Radio waves are invisible and travel at the speed of light. We are surrounded by harmless radio waves, sent out from TRANSMITTERS aboard satellites as well as those tall antenna towers you see on the horizon. Because radio waves rapidly decrease in intensity with the square of the distance traveled, we are safe from this energy comprised of electric and magnetic fields.
Radio waves oscillate at specific FREQUENCIES authorized by the Federal Communications Commission. Groups of broadcast frequencies are called RADIO BANDS. These bands are coordinated internationally because, sometimes, radio waves may skip around the world!
To keep us safe around nearby transmitted radio waves, federal laws impose strict guidelines regarding certain radio transmissions you could be near:
Cellular phones and cordless phones
Computer wireless routers
Motion-activated alarms on automatic doors
Radio RECEIVERS only pick up radio waves – they don’t transmit the waves, so snuggle up to your favorite receiver and enjoy! Even these receivers need the FCC (Federal Communications Commission) certification, so you are safe!
The AM (amplitude modulation) broadcast band extends from 540 kHz to 1700 kHz, the medium wave band. AM broadcast radio range, during the day, is typically as far as 100 miles. These GROUND waves have the ability to propagate up over hills and mountains, and through forests. The more powerful the AM broadcast station, the farther the ground wave will travel.
Receivers, with multiple built-in AM antennas may help extend this ground wave range out to about 150 miles from powerful AM broadcast stations.
At nighttime, AM broadcast station signals will also bounce off the ionosphere and “skip” back down into your little AM radio receiver from up to 1000 miles away. This extended nighttime range on AM (medium frequency) broadcast band is very dependable after dark. Seasons may change reception. At night, take your portable AM radio away from electrical noise in the house and away from nearby power lines, and then slowly tune around to enjoy long-range nighttime reception.
Shortwave broadcasters are assigned frequencies in the shorter wavelength bands above the AM broadcast band. These higher frequencies, from 3 MHz to 30 MHz, are where a shortwave receiver may pull in broadcasting stations, day or night, from thousands of miles away. The radio waves are all coming in via skywave, refracting off multiple layers of the ionosphere.
The ionosphere acts like a giant prism, refracting back to Earth all radio signals above 11,000 kHz during the day and below 10,000 kHz at night.
Shortwave skywave reception on broadcast frequency BELOW 10,000 kHz is best AT NIGHT. Shortwave skywave reception, on frequencies ABOVE 11,000 kHz is STRONGEST during the DAY.
Tune around the following frequencies for skywave excitement:
Around 15,400 kHz, daytime
Around 13,700 kHz, daytime
Around 11,800 kHz, daytime
Around 9,500 kHz, nights
Around 6060 kHz, nights
Tune higher, then tune lower, from these suggested frequencies, to enjoy refracted skywaves from the ionosphere.
Can you actually see the ionosphere? Yes, up in Canada and Alaska they are seen as Aurora Borealis or “Northern Lights”.
Sure, they are visible in Australia, too, looking south.
Radios may include the FM broadcast band as well. You will extend the telescopic whip antenna, as you did for shortwave, for best reception.
You can USUALLY pick up FM stereo stations from up to 50 miles away from their transmitters. Watch the weather maps for extended range FM reception! A weather phenomenon called tropospheric ducting, resulting from temperature inversions, may carry FM broadcast signals, plus scanner radio signals, hundreds of miles farther than under “normal” atmospheric conditions. Your local weather will be hot, with little wind, and the barometer will indicate you are under a high pressure ridge.
These atmospheric conditions may trap warm air within a boundary, called a duct. Scanner signals and FM broadcast signals may travel within this duct up to many hundreds of miles away for distant reception. This is usually a summertime occurrence, and is usually associated with a slow moving high pressure cell. See how far away YOU can pick up a scanner or FM signal!
You can enhance radio reception by adding an accessory outside antenna system.
Enjoy the sounds from the ionosphere for AM broadcast and shortwave skywave signals. Take advantage of local high pressure weather systems for much greater range on FM music radio frequencies and portable/fixed scanner channels. Let’s see who can pick up the most distant stations.
Share your story by commenting below on the furthest signal you’ve been able to reach with your radio. The winning comment will receive a special prize. Please have your stories posted by September 21, 2012.
This content was written by Gordon West, WB6NOA, a licensed Ham Operator for more than 50 years and founder of Gordon West Radio School offering amateur radio training classes. He has been named Instructor of the Year by the ARRL and received the 2006 Amateur Radio of the Year award. He’s also a writer, author and co-host of Twit TV’s Hamnation. Click here to learn more about Gordon West Radio School.