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considering an M400 starduster. whats the deal?
- Thread starter loosecannon
- Start date
I had a feeling I guessed wrong.
I don't think there is much that will cure the problem we see with the SD'r radials slanted down -80* degrees, using a coaxial choke...including a long 107" inch insulator from the radial hub down to the bottom tip of the radials.
EDIT: at this point, the mast probably has as much current as the radiator. I'm working on an idea I have for mounting a CFHW vertical however.
I don't think there is much that will cure the problem we see with the SD'r radials slanted down -80* degrees, using a coaxial choke...including a long 107" inch insulator from the radial hub down to the bottom tip of the radials.
EDIT: at this point, the mast probably has as much current as the radiator. I'm working on an idea I have for mounting a CFHW vertical however.
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i can't see how its possible for the mast to have more current than the radiator with that antenna Eddie,
the sum of all currents returning on mast coax radials should equal current flowing into the radiator, if that is not the case where does the extra current come from ?
I think w8ji says you need a very good balun/choke or extra radials below the balun to get rid of almost all of the cmc on the mast.
the sum of all currents returning on mast coax radials should equal current flowing into the radiator, if that is not the case where does the extra current come from ?
I think w8ji says you need a very good balun/choke or extra radials below the balun to get rid of almost all of the cmc on the mast.
The mast won't have more current than the radiator.
Based on prior modeling, with horizontal radials, the most optimal location for the choke is right next to the radials. As you angle the radials down, however, you are adding capacitance between the radials and the mast, and as we know capacitors allow RF to pass. That is the reason that the only set of antennas in my video above whos gain went down as the radials were angled down was the models with the mast. At minimum it would take two chokes to resolve that issue, one at the feed point, and one just below the radials about 1/4 wavelength below the feed point. When it comes to the mast, you would have to isolate it about 1/4 wavelength below the feed point.
The DB
Based on prior modeling, with horizontal radials, the most optimal location for the choke is right next to the radials. As you angle the radials down, however, you are adding capacitance between the radials and the mast, and as we know capacitors allow RF to pass. That is the reason that the only set of antennas in my video above whos gain went down as the radials were angled down was the models with the mast. At minimum it would take two chokes to resolve that issue, one at the feed point, and one just below the radials about 1/4 wavelength below the feed point. When it comes to the mast, you would have to isolate it about 1/4 wavelength below the feed point.
The DB
Bob, you got me on this one. I made the comment, but it was more in jest...being as I saw my model with -80 degrees radials looking so bad with CMC on the mast...that is connected to the radial hub...similar to DB's model. I too have a choke at the top of the mast near the FP.
Bob, I added two images to the PDF file below.
1. shows the -80 degree model that I posted earlier. I showed only the overlays. I also show the currents for wire #2, the radiator, and for wire #11, the mast. Here we see the maximum currents near the base of the radiator at 0.97396 (A), and for the middle of the mast at 0.39649 (A). My point was...there looks to me to be way too much current on the mast for the antenna to show good results and if you check the match...you will see this model is not a CFHW dipole.
2. shows the model fixed.
Steve talked about why this model at -80 degrees...with the radials being very close to the radiator...is very close to a CFHW dipole. I don't see that in my models.
I didn't mean to get you guys all in an uproar. I should have put a
face at the end of that comment.
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Your models show what i expect Eddie,
you have a worst case mast length for a grounded mast & radials bypassing the choke,
Try isolating the mast a little way below the radial tips, i think that will make the starduster act more like a 1/2wave dipole.
you have a worst case mast length for a grounded mast & radials bypassing the choke,
Try isolating the mast a little way below the radial tips, i think that will make the starduster act more like a 1/2wave dipole.
Hi guys could someone please tell me if the specs are the same with the newer Starduster copies? Like the Workman or the Sirio? I'd like to know as much detail about the original Antenna Specialist m400 Starduster. Any bit of info would be much appreciated .Thanks
Well, Bob according to these 3 models...your idea for a common mode solution on the SD'r model is the worst case situation among the 3.
If you want to look closer at the details that DB did in his video you will have to go directly to YouTube. There, all the little details are clear. You might even see what I complained to DB about regarding his main screen in 4Nec2...not updating as he changed from one model to another as he slanted the radials down for his model at -80 degrees. I also showed the start time for the important points I asked DB to consider. My ideas for more information had to do with my not seeing any CMC on the mast and the match for his -80 degree slanted down model not resembling a CF dipole as Steve said it would.
Because of the questions I had, I did not post my models...I wanted to ask DB some questions first. So, I posted the overlays only.
Some of my Real Earth models were showing me lots of CMC on the mast. I don't recall DB saying anything about common mode currents...except that he told us he added a choke when he went to his Real Earth models.
Below are the 3 models that show my concerns.The last one helps mitigate much of the CMC on this SD'r with -80 degree slanted down radials, uses no chokes and shows a match that looks like a CF dipole.
This is not to suggest this is a cure all solution, when I add a feed line it might be assumed by some that the model now has another path for CMC to flow.
We'll see when I add a feed line, OK?
DB and Bob just give me a chance and try and take a close look at this idea.
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Eddie, i don't understand your codes ovpe ?
if that's perfect earth nobody has that in real life much like few people have very poor industrial ground types, is that what ovpe means ?
did you break the mast up into a none resonant length in the last model ?
The feed-line is a common mode path just like the mast but its impossible to model accurately as you don't know that paths electrical length via your equipment to ground somewhere that could be miles away or in your back yard or multiple places if you practice beating ground rods in and connecting them to your coax.,
some say the coax need not be connected to a ground rod to cause a cmc path,
just laying on the ground is enough.
if that's perfect earth nobody has that in real life much like few people have very poor industrial ground types, is that what ovpe means ?
did you break the mast up into a none resonant length in the last model ?
The feed-line is a common mode path just like the mast but its impossible to model accurately as you don't know that paths electrical length via your equipment to ground somewhere that could be miles away or in your back yard or multiple places if you practice beating ground rods in and connecting them to your coax.,
some say the coax need not be connected to a ground rod to cause a cmc path,
just laying on the ground is enough.
Bob, below is the comment I closed my previous post with.
You must have missed this comment.
Yes, I have to use some codes to describe my models a little...I only am allowed 30 characters. I use OVPE to mean "over very poor Earth." Using my ground feature in Eznec and selecting "Very Poor" is as close to the Ground Description using Eznec as I can get and compare my models to DB's models and stay close on par with the patterns and gain. If I use my usual mode for Ground Description, "Average," my models look woefully inadequate and I know most viewers might get the wrong impression just looking at the pictures.
Check out the last model below again and see if the antenna's match does not look like what we might expect a CFHW dipole to look like?
Bob, you posted the following above.
Bob, you just asked me to ISO the model...below the tips of the SD'r radials, and now you're quarreling at me for doing the same thing. The only difference is I'm using 2 x 4" inch isolators instead of your idea just using only one...BTW that model does not show to work as well.
You obviously didn't check close as I asked, or you have on Rose Colored Glasses.
I typically use Average instead of Very Poor, but when DB uses VP soil and I use Average...everybody tends to get the wrong idea about what these models should show.
I have a vague recollection of you and I discussing this of recent and as far back as when Master Chef told everybody he was going to have a shoot-out in the Mojave Desert sometime back and his modified I-10K was going to blow all comers back to where they came from.
I've demonstrated this idea with models before, and just recently I did a post or two on the idea about the use of Eznec's Ground Description feature. I guess you missed that too.
Only until lately have I used codes to describe a little of what I was doing in a model. I figure if anybody has a question about the codes...they could just ask me...just like you did here.
Yes, I did add a 42" inch wire between two 4" isolators in my model.
Models only simulate what a real antenna might look like. I've never used "Perfect Earth" mode for any of my models.
I asked you and Steve to check these models out close and suggested where to look, but I think you missed the point I was trying to make. At times in the past when I've been in such a situation as this...Steve has told me...it went right over my head.
Bob, yes, I agree with you here. You have made the claim before and I have done the same thing hoping to solve a CMC issue a time or two.
My idea in that model, as flawed and as incomplete as a solution can be, shows to do what just adding a choke and or isolating cannot do...and that is to make the match for the -80 degree radial SD'r model look close to what a CFHW dipole will show.
I know you will have some questions. Look at the last model, #3 of 3.
You must have missed this comment.
Yes, I have to use some codes to describe my models a little...I only am allowed 30 characters. I use OVPE to mean "over very poor Earth." Using my ground feature in Eznec and selecting "Very Poor" is as close to the Ground Description using Eznec as I can get and compare my models to DB's models and stay close on par with the patterns and gain. If I use my usual mode for Ground Description, "Average," my models look woefully inadequate and I know most viewers might get the wrong impression just looking at the pictures.
Check out the last model below again and see if the antenna's match does not look like what we might expect a CFHW dipole to look like?
Bob, you posted the following above.
Bob, you just asked me to ISO the model...below the tips of the SD'r radials, and now you're quarreling at me for doing the same thing. The only difference is I'm using 2 x 4" inch isolators instead of your idea just using only one...BTW that model does not show to work as well.
You obviously didn't check close as I asked, or you have on Rose Colored Glasses.
I typically use Average instead of Very Poor, but when DB uses VP soil and I use Average...everybody tends to get the wrong idea about what these models should show.
I have a vague recollection of you and I discussing this of recent and as far back as when Master Chef told everybody he was going to have a shoot-out in the Mojave Desert sometime back and his modified I-10K was going to blow all comers back to where they came from.
I've demonstrated this idea with models before, and just recently I did a post or two on the idea about the use of Eznec's Ground Description feature. I guess you missed that too.
Only until lately have I used codes to describe a little of what I was doing in a model. I figure if anybody has a question about the codes...they could just ask me...just like you did here.
Yes, I did add a 42" inch wire between two 4" isolators in my model.
Models only simulate what a real antenna might look like. I've never used "Perfect Earth" mode for any of my models.
I asked you and Steve to check these models out close and suggested where to look, but I think you missed the point I was trying to make. At times in the past when I've been in such a situation as this...Steve has told me...it went right over my head.
Bob, yes, I agree with you here. You have made the claim before and I have done the same thing hoping to solve a CMC issue a time or two.
My idea in that model, as flawed and as incomplete as a solution can be, shows to do what just adding a choke and or isolating cannot do...and that is to make the match for the -80 degree radial SD'r model look close to what a CFHW dipole will show.
I know you will have some questions. Look at the last model, #3 of 3.
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Bob, I don't think I've given you and DB time enough to consider my "what if" idea...as to exactly what my SD'r model with -80* degrees slanted down radials is showing me. My model shows similar results to Steve's video model at -80* degrees of slant.
I ask again as a reminder, that you both consider the match for my fixed model showing to be very close to the match for a CFHW dipole, and in doing so I see very little CMC, improved pattern, and gain.
Below is only information that supports my claims here.
1. image of DB's video showing his -80* degree model with match and gain shown in my notes. The time of the video when this snip-it was taken. The video seen on YouTube is much clearer compared to the PDF file version on the forum.
2. Is my similar model to Steve's model (not fixed) showing heavy currents on the mast. This is what I've raised an issue about. I also added a snip-it of the L Network that I used for the choke noted at the top of the mast in both our models. Pay close attention to the shape of the patterns and the data for the match...our models are almost identical.
Now for my idea for a fix to this SDr.
3. Is my idea for a SD'r fix and the model includes a feedline.
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Eddie,
you are telling me a solution i have used & worked is the worst of all 3,
i don't think your choke is working like my real choke did,
im not sure what angle a real starduster is but less than 80 degrees & that could be skewing the result,
i only asked about ground type because you manipulated a pattern recently by changing ground type,
most folk have average ground, nobody has perfect & very few have very poor,
sticking to avg makes comparing models much easier,
its no good expecting me to look close at models like DB can,
i never made a model, i know a few rules such as segmentation in parallel wires & wires at acute angles and understand a bit about antennas & cmc from reading and actual fixing peoples issues but im no EZNEC guy.
you are telling me a solution i have used & worked is the worst of all 3,
i don't think your choke is working like my real choke did,
im not sure what angle a real starduster is but less than 80 degrees & that could be skewing the result,
i only asked about ground type because you manipulated a pattern recently by changing ground type,
most folk have average ground, nobody has perfect & very few have very poor,
sticking to avg makes comparing models much easier,
its no good expecting me to look close at models like DB can,
i never made a model, i know a few rules such as segmentation in parallel wires & wires at acute angles and understand a bit about antennas & cmc from reading and actual fixing peoples issues but im no EZNEC guy.
Bob I was not trying to impugn what you've experienced. I attempted to show what my modeling shows in that instance and I reported the results I got and that is what I said in my conclusion. Consider that I must have made a mistake in the model like DB is claiming. I hope you don't think I sit here and plan these models to show what I want and then knowingly report BS.
I do a model, right or wrong, and then I report the results. Does this concept even make sense to you?
I don't know either Bob, and the thought of skewing regarding the SD'r never occurred to me, but I don't see things in my minds-eye like you and Steve do.
I posted why I changed the Ground Description to Very Poor back when I posted #5 in my Sigma4 model: Just click here > Eznec model of a Sigma 4 with a gamma match
I'll also post some of that model with Very Poor Ground below. It includes the Eznec Ground Description screen and you were the only one talking to me in this thread with only 4 posts. I'll also post the model over my regular setting "Average," including the Ground reference page and the Setting Feature I used. If you have any questions...just ask.
Based on your comments here, which I agree with, you need to ask DB why he chooses to set his models over "Very Poor Ground," which IMO makes models at their very obvious best...and folks just don't know the real difference and why. That is why I posted what I did and you apparently don't remember this post from April 9, 2018. You even gave me a "LIKE" back then. But now your tone is very different, OK.
I have no way of knowing what I hear is this case...so I can't agree or disagree. What is your source for this claim?
I agree and I've basically always made my models set over Average per Eznec. If you realize this difference, as few do, why didn't you ask Steve why he uses a Ground that is over the most lossy soil in my list noted in the attached PDF below.
Bob. I regret you did not join me a long time ago...in one more stab at our trying to learn to use modeling tools. I only hope I've left a few tips and ideas in my posting these models as I was learning as I go.
I can only assume you will see what I intend these models to show.
The Sigma 4 over Average Earth.pdf
My old Sigma4 over Very Poor Ground.pdf
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I don't think you deliberately try confusing me with ground types Eddie,
clearly ground type effects the pattern at that height,
i can't say if a model is not done correctly,
i can look at segment length & relative height to the next wires segments & current distribution to see if its close to a 3/4wave vector/sigma or longer like the old vector,
right now a local is trying to cure CMC on a new imax install, the usual cures that worked on his a99 don't seem to work, tweaking choke turns does nothing you can detect from rfi changing level,
things that work most of the time don't work for everybody.
clearly ground type effects the pattern at that height,
i can't say if a model is not done correctly,
i can look at segment length & relative height to the next wires segments & current distribution to see if its close to a 3/4wave vector/sigma or longer like the old vector,
right now a local is trying to cure CMC on a new imax install, the usual cures that worked on his a99 don't seem to work, tweaking choke turns does nothing you can detect from rfi changing level,
things that work most of the time don't work for everybody.