Observing the Leonids by Car Radio.

• The Basic Idea
• What you need
• Radio Stations
• Links

The Basic Idea

Well, what happens is that the ionized gas in the meteor trails can reflect radio waves in the FM bands from distant transmitters back to earth, so when a meteor appears one can sometimes receive small portions of broadcasts from radio stations up to 2000 km away from the observing site.

This startlingly simple fact gives many amateur observers the ability to do serious, world class science for a relatively low cost. Of course, like many startlingly simple ideas, the Devil is in the details, and serious research must take account of many factors. You can learn more than you want to know at the International Meteor Organisation page on meteor radio reflection.

What you need is quite simple, a halfway decent Yagi antenna, a FM radio with digital tuning, and something to record the signal. These days people hook up their computers to the radios and perform computerized analysis. Again, if you want serious data, theres lots of things to be taken into consideration, and a serious bit of software to sort the grain from the chaff, so to speak.

Radio observation of meteors has many advantages, overcast skies and twilight don't interfere, and it's a lot easier to observe meteors from the city. If you want full details of how to build one of these set-ups, see the fantastic resources in the links section.

It's a bit late for people to set up a proper system to observe the Leonids, but the Geminids in December and the Delta Quadrantids in January are good candidates. And then again, the Leonids are probably going to be so overwhelming that you would need a seriously computerized sytem to get any real data out of the peak shower.

But what about the car radio? These days most people have a car radio with FM and digital frequency selection. Not altogether suprisingly, this rough and ready system works.

First, here's a list of things you need.

• An FM radio transmitter below the horizon, between 600-2000 Km away (preferably 600-800 Km)
• Said FM transmitter to transmit with at least 30 kilowatts of power
• Transmission frequency to be between 30-150 MHz (preferably 40-80 MHz)
• An FM car radio with digital frequency setting.

All you have to do is back your car down the driveway, put up your aerial, dial up a station that's 600-2000km away and listen to the static. When a meteor hits the atmosphere it ionises a bit of air which then can refect the distant radio station down to your aerial. In tests done by Bruce, this very basic method actually works just fine. The sound a meteor makes is a really sudden whoosh, much like it looks. It also works quite well during the day, so is ideal for following the Leonids after sunrise.

If you are really handy with electronics you can attach a Yagi antenna to the car ariel input feed for better reception.

For best results the station should be in line with the meteor shower, but stations off to one side will work. The Leonids will be coming from the north east, but the shower should be so strong that stations anywhere from north to east will be alright.

FM stations

The Australian Broadcasting Authority has no online lists of frequencies, but a phone call to them will get you a list of all FM radio broadcasters in the required area. Ham radio operators can also help. If you are in a remote area, a call to your local radio station might be a good idea, rather than run up lots of STD charges.

Links

• The International Meteor Organisation pages on radio observation of meteors. A fantastic detailed resource.
• American Meteor Society radio meteor page.
• Real Audio files of radio meteor sounds.
• This page gives the simplest explanation of the Radio Meteor effect and has some good sound files.