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A Dipole for your CB Base Station?
- Thread starter Robb
- Start date
Want to experiment with wire dipoles , everything I've read says build it 1/2 wave, question is : can I build it full wave or 5/8 or .64? for some reason I had it in my head to build each leg at around 18 feet, making the whole thing a full wave, keep seeing 102" legs for 11 meters, probably a reason for that
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Can you use other lengths than 1/2 wavelength?
Yes, but...
You will need to find a way to tune them as they will not naturally provide a low SWR, and most of them will not be resonant. If you are looking for broadside gain you can go up to about 5/8 wavelengths per side, which is about 1.25 total wavelengths. Most people call the 1/2 wavelength variant dipoles, and the non-1/2 wavelength viariants doublets. And more specifically, if it is one wavelength long, that is sometimes referred to as a Double Zepp, and 1.25 wavelengths it is referred as an Extended Double Zepp (or EDZ for short). The EDZ can be tuned to a reasonable impedance with a length of 450 ohm window line and is at or near the longest length of straight wire you can have and still have broadside gain.
The DB
Yes, but...
You will need to find a way to tune them as they will not naturally provide a low SWR, and most of them will not be resonant. If you are looking for broadside gain you can go up to about 5/8 wavelengths per side, which is about 1.25 total wavelengths. Most people call the 1/2 wavelength variant dipoles, and the non-1/2 wavelength viariants doublets. And more specifically, if it is one wavelength long, that is sometimes referred to as a Double Zepp, and 1.25 wavelengths it is referred as an Extended Double Zepp (or EDZ for short). The EDZ can be tuned to a reasonable impedance with a length of 450 ohm window line and is at or near the longest length of straight wire you can have and still have broadside gain.
The DB
Here's one you may want to try.
Take 450 ohm ladder line & cut a piece 18 feet long.
Next exactly in the middle cut one side only, leave the other side solid.
Next take some ladder line and solder one side of it to each side of the 18 foot piece
in the middle where where you cut it. This will be your feedline. Note: avoid lengths
that are multiples of a quarter wave 9,18,27, 36,etc.
Lengths 65' 81'100' should be fine. If the length you need is too close to a quarter wave
or multiple go to the next longer one.
What you now have is a full wave loop only squashed together(Think Moxon).
Get a good quality 4 to1 current balun, Balun Designs makes excellent ones.
String your ends where you can, don't need a lot of height. 25' is plenty.
Run the ladder line to the balun & use the shortest piece of coax to bring it into the
shack to the radio.
A full wave antenna in the same space a dipole takes. Has some gain & wide bandwidth.Win-Win situation.
Take 450 ohm ladder line & cut a piece 18 feet long.
Next exactly in the middle cut one side only, leave the other side solid.
Next take some ladder line and solder one side of it to each side of the 18 foot piece
in the middle where where you cut it. This will be your feedline. Note: avoid lengths
that are multiples of a quarter wave 9,18,27, 36,etc.
Lengths 65' 81'100' should be fine. If the length you need is too close to a quarter wave
or multiple go to the next longer one.
What you now have is a full wave loop only squashed together(Think Moxon).
Get a good quality 4 to1 current balun, Balun Designs makes excellent ones.
String your ends where you can, don't need a lot of height. 25' is plenty.
Run the ladder line to the balun & use the shortest piece of coax to bring it into the
shack to the radio.
A full wave antenna in the same space a dipole takes. Has some gain & wide bandwidth.Win-Win situation.
Take 450 ohm ladder line & cut a piece 18 feet long.Next exactly in the middle cut one side only, leave the other side solid.
What you now have is a full wave loop only squashed together(Think Moxon).
Ends of 18 foot section open or fused?
What you now have is a full wave loop only squashed together(Think Moxon).
Ends of 18 foot section open or fused?
Leave the ends uncut this way you have 36' one wavelength.Reinforce the center with some flat ABS.
Shadetree Mechanic
Delaware Base Station 808
Sorry but a Moxon is not a loop. It's basically a 2-element (or more) Yagi (driven+ reflector or driven+director) with the element ends folded towards each other. The driven element is based on a ~half-wavelength dipole. Altogether a different animal.
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BJ radionut
Supporting Member and 6m addict
Dipole
Free Online Engineering Calculator to find the Dimensions for a folded dipole.
Folded Dipole Antennas
The folded diple antenna is presented. The radiation pattern for the folded dipole is specified. The folded dipole antenna's input impedance is derived and discussed.
www.antenna-theory.com
