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Really any difference at height?
- Thread starter Heavy Metal
- Start date
Here is a model comparison of a 5/8 wavelength antenna at the requested heights over real/moderate earth. The antenna diameters are 6 millimeters, which is just under a half an inch.
The v on the model names is for vertical, the number next to it is the height in feet.
As you can see, the gain goes up as you elevate the antenna, although the 0.84 dB difference from one height to the other won't really be noticeable.
Another thing to note here is the angle of radiation. The angle of radiation of the antenna at 65 feet is about half that of the antenna at 36 feet.
Now for some horizontal antenna dipole models...
The h in the model names is for horizontal, and the numbers next to that are, again, the elevation of the antenna in feet.
One thing to note here is the antenna's gain doesn't change much. Going from 36 to 45 feet of elevation, the gain actually drops, then beyond that goes up. Another point of note is the overall difference of 0.38 dB, which is less than half of the change from the vertical antenna models mounted at the same heights. This difference is insignificant.
The angle of radiation, however, goes through the same type of change with height as the vertical antenna above. Doubling the antenna's height again cuts this angle pretty much in half.
The DB
The v on the model names is for vertical, the number next to it is the height in feet.
As you can see, the gain goes up as you elevate the antenna, although the 0.84 dB difference from one height to the other won't really be noticeable.
Another thing to note here is the angle of radiation. The angle of radiation of the antenna at 65 feet is about half that of the antenna at 36 feet.
Now for some horizontal antenna dipole models...
The h in the model names is for horizontal, and the numbers next to that are, again, the elevation of the antenna in feet.
One thing to note here is the antenna's gain doesn't change much. Going from 36 to 45 feet of elevation, the gain actually drops, then beyond that goes up. Another point of note is the overall difference of 0.38 dB, which is less than half of the change from the vertical antenna models mounted at the same heights. This difference is insignificant.
The angle of radiation, however, goes through the same type of change with height as the vertical antenna above. Doubling the antenna's height again cuts this angle pretty much in half.
The DB
vertically at these heights
So far looks like 55' is pretty ideal
Horizontally at these heights
So far looks like higher the better.
So far looks like 55' is pretty ideal
Horizontally at these heights
So far looks like higher the better.
How do verticals 1/4 1/2 5/8 .64 3/4 7/8 at these height between 25Mhz and 28Mhz act? As well as horizontally?
And how would it be local vs dx for this and the above you posted?
And how would it be local vs dx for this and the above you posted?
look at the 36' height per say one WL AGL.
not a whole lot gained by going to 55 feet AGL but it does throw some lobes and NULLS.
The nulls is what you should;d be concerned with as that will decrease your receive.
I did not see any 1/2 wl model or 18' AGL, 1/2 WL AGL will surprise the heck out of you for performance on DX.
Local talking then sure 1 wl or higher works better than 1/2 wl AGL.
not a whole lot gained by going to 55 feet AGL but it does throw some lobes and NULLS.
The nulls is what you should;d be concerned with as that will decrease your receive.
I did not see any 1/2 wl model or 18' AGL, 1/2 WL AGL will surprise the heck out of you for performance on DX.
Local talking then sure 1 wl or higher works better than 1/2 wl AGL.
Patterns like those above are really only relevant when discussing DX, they don't really say anything about local contacts and effects. For example, for a plot like those above that shows an angle of radiation at 10 degrees, 10 miles out that maximum radiation will be a height of 1.76 miles, and that is assuming the earth is flat, the earths curve will only make that height even higher. Mounting an antenna at that height is beyond infeasable, and even if you could manage it, your contacts with people much closer to you would suffer.
In general, lower angles of radiation, as well as stronger lower angle lobes, both increase the surface wave strength, but this is not a certainty. There are plenty of other factors in play as well. It is possible with some modeling software to model surface wave results, but those are not common, and I think posting such a plot would be more confusing to many people than helpful as they are very different.
One reason I think that you don't see them very often is many modeling programs don't support such models. EZNEC, for example, requires you purchase the pro version to access this functionality.
The DB
In general, lower angles of radiation, as well as stronger lower angle lobes, both increase the surface wave strength, but this is not a certainty. There are plenty of other factors in play as well. It is possible with some modeling software to model surface wave results, but those are not common, and I think posting such a plot would be more confusing to many people than helpful as they are very different.
One reason I think that you don't see them very often is many modeling programs don't support such models. EZNEC, for example, requires you purchase the pro version to access this functionality.
The DB
The DB has shown a 5/8 wave antenna in the vertical plot so that is what an I/MAX2000 is. (assuming you add 1/4 wave length ground planes to get it performing up to snuff) Or at a minimum the GPK kit (4 x 6 foot ground planes)
For local chat the theory suggests that a doubling of height should give you close to 3dB height gain. (you are close to doubling from 36ft to 65ft, it follows you should obtain approx 2dB general gain from the height increase for line of sight QSO's)
Although the TOA lowers as the height AGL increases we are still predominantly subject to what is happening in the F2 layer at any specific moment in time.
I do have to wonder if one moment might favour the 36ft install and the next QSO might favour the 65ft install TOA. We can never really tell which part/altitude of the 200 miles thick F2 layer is going to be charged, and where and how large (and how strongly charged it is throughout) the "puddle" of ionization is and it's relative strength where your signal happens to intersect it for refraction.
I think the goal is to have a nice spread of RF going out from 3 to 20 degrees ideally. The greater height should ensure the lowest lobe your antenna can achieve is at the lowest angle that the antenna used can technically produce.
(My own self set challenge at the moment is to see at my relatively low antenna heights AGL (20ft-30ft typical) albeit at up to 650ft ASL is to understand if the Gain Master or the MAX2000 is the best performer. I have a suspicion that I am trying to follow up that the MAX2000 produces a lower TOA than the GM at lower heights, with ground planes it may be better protected from earths negative effects (unconfirmed local signal increases reported with MAX2000 even without radials so far). I think given lack of expertise and technical equipment it is going to take a quite a long time using both antennas to get some kind of intuitive "in practice" understanding. I hasten to add that the GM has already proven itself at 20ft in height with numerous contacts into Australia from the UK, so the MAX2000 has it's work cut out.)
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Been trying to tell people that for 20 years or more. The less than 1 dB gain is far more than offset by the potential 20-30 dB LOSS from having a null in a critical area.
RatsoW8
Supporting Member, W9WDX ARC Member - WD8T
A 5/8 with and without radials will have very similar patterns, assuming you ensure there are minimal cmc's in play.
Someone has been paying attention, and built on whats been said.
The DB
You the man The DB !
I really did not know about the radiation pattern on the 5/8th being similar without the radials I was under the impression that they were critical to keep the lowest lobe down/protect against ground losses in the reactive near field.
I really did not know about the radiation pattern on the 5/8th being similar without the radials I was under the impression that they were critical to keep the lowest lobe down/protect against ground losses in the reactive near field.
This is why I disagree with people that try and maximize their main lobe at a very low angle. Sure the lower the TOA the better for long haul DX and by long haul I mean 5K+ miles and usually to the far side of the planet. Higher angles are quite useful for DX within North America. Ideally an antenna would have a broad fat lobe with flat gain from 3 degrees to about 45 degrees but that is not going to happen. Nulls are more important to worry about than exactly where the peaks in the lobes are.
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