Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
  • Click here to find out how to win free radios from Retevis!

Homebrew Merlin Experiment

That's fine Homer. No discussion is worthwhile unless all of the reasonable points of view presented are considered.

I did this project in batches trying to make each small enough to post on CT's Website, but that still didn't work over there. Most images were still too large.

I just duplicated that work over here, and I see now that can still make for some confusion. Believe me, I sometimes get confused with all these reports too. The problem here is I did not fix all models with individual captions to describe this project. I used hand written notes to try and better explain.

The 36' feet note in the captions indicates the height of the mast to the hub.

I think you are referring to my post #14 where I posted three pdf files and file 2 and 3 have two models in each. Check it again, and consider the 2nd model in these files 2 and 3 where I added some notes...instead of the first model that you refer to here.

Let me know if this just makes matters worse.
 
okay. I'll take a look.

Alright, I missed it. Here are the model figures for the different antennas with all three of them at the same tip height. Correct?

mercomp2.jpg


If so, in this case the improvement in the gain is clear: .25 wave>with CH>Merlin - 3.06 dbi>3.13 dbi>3.14 dbi
Correct me again if I am missing something.
 
Last edited:
HomerBB said:
okay. I'll take a look.

Alright, I missed it. Here are the model figures for the different antennas with all three of them at the same tip height. Correct?

mercomp2.jpg


If so, in this case the improvement in the gain is clear: .25 wave>with CH>Merlin - 3.06 dbi>3.13 dbi>3.14 dbi
Correct me again if I am missing something.
Click to expand...

That's right.
 
Okay, the models vindicate the claim for superiority over similar length antennas.
Next would be the part about whether it has more gain than most of the GP on the market today - 5/8, and 1/2 waves.
 
  • Like
Reactions: 1 person
HomerBB said:
Okay, the models vindicate the claim for superiority over similar length antennas.
Next would be the part about whether it has more gain than most of the GP on the market today - 5/8, and 1/2 waves.
Click to expand...

Homer, this idea will take some time and effort and may be in vain. That is because I will not be able to present some of the antennas you noted here with as near a perfect match as the Merlin presents. A 5/8 is closer to a perfect match, but an end fed 1/2 wave is way off. I will also have to make sure the models used to compare or close to the same...regarding all the Eznec settings. In the case of the Merlin project I basically use the same model for all configurations to safeguard the possibility of have models with really divergent settings and segment counts.

Personally I think within reason an antenna with a match that is off some, does not always make a noticeable difference in performance. For me this is sort of like working your radio within the bandwidth...away from the center frequency. With that said, this will certainly be a problem that some will argue. Again this might be another case of a difference that doesn't really matter...just using our radios to test for the difference that match alone makes.

You probably know that my real world testing results, for this idea with antennas at the same tip height, has not been very well received. So, modeling may result in a vain effort too, or surely create an argument in this case.
 
Last edited:
BOOTY MONSTER said:
the astroplane is a similar height antenna . how does it compare to that ?
Click to expand...

The same though came to me too Booty.

I will try to get the Eznec settings for my A/P to specs, as close to those for the Merlin first.

I have a recollection about the A/P however. I seem to recall it is very sensitive to changes in height. I did a thread on this in the past, and use the A/P to demonstrate the idea. I think I even asked Homer if he had ever experienced this with his A/P. So, I'll have to refresh my memory on how that all worked out and why, just in case it crops up and I'm asked. Homer, do you remember us ever talking specifically about this idea of height and the A/P?

On the other hand the Merlin model shows very little effect on match when I raised or lowered it between 18' and 54'. The A/P may not work the same regarding changes in height, but I will check that for sure.

However, right off the bat I would guess the A/P to be a bit better in gain and maybe angle. Booty, IMO this would be due to the A/P having a shorter radiator, by about 1/2, allowing the feed point to be installed higher...if we are comparing with the antenna tips at the same height. The difference in radiator height between these two is the A/P is about 47" and the Merlin is about 75" inches.
 
  • Like
Reactions: 1 person
@ Marconi - Yes, we had conversations, and over the course of several different threads on different antennas I have maintained that the AP became a very effective antenna when raised to the heights of the tips of longer antennas. In my Because I was asked thread I repeat that the AP needed height to work its advantages. In fact, I once raised it to 54' to the top in order to work it compared to a 5/8 wave that was mounted at 36' at the bottom. This resulted in some controversy over whether it is proper to compare antennas from the feed point or the top. I cited the AP was designed to be raised to maximum legal height and so it should be tested accordingly to give it a fair run.

@ Booty. I have not had the same experience with this Merlin style antenna that I have had with the AP. The Merlin is close to 18' over all length. As Marconi points out, it has it's feedpoint at 72" from the Cap Hat. The AP is 12' over all length, and has its feedpoint about 48" from the top. The Merlin is a 1/4 wave GP designed to maximise the potential of a 1/4 GP. The AP is a center fed 1/2 wave vertical. It is not a GP, but has more gain than the dipole it's feedpoint suggests, or at least it works significantly better. I am not arguing for what the AP is or isn't, I am just looking at the physical characteristics of it with respect to feedpoint location on each of the antennas.
I will get the Merlin up as high as I can currently run it and see how I feel it performs. At the moment the top is around 42'.
Up front, I do not expect it to do as well as the AP, but should it do so I will admit to it.
 
Last edited:
  • Like
Reactions: 1 person
Booty, I have about 30 different models for the A/P to check through, looking for one that is truly up to specifications. I don't have an original antenna to check either. My version is an old Copper's knockoff. I think it is good enough however, but it is not exactly the same dimensions as Avanti's original.

Plus, most of my models appear to have been created at the time I was studying the antenna for the effects on match. I was trying to understand the patent suggestion that changing the bow angle for the two down radials is what controlled the feed point impedance and how that worked using Eznec. As a result, I have a lot of models to check and find one that is what I call a model to the correct specifications, or a Spec Model. The problem is, while I was doing this study I did not consider any affect for changes to the gain for the antenna. Now I find I have a bunch of models that are not to specs, and I don't know for sure if these changes affected the antenna's performance results.

Since this Merlin project is exploring what Eznec might predict, and we are seeing differences in the range "of a fraction of a DB", I think I should use an A/P model that is to specs. I looked in my files and I have at least two sets of measurements I have taken over time, and one set that I got off the Internet. The set off the Internet is the one I sent to Homer, and I think it is the one he used for his homemade jobber. I don't know if he compared this spec sheet against his original A/P he got of a building or not, but I might have to remeasure my A/P and see which dimensions are correct, before I do this comparison with the Merlin at the same tip height.

It has been a while since I worked on the A/P model and I don't remember squat. As usual for me, I don't think this will make much difference in the end, but I just want to try and avoid a mistake in dimensions from becoming a point of contention, and doing the work all over.

The old A/P is not a simple antenna to model, has lots of little parts, and it looks to be very sensitive to everything around it.
 
Thanks, gamegetter.
I looked over that info and found the one you speak of.
Marconi entitled it the Astro Plane to Specs 48'


Marconi, I had already traded away the original AP by the time I went to work building my homebrew, however, handling them both so near a time together there seemed to be no apparent differences between the spec sheet you provided that I built mine from and the original I procured from the building.

Whether or not the AP would show significant diminished gain by bringing it down from 48' to 38' would have to be seen.
I still believe the AP would show gain over the Merlin. If so, it might prove to be the exception to the proposition that the Merlin will deliver more gain than any other antenna of its size, esp with the AP being smaller in every diminsion of height and width.
 
but you can't put 75 thousand watts into a astroplane . i've wondered if 55's claim was made with the idea of each antenna being used at it's peak power handling ability .
 
75 Kw? Where did that come from? Surely that's not claimed for that Merlin! If it is, I require that the 'claimee' never get within 3 blocks of my house! I hate cutting grass and that much 'poo-poo' would turn my yard into a jungle.
So what am I missing here?
- 'Doc
 

dxChat
Help Users
  • No one is chatting at the moment.
  • @ kopcicle:
    If you know you know. Anyone have Sam's current #? He hasn't been on since Oct 1st. Someone let him know I'm looking.
  • @ BJ radionut:
  • dxBot:
    535A has left the room.
  • @ AmericanEagle575:
    Just wanted to say Good Morning to all my Fellow WDX members out there!!!!!
  • @ BJ radionut:


      Top Bottom
      Back