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Guidelines for the observations
The following is just the check-list we use. Informations on how to
run a decametric radio observatory can be found in the NASA
Radio JOVE Project site and in the Dick Flagg's book Listening
Is the system ok?
The first step before starting the observations is to check if the
receiving equipment is ok and to calibrate the strip chart:
Let the receiver and the calibrator warm-up for few minutes.
Make sure that the receiver AGC is defeated.
Disconnect the antenna cable from the receiver input and replace it with
a 50 ohm resistor. Start Radio-SkyPipe, the plot shows the internal noise
generated by the receiver.
Re-connect the cable (and the antenna) there should be a rise in the noise
level. This noise is the background noise.
Disconnect the cable from the receiver and insert the noise calibrator.
Check that the receiver does not saturate when the noise temperature generated
by the calibrator is increased. If there is saturation then decrease the
receiver's RF gain and/or the soundcard recording level.
Now that the system has been calibrated run the Get-average-for-view function
of Radio-SkyPipe for each calibration step and note the values for later
use. Note also the value with the antenna cable replaced by the 50 ohm
This picture shows the calibration steps as recorded by Radio-SkyPipe.
The values on the Y-axis are in arbitrary units, these values can be translated
into noise temperatures using the Equation feature of Radio-SkyPipe Pro.
Have a look at the Jim Brown's article in the Radio
Jove newsletter(June, 2005) on how to calibrate SkyPipe to plot the
display in degrees kelvin.
My RF-2020 calibrator generates the following noise temperatures (kelvin
degrees): 38,000 75,000 150,000 302,000 603,000 1,200,000.
The base line corresponds to the room temperature (a 50ohm resistor
is connected to the receiver's input) followed by the 6 steps of the calibrator.
There are about 3 dB between two steps.
It can happen that after having adjusted the receiver's RF gain and/or
the recording level of the soundcard we use the receiver for other purposes
so that when starting another monitoring session the levels are not optimized
anymore for Sun/Jupiter observations and must be re-adjusted.
For that we use the function of Radio-SkyPipe that performs the averaging
on live data and this is the procedure:
How lossy is the antenna coax cable?
In the Radio-SkyPipe Options (Stripchart tab) there is a "Key Press averaging
period" parameter, it specifies the time during which the incoming data
Replace the antenna cable with the 50 ohm resistor (or insert the calibrator)
and start Radio-SkyPipe
Press ALT key and hold it down while pressing the "1" key (if incoming
data are on channel 1 or "2" if on channel 2 and so on) on the number pad
(Num Lock should be on). Release the keys
At the end of the configurable number of seconds specified in the Options,
the average data value will be displayed in the status bar.
Compare this value with the one noted when calibrating the system. Even
with a well adjusted system do not expect to get exactly the same values,
a difference of a few percent is acceptable.
If the difference is more important slightly increase/decrease the RF gain
and start again the procedure.
For each type of cable (Belden 8241, RG-213,...) the manufacturer specifies
the attenuation (dB) per 100 meters or 100 ft but after some time this
attenuation can increase because of the exposure at the outside weather
conditions. It is worth measuring the real attenuation some months after
the installation and replace the cable if the loss is higher than expected.
By means of the calibrator and of a precise attenuator we can estimate
the attenuation introduced by the cable.
The following is the resulting plot for 25 meters of RG-213 coax
Connect the cable to the receiver, disconnect the antenna from the other
end of the cable and insert there the calibrator. Set it at, let's say,
151,000 kelvin, check in the Radio-SkyPipe plot what's the corresponding
Disconnect the calibrator from the far end of the cable, disconnect the
cable from the receiver and replace it with the calibrator (set at the
same noise temperature as above), now the plot should show a higher value,
this because in the preceding measurement the cable introduced an attenuation.
We can now measure this attenuation: Insert the step attenuator between
the receiver and the calibrator.
Do not change the noise temperature of the calibrator.Play with the attenuator
switches until the plot shows the same value as when the calibrator was
connected to the far end of the cable.
The loss in the cable (dB) is equal to the dB introduced by the attenuator.
The values were averaged for each step using the Get-average-for-view
function of Radio-SkyPipe , this gave:
The outcome is that our cable introduces an attenuation of less than 1
dB (as from the cable specifications the attenuation for 25 meters of RG-213
is 0.64 dB)
Calibrator connected at the far end of the cable : Y = 3821
Calibrator connected at the receiver input (attenuator not inserted) :
Y = 3930
With 1 dB attenuation: Y=3677
With 2 dB attenuation: Y=3498
With 3 dB attenuation: Y=3328
The above procedure does not take into account the losses in the connectors.Use
high quality connectors, in particular the connector(s) to the antenna,
they can undergo degradation because of moisture. Use N-connectors that
If you use F-connectors check regularly that the body of the connector
makes a good contact with the shield of the coax. This is very importand
because in many cases the degradation of the received signal is caused
by lossy connectors.
Now the system is ready for monitoring the Solar and Jovian storms.
Have a look at the Jupiter Storms Predictions . Don't forget that the occurrence of a storm is
a question of probability. Even though a Jovian storm is predicted, it
could happen that nothing is heard. The Jupiter storm emission mechanism
is not yet completely understood.
There are no predictions for the Solar storms. But you can find a wealth
of sites dedicated to the Sun activity, start with NOAA
Space Environment Center and Solar
Terrestrial Activity Report.
Real time spectrograms covering the decametric range are available on the
internet. In Europe you can access the Nancay's
Decametric Radio Observatory.
Using the Spectrograph
software you can access the spectrograms of the University of Florida
and the Windward Community College Radio Observatory (WCCRO).
Looking at these spectrograms during the observations is very useful
in establishing if the spikes we see on the chart and the sound we hear
are really Jovian/Solar bursts.
Use Radio-Sky Pipe Pro to plot the data and to record the audio. The Radio-SkyPipe
audio recording feature is very useful to exactly correlate the plotted
data with the audio. No need to have a tape recorder and complicated procedure
to correlate the recorded audio to the plot.
Audio samples of Jovian and Solar storms are available in the UFRO
site and in the RadioJove archive.
The computer clock does not keep a precise time over a long period, it
needs to be synchronized with an atomic time standard before starting the
observations. Many sites can be accessed (NIST for example) for that. Radio-SkyPipe
Pro has a feature to automatically synchronize the clock through internet.
Clock synchronization is needed when comparing the results with other
observatories. It is then possible to see if there is a difference in time
when a burst is received, let's say, in Europe and in the US East Coast.
Start Radio-SkyPipe and calibrate the chart. The reference noise temperature
steps will allow to measure the temperature of the bursts that will (can)
And now we have to wait, drinking a cup of coffee to stay awake when waiting
for a Jovian storm in the middle of the night !
The worst enemies during an observing session are interference and power-line
buzz. Interferences can be from shortwave stations,TV sets in the neighbourhood,dimmers
and so on. Filters can help in some cases.
The power-line buzz can be very strong and destroy a session, this
noise is wideband and is caused by arching and lossy insulators in the
The observing session came to its end. Now the received data must be
HAPPY MONITORING !
Carefully check (by listening to the recorded audio) that the "signals"
in the chart are Solar or Jovian bursts .
Using the calibrated noise temperatures recorded when starting the chart
evaluate the temperature of the bursts and using the FluxDensity
program compute their flux densities.
The material collected during the session (strip charts, audio files) can
now be up-loaded to the RadioJove
archive for the benefit of all the other observers.
Before up-loading a strip chart we put in its Data File Info all informations
that can be useful to the other observers (type of receiver and antenna,
noise temperatures of the calibrator, time when a burst occurred, noise
temperature and flux density of the bursts).
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