How to observe with your RadioJove receiver

Joachim Köppen DF3GJ Kiel/Strasbourg/Illkirch Summer 2004

Whatever you do at the observatory, whatever you notice with the equipment, whatever you find extraordinary about the environment, always leave a precise and careful record in the observatory's logbook!

When you start the observing run with your receiver:

• in the menu Options, submenu Identity enter your name in the Field Observer Name, then click Save and Done
• connect your receiver to the 12 V power supply, its antenna terminal to the cable from the filter and/or calibrator, and the audio cable to the computer. If you have a loudspeaker with amplifier, connect its input to the second audio output of the receiver
• switch on the receiver. You should hear a hissing noise in the loudspeaker. When you connect the antenna to the antenna socket of the calibrator - and the switch is in 'antenna' position - you should hear an increase of noise.
• if you hear any tones, whistles, melodic or rythmic sounds, man-made signals, tune a bit away, until you hear a simple hissing or rushing sound.
• make sure that the calibrator is connected to the power supply, that it is at maximum level (0 dB attenuation), and that the switch is set away from "antenna" to "calibrate". You may have noticed that the hissing noise increases when you apply power to the calibrator and when you set the attenuator to 0 dB position
• click on the "Start" button of the SkyPipe software window
• adjust the volume control of the receiver to get a trace at about 1000 to 2000 units of the y-axis. (the exact level is unimportant. But don't make it too large (e.g. 20000) because the sound card cannot handle signals stronger than about 30000, and you want to be sure to be able to record also strong solar bursts without driving the sound card into saturation...)
• now commence the calibration sequence: make a trace for about 30 seconds of each attenuation step from 0 dB to -25 dB (full attenuation). It is useful to make a note in the logbook of the amplitude value of each calibration step...
• after that last step, remove the power lead from the calibrator, and make another 30 sec recording. This is the level of the internal noise of the receiver. You should get something like this: after the six calibration steps, the lowest step is the receiver noise - after which comes the signals from the antenna at about 600 units.
  

  You should see a clear drop of the level (e.g. in Strasbourg the level changes from 200 to 180 when I remove the calibrator power), because the internal noise of the front-end of the receiver corresponds to about +6 dB over thermal noise (i.e. a factor 4), but the last step of the calibrator gives a noise of +10 dB (factor 10). If you don't see this clear change, there's something wrong! Below is a calibration sequence (in 3 dB steps) from W3FAF who prefers to record the receiver's noise also just before the sequence:

  

• after that, switch from calibrator to "antenna". Now the receiver is connected to the antenna, and the observations start.
• Do not change the receiver's volume control after this calibration sequence , because it will change the calibration!!!
• it is useful to keep also a note in the logbook about the mean or the lowest level of this external noise, as well as any remarks of how the signal sounds like, for instance whether you hear the typical crashing sounds of distant lightnings...
• Use the calibration steps to make a rough estimate of the external noise level: Because of the background emission by the Milky Way, one expects a minimum noise of about 50 kK (= +22.4 dB over thermal). This will occur only during the night, and only if there is no interference. The level of the external noise tells us how noisy our site is, thus limiting the sensitivity of our 'radiotelescope'. In Strasbourg, we have usually around 100 kK background during the day - but sometimes higher because of the computers in the building - and on a few interference-free nights it was as low as 50 kK.
• at this time, it is practical to return the calibrator's attenuator to the 0 dB position, as well as to restore power to the calibrator. In this way, you are prepared for the next calibration squence. Also, it is good to keep the calibrator powered all the time, so it can stabilize itself and give a constant noise level.

• it is a good idea to listen - using the additional amplifier-loudspeaker. But do not touch the receiver's volume control
• if you hear some man-made signals, tune the receiver a bit away to a clear spot with only hissing noise.
• you might find the chart filled with strong signals, and if you find by listening that they are artificial - such as the melodious sounds of a radio teletype transmission - tune away. But please make a note in the logbook, so that later you know that that strong signal was found to sound like ..... and judged man-made!
• you may alter the horizontal and vertical zoom of the SkyPipe screen ...
• train your eyes to identify which sound makes which kind of recording. The brief impulses or whistling sounds you'll find will make only a sharp spike. Lightning crashes make a bit longer pulses. Any radio communications (voice or data) often shows up as very strong signals lasting some time and showing quite some structure... All this is rather different from a solar burst, as you can see in the examples from the RadioJove archives at NASA's GSFC.
• you can make a calibration sequence...

• make a calibration squence to compare with the one at the start of the run!
• then press the "stop" button
• then the program will ask you whether you want to save the data. Say "yes". You do not need to enter a file name!
• then you may disconnect your receiver, and hand over to the next observer.
• record all your actions in the observatory's logbook!