In case anybody is interested in the wires used in wm5k's Imax model above.
View attachment Wires for wm5k's Imax.pdf
View attachment Wires for wm5k's Imax.pdf
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Antenna Modeling Uploads
- Thread starter AudioShockwav
- Start date
I can do that and I suspect he might be right the gain will probably increase a little, but I don't think it will fix the out of phase and the lack of a collinear response issues I raised.
Dave, here is the model with 25* degree radials.
View attachment Increased angle Imax.pdf
Dave, are you in a position to try an Imax model like nm5k has suggested?
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Here are my models that modified the original of wm5k’s idea I posted earlier.
The first model is the original.
The second model has a mast added.
The third model is isolated (ISO) from the mast 6”.
The fourth model has a 40’ transmission line added to the mast that is isolated.
The long radials dominate this antenna. It might even be said by some that this antenna is the mast/feedline with the antenna serving as a dummy load on top.
View attachment nm5k's Imax ideas.pdf
The first model is the original.
The second model has a mast added.
The third model is isolated (ISO) from the mast 6”.
The fourth model has a 40’ transmission line added to the mast that is isolated.
The long radials dominate this antenna. It might even be said by some that this antenna is the mast/feedline with the antenna serving as a dummy load on top.
View attachment nm5k's Imax ideas.pdf
Well Dave, I guess the 25* degree slanted down radials didn't please you. I didn't expect the maximum angle to pop up like it did either. Maybe my idea of the 25* degrees angle I used...was just too much.
Here is the Imax with 72" and 108" radials both horizontal and slanted down. If these models are even close, then I don't understand the Imax GPK being made for slanted radials.
If you notice that the red line current indicators are strange looking an pronounced, not to worry...they are like that because the segmentation is still using less than 20 segments just like NM5K did using Eznec Demo.
If you do try this NM5K idea...keep us posted, OK?
View attachment Stock Imax ideas.pdf
Here is the Imax with 72" and 108" radials both horizontal and slanted down. If these models are even close, then I don't understand the Imax GPK being made for slanted radials.
If you notice that the red line current indicators are strange looking an pronounced, not to worry...they are like that because the segmentation is still using less than 20 segments just like NM5K did using Eznec Demo.
If you do try this NM5K idea...keep us posted, OK?
View attachment Stock Imax ideas.pdf
model number 3 with isolated mast looks very good with 5.9 dbi of gain and a 9 degrees toa but it all goes to pot with model 4 when the feedline is added .... i dont know if a choke will help and get it back to model 3
i just check the gain of the i10k and its 3.6dbi but i dont know the toa... so i still think i need to investigate more..
Many thanks Marconi for modeling it for me..i am still struggling with the software....i think i may have to make a 5/8 with 1/4 wave horizontal radials and then convert it to 5/8 sloping wire.......
i have been collecting tubing for some time
With modeling, there is more to consider than just the pictures of the gain and RF angles to be noted.
Real world experimenting is also important.
Good luck and keep us posted.
Ask me some questions about Eznec, and I'll see if I can help with your understanding.
well thats what i was thinking .. i was researching chokes...thats way i started the ugly-balun-choke thread ..well posting the info i had found as i think it may be useful
my logic was, if the RF cannot "see" for want of a better word the feeder then surely the TOA will return to model 3
http://www.worldwidedx.com/cb-antennas/154547-ugly-balun-choke.html
davev8,
multiple experiments with radials/mast isolation/chokes prove to me that a choke can reduce cm currents, reduce noise, reduce/eliminate tvi and improve signals, its not a cure all,
in some cases adding a choke can make cm currents worse if the choke happens to resonate with whatever length coax you are using, i have not experienced it but i trust smart folk who say that's what can happen,
if adding a choke made matters worse i would change the coax length to see if i had an unlucky length, you could do the same without the choke and find a length that reduces cm currents
you can't cheat kirchhoff's current law with regular transverse wave electricity
.
multiple experiments with radials/mast isolation/chokes prove to me that a choke can reduce cm currents, reduce noise, reduce/eliminate tvi and improve signals, its not a cure all,
in some cases adding a choke can make cm currents worse if the choke happens to resonate with whatever length coax you are using, i have not experienced it but i trust smart folk who say that's what can happen,
if adding a choke made matters worse i would change the coax length to see if i had an unlucky length, you could do the same without the choke and find a length that reduces cm currents
you can't cheat kirchhoff's current law with regular transverse wave electricity
.davev8,
multiple experiments with radials/mast isolation/chokes prove to me that a choke can reduce cm currents, reduce noise, reduce/eliminate tvi and improve signals, its not a cure all,
in some cases adding a choke can make cm currents worse if the choke happens to resonate with whatever length coax you are using, i have not experienced it but i trust smart folk who say that's what can happen,
if adding a choke made matters worse i would change the coax length to see if i had an unlucky length, you could do the same without the choke and find a length that reduces cm currents
you can't cheat kirchhoff's current law with regular transverse wave electricity
I am probably depending on the same source that Bob used to suggest that a choke can work both ways...right or wrong, do good things or do bad things.
I heard it said that a 1:1 coaxial choke has no ill-effects on the feed line matching. I believe that is only true as long as the feed line length does not change when adding the choke, and the antenna match is close to or equal a perfect match. This is not all, but it will do for this discussion I think.
I've also heard some users say something similar to the following: "...even if I don't need a choke it won't matter. Just in case, I'll install anyway...it doesn't ill-effect the antenna."
Somebody please explain to me any sensible reasoning with such a statement in light of what Bob has noted above.
The only issue I have with Bob's first comments are, I've never experienced anything similar to his results, and for sure have not seen and increase in signals.
One time I did think I heard some reduced noise on my Sigma4 after adding a choke to my feed line, but I could not be sure. I was not able to make the switch fast enough to really know for sure, plus sometimes around my location we see the band stretch out before our very eyes.
Another thing I noticed on that same experiment was that the resonance changed, because my antenna match was not match well enough to be near perfect, and I experienced feed line transformation. That is a situation that you might miss if you're not watching close...even when using an analyzer.
How about some comments from others on your results if you've experimented with a coaxial choke of some type.
if the smart folk are correct there is no sense in saying a choke can't hurt in any situation,
unlucky coax outer shield length + unlucky choke ={Cry_river}
we know the only thing that determines vswr is the load impedance in relation to the coax characteristic impedance ( look it up and or do tests don't blindly believe what you read on forums including what i post )
ignoring the unlucky choke/coax length scenario, adding a choke can still change the match,
common mode impedance is seen in parallel with the antenna load impedance,
if altering coax length alters your vswr more than what can be attributed to any change in coax loss due to the different length coax you very likely have cm currents on the coax outer shield and a common mode impedance seen in parallel with the load that changes with coax length and it been grounded or not grounded,
inserting a high series impedance in the coax outer shield by winding a choke or adding ferrite can raise the parallel common mode impedance to reduce the cm currents which will change the effective load impedance in the same way that changing coax length or grounding/ungrounding your coax can change the common mode impedance/current = changes load impedance = changes vswr.
unlucky coax outer shield length + unlucky choke ={Cry_river}
we know the only thing that determines vswr is the load impedance in relation to the coax characteristic impedance ( look it up and or do tests don't blindly believe what you read on forums including what i post )
ignoring the unlucky choke/coax length scenario, adding a choke can still change the match,
common mode impedance is seen in parallel with the antenna load impedance,
if altering coax length alters your vswr more than what can be attributed to any change in coax loss due to the different length coax you very likely have cm currents on the coax outer shield and a common mode impedance seen in parallel with the load that changes with coax length and it been grounded or not grounded,
inserting a high series impedance in the coax outer shield by winding a choke or adding ferrite can raise the parallel common mode impedance to reduce the cm currents which will change the effective load impedance in the same way that changing coax length or grounding/ungrounding your coax can change the common mode impedance/current = changes load impedance = changes vswr.
Bob, you comment:
BTW, at some point after I started using Eznec, I was suggesting that some times maybe changing the feed line length could help eliminate CMC. I remember that I suggested that idea to you once, and I thought you said you did not agree with that idea, right?
Or, was your thinking back then maybe based on the possibility that I might have couched the idea in terms of height...rather than feed line length?
It sounds like it may be a simple answer, but can you tell us specifically how a body would know when things got worse in this regard?Bob85 said:
BTW, at some point after I started using Eznec, I was suggesting that some times maybe changing the feed line length could help eliminate CMC. I remember that I suggested that idea to you once, and I thought you said you did not agree with that idea, right?
Or, was your thinking back then maybe based on the possibility that I might have couched the idea in terms of height...rather than feed line length?
if i ever said line length won't effect cm impedance and current i must have had a brain fart, i don't remember claiming that, ever since i came across maxwell & ji i have know that it does,
i don't think height is the issue, the electrical length of the outside shield and it been grounded or not effects cm impedance/current magnitude as i have said several times in the past.
you can see and hear when rf is screwing with pc speakers lamps tv's etc, many people have had their mic bite them,
some people can feel the effect without any bite when their hand has a strange aching/heating sensation, 600w+ fm in a mobile will often do that if the coax or mic lead is not choked,
my own experience tells me choking the line can cure all the above but not always,
you can also measure the currents with a current probe like one of the freecells suggested some time back or by using the very simple meter that w8ji and other guys show us,
since nec and others use the known laws derived from actual measurements by folk like kirchhoff, id be very surprised if current measurements did not closely agree with antenna models.
i don't think height is the issue, the electrical length of the outside shield and it been grounded or not effects cm impedance/current magnitude as i have said several times in the past.
you can see and hear when rf is screwing with pc speakers lamps tv's etc, many people have had their mic bite them,
some people can feel the effect without any bite when their hand has a strange aching/heating sensation, 600w+ fm in a mobile will often do that if the coax or mic lead is not choked,
my own experience tells me choking the line can cure all the above but not always,
you can also measure the currents with a current probe like one of the freecells suggested some time back or by using the very simple meter that w8ji and other guys show us,
since nec and others use the known laws derived from actual measurements by folk like kirchhoff, id be very surprised if current measurements did not closely agree with antenna models.
I don't think so Bob, I think if you did say anything you probably told me it was not height that mattered in this case...it was the length of the feed line.
I thought it might be something else you were alluding too.
That sounds reasonable to me Bob, in light of the fact I believe a choke can work, but not just any choke. To me chokes are complicated devices. I've just never experienced the fix that didn't change on me at some point. However with that said, I was always messing around with my antennas at the time, so I likely changed the height or something else. So to be fair, I can conclude that something else could have ill-effected the results I expected to happen.
You could be right Bob, but even though I've tried, I've never been able to get any useful data. IMO, if you or freecell ever did what you indicate here might be a simple task...then I think you two would have for sure posted your results to help prove beyond doubt your ideas on the Sigma4, right?
I'm still puzzled at times with Eznec current/phase results when they don't agree with how I imagine it in my mind's eye, or how these factors worked or didn't...compared to another model that looked to me to be working fine, and similar to what I would expect.
I have repeatedly tried to understand better by counsel from others, but the idea of currents/phase being somewhat predictable still evades me, even though I can still point out the currents on some of my current reports, when they are similar to what I imagined. It is when the currents/phase doesn't look right, and then I have a hard time explaining my thinking.
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