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 A suggestion that 5 degree is a myth

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FreqFreak
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A suggestion that 5 degree is a myth Empty
PostSubject: A suggestion that 5 degree is a myth   A suggestion that 5 degree is a myth Icon_minitimeSun Jun 23, 2024 12:44 pm





In what context is important firstly. Seemingly verticals.

I found this video and watched it once. I am going to investigate and formulate my own thoughts. I have been aware of PBA (Pseudo Brewster Angle) for quite a few years now.

My first thought is that as PBA relates to ground type i.e. soil or salt water body the as such PBA is probably built into the ground type that you can select in a modelling software. There are 2 parameters involved. Dielectric and ground conductivity.

If it (PBA) was not built in to the software why do we see significantly less losses at low angles when we model a vertical antenna near sea water ?

I am all for differing views on all antenna subjects if they have some info to back them up. Let's take a good look into this. I will collect my thoughts on this and present them.

A few immediate thoughts spring to mind.

If we are getting less losses at lower angles by elevating where are these reduced losses being achieved ?

Either there are or are not reflections from ground and we know there are. So we have that clear and as a fact we can all agree on. As ground and/or salt water is reflective to RF.

So by elevating we achieve less ground loss with certainty.

Reflections from the ground either reinforce or attenuate at differing angles based on the phase of the interactions between direct waves and ground reflected waves (they combine). When waves are in phase or more in phase, radiation increases and when they are out of phase or closer to out of phase, they are cancelling or attenuating.

This is clearly seen when we take any given antenna and elevate it above earth. We get "ground gain" from a horizontal dipole as a case in question.

I have never rated 1/4 wave ground mounted antennas myself. Especially on 10m band they are not great. But that is not to say that elevated verticals are not good performers.

Neither have I consider a model to be a substitute for a real world antenna in any given position. They are merely a very idealized starting point.

If the PBA is not changed by elevation (I am not sure if this is a fact by the way I take only what is said in the video at face value) Then is ground loss the only mechanism where these reduced losses can be accounted ? Not sure about that.

It also beckons the question as to what he would think of this data which clearly shows significant percentages of contact on this specific path being sub 5 degrees cross multiple bands. And at higher angles nothing.

Is this a myth then ? i.e. percentage of contacts on a given path that arrive under 5 degrees (none virtually non above 20 degrees) - I think not.

A suggestion that 5 degree is a myth A_copy10




Taken from this article and similar tables can be found in the ARRL Antenna book:


https://www.arrl.org/files/file/QEX_Next_Issue/May-Jun_2011/QEX_5_11_Siwiak.pdf
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FreqFreak
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A suggestion that 5 degree is a myth Empty
PostSubject: Re: A suggestion that 5 degree is a myth   A suggestion that 5 degree is a myth Icon_minitimeSun Jun 23, 2024 6:21 pm

Here is what I can find to quote the ARRL book. This relates to vertical antennas to be clear.

PBA = angle at which waves reflected from the ground are at 90 degrees out of phase with direct wave from antenna i.e. direct wave being the energy going directly into free space above ground. (notwithstanding obstacles which of course attenuation but this is the same for any antenna vertical or horizontal, they both have elevating to work better common to them be it vertical or horizontal.)

"The factors that determine the PBA for a particular location are not related to the antenna itself but to the ground around it. The first factors is earth conductivity, which is the measure of the soils ability to conduct electricity the second factor is dielectric constant that corresponds to the capacitive effect of the earth." Both of those are parameters in red you can adjust in the most basic and free antenna modelling software.

I suspect that whilst a modelling software does not necessarily show a specific line that represents the PBA (like shown in the video) for a model over any given ground, that does not mean to say that the response pattern has not taken it into account when producing the model of the pattern. i.e. Just cause you do not see PBA mentioned does not mean it is not included in the resulting model.

Also I read :

Under the PBA, radiation is in between 90 and 180 degrees out of phase. And that at 0 degrees max cancellation occurs 180 degrees out of phase. Above this steadily less cancellation occurs as the PBA is approached.

Over very good ground I can see for example a PBA of 10 degrees on 21MHz so it far from the case that below 10 degrees there is a very quick drop off of emissions. And the higher you get your antenna off the ground, poles roofs etc. the less the grounds exerts its effects on the antenna are using.

So yes ground mounting is not ideal by any means, it can work but it certainly not a high performance option. At low frequencies it becomes your only option
for verticals as 1/2 and 5/8 become enormously tall and impractical.

Elevate a 1/2 wave or a 5/8 wave and then you are talking you get much more low angle energy going out.


There is nothing wrong in using 5 degrees a base line angle as much DX does in fact come in at those angles. Yes there is less energy because of the laws of physics but when that path is pen and looking at the data in the graph above suggests that the majority of DX comes in at that angle.

Just cause that is not the peak radiation level down there you are 100pct right to try and optimize take off the a low angle as ALL angles benefit and that is a good goal. I am not sure what his point is frankly ?

I cannot be certain I am right, but my suspicion is that PBA does change with antenna elevation and that the models take into account PBA in the resultant model (even if there is not a specific line representing it)

No one is under any illusions a 1/4 wave on 10m is not going to be a pile up busting  antenna, unless you are directly in front of the sea on a beach getting 9dB gain on TX and RX running some QRO (high power).
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A suggestion that 5 degree is a myth Empty
PostSubject: Re: A suggestion that 5 degree is a myth   A suggestion that 5 degree is a myth Icon_minitimeSun Jun 23, 2024 6:54 pm

Ground mounted 10metre quarter waves work some times, depends on ground clutter/location.

Quarter waves on the low bands with some non resonant radials work really good.

Personally I don't care what the angle is as long as I can work the other station.

Victor, Alan Pilot and strangeplains like this post

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A suggestion that 5 degree is a myth Empty
PostSubject: Re: A suggestion that 5 degree is a myth   A suggestion that 5 degree is a myth Icon_minitimeMon Jun 24, 2024 9:24 am

Sometimes, being the operative word, far less well than an elevated 1/2 wave. 

If ground mounted 1/4 waves were good CBers would use them.

"Personally I don't care what the angle is as long as I can work the other station."

If the DX is coming at an angle that your antenna is not optimized for, you may not be able to work the other station, you would not even know it is there.

Maybe ignorance is bliss ?

And if you are still ok with that, excellent for you. FT8 and FT4 is much easier so you are working in a very different way than myself as I like SSB phone only.

I would be inclined to want to know why I could not work the station and would push myself to do better within the realms of practicality for my station. This would mean more difficult and probably more rare dx can potentially be worked.

I am hoping someone knowledgeable about antennas can come from one the the 'antenna heavy' forums and clear up some of my questions, re PBA being included in the model and whether PBA is static irrelevant of elevation above ground. 

I find it difficult to believe it is static given that elevation of an antenna changes incident angles of RF into the ground and I would have thought their reflected angles.

I have no objection to relaxed radio that's fine, but it should not get in the way of others trying to understand more and improve for themselves and others also interested.
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