Originally Posted by Needle Bender
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.