Posted on 10-02-2008
Filed Under (Antenna, HD Radio) by popwireless

In an earlier article on improving AM broadcast reception the emphasis for signal improvement was placed on improving the antenna circuit. FM radio is no different.

Perhaps your situation is like mine. When I first turned on my Accurian HD FM Radio at home I decoded just one local FM HD radio station. Any FM radio using the supplied wire antenna had fuzzy reception. The major reason is that my home is far away from the major radio markets of D.C., Virginia , and Baltimore, and Delaware. The laws of physics always apply.

FM radio has different characteristics than does AM because the intelligence on the radio wave is frequency modulated rather than amplitude modulated. The major differences between the two modes of operations can be explained by:

The short explanation is that if you have two stations heard on the same frequency the station with the strongest signal wins. When signals compete with one another the stations are alternately heard as the signal strength of each rises and falls. One moves to the front while the other is suppressed and inaudible.

The most important of the characteristics is the height above average terrain of the FM radio station’s transmitting antenna in relationship to the height of your FM-radio receiving antenna at home, terrestrial obstructions, buildings, and local vegetation. FM radio stations vary in output power as do AM stations but height is king. Antenna height has more to do with improving range than does the output power of the radio wave. A station has to quadruple the power to double their useful range but only to double their antenna height to accomplish a major improvement. The relationship is characterized mathematically as an improvement of about 40%. Distance is the square root of two times the geometric mean of antenna height and earth radius. The distance a wave travels improves as the square root of antenna height.

Let’s review what Wikipedia says about the inverse square law from the perspective of the radio receiver in your home:

Doubling the distance from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value.

As you travel farther from the radio station signal strength dramatically decreases but improves as you put your receiving antenna as high and in the clear as possible.

FM stations may also have some directional characteristics and portions of their output power specifically used for vertical, horizontal or circular polarization of their transmitted wave. The simplest way to understand polarization of the radio wave is to look at two antenna types your car antenna and the TV antenna atop some homes. The car antenna stands straight up, vertical, and the TV antenna is sideways or horizontal. FM stations send out waves using both polarizations to give receivers in cars and receivers connected to antennas at home a better chance to receive a stronger signal. When you rotate an antenna ninety degrees from the horizontal or vertical from a station transmitting only horizontal or vertical you reduce your received signal strength significantly. Circular polarization takes horizontal and vertical polarization into account as the wave literally screws through space.

So how does this all effect you? Well we have read that an antenna has high and in the clear as possible, using the right polarization directed at the station I want to hear is the antenna I need to improve the signal strength at my home or office. When the antenna we want is selected we also have to determine how the signal is going to move from the antenna into the home and get distributed to all of our FM radios. Excellent quality antenna cable and a good signal amplifier are a must when cable lengths may exceed 25 feet and if you expect to distribute the signal with splitters to multiple receivers.

Let’s Look at Antenna Systems

First let’s consider the human part of this equation. Not everyone in a family or in a home owner’s association thinks antennas are beautiful. Every time I see an 2007_12310023antenna I sees a work of art. I wonder about how it was made, how well it works, it’s design frequency, what is connected to the antenna and so on. Another person sees an ugly jumble of metal just ruining the otherwise wonderful appearance of a beautiful home. Been there. (That’s my chimney. The six-meter Amateur radio ground plane antenna at the lower left was formerly atop the flag pole where my family could see it from the living room. I thought it was a clever idea but the antenna didn’t fly with the flag in that spot for long. The antenna to the lower right in this picture is my FM HD omni-directional antenna. The antenna on the chimney is a DB408 commercial radio antenna used for GMRS. Poetry in a bad photograph.)

But wait! What if everyone wants to listen to a specific radio station and that radio station is too weak using the rabbit ear antenna on top of the FM radio? Do you smell a possible compromise? Whatever the compromise, you may be able to get past the objections by placing an antenna in an attic or at a less noticeable place on your home or property. What I did was group my scanner antennas and FM antenna on the backside of a large wooden chimney not easily seen from three sides of the house. The grumpy is only heard walking toward the house from the wrong direction. ;)

There is one very important thing you must check before putting up that antenna. Look at the back of your FM radio and determine if the manufacturer put an antenna connector there. Many boom boxes came exclusively with rabbit-ear antennas. On some radios there is no way to connect the typical 300 ohm or twin lead or 75 ohm coaxial cable. Your only recourse with a radio like this is to move the radio to a higher place our home or office. Get it out of the walk-in basement and on the third floor of your home facing a window in the direction of the radio station you want to hear. Buy a new receiver you can connect an antenna to when your results do not meet your expectations. It is possible to add an antenna connector jack to some radios but it is a task best left to someone that knows how to make the modification.

Before we put the antenna up allow me to emphasize the importance of the cable used to connect the antenna to the radio. Buy the best coaxial cable you possibly can. Do not skimp on quality. Purchase a better-quality quad-shielded low-loss cable. A weak signal received at a well-placed antenna still needs to travel the length of the coaxial cable top the FM receiver. Low-quality cable guarantees your attitude about the antenna investment is discouraging.

On runs over fifty feet I recommend an antenna mounted signal amplifier. Given that you ignored my plea to buy good cable or you are using an older unknown quality cable already in your home an amplifier will give you a fighting head start. The signal is amplified at the antenna so that it is actually usable at the FM tuner. An amplifier can make the difference in FM HD radio reception. In my case the outdoor antenna was not enough, an amplifier was required. There was just enough attenuation on fifty-feet of good-quality cable to prevent decoding of WAMU-2. Back up on the roof I went to install the amplifier. A pole mounted amplifier also permits using a splitter in the home to route cable feeds to multiple receivers. When a pole mounted amplifier is not available consider a distribution amplifier in lieu of a splitter. Your local TV ad radio store or neighborhood RadioShack can help you make the choice.

Weather proof your connections with liquid electrical tape or a product like STUFF. You do not want to be back on the roof after every storm season replacing connectors and cleaning out moisture when your reception fails.

HD-6010 by WinegardNow to antennas. You have some choices. There are vertical antennas, horizontal antennas, and directional antennas. I opted for a horizontal non-directional antenna made by Winegard, the HD-6010. I wanted omni-directional capability without the need for an antenna rotator. These antennas are available starting at $39.99 and up. It mounts to an antenna mast of 1 1/4 to 1 1/2 in diameter. Five and ten foot masts are available at your neighborhood RadioShack or hardware store and appliance store. The HD-6010 has two phased 300 ohm dipoles looking for signals in four directions with equal effect

dangerYOU CAN BE KILLED raising an antenna if the antenna and mast fall on live power lines or other electrical transmission sources. Know what is over head and within reach of a falling mast. Climbing ladders and walking on roof tops is DANGEROUS. Know what you are doing or PAY A PROFESSIONAL to set up your antenna for you. When working in an attic ALWAYS lay down plywood sheets or other suitable boards to permit safe movement above ceilings. Falling through the ceiling can cause injury and really tick off the rest of the family.

An omni-directional antenna is great when you are just on the fringe of an urban reception area. When in a truly reception challenged area consider a directional antenna. A special FM directional antenna is available like Winegard’s HD-6000 or HD6055P antennas. The latter has more elements making it more directional and very sensitive to signals in one direction. Directional antennas should have an antenna rotator to turn the antenna in the direction of the desired station.

The C. Crane Company offers a unique vertical antenna design called the Fanfare FM Antenna you might consider. The C. Crane SE-879 FM Stereo Antenna can be mounted for horizontal or vertical polarization depending on your receiving conditions. The C. Crane folks know AM and FM radio. Browsing their catalog is a real rush for the radio enthusiast.

Since listening to far-away FM stations is a wireless hobby and fringe areas are also numerous you find other excellent choices for horizontally-polarized directional antennas. Google it! Also take time to visit the various on-line websites that support the FM-DX hobby like the Worldwide TV-FM DX Association, and DXFM.COM. Google “FM DX.”

Do not pass up using your television antenna as an excellent outdoor FM antenna. The FM band is 88-108 MHz. TV channels three through six are just below 88 MHz. Channel seven is just above 174 MHz. The elements on most TV antennas do an excellent job of receiving FM. The TV antenna may already have an antenna rotator installed on it making reception of the more distant FM HD stations easier.

The Internet is a wonderful place. You may find other excellent do-it-yourself articles like this one written by Mr. Bruce Carter entitled, An FM Antenna Case History. This is where I swiped the antenna safety label photograph above. Good authors are cognizant of safety issues when writing on the topic of antennas. Carter has some good tips in this article.

Ask questions here in the blog or join the PopularWireless on-line community at our Personal Wireless Bulletin Board. Many of our readers have put up outdoor FM antennas. Once you complete the project and get your radio hooked up you will be glad you did.

Lastly, consider purchasing an excellent quality FM tuner designed for exceptional FM reception. Selecting a good FM broadcast receiver explained here by FM-DX enthusiast Todd Emslie can make difference in sound quality and hearing that elusive radio signal. Just in case you have more antenna questions a Google search produced this article by Galen Carol entitles FM Antennas. Need help finding FM stations near you or wondering what the station’s coverage map looks like? Mr. Carol recommends RADIO-LOCATOR.COM.

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