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Thursday, April 26, 2018

AO-92 & 3 steps for communication success


In January of 2018, the AO-92 satellite was put in orbit and was soon operational for amateur radio operators looking to communicate with other like minded enthusiasts.

A recent contact made between Steve K2GOG in FN30 and Alan VY2XU in FN86 using AO-92 satellite on April 26th morning to show a typical satellite communication footprint.

The AO-92 satellite, also known as Fox 1D was launched from the Satish Dhawan Space Centre in Sriharikota, India.  This small "cubesat" allows users on Earth to transmit on 435.350 MHz and then get real time repeated back out from the satellite over 145.880 MHz for others to hear.

The orbit height is about 250-320 miles above Earth at any time, so any station within a radius covered below the satellite is possible for just a few minutes until the next time the satellite passes over again. The potential range of communications is almost 800 miles!

30 other "cubesats" were deployed at the same time from the PSLV-C40 rocket

It is very easy to hear the AO-92 using a basic directional or whip type of antenna and appropriate radio. The receive or "down-link" frequency of 145.880 MHz is not as affected by the speed at which the satellite is traveling which is about 5 mile per second.

However, the transmit or "up-link" frequency is and the user needs to slightly adjust above or below 435.350 MHz depending if the satellite is headed towards or away the user location. This is known as "Doppler Shift".

The AO-92 satellite will appear to be on frequency when it is as close to the user as possible, but as it moves further away it will seem up to 15 kHz different which makes communicating through a satellite like this a little challenging at time.

The higher up in frequency has a greater affect when it comes to the Doppler affect which is why the satellite uses a lower 145.880 MHz in order to make it easier hear and encourage people to listen for it.

Beyond knowing the correct transmit and receive frequencies, the user also needs to transmit a sub audible tone of 67 Hz.  This is needed to prevent interference from getting into the satellite.  This tone is almost like a secret password needed to use the satellite. Without it, you can hear the satellite fine, just not be able transmit and be repeated back to Earth.

Helpful tips for using the AO-92 satellite

  • Listen a few times to get familiar what satellite users talk about before transmitting
  • Program your radio in advance of the satellite pass
  • Be courteous to other users and keep communications short
Using less than 2 watts of transmit power is all that was needed to contact Alan 600 miles away thanks to the AO-92 satellite.   To generate a helpful grid overlay to easily identify where other stations are located using as few as 4 characters, here is a nice file provided by Ari  OH2ECG to be used with Google Earth.




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