hz)
-230  dbm/(m^2*Hz)
flux density per hz
k/Jy:boltzmans constant/Jy
1380  (m^2/K) for 1 Jy dual pol?
2760 (m^2/K)  for 1 Jy single pol?
A telescope with Ae=2760 m^2 give:
Ae/2760 = 1K for a 1 Jy source
Gain 1K/Jy = 2760m^2

G = K/Jy = Ae/2760.

G/T = (Ae/T)/2760.

SEFD=T/G = (T/Ae) * 2760.
plot sefd vs T/Ae  (.ps) (.pdf)

nrao Brightnes and Flux density


Satellite orbits

    The plots show satellite orbital velocities, angular velocity, and orbital periods vs radius (.ps) (.pdf)

processing: x101/131107/

170821 sun moon separation as see from AO

    I plotted up the sun,moon separation for the 21aug17 eclipse (as seen from arecibo observatory).
I used the jpl horizons ephemerides to compute the separation.

    the plot  shows the sun moon separation (.ps) (.pdf)

processing: x101/170821/


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