What is a Parabolic Antenna?
A parabolic antenna is an antenna that uses a dish that is shaped like a shallow bowl. These are used for satellite television, radio, astronomy, cellular telecommunications, and radar. They can also be used to boost the signal of a wireless Internet router. Parabolic antennas are also known as dish antennas.
The first parabolic antenna was created by Heinrich Hertz in the late 1880s. His early design was created using a brass sphere, zinc sheet metal, and wood. Hertz used one antenna for transmitting signals and another for receiving signals.
Hertz used his antenna to help prove the existence of electromagnetic waves. As a result of this and other accomplishments, his name is now the term used for radio and electrical frequency measurements. These include hertz (Hz), kilohertz (kHz) and megahertz (MHz).
Today’s antenna designs improve upon Hertz’s early work. A single antenna can transmit and receive signals. A parabolic antenna is a unidirectional antenna since it transmits signals in only one direction. The dish part of one is known as the reflector.
The reflector creates a large surface area that the antenna uses to receive and transmit signals. The innermost part of the dish is the vertex. The reflector gathers and strengthens the signals it collects. This strengthening of the signal is called gain.
The strengthened signal is aimed at the transmitting and receiving element at the focal point, or focus, of the parabolic antenna. The focal point is usually directly opposite the bottom of the dish. The element, or feed, sends signals to and from the appliance receiving the signal, such as a television receiver or radio.
The distance between the focal point and the vertex is called the focal length. For a parabolic antenna to work properly, the focal length must be correct. It is based on the diameter of the dish. To calculate the focal length, the reflector diameter is squared, and then divided by 16 times the depth of the reflector. The result is the correct distance to use between the focal point and the vertex.
Parabolic antennas are usually mounted on a roof, the side of the building, or on a stand outdoors. They can also be placed indoors when used with Internet routers. The device must be aimed in the correct direction to collect the signal. Usually, the appliance connected to the antenna will indicate the antenna signal strength. This helps the user better aim the antenna to get a stronger signal.
Can you tell me what will be the dimensions of a parabolic disc for transmitting a 100khz signal?
@Charred - We actually for a while got rid of the dish altogether and just used an exterior, 30-foot digital antenna to pull in local channels. That way, we never missed a show! The problem with the antennas like that is that it's hard to find someone to service them.
Another nice backup option is Hulu. If you have a newer laptop, you can often connect it to your TV using an HDMI cable. It won't be quite the same picture quality, but it's pretty close. (If you have a Macbook, you'll need a special connector, but we picked one up quite cheap.)
We use Hulu basically instead of having a DVR. If we miss a show, we can often catch it the next day. (Be careful, though - some shows are not available at all or are available only on an 8-day delay. Which I don't understand at all. You'd think the producers would want you to keep up with their show!)
@everetra - I have kind of a love hate relationship with satellite television. While I appreciate the fact that with such an antenna I can get signals from all over the world, I do have problems with signal strength from time to time.
This is true regardless of whether you have a big dish or a small dish. Satellite television is notorious for weather related problems, for example. Sometimes it’s not even a big storm that will mess up my signal. It can be the constant drip of a light, steady sprinkle, and the next thing you know my video signal starts streaking.
The only workaround I’ve found is to record all our favorite TV shows and watch them when, hopefully, the weather is not too bad. Some of the episodes get repeated so I have multiple chances to record them properly. If it's still raining when the DVR is recording, I’m out of luck.
The parabolic outdoor antenna used for satellite transmissions has come a long way since the early days.
I used to live overseas and remember using these massive dishes mounted on top of my house in order to get satellite transmissions. I had to use a controller to precisely move the antenna so that it was aimed directly at the satellite’s line of sight.
Every now and then it would need calibration. I was receiving transmissions from China, India and parts of England. It was kind of a hassle to learn to use that thing but after awhile I got used to it.
Nowadays the dishes they make are so small you can mount them on the outdoor patio of an apartment building. You still have to make sure you have a clear line of sight however.
Post your comments