2017 February 19 Electronics Radio
Today, many people are re-discovering the enjoyment of listening to a traditional AM/FM radio. Unlike the Internet, which is digital-- it's either on or off-- radio listening has the challenge of how to get better reception.
This article is a collection of 7 tips for better radio listening. Enjoy!
1. Know The Frequency Bands
LW is below 0.3 MHz, or 300 KHz. This is a really interesting frequency band that I don't have a whole lot of experience with.
AM or MW band is 0.535 MHz to 1.7 MHz. It is normal to write AM frequencies as KHz (kilohertz); example: 0.550 MHz is equal to 550 KHz.
SW or HF band is 5.9 MHz to 26.1 MHz. Sometimes these are also written as KHz, depending on your radio. Example: 11 MHz would be written as 11000 KHz.
VHF (Very High Frequency) is the catch-all for frequencies in the 30 to 300 MHz range. These include FM, WX, and AIR bands. Many of the old broadcast-TV stations were also in the VHF range, while others were UHF.
FM band is 88 MHz to 108 MHz, which makes it part of VHF. These are rarely, if ever, written as KHz.
AIR, short for Aircraft or Airband, is 108 to 137 MHz, also part of the VHF band.
WX, or NOAA Weather Radio, is seven channels in the VHF band. These are 162.400 through 162.550 MHz. (They sometimes rebroadcast NOAA weather on AM, but lately I haven't heard it.) You can get cheap solar & crank powered radios that have this band, usually with AM and FM. See also my article on How To Power Almost Any Radio With Solar.
Once you know a frequency, you can calculate the wavelength easily. This website is just one example. The AM frequency of 550 KHz has a wavelength of 545 meters.
You can also see there is a huge difference in wavelength between AM and FM. These require two different types of antenna.
2. Know About Band Propagation
LW propagates by groundwave, which means it can refract over the ground at long distances.
AM, shortwave, and CB can propagate by "skip", which means the signal can bounce off the ionosphere and travel a couple thousand miles. Sometimes LW also propagates by skip.
Shortwave radio (HF or SW) is well-known for propagating very far. Sometimes you can bring in stations from the other side of the world.
AM propagates far enough to make distance (DX) listening very possible. On AM radio I've been able to hear nighttime broadcasts from 1,200 miles away. There is no direct line of sight on such a great distance; it would have to be refraction or skip. You also need the right antenna (see Tip # 6).
FM radio is more line-of-sight, but there is some atmospheric propagation. It is possible to do FM DX listening, but it might not be as predictable as AM. Under the right conditions you can even get FM signals that bounce off the Moon.
3. Find & Eliminate Interference Sources
Sometimes it's not really possible to eliminate local interference, but at least you can identify what's causing it. Lately our culture has been causing more and more radio-frequency interference. Switching power supplies, CFL's and LED lights, dimmer switches, wall-warts, generators... sometimes even the utility lines outside your home can cause RF noise. A bad connection or something wrong with an insulator can create a spark gap... which generates RF noise. It also wastes power.
Walk around your building with an "empty" AM station tuned in, and listen for RF noise. Try to find a location in the building where the noise goes away. Sometimes the noise source will be an electrical appliance, and if you're lucky it will be something you can turn off while you listen to the radio.
Another source of interference could actually be a distant station. Some of these are broadcasting way up in the 50,000 watt range, which means that a radio station 100 miles away could be obscuring a station that's only twenty miles from you. There are only a limited amount of frequency allocations available, so it does happen.
4. Avoid Reception Blockers
One of the worst places I ever found for AM radio reception was (ironically) in a Radio Shack store. Buildings made with metal panels, rebar, wire mesh, or steel beams can interfere with radio reception. They're not noise sources, so much as they actually block the signal by attenuation. Think of it as dimming a light.
Instead of a transmission turning to loud static, it might just get quieter. This is a good indication that something in your building is attenuating the signal.
Sometimes you'll have a dead zone on the ground. It could be from a hilltop or some other land feature. This happens more with VHF and UHF signals, which means FM and WX can be affected. So, if your radio is in a dead zone, try somewhere else!
5. Get A Book of Broadcast Frequencies
The World Radio and TV Handbook has a new edition every year. (Get the 2017 edition here.) It lists radio stations by country, both national and international broadcasting. It lists the frequencies, broadcasting times, and wattage.
It's helpful to know ahead of time what stations you're trying to hear. One reason: wavelength determines the antenna length you will need. See Tip #6.
6. Use The Right Antenna
This is a huge topic that fills many books. Here let's talk about a couple of very basic options.
The nice thing about receive-only antennas is that you don't have to mess with impedance-matching, standing-wave ratio, or that sort of thing. You can use a wire length that would be the wrong SWR for a transmit antenna, with no damage to the radio.
Now, if you're a newbie to this whole topic, you might be surprised to learn that a good antenna will also pick up more static!! This is why you need a radio with good tuning circuitry. Actually, what's even more important is to pick a spot with low interference. (Tip #3, above.)
In theory, a long wire antenna should be at full-wavelength. But who's going to do that for AM radio? Quarter-wave antennas work, and I know this because I've tried them. However, if you wanted to receive 550 KHz (AM), the wire would still be about 136.27 meters long for just 1/4 of the wavelength. That's about 447 feet. (A full-wavelength wire would be about 1788 feet long, or about a third of a mile....)
Higher AM frequencies require shorter wires, but they're not drastically shorter. A full-wave antenna for 1000 KHz would still be about 300 meters long. Quarter-wave would be about 75 meters. Doable, but still kind of much.
Most enthusiasts make "random wire antennas" that are much shorter than 1/4 wavelength. For short wire antennas that are indoors, I've used this type of wire. This can work if you have the space and your building isn't interfering. 30 feet of wire is a good starting point.
For wire antennas that have to be outdoors, you'll need heavier wire. A 500-foot roll of 12 gauge wire is not terribly expensive; should be OK for such antennas. These are typically attached with a couple of antenna insulators to fasten at each end to something, such as a tree or building. Just remember that external wire antennas can receive lightning, not just radio waves... use them at your own risk. (Disclaimer, again.) Make sure you know how to install a lightning protector on the antenna.
Random-wire antennas usually require tuning with inductors and capacitors. In a future article I'll post my design for an AM antenna tuner, which can be made in one or two evenings. This could be more effort than you're looking to get into at the moment, so let's talk about an easy alternative.
AM listeners can benefit greatly from a passive loop antenna such as this one or this one. (Try this link for one that's even lower-priced.) These antennas sit on your tabletop. You can even use them without attaching them to the radio, because they couple inductively.
Most of these have a knob which you "tune" to the particular station. This adjusts a variable capacitor, which I mentioned before, but it's built-in so you don't have to get one and wire it up yourself. Tuning one of these loop antennas does requires a bit of guesswork, though; you won't know where on the dial is correct for the frequency you want, until you try it. That said, I would highly recommend an AM loop antenna. They're not that expensive, and having one could make all the difference for your favorite station.
Then, later on, maybe you'll want to get into long wire antennas and homemade loops. There's a lot to antenna building, and I don't pretend to understand it all (or even that much). Consider a good book on the subject, such as this one.
7. Try a Couple Different Radios
You may find that a certain model of radio works better for receiving your favorite station. Some have better tuners than others. That's not always the reason, though.
One radio might get a station that's nearly silent on another radio. It can be tough to predict; sometimes you just have to try it.
Some radios have a feature known as "dual conversion". This is supposed to help you receive a station with less interference from other stations. A single-conversion radio is generally more sensitive for distance (DX) listening, but dual-conversion often sounds clearer for those stations you are able to receive. That's because it has two stages of intermediate frequency (IF) bandpass filtering.
If you want the ultimate in AM DX listening, start with a serious receiver such as a Palstar (you might be able to find one lower-priced through this link.) Generally you get what you pay for; serious listening requires serious hardware.
Some of the consumer-grade and portables do have a lot of satisfied owners; here are a few:
Sony ICF-2010 .... not made anymore, but widely recognized as the best. Get one, but make sure to buy a working one. There are a lot of "parts or repair" and "untested" ones out there, sometimes for way too much money.
C Crane CC Pocket AM/FM AM/FM/WX
Sangean WR-11 AM/FM (Full review here)
Grundig G8 Traveler II AM/FM/SW
Tecsun PL880 AM/FM/LW/SW (this one has LW!)
Eton Grundig Satellit 750 AM/FM/SW/Aircraft
This was not a comprehensive guide, but these seven basic tips can improve the radio listening for many people. Wire antennas may seem like a bit much for an absolute beginner, but I included them in this list because they're not expensive, and they're actually fairly easy to rig up if you want. Even if you have it tuned all wrong, a random-wire antenna will often improve AM reception at least somewhat.
If you don't want to deal with the lightning hazard and the attendant protection devices for an outside wire, you can sometimes get good reception from a shorter length of magnet wire strung along your ceiling, indoors.
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