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Antenna height


Slow, to be sure I don't know if 2 meters can talk that far or not, but that was what he use to tell me about his brother.

A while later Sanders called me an told me his brother had a HG CLR2 base antenna he'd give me if I would pick it up. I said, no way man am I going to Ok to pick up anything today or tomorrow. Then Sanders told me his brother lived right close by in his neighborhood. So, I got the antenna and it could have been all BS when I heard them talking on their radios. See how evil works in idle minds...I've likely told a story that makes me look foolish again.:LOL::LOL::LOL:

Maybe them two old bastard got a laugh over making me look silly. I still see hams doing that even today, and I'm NO Ham.

It's all radio man and you are DEDICATED there is no doubting that.(y) No one knows it all. I only know what I know because I was selectively listening to those who I knew know much much more than I probably ever will.
 
There are real time maps available online to locate the E clouds.

I have never heard of the "negative gain" term either.


What many in this thread refer to as "short skip" is really DIRECT wave propagation.

I am curious to know where the E cloud maps are, a link up would be great. Given the phenomena is not well understood I would be very surprised if there is a forecast. Given they come and go without any warning. Sporadic E openings could be for 45mins or 45 seconds. that can be predicted ?
 
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Well there you go, you learn something new all the time. Is that a prediction or a detection ? I like that website but never saw the E layer page, not quite sure how useful it might be but I guess it gives a rough day to day idea thanks for the share.
 
Do you make this screen grid or is there a type of object in 4Nec2 that does that as a choice?

I see this feature.


I have used the geometry builder in the past, but I don't really use it much anymore. More recently I tend to make this type of thing by hand, in most cases it really isn't that much slower for me anyway, and I can make certain customization that said program don't include.

Nice one The DB.. I have a 1:1 choke balun as feed point on my GPA (although initial test was using just a S0-239 not a baanced antenna so not strictly necessary as I understand) I went for a 1:1 choke/balun as it made the feed point and antenna more robust and "belt and braces" for the CMC suppression. I have yet to test the balun version but it sits here next to me in readiness.

I guess you used a mast as the radials resonance will become blurred as they hit the ground.

There are a lot of people the subscribe to the idea that balance is why CMC's happen. I am not one of them. To me, its just a matter the impedance of the different paths. AC current takes the path of least impedance.

Here is an example for you. You have a full wavelength doublet, an electrical half wavelength on either side. Their is also a matching system, say an L network, or perhaps a stub match, to match the 1000+ ohms of impedance that this antenna will have at the feed point down to 50 ohms.

In spite of it being a balanced antenna, you will almost always have a significant amount of CMC's with this antenna unless you get a very lucky feed line length. Why? Because in most cases the outside of the coax shield will present a lower impedance than the side of the antenna said shield is attached to... You can essentially see it as the same as a parallel resistor network as far as RF current is concerned...

It is important to note that with a choke you are not cutting off the current path that is the outside of the coax, you are simply raising the impedance of said coax shielding to be noticeably higher than where you want to current to flow. The antenna isn't any more or less balanced than before. All you really did was change the equation between where the currents will flow. Actually, taking this a step further, a choke right at this antenna's feed point will have little effect, the reason? There is almost no current flowing at the feed point of this antenna and RF chokes are current devices. Putting the choke about 1/4 wavelength down the coax from said feed point will be more effective.

Another spanner in the works with this antenna is that the radials are commonly bent to 43 degrees to match 50 Ohms (as is my own) and not left at 90 degrees to the radiating element. As I gather this also affects the radiation angle.

Yes said radials are commonly angled down, although not in the models I created as I used the model in sp5it's link as a base. On that page, they clearly show a 1/4 wavelength antenna with 4 horizontal radials, so that is what I used. Although in that case there was no mast, and I did use a mast...

I've done a study on this a while back, and when it comes to the idea that angling radials down from horizontal will lower an antennas radiation angle, this is a common idea that I have seen many very knowledgeable people post as a fact. I have seen some evidence against this, and none for it. I don't want to definitively say it can't happen, I'm just saying the evidence that I have seen does not support this idea. That being said, there are a lot of thing that many people think affect an antennas radiation angle than I have found at best suspect over the years, so this is no surprise to me.

I have always had a fond place in my heart for the humble GPA.. simple as it gets and it works. It may not be a high gain mega blaster of an antenna but it is an effective antenna and looks great as well.

I would be very interested to see a "ground mount" model though when radials are bent 43 degrees feed point will likely be higher up depending on what band you are using the GPA for.

Assuming by GPA, you means ground plane with angled radials, I have read in engineering texts about impedance tuning on near earth mounted antennas, including lowering an antenna's impedance by mounting the antenna some distance above the earth, angling the radials down until they reach the earth, and then runing along the earth. They also talk about raising the impedance by putting the feed point below the earth in a hole, then running the radials at an angle some distance up to the earths surface, and then running said radials along the earth. The problem here is, like any near earth mounted antenna, you really do need more than three or four radials to make the antenna efficient, and I don't mean just a few more...


The DB
 
Great post appreciated. A lot to take in and consider.... yes the balun was in the main because it is a much stronger mount for all elements as opposed to soldering onto a SO-239.. solder takes the strain. And interesting point about the balun not having an effect at CMC rejection. I kind of get that.. I guess some coax wraps around a big ferrite would be better for this.

Very interesting with the radial versions and layouts. Rather beyond my scope with no antenna analyser to test what is happening relative to height of this antenna.

I was under the impression that a GPA was an efficient antenna. 4 radials being deemed a "perfect ground". I imagine this more related to VHF where it is mounted 10m up some
multiple wavelengths and I have had some concern that at lower frequencies getting up high can become more difficult as the antenna becomes rather large and impractical to get very high off the ground. (as in radial at 10m high or so)

Anyway I am having fun with it and shall see how it performs. I hope the 1:1 balun will not have any detrimental effects relative to a SO-239. Seem to get a decent match and quite forgiving of the radial positions relate to that... i.e. along the ground a bit or pegged at the ground.. or frankly literally anywhere thrown about up down on ground not on ground which is how I initially tuned it in a very confined awkward outdoors space. SWR sits around 1.4:1 on first real use.

Decent QRP contacts made in mediocre conditions 1,300 miles away as well. I shall look forwards to optimizing it as far as is possible. (and just using it cause it is one the only antennas that I can use at the moment.)

I hope it has greater efficiency than a ground mounted dipole and one reason why I opted for it. (given it has 4 x 1/4 wave radials as oppoed to 1)

Anyway easy wizard ways of mitigating some of the ground losses? (which I assume is why it is not efficient at HF frequencies) I did read that many shorter radials can be as or more effective than fewer longer ones, although I also operate portable out in the field so if antennas become too hassle-y and tangled it can create problems putting it up.
 
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I have used the geometry builder in the past, but I don't really use it much anymore. More recently I tend to make this type of thing by hand, in most cases it really isn't that much slower for me anyway, and I can make certain customization that said program don't include.

DB, I would have to do this by hand too. I built a mobile model with a base, roof. and hood like this using the copy, move, change height, and connect features.

How about showing me a model...how this idea works compared to a regular ground model. I would like to see your idea.
 
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One other thing to add.. I thought the " I max " on the GPA was feed point.. much like a dipole... i.e. 1/4 wave down from the top. So I would have thought there would be current there at feed point unless I am misunderstanding something. (maybe you meant the full wave dipole.. that sounds like a rather uncommon antenna)

As far as a match they (GPA) are very unforgiving antennas when it come to where the ground planes are and still achieve a low SWR.

I am interested to understand what a broad efficiency figure might be for one quite close to the ground with 4 radials compared to a dipole close to the ground.
 
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Antenna Radiation Efficiency % is equal to radiation resistance divided by radiation resistance + radiation loss. The top five sources of vertical monopole radiation loss in no particular order are:

#1. Conductor RF Resistance.
#2. Parallel Losses from Insulators.
#3. Equivalent Series Losses from the Loading Elements.
#4. Ground Losses in the Antenna Current Return Circuit.
#5. Ground Absorption in the Near Field.

The last two are the main sources of radiation loss in elevated-radial monopole antenna systems. In most cases they make up a large amount of the input resistance or impedance seen at the input to the load. Levels of efficiency approaching 100% occur ONLY when the measured load input resistance or impedance does not include any resistance from radiation losses whatsoever. All power absorbed resulting from radiation loss is not radiated from the antenna.

An antenna measures 50 ohms at the load but upon closer inspection and measurements the radiation resistance is only 0.1 ohms while the other 49.9 ohms is determined to be the result of radiation losses. Radiation efficiency is 0.2% @ a 1.0:1 VSWR, which as is clearly demonstrated is never an indication of antenna radiation efficiency. 100W into this antenna equals 200mW out.
 
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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.

there is no skywave ionospheric propagation taking place @ 144-148 mhz.. i've never seen the muf anywhere close to that and neither have you.
 
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Here I set the SP 500 at 1.25% wavelength.

This looks like a little benefit to me, and I sure don't see the maximum gain and angle shooting up to 27* - 45* degrees, but it does produce an additional lobe at a high angle. Adding high angle lobes is sometimes what we see when we go higher.
I wonder how the pattern would look at 1/2 wavelength above ground to the feed point.
 

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