Figure 4 — You can see the increased gain of the quad loop compared to the dipole in this polar plot. Unlike the dipole that you can just rotate to obtain horizontal or vertical polarization, you have to move the feedpoint of the quad.
The shield of the coax goes to one side of the wire and the center conductor goes to the other. See figure 1 for a close up of how the coax is suppose to attach to the loop.
Have you ever had rain static pound your receiver when a rain storm was rolling in? Things such as sand and rain carry an electrical charge that cause a lot of noise on verticals and yagi beams. Surprisingly, the closed loop of the quad does not respond pick up to this type of noise.
As a matter of fact, in Operation Desert Storm, Yagi beams where unusable because of the sand storms that cause huge static noise problems! The U. Lets take a look at some 4 element cubical quads. Figure 6 shows a 4 element cubical quad fed for horizontal polarization. The parasitic elements are closed loops, meaning they are not electrically broke at any point around.
All the wire loops must be insulated from the boom. Fiberglass is usually used on durable quads. Figure 6 — 4 element cubical quad shown fed for horizontal polarization. Another huge advantage of the the quad parasitic element is the fact that it is not polarization sensitive. By this we mean, quad parasitic elements reflector and director s respond to all types of signal polarization equally well. Compared to the yagi elements, where the element is either in the vertical plane straight up and down or the horizontal plane side to side.
These yagi elements only respond to signals that have the same polarization as their self. Keep in mind the driven element is broken where the feedline connects, which means the driven elements IS polarization aware. What this mean is, during DX contacts when signals arrive at your antenna with its polarization changing constantly this is one reason signals fade and pop back up suddenly , on the quad this effect is reduced because quad parasitic elements still pick up these changing flip-flopping polarization signals.
You must keep in mind signals bounce off of objects water towers, radio tower, water, the ionosphere and their polarization gets rotated somewhere in between horizontal and vertical most of the time. Since our antennas are generally set up to receive only one polarization at a time usually horizontal or vertical , polarization changes due to reflections can cause signal fade signal strength waving up and down. This fading is reduced on quad elements! Enough said. Lets look at the 4 element cubical quad fed for vertical polarization.
In this instructable we demonstrate how to build a simple but power double bi-quad WiFi antenna. Parts List A single-sided copper clad PCB sheet - I found a 20x10cm sheet with an incomplete circuit printed on it but not etched. The print was cleaned off with wire wool. A length of 1mm diameter bare copper wire - I found a length of mains cable and removed the earth wire.
Four nuts and bolts for attaching the N-type chassis connector to the PCB. Drill, soldering iron, solder, pliers and your favoured nut and bolt tightening tools Your WiFi adaptor. I use an Alfa awush. Here we see a close-up of the antenna. A hole has been drilled into the PCB to accept the N-type chassis connector. Note the sheet of plastic. My initial thought was to shied the plate from the antenna but subsequent experiments have shown no change in signal strength so you do not need this plastic shielding.
You can also see the antenna constructed from the 1mm earth wire. You need to bend the wire so that it forms the diamond pattern as in the photo. Each side of the diamonds are At the crossovers the wire does not touch itself. One end of the antenna is soldered to the N-type at a height of 15mm from the collector plate.
The other end is attached to one of the bolts holding the N-type chassis connector in place. Here we see the rear of the collector plate, with the N-type bolted in place.
Here is where we screw on the N-type to SMA adaptor. This is the N-type to SMA adaptor. There was an improvement of signal over my previous cantenna and the supplied stick antenna.
In some ways the slot provides more flexibility because it enables the length of the loop to be altered to tune the 2 metre quad to exact electrical resonance. The two small sections removed from each cross member should slot neatly together. The wire should be of a reasonable diameter, typically 12 or 14 SWG is good. The wire is brought to a two way terminal block and secured in this way. The coax or stub can then be attached to the connections in the terminal block and held securely.
The weight of the coax should not be left to be held by the antenna wire, but the coax should be loped and secured to the boom or the mounting pole. The stubs should be around 7 or 8 centimetres long — their length is not terribly critical, and can be adjusted. The wires can be around 14 SWG and left to remain parallel under their own strength. These dimensions must be adhered to as accurately as possible. The idea being that the Driven element is tuned to resonance at the middle of the band which it is designed for.
Once cut to the correct dimension then the feedline can be attached and the element can be finely adjusted by either a dip meter or some kind of antenna analyzer. Once again a dip meter is extremely handy to make sure that all of the elements are tuned to their corresponding frequencies.
This is the reason that it is critical to adjust the length of each element as accurately as possible to obtain the highest gain and relatively low SWR. This will work fine however the maximum forward gain will be sacrificed slightly to gain the wider bandwidth. For more information on quad antenna dimensions you can use this Quad Antenna Calculator. The quad calculator is a very useful tool which not only calculates element dimensions but also works out the ultimate element spacing for maximum gain and gives you the spreader arm lengths as well.
Note: this calculator is designed to give maximum gain and does not take into consideration the feed point impedance. To feed directly with 50 Ohm coax and a balun spacing needs to be kept around 0. If you are using some kind of impedance matching device then these dimensions are fine and will give you maximum gain. One of the most crucial aspects of the quad design once the actual elements are all tuned and sorted is the matching system.
The idea of the matching system is to provide a relatively close impedance match between the feedline and the driven element feedpoint. The feedpoint impedance varies according to the spacing between the driven element and the parasitic elements.
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