checking antenna system with sun noise
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Checking antenna system with sun noise. Why the sun?. The sun is most powerful radio source seen from the earth. The next powerful radio source is Cassiopeia which is 100 times weaker than the sun. The sun noise can even be detected with smaller antennas (as mines)

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Presentation Transcript
slide2

Why the sun?

  • The sun is most powerful radio source seen from the earth.
  • The next powerful radio source is Cassiopeia which is 100 times weaker than the sun.
  • The sun noise can even be detected with smaller antennas (as mines)
  • The pointing system can follow the sun
  • Is visible during day!
slide3

Setup of equipment #1

EPFL

PC with

audacity

MixWDownloader

Audio

Voltmeter true RMS

Preamp

+20dB Gain

1dB nF

Transverter 437mc to 29mc

20dB Gain(EPFL filter and postamp)

slide4

Setup of equipment #2

  • Point the antenna to 40deg. elevation az to north (not in the direction of the sun!)
  • When preamp, transverter (postamp @EPFL) is switched ON the S-Meter on the RX should clearly increase and the with moderate Audio in speaker the increase of noise is well to hear. (watch video s_meter.mpg) [as with ICOM!]
  • Set the RX frequency close to 437.502mc.
  • Listen carefully that you hear no signal! (move VFO knob slightly up and down to check that there is no signal to hear)
slide5

Setup of equipment #3

  • The whole system should be linear working (not saturated in any stage, this is the most critical point to ensure this. Sometimes you have to repeat all the steps to check if you get always the same result)
  • Set sensitivity of Voltmeter so that it indicates around 0dB.
  • Reduce audio output of RX to reach about 0dB if the 10dB steps are to big.
slide6

Setup of equipment #4

  • Disable AGC of RX. (The audio output should increase very much because it was reduced before by the agc [and indicated by the S_Meter] .
  • With the manual rf-gain control knob set the audio that the voltmeter shows again the same value as before. Don’t touch audio volume at that moment!!
  • Set sensitivity of Voltmeter so that it indicates around 0dB.
  • Reduce audio output to reach the about 0dB if the 10dB steps are to big. [only small correction]
slide7

Measuring the increase of noise

  • Now we are ready to watch the increase of the sun noise in the audio
  • “Watch” because it is very difficult the hear a slight increase with our ears. (listen to the example sunnoise.wav it is difficult to say when you hear the sun)
  • Look to the voltmeter and let now point the antenna to the sun.
  • If all is well it stops at the maximum. (watch increase.mpg for my system)
  • If not adjust AZ and EL and note the difference in deg. >> Offset for the pointing system. Repeat after offset, all steps!
slide8

Expected results

  • If the nF of your preamp is close to 1dB and the gain about 20dB
  • With the “big filter” and the postamp (actually 30dB)
  • The increase of noise due to the sun must be bigger than for mine and about 3 to 4 dB!
  • The gain of your antenna is much higher than mines.
  • (With much bigger antennas you can detect the noise of sun via the moon [moon noise] and other comic sources)
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