Tech Talk #2 – Measuring Antenna Temperature with Radio SkyPipe

by Richard Flagg, WCCRO

In the Tech Talk #1 we discussed antenna temperature. This measure of received signal strength is now being used by several Radio Jove observatories.

Most of us are using Jim Sky’s excellent Radio SkyPipe software to record and display signal strength data. The signal trace on the SkyPipe screen can be adjusted with the Jove receiver volume control and also the software volume control in Windows. By changing these gain settings, the trace can be moved up or down and compressed or expanded. However, there is no absolute reference point. The SkyPipe vertical scale units (SkyPipe units – SPU) are not engineering units like volts, watts, or degrees.

By converting SPU to absolute antenna temperature you can:

  1. Determine (in quantitative terms) how radio quiet or noisy your site is.
  2. Measure the strength of Jupiter bursts and solar bursts and compare measurements with those of other observatories that are also calibrated in terms of antenna temperature.

A calibrated noise source is necessary in order to convert SPU to antenna temperature. If you are using a Jove receiver, the noise source need only provide a single reference temperature. Other receiver types (those with a diode detector) require a multi-level noise source.

The calibration wizard in Radio SkyPipe 2 does all the computational work for the Jove receiver and one-step noise source. It nulls out soundcard noise and uses the calibrated reference temperature signal to perform the conversion to antenna temperature. By using information about your antenna type and coax cable SkyPipe 2 references the measured antenna temperature to the antenna terminals.

This means that signals displayed on SkyPipe can be directly compared with signals from other observatories — even if they use different gain settings or different lengths of coax between their antenna and receiver. Furthermore you will know the background temperature at your receiving site — how radio quiet or noisy it is in comparison to an ideal galactic background temperature of around 40,000 °K.

The RF-2080 C/F, a single temperature, calibrated, noise source is described in an accompanying article.