We all like to see a shooting star flash across the sky but as they are so fleeting you have to be looking up at just the right part of sky at just the right moment, in other words you have to be lucky to see one. At certain times of year the chances of seeing a meteor ( shooting star ) increases dramatically. This is because as the Earth goes around the Sun its orbit intersects the path of sun orbiting objects like comets and as a comet orbits the sun it leaves a trail of debris behind. This debris is made of material ranging in size from a grain of sand to a marble, they also follow the same orbit as the parent comet.
We call these times when the earth and the debris trails intersect meteor showers, which happen at the same time each year. The number of meteors that are seen per hour vary between 20 – 120. Sometimes, when the earth passes through a particularly dense part of the debris trail we get what is called an outburst, when several hundred an hour can be seen.
The weather in the UK has an unfortunate tendency to be just awful when astronomical events take place; the 11th August 1999 Total Solar Eclipse and 9th May 2016 Mercury Transit for example. Meteor showers are no exception to this seeming Golden Rule ( also known as SODS law). There is a way however to observe these showers regardless of the weather, by using Radio or more precisely Radar.
As a meteor burns up in the earth’s atmosphere it leaves a trail of ionized gas behind and any radio or radar waves that hit the trail are bounced back. This is called meteor scatter and we can detect this bounced signal with very inexpensive equipment. It happens that the French have a Space Radar system called GRAVES which detects planes, satellites and believe it or not the moon so we dont have to transmit the signal ourselves – just detect the returned Pings.
You will need some hardware and free software. The set up I use cost less than £50 to construct but you may have some of the materials already. The key components are the RTL SDR Dongle that has the rtl2832 and 820t or 820t2 chips inside and a J Pole antenna configured for 144 Mhz.
HARDWARE- RTL SDR Dongle ( modify the supplied Micro Co-ax or MCX antenna lead to fit a co-ax connector like on your TV aerial lead), J pole antenna ( once you have made your antenna it will need to be placed as high up as possible ). At least 10 metres of Co-ax cable 75 Ohm ( 50 Ohms is better ), a TV Signal booster covering 144 Mhz range ( I used a SLx1 signal booster), 1 metre USB extension lead ( to keep your computer/laptop away from the dongle to keep RF interference down ) and a computer Windows XP, 7 or later.
Connection is as follows:- Antenna – Coax – Signal booster – MCX lead – RTL Dongle – USB extension – Computer.
IMPORTANT : DO NOT INSTALL ANY SOFTWARE THAT CAME WITH THE DONGLE
Install HDSDR, copy the Ext io dll into the HDSDR directory ( c/program files/HDSDR ). Start ZADIG and click install driver, click options-list all devices and choose Bulk in Interface ( interface 0 ), click install driver.
When everything is installed and everything is connected start HDSDR, turn on signal booster and tune to a radio station of known frequency ( I use BBC Radio Somerset on 95.5 Mhz FM Ctrl F ), turn Bandwidth ( Shortcut F6 ) to 19200, click Ext io and use the following settings.
Tuner AGC off, RTL AGC off, Offset tuning on, Sample rate 1.02 Msps, Buffer size 64 kb and RF between 20 and 30.
Adjust the Frequency correction until the station is centered and return bandwidth to 12000, Select USB ( Upper Side Band ) from the AM,FM Bar or use Ctrl U and tune to GRAVES on 143.049 Mhz. The tuner should look like this.
LO A 0143.073.000
This is to offset the Local Oscillator or all you will hear is a continuous tone. Adjust the bandwidth in the lower ( smaller ) spectrum panel to 0 to 800 Hz. With these settings and if all is well, you should detect meteors, see the trace on the waterfall display and hear the Pings.
Below are some samples recordings which you can also do with HDSDR.
There’s only one problem. Because the GRAVES radar scans an area to the south the meteor scatter we receive is from meteors that are below our visible horizon so we can’t see them only hear the reflected echo.