The car-mounted antenna in this picture is a SIRIUS XM Satellite Radio antenna for receiving music and news radio broadcasts from satellites orbiting around the earth. The simplified block diagram shows how to use Oscium’s WiPry-Combo Peak Power Meter to investigate the signals from radio, GPS, or other use satellites. This mock setup uses the conducted measurement kit from Oscium for making a coaxial cable connection between WiPry-Combo and other pieces of equipment.
Satellite Radio 101
The satellites transmissions are the company’s proprietary signals. It’s possible to detect the peak power of the satellite’s transmissions even if the signals can’t be used for intelligent content. Decoding the received satellite signals requires specialized receiver hardware and a subscription to the service.
SIRIUS and XM Satellite Radio transmissions are broadcast at 2.3 GHz with 12.5 MHz bandwidth.
The first XM Satellite Radio satellites were launched and placed in orbit above the earth in 2001. These two Boeing 702 satellites, used solely for satellite radio broadcasts, are aptly named XM-Rock and XM-Roll. To learn more about this class of satellite, check out the article attached to the end of this post.
The first artist and song ever to be played on satellite radio was Tim McGraw’s song “Things Change”.
Low Noise Amplifier (LNA) & Measuring Weak Signals
Satellites are powered by solar panels and batteries so their transmit power is limited, and high frequency power amplifiers are notoriously inefficient. The strength of electromagnetic waves decreases sharply with the distance traveled. Specifically, the equations for calculating radiated power density show that energy received decreases as the inverse of the distance from the source squared (1/R^2). Consequently, among the first elements in satellite receivers is an amplifier that is used for boosting the received signal to levels adequate for processing. Not just any kind of amplifier will do, however.
There’s a special category of amplifiers used in RF and microwave receivers called “low noise amplifiers”, or just LNAs, with high gain (20 dB) and low noise figure (< 2dB). There’s a tradeoff between performance parameters when selecting low noise amplifiers. It’s sometimes a tug-of-war between power, gain, noise figure, and bandwidth. For example, an LNA with very high gain over a wide frequency span might draw too much power (typically higher voltage requirements) to be used in low power applications. Conversely, there are LNAs designed for specific application, like satellite radio and GPS, with high gain and noise figure, and acceptable power requirement, that operate over a very narrow frequency span. It’s important to keep this requirement and type of amplifier in mind whenever a test setup is intended for measuring weak signals.Boeing 702 Fleet.pdf