One of the great features of Amateur Radio is that it is several hobbies rolled into one. If you get bored with one aspect of the hobby, there is always something new and different to try. For the last 40 years or so, using Amateur Radio satellites' fleet to communicate has always been one of the most exciting aspects of Amateur Radio.
An amateur radio satellite is an artificial satellite built and used by amateur radio operators for various fun activities and experimentation.
However, suppose you are new to amateur satellites, or the "birds" as satellite operators often call them. In that case, it's essential to establish a general understanding of how to find, track, and decode these modern-day wonders.
Tracking the birds
To listen or communicate through an Amateur Radio satellite, you first have to find out when it will be within the range of your station. Fortunately, most of us now have a computer in our ham shacks and access to the Internet, so tracking satellites has become much more comfortable than it used to be.
Though there are many commercially open-source software like Gpredict and Orbitron, which can be used for tracking the satellite, the one most popular among Amateur Radios is Heavens-Above, which is available both in the form of a web and a mobile application.
Types of equipment used
Contrary to what you might believe, you don't need a super-powerful FM transceiver and a vast antenna to work the "birds". I (and many other amateur satellite operators) have sometimes met success using just a simple dual-band hand-held radio and an antenna with just a bit more gain than the ordinary "rubber duck."
Nowadays, many off the shelf cheap transceivers are available to hear and record the "birds." Some of the inexpensive transceivers used are the RTL family of SDRs or the Baofeg Radio HDRs(these transceivers generally cost less than $40).
You would also require a smartphone to track and record the signals and a laptop to decode the signals.
Receiving my first ISS SSTV image
The ARISS RUSSIA TEAM transmits slow Scan Television (SSTV) from the amateur radio station in the Russian Service Module of the International Space Station using the callsign RS0ISS. The equipment used is a Kenwood D710 transceiver running about 25 watts output, which provides a robust signal enabling reception with simple equipment pieces.
SSTV events are generally scheduled once every three months; however, they do not have a fixed schedule and are generally kept as an event to celebrate the Russian Federation's achievements.
In the past, twelve different images were sent on 145.800 MHz FM using the SSTV mode PD180 with a 3-minute off time between each shot. This has now changed to use the faster PD120 mode with a 2-minute off-time, allowing more images to be received in an orbital pass.
To receive an image, we must find the ISS-SSTV events' schedule from 'amsat-uk.org' and pass timings & other details using the Heavens-Above app. We must make sure that we have a high elevation pass; otherwise, the images would be highly distorted. Also, we should make sure we have the right-pointing direction of the antenna for maximum gain. I used my phone to record the signal from the baofeg radio and later used the MMSSTV PC application to decode the signal. We can also use the conventional mobile application Robot36 to decode the image.
Receiving NOAA weather satellite images with Baofeg radio
The NOAA Satellite and Information Service provide timely access to global environmental data from satellites and other sources to monitor and understand our dynamic Earth.
Only NOAA 19,18 and 15 are currently active and are transmitting images continuously in the VHF spectrum.
Unlike the SSTV transmissions, receiving NOAA weather images with a Baofeg radio is relatively rare and complex. The steps used in receiving SSTV transmissions are similar to the steps used in receiving NOAA transmissions. However, after recording the signal, the recording has to be resampled to 11025 Hz to help the software decode. The resampled signal ( .wav file) is then used to create the final image using the WXtoImg software.
The meteor M2 satellite transmits much more high-quality images at speeds up to 80kbps in VHF with QPSK, remarkable at such low frequencies. Though it is comparatively difficult to receive these images, as the Russian government has not released proper documentation , however many commercially available software's are available to decode them. These signals can be quickly received using an RTL SDR.
They use a unique form of transmission known as LRPT(Low rate picture transmissions). The low-rate picture transmission (LRPT) is a digital transmission system, intended to deliver images and data from an orbital weather satellite directly to end-users via a VHF radio signal. It is used aboard polar-orbiting, near-Earth weather satellite programs such as MetOp and NPOESS. LRPT provides three image channels at full sensor resolution (10-bit, 1 km/pixel, six lines/second) in addition to data from other sensors such as atmospheric sounders and GPS positioning information.
One of the first things you will learn to do after finding out when a particular satellite will be within your station's range is to listen for the satellite's beacon. Most satellite beacons consist of one or more transmissions coming from the satellite at a fixed time interval that will assist you in your searches and get information about the satellite's health and the types of transponders that the satellite might have.
Most satellite telemetry signals, which consist primarily of transmissions about the satellite's health, are also sent to ground controllers via the beacon. What's more, some satellites even provide information regarding their transponder schedules, along with other items of interest to satellite operators using their beacons. However, in AO-51 and most of our other FM satellites, the single-channel downlink is itself, the beacon. Sometimes beacons are a significant determinant of a satellite mission's success and are also used to help track down long lost satellites.
The activities mentioned so far can be easily performed without having an official license. However, to transmit signals in Ham bands, one must obtain a regulatory body's ham operator license.
A transponder is a circuit that receives your uplink signal and then retransmits what it hears via its downlink transmitter, much like an FM repeater does. However, unlike a terrestrial FM repeater, which has a specific input and output frequency in the same band, most amateur satellite transponders receive and then retransmit what they hear on another frequency (or frequencies) another amateur band entirely. In short, most amateur satellites act much like cross-band repeaters in the sky.
As a satellite is a moving target, signals being passed through it will exhibit a pronounced Doppler shift, just like the changing pitch of a train whistle as it approaches and then departs. As the satellite comes near us during a satellite contact, both uplink and downlink frequencies will appear higher than those published. As the satellite passes overhead, both the uplink and downlink frequencies will then appear to drop in frequency than those published slowly. And, as if that wasn't confusing enough, this apparent frequency shift will seem to be more pronounced on the higher frequency (shorter wavelength) amateur bands than on the lower ones.
An exciting story of transponders is the case of the AO-7 satellite. In the summer of 1982, the Fighting Solidarity in Wrocław learned that AO-7 became periodically functional when its solar panels got enough sunlight to power up the satellite. It was then used to communicate with Solidarity activists in other Polish cities and to send messages to the West. Satellite communication was invaluable, as the regular telephone network was tapped by the government and shut down when martial law was imposed in December 1981. Ham radios were not of much use as they were easy to track.
On the other hand, a satellite link required highly directional antennas, which were impossible to track by the regime. In 2002 Pat Gowen (G3IOR), inspired by Fighting Solidarity's history, attempted to communicate with AO-7 and confirmed it to be operational. AO-7 is till date the longest-serving amateur satellite.
The amateur community, though present, is tiny in India, partially due to a lack of proper guidelines by the government. Two popular websites where you can find updates and support are https://amsat-uk.org and http://n2yo.com. Apart from these you can perform other fun activities as well, like hear the astronauts in ISS (if lucky even talk to them) and talk to your friends far apart using these radios. During a natural calamity, you can even help your localities by receiving important broadcasts by the government. Amateur radio is pervasive in the West and is the only hobby supported by the International Space station.