Canadian Amateur Radio Heritage

For a while now I have been experimenting with tracking and decoding the radio transmissions from various satellites. Some of these are Orbiting Satellites Carrying Amateur Radio (OSCAR satellites), used for two-way Amateur Radio communications during the brief few minutes of a satellite pass. And, I’ve had a lot of fun with decoding weather satellite images from the NOAA satellites, and the Russian Meteor-M2 weather satellite, using my own home-built antennas.

Antennas used for satellite reception need to be designed for the specific frequency band and transmission pattern used by the satellite who’s signals you are trying to monitor.

Both of the antennas that I am using for these signals are home-built using 1/4 inch copper tubing, and white PVC. I have a PDF document posted here describing construction of my QFH antenna.

There are also numerous other construction documents outlined on various internet websites. Just search do a search using key words 137 MHz, QFH.

The weather satellites that I am receiving are all using frequencies in the 137 MHz band, and the signals are being broadcast from the satellite with an antenna pattern that is oriented for ‘Right Hand Circular Polarization’. The Quadrafiler Helix Antenna (Top Image) recieves those signals well.

The Amateur Radio OSCAR satellites use a full duplex transponder arrangement of communication, whereby the ‘Uplink’ and ‘Downlink’ signals are transmitted on two different bands (usually, the 144 MHZ and 440 MHz bands). For monitoring (receive only) the satellites that are transmitting the ‘Downlink’ signal on 144 MHz, I am using the ‘Eggbeater’ style antenna (Bottom Image) shown here. This antenna is also designed to receive R.H. Circular Polarization. Interestingly enough, and unlike the weather satellites with their stabilized orientation, the OSCAR satellites are slowly tumbling during their orbits. Consequently, polarization of the ‘Downlink’ signals is never constant, negating the necessity for the antenna design to accommodate circular polarization, when receiving those.

For the weather satellites I am using my Airspy HF+ SDR receiver and a small Low Noise Amplifier (LNA) designed specifically for the 137 MHz weather satellite signals. This little Airspy SDR receiver has been in use now for about 4 years, and is a great addition to my shack for both HF and VHF.

Two of the 137 MHz Low Noise Amplifers that I have used. Both of these also contain a 137 MHz bandpass filter.

The ‘Uputronics’ NOAA/APT 137 MHz FILTERED PREAMP (Top),

and ‘Nooelec’ SAWbird +NOAA 137 MHz LNA

The LNA is best placed as close to the antenna terminals as possible (rather than at the receiver end of the antenna feed line) to achieve the best Signal to Noise Ratio (SNR) amplification, which then necessitates getting power to the LNA, either with a Bias-T arrangement or external cabling.

Interestingly, the Nooelec design has provisions for front-end protection of the amplifier, but that component was not installed on the board. This LNA worked well, until I burnt out the front-end stage while running 500 watts to a nearby 20-meter antenna. Lesson learned.

For reception and decoding of the NOAA (National Oceanic and Atmospheric Administration) satellites I am using my SDR Console program which provides great features for tracking and displaying of the satellite signals. Output from SDR Console is then piped through my PC using Virtual Audio, and input into ‘WXtoImg’, a decoding software program specifically designed to decode the APT images transmitted by the NOAA weather satellites. This program shows the satellite images line by line as the transmission is being decoded in real time, during the satellite pass. The program also has some provisions for enhancement of the received images, by combining data from the satellites visible light and infrared light camera, which are both transmitted simultaneously by the satellite.

Another popular NOAA decoding software available is the NOAA-APT Decoder at https://noaa-apt.mbernardi.com.ar/

This image from NOAA-15 on 14 September 2020 showing hurricane ‘Sally’ approaching the Atlantic Coast. This is the ‘WXtoImg’ High Contrast image created from the satellites Raw Data. Map grid and geographical outlines are overlayed by the software, based on Keplerian data for each satellite which. Kepler information, is based on each satellite’s orbital calculations and needs to be updated routinely in order for the software program to know the exact location of each satellite on a given date and time. Kepler Two Line Element (TLE) data for the orbiting weather satellites is available from https://celestrak.org/norad/elements/weather.txt

At the time when I first created this page, three NOAA weather satellites were in service, orbiting in near-polar, sun-synchronous orbits NOAA-15, NOAA-18, and NOAA-19. Today however, these satellites are either nearing end of service life, or have already been decommisioned. During daylight hours orbital passes appear in a southerly path, and at night the passes appear to be in a northerly direction. (It took me a long while to figure out how that should be. No, the satellites do not actually stop and reverse their direction. Something to think about)

Subsequent orbits also appear further to the west than the previous pass (something else to think about). And sometimes passes of multiple NOAA satellites can occur within a few minutes of each other. At a few of these times, I have been able to capture sequential weather images and then been able to paste the images together in a kind of mosaic showing more geography, than I am able to for any single pass.

I’ve also experimented with decoding mages from the Russian Meteor-M2 weather satellite. Because most of the satellites are using different radio transmission types, each one of them requires a different software decoding package.

Orbitron is configured to start the SDR# program in conjunction with your SDR receiver to capture the Meteor M2 radio signals. Necessary settings for configuring the SDR# program are written into the Meteor LRPT Suite.

So SDR# is configured specifically for receiving the Meteor M2 signals. Specific SDR# ‘plug-ins’ are provided for tracking and decoding the M2 signals. SDR# will automatically start the Meteor Demodulator once the received signals are strong enough to achieve a ‘Locked’ condition.

Once the Demodulator is running, the Meteor LRPT Suite starts the LRPT Decoder. This is the point at which the whole process starts to become exciting, and you can watch three simultaneous channels decoding the weather image, line by line in real time as the M2 satellite is passing over.

When the pass is completed, the LRPT Decoder writes a number of image and data files to a specified folder. You can then open those image files to see the weather images.

You can also take those files that were written by the LRPT Decoder and load them into yet another software program called the LRPT Image Processor, to produce enhanced color images from the 3 channels of data received.

The M2 satellite produces high resolution images. Cloud free conditions during daylight hours can produce some pretty dramatic images, with considerable detail, as shown in this image.

One more interesting note! The Russian M2 satellite and NOAA-19, both use exactly the same frequency for their radio transmissions 137.100 MHz. And occasionally the orbits of these two satellites are very close to each other. When both appear in the sky at the same time, their radio signals interfere with each other to the extent that neither are decipherable.

Here in Kingston, I am a member of our Kingston Amateur Radio Experimenters (KAREX) group. One of our members, Joseph Buckley, is a Physicist with extensive background in imaging sciences. When a few of our group got into decoding WX satellite images, Joseph put together a great tutorial to explain just what it is we are actually looking at in these weather satellite images. His PDF document is available here. Very informative and well worth a read for anyone interested in weather satellite imagery —>

In addition to their communication transponders, the OSCAR satellites also transmit a beacon identification signal, as well as telemetry data, to provide continuous system status monitoring for the satellite.

An SDR receiver and accompanying software are wonderful tools for displaying and receiving these radio signals, which the satellites transmit at frequencies just above or below their transponder ‘downlink’ frequency.

The following segments show sequential stages of processing through various software programs, from initial reception of the satellite signals through to actual display of the satellite’s telemetry data during its’ pass. Admittedly, another convoluted process. But the challenge is there, and I wanted to see what telemetry data looked like. Perhaps my wife is partly correct about me being somewhat obsessive.

This image shows the Beacon and Telemetry Data signals being transmitted by the CAS-4A satellite while passing over our part of the globe during its’ orbit, on 29 Feb 2020.

The signals are being received using my Airspy HF+ SDR receiver with my 2-meter ‘Eggbeater’ antenna, and the SDR Console software. the CAS-4A ‘downlink’ signals are transmitted on the 2-meter Amateur band at 145.8 MHz.

Another great feature in the SDR Console software program is its’ ability to record and save to an audio file, the received signals across a portion of the frequency spectrum being monitored. This recording can then be replayed at a later time to allow processing of the received data in other software.

Here I have the recorded signals from SDR Console, being demodulated in another Amateur software program (SoundModem by UZ7HO) designed to process the telemetry signals that were transmitted from CAS-4A using AX.25 4.8 baud GMSK modulation. (This form of modulation is also used in other Amateur modes that this software can be applied to.)

The demodulated data shown in this image, will then be moved into another software program for further processing.

The satellites use differing methods of modulation and data formats, so each requires software written for that specific satellite. DK3WN has compiled an impressive collection of information and decoding software for numerous satellites at his ‘SatBlog’ website

Next step in processing the data is the ‘Online Telemetry Forwarder’ written by DK3WN for the CAS-4A and CAS-4B satellites

Hooray! The final step. The ‘CAS-4A, -4B Telemetry Beacon Decoder’, also by DK3WN. Pretty cool! Showing status of numerous parameters onboard the satellite, as it passed over earlier in the day.

Clicking on the button next to a parameter, displays a bar-graph of the recorded values. Here the RF PA Temp, which is no doubt the temperature of the final Radio Frequency Power Amplifier output transistor for the satellite’s transmitter.

Another parameter showing ‘RF Power forw’ (the transmitter’s output power) as being 153.00 mW (milliwatts). In other words, the transmitter is running at very low power output, less than 2/10 ths of a Watt. At 524 km above the earth and transmitting on 145 MHz that is enough power to be heard over a wide footprint of the earth’s surface as the satellite is passing by.

Without going through the entire process again, here is another somewhat simpler decoding of the telemetry data for AO-91 (Fox 1) orbiting Amateur Radio satellite, on 1 March 2020.