Homebrew Merlin Experiment

[BOOTY MONSTER]

a different ground element angle is why i want to try another star-duster down the road . my first one had 45 degree ground elements but (somewhere) i recall marconi posting a link to the star-duster stating that the angle of the ground elements is important and that i should have had a steeper angle . i don't expect much difference , but it's on the to do list DTR .

 

[Marconi]

a different ground element angle is why i want to try another star-duster down the road . my first one had 45 degree ground elements but (somewhere) i recall marconi posting a link to the star-duster stating that the angle of the ground elements is important and that i should have had a steeper angle . i don't expect much difference , but it's on the to do list DTR .

I hope I said maybe BM. I had an old knockoff SD from years ago when the SD was not available, and I didn't think it was worth a hoot. The radials were notably wider.

When I did the Starduster, using Eznec, it was one of the first models I did. I have learned a lot since that time, but we'll see. I'll have to check that too before I get too categorical with the idea.

 

[BOOTY MONSTER]

i thought it was a cbtricks , but it was on the quackshack forum .

http://thequackshack.com/radio/inde...ld-a-ham-say-this/page__p__308140#entry308140

here's the link to the patent .

Patent US4208662 - Omnidirectional, vertically polarized antenna - Google Patents

page 5 left column , second paragraph

 

[Marconi]

i thought it was a cbtricks , but it was on the quackshack forum .

http://thequackshack.com/radio/inde...ld-a-ham-say-this/page__p__308140#entry308140

here's the link to the patent .

Patent US4208662 - Omnidirectional, vertically polarized antenna - Google Patents

page 5 left column , second paragraph

That may explain it pretty well BM. I never saw this patent until a year or so back. For some reason it just alluded me, one of my favorite antennas.

Like you say, I think you and I talked about this angle thing once, but I don't remember the issue going anywhere. BTW, I think the same thing is true of the angle on the Sigma4.

I seem to recall that the only problem I had with it using Eznec was that the resistive part of the match sometimes got out of whack with the angle going too close to the mast, and I don't think adjusting the length of the radiator and the radials would fix the match after a point, in order to get the lowest SWR.

I know as you go down in angle from 90* degrees...the value of R= goes higher and can even pass the 50 ohm point.

 

[HomerBB]

I want to continue my experiment to see what the real world from my QTH looks like.
As for the similarity between the AP and the Merlin, the two are similar because they both have a Cap Hat and raising them up to the same tip elevation as other antennas result in improved performance. That is where the similarities end.
The claim for the Merlin is it will perform better than antennas of the same size when raised to the same tip height.
The patent on the AP claims it will result in improved performance over antennas twice its length when raised to the same tip height as those longer antennas.

I have satisfied myself in the real world that the claims for the AP are true.

I have yet to be convinced I will observe any detectable improvement in performance from the Merlin over antennas it own size nor, as some of its supporters claim, over antennas longer than itself.

We shall see.

 

[HomerBB]

1. Improved the downward angle of the radials some.
2. Improved the coax choke arrangement.
3. Shortened the length of the vertical radiator from 75" to 73"


These changes resulted in shifts in the SWR readings:

Channel 01 - 1.0:1 to 1.05:1
Channel 40 - 1.1:1 to 1.05:1

Although the SWR on channel one seems to have worsened it has in reality improved seeing the curve is equalized. Additionally, I have more bandwidth above channel 40 than before.

The CMC into the house appears to be non-existent. When my wife gets home I will let her listen to the indoor equipment that was being affected by RF to confirm this result.

 

[Needle Bender]

When I removed the coil on my 55, it no longer outperformed my stacked Moonraker 6s

 

[HomerBB]

We've all heard or read the praises of this antenna. My purpose is to simply test drive it myself and report on it without injecting any bias for or against it. Like I said, were it to reveal any particular advantages or strengths to me I will say so. If it shows any particular deficiencies I'll say that, too. Neither of them will be enhanced by hyperbole.

 

[HomerBB]

I must correct myself on this above written statement:

The claim for the Merlin is it will perform better than antennas of the same size when raised to the same tip height.

The maker of the Merlin additionally claims that his antenna will show gain over (is greater than) "most conventional groundplanes on the market today".

Because he prequalified the size of the Merlin to similar sized antennae in the preceding statement I believe it may be correctly assumed that the above quote refers to other sized groundplanes on the market of other sizes ie. 1/2 and 5/8 wavelength.
If in doubt read again the material BM posted from the manufacturer.

 

[Marconi]

Homer, per your request on the TC site I lowered the coil 12" below the top hat. I see a little reduction in gain, and a little change in the match. I fixed the match to resonance by reducing the size of the top hat a couple of inches.

Image of the modified antenna
View attachment IMG.pdf

Pattern for the modified antenna
View attachment IMG_0001.pdf

Below is the overlay of the original Merlin and the modified version, tuned and not tuned. It is hard to see the colors again, because the patterns are all about the same. The last pattern in green is the original Merlin showing a gain and angle = 3.01dbi @ 10* degrees.
View attachment Merlin overlay.pdf

Looks like my Eznec models are not going to show the difference the theory tells us is so bad concerning top hats and coils.

I have a feeling that maybe this top hat and coil issue may be better perceived with low frequency mobile installations where we seldom have a good ground and thus in order to make a good match we encourage losses.

If this is true, then it may be the good news for low band mobile operators that allows them to work their mobiles utilizing losses. I don't think I can prove it with my mobile models, but maybe I'll give it a try.

 

[HomerBB]

Thanks, Marconi.
These models are very helpful for getting a better understanding of what is in play.
I may have to make an antenna with the two parts separated by at least the radius of the cap hat just to see if I detect any differences.

 

[HomerBB]

1. Improved the downward angle of the radials some.
2. Improved the coax choke arrangement.
3. Shortened the length of the vertical radiator from 75" to 73"


These changes resulted in shifts in the SWR readings:

Channel 01 - 1.0:1 to 1.05:1
Channel 40 - 1.1:1 to 1.05:1

Although the SWR on channel one seems to have worsened it has in reality improved seeing the curve is equalized. Additionally, I have more bandwidth above channel 40 than before.

The CMC into the house appears to be non-existent. When my wife gets home I will let her listen to the indoor equipment that was being affected by RF to confirm this result.

I have to share that when my wife came in yesterday I transmitted over the antenna both with and without amplified power. The antenna was less a bleeder into the legacy TV and speakers than it had been, but it was still there to some extent.

 

[Marconi]

I have to share that when my wife came in yesterday I transmitted over the antenna both with and without amplified power. The antenna was less a bleeder into the legacy TV and speakers than it had been, but it was still there to some extent.

Homer, I'm really interested in the issue regarding TVI. What exactly did you do to your antenna that might have help the TVI problem?

I've tried to never change more than one thing at a time, but if you changed more than one thing and you don't know for sure what did what, is it possible you could set one modification back the way it was, and check what did what?

Do what you have on your agenda, but if you ever have time and are interested, I would sure like to know what you found out. I've done this many times and my results were almost always the same problem.

 

[HomerBB]

I shortened the vertical 2"
I lowered the angle of the radials dangle a few (unmeasured) degrees.
and I went from the first choke to the second as noted in the two photos below. The new choke raised the antenna up about 4".

 

[HomerBB]

Marconi,
I decided to bring back the three model .pdf files, but into one. The only parts of them I combined in order to review them side-by-side is the data with respect to gain and cursor elevation, etc.

The measure of difference seems to be negligible until viewed in light of the stated presupposition of the manufacturer's paperwork that the addition of the coil and cap hat will cause this antenna to be superior to others in it height class. It is clear that the full 1/4 wave model shows the most, although slight, amount of gain. I am assuming that all these are mounted with tip height at 36' according to the stated titles/descriptions.

I am not trying to disprove anything. I am trying to stay within the facts of the models as Eznec showed them to be.

Am I reading this right or wrong?