Detecting Meteors
Use a Radio Receiver Tuned to a Radio Beacon to Detect Meteors
Equipment
- Yagi Antenna
- Software Defined Radio
- Computer running SDR software e.g SDR#
Throughout the year there are consistent and reliable meteor showers. These often occur when the Earth passes through the path of a long distant comet. The Perseids in August is a good example. However, meteors are just grains of dust and they can occur sporadically at any time of day or night. One way of detecting when a meteor is passing into the atmosphere is to use an indirect method involving a distant radio transmitter and a computer controlled radio receiver called a Software Defined Radio.
The basic idea is that a radio receiving system is tuned into a radio beacon that transmits a continuous signal, known as CW or Continuous Wave. The radio wave bounces off the underside of the Earths ionosphere as shown in the image below. A meteor, which could be travelling at around 40km per second, or even more if it is coming directly towards earth, creates a stream of ions when it passes through the ionosphere, and these ions reflect radio waves. The reflected signal is greatly amplified, and this shows up as a bright signal on the screen as explained below.
The setup is quite simple: you will need a suitable antenna, a receiver and some means of displaying meteor "hits".
Let's start with the antenna. The type of antenna often used is shown in the illustration below. It is known as a "Yagi" after Yagi and Uda, the Japanese inventors of this type of aerial.
The dimensions of the antenna and the number and spacing elements will depend on the radio frequency that you choose to tune into. In the resources on the right there are links to help you choose. Amateur meteor hunters in the UK tend to tune in to one of three radio stations.
- A military radio beacon called GRAVES near Dijon, France, transmits at 143.05MHz.
- A radio beacon at BRAMS in Belgium transmits at 49.97MHz
- A radio beacon specifically designed for meteor detection has launched at Sherwood Observatory near Mansfield in the East Midlands, UK. It transmits at 50.408Mhz.
The aerial is connected by coax cable to a Software Defined Radio (SDR). This is a computer controlled radio receiver with associated software to tune and display the signal. SDRs are inexpensive and can cover a wide range of frequencies. Make sure yours is capable of tuning in to the radio beacon that you wish to use. Nooelec and RTL SDRs with a range of up to 1.7GHz are useful.
The SDR is connected to a PC and the SDR software runs as a continuous waterfall. A software package used for meteor detection is Echoes and the image below shows what a meteor hit would look like. It is recommended that the user should very slightly detune the receiver so for either BRAMS or the UK radio beacon 50MHz is a good starting frequency. When a meteor is detected it will show up as a bright signal on the waterfall.
The image below is from RTL-SDR.com
This shows the meteors, which is in itself very rewarding, but to go a step further you can record the meteors and see patterns in your data, particulary when there is a meteor shower.