In Pursuit of the Top Band: Brian describes how he built and tested a field-portable 160 meter EFRW antenna

Many thanks to Brian (K3ES) who shares the following guest post:

The VK160 Antenna packed on its Winder/Feedpoint for storage, transport, and deployment.

Building and Testing the VK160 Antenna

by Brian (K3ES)

The ability to set and achieve long- and short-term goals keeps me interested and active in the Parks on the Air (POTA) program.  Often these goals are associated with POTA awards.  Currently, I am working slowly to complete the activator version of the James F. LaPorta N1CC award, which requires an activator to make QSOs on 10 amateur bands from 10 different parks.  With my operating style, I have found it achievable to make QSOs on the 9 available HF bands (80m, 60m, 40m, 30m, 20m, 17m, 15m, 12m, and 10m), and this has become easier with the rising solar cycle.  I have completed QSOs on non-HF bands using 2m and 70cm simplex.  The other options to pick up 10th band QSOs include the 6m band and the 160m band.

I have found it difficult to make unscheduled POTA contacts on 2m and 70cm, and scheduled contacts can be difficult to arrange in parks that are remote from population centers.  I have built a 6m antenna, but contacts are seasonal (and for me very elusive).  So I started looking for a way to add 160m capability to my portable station.  Ultimately that resulted in homebrewing a new antenna that I now call the VK160, and here is its story.


I needed a field-deployable 160m antenna.  My operating style requires that the antenna system be both light and compact.  QRP power levels are sufficient for my purposes.  I am very comfortable deploying wire antennas in the Pennsylvania woods, and QRP wire antennas can be both light and compact.  I have found that end-fed antennas are simpler to deploy in the field, because they can be configured as an inverted V or as a sloper, using only one point of support.

An end-fed half wave (EFHW) antenna would be naturally resonant, but would need to be over 250 ft (76m) long.  A wire antenna of that length would be challenging to deploy, even in more open areas.  So, I decided to pursue a 9:1 unun-based end-fed “random wire” (EFRW) antenna.  In fact, I have two commercial EFRW antennas available, but have never been successful in tuning them for 160m using the ZM-2 tuner in my field kit.  So, I concluded (probably incorrectly, but more on that later) that I needed to build a 9:1 random wire antenna with a longer radiating element than the 71 ft wire built into my largest existing EFRW.  I also wanted to build this antenna myself, using available components, so that it would be both inexpensive and customized to my needs.

I broke the task into four parts:

First, I needed to build a 9:1 unun suitable for use at QRP power levels.  The 9:1 unun is an autotransformer that reduces antenna feedpoint impedance by a factor of 9, hopefully a level that a wide-range tuner can match to the 50 ohm transceiver impedance.

Second, I had to design and build mechanical elements of the antenna system, incorporating the electrical components needed for the feedpoint.

Third, I needed to select a suitable non-resonant wire length for the radiator.

Finally, I needed to deploy and test the finished antenna on the air.  If successful, testing would culminate in completing an on-air QSO with the antenna being driven at 5 watts or less.

Building the 9:1 Unun

While I have built successful 49:1 ununs as the basis for EFHW antennas, I had no experience building 9:1 ununs.  Accordingly, I started with the ARRL Antenna Book, then a web search.  VK6YSF’s excellent web page provided very detailed instructions for 9:1 unun construction. His 9:1 Unun design was based on a FT140-43 toroid wrapped with heavy gauge magnet wire, with design power rating around 100 watts.  My application was focused on 10 watts maximum, and I wanted a lighter-weight solution to the unun design.

Looking at the components I had available, I found FT50-43 toroids and 24 AWG magnet wire in my inventory.  I had used those during construction of successful 49:1 EFHW antennas.  The VK6YSF design, built with the smaller toroids and lighter magnet wire, seemed to be a good (and cheap) starting point.

The “50” portion of the FT50-43 toroid designation specifies its 0.50 inch (1.27 cm) outside diameter.  The “43” portion designates nickel/zinc composition that is suitable for high frequency inductive applications.

The next problem that presented itself was a problem with translating the winding technique to smaller wire and a smaller toroid.  Put simply, my fingers do not have the dexterity to wrap three parallel 24 AWG wires around a ½ inch OD toroid without getting them crossed, twisted, or worse.  So, why not twist the three conductors from the start, and wrap the toroid with “trifilar” windings?  It would be simple enough to identify the mating wire ends after wrapping, just with a set of continuity tests.  That would facilitate proper connection of the wires to yield the final auto-transformer configuration.

FT50-43 toroid with three-10 inch (25.4 cm) segments of 24 AWG enameled magnet wire staged for construction of the 9:1 unun.

I posed the “trifilar” winding question to my friends over on the discussion board.  Nobody identified a significant flaw with the proposed method, but neither did anyone have experience that would assure success.  So, I decided to use the “trifilar” winding technique to construct my 9:1 unun, with the full recognition that its success would be uncertain, and only proven by testing the finished product.

In the end, I found that 10 “trifilar” turns fit neatly on the FT50-43 toroid, so that is how I assembled the final component.

FT50-43 toroid with three segments of 24 AWG enameled magnet wire twisted together to support wrapping the toroid with the trifilar conductors.
FT50-43 toroid partially wrapped (3 turns) during construction of the 9:1 unun.
Completed 9:1 unun, the FT50-43 toroid was fully wrapped with 10 turns of trifilar magnet wire.

Mechanical Design

One of the antennas I purchased commercially is a Packtenna 9:1 EFRW.  I have always marveled at KJ6VU’s elegant design, where the circuit board for the electrical components is also shaped to serve as a wire winder.  Without the sophistication to build my antenna feedpoint directly onto a circuit board, I still recognized the wisdom of attaching feed point circuitry to a wire winder for ease of deployment, retrieval, and transport of the antenna.  I planned to repeat the successful format of using a combination feedpoint/winder (FPW) with the new antenna build.

The completed VK144 antenna wrapped on its feedpoint/winder (FPW).  The FPW is propped up on a small plastic box to improve the view of the BNC female connector.

With my first antenna projects, I searched for suitable and easily-formed construction material from which to assemble the FPW.

Among the materials in my shop, I found some pieces of 1/16” transparent acrylic sheet left over from a previous project.  With a bit of experimentation I have found that this material serves quite well in constructing antennas.  It can be cut, sanded, drilled, and solvent-glued, and it can also be formed into convenient shapes by softening with a heat gun, and bending while soft.  I retrieved some acrylic sheet and set to building.  I built FPW longer normal to minimize the number of wraps needed to store the radiating wire, since I expected the wire to be more than double the length of any of my other antennas.

The FPW body is about 12 inches (30 cm) long.  It has U-shaped notches at each end and a relief cut along one side to simplify winding the wire in a figure-8 pattern, which prevents tangling during antenna deployment.

This view of the FPW body shows overall configuration, but with damage from a deployment accident that caused one side of a winding notch to break off.  Repairs were simple, and are discussed below. (Click to enlarge)

I attached the electrical components to the FPW.  This included mounting the female BNC connector to an acrylic bracket that was heat-formed into an L-shape, then solvent-glued to the winder.  This bracket also served as an anchor point for the 9:1 unun and for two miniature banana jacks used to electrically connect the radiator and counterpoise wires.  Once the wiring of all components was complete, I applied a generous amount of hot melt glue to secure and weatherproof the electrical components and connections.

This view of the BNC-side of the L-shaped bracket shows the attached electrical components.  The BNC connector is mounted through a hole in the bracket.  The miniature banana jack for connecting the radiating wire is located above the BNC connector on the back side of the bracket.  The toroid is also attached to the back side of the bracket to the right of the BNC connector.  To the right of the bracket, on the body of the FPW, is a split ring with a small carabiner, used to support the FPW when deployed.
This view from the back side of the L-shaped bracket shows the toroid, soldered connections on the BNC connector, and the miniature banana jack for the radiator.  The whitish material covering many of these components is hot glue applied both for structural attachment and weather proofing.  Below the angle bracket, and attached to the underside of the FPW is a second miniature banana jack available for connection of counterpoise wires.

In attaching the radiator to the antenna feed point, I consider it essential to provide strain relief.  Drilling 3 or 4 small diameter holes through the acrylic sheet structure, then stitching the wire up and down through those holes, supports any load on the wire without stressing the electrical connection.  I used the same method to attach the far end of the antenna wire to a small link cut from acrylic sheet that supports it when deployed.  The FPW and the link have drilled holes holding split rings with small carabiners for quick attachment to ropes, trees, or other support structures during deployment.

The feedpoint end of the radiator wire is shown ready for installation on the FPW.  The wire is terminated with a miniature banana plug, with the connection covered by red heat shrink tubing.  Visible above this plug are four holes through the FPW that are used to form the mechanical connection and strain relief for attachment of the radiator wire.
The feed-point end of the radiator wire has been stitched through the strain relief holes in the FPW, but not yet tightened.  The miniature banana plug is positioned for connection to its jack.
The finished radiator wire connection to the FPW has the miniature banana plug fully inserted into its jack, and the stitching of the wire through strain relief holes has been tightened.  This method of connection was adopted to enable easy swapping between different length radiator wires, should that become necessary.
The far end of the radiator wire is stitched through holes on a small link cut from acrylic sheet, in a manner similar to the strain relief provided for its connection to the FPW.  This link also contains a hole with a split ring and small carabiner to support the end of the wire when deployed.

I broke the FPW when I deployed the antenna for Winter Field Day (WFD).  I tossed it across a 10 foot (3m) section of frozen pond to avoid walking across the thin ice, and it hit the base of a sapling on landing, and the side of one of the winding notches broke off.  The break resulted from impact combined with the acrylic being brittle from the cold.

The damage prevented wire from being wound onto the FPW, so mechanical repair was necessary.  This repair consisted of gluing additional layers of acrylic sheet across the broken end, reinforcing it and providing sufficient material to rebuild a notch.  A bit of hand-work with a file created the new notch, so that the FPW could again be used for storing the radiator wire.

The end of the FPW has been re-built by gluing additional thicknesses of acrylic sheet over the broken end.  The winding notch was re-formed by hand-filing the reinforced material to shape.

Selecting the Radiator Length

The “random wire” to be paired with a 9:1 unun can be better described as a non-resonant wire.  Recall that a resonant wire fed at its endpoint has very high impedance, the reason that EFHW antennas use an unun with 49:1 or greater impedance transformation ratio.  For a non-resonant end-fed “random” wire (EFRW) the length must not be resonant on any of the bands of interest, or the 9:1 transformation ratio would be too small to permit matching with most available antenna tuners.  This means that the selected length must be neither a half wavelength, nor an integer multiple of a half wavelength, on any of the bands of interest.

My intent was for this antenna to function on all amateur bands from 160m to 10m.  To improve the likelihood of success, I restricted my focus to the CW portions of those bands.  Table 1 (below) presents the key elements of the analytical method, along with the analysis results.  The first column identifies the band of interest.  Columns 2 and 3 specify the maximum and minimum frequencies in MHz.  Wavelength calculations are based upon the standard dipole formula:  λ/2 [feet] = 468 / f [MHz].  Columns 4 and 5 present the minimum and maximum half-wavelengths associated with the CW frequency interval (all lengths in Table 1 have units of feet).

Further analysis is based upon a target radiator length range of 130 – 150 ft.  Column 6 presents a series of integer values (n) for each band for which nλ/2, (n+1)λ/2, and sometimes (n+2)λ/2 bound the target range for radiator length.  Column 7 and 8 present the minimum and maximum, respectively, of nλ/2 for each resonant interval being examined for that band.  Finally, Columns 8 and 9 present the usable minimum length [nλ/2max] and usable maximum length [(n+1)λ/2min] for that band in the target range (130 – 150 ft).

By taking the maximum (across all bands) value of Usablemin and the minimum (across all bands) value of Usablemax, an all-band non-resonant interval of 139.0 – 148.8 ft emerges.  I selected my radiator length as 144 ft, the midpoint of that interval.

I fabricated the radiator from 26 AWG PolyStealth antenna wire, a strong, light-weight material which has served me well with past antenna builds.  I cut a 144 ft length, and soldered on a miniature banana plug that mates with the radiator jack built into the FPW.  Using a banana plug provides the option to easily replace the radiator wire with one of a different length, if necessary for this experiment, or to meet a future need.

I provided the option to add a rapidly-deployable counterpoise system to the antenna, enabling adjustment of the antenna tuning characteristics, if necessary.  I arbitrarily cut three 17 ft lengths of 26 AWG PolyStealth wire and soldered them together into a miniature banana plug that mates with the counterpoise jack on the FPW.  During testing, this counterpoise system was always installed, with the three wires spread out on the ground, radially from the FPW.

Table 1:  Analysis of Non-resonant Length Windows Between 130 ft and 150 ft

(f in MHz, and lengths in feet)

Band fmax fmin λ/2min λ/2max n nλ/2min nλ/2max Usablemin Usablemax
160 2.00 1.80 234.0 260.0 1 234.0 260.0 0.0 234.0
80 3.60 3.50 130.0 133.7 1 130.0 133.7 133.7 260.0
80 2 260.0 267.4
60 5.41 5.33 86.6 87.8 1 86.6 87.8 87.8 173.2
60 2 173.2 175.5
40 7.13 7.00 65.7 66.9 1 65.7 66.9 133.7 197.1
40 2 131.4 133.7
40 3 197.1 200.6
30 10.15 10.10 46.1 46.3 2 92.2 92.7 139.0 184.4
30 3 138.3 139.0
30 4 184.4 185.3
20 14.15 14.00 33.1 33.4 3 99.2 100.3 133.7 165.4
20 4 132.3 133.7
20 5 165.4 167.1
17 18.11 18.07 25.8 25.9 4 103.4 103.6 129.5 155.1
17 5 129.2 129.5
17 6 155.1 155.4
15 21.20 21.00 22.1 22.3 5 110.4 111.4 133.7 154.5
15 6 132.5 133.7
15 7 154.5 156.0
12 24.93 24.89 18.8 18.8 6 112.6 112.8 131.6 150.2
12 7 131.4 131.6
12 8 150.2 150.4
10 28.30 28.00 16.5 16.7 7 115.8 117.0 133.7 148.8
10 8 132.3 133.7
10 9 148.8 150.4

Testing the Antenna System

With the antenna build complete, I made two attempts at testing.  The first, which was not fully successful, involved deploying it in the back yard, and attempting to tune it using my Emtech ZM-2 QRP tuner.  I used my conventional inverted-V configuration with the apex up about 30 ft (9m), and I deployed three-17 ft counterpoise wires on the ground around the feedpoint.  I set up my Lab599 TX-500 Discovery with the ZM-2 in the feed line, and went through the following tuning routine on each amateur band from 10m to 160m.

I first adjusted the ZM-2 controls to maximize the volume of received noise.  Next, on a clear frequency, I switched the ZM-2 to its tune mode, sent a continuous tone signal from the TX-500, and adjusted the ZM-2 controls to minimize brightness of its tuning LED (ideally the LED went fully dark).  Following adjustment, I switched the ZM-2 back to operating mode, and noted the SWR level indicated on the TX-500, and stopped sending the tone.  On all bands, the indicated SWR was 1.5:1 or less (often 1:1), with one exception.  I was unable to achieve an acceptable tune on 160m.

When deploying the antenna as an inverted-V, I use an arborist throw line (shown at the top of the picture). A shot-filled throw bag at the end of the line helps to launch the line over a tree limb for support.  I leave the throw bag (shown in the middle of the picture) attached to a loop of line that runs around the middle of the antenna wire (shown on the left and right of the throw bag in the picture).  The throw line can then be used to pull the bag and the midpoint of the antenna wire up to a point below the tree branch.  I leave the bag attached, because the added weight simplifies lowering of the antenna wire for retrieval.
The Lab599 TX-500 Discovery 160m to 6m QRP Transceiver paired with its speaker-mic and a BaMaTech TP-III CW key.
Emtech ZM-2 Z-match tuner for amateur bands from 80m to 10m.  It is rated for 15 watts.

The ZM-2 performed flawlessly in its specified frequency range, comprising amateur bands from 80m to 10m.  Using the ZM-2 to tune the 160m band was a bridge too far, so an alternate solution was required.  I had hoped that the ZM-2 might achieve an acceptable tune on 160m with the longer 144 ft radiator wire, where it had been unsuccessful tuning 160m with my 9:1/71 ft random wire antenna.

I thought the experiment was worth trying, because the ZM-2 is light, robust, and requires no power beyond the transmitted RF signal for operation (all features that are beneficial for portable operations).  But alas, it was not to be.

For the next test of the new antenna, I brought out my LDG Z-11Pro II autotuner.  It is a wide-range tuner rated for 100 watts on amateur bands from 160m to 6m.  While not as light as the ZM-2, the Z-11Pro II works well for portable operation.  It requires power for operation, but can run on an internal AA battery pack, or can be powered by the same 12V LiFePO4 battery that powers the radio.

LDG Z11-Pro II wide-range autotuner for amateur bands from 160m to 6m.  It is rated for at least 100 watts across all bands.

With Winter Field Day coming up, I decided to take a risk and use it as an opportunity to deploy, test, and hopefully operate with the new antenna.  Once again I set it up again as an inverted-V, but this time with the apex only 20 feet (6m) in the air.  Again, I used three-17 ft counterpoise wires arranged on the ground around the feedpoint.  This test was more than successful, ultimately giving me cause to name the new antenna VK144.  The details of my Winter Field Day operations were reported in a previous Field Report, linked here: Brian puts a new antenna to the test during Winter Field Day!

Here, suffice it to say that I successfully tuned the antenna for operation on 10m, 15m, 20m, 40m, 80m, and 160m.  Further, I made successful WFD contacts on all bands except for 160m.  Due to the concurrent CQ 160m contest, I made a successful 160m contact with a contest station rather than a WFD station.

For Winter Field Day operation, I also included a SWR and Power Meter in the antenna feedline.  I monitored power to assure that I kept it within QRP limits.  This device, manufactured by Monitor Sensors, is capable of 5% accuracy over most of its extensive range (10mW to 2000 Watts).


Some of the electrical components used in construction of the VK144 antenna.  Clockwise from the top right:  miniature banana jack and plug, Female BNC connector, FT50-43 toroids, and 24 AWG enameled magnet wire.

I am very pleased with the performance of the VK144 / Z-11Pro II autotuner antenna system.  I will be looking for opportunities to put it on the air to get 160m contacts from POTA parks, furthering my slow pursuit of the James F. LaPorta N1CC Activator award.  I really hope my story has demonstrated that building your own antenna is achievable, rewarding, and fun.

If I can do this, you can too!

Materials List

Following is a list of the specific materials that I used to build the VK144 antenna.  I have successfully used it to make CW contacts on HF and 160m amateur bands at QRP power levels.  Other methods and solutions are numerous, limited only by your imagination and ingenuity.

  • 1/16 inch (1.5mm) transparent acrylic sheet (Plexiglas®) as FPW structural material
  • Solvent for acrylic welding (use with caution, according to manufacturer’s instructions)
  • female BNC connector
  • 2-miniature banana plugs and 2-mated jacks
  • FT50-43 toroid
  • 24 AWG enameled magnet wire
  • 26 AWG PolyStealth antenna wire
  • Flux-core solder suitable for electronic use
  • Hand tools for measurement, fabrication, and soldering

Best 73 de Brian – K3ES

18 thoughts on “In Pursuit of the Top Band: Brian describes how he built and tested a field-portable 160 meter EFRW antenna”

  1. Great post Brian, very detailed. Thanks.
    I’m not sure my eyesight and finger dexterity would work well for a toroid that small. I wish someone sold just the wrapped toroid ready for installation. I think there is a market for that.
    I am a big fan of the random wire antenna even though they require a tuner. I like the versatility of being multi band and for some reason they just feel better to me than the EFHW that everyone seems hooked on. I have both but like I said, the EFRW just “feels” right to me. Kind of like Thomas’s speaker wire antenna.


    1. I am right there with you, Marshall! I really like my EFRWs. Especially with the KX-2 – frequency agility with the push of a button! Of course that doesn’t work for 160m, because it’s not a KX-3.

      73 de Brian – K3ES

      1. I only have the IC-705 and it does do 160.

        But I am really tempted to find someone interested in trading a KX2 for my 705. Trying to decide if I would regret it.

        73 de W4MKH

  2. Great article Brian and excellent detailed description. I have found that 1/8″ linen or canvas micarta makes a durable wire winder useful in very cold climates.

  3. Brian, this is truly an outstanding article. Thank you so much for all of the detail you include with your build. This has inspired me to build an antenna for the top band as well! I love the challenge you’ve made for yourself this year for POTA. Please let us know how that comes along!

    Thank you again!
    Thomas (K4SWL)

  4. Brian,

    Great project! I am working on a portable 100W EFHW for 160 to use in the upcoming CQ160M SSB contest and can see a use for those inline miniature banana connectors. What is a good source for those? All the ones I can find so far are for panel mounting.

    Henry – K4TMC

  5. I have a Chameleon QRP EFHW that is supposed to do 160 to 6, though it was a limited run. I’ll set it up and do a field report with the ft818 soon.

  6. Im sure that many hams appreciate your terrific instructions and the time you spent with all the photos, table, detailed steps and background for this antenna project. My geeky mind craves all the information.
    You join another talented Pennsylvanian, WA3RNC, in his artful design of the TR-35 QRP XCVR. His circuit design and packaging are terrific. Growing up in New Jersey, I didn’t know what youse guys in the woods were capable off. I am not as adventurous as I once was, so I only hike out to the local Silicon Valley parks and I enjoy these QRP adventures.

  7. I built homebrew 9:1 ununs based on the EARCHI (Emergency Amateur Radio Club of Hawaii) design: .

    I use one 9:1 unun with roughly 125 feet of wire at the home QTH and easily tune up 160 meters and other HF bands. In the last CQ 160m contest I put my ICOM 703 plus on the air to test it out at QRP levels. I easily made 10 contacts in a short time while operating in the contest. Full disclosure – I forgot to turn the power down so I was running a “blazing” 10 watts on CW.

    My second 9:1 unun is used with a 25 to 35 foot long wire and a fiberglass pole as well as one or two 16 foot counterpoise wires. It tunes up nicely on 40M thru 10M using a tuner. This setup works for “park bench portable” adventures.

    PS. You probably want to stay away from this website unless you want to become addicted to QRP, It will make you want to buy more equipment too. Thomas does an EXCELLENT job with all of it. I don’t currently do POTA/SOTA but I feel myself being pulled into the K4SWL vortex.

    1. Thanks Bob,

      LOL. Building my own antennas lets me do things on the cheap! That way I save my money to buy new QRP radios… 🙄

    2. Thank you for that info Bob! And thanks for the warning to others (ha ha!)–I hate to take people down the path of QRP addiction! (Actually, no I don’t!) 🙂


  8. Thanks Bob,

    LOL. Building my own antennas lets me do things on the cheap! That way I save my money to buy new QRP radios… 🙄

  9. A quick update…
    I put the VK144 on the air in Allegheny National Forest (K-0619) at 0000Z 24-Feb-2023. In about 15 minutes, I was able to make three POTA contacts on 160m, giving me my 10th activated band at the park.

    73 de Brian – K3ES

  10. Brian & all,

    I just completed my back yard test of the VK160 with great success. I made 14 FT8 QRP contacts on 160 meters as far away South Carolina (I’m in CT) and better yet, was able to make contacts on 80, 40, 30, 20 & 17 meters. I installed it as a sloper, with the feed point at the top of a 20′ fiberglass mast and secured at the other end with an electric fence post. Next stop is a park for a POTA activation! Thomas, I think another field report may be heading your way.

    73 all and thanks again to Brian for his excellent idea!

    1. Excellent, Paul! I am pleased you tried out the design, and very happy it worked well for you.


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