W5GI Mystery Antenna

A multi-band wire antenna that performs exceptionally well even though it confounds antenna modeling software
Article by W5GI ( SK )

W5GI-Multiband-AntennaThe design of the Mystery antenna was inspired by an article written by James E. Taylor, W2OZH, in which he described a low profile collinear coaxial array. This antenna covers 80 to 6 meters with low feed point impedance and will work with most radios, with or without an antenna tuner. It is approximately 100 feet long, can handle the legal limit, and is easy and inexpensive to build. It’s similar to a G5RV but a much better performer especially on 20 meters.

The W5GI Mystery antenna, erected at various heights and configurations, is currently being used by thousands of amateurs throughout the world. Feedback from users indicates that the antenna has met or exceeded all performance criteria. The “mystery” part of the antenna comes from the fact that it is difficult, if not impossible, to model and explain why the antenna works as well as it does. The antenna is especially well suited to hams who are unable to erect towers and rotating arrays. All that’s needed is two vertical supports (trees work well) about 130 feet apart to permit installation of wire antennas at about 25 feet above ground.

The W5GI Multi-band Mystery Antenna is a fundamentally a collinear antenna comprising three half waves in-phase on 20 meters with a half-wave 20 meter line transformer. It may sound and look like a G5RV but it is a substantially different antenna on 20 meters. Louis Varney’s antenna, although three half waves long, was an out-of-phase aerial. Mr. Varney had two specific reasons for selecting a 3 half waves on 20… he wanted a four-lobe radiation pattern, at least unity gain and a low feed point impedance. The Mystery antenna, on the other hand, presents a six-lobe pattern on 20 meters, gain broadside to the antenna, and also low feed point impedance to simplify matching the antenna to the rig. Additionally, the Mystery antenna is designed to work at least as well, on the other HF bands as a G5RV. In short, the Mystery antenna is a sky wire that incorporates the advantages of a 3 element collinear and the G5RV antenna.

In its standard configuration, a collinear antenna uses phase reversing stubs added at the ends of a center fed dipole. These stubs put the instantaneous RF current in the end elements in phase with that in the center element. You can make these phase reversing stubs from open wire line or coaxial cable. Normally, a shorted quarter-wave stub is used, but an open-ended half wave stub would also work. The problem is that the dangling stubs are unwieldy and or unsightly.

An article written by James E. Taylor, COCOA- A Collinear Coaxial Array,  published in 73 Amateur Radio, August 1989, describes a low profile collinear coaxial array.

According to Taylor, when you apply a RF voltage to the center conductor at the open end, the stub causes a voltage phase lag of 180 degrees at the adjacent coax shield. This happens because the RF is delayed by one quarter-cycle as it passes from left to right, inside the coax to the shorted (opposite) end. There’s another quarter-cycle delay as the wave passes back from right to left inside the coax and emerges on the shield at the open end. Add up the delays and you get a total time delay of one-half cycle, or 180 degrees. In essence, the coax section serves two purposes: it provides the necessary delay and provides part of the radiating element in a collinear array.

The first prototypes of the Mystery antenna used the Taylor formulas, which which called for cutting the wires to a quarter wave length using the formula 234/f(Mhz) and the coax, using the same formula, but applying an appropriate velocity factor. The first version of my antenna worked well on 20 meters but failed as a multi-band antenna.

The second antenna was built with constructed with the coax cut to the same length as the wire. This was done with the belief that perhaps the coax didn’t behave like coax and therefore the velocity factor wasn’t applicable. Surprisingly, the new antenna performed exceptionally well on 20 meters, had low SWR and performed just as well on the other HF bands and 6 meters as my G5RV reference antenna.

Step-by-Step Construction

The W5GI Multi-band Mystery Antenna looks like a plain dipole (see figure1 and photo A below) and is very simple to build.

Photo A – Full view of the W5GI multi-band Mystery Antenna with all sections shortened considerably for illustration purposes.
W5GI Mistery Antenna
Figure 1 – Schematic drawing of the W5GI Multi-band Mystery Antenna. See text for details on connection of coax sections in center of antenna legs and on length of of twin lead stub.

Builders of the Mystery antenna will need the following materials:

  • 3 wish bone insulators
    About 70 feet of wire (14 gauge household electrical wire works well,)
    Sufficient twin lead or open wire to make a half wave section on 20 meters. Window-type 18 gauge 300 ohm ribbon works best. The Wireman is an excellent source for antenna wire and 300 ohm line.
  • 34 feet of RG8X mini-coax
  • An electrical connector, available from most electrical parts stores, to connect the twin lead and coax
  • Shrink tubing to cover the exposed coax joints

 

The antenna can be built in less than an hour when you have the above materials. When you’re ready to proceed, perform the following steps:

  1. Cut the electrical wire into four equal lengths of 17 feet.
  2. Cut the two lengths of coax to 16’6 each.
  3. Cut a 20 meter half-wave section of twin lead. This piece needs to be adjusted by its velocity factor. If 300 ohm window type line is used with a VF of .91, the total length will be 30 ft. Alternatively, 450 ohm, solid 300 ohm or homemade open-wire line can be used provided the electrical length is on-half wave on 20 meters. Actual length will vary, typically between 27 and 35 ft., depending on type and velocity factor.
  4. Trim two inches of braid from one end of both lengths of coax (Item A).
  5. Trim one inch of braid and center insulator from the opposite end of both coax sections (Item B).
  6. Build a 20-meter dipole without end insulators. Note: The next two steps 7 and 8 of the construction process involve connecting only the “inner” end section of the coax section to one end of the dipole; the shield is not connected to anything here. At the other end of the coax section both the coax shield and second wire section are connected to the coax center conductor.
  7. Connect one end of the dipole to the center conductor of the coax (Item A) and cover with shrink tubing as shown in photo B below.
  8. Connect the opposite end of the coax (Item B) to braid AND quarter wave wire section, cover with shrink tubing, and connect to end insulator as shown in Photo C below.
  9. Install the twin lead through the holes of the center insulator (you may have to enlarge the holes) and solder to antenna wire as shown in photo D below.
  10. Connect the opposite side of the twin lead to the coax as shown in photo E below. Almost any type of connection will work provided the connection is stable and sealed properly.
  11. Install the antenna with the center conductor at least 25 feet high. Mine is installed in a horizontal plane; however, others have installed the W5GI antenna as an inverted-vee and are getting excellent results.
Photo B – Connection of inner end of coax section (closer to center). Note that only the center conductor is connected to the wire.
Photo C – Connection of outer end of coax section (further from center). Note that both center conductor and shield are connected to the wire.
Photo D – Connection of twin lead to inner antenna wires at center of antenna
Photo E – Connection of twin lead to coax. Short length of coax section is for illustration purposes only. All connections should be weatherproofed with shrink-tubing, CoaxSeal, or similar.
Mystery Antenna Table
Table 1 – Measured performance of the W5GI Mystery Antenna at various frequencies. Columns list frequency, SWR (all as a ratio to 1), Resistance (R) in ohms, and Reactance (X) in ohms.

On-the-Air Performance

On 20 meters, you should expect 3-6 dB gain over a dipole and a 6-lobe radiation pattern with an elongated figure 8 pattern perpendicular to the plane of the antenna. This is typical of a 3 element collinear array. For a simple explanation of collinear arrays read “Troubleshooting Antennas and Feed lines” by Ralph Tyrrell, W1TF. On all other bands the antenna performs like a G5RV, which is really a random length dipole on all but 20 meters. M. Walter Maxwell, in “Reflections II, Transmission Lines and Antennas”, aptly describes this phenomenon. Several users report it is possible to use the antenna on 160 meters but you will need to connect the twin lead together at the point where it connects to the coax. On 160, the antenna performs like a Marconi. Those who have used the antenna on 160 say the W5GI Mystery antenna is a quieter receiving aerial compared to other 160-meter antennas.

As for the theory of operation, it remains a mystery. At least three experts tried computer modeling the antenna. All three rendered completely different findings.

You will enjoy building a W5GI Multi-band Mystery Antenna! Many hams has done so and find it to have been a fun project and an excellent performer.

Notes:

(1) Information on this page has been taken from an article published in the July, 2003 issue of CQ magazine. You can download a copy of the article in Adobe Acrobat format by clicking HERE.

(2) W5GI will build an antenna for a nominal fee. Discount prices start at $65.00, plus shipping, for the W5Gi multi-bander. Mono band antennas cost more because a 4:1 balun is used.

(3) For additional information, or to order an antenna, please call or send an mail.

(4) Dimensions for the mono-band antenna:

 

AND Inside wire Coax Outside wire Overall length
10.1 23′ 10″ 23′ 4″ 23′ 6″ 141 ft 4 inches
14.18 17′ 2″ 16′ 8″ 16′ 10″ 101 ft 4 inches
18.13 13′ 7″ 13′ 1″ 13′ 3″ 79 ft 10 inches
21.25 11′ 9″ 11′ 3″ 11′ 5″ 68 ft 10 inches
24.9 10′ 1″ 9′ 7″ 9′ 9″ 58 ft 10 inches
28.5 8′ 11″ 8′ 5″ 8′ 7″ 51 ft 10 inches
50.125 7′ 10 “ 7′ 4″ 7′ 6″ 45 ft 4 inches
  • The above dimensions are for a dipole hung in the horizontal plane.  They were calculated by using the formula 234/freq (MHz) plus additional length for attaching to connectors/insulators.
  • If the antenna is to be installed an Inverted V, increase all lengths by 5%.
  • Any of the above antennas can easily be used as multi band antennas by eliminating the 4:1 balun and using open wire/twin lead directly to an antenna tuner

(4) Dimensions for the multi-band antenna:

 

Inside wire Coax Outside wire Overall length
17′ 2″ 16′ 8″ 16′ 10″ 101 ft 4″

 

This antenna uses a twin lead matching stub instead of a 4:1 balun.

 

 

  • Use only 300 ribbon line for the matching stub.  Start with 34 ft 7″, trim as necessary to obtain lowest SWR.
  • Mono-banders with either a voltage or current (preferred) 4:1 balun.
  • This antenna exhibit significant gain only on 20 meters. On all other bands the antenna performs like a G5RV.

 

 

 

 

FAQ

Can RG-58 [or any other coax] be substituted for RG-8X (mini)?

Theoretically it should work, at least electrically. The main concern is the strength of the smaller wire. A portable Mystery Antenna using RG-174 is in the planning stage. If anyone has tried using different cables, please pass along your thoughts and observations for posting on this website.

[Note: disregard velocity factor (VF) of coax-it is not applicable in my design]

Can I use twin lead or open wire line directly to an antenna tuner in lieu of coax and a twin lead stub?

Absolutely. The twin lead stub is only necessary to give the antenna its multi-band characteristics.

How can I determine the twin lead  Velocity Factor?

The best way to determine velocity factor is to ask the distributor or manufacturer. It is very important that the correct VF be used in calculating the length of the twin lead. 300 ohm ribbon is a good choice. There are numerous types available. The VF range from 80 to 90 percent-for 300 ohm line, which means the half wave line could be anywhere from 26.4Ft to 29.7FT. 450 ohm ribbon line typically has a VF of 95%, which means the length should be 31.35 FT. The ARRL Antenna book list VF for different lines.

[Note: Use 33 feet as the 20 m half wavelength for the above calculations.]

Should I use a balun?

A balun is unnecessary and will only degrade performance. A line isolator between the end of the twin lead and the coax is recommended. It helps minimize feed line radiation and stray RF, which can cause problems in the shack.

[Note: The original article recommends the use of a 4:1 balun for a mono-band version of the Mystery Antenna; however, a balun is no longer recommended. Instead, try a quarter wave 75 Ohm matching transformer. RG59 (Beldon 8241) is a good choice. A section of 75 ohm cable cut for 20 meters 10.89 feet can be used with the the multiband antenna. It will lower the SWR on 20 m to close to 1:1 and is transparent on the others bands.]

I get higher SWR readings than appeared in your article, am I doing something wrong?

Probably not. SWR is a function of several variables to include wire and cable type, height above ground, etc. The best measure to ensure the antenna is constructed correctly is the 20m SWR. It should be under 2:1 across the entire 20 m band, and if you use a 75- OHM match transformer (see above) closer to 1:1.

Can I install the Mystery Antenna as an Inverted V?

Absolutely. There are thousands of Mystery Antennas in use in many different configurations. Feedback from builders indicates that the antenna is very forgiving and will work under almost any condition to include indoors and with the ends bend.

Where can I buy a Mystery Antenna?

The W5GI Mystery antenna is available as a kit from the Wireman or, if you prefer, direct from W5GI ready to install for $100 shipped within the U.S. W5GI can also build mono-band antennas for any band 40 to meters. Call or email for a cost estimate.

PS be informed that article, text and pictures are  Copy Right by W5GI now SK

 

33 thoughts on “W5GI Mystery Antenna”

  1. I’m not sure how I would use 75 ohm coax as a transformer on W5GI antenna for 20 meters as I feed my inverted vees with 75 ohm coax per ARRL antenna book. They claim that an inverted vee feed point is closer to 70 ohms than 50 ohms. Explain please! I would rather use the 75 ohm for a transformer because of the shorter length and lower SWR. It seems to me that my whole feed line would be a 20 meter antenna but that can’t be because it wouldn’t be tuned for 20 meters.

  2. Well I tried to build me one of these mystery antennas and it dont work and has a very high SWR. I have built many diapoles and this does not work like the design I have says so. The design I have says as followed: Cut 4 sections of 14 guage electrical wire at 16’6″ and 2 sections of RG8X coax. Then solder the inner section of 14 guage wire to the center conductor of the RG8X coax wire. This end “does not” get the shield soldered to the 14 guage wire. The solder the outside end of the shield and center conductor to the 14 guage wire. The as the design claims to use a piece of 450 Ohm ladder line at 31′ 10″. and solder to the inner ends of the 14 guage wire (using a center insulator of course). And then solder your coax directly to the 450 Ohm ladder line. And according to the chart for this I should have an SWR on 20 meters of about 1.5. My SWR is 3.5. I went over this antenna many times to figure this out and its got me stumped. And yes I do have it mounted right and away from all metal objects and its about 35 feet or so up at the apex. If anyone has any sugestions feel free to write me at my call sign at Yahoo.com….Thx…Mark (KD4QHG)

  3. SIMONE
    complimenti per articolo e per l’analisi che fai … ma una cosa ti devo chiedere ,
    per favore posso leggere larticolo in ITALIANO , sai il mio inglese è veramente scarso.
    Ho bisogno di chiarirmi qualche idea .
    TNX
    73 de ik3ery
    Sergio

  4. Curious if the is a minimum length for the coax line from end of ladder line to the radio ?
    Thanks
    Paul
    K5QGL

  8. Not having a coaxial choke and “crossing fingers” is why this outperforms a G5RV on lower bands. No mystery at all – use your coax as the antenna. Enjoy lots of noise pickup and RF in your shack!

  10. I saw the article in a magazine years ago and built and have been using this design ever since. No baluns, no chokes. I have new cut lengths of wire ready to be soldered together to replace my original antenna as it has been re-soldered a couple of times due to mother nature and branches that have reached out for it over time. Time to refresh. No new mods, building it right from the original article. I actually had the pleasure to make on air contact with W5GI a couple years before he went SK.
    Follow the instructions and you will enjoy the performance of this design for years to come.

    ’73

  11. Simone, I have successfully used a home made antenna called “coax antenna”. I received the design from WB5CPO (SK) many years ago. I can send you a single sheet copy of the design. Its simple and uses only 50 ohm coax in its entirety.
    Let me know how to send you a copy if you care to see it.

  13. Robert
    I played with antenna Since John was published in CQ magazine , Over the years I wanted to try use it on 160. 2 years ago I found the Length needs to be 30 FT each side is 90 ft at least 65 feet of 300 ohm ladder line with using a DX engineering 4:1 Balun I have 1.25 swr at 1980 at 1920 1.45 swr. I also by using a 4:1 Balun you can use it on all the band once below 20 meters swr is less than 2:1 Total length is 180 ft flat top or inverted V config . I found a balun solves a lot of issues when running power . I tried many Baluns that will not hold up about 14 years ago I switched DX engineering AT type baluns, and I never lost one yet . ON 10-80 antenna I use a 1:1 balun . if your only running a couple 100 watts you could use the method John Describes in the original article , But when running power I melted those butt connectors . Also a reminder on this antenna 300 ohm ladder line can not be bunched up it has to hang in the air It will effect the tuning . Also id use 450 ohm ladder line you will need to shorten the length.
    73
    Phil K4GY Louisville KY.

  14. I built one of these back in 2007 and I have used it VERY successfully on 80/40 virtually every day since. The apex is suspended by HB mast made from 18′ of galvanized Schedule 80 pipe through bolted to a 6″x6″ fence post (concrete base), followed by another 18′ of fiberglass tubing (tapered sections nested into each other). Total height AGL is 36′. The ladder line feedline is fed inside the fiberglass tubing and out through a slot near where the fiberglass tube base (where it fits into the galvanized pipe) then out to the 1:1 balun mounted onto the main mast and the other side fed with 50 ohm coax back to my radio. It is VERY important NOT to keep the ladder line away from any conducting mast. It is in a more or less flat top configuration with only a slight drop at the ends. Works very well and it has been very durable.

  15. Simone:

    You mention a version made of RG174. How did that work out? I’m interested in a QRP antenna, using RG174 and 26 gauge wire, and maybe 300 ohm solid twin lead. Did you end up making something similar?

    Tnx.

    Rick K9RBH

  16. I always thought that the “mystery” comment was pushing it a bit. I even talked to W5GI about it at Dayton one year and advised him of the operational theory of it was outlined in the 1945 book “Transmission Lines, Antennas and Wave Guides” by King, Mimno and Wing. Chapter 2, Section 22 Collinear Array as a coupled Circuit — Phase-reversing Stubs. Figure 22.3.
    If you model it the way it works, as described above, and not the way it looks, modeling wire and coax, it models fine and does indeed work great too. Similar to a Franklin antenna, but using coax as the phasing lines See https://owenduffy.net/blog/?p=15636

  17. Hello Simon,
    I like this article and would like to follow Robert’s directions to build the antenna:
    ” Robert Tusch says:
    August 19, 2018 at 10:43 pm
    Simone, I have successfully used a home made antenna called “coax antenna”. I received the design from WB5CPO (SK) many years ago. I can send you a single sheet copy of the design. Its simple and uses only 50 ohm coax in its entirety.
    Let me know how to send you a copy if you care to see it.”

    I was wondering if you would be able to share Robert”s design with me. Thank you. Vlad VA7 LKO

  18. Dear Simon,
    I have built this mystery antenna years back, I have used this with my I COM 746, it works very good. Especially I get very good reports from our Local hams working on 40 ! I have also worked some DX with the other bands! But on six meters I haven’t heard any one!
    I am a Ham operator from Srilanka, my Call sign, 4S7LF.
    Handle. Leonard Fernando.
    Kind Regards and Best of 73!

  20. I have a request. Im using this antenna for past 3 weeks. So far has passed all expectations. I have volunteered to do a presentation at our ham meeting next month on this antenna and a review and how to on installation.
    would it be ok if I use some of the above information including pictures for the presentation?
    If so can you send me a link to a more readily printed format . Some of the data you have put together I think, needs to be word for word to be correct in some areas.
    hope to hear back.
    John KI5UCM

  21. I can’t imagine why anyone would make a mechanical, unsoldered connection (coax feedline to window line) even if it’s sealed (photo E, ,above)M. That’s just asking for problems.

  22. Phil Zavagli K4GY
    I used this antenna when the original CQ Magazine article came out , It was the First antenna I worked DX on 80 with were I could here . If you changed the design it wont work. Since Johns passing the author of the article,
    W5GI < I am using short Version of this antenna For 160 meters total length 180 ft works 6-160 each side 90 ft and the ladder line is 65 ft to 1:1 tuner Balun . Wa5 QPZ use the same version on Flex net every Sunday on 20 . Antenna Does work and well.
    73
    Phil

  23. Simone –

    There are 2 different sets of lengths for the wire / coax to build this antenna in the article above:

    initially, it says to cut 4 pieces of wire to 17′ – but at the end under “Dimensions for the multi-band antenna”, there is a diagram showing 2 pieces at 16′ 10″ and 2 pieces at 17′ 2″ – and also different lengths of coax as well.

    Which is the correct set of lengths for the multi-band antenna ?

    Thanks and 73,

    Dave KG7WOC

  24. Hi my Ham friends,
    I am from Srilanka with a call sign, 4S7LF, I have constructed this Mistry antenna years back and had great results on all HF bands! Presently I use this on Forty meters
    ( 7060) daily in the morning at about 0820 hours local time and the results I get is excellent!
    Kindest Regards! ………73!
    Leonard Fernando.
    4S7LF

  26. I have a W5GI antenna, manufactured by K4TR Antennas. I have never been able to get it properly installed. It is tied off in a tree at about 20 feet, and even at that it is a great performer. I have talked all over the US and into Europe. It works on all bands 80M thru 10M, with minor assistance from the tuner in my radio. I count that as a win!

  27. Meu espaço no QTH deu só para usar um lado. Transformei longe wire. Balun saída acoplador. Cabo coaxial de transmissão usando positivo e a malha contrapeso no telhado. A malha na estação fica aberto. Elogios em 80/40 metros. Toda banda.

  28. Question about the mystery antenna, It talks about adding a 75 Ohm coax 10.89 feet long to lower SWR on 20m
    Do you remove the 300 Ohm twin line and add the 75 ohm cable instead?
    OR do you add the 75 ohm coax below the 300 Ohm twin lead, the instructions are very vague

    Thank You
    James

  29. I’ve been very pleased with my W5GI Mystery Antenna that I’ve had in service in my limited residential lot since 2010. Over the years a couple minor repairs, but nothing that ever caused any serious damage that would have stopped me from operating.

    I got my W5GI from Joe – K4TR Antennas and he has been very good support. Also his construction of the antenna is simply excellent and my years of long use speaks well for his quality of work.

    I’m considering replacing the old W5GI with a new W5GI only because I need to lower my center mast to replace a couple ladder-line standoffs that had their Ty-Wrap securement break in a heavy storm wind just in the past 3 days.

    I figure if I have to lower the mast for the repairs I’ll just do a complete end-to-end rebuild so it will last another decade or two. I’m also now in my mid 70s so the mast lowering and such is not as easy as it once was.

    Now, finding good and stable standoffs (like those I used back in 2010) are not as easy to come by and I’m still searching.

    As for performance … my W5GI Mystery Antenna was matched up against a 43-foot vertical as well as a Butternut HF9V that I’ve tried over the years and it outperformed both of them. Especially related to suburban noise levels … which verticals seem to attract … especially in noise-laden suburban municipalities.

    A great antenna the Joe – K4TR Antennas makes an excellent quality product.

    Cheers,

    Nolan K.
    KI5IO

  30. Hi Simone, ref the 1w5di could I use a 9-21 balan in stead of the 450 wire and feed with rg58, regards ken m3zkb = the double bazooka is 2 s pionts up on a h/w dipole on 7 megs

  31. I am thinking about building one of these and I do have a grounded tilt down mast available, the question I have… does the 450 ohm ladder line have to be isolated from the mast or can it be connected to the Mast , or is it impossible to use?

  32. the w5g1 looks good, but would a 9 to 1 [450] balun work instead of the ladder line which is 450 ohm also as I DONT LIKE or have any ladder line ken m3zkb

  33. having built the w5g1 using a co ax feed the swr ave from 14 right up to 50 megs at 1,5 to 1.9 at 80 and 40 its 2 to 2,4 so tuning the ends might cure that , regards ken m3zkb

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