FM Reception FAQ
There are several factors that contribute to poor reception of the WAMU 88.5 signal, ranging from weak signal to the phenomenon known as multipath. Here are a few hints that may help ensure better reception.
What's the first thing to check if I’m having trouble receiving WAMU 88.5's signal?
Does my radio need an antenna?
Okay, so why do I need to worry about how my antenna is set up?
Will an amplifier help reception?
How do I mount an outdoor antenna?
What if I already have a good antenna installation?
What if my question wasn't answered here?
Facts About WAMU 88.5’s Transmitter and Antenna
What's the first thing to check if I’m having trouble receiving WAMU 88.5's signal?
One of the easiest solutions to a reception problem is to move the radio to a different part of the room. If you are in the metropolitan area, moving the radio only a few inches or several feet sometimes will bring in a clear signal. Most portable and clock radios use either a telescopic whip or the AC power cord as an antenna. The whip can be extended, retracted, and rotated to change reception. The AC cord can be moved around and draped across objects for the best signal or wrapped up to reduce signal. If your clock radio has no visible antenna or connections for an antenna then the radio is likely using the power cord for an antenna.
Does my radio need an antenna?
Stereo tuners and receivers require an external antenna — an antenna that is not a part of the radio. Many tabletop and clock radios have connections for an external antenna, but also allow you to use the power cord if you don’t want to use an external antenna.
The antenna connects to either two screw terminals marked 300 Ohm or an "F" connector for coaxial (round) cable located on the back of the unit. A "twin-lead" dipole antenna is usually boxed with a new receiver or tuner. Many people attach this dipole antenna to their new set and then ball it up and stuff it behind the equipment. For strong stations this may work just fine, but for weak stations it will not work. If you don't have an antenna connected to your stereo, you can purchase or make a dipole.
The dipole consists of about five feet of flat antenna lead-in wire with the ends bared and twisted together Another five feet of wire is attached to the center of the first piece of twin-lead at the middle of ONE of the wires by cutting it, baring the wire, then twisting it together. If you want to make a dipole yourself specifically tuned for WAMU's frequency of 88.5MHz, the length of the first mentioned piece of twin-lead should be 63 inches. The length of the center piece of wire can be as long as needed to reach the set, but no shorter than five feet.
The dipole has a “figure-of-eight” reception pattern. It picks up signal on the broad sides of the antenna, provides some antenna gain, and receives no signal on the ends. If the dipole is stretched out and rotated, it’s possible to point the antenna for best reception or to "null" a station that is interfering with the desired signal. The disadvantage of the dipole is finding a way to locate it in the room. If you are lucky, the direction of the desired station will correspond with one of the walls in the room and you can simply attach the stretched out twin-lead to the wall. Some people mount the dipole on a "TEE"-shaped frame made of wood and position it in the room for best reception. Others have mounted this same frame in the attic.
It may be easier to buy a "rabbit ear" antenna like you would use for television reception. The rabbit ear is another form of dipole antenna. Each telescopic section should be adjusted for a length of 31.75 inches. The rabbit ear is often easier to place in the room or on the stereo and can still be rotated for best reception.
There are a number of indoor specialty antennas available for FM reception. Some work very well and some do not; ensure that the antenna could be returned before purchasing it.
Okay, so why do I need to worry about how my antenna is set up?
Both TV and FM reception are referred to as "line-of-sight." This means the transmitting and receiving antennas must be able to "see" each other. For reception outside of the metropolitan area, a roof or attic-mounted antenna is recommended, both for the increased height and for the additional antenna gain (the increase in signal strength over a reference antenna) that comes with a directional antenna. Line-of-sight reception of WAMU 88.5 should be possible for distances up to 50 miles. Hills and mountains may extend this range by providing increased height, or reduce it by placing an obstruction between the transmit and receive antennae. Directional antennas also may be mounted in the attic, still providing increased height over lower level locations.
A directional antenna can help in reducing “co-channel” interference from a station on the same frequency as the desired station but located in a different direction—or adjacent channel stations that are interfering with the desired station. People who listen to a number of distant radio stations often use a rotator to position the antenna correctly for each station. Directional antennas can be found at Radio Shack, as well through many TV and antenna dealers, who will also stock higher gain antennas. Be wary of the antenna claims of "reception from 110 miles.". Uunless you’re looking down from the mountains with an unobstructed view or have a high tower for your antenna, curvature of the Earth prevents reception from that distance. Be more interested in whether the antenna has 3 db, 6 dB, or 9 dB of gain. The more gain the better for distant stations but, the antenna is going to be larger for each increase in gain.
The WAMU 88.5 Coverage Map
This coverage map can help determine the signal strength of the WAMU 88.5 signal in your area. The signal levels are:
| Color | Signal Strength | Antenna | Expected Result |
|---|---|---|---|
| Red | >70 dBu | Indoor antenna, i.e. dipole | Excellent |
| Green | >60 dBu | Indoor or attic antenna | Good |
| Yellow | >50 dBu | Attic or outdoor directional antenna | Possible |
| Violet | >40 dBu | Outdoor directional antenna | Difficult |
| Gray | <40 dBu | Unlikely |
Will an amplifier help reception?
You should also be aware that an amplifier, either a pre-amp at the antenna or a distribution amp in the house, won’t produce a better signal. Only antenna gain will give you a better signal over noise. Amplifiers are used to make up for the signal losses in long runs of cable, such as from the roof or tower mounted antenna into the house, or from splitting the signal to feed multiple sets. The amplifier should always be inserted before the loss occurs.
How do I mount an outdoor antenna?
If you install an attic or outdoor antenna, be sure to follow good engineering practices by twisting the twin-lead (flat) cable and mounting on stand-offs, or by using coax (round) cable. Always ground the antenna and the lead-in cable. Always use "splitters" or "couplers" for multi-set installations or joining several antennae to one lead-in cable. These practices insure the rejection of unwanted and interfering signals being picked up by the cable (or sometimes retransmitted by YOUR antenna to the neighborhood) and afford protection against lightning. Books on proper antenna and lead-in installation can be found in many libraries or at Radio Shack.
What if I already have a good antenna installation?
Interference can be caused by a number of factors. Interference in receiving the desired station is often caused through overloading of the radio's first amplifier by a different but nearby station. If you know that you are in an area where a radio or television transmitter is located, this may be your problem. There are several cures for this problem. If the signal of the desired station is more than sufficient, then reducing the level of all signals into the radio, receiver, or tuner will help. On radios with telescopic antennas, you can make the antenna smaller by pushing the sections together. On clock radios, wrap up the power cord as short as possible. With stereo receivers and tuners you will need to install a "pad" between the antenna lead-in and the input connection to the set. Radio Shack makes fixed 6 dB pads for coax (round) cable . They also make an adjustable inline attenuator for coax connections that allows you to reduce the signal until the interference disappears. These pads and the attenuator can be adapted for 300 Ohm (flat) twin lead cable.
If the desired signal is weak because you're a long distance from the station the best solution is to reduce the signal of the station causing the interference. This is done with a filter and is most easily accomplished on a tuner or receiver with external antenna connections. The cheapest filter is a quarter-wave open stub which you can make at home. If your antenna lead-in is the flat twin lead, start by cutting a length 33 inches long. Bare the wires at one end and attach it to the set's antenna terminals along with the lead-in from the antenna. Now, with the set tuned to 88.5MHz, start snipping off a 1/4 of an inch of the cable at a time until WAMU 88.5's signal improves. Stop cutting when the signal sounds good to you. You are tuning the stub filter to the interfering station's frequency. If you know that the interfering frequency is above 100MHz, you can start with 29 inches of cable and save some time in cutting.
A filter can also be made for antenna systems using coax (round) cable but is more involved. A coax filter would require a "TEE" connection—three connections; one for the antenna lead-in, one for a jumper cable to the set and one for the filter. A TEE adapter is not made for the "F" connector used for coax cable so an adapter would have to be made from separate adapters. This would consist of three "F" to "BNC" adapters and one "BNC" TEE. Then the coax is cut as described above for the flat cable, attached to the middle connector on the "BNC" TEE and snipped in 1/4 inch increments as described above.
Some interfering stations may be so strong that the open stub filter is not sufficient. There are filters that can be tuned for greater rejection at the offending frequency made by antenna manufacturers such as Winegard, Blonder-Tongue, Channel Master, and Jerrold; however, these filters are quite expensive.
What if my antenna is fine, I've eliminated the interference from other station signals and I am still getting interference?
Some interference is intermittent. This can be caused by a nearby amateur radio or CB transmitter. Many of the suggestions recommended in the FAQ above can improve reception. Also filters are available from Radio Shack for amateur and CB bands.
Intermittent static interference is usually caused by electrical appliances such as refrigerators, furnace blower motors, and air-conditioners. If this interference is coming into the radio via the AC power line (if it sounds O-K running on batteries, this is the problem), an AC line interference filter from Radio Shack or hardware and department stores such as Wal-Mart and K-Mart can be placed between the wall outlet and the power cord.
Multipath distortion is common in the metropolitan area. It is caused by signal reflections from buildings and is often heard in the car as tics and pops as you drive around or, if you are driving more slowly, as small "areas" of distortion that you drive through. In the home multipath distortion will appear in one area of a room but not if the radio is moved to another part of the room. If your radio sounds distorted, particularly if the distortion comes and goes, one of the tips discussed in the first few paragraphs should clear up the problem.
What if my question wasn't answered here?
The engineering staff of WAMU 88.5 welcomes the opportunity to assist you in receiving the best possible signal from our station. If we can be of further assistance with your reception problems, please contact us via email or writing us at the following address:
Engineering and Operations
WAMU-FM
4000 Brandywine Street NW
Washington, DC 20016-8082
Facts About WAMU 88.5’s Transmitter and Antenna
WAMU 88.5's effective radiated power is 50,000 watts (50kW) in both the horizontal and vertical planes. The vertical component is for your car and portable radios and the horizontal component for reception by a roof mounted antenna similar to a TV antenna. WAMU 88.5's transmitter output power is 17,000 Watts (17kW). This power, minus the loss in the transmission line, is multiplied by the gain of the antenna to produce the effective power of 50kW.
WAMU 88.5 broadcasts from a tower located on American University's campus near the corner of Nebraska and Massachusetts Avenues in Northwest Washington. The tower is a four legged self-supporting structure originally erected for TV channel 7 in 1947. It was turned over to American University in the early 1960s. For those who are interested, the geographic coordinates are North Latitude 38-56-10 and West Longitude 077-05-33.
The tower is 319 feet tall. The pole on which the antennae are mounted and projects through the top of the tower extends the height to 428 feet. The center of radiation from WAMU 88.5's six bay Shively FM antenna is 499 feet above average terrain. WAMU 88.5 also has an auxiliary antenna lower on the tower in case of a failure of the main antenna. Ground elevation in the Tenleytown area of Washington, the highest point in the District, is 410 feet. Television and FM reception requires line-of-site between the transmitting and receiving antennae, which is why most of the TV and FM transmission facilities in the District are located in or near Tenleytown.
WAMU 88.5 has two solid-state Nautel transmitters rated at 10kW each, the outputs of which are combined to produce the 17kW transmitter power output. If either transmitter fails the one remaining transmitter is automatically switched into the antenna with minimal interruption of service. Each transmitter has six modules and a failure of any one only reduces the power by a small amount.
WAMU 88.5 also transmits a HD Radio© signal with a Harris solid-state transmitter combined with the analog signal into the existing antenna. HD Radio© is a new development for producing a near CD quality audio without the annoying tics, pops, and other artifacts of analog FM broadcasts. The digital transmitter has a power output of 1,750 Watts (1.75kW). After combining with the analog signal the power is 170 Watts. This much lower power provides a HD Radio© service area roughly equivalent to the service area of the analog FM system.
