Homebrew Merlin Experiment

[Marconi]

Where in the world did you get this overlay. Must be a buddy.

I see their models are very close to mine. It is remarkable that someone else has modeled the I-10K with a matching device. I can see the vertical pattern inside the total field pattern in red, but I don't see the horizontal.

Looks like a different version of Eznec too.

If I need some Eznec advise Homer, can I call on you?

 

[HomerBB]

That is from your models.
I took them to Photoshop and overlayed them illuminating only the patterns that you had put your cursors on. The other patterns were too cluttered when I left them visible and made me crossed-eyed.

 

[Marconi]

That is from your models.
I took them to Photoshop and overlayed them illuminating only the patterns that you had put your cursors on. The other patterns were too cluttered when I left them visible and made me crossed-eyed.

I guess Photoshop allowed you to edit the caption to @75' and change the colors for the cursors.

The reason the patterns were so busy has to do with the matching device I added to the I-10K. I just designed and configured the trombone to the proper dimensions, and it looked just like the real thing. I can also tune the antenna a little moving the end elements, just like on the real antenna, and it does work to fix the mild mismatch.

If this result is correct then it is somewhat unique for me, however I also see this tendency in the Wolf .64wave GP's pattern.

The I-10K looks to produce both vertical and horizontal signals in the pattern. According to Eznec, the red lines are the vertical pattern, the green lines are the horizontal, and the black is the combination for the overall gain developed by both.

Regarding your eyes going cross eyed, you have to stop looking for those lobe patterns.

Here is a video I did a while back showing my Gain Master against my Starduster using my TS 579D and the internal switch box to change the antennas.

Marconi comparing Gain Master vs. Starduster 03-22-11 - YouTube

 

[Marconi]

Here is the Merlin vs. Starduster at 43'

View attachment Merlin vs. Starduster 43'.pdf

Personally I think the only difference is that the Starduster has the radials slanted down at a lower angle.

 

[The DB]

I just happened across something out of an old book that may be of interest from the 160 meter portion of the book.

Fig. 1212 - Top-loaded antenna. A parallel-tuned circuit independently resonant at the operating frequency, is required for coupling to the transmitter when the top loading is adjusted to bring a current minimum at the lower enf of the antenna.

Part of the text from the book.

The top-loading apparatus may consist simply of a capacity or, better, a capacity and inductance suitably proportioned. The capacity used is not the usual type of condenser, which would be ineffective since the connection is one-sided, but consists of a metallic structure which exhibits the necessary capacity to space.

I'm happy to type up the full text (over a page of it with four additional diagrams) if you think it will help in any way. I have noticed that in the next versions of the ARRL antenna book that I have (10'th edition and beyond) this information is not present, at least it is not in the 160 meter chapter.

It seems with this design you use a field strength meter while tuning. You start with the tap at the bottom of the inductor near the top hat, then tune the bottom circuit and measure field strength, then raise the tap on the coil, tune the bottom circuit again, measure with a field strength meter again, and repeat until the field strength peaks. I'm wondering if an analyzer could speed up this process any.


The DB

 

[HomerBB]

It's an interesting post.
I suppose that traps have pretty much displaced that setup . . .

At any rate, it certainly isn't a "new" base antenna technology.

 

[BOOTY MONSTER]

 

[W5LZ]

That's probably the most generic diagram of a vertical antenna (broken into it's component 'parts') that you can find. It does a very good job of showing those 'parts' and giving the idea behind them. It 'shows' what happens with any/all vertical antennas, depending on how they are made of course, and the placement of the antenna. Each of those 'components' may be in a different form/shape but they are all present in all antennas.
Not bad...
- 'Doc

 

[The DB]

That's probably the most generic diagram of a vertical antenna (broken into it's component 'parts') that you can find. It does a very good job of showing those 'parts' and giving the idea behind them. It 'shows' what happens with any/all vertical antennas, depending on how they are made of course, and the placement of the antenna. Each of those 'components' may be in a different form/shape but they are all present in all antennas.
Not bad...
- 'Doc

This is correct, however, in the context of the text of the article, as well as the context of the small part of it that I quoted, they are specifically talking about a capacity hat and a tapped inductor below it. It also talks about raising the current node, and with tuning mechanisms both at the bottom and top of the radiator that is a definite possibility. I don't know of the gains from such a setup would be enough to counter the losses of the additional tuning hardware. This was out of the portion of the book for 160 meter antennas, where even a ¼λ antenna would be more than 200 feet high, which is out of feasible limits of most people.

Since I found that I found, in the ARRL Antenna Book 13'th edition, there is a 40 meter antenna pictured there that is 6 foot tall with a 7 foot diameter top had, and an inductor a few inches under the top hat. They claim it is nearly as efficient as a ¼λ antenna which for those frequencies would be around five times taller. I personally question this claim as their only evidence is DX contacts, which doesn't really tell us anything except the conditions were open for those frequencies when he made those contacts... They also give much less information than the 3'rd edition book on the subject. This is not uncommon as on many antenna books, the old very thin book did a much better job at explaining many things than the newer versions, which are, ironically, much thicker.

I found some info that might be useful to someone playing with such an antenna and posted a small snippet of it. If the people modeling/building such an antenna to experiment with would think the rest of the information would be useful I would be happy to post the rest of it up for their benefit.


The DB

 

[The DB]

Booty, at first glance I thought that looked like a reasonable example, but now I'm not so sure. To me it looks like a dual coil ¼λ antenna with a top hat for additional loading. I don't see the current node actually being moved any with that design, although I could be wrong. If the loads plus the top hat looked large enough to add enough electrical length to make it a ½λ overall perhaps, but they just don't look like they would to me.


The DB

 

[Marconi]

Booty, do you know how tall this antenna is?

 

[Marconi]

Here is my Eznec model idea for the Immortal using a 4 element slanted down radial setup.

View attachment Immortal at 12' feet.pdf

DB, I checked the current report, and it is pretty evident that this setup raises the current distribution higher up on the radiator. The current right under the top hat shows to be >.56 amp/segment at this point, and then the currents fall of sharply to near zero in the Top Hat. I have the feed point imput set at 1 amp/segment and this makes for 50% of the current within an inch of the tip.

This one is 46" tall, but it could be shorter. I don't have the correct dimensions, but I have the top hat set shorter than I think it should be in this model.

 

[The DB]

Here is my Eznec model idea for the Immortal using a 4 element slanted down radial setup.

View attachment 8772

DB, I checked the current report, and it is pretty evident that this setup raises the current distribution higher up on the radiator. The current right under the top hat shows to be >.56 amp/segment at this point, and then the currents fall of sharply to near zero in the Top Hat. I have the feed point imput set at 1 amp/segment and this makes for 50% of the current within an inch of the tip.

This one is 46" tall, but it could be shorter. I don't have the correct dimensions, but I have the top hat set shorter than I think it should be in this model.

Can you post the current report?

Elevated current distribution aside, it still looks like a ¼λ antenna to me. That diagram you posted still shows the current node at the base of the antenna.

What I was theorizing from the diagram I quoted above would not be possible with a ¼λ antenna (even shortened) as, unless I'm missing something, the current node would always be at the base. With the ability to adjust tuning on both sides of a shortened ½λ, you should be able to center the current node or raise it towards the top of an antenna, at least in theory. I'm also still wondering if such a design would decrease the efficiency to the point that any gains you would see would be lost.

I personally don't need such a capability, but, if you are limited by a height restriction, would it not help to be able to move the current node itself higher on the antenna? Isn't that part of the design goals for the Astroplane and Merlin antennas with their higher feed points (one of which this thread was created to share the op's experiences with said design?) Or how about a mobile setup, same overall shortened lengths, but with a higher current node in the antenna raising the most effective radiating part of it several feet above the vehicle itself?

Or perhaps I'm just daydreaming here, after all, it is just theory at the moment...


The DB

 

[BOOTY MONSTER]

Booty, do you know how tall this antenna is?

no eye deer

 

[HomerBB]

Db, if you would like post up more of what was written about that antenna it may have something to teach some of us, or at least to show how this antenna type has been around for a good while.

I have been listening and talking with both the dipole and the Merlin. Most of the time receive is the same on either, and switching off from one to the other elicits no comments from anyone regarding my signal. When there is a difference I can detect, or see on my radio face it has been in favor of the 1/2 wave dipole. I placed the tops of the to antennas at the identical heights because this has been suggested as where the design advantage for the Merlin is, or by the feed point being higher because it is nearer the top. This I tend to doubt as all 1/4 wave antennas, or short antennas would have that advantage. Not that it doesn't contribute, but it is not, IMO, the secret ingredient.

Because the upper half of the dipole is about 8.5' long, and the Merlin's upper section is 6' long the Merlin ought to have had a higher feedpoint advantage, but it hasn't revealed itself at my QTH.

I attempted to put up a EFHW without any radials but grew frustrated with getting the match where I wanted it. But that's another story . . .

So I added length to the vertical, added a set of GP radials,removed the capacitor from the matching network, re-tapped the coil, mounted the 5/8 Groundplane in the place of the dipole. Then I lowered the mast so that the tops of these two antennas are at equivalent heights. Of course, this puts the feedpoint of the 5/8 GP roughly 16.5' lower than the feedpoint of the Merlin. I will fine tune it tomorrow, although it sets at a 1.0:1 across the CB 40.

It had gotten dark by the time I was done with this chore, and I had to be out of the house for a while so tomorrow I will try to see what's up.

1. So far the models of the various 1/4 wave iterations gave a slight edge to the Merlin, I did not see enough in the models to suggest there was any value to building a second 1/4 wave antenna to do side-by-side comparisons. It can still be done should it be deemed necessary.

2. I placed a dipole and the Merlin more than a wavelength apart and monitored and transmitted on both SSB and AM working both local and DX without either of the two showing significant advantage over the other. When slight advantage was perceived it went to the dipole.

I can imagine there are setups that have placed the Merlin at an advantage, but it hasn't developed here, yet. There may be more to come. We'll see.