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The 5/8-Wavelength Antenna Mystique by Donald K. Reynolds

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  #9  
Old 08-16-2011, 07:33 AM
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Well I'm back to the question Bob asked.

I was successful in duplicating the modeling dimensions that Cebik used for his .625 wave with horizontal GP radials, at 25' feet, over Very Poor soil.

I figure if any models were correct, it would be Cebik's models. I checked this one to all the soil conditions he tested in his report noted above and the numbers for gain, angle, lobe #, and the feed point impedance were all surprisingly the same.

I then added 6.2" to bring his .625 wave model to .64 wave and here is the following output I compared. I also did a pattern overlay for both models as noted on the first sheet in my supporting images. Note that the .625 is ahead in gain by a modest amount while the .64 shows a modest advantage in the match.

Bob's question .64 vs, .625.pdf
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Old 08-16-2011, 01:23 PM
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why are the ground planes nine inches shorter than a 1/4 wave? can you elevate the radilas like the new penetrater and see if that changes anything?

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Old 08-16-2011, 04:18 PM
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Originally Posted by Needle Bender View Post
why are the ground planes nine inches shorter than a 1/4 wave? can you elevate the radilas like the new penetrater and see if that changes anything?
I'm glad you asked NB, because I don't understand it either. My models were set to the measurements that Cebik noted in his report and they also seem to go against the radiator/radial length ratio of 5%, a rule we often read about.

I used his models instead my own to give my basic point of view to Bob's question regarding the .64 wave vs. 5/8 wave, just in case some questioned my modeling skills. I can't argue the point that Cebik's dimensions are wrong, because my versions of his models show better results than my own do.

In the process of trying to figure out what he did and get these models to show exactly the same matching and gain results as Cebik, I had to tweak the segment counts, which he didn't provide. He used about twice as many segments as I would have, and that is the only difference that I found.

His measurements are a bit shorter all the way around than my model for a similar wavelength and frequency...using my notions for the math. I would have tended to make the 5/8 wave radiator for 28.500 mhz about 258.8" and the radials close to 105", more or less, but he must be right, because his results are a little better than my own models.

When the new Penetrator came out I tried to model the idea of raised radials, but I wasn't successful in figuring out the bracket. For years my thinking was the 500 design may have some advantage in performance due to their raised ground plane. I never owned one, but have heard a lot of reports about how good they are, but it was nothing but CB talk. Nobody's reviewed their new 500 yet, so I decided to wait before getting back to the model.

I tried to physically measure the current in the radials for my I-10K using a MFJ854 and a standard electrician's clamp on amp meter, but never detected anything. Maybe the current was just too small. You'll note that Cebik may have alluded to this lack of current flow issue in 5/8 wave antennas in his report, when he talked about the current standard he used on the 1/4 wave antenna without a word in this regard for the 5/8 wave. I'm assuming here, but sometimes you have to read between the lines. It is also possible his standard idea does not apply to 5/8 waves. My modeling also shows these 5/8 wave antennas with very little current flowing in the radials and you can see some indications of that in the images above.
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Last edited by Marconi; 08-16-2011 at 07:53 PM.

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Old 08-16-2011, 05:55 PM
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isn't the current highest about 1/4 wave down from the top?

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Old 08-17-2011, 06:22 AM
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Originally Posted by Needle Bender View Post
isn't the current highest about 1/4 wave down from the top?
I believe you're right.
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Old 08-17-2011, 09:34 AM
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Quote:
Originally Posted by Needle Bender View Post
isn't the current highest about 1/4 wave down from the top?
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I believe you're right.
had to happen sooner or later
BOOTY MONSTER likes this.

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Old 03-13-2012, 09:20 AM
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Quote:
Originally Posted by Needle Bender View Post
isn't the current highest about 1/4 wave down from the top?
since the merlin base antenna and most mobile antennas are less than 7 ft tall above their feed-point ...... does that mean the current is highest 2 feet (or lower on shorter verticals) below the feed-point on the ground planes or car body ?
does it mean when my 3 ft lil will in on the 6 ft high roof on my vehicle that the current is highest just under the tires ? if it were on a trunk , would it be 3 ft under ground ?

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Old 03-13-2012, 10:50 AM
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Quote:
Originally Posted by BOOTY MONSTER View Post
since the merlin base antenna and most mobile antennas are less than 7 ft tall above their feed-point ...... does that mean the current is highest 2 feet (or lower on shorter verticals) below the feed-point on the ground planes or car body ?
does it mean when my 3 ft lil will in on the 6 ft high roof on my vehicle that the current is highest just under the tires ? if it were on a trunk , would it be 3 ft under ground ?
No, because that was months ago and is no longer current.


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