Not if you choke both the coax, and the ground wire (if needed) using a small in-line series choke coil to block AC/RF.
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Workman W-58 Help needed please!
- Thread starter d1g1man
- Start date
Not if you choke both the coax, and the ground wire (if needed) using a small in-line series choke coil to block AC/RF.
Your right Bob, I went back and checked and all of those models and they were all grounded and none were isolated. In that thread I just posted models that showed the affects on performance due to changes in the angle, and how the 30* degree angle made a nice performance difference in performance vs. the angle for the stock GPK. I wasn't even thinking about isolation at the time, and frankly the only thing on my mind then was Tech 833's article on the subject I referenced in the thread.
I recall now that the models didn't bring to my attention how bad slanting the radials down lower from horizontal tended to make the performance get worse with slanted down radials. That's why I was surprised when I applied your idea...using slanted radials on the Imax GPK, and then I saw how bad the model was. Again, I didn't realize what was going on, until I read your questions above. I went back to check to make sure, so I could try and answer your questions. I said earlier, I was confused at these slanted radials results, but now it is clear...these models show that slanted radials on the Imax GPK do not perform as well as horizontal radials would...and that is puzzling.
Concerning your question about the little circle with the dot in the middle at the bottom of the mast, for the models in the link on my other thread...all models had the mast attached to ground and none were isolated.
I realize now that when I'm talking about isolating the mast, I need to make the view clearly show the ground connection for the viewer, because it can be confusing if it doesn't show the little circle with the dot in the middle.
And, you're right again, some of the masts do not show the little ground icon at the bottom. Bob, this problem has to do with how large I make the image and the limitations in printing out the whole antenna. The models in that link are all grounded with no isolation, but the bottom is just cut off a little.
Just as a note, the other little circle that is red, gives a general idea for approximately where the feed point is located, but the image view does not always put this circle exactly where the program has the FP source actually set. It's just a fluke in the software, and the manual talks about this anomaly.
I made notes all over these models yesterday, after I said I would post the models, but after I checked the models in the link to my other thread and saw the same bad results with the Imax GPK with slanted down radials, I decided to send them anyway.
I have no idea why these models show such bad results when the Imax GPK radials are slanted down. I know it flies in the face of all the evidence ever published about the Imax with radials, and probably the same in your testing the idea with your buddies, but this is what Ezcec5 shows.
I would have never dreamed this to be true, but I was always puzzled why Tech 833, claimed better performance with the Imax GPK radials at 30* degrees rather than the stock GPK setup at about 40*- 45* degrees. I always thought that Tech 833, was claiming the radials should be angled lower, not higher and when I found this out the other day I decided to model the idea and this is what I find, the Imax with radials set to horizontal produces a better pattern by a nice margin in gain, and when the radials were slanted, the pattern goes to heck in a hand basket, and I was totally surprised.
However, these models did confirm what Tech 833, claimed several years ago in his article on the Imax with the GPK. He just didn't try his test to see how the Imax acted with radials horizontal.
View attachment Bob's Imax with slanted radials..pdf
I understand about the convience for setting up the Imax, makes perfect sense too, in light of the fact the GPK comes that way, but now I have to wonder why, if my models are close to correct.
booty,
i posted what mr Cebik said about folding the radial up in the sigma4 alternative viewpoint post,
http://www.worldwidedx.com/cb-antennas/31799-avanti-sigma4-alternative-view-point.html
the mast been grounded changes what length mast would be a bad length for cm currents vs a floating mast, common mode impedance is explained in walt maxwell's "reflections 2"
if you find anything that contradicts w2du or w8ji i would like to read it.
B
BOOTY MONSTER
Guest
i had no idea a ground wire could be choked so that it didn't act as a ground element . how is it done ? is it made the same way and size as a air core coax choke ? is the size of the coil frequency dependent ? or does one size fit all ?
eddie,
i see an advantage with isolation, certainly in the potential for rfi from mast/coax,
garry happens to have his imax on 40ft of crankup mast while other folk used different length masts,
i think it would be easier to digest if you always put the green curser on the usefull lowest lobe for direct comparison,
max slice gain can take care of cloud warming duty's.
i see an advantage with isolation, certainly in the potential for rfi from mast/coax,
garry happens to have his imax on 40ft of crankup mast while other folk used different length masts,
i think it would be easier to digest if you always put the green curser on the usefull lowest lobe for direct comparison,
max slice gain can take care of cloud warming duty's.
I also agree with the isolation idea helping with RF on the mast, just like you say. I don't see how it will help with the coax however, unless a suitable choke is added there, but if a choke is installed it seems to me that would work for the mast too, so maybe isolation is not necessary. That doesn't address the need for radial though.
Yep I noticed that I didn't always put the green cursor on the lowest lobe after I scanned the models. Sometimes it is hard to capture all aspects of the model information I hope to present to help tell my message.
Bob, I was just doing a model for Needle Bender for his Imax in a tree idea at 65' feet and when I added the GPK with 40*- 45* degrees slanted I didn't notice the problem I just presented to you earlier.
The only difference in his model over your's was the height and the length of the radials. NB, asked me to use 72" radials like the GPK comes. I didn't check that out as a possible reason here, but I'll have to consider that maybe 1/4 wave radials are too long, and maybe that is why the kit is made with 72" radials. Of course the height difference affects the results too.
See below the model I did for NB.
View attachment NB's Imax in the tree idea.#1.pdf
BM, a small air gap will do what you ask here as long as its gap is protected from opening up too wide.
B
BOOTY MONSTER
Guest
thanks marconi 
"he said that in the real world of earth masts and feedlines as opposed to freespace models, the radial angle makes little practical difference to the angle of radiation, that is untill we fold the radials up towards the radiator,
then a none aparent colinear array is possiblle that will outperform any conventional groundplane,
he said my test results were very much possible but was reluctant to get involved with the pages of meaningless arguments that such misunderstood antennas can generate ... "
who said this ?
"he said that in the real world of earth masts and feedlines as opposed to freespace models, the radial angle makes little practical difference to the angle of radiation, that is untill we fold the radials up towards the radiator,
then a none aparent colinear array is possiblle that will outperform any conventional groundplane,
he said my test results were very much possible but was reluctant to get involved with the pages of meaningless arguments that such misunderstood antennas can generate ... "
who said this ?
??? said:
Yep I think that is what happened, a worst case scenario. You must have polished your crystal ball this morning.
I'm still working on changing the radials to 72" to check the length radial length issue, and raising to 65' feet, like I did with NB's Imax, to check the height issue. Then I'll do the isolation/no isolation bit on both groups. I'm not saving any of this stuff, so the captions in groups will all be the same, but I added notes so we can see the differences. I hope I don't have to go back and try and recheck something, because it ain't there to check.
Bob, you may be the only one who's head is not spinning. I had to take a nap.
All I have to do now is recap everything so I can compare the results without flipping pages and make my notes. Maybe I'll see some sense in all of this soon. I hate surprises.
eddie looking at the models you did for nb i would remove the model without mast coax or radials as its not possible in the real world, its half of an antenna,
the sloping radials with isolated mast model seems to be coupling rf back into the mast,
you could try isolating the mast just below the radial tips rather than @ the feedpoint,
the sloping radials with isolated mast model seems to be coupling rf back into the mast,
you could try isolating the mast just below the radial tips rather than @ the feedpoint,