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When I try to plot a map, it Elevation angle amateur for azimuth, so which I'm setting to 60deg. This sort of instability is generally short-lived - minutes to tens of minutes. I am mystified how the focussing effect as described could consistently fall on one antenna in preference to another over such a long period of time. Remarkably, that ray focusing results in very high signal augmentation in quite small areas and very deep signal depletion either side ie. The field-aligned curtains appear and disappear.
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Try the given examples, or type in anvle own problem and check your answer with the step-by-step explanations. Sign up Elevafion our Newsletter Get our latest news and links in your email. Not using it as a primary path, but is usable for control if I lose my primary link. So far no one has rated yet, so be the first to rate this link! In the days of slide rules, Elevation angle amateur Smith chart was packed with lines, curves, grids and nomographs. Not far off. Thank you for the info. Great Psychiatrist in cumming ga. Reflection coefficients Elevaion be read directly from the chart as they are unit-less parameters. It just looks like gibberish text. It would be nice if somehow one could "pad" links, so that OLSR could have more info. I'm curious what those deploying sectors have found their effective distances Elevation angle amateur
- I'm curious what those deploying sectors have found their effective distances are?
- The Smith chart , invented by Phillip H.
- In the diagram below, AB is the horizontal line.
- About Elevation Angles The resource is currently listed in dxzone.
Users browsing this forum: Google [Bot] and 20 guests. Flat Style by Ian Bradley. Privacy Terms. Skip to content. Quick links. Forum rules By registering any account on vklogger. He writes, "Agree strongly with the concept of being a big station on six meters can be done much easier than 20 meters. Sporadic E clouds or patches mostly occur between 95 km and km height.
As skip distances typically range from km to km, the elevation angle of the ray path ranges between 8 degrees and 2 degrees for Es reflection at km. And that also holds for multi-hop. Es clouds or patches are thin — very thin — from metres to 5 km often less in thickness. So why would a 6m antenna at 45 feet height perform better than one at 95 feet? A common characteristic of sporadic E propagation, often forgotten, is ray focusing.
The distance between the lower height and the upper height, remember, ranges between metres and 5 km. A signal below the MUF approaching the Es patch at a given ray path angle will be refracted from a low level ie.
At a slightly higher angle say, half a degree the signal ray path will penetrate the Es patch at a slightly higher level, encountering a greater electron density, to be refracted at an angle equal to the angle of incidence. As the ray paths diverged from the transmitter antenna, so the ray paths after refraction reflection will converge and focus in the vicinity of the ground at the path terminal.
Remarkably, that ray focusing results in very high signal augmentation in quite small areas and very deep signal depletion either side ie. I have experienced this effect directly.
If the antenna at 45 feet is in the signal augmentation zone, the antenna at 95 feet will likely be in the signal depletion zone. Antenna radiation patterns in the vertical plane have little to do with it! Posted in the interests of dispelling myths and fallacies.
Just puzzled by one thing - he said the lower one was better during a contest. I am mystified how the focussing effect as described could consistently fall on one antenna in preference to another over such a long period of time. Given your explanation and his observation perhaps he meant "the lower one was better some of the time" which would make more sense to me all round.
He's a bit short on detail. It's equally likely that, after a few contacts gained by switching between antennas during which time the DX's ray path favoured the antenna at 45 feet, he stuck to the latter antenna.
QED: the antenna at 45 feet is favoured over the antenna at 95 feet. Without more details, it's conjecture. The angle of the ray path is determined by simple spherical geometry: the height of the refraction reflection point and the ground distance between the two stations.
At the greatest skip distances ie. Substitute "response" for "gain" The point I was trying to make was that the theoretical "response" at 3 degrees of the 95 foot antenna is only about 3db higher than the 45 foot antennna assuming equal main lobe gain- i. At a few degrees higher they are equal, and at 6 degrees the 45 foot antenna has a theoretical "response" many db higher 20db if you believe the simulations and assuming local ground does fill in the nulls to a extraordinary amount.
So my question is - is it proven that 6M signals always follow the simple geometry scenario, i. Is it possible that under some circumstances signals can arrive from a distance at angles higher than 1 or 2 degrees say 4 to 7? From what you say, I take it that this has been proven NOT to occur in practice and beyond doubt. Please, please take this as a genuine question - not a challenge to your explanation Cheers Steve. Trying to understand what's happening, or might be happening, by musing over the theoretical or even guessed-at radiation patterns of antennas doesn't help characterise the situation.
You need to look at it from a ray path perspective, as I outlined above. In the simple geometry case, yes, someone has conducted experiments - actually, regular observations - using oblique swept frequency ionospheric sounders Tx at one end of a path, Rx at the other, with synchronised operation.
The IPS station at Townsville had a Rx and a large log-periodic vertical antenna array used for making observations recorded on 35 mm film of a Tx in St Kilda South Australia, for example. Although angle of arrival wasn't measured, it was readily deduced from the path delay. Having seen many oblique ionograms during the time I worked at IPS, Es traces on the records are quite characteristic. There are numerous other examples of oblique sounder operations across the world. Studies from records of the current Jindalee OTH backscatter radar also support the simple geometry case.
However, Es propagation doesn't always follow the simple geometry. When backscatter occurs, for example. Es backscatter arises in one instance from field-aligned 'curtains' of electrons that form in an Es cloud as a result of turbulence in the wind shear that forms Es and electric fields that arise as a result.
Then you get propagation on off-great-circle paths. This sort of instability is generally short-lived - minutes to tens of minutes. The field-aligned curtains appear and disappear. And they move - faster than an Olympic m sprinter up to race-car speeds.
Backscatter also occurs when turbulence in the winds that created the wind shear forming the Es make 'billows', which distort the Es patch or cloud into ripples but not field-aligned. The ripples may be stable over short periods, but also drift. All of this yields propagation that appears and disappears tormentingly. The simple geometry also breaks down so to speak when tilted clouds or patches form not a rare phenomenon, apparently.
And another thing: Es clouds often form into a dual-concave shape, like a pair of saucers. The concave side facing the ground acts like a magnifying shaving mirror and results in signal focusing. This fact has kept ionospheric and radio propagation scientists busy for many decades.
And they're at it still. Hoping I've helped explain a few more things. Thanks to you I now have a much clearer understanding of the subject. The oblique ionogram is one of the most fascinating things I watch here Narrabri-Auckland. Much more satisfying than simulations or predictions - for me anyway. At the risk of wearing you out please feel free to answer this at a later date - or, indeed, not at all The particular case I am thinking about is a QTH situated near a cliff.
For example, say you have an 6M dipole at 3m height over flat ground which is 47m ASL but no cliff. This produces radiation lobes at various angles above the horizon. Move that antenna over and way past the cliff edge so it is now suspended 50m ASL. This produces a larger number of lobes, the lower one being much lower than the case 3m above ground as before. Now move the antenna back towards the cliff such that it is still at 50m ASL but at the cliff edge the ground comes up to meet it but remains 3m below At what point does the radiation lobe pattern transition from the 50m case to the 3m case?
Right on the edge of the cliff or some way back from the cliff edge? As I said - if it is too time-consuming - don't bother to spend time on it. I just would like to know This very technique - of mounting antennas on a cliff overlooking the sea - was used by CSIRO scientists just after WW2 in radio astronomy investigations of celestial noise sources. The objective was to get "free" gain from the sea reflection.
Their antennas were quite close to the cliff edge, as I recall. I'm not sure if there's a "sweet spot" for this situation though I suspect there is , which is what I perceive you're asking about.
I understand you may be able to investigate the effect of ground topography on antenna radiation patterns using some of the antenna simulation software packages available maybe EZNEC or 4NEC? I've not done it myself. Actually, after lying in bed thinking about, I fired up NEC4WIN95VM and did a rough simulation not many segments and wires to simulate the cliff which showed the effect quite nicely.
Unfortunately by about 2am I was getting bleary-eyed and hallucinatory and I will try a more detailed simulation later at a time when I am a bit more with it. Gut feel at the moment is that how far back from the edge you can go before the nice low angle lobes break up is dependent on the height of the antenna over ground behind the cliff edge and probably the aperture of the antenna. Anyway - I will have a play. Thanks Cheers Steve. I'd be interested in your results probably, so would others.
Just read your postings. One mode that you did not mention was "Ground Gain ". I assume this also applies to Sparodic E type propagation. What I have found on my moonset I have almost flat ground and my optimum "gain angle" is around 8 deg.
So I assume that the net result depends upon the Received incidence angle of the incoming signal and the height of the antenna. As in Adams case it is good to have a choice of antennas. During the week I have also been evaluating my antenna system. Norm VK7AC using an end fed half wave vertical quite often hears stations better than I do , this was a cause for concern so I carried out a few experiments. I erected a Discone , unity gain on 6M and also used my HF antenna. Half wave dipoles on 80 , 40 and 20M with a common feed.
The angle of elevation is the angle between a horizontal line from the observer and the line of sight to an object that is above the horizontal line. Last edited by qubit. It would be nice if somehow one could "pad" links, so that OLSR could have more info. Powered by Drupal. I gained dB on a mile link that way. Register to edit. The circles, all tangent to each other, represent different resistances.
Elevation angle amateur. Elevation Angles
Smith charts have to do with Impedance matching Resistance. The coordinate system used is resistance circles, and curves. Last edited by ipwnnoobs. See wikipedia article for more information. Last edited by kd7bbc. The circles, all tangent to each other, represent different resistances. The one closest to the tangent represents an infinite resistance, and the one furthest out largest circle represents zero resistance.
The curved lines represent reactances, from zero the straight line to shorter curved lines, the ones representing larger reactances. Last edited by k6yxh. Last edited by kd5isa. Last edited by kornesque. The Smith chart is plotted on the complex reflection coefficient plane in two dimensions and is scaled in normalised impedance the most common , normalised admittance or both, using different colours to distinguish between them.
The most commonly used normalization impedance is 50 ohms. Once an answer is obtained through the graphical constructions described below, it is straightforward to convert between normalised impedance or normalised admittance and the corresponding unnormalized value by multiplying by the characteristic impedance admittance.
Reflection coefficients can be read directly from the chart as they are unit-less parameters. Last edited by k4ago. The circles already present on the Smith chart include those for the resistive and reactive components of the normalized load impedance. One would normally use the intersection of these circles to identify the magnitude and angle of gamma, the voltage reflection coefficient. By maintaining a gamma of constant magnitude about the origin, one can draw a third group of circles.
Because standing wave ratio only depends on this magnitude, these circles define the standing wave ratio. The arcs represent points with constant reactance. To interpret impedance on the Smith chart, it is necessary to understand constant resistance circles and constant reactance arcs. A very comprehensive and in depth depiction of Smith Charts can be found at Wikipedia. Last edited by grinningphd. The wavelength scales on a Smith chart are calibrated in fractions of transmission line electrical wavelength.
The outer ring of a Smith Chart defines fractional electrical wavelength of feedline starting at zero and ending at 0. It also defines the direction toward the generator. This is a hint, indicating that this is a feedline length and not antenna length. Smith Charts are useful to determine feedline line length required to match a load to a radio transmitter. Last edited by qubit. Visit this link Elevation Angles Visit Site Share this resource Share this link with your friends, publish within popular social networks or send it via email.
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Sporadic E: the lowdown on elevation angle - VK LOGGER Amateur (Ham) Radio Forum
The dish is circular in shape, not oval. The dish has an arm coming from the bottom that makes a 90 degree angle with the dish. I will be adding a second arm to the end of the dish's arm that will allow me to mount an SMA antenna connected with RG cable precisely where it will utilize the dish's geometry.
I need to figure out the proper position of the antenna on the dish. I want the dish to receive signal directionally where there is a zero signal elevation angle. From my previous understanding, dishes receive their signal from space where there is an angle of elevation from the transmitter and the receiver part of the dish.
I created a diagram that illustrates my plan with dimensions and calculations. I need some verification with my diagram and suggestions on how to maximize the reception strength.
I think that the antennae should be placed somewhere along line C in the diagram but I want to be sure before I start modifying the dish. I only need about 6 inches of cable so I will try it with and without the jumper cable and compare signal levels. To find the focal point of a symmetric parabola, measure the diameter of the open rim of the dish, call this D. Measure the depth of the dish at its center, call this c.
Note that the focal point is in the center of the dish, it is not offset as in your drawing. So your receive antenna will slightly shadow aperture of the dish. Due to the physical aperture of your receive antenna, you may need to adjust it in or out from the focal point in order to fully illuminate the dipole or other element.
If the dish is an asymmetric parabola, the focal point will be offset from the center in order to avoid blocking the aperture. This is the type of parabola that nearly all modern home satellite dishes use. They are identified by an LNA support arm that extends from the bottom of the dish and the dish apparent elevation angle appears to be lower than the satellite capture elevation. In the case of an asymmetric dish, the existing LNA arm should be used as a starting point to find the appropriate focal point for the dipole or other antenna element since the focal point is largely frequency independent.
Please post a photo of the dish. Ku band satellite TV dishes are always offset feed, whatever their shape. The direction of firing is roughly along the feed arm. The dish is "minimally offset" my term to avoid feed blockage but not much more.
So if you draw a line from the bottom edge of the dish, over the feed, that's about the direction. When aimed at the horizon, the dish will look like it's pointing about 30 degrees down towards the ground. I've made many feeds for 2. A patch antenna might also work, or a short CanTenna.
Unless you have some fancy test gear, the absolute best plan is to use the original feed arm and LNB holder. Then you only have one axis to optimise, the in-out position of the feed. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 2 years, 4 months ago. Active 2 years, 4 months ago. Viewed times. EDIT: I've calculated the focal point on the dish to be approximately mm.
Jake Psimos. Jake Psimos Jake Psimos 5 5 bronze badges. I appreciate your input. This is described as shadowing or shading. There's no reason the focal point needs to be right in the center.
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