Hey everyone,
I recently built a Half wave folded dipole antenna (placed vertically) for my tuner. It worked much better than I expected. I'm now getting a great coast radio station from about 80 miles away. Depending on the weather it comes in crystal clear or really bad.
My questing is would it be helpful to build another folded dipole antenna for the other end of the garage and connect them both? Or do I need to look into another antenna? Hopefully something I can build from scrap wire and pvc pipes I have laying around.
Thanks
Jordon
I recently built a Half wave folded dipole antenna (placed vertically) for my tuner. It worked much better than I expected. I'm now getting a great coast radio station from about 80 miles away. Depending on the weather it comes in crystal clear or really bad.
My questing is would it be helpful to build another folded dipole antenna for the other end of the garage and connect them both? Or do I need to look into another antenna? Hopefully something I can build from scrap wire and pvc pipes I have laying around.
Thanks
Jordon
Attachments
I suggest looking into a directional antenna, such as a Yagi antenna. I used to have a PC DOS program to calculate the position and length of the elements. I'm sure you can find similar software that'll work on modern PCs in HAM radio circles.
Mounting the antenna outside improves reception dramatically as well.
Tom
Mounting the antenna outside improves reception dramatically as well.
Tom
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Use what works for you. If you want to use two antennas though, with 300 Ohm twin lead, have a two pole knife switch to select one of them,
near the tuner. You can't connect them directly together and get proper functioning.
Sure you can. It's called 'stacking' and is done all the time. The antennas have to be connected with a splitter running 'backwards' as a combiner. The antennas have to be identical, separated from each other by 1/2 wavelength and the leads from each antenna have to be the same length to keep them in phase. Stacking antennas raises signal level and makes the array more directional - often good things.
Initially I thought Jordon had stations in different directions and was trying to make an omnidirectional antenna. That's a lot more complicated.
G²
Exactly what are you trying to achieve?
Some types of signal fading can be overcome by "diversity" techniques. These use two (or more) antennas, separated by at least a few wavelengths, each feeding a separate receiver, or at least the pre-detection stages of a receiver. Logic circuitry - typically driven by each receiver's AGC voltage - either selects the strongest received signal, or sums the signals using variable gain factors proportional to each signal's strength. While the antenna and receiver for each diversity path should have the same performance characteristics, diversity systems can be relatively immune to minor variations in equipment, construction, as well as aging and drift over time. However, at a fundamental level, diversity requires you to have essentially two (or more) receiving chains to acquire one received signal.
It is probably a better idea for you to antenna designs until you find a satisfactory solution.
You may find that your current antenna can achieve satisfactory performance if it is boosted to a higher elevation - free of trees, buildings, power lines, etc within a few hundred feet. Building codes and subdivision restrictions may be restraining factors but sometimes just getting your antenna "in the clear" - 5 to 10 feet above nearby trees and rooftops - may be all the improvement you require.
Antennas, like loudspeakers, are essentially transducers converting energy in one form to another form. And, like loudspeakers, there are dozens of ways to aid that conversion. In nearly all cases, increasing antenna gain will be accompanied by narrowing the antenna's directional pattern. This is good if you are interested in receiving one particular signal from a fixed location, since your antenna will not only gather more of the desired signal but also reject noise and co-channel signals arriving from different directions. But it poses additional problems if you are interested in several stations' signals arriving from different points of the compass.
As already mentioned, two (or more) of your basic dipole antennas can be stacked vertically or horizontally and their signals combined with suitable phasing lines. The individual antennas are typically spaced a quarter wavelength to a wavelength apart. The phasing lines vary from equal length, to a quarter wave difference. Depending on antenna spacing and length of the phasing lines, the direction of maximum sensitivity may be either perpendicular ("broadside") to the plane of the array, or in the plane of the array ("endfire"). Keep in mind that the wavelength of an FM broadcast signal is on the order of ten feet, so an array of half-wave elements spaced one-wavelength apart can quickly become a sizable structure.
If the narrowed directionality isn't a problem - as I mentioned, this is sometimes a very desirable characteristic - I'd look into either a Uda-Yagi style design, or possibly a log-periodic. Variations of these designs are the classic roof-mounted antennas for over-the-air television reception. The project write-ups, web pages and literature for these antenna styles would easily fill several yards of bookshelves. Projects based on some well-proven standard designs are easy to come by. As a starting point, think of your dipole with a "reflector" element placed about 1/4 to 1/8 wavelength behind the dipole, and about 10% to 20% LONGER than the dipole. There are theoretical optimum values for these dimensions but performance degradation is relatively minor if you depart from optimum, and to some extent you can trade off increased reflector length for reduced spacing. Adding "director" elements in front of the dipole - spacing similar to the reflector, but 10% to 20% SHORTER than the dipole - will further increase gain and reduce pattern width. Adding more director elements increases gain, but there's a law of diminishing returns at work. As a practical matter a Yagi antenna with about half a dozen director elements can get 10 dB to 12 dB gain over a simple dipole but there's little point in adding additional elements, even if you're not concerned with physical size.
Dale
Some types of signal fading can be overcome by "diversity" techniques. These use two (or more) antennas, separated by at least a few wavelengths, each feeding a separate receiver, or at least the pre-detection stages of a receiver. Logic circuitry - typically driven by each receiver's AGC voltage - either selects the strongest received signal, or sums the signals using variable gain factors proportional to each signal's strength. While the antenna and receiver for each diversity path should have the same performance characteristics, diversity systems can be relatively immune to minor variations in equipment, construction, as well as aging and drift over time. However, at a fundamental level, diversity requires you to have essentially two (or more) receiving chains to acquire one received signal.
It is probably a better idea for you to antenna designs until you find a satisfactory solution.
You may find that your current antenna can achieve satisfactory performance if it is boosted to a higher elevation - free of trees, buildings, power lines, etc within a few hundred feet. Building codes and subdivision restrictions may be restraining factors but sometimes just getting your antenna "in the clear" - 5 to 10 feet above nearby trees and rooftops - may be all the improvement you require.
Antennas, like loudspeakers, are essentially transducers converting energy in one form to another form. And, like loudspeakers, there are dozens of ways to aid that conversion. In nearly all cases, increasing antenna gain will be accompanied by narrowing the antenna's directional pattern. This is good if you are interested in receiving one particular signal from a fixed location, since your antenna will not only gather more of the desired signal but also reject noise and co-channel signals arriving from different directions. But it poses additional problems if you are interested in several stations' signals arriving from different points of the compass.
As already mentioned, two (or more) of your basic dipole antennas can be stacked vertically or horizontally and their signals combined with suitable phasing lines. The individual antennas are typically spaced a quarter wavelength to a wavelength apart. The phasing lines vary from equal length, to a quarter wave difference. Depending on antenna spacing and length of the phasing lines, the direction of maximum sensitivity may be either perpendicular ("broadside") to the plane of the array, or in the plane of the array ("endfire"). Keep in mind that the wavelength of an FM broadcast signal is on the order of ten feet, so an array of half-wave elements spaced one-wavelength apart can quickly become a sizable structure.
If the narrowed directionality isn't a problem - as I mentioned, this is sometimes a very desirable characteristic - I'd look into either a Uda-Yagi style design, or possibly a log-periodic. Variations of these designs are the classic roof-mounted antennas for over-the-air television reception. The project write-ups, web pages and literature for these antenna styles would easily fill several yards of bookshelves. Projects based on some well-proven standard designs are easy to come by. As a starting point, think of your dipole with a "reflector" element placed about 1/4 to 1/8 wavelength behind the dipole, and about 10% to 20% LONGER than the dipole. There are theoretical optimum values for these dimensions but performance degradation is relatively minor if you depart from optimum, and to some extent you can trade off increased reflector length for reduced spacing. Adding "director" elements in front of the dipole - spacing similar to the reflector, but 10% to 20% SHORTER than the dipole - will further increase gain and reduce pattern width. Adding more director elements increases gain, but there's a law of diminishing returns at work. As a practical matter a Yagi antenna with about half a dozen director elements can get 10 dB to 12 dB gain over a simple dipole but there's little point in adding additional elements, even if you're not concerned with physical size.
Dale
Thanks for all the info, I played around with placement in my garage and it looks like the horizontal position is much more effective. My tuner has no meter so it makes it pretty difficult to adjust.
I think I might play around with some reflectors behind the dipole and see what happens.
I think I might play around with some reflectors behind the dipole and see what happens.
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