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Homebrew Merlin Experiment
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| Homer_2WR183 |
Posted on 14-12-2012 18:15
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Junior Member
Posts: 40
Joined: 12.12.12
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Okay, I am in the process of transforming the homebrewed 1/4 wave GP into a Merlin style antenna. I have some more details to attend to get it where I want it - radials at a greater angle, improvement to the CMC choke, and shortening the length.
I truly wish I had first hand experience with the Merlin in order to be certain of every single detail of it, but I am proceeding anyway with what I have been able to glean by reading threads across the www. There isn't much out there from the manufacturer, and most of what I've read in the way of arguing for or against it has not offered any substantial details about the antenna itself. Anecdotal info is abundant, but little else of use for replicating the antenna.
As you can see in the photos it was growing dark quickly here this afternoon due to overcast skies. I put it in the air with a few things to do. At this point it showed some promise in terms of dialing in the SWR.
Channel 1 is a 1.0:1, and Channel 40 is at 1.1:1. From what I've read the antenna length above the insulator should be around 72" - 73" tuned for center of CB band. Mine is 75" long, yet it is reading an acceptable SWR. It grew too late and my day started at 3:00 AM this morning. Ill get back to it as soon as I can.
I was able to talk to three locals today. A base station 2 miles east, and base station 10 miles west, and a mobile traveling away from me 15 miles out to about 18 miles with great signals and audio into my receive. There has been no DX activity this afternoon, and that was all the local activity. This evening was a bad one for noise in the air, and the antenna was typical of the normal 1/4 wave GP in terms of noise. Switching off to the horizontal Moxon resulted in a significant reduction in noise.
A member of an EU forum said he had not seen a Merlin, so I offered him a summary of the purpose of my build. I wanted to answer the question once for all for myself and any who cared to see my experiment.
"Crusty, it is a controversial design over here. It is loved by and sworn upon by those who use it, but vilified by those who think it a flawed design.
Typically placing an Inductor (coil) immediately against a Cap Hat results in the two components cancelling out the work each of them are by nature of design supposed to do. The camp that disbelieves in the antenna say the stuff on the top is essentially eye candy, and a truer more efficient antenna would be a straight shaft 1/4 wave groundplane, or just dump the coil and use the Capacitor Hat if height is an issue. Those who believe the antenna to outperform everything else they've used think it is special and misunderstood, and refute it to be a variant of the simple 1/4 wave groundplane, but is some special concoction of a 1/2 wave.
The second idea (of the 1/4GP being a 1/2 Dipole)presents itself too commonly with the common 1/4 wave groundplane like the Starduster to not think it would be used in the argument in favor of this antenna. Personally I have an opinion on the antenna, but refrain from expressing it until I run it to see what I think is in play."
Original Merlin for comparison to my Homebrew:
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.
The Merlin was put to the modeling test by a friend. As per the expectations set by the maker of the Merlin the antenna shows to be at an advantage in gain over antennas of similar dimensions. This gain advantage is not huge, but no claims were made for gain figures by the manufacturer.
From top to bottom at 36' tip height in the accompanying material are:
1. The Merlin (as 1/4 wave GP) with a standard 1/4 wavelength vertical, no Cap Hat, no Coil
2. The Merlin without the coil, but with the Cap Hat and length adjusted to bring it back into SWR match
3. The Merlin as it is made by the manufacturer with Cap Hat and Coil
Here are the model figures for the different antennas with all three of them at the same tip height.
In these models the improvement in the gain is clear:
.25 wave>--- with CH>--- Merlin -
3.06 dbi>--- 3.13 dbi>-- 3.14 dbi
Until I get a 5/8 GP together over the next few days I have put a vertical Dipole up for comparison to the Merlin.
The dipole is constructed of wire within fiberglass crappie poles, and is a common center fed type.
Both of the antennas are mounted at the same top tip height of 43'.
The Cap Hat on the Merlin is at the same upper elevation as the tip of the upper end of the dipole.
According to an operator about 2.5 miles distance from me, the dipole was the best for dead key and forward drive.
Without knowing what antennas I was operating, nor which I was at the moment keying/modulating he simply reported that the dead key was "8 swinging to 9 on that one" and "it's a little above 8 swinging past 9 on that one and you sound a little clearer"
Such a report, if his meter could be trusted on his RCI2995, would indicate around 3db (half an S-unit) of improvement from the Merlin to the Dipole, or twice the power out of the antenna and into his receive. My radio output is a modest 1 watt DK swinging to 4 watts AVG on both antennas. Draw your own conclusions about what he saw and why . . . SWR on both is 1.0:1 on 26.755 AM.
Naturally, with the characteristic lobes of each antenna at different elevations there would be a difference to be expected.
There in lies what may be the reason some report improvement that seems out of character to a particular antenna. Where is the RF strongest, and where are the stations that are reporting dramatic differences between one antenna over the other.
Perhaps by Monday or Tuesday I can have an operating 5/8 GP to replace the vertical dipole. We'll see . . .
Edited by Homer_2WR183 on 14-12-2012 18:22
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| Homer_2WR183 |
Posted on 16-12-2012 21:02
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Junior Member
Posts: 40
Joined: 12.12.12
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I'm glad you enjoyed it, Renee.
If anyone has something to add, or any questions I'll be glad to trya nd address them.
I will be posting some conclusions for this experiment in due time. |
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| Joe_2nc605 |
Posted on 18-12-2012 04:03
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Junior Member
Posts: 12
Joined: 12.10.12
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Excellent project. I am not familiar with Merlin until I read your experience. Looks like fun and nice results. --73
I hope to hear you on the band. --73, Joe
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| Homer_2WR183 |
Posted on 18-12-2012 22:13
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Junior Member
Posts: 40
Joined: 12.12.12
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Thanks, Joe.
I have never run one, either, but I decided to try it and see how it compared to others I have made.
I'll try to share some more as I go. |
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| Homer_2WR183 |
Posted on 19-12-2012 02:09
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Junior Member
Posts: 40
Joined: 12.12.12
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I took the cover off the MFJ-259. The solder joint to the coax connector was broken loose. I soldered it back together and put the dummy load on it. It was "good as shootin'" as I've heard them say . . . I put the dummy load on the end of my e1/2λ jumper and it read good, too.
So I can get back to tuning these things with more than an SWR meter and see where it takes us.
Been working with the 5/8 today.
I think I'm going to simply make a more traditional 4 radials GP for it. I am not satisfied this one in the photo is as mechanically solid as I want. It is either rebuild or make a full sized one. I'm going with the full sized.
In the photo the two of them can be seen. Even as it is, with the Merlin higher to the feedpoint by far, the 5/8 is doing better. A full bar minimum on the 2950 face whether local or DX. Receive is easier to read as it is stronger and quieter on the 5/8, but that will be better addressed when I swap their locations before I'm done.
My match is good for SWR, but the GP needs tightening up as I can change readings if I manipulate the radials by hand - they may have developed corrosion sitting behind the shed. I will only put faith in my analyzer readings after I get the new one together.
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| Homer_2WR183 |
Posted on 21-12-2012 01:28
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Junior Member
Posts: 40
Joined: 12.12.12
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5:00 AM 12/20/2012
Winds at the moment are 27 MPH gusting to 48 MPH. They will increase for the next two hours to 33 MPH and it is to be seen what the gusts will be. So far the antennas are still up and the SWR rock steady.
We shall see . . .
temps 31° w/wind chill to 14° I ain't working on anything outside today.
7:00 PM
As you know, it was far too cold and windy today to be working on the antennas outside. Instead I went to work in the garage on the replacement full GP for the 5/8 antenna. While in the garage I was able to monitor the frequency - 27.385 LSB - for traffic and do some switching off between the two antennas for differences. They were back and forth, neck-to-neck today. A lot of fading and neither antenna as they are mounted (tip heights the same) could hold the prominent performance position for any consistent period of time.
Winds have been in the 25 to 35 MPH range with gusts in the 40 and 50 MPH range all day. Both antennas have held their SWR tightly despite that continuous treatment. Nothing looks bent or broken on either antenna. So good so far.
The progress on the GP is noted below in the photos. I am using a spreader assembly that resembles that of on a type used on a Quad. This make s it much easier to mount the radials. I can lean the antenna over, redo the GP set up, and then add the radials on at a time by sliding them into the spreader. I don't have to wrestle with 9' radials during the reconstruction.
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| 19LV002 PJ |
Posted on 21-12-2012 08:20
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Admin
Posts: 44
Joined: 15.09.12
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Thanks for sharing this Homer, keep us posted very intresting!
stuf.. Henry told us you are real pionier!! hi
73 buddy
and Merry xmess and happy news years
PJ |
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| Homer_2WR183 |
Posted on 21-12-2012 18:18
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Junior Member
Posts: 40
Joined: 12.12.12
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Thank you, PJ.
Clearly Henry is a nice guy. |
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| Homer_2WR183 |
Posted on 21-12-2012 22:48
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Junior Member
Posts: 40
Joined: 12.12.12
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GP radials are installed. No more time today to do anymore. SWR is low on the band, but I want to try to fine tune it a little more.
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| Homer_2WR183 |
Posted on 22-12-2012 13:17
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Junior Member
Posts: 40
Joined: 12.12.12
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Hello Henry
I have considered making my own feedline!
When my shack is built beneath the tip-over mast I may make some hardline going up the side of it.
I will run the two antennas a few days as they are at same tip height. Next I will raise the 5/8^ to the same feed point height.
The tip-over mast laying over as I work on the 5/8^ yesterday.
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| Homer_2WR183 |
Posted on 22-12-2012 20:44
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Junior Member
Posts: 40
Joined: 12.12.12
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I have had a second Merlin owner offer to fix me up with some exact measurements. I'm looking forward to that from either or both.
So far, things as they are, I have seen the conditions hand the performance edge by very small differences to either antenna.
I will say that over the past few days the Merlin has begun to show a trend of performance advantage reflecting its design intent. Until I double check my dimensions against the originals I anticipate coming to me soon (fingers crossed) I will not give a definitive statement to that point. On the other hand, if asked what I think at this point in the situation where someone was considering buying a full length 5/8 GP or a Merlin to run in a height restricted area, I would advise they consider an antenna such as this Merlin - Top One, Astroplane - that is designed to provide more consistent performance under the conditions.
Why I am leaning this way at the moment is:
Although there are no, again I repeat, zero S-units (bars) of difference on my meter except for when I reported earlier in the above thread for the 5/8 GP, the Merlin does report to my ears a detectable audio increase most often and most consistently. Regardless of the debate that will potentially ensue regarding how the human ear can not detect audio gains except with a given amount of measurable db increase, I will not rescind the statement. I, Homer, clearly can detect the difference. Some (or all) of this may be due to the fact that the noise floor is clearly lower for the Merlin with its feedpoint at 36' as opposed to the 5/8 GP fed at 19.5' with tip heights the same.
In as close as 10 - 15 miles the performance of either seems similar, but whichever has a quieter noise floor at the moment (usually the Merlin) becomes the antenna of choice. When I work local stations, mobile or base, beyond that distance out to 30 miles (I have not heard any farther out when I was in the shack) the Merlin has been better over 90% of the time.
Am I ready for a conclusion? As I said, not yet. I will be out of town over the next 5 days and will be unable to report on anything, nor make changes until afterwards, so the tweaks and tunes I will be making to both antennas will have to wait until after. It will only be then that I will say how I finally believe this washes out for the Same Tip Height Test (STHT).
I will likely be adding a twist to the .625 antenna before I am done. Claims to the effect that the I10k was bested by the Merlin has me considering adding a Top Hat of the dimensions that the I10k uses and run a test between the .625/.64 vertical configuration where both of the antennas potentially use the capacitance hat technology to adjust toward optimum current maximum on the vertical radiator.
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My friends call me Homer |
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