Can anyone tell me what spacing to put a reflector on this antenna? Thanks
http://w4rnl.net46.net/fdim6.html
http://w4rnl.net46.net/fdim6.html
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Twin X-Mount Dipole Idea
- Thread starter Lil'Yeshua
- Start date
Antenna boom and reflector tubing
Okay. This is what I'm about to purchase for the purpose of adding a boom and reflector elements to this CP antenna. The .375 slides into the .500 for each reflector element. The .065 goes crossways through the boom and is an attachment point for the reflector elements. The boom is 1.25". As I have never made an antenna before, I invite whosoever to critique this if you have an better idea of what to buy. The pic is my yet completed order from DX Engineering.
Okay. This is what I'm about to purchase for the purpose of adding a boom and reflector elements to this CP antenna. The .375 slides into the .500 for each reflector element. The .065 goes crossways through the boom and is an attachment point for the reflector elements. The boom is 1.25". As I have never made an antenna before, I invite whosoever to critique this if you have an better idea of what to buy. The pic is my yet completed order from DX Engineering.
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2 X 1 = 4
I'm getting there!
"
Similar design considerations go into setting the SWR curves, shown in Fig. 10. The narrow-band version has an SWR under 2:1 for the 28-29 MHz region, while the wide-band version shows under 2:1 SWR for the entire 10-meter band.
However, to fully understand the curves, let's note that each is based on a different resonant impedance. The resonant feedpoint impedance increases as we separate a driver and reflector. The wide-band version is based on a direct 50-Ohm feed and uses 50-Ohm resistive impedance as the baseline. The gradual curves--which almost always are steeper below the design frequency than above it--result from the increasing reactance that occurs off resonance: capacitive below resonance, inductive above it.
The narrow-band antenna shows a resonant impedance of about 35 Ohms resistive. The same levels of reactance--when added to the lower resistance--result in steeper SWR curves. We use these curves because they generally trace the performance you will get relative to 50-Ohms once you place a proper matching network at the feed point."
I'm getting there!
"
Similar design considerations go into setting the SWR curves, shown in Fig. 10. The narrow-band version has an SWR under 2:1 for the 28-29 MHz region, while the wide-band version shows under 2:1 SWR for the entire 10-meter band.
However, to fully understand the curves, let's note that each is based on a different resonant impedance. The resonant feedpoint impedance increases as we separate a driver and reflector. The wide-band version is based on a direct 50-Ohm feed and uses 50-Ohm resistive impedance as the baseline. The gradual curves--which almost always are steeper below the design frequency than above it--result from the increasing reactance that occurs off resonance: capacitive below resonance, inductive above it.
The narrow-band antenna shows a resonant impedance of about 35 Ohms resistive. The same levels of reactance--when added to the lower resistance--result in steeper SWR curves. We use these curves because they generally trace the performance you will get relative to 50-Ohms once you place a proper matching network at the feed point."
This answers my questions about CMC.
"2. What can I do to match the narrow-band antenna to my coaxial cable? The wide-band Yagi has served us well for several demonstrations. It showed us how increasing the element spacing increases the feedpoint impedance of a 2-element driver-reflector Yagi. It also showed us that complete coverage of 10 meters is possible. However, we shall turn away from this design in favor of the narrow band design. The narrow-band design is suitable for scaling to 20 and 15 meters with complete band coverage in each case.
Before we leave the wide-band design, let us remember that it is intended for direct connection to a 50-Ohm coaxial cable. However, the potential for common-mode currents on the cable strongly suggests that we insert a 1:1 choke--sometimes called a choke balun--at the antenna feedpoint. Whether we choose the W2DU design of placing ferrite beads on a 1' length of coax or some other design, the use of a choke is a wise precaution to prevent pattern distortion that might occur under certain conditions due to some antenna current being present on the outside of the coax braid. As well, the choke tends to suppress RF that gets back into the shack, distorting the SWR readings and possibly disrupting some sensitive circuits in our transmitters. Some folks wait until trouble shows itself before adding a choke at the 50-Ohm feedpoint. My preference is good preventive engineering, so I add one as a matter of course."
"2. What can I do to match the narrow-band antenna to my coaxial cable? The wide-band Yagi has served us well for several demonstrations. It showed us how increasing the element spacing increases the feedpoint impedance of a 2-element driver-reflector Yagi. It also showed us that complete coverage of 10 meters is possible. However, we shall turn away from this design in favor of the narrow band design. The narrow-band design is suitable for scaling to 20 and 15 meters with complete band coverage in each case.
Before we leave the wide-band design, let us remember that it is intended for direct connection to a 50-Ohm coaxial cable. However, the potential for common-mode currents on the cable strongly suggests that we insert a 1:1 choke--sometimes called a choke balun--at the antenna feedpoint. Whether we choose the W2DU design of placing ferrite beads on a 1' length of coax or some other design, the use of a choke is a wise precaution to prevent pattern distortion that might occur under certain conditions due to some antenna current being present on the outside of the coax braid. As well, the choke tends to suppress RF that gets back into the shack, distorting the SWR readings and possibly disrupting some sensitive circuits in our transmitters. Some folks wait until trouble shows itself before adding a choke at the 50-Ohm feedpoint. My preference is good preventive engineering, so I add one as a matter of course."
Just ordered aluminum tubing from DX Engineering to make a reflector array. I'll use my new fancy pop rivet set to attach the reflector to the boom. Here's a drawing of the element hold downs. Note:There's only a short section that's pop riveted to the boom. The element sections will be attached by C-Clamps and slitting the ends of the tubing.
Update: the bracket will be shaped to confirm to the shape of the boom for a closer fit and the pop rivets attaching it will have a different configuration. No wibbly Wobblies allowed.
Update: the bracket will be shaped to confirm to the shape of the boom for a closer fit and the pop rivets attaching it will have a different configuration. No wibbly Wobblies allowed.
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Question : my antenna boom I ordered is 6 ft long. For a wide band spread on 11 meters, it's calling for a 6.315576 ft spacing between the driven element and the reflector elements. I guess no fudging here. Any comments?
I don't know what a Moxon antenna is but it sounds pretty good
"However, if we judiciously bend the element ends toward each other, we can achieve very nearly ideal current conditions--about 30+ dB worth of front-to-back ratio. By now, almost everyone knows the bent-element array as the Moxon rectangle."
http://w4rnl.net46.net/index.html
"However, if we judiciously bend the element ends toward each other, we can achieve very nearly ideal current conditions--about 30+ dB worth of front-to-back ratio. By now, almost everyone knows the bent-element array as the Moxon rectangle."
http://w4rnl.net46.net/index.html
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When I get my co-phase 75 ohm cable I'll have to adjust the lenght to reflect 1/4 wave on each leg as well as the 50 ohm 9' jumper. Like I said before,I have to get the electrical wavelength just right to get the right pattern. RG59/U:"5.952 feet (5 feet 1127⁄64 inches)"
The Defpom coax length page
The Defpom coax length page
36.089 feet is one wavelength on 11 meters. Using 1/2" element spacing,6.315575feet spacing can be used not having a gamma. This is true concerning a yagi two element beam with wide bandwidth. The impedance at the antenna feed point is around 50 ohms. Guys,this is what I studied yesterday so any hints are welcome. Also,the phasing harness I'm using isn't like Maco's. mine is a 75 ohm RG59/U co-phase with two 75 ohm cables(1/4 wave each leg) terminating into a single PL-259 male connector. The 1/4 wave jumper is a 50 ohm RG8X 9' jumper. I'll use two SO239 double female barrel connectors. One at the jumper to co-phase harness,one to connect the co-phase harness to the feed line.
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My solution
P.S. I may just build the twin-X dipole section out of aluminum tubing. That will require educating myself on how to make one and what material to use for insulators and how to make a hub for the driven elements.
The 1/4 wave SS whips could be supported clamping a small hanger on the upright vertical whip about halfway up and supporting the horizontal elements with Dacron?
P.S. I may just build the twin-X dipole section out of aluminum tubing. That will require educating myself on how to make one and what material to use for insulators and how to make a hub for the driven elements.
The 1/4 wave SS whips could be supported clamping a small hanger on the upright vertical whip about halfway up and supporting the horizontal elements with Dacron?
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- No one is chatting at the moment.
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