007, I took a few minutes to adjust a 5/8 wave cut for 27.205 mhz at 270" vs. 276.5" as you suggest. I'm using 102" radials over real Earth and in free space for the comparison. I had no idea what differences I would find by modeling the .625 vs. 64, but CDX007's conclusions and No's turned out to be pretty close. So close in fact, as to likely be meaningless differences, but he was close. His conclusion about the unmatched impedance being a bit lower with the longer .64 radiator was also good. I don't know if it means much, but good work 007.
I did not have a .64 model made, but adjusting the .625 model to a .64 wave model at 6.5" longer was easy and all it took was one adjustment, then I ran the scans for results. The following results are for a 5/8 and .64 wave radiator in free space and over real Earth using 4 x 102" horizontal radials @ a 40' foot elevation with no mast, feed line, or matching. Sorry, but I did not record the matching info for the real Earth models. I can post the Eznec5 stuff, but I prefer to just recap in the following format.
Free Space = "FS", and Real Earth = "RE".
Radiator Length inches, Gain, Max Angle, Resistance, Reactance, FS/RE.
276.5", 3.20dbi, 40*, RE
270.0", 3.29dbi, 10*, RE
270.0", 1.89dbi, 20*, 83.14, -J273.7, FS
276.5", 1.92dbi, 20*, 70.70, -J234.3, FS
The differences are not much and I would find one hard pressed to measure the difference, except maybe by modeling, or using very high tech lab grade devices to do specific comparison testing.
I think Jazzsinger is right the difference between the .625 and the .64 is a difference without much of a distinction.
Don't ignore the .64 model above that shows a change in maximum angle from 10* to 40*, where the max lobe position goes to a higher lobe when adding the 6.5" to the radiator. Maybe this is what is being talked about when folks make the statement that the .625 wavelength is the maximum length radiator at resonance for continued low angle radiation from a single element vertical monopole.
Seems to me these scientists types only talk about models and antennas in free space and I think this is a classic example. IMO, it is also the same issue (free space and infinite ground plans) that often confuses the conversation when discussing radiator length vs. gain.
I did not have a .64 model made, but adjusting the .625 model to a .64 wave model at 6.5" longer was easy and all it took was one adjustment, then I ran the scans for results. The following results are for a 5/8 and .64 wave radiator in free space and over real Earth using 4 x 102" horizontal radials @ a 40' foot elevation with no mast, feed line, or matching. Sorry, but I did not record the matching info for the real Earth models. I can post the Eznec5 stuff, but I prefer to just recap in the following format.
Free Space = "FS", and Real Earth = "RE".
Radiator Length inches, Gain, Max Angle, Resistance, Reactance, FS/RE.
276.5", 3.20dbi, 40*, RE
270.0", 3.29dbi, 10*, RE
270.0", 1.89dbi, 20*, 83.14, -J273.7, FS
276.5", 1.92dbi, 20*, 70.70, -J234.3, FS
The differences are not much and I would find one hard pressed to measure the difference, except maybe by modeling, or using very high tech lab grade devices to do specific comparison testing.
I think Jazzsinger is right the difference between the .625 and the .64 is a difference without much of a distinction.
Don't ignore the .64 model above that shows a change in maximum angle from 10* to 40*, where the max lobe position goes to a higher lobe when adding the 6.5" to the radiator. Maybe this is what is being talked about when folks make the statement that the .625 wavelength is the maximum length radiator at resonance for continued low angle radiation from a single element vertical monopole.
Seems to me these scientists types only talk about models and antennas in free space and I think this is a classic example. IMO, it is also the same issue (free space and infinite ground plans) that often confuses the conversation when discussing radiator length vs. gain.
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