Steve Courtis - Starduster Install in Melbourne

[Marconi]

The following is a series of emails I received from a Starduster user in Melbourne, Australia.

Hi eddie, I finaly put my 1/4 wave up, on my apartment building in Melbourne, Australia, it is approxamatly 900 ft . It has a flat SWR reading (1:1,) across the the entire 11 meter band with the ground plane radials on a 45 degree angle
I hope you enjoy the pictures. cheers 931 stevo

On Saturday, 27 December 2014, 8:42, Eddie - Marconi <edromans@comcast.net> wrote:


Hello Steve.

This thing simply uses:

1. 4 to 6 102" stainless whips...depending on the number of ports you have for the whips.
2. a radial hub from a GPK for an A99
3. a mobile mirror mount L-bracket for the radiator
4. and a short mast pipe that these items will fit on.
I have several radial hubs I have made, but I also use an original with only 3 ports that slant down at about 30* (/\) degree angle to the ground. I find just as good of working success using only 4 x 102" whips as I do with more. This would be 3 whips for the radials, and 1 whip for the radiator and you will see a great match. Get it up as high as you can, at least 40' feet if possible and you will be surprised how well it works and it is very durable in this configuration.

Keep me posted via email, and leave me a post on you progress on: http://www.worldwidedx.com/forums

Thanks for the contact,

Eddie - Marconi

Ole Grampa from Corpus Christi Texas...when I'm on the air at 27.385 LSB or there abouts.


----- Original Message -----
From: Steve Courtis
To: edromans@comcast.net
Sent: Thursday, December 25, 2014 5:40 PM
Subject: 1/4 WAVE ANTENNA
Hello Marconi.
I read a post on copper talk, I would like to see your pictures of your home made 1/4 wave antenna with the six ground plane radials, as I would like to build my own.
Cheers 931 Stevo
Johnson viking 4740
Melbourne Australia

Below are some images of Steve's installation.

 

[Needle Bender]

You know, I've often wondered if a folded DC shunt wire, (maybe 7" x 1"?) could be added at the feed point across the 2 poles of this center-fed vertical dipole to help provide a path to ground for static.

-and if that's a spring at the base of the radiator, get rid of it!

Now that I take a better look at all the pics, nice job of machining and good choice for the antenna design that will endure high wind and be nicely broadbanded!

...and this is NOT a 1/4 wave! If you want a 1/4 wave then get those radials up to horizontal, but this 1/2 wave dipole provides both a much lower TOA and about 3dB gain over a 1/4 wave.

I'm looking forward to enjoying a QSO, if/when conditions permit.
73,
Needle Bender 'Prime'

 

[space cowboy]

is it really a starduster without the tophat?

 

[222DBFL]

NB how can it be a 1/2 wave antenna with only 102" whip and a 6" spring at top?? Do the 3 radials create the other 1/2 of the antenna or the coax? I am just curious. I am no antenna expert by any means, like said just curious and like to learn. It is a nice build and looks like it will handle a heck of a storm. Thanks for any responses.

 

[midnight special]

looks like something i have up right now,, made from a hub that i bought years ago off of ebay and 4 102 whips,,,mounts just like a starduster with 1.2 swr across 11 meters,,have it on a 35 foot tower,, cant tell much difference between it and my maco that is at 30 feet,, but maco has huge oak tree on west side of it and that does knock some signals from the western part of county here,,,the radial whips angle down just like a starduster and i used a mobile beehive style mount on the hub for the vertical whip... when i won the auction on the hubs it was for 5 of them so about 8 years ago i noticed when looking at them they were the same diameter as a antron 99 so i dremeled and filed the center hole out and it slid right on the bottom part and i tightened the set screws and put 3 102 inch shakespeare fiberglass whips on it but i didnt at the time think it improved the in or out going signal and ended up taken it all off,,,,

 

[RatsoW8]

Starduster? It's a 1/4 wave GP or looks like it at least and nothing like the Antenna Specialists Star Duster antenna from the 70's.

 

[The DB]

Starduster? It's a 1/4 wave GP or looks like it at least and nothing like the Antenna Specialists Star Duster antenna from the 70's.

The question of what type of antenna this (and the Starduster) is (and others like it for other frequencies) has been asked many times over the years. Some, like the Starduster advertising, will tell you it is a 1/4 wavelength groundplane antenna. Others will swear it is a half wavelength center fed dipole. These opinions are both right, and wrong at the same time... Something that strikes me as strange is only a small number of people ever seem to consider that it is something in between these two possibilities.

This antenna will act somewhat like a 1/4 wavelength groundplane antenna and somewhat like a center fed dipole, but not exactly like either one.

For example, the RF radiated from a set of horizontal radials, aka a groundplane, will cancel in the far field. With the lower vertical element of a dipole, this cancellation won't happen. If the radials are angled, some of the RF will be canceled in the far field and some will not. The degree of how much will cancel depends on the angle of the radials. The closer the radials are to horizontal the more RF will cancel. the closer the radials are to vertical the less of the RF will cancel.

If you limit yourself to calling his antenna either only a 1/4 wavelength groundplane or only a 1/2 wavelength dipole you will only ever be half right.


The DB

 

[Robb]

This antenna will act somewhat like a 1/4 wavelength groundplane antenna and somewhat like a center fed dipole, but not exactly like either one

So because we know that a 1/4w GP has no more than unity gain whilst a 1/2w dipole has +3db gain; then field testing should quantify if a Starduster has gain or not. If it does have gain; then it is behaving as a dipole . . .

 

[wavrider]

HMMM

DB I am surprised and interested as to why you think it is more than a 1/4 wl vert?

I think It is nothing more than a 1/4 wl vertical.

The ONLY reason that the ground radials are angled down is to present a 50 ohm impedance.

The ground radials can be horizontal but then the impedance would be around 33 ohms, true vertical.

If it is a true vertical dipole then the impedance would be around 72 ohms, give or take. same as a 1/2 wl TRUE horizontal dipole not an inverted V.

Plane simple 1/4 wl vertical that works very well for what it is.
I can say this as I have one up the tower at 65', it works well for what it is.

 

[The DB]

So because we know that a 1/4w GP has no more than unity gain whilst a 1/2w dipole has +3db gain; then field testing should quantify if a Starduster has gain or not. If it does have gain; then it is behaving as a dipole . . .

Actually, a 1/4 wavelength groundplane antenna has a standardized gain figure, dBq, and it isn't unity gain, although it isn't much higher than unity gain. dBq = 0.15 dBi. This compared with the well known dBd, which is 2.15 dBi. The thing is, both of these gain figures are only relevant in freespace. Also, in freespace gain is more or less proportional to the angle of the radials. Things are a bit different when we go and put an earth under the antennas. Put both a 1/4 wavelength groundplane and a 1/2 wavelength vertical dipole above an earth at the same tip height, and honestly, in most cases most people can't tell the difference. At lower heights the 1/4 wavelength groundplane will edge out the dipole, and as you elevate the antenna tips to a wavelength or more the opposite will be true.

DB I am surprised and interested as to why you think it is more than a 1/4 wl vert?

I think It is nothing more than a 1/4 wl vertical.

I mentioned one of the reasons above, if the radial set is equally spaced around the antenna on a plane, aka horizontal, or 90 degrees off of vertical, then any radiation from said radials will cancel in the far field. Once you begin to angle the radials in the same direction, in the case of the antennas we are talking about down, that cancellation isn't as complete. The more the radials are angled the less RF cancellation there is from said radials, and by extension the more radiation that makes it to the far field.

The ONLY reason that the ground radials are angled down is to present a 50 ohm impedance.

The ground radials can be horizontal but then the impedance would be around 33 ohms, true vertical.

If it is a true vertical dipole then the impedance would be around 72 ohms, give or take. same as a 1/2 wl TRUE horizontal dipole not an inverted V.

A better SWR match might be the reason the design has them angled, however, that does not mean that there aren't other effects form angling said radials as well. Seriously, if SWR is the only reason to angle a set of radials then don't bother, the extra effort is a waste for the insignificant difference it will make.

Plane simple 1/4 wl vertical that works very well for what it is.
I can say this as I have one up the tower at 65', it works well for what it is.

I agree, 1/4 wavelength antennas do work very well, and often better than many people realize.


The DB

 

[The DB]

I just did some modeling to check what I said, and apparently I was wrong about the gain figure associated with dBq, it is much higher than what I listed above. I have never tried to confirm it before now, but I have read about it from multiple sources, some of them are very reliable. The model I made puts it in the range of 1.47 dBi, which is much further away from unity gain than I previously realized. I guess I need to do some more research on dBq...

Another quicky that I noticed before and was reminded of again, if the radials are 15 degrees off of vertical, the antenna actually has a higher gain than a vertical dipole... I've seen this before with models over an earth, and now I see it again in freespace...


The DB

 

[M0GVZ]

Lovely machined mount, nice install and then he goes f'ks it up by using one of those stupid 6 spoke "ground plane for CB radio" things that doesn't even fit on the ground side of the antenna.

 

[wavrider]

http://play.tojsiab.com/LVZSZmQyRjhvRm8z

Marconi explains it real good here in this link.

 

[The DB]

That video was before he was instructed how to duplicate the 36 (he said 35 in the video I think) ohms for a 1/4 wavelength antenna. The four radials as a groundplane were not enough to simulate the perfect ground needed for said 36 ohm impedance.


The DB

 

[Marconi]

Here are some email responses from Steve regarding questions I emailed him. I also invited him to join the forum and give us some more details about his install.

My feed is lmr400 100 ft , I run a kenwood 480 hx in to a Texas star dx 1600x linear amplifier that pushes 60 db to the outer suburbs of Melbourne (4.5 million. Population). My receive is excellent and my noise level is low, but it works better as a local antenna rather than for dx, for some reason. Steve 931

Sent from Yahoo Mail for iPhone

http://play.tojsiab.com/LVZSZmQyRjhvRm8z

Marconi explains it real good here in this link.

Thanks for the kind words Wavrider, but after looking back, I think I should have done a much better job at trying to explain what I was thinking at the time. It turned out, after I got stuck with a few miscues I made in the video (not re-selecting the correct models as I attempted to look back and compare models), I think I just gave up.

Now I'm surprised I even posted the video to YouTube.

Without being well prepared, and being able to edit your work, doing such a video using your monitor to see your working model and the camera results you want the viewer to see in the video at the same time, is not always as easy as it might appear. Plus I was trying to show all my key strokes as I worked the model in the background so to speak. That too is not good procedure to have included without editing. Sorry, but I did not think that project out very well ahead of time.

My basic idea was why did this Eznec model of a resonant 1/4 wave vertical with 4 horizontal radials...not show us the typical impedance results of 36 ohms that theory tells us...such a resonant device should.

In the process of doing the video, and based somewhat on an idea that some folks argued, saying that Eznec was worthless and inaccurate, I wanted to try and compare the results of the 1/4 wave GP with horizontal radials as it varied with the accurate theoretical results of my center fed 1/2 wave dipole. Said another way, I thought it might be helpful to show everyone how my good results for a 1/2 wave center fed dipole were right on the money accurate with the theoretical match of about 72 ohms at resonance.

I think I talked about this in the video as well.

Now this thread begins the discussion as to whether the Starduster design is a1/4 wave ground plane or a center fed 1/2 wave dipole. I made a post about my ideas on this issue sometime back during our discussions about collinear Sigma 4 with Bob and Donald, and I'm still not sure how best to describe the Starduster, but I no longer think it is a center fed dipole.

That video was before he was instructed how to duplicate the 36 (he said 35 in the video I think) ohms for a 1/4 wavelength antenna. The four radials as a groundplane were not enough to simulate the perfect ground needed for said 36 ohm impedance.


The DB

In DB's comments above, I think he tells us why he thinks my model does not show the theoretical 36 ohm results we might expect...basically 1/2 the value of a center fed dipole.

DB may be right, but in my further application below of his idea...adding many more radials (60) to the model...does not produce the results he has suggest it should.

See In my model below, just adding radials does not appear to effect the model's resistance much at all. I do see the reactance change however and I did not fix that. Maybe if I changed the frequency to remove the reactance...the resistance may raise back up to near 36 ohms, but at this point I'm inclined to doubt it.

Both models are at 11' feet elevation, and show currents turned on. You will also note the very small gain difference adding many more radials really made. Disregard the currents report...it is for another discussion.

DB, maybe you have a model that can show us your point that adding more radials to this 1/4 wave ground plane will fix it and produce the theoretical impedance near 36 ohms we are looking for.