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Sunnoise measurements

 

Measuring the sunnoise will provide you with an overall performance indication of your total antenna and receiver system.

Related to the indicated sunflux it will give you a possibility to calculate the system performance parameter indicated as the G/T value. This figure can be used to compare the performance of each EME station.

Because several people asked me on the G/T performance for my system, i tried to find a way how to measure and calculate this figure.

Measuring Sunnoise

There are several ways to perform this measurement. Since i don't like to change things in my transceiver I used a calibrated attenuator in front of my transceiver to determine the sunnoise value. The measurement is straight forward. While your antenna is not pointing to the sun, adjust your system in such a way you have a traceable S-meter indication. Make sure it is not to far from the zero indication in order to avoid the AGC circuit to become active. Then point the array to the sun position and reduce the S-meter indication by enlarging the attenuator until the S-meter indicates the set-up value. Your calibrated attenuator will show the amount of sunnoise (dB's) you receive. Repeat this measurement several times to ensure no mistakes have been made.

A remark I need to make regarding this method. Sometimes it will be difficult to find a quiet zone around your location. Particular in city environments you will find noisy directions and very noisy directions. This of course will heavily influence your total dynamic range and thus the amount of sunnoise measured.

Indicated Sunflux

Besides the performance of your antenna and receiver system, the measured sunnoise is dependent on the sun's activity. This figure is measured daily by several radio stations. The figure is frequency dependent as well. This makes it little difficult since not all stations provide the proper information. For 432Mhz measurements I used the sunflux figure given on 410Mhz.

It can be found on following websites:

  1.         gopher://solar.sec.noaa.gov:70/00/latest/curind
  2.         http://www.ips.oz.au/asfc/data/sol/learmonth/iflux.txt

Initially it was somewhat misleading since i found stations indicating their sunnoise values on 432Mhz and indicating the sunflux value of a much higher frequency, like 2800Mhz.

G/T calculation

Although I'm unsure on the importance and how to do the interpretation of the resulting figures, i used information appearing on the SETI site to prepare an Excel sheet for this calculation. Basically two figures are needed to fill in for this calculation. The indicated sunflux  on 410Mhz and the measured sunnoise for your system.

Please find the Excel sheet here: G/T calculation

 

Special thanks to Richard Flagg, AH6NM providing more information on G/T determination published on the SETI site.

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