Bob, I know the best we can do to depict AC currents flowing on a wire is to indicate them at some particular point...frozen in time, so-to-speak. But, what determines the direction those arrows point when EzBob plots such an image?
I think I saw that post also, and thought it was interesting. If the phase idea works with this 1/8 wavelength idea like current flow is reported to work on a 1/2 wave dipole, then the antenna system would necessarily have to waste another 1/8 wave above it on the good phase portion of the element...in order to show cancellation due to opposing forces. IMO, that is why the dipole is depicted to have the currents on both sides of the source flowing in the same direction (in-phase) and hopefully both legs with the same magnitude. And if there is no in-phase flow, then the RF is canceled just like it is inside the coax. If the magnitudes are not equal then we can experience common mode currents of the feed line shield as well.
For a long time I've had this thought - even if the RF from the 1/8 wave segment at the base of a 5/8 wave radiator was canceled somewhat, that its major contribution to the antenna's effectiveness was to raise the 1/2 wave current portion higher up on a longer and higher radiator. I assumed this would show an improvement in maximum radiation...and this is why the 5/8 wave is said to show more gain at a low angle. Notice that I said "...at a low angle," not a lower angle. I was never convinced however, that this small increase in elevation was quite enough to really lower the maximum angle of radiation in a primary lobe. In the modeling I do I most often see changes affecting the higher angled lobes rather than the lowest lobe. I believe it likely works that way in real life antennas too, except to some degree how antenna elevation changes have their affects the lower lobe may be affected a little. In the 18' to 50' range we often see in CB, I doubt this low angle change would be much however.
Bob, I'm surprised you never looked at what is going on at the base of a 5/8 wave antenna. Surely you've had some thoughts about how the 5/8 wave element works.
Bob, I don't really know either why the currents are as they appear and you're right about my lack of expectations. I don't make the models to show anything in particular. I'm sure whatever I do has some affects, but my activities in the area of currents are not deliberate or planned. I just try to get the physical dimensions right and keep the Eznec errors from popping up. I figure if the dimensions are close enough, then let Eznec worry about the scientific calculations.
I did fix the model to agree with your argument about mast currents the other day, but I can't honestly say what I did to get those results. When I do a model, I don't plan with currents in mind. I just don't understand enough about currents, direction, or phase to plan that stuff. I'm sure to be very accurate in modeling it is desirable to get currents right...since the whole NEC engine uses pre-determined scientific factors regarding currents to do its calculations.
Yes Bob, you've done an excellent job of getting your experiences out and finding a logical source for the collinear idea and I personally believe that is what makes the Sigma 4 design work like it does.
Well Bob, that leaves me with some very big steps to try and follow. I have to say, I don't think I'll ever be able to satisfy such goals, even if I promise to never mention the J-pole. Personally, I think the J-pole is a mute issue when considering the Sigma4 design.
Bob, you mention your CB band is different from the US. I think it is higher in frequency, right? Why then, back in the day, did you ever consider to making the antenna longer? I would have thought that would be putting me further away from the desired frequency range. Just curious about that.
There is absolutely nothing wrong with modifying stuff. I admire folks that experiment in life. Among other things, I cut my teeth on modifying a couple of 55' Chev's in my younger adult days. One for street modified, with a 283" small block. I competed successfully and won often in NHRA "C" & "D" Modified Stock classes in the 50's and 60's. I was never satisfied. I could change nothing on the exterior of the engine, drive train, body, or suspension, but I worked midnights under a shade tree on the guts of the business, to run that thing in the high 12's, over 100 mph @ 1/4 mile tracks around Texas. That is nothing with today's technology, but it was hot back then, or at least I thought so as l left a lot of better cars in the rearview mirror. I've always done things that you might call "out of the box" even if I don't see the subject that way. I hate buzz words.
We also see now that Sirio has elected to go longer on the radials, but shorter on the radiator while they claim to have retained all their previous gain and angle advantages compared to their previous Vector 4000. This one is a sleeper too. I've not heard a sole proudly reporting on his New Vector 4000, even though several guys on this forum have one. Bob, you told me that it's still not built well enough for the UK climate. You mentioned that Multimode said something, but I can't recall what. I don't think he had a report however. That is strange that no body in Europe or the US has tried it and reported what the New Vector 4000 design can or can't do? I don't think it was a new design that Sirio discovered, I think they were probably forced, due to antenna failures, to make it shorter somehow and to try and mitigate the bad reputation it has.
i do have that in mind even though it is the hardests one to put up and tune. My new mount is close to the house and I can still get up that high safely. I designed it that way for that reason.
I'm impressed by the Gain Master, but there are some exceptions to my stellar reports so far. None exceed the SGM, but I do see a few signals that match it and one today where a guy reported the GM showed him less signal. Bob, it is like summer before last, I'm seeing conditions in terrible shape and I have a lot of static. As our weather becomes cooler and less humid the noise seems to really affect signals and hearing, at least that is what I think. Our recent summer was very dry late in the year so I may be seeing some change that is affecting how the antennas here typically act. This may even be affecting the water table in my area. I'll know more about that when I get the I-10K up if I do that too. My new mount allows me to work those bigger antennas without having to build them and attach them to the mast and then raise all that up.
73's
Eddie
