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.

Amateur Satellite Basics: Where, When & What to listen for

Interested in trying something new using your handheld VHF or UHF radio?  How about putting that old scanner to use or using one of those other bands not used in your "all mode/all band" HF radio?  What about using that $20 software defined radio dongle you may have gotten for Christmas?

Diana Eng photo with home made antenna in a 2009 Make magazine article.  Look here for more info

Consider satellite listening as your next adventure!

This article will only focus on when, where and what to listen for. Later articles will cover transmitting and other related best practices in using the amateur radio satellite constellation for your enjoyment.

What is out there to listen to?

The below chart from the radio amateur satellite corporation or AMSAT for short shows the name of current satellites and general usage patterns. As you can see, there is a lot floating and spinning around Earth that are amateur focused satellites.

Where to listen for these satellites?

There are sub-bands set aside for satellites and to ensure there is minimal interference from other users in different parts of the world or for those with other interests not related to satellite operations.

In the United States, the ARRL and FCC have negotiated a general band plan along with the ITU and other regulatory bodies such as OFCOM, JARL and many others. Here is a summary taken from the ARRL website for where these special allocations of frequencies exist for satellite only activity.

• 10m band  satellite down-link from 29.3 to 29.510 MHz
• 2m band new OSCAR sub band from 144.3 to 144.5 MHz
• 2m band linear translator inputs from 144.5 to 144.6 MHz
• 2m band linear translator outputs from 145.1 to 145.2 MHz
• 2m band OSCAR sub band from 145.8 to 146.0 MHz
• 70cm International satellite sub band from 435.0 to 438.0 MHz
• 23cm band satellite up-link sub band from 1260 to 1270 MHz
• 13cm band satellite sub band from 2400 to 2410 MHz

The above adds up to almost 24 MHz of total band width available for two way satellite communications.  Not included above are other frequencies available for "Earth-Moon-Earth" communications where you can bounce your signal off the moon as a passive repeater to communicate to other stations elsewhere on Earth. Also not included are frequencies at the 3.3 GHz, 5.6 GHz and 10 GHz frequency bands also used for satellite communication.

Have a look for more detail here on the ARRL website: http://www.arrl.org/band-plan 

Making it more simple

The below frequencies would be a good starting point for just listening, so save them into a radio that you have plenty of left over empty channels in or some other radio you do not use too often.

FM based satellites (down link frequencies)

• SO-50 on 436.795 MHz
• AO-85 on 145.980 MHz
• AO-91 on 145.960 MHz
• AO-92 on 145.880 MHz
• ISS on 145.800 MHz ( Over North America only)

There are a few others that can be looked up on the AMSAT website and the above are the most easy to listen for currently.  https://www.amsat.org/fm-satellite-frequency-summary/ 

SSB based satellites (down link frequencies)

• FO-29 on 435.8 to 435.9 MHz 
• AO-73 on 145.950 to 145.970 MHz

These will be in side band mode and may either be USB or LSB depending on what is sent up via up link and is then inverted on the way down. Other SSB or "transponder" satellites can be found here: https://www.amsat.org/two-way-satellites/

Data focused satellites (down link frequencies)

• APRS via the ISS on 145.825 MHz
• APRS via NO-44/PCsat on 145.825 MHz

There is a lot more not even touched on in this article such as FalconSat, LilacSat, XW-2 Series and others, but all the above should be easy to hear with even modest antennas such as a 3 element tape measure beam or a simple gain "rubber duck"

How to find when to listen?

There are many applications such as Orbitron, Gpredict and others for PC or MAC based computers, but are not very portable.  For an Android based smart phone, look for "ISS Detector" in the Google Play store. It does much more than just predict when the space station is overhead.

AMSAT has a prediction tool on its website here:  http://www.amsat.org/track/index.php

Also, NY2O has a great website as well for finding when to listen: http://www.n2yo.com/passes/amateur-radio.php 

Next steps?

K6KLS has a great website for getting started called http://www.work-sat.com and is worth having a look for more info.

There are also a number of dedicated discussions taking place on Echolink, D-Star and DMR where satellite enthusiasts gather to talk about best practices, so have a look at the HVDN activity calendar to learn more.