LARGEST YU MOXON

BY

YU1QT, YU1EP, YT1DU, 9A2KL, YU1DO

Without a doubt, the most experienced moxon antenna designer and builder is Andreja Todorovic, YU1QT.  Andra has conistently pushed the envelope of experimental moxon antenna arrays.  Andra was the first to post his designs for low bands and multi-band moxons on this website.  He and his friends have used moxon antennas for major DX contests in Europe and have many 1st places.  So, I was thrilled to hear that he and his friends built a "Monster-Mox" for 80-40-20 meters for use in the recent CQWW phone contest.  Seen above, it is a tent-like Moxon structure and it is BIG!  Andra has documented the construction both in words and pictures.  Andra's english isn't too good but he makes for very good reading.  So, spend the next ten minutes enjoying story of the construction of the "Largest YU Moxon".  (many thanks to Simke for the translation)

PART 1:  DESIGN

Autumn ,mid Oct. 2006.  Chortanovci, small village on Fruska gora mountine, best serb wineyard's place. My best friend Zoki,YU1EP has a wineyard and we helped him to collect Grapes. A sunday afternoon(not leasy,like by “Small faces”),” Mr.Brain” (they,my HAM gang, call me that) sitin' on balcony (like Waldorf in Muppet's), and counting yard's.

Then I take a long rope,and Dule(YT1DU) under hand to measuring whole yard. It's 5 o'clock, sun is on left side, front azimut is just what I need--between 300 and 360 degrees!

300 step's to heaven! Yard is 47 x 38m; Azimut is 340 degrees. OK for States from YU, but with other also interesting DX-'s?  So 2, or 3, or 4 el for 80m with 40m and 20m inside, over the rope. I have lot of  “tent-like” fixed Moxon's in my archive, very good in use many 9A op's work with that combination, but primary idea came from 9A6C, my friend Gogo from Split.  They collect many 1.st places with 40m/2el tent-Mox.

Also, VE3ZIK is my Mox respecteur,specialy 40m/2el. He is ex-YU in small;Born in Belgrade-Zemun,father is one,mother is other ex-YU nationality; Zik spoke 6 foreign language's very good,QRQ at CW one of best,marryed to Zaklina,(which I love very much), we together are waitin' for my granddaughter. Leon,9A2KL is collector of my prototypes. Every time he is in Belgrade, Leon take last one antenna from bench rest! But, this one was too big morsel even for Leon (sorry my friend,I had that on my mind, when I modeled Monster).   OK! How I sleep with my notebook, poor computer operator but with some antenna knowledge I take it from a car.

Two elements on 80 is to small for my taste, it's possible to make 4el, but fixed?  No good for many directions with so narrow shape. What do I need? Three el wide AZ angle, with 4el gain + min 30dB F/B (shack is 5m behind 80m reflector)!

I know that, that is possible with some reduction in gain. Every one of my antenna is with strong F/B, instead of max gain (gain loss is everytime ca. 0.5-0.6 dBi, but non  of my antenna have under 26 dB F/B). My final counting for 4el/80m Moxon have a 37 (in real measured with MFJ full 69)dB Front/Back relation,free space gain is 7.81 dBi, instead 8,56 dBi with max gain configuration,on 47m boom. Front Az angle -3dB is 50 degres,enough for SA to JA from YU. See 4nec2, diagram 1!

I have many expirience with NEC based ant simulation programs (like Eznec,AOP,4nec2,SuperNEC),and my frequency shift is used on every antenna counting. Aprox. that is 4% higher from wished resonance, you'll see at the end measuring on antenna in real. With very low noised antenna, first step is behind me. Base is over!

Before step 2!  I counted every antenna for that multibander like mono, with my taste wished diagram's. After that,I need to finish more antenna interaction in between.

Step 2 is a making 40m (why not 4el also?) Moxon with bi-directional diagram 0 – 180; (340 -160 dgs from YU),while Russian op's with “just 40 W” came with 5/9 without +50dB  on side of my antenna,very good.

Third step was too heavy, for my wishes with Zoki's antenna.

final SWR results:

from 3.650 - 3.800 = 2,0:1, best 1,2 : 1 on 3,710;
from 7.000 - 7.100 = 1,4:1, best 1,1 : 1 on 7.060; (1,67 :1 on 7,300)
from 14.000 - 14.350 = 1,3:1, best 1,0 : 1 on 14.250;

I see space inside for 6el on 20m,with many problem in fixed configuration. How can I “work like thunder” with States, but with “little” LU&JA? Answer is simple: With normally called, error in diagram shape!  Small loss in front gain, but with two big side lobes in right angle to LU/JA.

In final counting for 6el/20m  Moxon, I lost whole dB in front gain(just 14,7 with 44 degres wide in -3dB gain),but with becomin' two big side lobes in AZ 298/42 (on terrain is AZ 278/22 from YU).  Pure occasion is two additional side lobes in AZ 216/144 (on terrain is AZ 196/124 from YU). Nice combination for fixed work, hi!.  So much about antenna in simulator.

 Part II: The Build

We (YU1EP - Zoki, 9A2KL - Leon, YU1DO - Simke, YT1DU - Dule, and me) needed that 3b antenna for the CQWW phone contest. Building the antenna started on saturday, oct 21. at 7 pm local time, one week before the contest. ” Statler ”&” Waldorf” (YU1EP & me) arrived in Chortanovci late afternoon. We started with cutting the wire, and making preparations for tomorrow so we could attach the wires to the rope. All wires are connected with each other by a 3mm thick rope, and small loop on corner's for 3mm rope to the ground.These loop's I made using a cable tie's which I tightened over corner-place on wire. That work was finished at about 3 am in the morning.  Early next morning, Simke and Dule arrived to help with a more dificult part of this project but we were very tired and lacking sleep. We started again at 10 am next morning. One whole day of work is not enough for that type of antenna building, the minimum is two whole day's. I alone made (31 pieces until today) 3b Moxon 14/21/28 for 5-6 hours,but...? We had a problem with the height of the walnut trees. One was 12m, the other 16m high. Just attaching the rope to a stone and throwing it wouldn’t do it. Dule, the youngest amongst us, had to climb the tree. Zoki gave him special climbing gear, like the ones used to climb on high poles.(150mm long/8mm) We thought this way would be easier for Dule to climb the trees. As it was very difficult to get the extremely long rope up in the air, our “boom” was finished late sunday afternoon. We worked all next day as well.

Zoki, YU1EP and Dule, YT1DU up a tree.

Thank God that in the mean time I finished 3 antenna feed lines with baluns and cables.  All the cables are RG-58,ca. 20-22m long. Usually, I use a  terminal strip, this time I used a heavy duty version in small plastic boxes. All connections were filled with melted plastic not with silicon glue, which has acid inside. I made simple “ugly” baluns, air-choke type,made of original RG-58 cable, wounded close on plastic bottles. For 14 Mhz on 2l beer bottle (8'/8turn's), for 7 Mhz on 3l wine bottle (15'/8T) , and for 3,5 Mhz on 5l mineral water bottle(22'/12T). Every cable on the balun is first tightened with some cable tye's, then is covered with a wide tape.  Baluns made in such a way work fine.  There was no interfierence on our TV which had a room active antenna. We didn’t have any interference between two separate antennas even when we worked with both antennas on the same band.

So, what should we do now?  We decided to go on until we finished the job under strong lamp light.  At the end we worked with battery lamps, to tightening 3mm ropes to small trees on the wineyard sides.

your humble author, YU1QT making connections

 Zoki is a very precise man and I'm the opposite! I gave him a job, making knot's on the “boom” on calculated distance's, beginning from the middle of the boom. Ends of the boom we needed to attach to two tall trees. In every knot he put a small (30/2mm) alpinist clamp.  Every wire is equipped with a small loop in the middle. In the dark we started with elements hanging on those clamps and spreading on the ground until at midnight (it's 14 element's). After midnight Zoki took one, Dule other part of “boom” ends , pulling them up.  In the air,finally!  Next two hours we spent spreading and fastening 3mm ropes to the side trees.  It was pitch dark!  

We finished at 2am in the morning.  I really wanted to see this antenna working! Without connector's directly in MFJ 259 the first measurement was excellent! SWR 1,1:1 on 3,710 (instead on 3,730); 1,2:1 on 7.000(instead on 7.050),and 1.0 :1 on 14.250 (instead on 14.180-190).

I connected the RG-58 without the antenna connector, to my IC-706 and started listening to signals. This 80m antenna has definately the lowest noise I've ever heard, including Hrane's YT1AD,  3el M Square for 80 on 50m high mast!  The reason being probably it is mounted too low.

Seven MHz antenna is bi-directional!  I make a QSO with States OVER a IZ8... with couple kW in antenna!  And 14?  I have QSO with someone in W3 at 3 in the morning at the end of Oct.ober! Brilliant!  It’s time to go home.

the original Beer Bottle Balun

vineyard in RF Field

view from above

that's a lot of wire and rope!

looks like chicken for dinner? Simke, YU1DO

YT1DU, Dule

9A2KL, Leon

(from left) Leon, 9A2KL, YU1QT, Vera (neighbor), Zoki, YU1EP and Dule, YT1DU (Simke, YU1DO behind camera)

Waldorf & Statler (YU1QT, Andra (L) , YU1EP, Zoki (r))

Simke's 4-Band Moxon including 50mhz!

 Impresions and final tuning of the antenna and work in the contest must wait until Oct.  28./29/!  On monday Oct. 23rd I called my friend Leon,9A2KL  and said: ”Come, it's finished and works very well”. No problem for Leon, who lives in Zadar, Croatia and what's 1.000 km distance for good friend's?  He came to Belgrade on Thursday Oct. 26th .

Friday was a busy day for all of us, we arrived at the contest location at 16h local time. I started final tuning of the antenna (SWR results were extremely good) while the other's were preparing the second antenna system for hanging-up!  That's Simke's small portable 2el/4b Mox including 50 Mhz, (which always gives us a lot of problems as the elements get all tangled up. Leon is in the living room with Yaesu FT-847 on 80m, and doesnt want to waste any time he wants to see it working rith away. Night come, small Moxon is on ground! Leon prepares YU2B shack picture 14, for 14 Mhz with Yaesu FT-1000 Mk V and my IC-706 for cluster, but without antenna. Simke takes from truck my construction 2b FM with 5elQQ144/7el Quagi 432,and one “No problem” antenna is on air.  We are hungry, and our bestboy Simke, picture 10,makes a barbacue for us.

 It is now midnight, just two hours before the contest. Dule is cooking his famous Serb beans, Leon is on 80m in main shack, Simke is making photos, Zoki and me are having trouble with SMALL Moxon rope's. When all the other's gave a hand we finished the job. All we needed to do now was to put it up on the top of the mast!

One past midnight! Me on the roof, Zoki and Leon on the second balcony, Simke and Dule on the first balcony, small Mox is in 80m reflector, positioned upside down. ” Watch out we don’t break the 80m reflector of the big moxon”, Leon shouted. The five of us finally managed to place the 4bander on the top of the mast, picture 11. Just two minutes after that, I'm alone on the roof. Dule is in the kitchen eating beans,  Zoki is smoking, Simke is making photos (“Nikon” fan), Leon is with headphones in the 80m shack.All I needed to do now as to put the connectors on both antenna systems.

GMT 00: contest begins, Leon with my contest call sign YU2B,on 80m like Woody Woodpecker with 4 pair of ears despretly listening!  Dule is desperate as his shack is not ready yet, it’s without cable's and connector's, while14 MHz is still open, picture 15, I had to improvise and made it possible for him to start working.

It is 3am, local time, it’s the second hour of contest and I'm hungry! From top floor (YT5S, Simke's contest call sign) Dule screamed: ”Don't touch the beans. It's for tomorrows lunch”! That didn’t stop Simke and me for taking a few plates of beans. Seeing that Zoki and Leon joined and attacked the beans, at that moment Dule Pit Bull op. (real contest enthusiast ) had enough, switched of his 847 rig (his text is censored), came down and joined us.  From 8kg of beans, there was just a small bit over for breakfast next morning. Beans are not exactly breakfast material but we are just beans crazy. Rest of the first night is out my perception, picture 16.  

Saturday noon we were joined by Sloba, YU7HI, from nearby town Novi Sad, and we became a real multinational team.  We shared a tremendous amount of fun and laughs during this contest. One of the reasons for my HAM activity. It's too much to write about, here, but picture 1 tells the tale.

Expectations and results:

Bullseye!  Lot of fun with big Mox, silent, big gain, good positioning, cheap (under $150 with all ropes and clamps), and 3 band for contest also. Leon is one of biggest,HI! (allmost 7 feet tall) first class operator from 9A (Croatia), like an English Lord, gentle on the mike, with interest just for multipliers, his “fuel” is milk!  In CQWW SSB SO SB 80m he made 14.144 points with 159/11/53. Under YT5S Dule had 600 QSO/17/113. Enough for ordinary HAM in fun!  On Sunday at 21 GMT, especially for us came, first a storm with wind gashes 24m/sec, and we had to QRT. Just when we were packing it up, the electricity went down!

For all that have interest to built our monster, I'll give advice-MAKE IT!

My contact e-Mail is:

73 Andra YU1QT

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