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Post by homerbb on Dec 7, 2012 20:56:30 GMT -5
Okay, I am in the process of transforming the 1/4ƛ GP - Clothes Line Groundplane - 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 1/4ƛ GP in terms of noise. Switching off to the horizontal Moxon resulted in a significant reduction in noise. |
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Post by homerbb on Dec 8, 2012 13:00:02 GMT -5
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. Original Merlin for comparison to my Homebrew:   |
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Post by Night Ranger on Dec 8, 2012 13:03:12 GMT -5
I've never heard of a Merlin.
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Post by homerbb on Dec 8, 2012 15:23:37 GMT -5
I hadn't until I ran across a reference to it. I Googled it and sure enough there was a divided camp regarding its true worth.
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**GRUMPY**
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Classic Radio Operator Olde Timer 8220 [/color][/center]
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Post by **GRUMPY** on Dec 8, 2012 15:36:22 GMT -5
I've never heard of a Merlin.  |
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Post by homerbb on Dec 8, 2012 18:54:53 GMT -5
I think it is the hillbillies that favor the Merlin ;D
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**GRUMPY**
Administrator/The Boss
Classic Radio Operator Olde Timer 8220 [/color][/center]
"The King of Ping"
Posts: 4,342
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Post by **GRUMPY** on Dec 8, 2012 18:59:53 GMT -5
I think it is the hillbillies that favor the Merlin ;D |
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Post by homerbb on Dec 10, 2012 17:53:02 GMT -5
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.     |
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Post by Marc on Dec 10, 2012 18:51:39 GMT -5
Homer not to get off subject but when you connect your Mfj-259 how long of a jumper do you use??
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Post by homerbb on Dec 10, 2012 19:44:46 GMT -5
I use an Electrical 1/2 wave jumper if I can not connect right onto the antenna feedpoint.
The formula is:
492 x (Velocity Factor) / Frequency (MHz)
or, if you want it to run on the center frequency of 27.385 like I do and use an RG58 jumper -
492 x .66 = 324.72 / 27.385 = 11.85758626985576' or 11' 10-1/4" long
For channel 19 it would be:
492 x .66 = 324.72 / 27.185 = 11.94482251241493 or 11' 11-3/8" Probably a 12' section would get you there.
The reason is because electrical half wave coax sections tend to repeat impedance values, as I understand it.
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Post by Marc on Dec 11, 2012 11:24:08 GMT -5
Thanks that is what I use also. Multiples of a half wave seams to work for me also.
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Post by homerbb on Dec 12, 2012 6:01:43 GMT -5
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 |
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Post by cbrown on Dec 12, 2012 9:58:51 GMT -5
Gain figures are about what I thought. Really appreciate you going the extra mile to provide them!
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Post by homerbb on Dec 12, 2012 10:40:37 GMT -5
Until either I learn to model, or I no no longer can get it done I'll try in situations that call for it in order to better understand a particular antenna.
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Post by homerbb on Dec 14, 2012 12:42:38 GMT -5
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 . . .  |
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Post by homerbb on Dec 18, 2012 20:59:19 GMT -5
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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Post by homerbb on Dec 20, 2012 20:17:55 GMT -5
5:00 AM 12/20/2012Winds 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 PMAs 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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Post by homerbb on Dec 21, 2012 17:41:57 GMT -5
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Post by homerbb on Dec 22, 2012 12:23:10 GMT -5
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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Post by Night Ranger on Dec 22, 2012 21:01:45 GMT -5
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.    Very nice. My J-Pole is working well, but the 5/8ths / .64 wave vertical is still my favorite. I may have to try my hand at building one myself. Night Ranger |
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Post by Sandbagger on Dec 22, 2012 23:07:36 GMT -5
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. I'm having a hard time understanding how a shortened 1/4 wave radiator can outperform a 5/8th wave radiator. The gimmickry at the top is basically making up for the shortened physical length, and at the end of the day a 1/4 has unity gain. Now the shape of the E-plane lobe, and differences in the take-off angle compared to a gain antenna like a 5/8th wave might result in circumstances where it may work a little better. And local terrain may also play a factor. In my area, we've been coming across situations where 2 identical antennas mounted maybe 200 feet apart have radically different signal differences between one or two stations, but not anyone else. The only thing I can figure is that there are multipath phase cancellations or some other terrain-induced condition that would account for this. That's both the beauty and the frustration of playing with antennas and trying to come up with meaningful comparisons. Most of the time it's very difficult for one antenna design to universally outperform another in every case thanks to the effects of local terrain. |
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Post by homerbb on Dec 23, 2012 2:22:00 GMT -5
I guilt understand your frustration with how or why. Terrain plays Abigail role here in the Ozarks. Also, this comparison is between two antennas that have the tips at the same height. This gives the shorter antenna a 16' minimum feed point advantage
Modeling shows the Merlin has as low a TOA as the 5/8 GP has. I think the trend will change when the feed points are set the same.
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Post by homerbb on Jan 23, 2013 4:42:09 GMT -5
I got sick, and it got cold, so I lost time on it. But, I can tell you what my impression is so far, and that it could change with more testing.
So far:
the Merlin I made is not perfect, but close. But close enough to have observed a trend. I can say that so far the antenna proves over and over again that it is a good design in terms of getting the job done. It consistently hears better 8 of 10 times than the 5/8 I made for the project, and slightly better than the 1/2 wave oddball antenna I threw together, and gets my signal back to who I hear. Because the noise level is lower than the 5/8, and slightly lower than the 1/2 wave, I am usually able to get a bit better noise to signal ratio which sends me to the Merlin most often. What I have not been able to check so far is whether the noise floor is due entirely to the antenna design, or the location of the antenna mast it is on. I'll have to move the antennas around to be sure.
I have not seen any of the 1 - 2 db or more signal improvement over the other antennas some have claimed for this one, but I can say it is a good antenna.
I like it.
If one wants a consistent performer, small sized, light weight and apparently well built by all reports, this somewhat pricey antenna will do the trick.
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