HD7698P - Unfolding rear elements

[CTYankee51]

Does it matter which way these are unfolded? There are 7 pairs of 2 elements grouped together, one on top of the boom and another on the bottom. Depending on which way you turn them, the top element can be pointing to the right or to the left, and the one under the boom will be pointing in the opposite direction.

I have it so all the elements on top are pointing one way and the ones on the bottom are pointing in the opposite direction.

The instructions refer to tags on the elements but my unit did not have any tags.

[KNP 2516]

If your antenna is new, there should have been a plastic paper tag under every element that told which direction to turn and the instructions probably have the elements numbered.

What happens is that as you start from the front to the back, the elements are folded back against each other.

The first element should go to the right or left and then every element after that would be staggered in the opposite direction as you go down the log periodic.

If you look at the phasing lines you will see that they do not run parallel across the boom of the antenna,

They should cross between each element.

Also, the phasing lines cannot touch the boom or it will interfere with the signal.

Maybe Mr. Winegard can look at this situation and can rectify the problem by putting a simple piece of shrink tubing over both of the phasing lines where it goes past the corner reflector - so we wouldn't have these problems.

[KNP 2516]

http://www.solidsignal.com/prod_display ... 7698P#MORE

Here is a picture of assembly.

The instructions are pretty vague.

[RBAUD]

KNP not meaning to offend.

Your info is not quite right for his antenna.

The phase lines do not crisscross, and as of last year when i got mine there are no labels.

Download the PDF manual from Winegard HD7698P.pdf and look at the picture.

[CTYankee51]

I found some photos of this antenna on the web, and from what I can see the pictures I found do not match what I can determine from the illustration in the manual.

From the illustration (which leaves a lot to be desired) it appears the elements are alternated.

That is, looking from the rear of the antenna:

Pairs 1, 3, 5 and 7 - the top element is folded out to the right and the bottom element is folded out to the left.

Pairs 2, 4 and 6 - the top element is folded out to the left and the bottom element is folded out to the right.

Does everyone agree? (I'm hoping for a response from Winegard) Thanks.

Also, how much does this really matter?????

[KNP 2516]

I found some photos of this antenna on the web, and from what I can see the pictures I found do not match what I can determine from the illustration in the manual.

From the illustration (which leaves a lot to be desired) it appears the elements are alternated.

That is, looking from the rear of the antenna:

Pairs 1, 3, 5 and 7 - the top element is folded out to the right and the bottom element is folded out to the left.

Pairs 2, 4 and 6 - the top element is folded out to the left and the bottom element is folded out to the right.

Does everyone agree? (I'm hoping for a response from Winegard) Thanks.

Also, how much does this really matter?????

In telecommunication, a log-periodic antenna (LP, also known as a log-periodic array) is a broadband, multi element, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. The individual components are often dipoles, as in a log-periodic dipole array (LPDA). Log-periodic antennas are designed to be self-similar and are thus also fractal antenna arrays.

It is normal to drive alternating elements with 180° (π radians) of phase shift from one another. This is normally done by connecting individual elements to alternating wires of a balanced transmission line.

The length and spacing of the elements of a log-periodic antenna increase logarithmically from one end to the other. A plot of the input impedance as a function of logarithm of the excitation frequency shows a periodic variation.

An antenna array is two or more simple antennas combined to produce a specific directional radiation pattern. In common usage an array is composed of active elements, such as a linear array of parallel dipoles fed as a "broadside array". A slightly different feed method could cause this same array of dipoles to radiate as an "end-fire array". Antenna arrays may be built up from any basic antenna type, such as dipoles, loops or slots.

The directionality of the array is due to the spatial relationships and the electrical feed relationships between individual antennas. Usually all of the elements are active (electrically fed) as in the log-periodic dipole array which offers modest gain and broad bandwidth and is traditionally used for television reception. Alternatively, a superficially similar dipole array, the Yagi-Uda Antenna (often abbreviated to "Yagi"), has only one active dipole element in a chain of parasitic dipole elements, and a very different performance with high gain over a narrow bandwidth.

An active element is electrically connected to the antenna terminals leading to the receiver or transmitter, as opposed to a parasitic element that modifies the antenna pattern without being connected directly. The active element(s) couple energy between the electromagnetic wave and the antenna terminals, thus any functioning antenna has at least one active element.

Parasitic elements have no direct electrical connection to the antenna terminals, yet they modify the antenna pattern. The parasitic elements are immersed in the electromagnetic waves and fields around the active elements, and the parasitic currents induced in them interact with the original waves and fields. A careful arrangement of parasitic elements, such as rods or coils, can improve the radiation pattern of the active element(s). Directors and reflectors are common parasitic elements.

There are several critical parameters affecting an antenna's performance that can be adjusted during the design process. These are resonant frequency, impedance, gain, aperture or radiation pattern, polarization, efficiency and bandwidth. Transmit antennas may also have a maximum power rating, and receive antennas differ in their noise rejection properties

The "resonant frequency" and "electrical resonance" is related to the electrical length of an antenna. The electrical length is usually the physical length of the wire divided by its velocity factor (the ratio of the speed of wave propagation in the wire to c0, the speed of light in a vacuum). Typically an antenna is tuned for a specific frequency, and is effective for a range of frequencies that are usually centered on that resonant frequency. However, other properties of an antenna change with frequency, in particular the radiation pattern and impedance, so the antenna's resonant frequency may merely be close to the center frequency of these other more important properties.

Antennas can be made resonant on harmonic frequencies with lengths that are fractions of the target wavelength. Some antenna designs have multiple resonant frequencies, and some are relatively effective over a very broad range of frequencies. The most commonly known type of wide band aerial is the logarithmic or log periodic, but its gain is usually much lower than that of a specific or narrower band aerial.

Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use. The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, the impedance is adjusted at the load (see below) with an antenna tuner, a balun, a matching transformer, matching networks composed of inductors and capacitors, or matching sections such as the gamma match.

The bandwidth of an antenna is the range of frequencies over which it is effective, usually centered on the resonant frequency. The bandwidth of an antenna may be increased by several techniques, including using thicker wires, replacing wires with cages to simulate a thicker wire, tapering antenna components (like in a feed horn), and combining multiple antennas into a single assembly and allowing the natural impedance to select the correct antenna. Small antennas are usually preferred for convenience, but there is a fundamental limit relating bandwidth, size and efficiency.

The polarization of an antenna is the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation. It has nothing in common with antenna directionality terms: "horizontal", "vertical" and "circular". Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally.

Reflections generally affect polarization. For radio waves the most important reflector is the ionosphere - signals which reflect from it will have their polarization changed unpredictably. For signals which are reflected by the ionosphere, polarization cannot be relied upon. For line-of-sight communications for which polarization can be relied upon, it can make a large difference in signal quality to have the transmitter and receiver using the same polarization; many tens of dB difference are commonly seen and this is more than enough to make the difference between reasonable communication and a broken link.

Antennas designed specifically for reception might be optimized for noise rejection capabilities. An antenna shield is a conductive or low reluctance structure (such as a wire, plate or grid) which is adapted to be placed in the vicinity of an antenna to reduce, as by dissipation through a resistance or by conduction to ground, undesired electromagnetic radiation, or electric or magnetic fields, which are directed toward the active antenna from an external source or which emanate from the active antenna.

A Yagi-Uda Antenna, commonly known simply as a Yagi antenna or Yagi, is different than a log periodic antenna because it is a directional antenna system consisting of an array of a dipole and additional closely coupled parasitic elements (usually a reflector and one or more directors). The dipole in the array is driven, and another element, 10% longer, operates as a reflector. Other shorter parasitic elements are typically added in front of the dipole as directors. This arrangement gives the antenna directionality that a single dipole lacks. Yagis are directional along the axis perpendicular to the dipole in the plane of the elements, from the reflector through the driven element and out via the directors.

Sorry if I got so long winded.

Other than a di pole antenna - rabbit ears, a antenna is a complex arrangement of elements and wires.

Having one of those elements in the wrong direction would cancel out the signal, as will having one that is bent. Fortunately where I live there is only one VHF signal and even though it is 40 miles away and only transmitting on low power - say 65 kw on channel 8!

It still comes in better than a signal on channel 48 with 1000 KW of a distance of 65 miles in the same direction with a receive antenna with twice as much gain.

My only opinion is that one of the reasons it does so well is because it is the only station in 80 miles that is on the VHF and there is not as much competition - interference from the other transmitters in my area.

On a VHF log periodic antenna, there is only about 3 sets of elements that are being used at any one time. The antenna looks back through the array of elements and adjusts it's self to use the elements it needs.

In a special cut antenna, the antenna is tuned to one specific frequency to achieve the most gain for that frequency.

[CTYankee51]

Thanks for the explanation. I won't pretend to understand most of it.

I think you're saying the elements should alternate as I described in my previous post.

Is there anyone from Winegard out there????

[winegard]

Good morning CTYankee51 -

I apologize for not answering your question last week. KNP 2516 had answered your question correctly so I did not feel the need to comment.

What happens is that as you start from the front to the back, the elements are folded back against each other.

The first element should go to the right or left and then every element after that would be staggered in the opposite direction as you go down the log periodic.

This is also diagrammed in your manual. Please refer to http://www.winegard.com/kbase/upload/1450292.pdf