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Marconi testing an original Starduster vs. Gain Master

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  #17  
Old 06-01-2011, 11:17 AM
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Quote:
Originally Posted by gamegetter View Post
What W8JI says about a 1/4 wave vs. 5/8 wave

i believe there are 1/4 wave antennas that can out perform 5/8 wave antennas especially if the 5/8 has no ground plane. see above thread. the problem i have as well as other's is that the merlin 55 has both a capacitance hat as well as a coil...but i have not personally ran that merlin 55, model, but i have run a a 1/4 wave ground plane i constructed back in the early 70's that gave me very good performance. between my 3 element and my 1/4 wave gp i enjoyed many many hours of fun on the air waves.

hope i'm not
Well gamegetter, I can't disagree with you much, I too have high regard for my Starduster and Starduster styled Marcon X antennas. I can't convince anyone what I see, but I think I'm close with my observations. I can't always claim that my SD'r models will produce the best signal RX/TX, but I don't think I've ever lost a contact, local or DX, while switching from one to another.

Regarding the Merlin, if it has radials that are slanted down near the same as my SD'r or my Marconi, then I think it should work about the same.

For me, both of these antennas operate at or near the center of CB with a little reactance at the feed point. On the other hand the resistance for both is pretty steady at around 50 ohms so the match is pretty good and the bandwidth is excellent, so they work well for me.

My thinking is, however, that maybe the Merlin, with the matching coil right below the top hat, is able to provide and even better reactive match and maybe show a little extra gain as a result. If so, will it be enough to see operating my radio? I DON'T KNOW!

But I hope one day to be able to test that idea that Terry uses in his design with my ground plane design below it...and see. IMO, the radials really must be slanted down more than 55 makes his on the Merlin, so I would like to be able to place his top radiator over my radials slanted down at about 27* degrees or more using my custom made A99 styled GPK hub, and see just how if works in that configuration.
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  #18  
Old 06-01-2011, 02:11 PM
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Quote:
Originally Posted by Marconi View Post
Thank you Blue Max, I'm a Starduster fan, an antenna nut if you will.

The shortened SD'r sounds interesting, how about a picture or two and tell us why and how you came about that design. I'm always interested in hearing about other guy's ideas and to see how and why they do what they do. Is what you have similar to the old Starduster 800? I've only see pictures of it, but I read that it was produced at one time. I don't think it was shortened very much however, but I'm not sure either.

Welcome to the forum.
I didnīt mean that I shortened the radials by myself. I only thought that there is also a model existing, where the radials have the same length than the beam. I bought it like this, here is a picture of mine:




I own this antenna now since nearly 20 years and I canīt remember the exact name or type. For about the last 10 years it was installed on the roof of my parentīs house without beam, because it felt off during a storm and I couldnīt reinstall it because I had no time.

This yearīs spring I did mount it now on the roof of my house. Also if it doesnīt look like from this position, the bottom of the beam is 10cm higher than the top-end of the chimney...

The only modification I did to the antenna was that I reinforced it a little. As you know the beam consists of two parts, the lower aluminium hose with an outer diameter of 11mm that includes at the bottom the brass-bush with the thread and the upper aluminum hose with an outer diameter of 9mm. The lower part of the beam has a length of about 150cm. I got now a aluminum hose that had an inner diameter of 11mm and an outer diameter of 15mm and a length of 75cm. For the first 2cm of this hose, I increase the inner diameter on the lathe to 14mm, so that the brass-bush fits inside an then I fitted it over the lower part. Then I fixed everything with a small grub-screw at the bottom. The little gab between the two hoses I sealed with aluminum-fluid.
So now I have much less bending and vibrations. Here is a photo in bigger size maybe itīs visible... http://my.twingo.rs/d/2962-1/Starduster_M400.jpg

I canīt say if this has any effect on electrical behaviour.

Last edited by Blue_Max; 06-01-2011 at 02:25 PM.

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  #19  
Old 06-01-2011, 02:36 PM
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Quote:
Originally Posted by Marconi View Post
Thank you Blue Max, I'm a Starduster fan, an antenna nut if you will.

The shortened SD'r sounds interesting, how about a picture or two and tell us why and how you came about that design. I'm always interested in hearing about other guy's ideas and to see how and why they do what they do. Is what you have similar to the old Starduster 800? I've only see pictures of it, but I read that it was produced at one time. I don't think it was shortened very much however, but I'm not sure either.

Welcome to the forum.
the coils on the starduster 800 served a similar purpose to the traps on multiband antennas, to allow it to be used on more than one band, in the starduster m800's case 27 mhz and 88-108 mhz fm stereo. i think they would have only shortened the radials by a short amount as you say.

i doubt the starduster with coil loaded radials would be much less efficient than the full size version, when uk cb was first legalised the thunderpole antenna was the reverse of the shortened radial starduster in that the radials were full sized but the radiator was shortened, anyway to cut a long story short it was a very much underrated and very effective antenna here, efficiency wasn't hugely or even noticeably down on a standard starduster m400.

funnily enough the sirio tornado 27 or 827 with shortened
radials ain't that far down on antennas with full sized radials either. i think once you go by a certain length of radial,approx 1/8 of a wave then the gain becomes less and less, but the benefit that its less of an eyesore may well outweigh any performance gains, especially if you have retarded neighbours.
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  #20  
Old 06-01-2011, 11:05 PM
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Quote:
Originally Posted by jazzsinger View Post
.... in the starduster m800's case 27 mhz and 88-108 mhz fm stereo. ...

My antenna isnīt a multi-band, it wasnīt sold as one. It also wouldnīt make sense (here in Germany) as UKW-radio is allways horizontally polarised and not vertically.

Quote:
Originally Posted by jazzsinger View Post
....
i doubt the starduster with coil loaded radials would be much less efficient than the full size version, when uk cb was first legalised the thunderpole antenna was the reverse of the shortened radial starduster in that the radials were full sized but the radiator was shortened, anyway to cut a long story short it was a very much underrated and very effective antenna here, efficiency wasn't hugely or even noticeably down on a standard starduster m400.

funnily enough the sirio tornado 27 or 827 with shortened
radials ain't that far down on antennas with full sized radials either. i think once you go by a certain length of radial,approx 1/8 of a wave then the gain becomes less and less, but the benefit that its less of an eyesore may well outweigh any performance gains, especially if you have retarded neighbours.
I canīt imagine that the physical shortening of the radials has such a big impact on its performance. Electrically they are long enough and there is still the long pole in the middle that is, like the radials, connected to the ground. Maybe the band-with is shorter. All im all itīs a good antenna for its size and it looks good...

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  #21  
Old 06-02-2011, 12:57 PM
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Blue Max can you tell us what is going on at the ends of the radials that look to be black?

Can you tell us the top element and radial lengths for your antenna?
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  #22  
Old 06-03-2011, 12:14 AM
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The black ends are coils. The top-element has a length of about 2.70m (depending on SWR-adjustment) the radials about 1.60m.

Here is a better photos to see the length-ratios:


Last edited by Blue_Max; 06-03-2011 at 03:22 AM.

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  #23  
Old 06-03-2011, 04:49 AM
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Quote:
Originally Posted by gamegetter View Post
What W8JI says about a 1/4 wave vs. 5/8 wave

i believe there are 1/4 wave antennas that can out perform 5/8 wave antennas especially if the 5/8 has no ground plane. see above thread. the problem i have as well as other's is that the merlin 55 has both a capacitance hat as well as a coil...but i have not personally ran that merlin 55, model, but i have run a a 1/4 wave ground plane i constructed back in the early 70's that gave me very good performance. between my 3 element and my 1/4 wave gp i enjoyed many many hours of fun on the air waves.

hope i'm not
Many of W8JI's posts are designed to make you think to get your answer. What he really says is that there are applications where a 1/4 wave will perform as good as a 5/8 wave. He goes on to say that the 1/4 wave will not really outperform the 5/8 wave but it could equal the performance in some cases.

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  #24  
Old 06-03-2011, 06:59 AM
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Default interesting comment

i post w8ji's thread here.

"Originally Posted by KA7NIQ
If you tried to tell most any CB Operator that a Starduster will outperform a full size 5/8 wave antenna for local or DX, you will get little agreement.
IS it possible the computer model is incorrect, and/or something else is going on that makes the big 5/8 wave vertical out play the 1/4 wave ground plane with sloping radials in actual practice ?"

"Nope.

The 5/8th wave depends heavily on a large highly conductive reasonably flat groundplane at the BASE height of the antenna. That groundplane has to extend out in all directions for a considerable distance. The reflection out some distance is how the antenna works and gets gain. Without that groundplane at base height for some distance, the feedline will radiate and the pattern also will not form properly. You ALWAYS wind up with an unpredictable mess because key parts of the system are missing.

The 1/4 wave with sloping radials acts as a vertical dipole. It decouples a bit better from the feedline shield, and it has no area carrying out-of-phase currents.

What you will find is the 5/8th wave can vary from being just slightly better than a 1/4 wave with three or more sloping radials to being much worse at low angles. Statistically the 1/4 wave is more reliable.

The reason you won't find CB'ers who support that is they:

1.) Generally don't understand antennas

2.) Generally don't do valid A-B tests, just like Hams don't.

3.) Like Hams, they are trained to think a 5/8th wave antenna universally has 3 dB gain.

4.) Went through the work of installing the 5/8th wave, so like a Ham it makes them "feel" it is better.

Models are, within known limits of the model, very good. When given the right input they are much better and more accurate than most people are."



I am sure everyone can understand why i would be reluctant to shell out $200 bucks for a new antenna when like most other old operators already have spent a lifetime tweaking dipoles, 1/4, 5/8, and beam antennas to work well for me, ie give me the coverage I need for my situation. I guess if i was new to the hobby I would prolly go the gm route as a good all around antenna. But I understand that no one single antenna does it all. And folks need to understand that, because sometimes they think that they can have one "best" antenna and then encounter situations where they don't have coverage and become upset or disillusioned with that product. So many variables, so little time..........Any way thanks for the observation and opportunity to share views.

Last edited by gamegetter; 06-03-2011 at 07:33 AM.

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