Antenna height

[Marconi]

My Eznec 2-D plots show the beam width of models as noted below. I think this hat demo is suggested in this Eznec detail and the idea is worth considering for the effectiveness of the lobe produced by models.

The model shows the 1/4 wave antenna with beam-width = 41.4 degrees and that is why we see the broad face of the maximum lobe at low heights.

 

[HomerBB]

I had a vertical dipole, center fed, at 33' at the bottom. A friend 6 blocks from me has his A99 mounted 50' up from the bottom. Typically, he does better in the local area to both base and mobiles. We are in hilly tree filled Ozarks terrain.
However, there was this one instance that maddened him. A mobile driving into town equidistant from us at roughly 12 miles called. I read him and spoke to him easily. My friend could not hear him at all.
I think we all may have noticed low to no bars on our cell phones while looking directly at a 300 foot cell tower 1/4 mile or less away. Being in a reverse lobe relative to the bandwidth of the band one is working is more impacting on making contacts than gain.

My 80m wire at 40' height can get me contacts out to 150 to 600 miles all the time. Rarely anything closer or farther than that. At that height my 20m contacts are all over the US and international into other continents. Which band, what height, and where you need/want to talk.

I built a homebrew Merlin antenna. There was debate over how it either did or did not outperform other antennas, especially 5/8 GP types. I wanted to see what I thought first hand but wasn't going to spend my house note on one.
My eventual conclusion was it was a decent antenna. I also tracked its performance personally and as much as possible where contacts were being recorded by some who argued its merit loudest. What my observations showed me is that the antenna met the needs of those who loved it, the channels 6 and 28 types who loved to talk in riddles and puns to domestic "DX" stations like themselves. The 5/8 GP remained more effective beyond US borders.

My point is, height works best sometimes, as does antenna rf patterns that can work for or against you.
Where high up does the most for me is bragging rights.

 

[TheBlaster]

The F2 dx is in the bottom part where there is greater gain as indicated in the lobe along the X axis. And it is greater than both the 2 figures before it, yet the text says : "no don't do 0.5 wavelength or your Dx count will drop off". Nonsense. Not to mention that low lobe looks greater than the null at the higher angle.

In fact the null looks less like a null (like those large indentations on the overlays of various CB antennas Marconi kindly produced of what appears to be around -7dB) and just an area of less antenna gain compared with the low angle lobe.

 

[TheBlaster]

"Being in a reverse lobe relative to the bandwidth of the band one is working is more impacting on making contacts than gain."

I cannot decode that sorry.. it could just have been a metal framed building drawing the signal out of the ether in the path of your friends route to the mobile station (or the mobile station had his or her antenna on the rear of the vehicle beaming his RF forwards to your location and not your friend's)

It could be this or it could be that, who knows.

I have never come across the terminology "reverse lobe" before.

 

[HomerBB]

Okay. Call it a null, or a reverse lobe.
As I've said many times, a person's experience is never the servant to another's argument.
Yes there is gain in the null, but not as much, therefore referred to as negative gain.. You should know that where contacts are concerned, local or dx, the difference in percents of gain can be the difference in whether a contact is or is not made.
Now, if I were going to begin a new thread on a subject like this that has been discussed many times, I would have begun with something like this, "I have experienced this phenomenon. Have any of you thoughts on why this occurs?" In this way folks might have some clue that I wanted some clarification rather than an argument.
My Daddy used to tell be that the difference in ignorance and stupidity is that ignorance is a choice. Ask to learn. And listen occasionally.

 

[freecell]

Hi, TB.
The text is a statement of quantity, not gain.
The hat brim shows more gain along a very thin slice over the overall 'quantity' of rf radiated. Above that thin hat brim there is a deep null.
Above that there is a big bulge (lobe) of radiation. That big lobe has the largest 'quantity' of rf.

View attachment 41672
Most of this hat is in the big lobe, not the brim, but the brim sticks out laterally more than the bulk of the hat material.

Groundplane Antennas at Various Heights (qsl.net)
https://www.qsl.net/df3lp/projects/vertical/index.html

Beginning with Figure 5 the Max Slice Gain and the lobe volume begins increasing at the lower angles required for long distance dx while the volume at the upper angles diminishes. (pay attention to the transition from figure 5 to figure 8) You'll notice that this improvement in the amount of power at the lower angles (including increased gain) begins at 1.00 WL above ground finally ending up with 3.3 dB at an elevation angle of 9 degrees.

Figure 2: Height: 0.02 wavelength
Impedance: 42.7 + j4.9 ohms.
Max. Gain: -0.3 dBi at 24°.

Figure 3: Height: 0.25 wavelengths
Impedance: 24.2 - j6.4 ohms.
Max. Gain: 0.6 dBi at 15°.

Figure 4: Height: 0.5 x wavelengths
Impedance: 25.7 - j0.7 ohms
Max. Gain: 1.9 dBi at 45°.

Figure 5: Height: 0.75 x wavelengths
Impedance: 26.0 - j3.2 ohms
Max. Gain: 2.9 dBi at 36°.

Figure 6: Height: 1.0 x wavelengths
Impedance: 25.5 - j1.9 ohms
Max. Gain: 3.0 dBi at 27°.

Figure 7: Height: 1.25 x wavelengths
Impedance: 25.5 - j2.2 ohms
Max. Gain: 2.8 dBi at 9°.

Figure 8: Height: 1.5 x wavelengths
Impedance: 26 - j2.6 ohms
Max. Gain: 3.3 dBi at 9°.

The highest gain and the lowest elevation angle occur simultaneously at a feedpoint height of 1.5 wavelengths above ground. Take notice that a low feedline vswr (1.92:1 in Figure 8) is no indicator of antenna effectiveness. The best performing antenna here has the highest feedline vswr, the antenna feedline represented in Figure 5 not withstanding.

 

[Marconi]

Here are my models that show what Eznec predicts for a tuned A99 model at 54', 48', 42', 36' feet over Real Average Earth.

This A99 uses a transformer to tune, so it is a bit different than the Solarcon design...figuring that could make for different results.

The 1st page shows the Average Gain Test = 0.982 - - 0.08 db as an understated error in the gain, to start with for these models.

I did not see the match change noticeably on raising these models, so IMO the Transformer manages the match well in this case.

Do you see anything with the patterns in particular in this mix of models? I see a glaring indication of one model controlling the high angle lobes better even while indicating a little less maximum gain.

Note also that the model at 54' feet shows a 1* drop in angle as increased height often predicts. 2 models show the same gain and in both cases they were the models at the lowest heights.

Your mileage may vary.

 

[TheBlaster]

A final thought to ponder.. is the hat rim a wider diameter, or is the top of the hat a wider diameter ? I rest my case. Unless you are living in an alternate reality it is crystal clear it is the rim.

I learn by making high effort inputs and doing, making lots and lots of contacts. So I trust myself through my experiences.

Notwithstanding that, you seem like a nice person and I can see what you allude to with the bulk of RF in the top of the hat, I also see that, but for the article writer to say lower angle gain is less in the text relative with what can be seen with one's eyes is very obviously not correct. When I see something with my own eyes and then there is text that is directly in opposition to what can be clearly seen I will point that out.

Maybe something went wrong with the model or some factor was omitted from the model. In any event enough time has been spent on "fantasy" antennas that don't even
exist in your, mine or anyone else's world.

Your success at the contacts you want will tell you everything you need to know, keep adjusting the setup until it is the best you have ever experienced.

 

[HomerBB]

I would never dispute there is more gain in the brim slice. I will stand pat on there is more rf in the upper lobes. In fact, I believe it is very likely that far more contacts will be made with the fat upper lobes than with the lower thin lobe. In the best and worst of conditions from my Midwest perch using an omnidirectional monopole antenna at various heights I've made many more contacts out a few hundred miles than I have a few thousand miles. All of the gain available in all of the lobes can net contacts.
It is a simple, and likely accurate, expectation that getting more of the pattern toward the horizon in a broader higher gain lobe than in the upper lower gain lobes would be better for dxcc. If your goal is all 50 states, or grid squares accumulated, then the derby hat rf pattern might be best. If international contacts, then place more gain against the horizon.
Therefore, I see the text and the image in agreement.

 

[TheBlaster]

Whilst we have a conciliatory tone now which is great I think you might need to reconsider the high angle lobes being responsible for the circa 200 miles contacts. I can of course be wrong but I can explain the way I tend to view it.

Contacts up to 200 miles will not likely be coming from high angle lobes on 11m, they won't be skip contacts.. they will be coming from the low angle near "line of sight" lobe, most probably being bent over the horizon by some weak ducting (of course we cannot know for sure where from where the RF enters the duct as we don't know where the duct is)...high angle lobes are likely to be well on their way into the low ionosphere at 200 miles from your QTH at those high angles. Ducting tends to happen much much closer to earth.

As some background I regularly speak to stations circa 50-150 miles, pretty much at least one at 150miles every time I go out in fact.. commonly other high ground stations, sometimes when there is good tropospheric ducting 200 miles. And sometimes even further can be achieved with good height at both ends and ducting.

My dead zone for contacts tends to be 250 - 450 miles roughly. Too distant for near line of sight and too close for E layer skip (incident angle required would be too great and pass straight through the ionosphere rather than refract). There have been the very occasional rare exceptions, maybe once or twice a year on 11m.

The higher lobes are likely at E layer skip angles as a rough guess. As we know a phenomena that is all year round but predominantly during a summer time peak of activity, though you can get nice surprises any time of the year, albeit both weak and very unstable out of the summer peak.

500 - 2,000 miles skip for me tends to be mainly E layer propogation. 2,000 miles being the very outer reaches. Regions such as Cyprus and The Azores from here which are almost certainly multiple hops E layer. I managed Israel one summer 5-6 years ago and never quite worked out if that was high angle E layer multi hop or short higher angle F2 layer (it was in a time of good sunspot activity)

IMO the best antenna will be one that has very low angle radiation up to higher angles with no nulls.

This is a great thread for that exact topic, with a broad sweep you will get all the DX that is available on both RX and TX.

https://www.worldwidedx.com/threads/the-myth-surrounding-antenna-take-off-angles.140770/

 

[The DB]

So the claim is to not mount a vertical antenna within a certain range of heights because of a significant portion of high angle radiation? I guess I need to model this and see for myself.

So, I guess I will start with a 1/4 wavelength antenna at 1/2 (.5) wavelengths in height and work my way up...

[photo=medium]6476[/photo][photo=medium]6477[/photo]

Is their a fair amount of signal going high? Yes.
At low angles, will this antenna exceed the performance of antennas mounted lower than this antenna? Yes
(While I am not showing them here, I am basing this yes on years of prior modeling experience)

Next, same antenna mounted 3/4 (.75) wavelengths in height.

[photo=medium]6480[/photo][photo=medium]6481[/photo]

Is their a fair amount of signal going high? Not really
At low angles, will this antenna exceed the performance of antennas mounted lower than this antenna? Yes

So, how about the same antenna mounted 1 wavelength in height?

[photo=medium]6474[/photo][photo=medium]6475[/photo]

Is their a fair amount of signal going high? Yes, quite a bit
At low angles, will this antenna exceed the performance of antennas mounted lower than this antenna? Yes

I'm seeing a pattern here, should I continue through the range being discussed? Here is 5/4 (1.25) wavelength in height.

[photo=medium]6482[/photo][photo=medium]6483[/photo]

Is their a fair amount of signal going high? Not really
At low angles, will this antenna exceed the performance of antennas mounted lower than this antenna? Yes, by quite a bit

And finally, 3/2 (1.5) wavelengths in height.

[photo=medium]6478[/photo][photo=medium]6479[/photo]

Is their a fair amount of signal going high? Yes, quite a bit
At low angles, will this antenna exceed the performance of antennas mounted lower than this antenna? For the first time, no.

*****

So, going back to the original argument, and those that agree with it, I have a question.

Do not mount groundplane antennas at heights between 0.25 and 1.25 wavelength. At those levels above ground most of the energy will be radiated at angles of 27° to 45° into the ionosphere. This phenomenon seems to be independent to the number of radials or other counterpoises. Further simulations indicates that this is true for all other variants of vertical antenna systems too.

No disrespect to sp5it, but in my opinion, this entire argument is little more than a distraction from what is important.

If I continue to see a benefit at the low angles that I desire, why should I care about the higher angle radiation?

Further, based on prior modeling experience, the trends we see with these models does not stop at 1.5 wavelengths in height, and in fact get worse. The low angle lobe continues to get narrower and narrower, and more and more lobes are added to the overall pattern pulling more and more of the radiation to said higher lobes, so its not like going above said range of heights improves anything from the point of view being argued.

And still more, going below this range of heights negatively affects the gain of the antenna to an ever increasing degree.


The DB

 

[Marconi]

Whilst we have a conciliatory tone now which is great I think you might need to reconsider the high angle lobes being responsible for the circa 200 miles contacts. I can of course be wrong but I can explain the way I tend to view it.

Blaster, I'm not sure I agree, but I'll give this idea due consideration, and I may also model the antenna I speak about below to see if it shows us some indications of high angle lobes at 50' feet.

My mentor was a Master Sergeant retired with 24 years in Japan after the WW2, training in radio communications. I met him fishing on the Texas City Dike in 1967. Soon he introduced me to radio.

He had a fix mounted 14 element 2 meter horizontal yagi at 50' and he could talk to his brother on the SW border of Oka/Ark. It seemed to me he could make contacts just about any time he wanted...that could have been my imagination working however, because he was often talking to his brother when I visited him.

He would say, he was using the high angled short skip to make it to his brother.

I was 20 years younger than he was and I hung on to every word the man said when talking radio.

I loved the guy, but I did not like him...he was bossy, loud, rude, would fight with words at the drop of a hat. I even saw him fight for real too...and it wasn't good for the other guy.

 

[TheBlaster]

Ok I will edit this... 0.25 lambda and ground mounted would have been very useful The DB. From my perspective ground and 0.25 are convenient (as it would be for many with a large) GPA. The premise being..

Between 0.25 and 1.25 = is bad don't do that.

 

[Marconi]

If I continue to see a benefit at the low angles that I desire, why should I care about the higher angle radiation?

DB I agree.

That said however, I've seen times when I my local buds were able to talk 200 miles, of a morning, into the San Antonino area and we all agreed...it was likely short skip...and higher angled lobes were working our signals higher into the sky.

 

[Marconi]

Based on my comments in post #59, I like the pattern of the image below for the model at 42' feet, because it not only shows the high lobes compressed, but the wider maximum lobe face is much wider, and this lobe shows maximum gain over this broader range that any of the other models in this overlay with lower angles and a little better gain.

Again IMO, the maximum gain and angle lobe for the model at 42' looks the best of all as compared here and it stand out if you look close.