Projects – WB3GCK QRP Amateur Radio

Covering More Bands with My 12-ft Whip

Back in 2017 I built my 19-foot wire vertical, which was my go-to portable antenna for about 4 or 5 years. The concept was simple: It functions as a base-loaded resonant vertical on 40M & 30M and as a random wire on 20M and up. The matching unit contains a tapped toroid for 40M & 30M and is fed through a built-in 1:1 choke. It occurred to me I could do something similar with the 12-foot telescopic whip and homebrew loading coil I’ve been using on my truck of late.

My 12-foot whip setup is resonant on 40M through 17M. You’re probably thinking: “Why not just bypass the loading coil and adjust the length of the whip for 15M through 10M?” Well, being as lazy as I am, that would make band changes a little more involved than I want to deal with. I like having some “frequency agility,” and I’m not above using an ATU to achieve that.

To emulate the scheme I used for the 19-foot vertical, I just needed a choke at the input to my homebrew loading coil. (I could probably go without the choke, but I wanted to keep the coax from becoming part of the antenna.) So, I use the 12-foot whip as a base-loaded resonant vertical on 40M through 17M. For 15M through 10M, I would bypass the coil and use an ATU.

To test this out, I threw together a choke using parts I had on hand. I wound 10 turns of RG-174 on an FT-140-43 toroid. A Radio Shack project box I had in my stash of parts was the perfect size to house the toroid. (I bought it a decade or two ago, and it was still unopened in the original Radio Shack packaging.) Since I installed SO-239 connectors on each end, I had to use an adapter to connect the choke to the SO-239 on the antenna. To hold the coil in place, I wedged a piece of foam packing material between the lid and the core. The completed choke is functional, albeit a little cheesy-looking.

The choke is 10 turns of RG-174 coax on an FT140-43 toroid.

My first test using the 12-ft whip on the higher bands was a success. While activating Ridley Creek State Park (US-1414, KFF-1414), I used my KX3 (5 watts, CW) and installed the choke at the antenna feedpoint. On 40M through 17M, the loading coil functioned as it normally does. On 15M, 12M, and 10M, I bypassed the coil entirely and relied on the KX3’s internal ATU to load up the whip.

The choke installed at the antenna's feedpoint — The choke installed at the antenna’s feedpoint

The KX3 easily found matches on all three bands, and my results on the air were encouraging. On 15M, I worked stations in Poland, Belgium, France, Ukraine, Germany (3), and the Slovak Republic. I made two stateside contacts on 12M. Up on 10M, I worked some more DX: Germany (2), Italy, and Czech Republic. One of the German contacts was park-to-park.

I’ve used this arrangement on a few more activations since then, including Winter Field Day. My results have been consistently good.

I haven’t done any modeling, but the 12-foot whip seems to be a pretty good length for operating like this. It’s just a little longer than a ¼-wave on 15M and a little shy of ⅜-wave on 10M. On 12M, it’s somewhere between ¼ and ½-wave; so it isn’t resonant on any of the bands of interest.

Although I was pleased with these initial results, I might do a little more tinkering with this setup. I’m toying with repackaging the choke to make it a little more weather resistant. I encountered some rain during the first activation using it. There was no damage to the choke at all, but I always have a tendency to over-engineer things—it keeps me occupied and out of trouble, I suppose.

No scientific breakthrough here. Just a lazy guy “force feeding” a fixed length whip to squeeze a few more bands out of it.

72, Craig WB3GCK

Adding Radials to a Mag Mount

Reading through some blog posts recently, I came across an interesting idea from John AE5X. In the comments section of a recent post, John mentions adding a ground stud to a magnetic mount. The ground stud allows him to connect two ¼-wave radials (for 20M) for his MFJ-1979 telescopic vertical. So what follows is my implementation of John’s clever idea.

On occasion, I’ve used my Gabil GRA-7350TC vertical with a small magnetic mount salvaged from an old 2M/440 antenna. I plan to use this configuration on my (far) better half’s car while visiting family over the holidays. The mag mount is only 3.5 inches in diameter, so I’m sure it’s not providing much of a ground connection. While the Gabil vertical is certainly usable with this mount, I’ve always felt that it needed more of a counterpoise on 40M and 30M to obtain a better match. I figured John’s idea might be the way to go.

Since I needed to drill a hole from inside the mount, I had to remove the foil covering from the bottom of the mount. This magnetic mount is probably around 25 years old, so removing the foil wasn’t too difficult. Using my pocket knife, I was able to peel the foil off, while keeping it intact.

Next, I drilled a ⅛-inch hole through the ground plate and out through to the top of the mount. It was a tight squeeze, but I was able to get a 4-40 bolt and a star washer in there. On the outside of the mount, I used a nut and lock washer.

Interior view of the magnetic mount. It was a tight squeeze, but a 4-40 screw and star washer just fit in there. — Interior view of the magnetic mount. It was a tight squeeze, but a 4-40 screw and star washer just fits in there.

The final step was to re-apply the foil covering on the bottom of the mount. I used some rubber cement to reattach it. I don’t know how well the rubber cement will hold up over time, but it won’t be seeing heavy use. It seems fine so far.

Exterior view of the old magnetic mount. I later removed the second nut from the screw I installed.

While I was at it, I replaced the PL-259 connector. The years had not been kind to the connector that was on there.

I gave the modified mag mount a try during a recent activation at US-1380, KFF-1380. I used the GRA-7350TC and mag mount on the roof of my truck. With no counterpoise wire attached, the best match I could get on 40M was just a hair under 3:1.

Next, I attached a 33-foot counterpoise wire to the mag mount. I ran the wire off the back of the truck and onto the ground. To avoid creating a trip hazard for others, I wrapped the wire around the side of the truck. In this configuration, I got the SWR down to about 1.2:1. Success!

The Gabil GRA-7350TC and magnetic mount with one 33-foot counterpoise attached. The wire dropped to the ground behind the truck and wrapped around the side.

Using the same counterpoise, the best I could do on 30M was a little under 2:1. I tried two 16.5-foot wires, but the result was about the same. No worries. An SWR of 2:1 is a piece of cake for the Elecraft T1 tuner.

In this configuration, I had two 16.5-foot counterpoise wires attached.

I ran the entire activation on 40M and 30M with great results (40 contacts in less than an hour). In fact, it was the best I have done with the Gabil antenna and mag mount. Was it because of the counterpoise wire? Maybe. Regardless, my five-watt signal was getting out just fine with this thing.

Thanks again to John AE5X for the inspiration.

72, Craig WB3GCK

No Counterpoise Speaker Wire Antenna

It’s been a while since I’ve done a cheap speaker wire antenna, so here’s another one for you. Back in the early to mid-2000s, an antenna commonly referred to as the “No Counterpoise Antenna” was making the rounds on the Internet. I thought I might give it another look.

The No Counterpoise Antenna is either a 25-foot or 50-foot length of two conductor wire with half of one conductor removed. Essentially, it’s a radiator fed through a balanced line feeder. The 25-foot version is said to cover 20M through 10M, while the 50-foot version is supposed to cover 40M through 10M. It was usually connected to a balanced tuner of some sort or sometimes fed through a 4:1 balun. It was typically constructed from zip cord or speaker wire. So, this is perfect for another speaker wire project. (Actually, I built the 50-foot version years ago, but I don’t recall ever putting it on the air.)

A picture is worth a thousand words, so here goes:

I’ve seen this antenna sometimes referred to as a Zepp. A true Zepp is basically a half wave radiator with a quarter wave balanced line matching section. Unlike a true Zepp, the No Counterpoise Antenna is non-resonant, so I guess it’s actually “Zepp-ish.” Because it’s non-resonant, a tuner is required for this antenna.

I did some extensive research into the origins of this antenna. (OK… I just did a few Google searches.) Jeff Imel K9ESE came up with this design. I remember Jeff used to sell a high-quality version of the antenna on eBay. The reviews were generally positive.

Pete Millis, M3KXZ, is another name often associated with this antenna. I think that’s how I first came across it. Pete once made a phased array from two 25-foot versions.

In the August 2020 edition of Ozark QRP Banner, the Four State QRP Group’s newsletter, Terry Fletcher, WAØITP, had a nice write-up about it. He discusses his experience with both the 25- and 50-foot versions.

This antenna design has been around the block a time or two. So, there’s no innovation here on my part whatsoever.

Construction

I happened to have a 25-foot roll of #18 awg speaker wire on hand, so this time around, I opted to build…you guessed it… the 25-foot version.

Construction was about as easy as it gets:

I split the speaker wire halfway and cut off one side
Next, I twisted a loop at the end of the single wire and secured it with some Goop® adhesive. As an alternative, you could just tie a loop at the top or crimp a ring lug over the wire’s insulation.
I stripped and tinned the wires at the feedpoint and installed spade lugs. You can just strip and tin the wires, if you like.
To keep the speaker wire from splitting further, I put some heat shrink tubing a couple of inches up from the lugs. I also added a dab of Goop® in the middle of the antenna where one side of the wire was removed. All of this is completely optional.

Construction probably took me all of 15 minutes or so. That doesn’t include allowing the adhesive to cure overnight. However, the antenna was certainly usable without the adhesive and heat-shrink tubing I used. I’m just prone to overkill.

On the Air

To test the No Counterpoise Antenna, I drove down to Ridley Creek State Park (US-1414, KFF-1414). Using my drive-on mount, I supported the antenna from a 28-ft Jackite pole. I used a homebrew 4:1 unun at the feedpoint and ran 15 feet of coax into the cab of my truck to my KX3 (5 watts, CW). I used the long side of the antenna as the radiator.

I used my roll-on mount to support a 28-ft Jackite pole

Before I got started, I checked to see how the tuner in the KX3 would handle the antenna. The KX3 easily found a 1:1 match on all bands from 40M through 10M. Just for the heck of it, I tried 60M and 80M. The KX3 was able to find a good match on those bands, too. (That’s not too surprising, given that I once forgot to attach my coax to an antenna, and the KX3 still found a match.) I doubt this antenna would work well on 60M and 80M—but stranger things have happened. I wasn’t able to try it, but I’m sure the KX3 would be able to match it directly connected to the radio without the 4:1 and coax.

Band conditions weren’t very good, so this wasn’t an ideal test. Despite the mediocre band conditions, I logged 13 contacts during my short activation. Most of my contacts were on 40M. There was considerable fading on 30M and 20M, but I made a contact on each of those bands.

This was hardly a rigorous evaluation, but the 25-foot No Counterpoise Antenna got the job done. I need to give it another try, when conditions are better.

Anyway, if you have some speaker wire and a few minutes to spare, give this one a try and see what you think.

72, Craig WB3GCK

Drive-on Antenna Mount Article

Back in December, Becky Schoenfeld W1BXY, Editorial Director for ARRL’s On the Air magazine, asked me if I would be interested in writing a detailed set of step-by-step instructions for my Drive-on Portable Antenna Support. Naturally, I said I would.

I submitted my manuscript, along with an all-new set of pictures. The article was published in the current issue (May/June 2024) of On the Air (pages 20-22).

If you’re interested, have a look. ARRL members have access On the Air as part of their membership.

73, Craig WB3GCK

Junk Box Loading Coil

Whenever I buy parts for a project, I always buy one or two extras. Over the years, I’ve amassed a sizable collection of random parts. Some of it will never be used, but sometimes my collection of parts has just what I need for something I want to build. I like when that happens.

A while back I wrote about an old homebrew coil I resurrected and paired with a 12-foot telescopic antenna. The coil, while effective, was built to use with a much shorter whip and is larger than what I need. I scoured my junk box and came up with most of the parts I needed to build a scaled-down version.

I should note that I built this coil specifically to use with my old MFJ-1956 12-foot telescopic whip. In this configuration, this coil covers 40M through 17M. So, if you have a different whip or want to cover different bands, you’ll need to modify the design accordingly.

Completed loading coil. Used with a 12-foot telescopic whip, it tunes from 40M through 17M.

I used the old coil as a guide to determine the number of turns I needed to cover the bands of interest, adding two turns for good measure. Using an online shortened vertical calculator, I figured I would need about 13.4μH to load the 12-foot whip on the 40M band. Using an online coil inductance calculator, I estimated the total inductance of my coil to be 14.8μH. So, it covers 40M with a turn or two to spare.

The new coil assembly measures 8.25 inches end-to-end, making it 2.25 inches shorter than the old coil. While it’s about 3.3 ounces lighter than the old coil, this new coil still weighs in at a hefty 10.8 ounces.

Parts List

With a few exceptions, my junk box provided the parts I needed to build the coil.

5-3/8 inches of 1.5 inch PVC pipe
(2) PVC end caps for 1.5 inch PVC pipe
(4) pieces of nylon grommet edging, 3.25 inches each. (The material I used has about 8 notches per inch)
16 gauge bare copper wire, approx. 12.5 feet
(1) 3/8-24 coupling nut, 1-1/8 inches long
(1) 3/8-24 x 1-1/4 inch stainless steel bolt (bottom mounting stud)
(1) 3/8-24 x 1 inch stainless steel bolt (top bolt)
3/8 inch flat washers & lock washers
(2) #10 x 3/4-inch self-tapping screws
Approx. 6 inches of RG-174 coax
Small alligator clip
Misc: ring lugs for ⅜-inch & #10 screws

Construction Notes

As shown in the accompanying photo, I drilled the end caps to accommodate the ⅜-24 bolts. The 1-1/4 inch bolt was used for the bottom of the coil, along with a flat washer and a lock washer. The 1-inch bolt was used for the top, along with flat washer, lock washer, and the coupling nut.

This is the coil form with the four strips of grommet edging glued on. The ends were drilled to accommodate the 3/8-24 bolts.

The coupling nut was one item I didn’t have in my junk box. My local hardware store is well-stocked, but they didn’t have them with the ⅜-24 thread. I eventually found what I needed on Amazon. It was a little pricey, but I didn’t have any better options at the time.

After cutting the PVC pipe to length, I temporarily installed the end caps. Then, I cut four pieces of the grommet edging to length and glued them on, using Goop® adhesive. Unfortunately, I can’t provide a part number and source for the edging. A local QRPer, Ron Polityka WB3AAL (SK), gave me several pieces many years ago. I’m pretty sure Panduit was the manufacturer. My stash was nearly depleted, but I had enough left for this project.

Before assembling the end caps, I made two short jumpers, each with a ⅜-inch ring lug on one end, and a smaller ring lug on the other. Then I tightened everything up. I left about a ½ inch of thread on the top bolt to go into the coupling nut. I was careful to ensure that my whip antenna would fully thread into the coupling nut.

Before winding the bare wire on the coil form, I installed a ring lug on one end. I drilled a pilot hole in the side of the lower end cap and used a self-tapping screw as a connection point. When you wind the wire on the coil form, try to get the turns as tight as you can. (I didn’t do as good a job winding the coil as I would have liked.) Once I finished winding the coil, I cut the wire to length and installed a ring lug. I used some more Goop adhesive on the grommet edging to hold the turns in place.

The last step was to build the clip lead. For this, I used a piece of RG-174 coax. There’s nothing magical about the RG-174; stranded hookup wire would be fine. I used RG-174 primarily because of its flexibility, plus the shield would be a good RF conductor. (The center conductor was unused.) I crimped and soldered a ring lug to the braid on one end, and soldered an alligator clip to the braid on the other end. Then I used another self-tapping screw on the top end cap to connect everything together.

On the Air

I wrote about my initial tests of the coil in a previous post. Using an antenna analyzer, I determined where to place the tap for each of the four bands. I then used a permanent marker to mark these locations on the coil, so I can quickly change bands without resorting to the antenna analyzer.

This is the completed loading coil installed on my truck for a POTA activation.

With the antenna mounted on my truck, the SWR is higher than I would like on 40M and 30M. This is not unlike other shortened, base-loaded verticals I’ve used in this configuration. An additional counterpoise wire or two might help. Also, grounding the bottom of the coil and feeding it a couple turns up from the bottom would provide a precise match on the lower bands. I’ve used that technique in the past. That configuration , however, is a bit more complicated to implement, given the way I plan to use this coil. So, I just use a tuner to keep the radio happy, and the antenna seems to work fine.

Wrap-up

My older, larger coil worked fine; so technically, this project was unnecessary. But, since I had most of the parts on hand, what the heck. It was a fun project, and I’m sure it will see a lot of use in the future.

73, Craig WB3GCK

Repurposed Antenna Parts – Round 2

In a recent post, I wrote about a vertical antenna I put together with an old homebrew loading coil and a 12-foot telescopic whip. I intended to add some marks on the coil for each band, so I could eliminate the need for an antenna analyzer during band changes. This time, I actually remembered to bring a permanent marker and got it done.

I drove up to Evansburg State Park (K-1351/KFF-1351) this morning for a quick POTA activation. Before I got going, I used my antenna analyzer to determine the tap points for each band. I used a Sharpie® marker to mark the coil for 40M, 30M, 20M, and 17M. Since the coil has sufficient inductance to load the 12-foot whip on 60M, I also marked that band (the top-most mark on the coil). Before I started operating, I went back and checked each tap location to confirm repeatable results. Using a Sharpie marker is a decidedly low-tech approach, but it serves the purpose.

My homebrew loading coil. If you look closely, you can see the marks I added. As shown, the coil is tapped for the 30M band.

To change bands now, I just move the tap to the appropriate mark. I still use an antenna tuner to deal with any minor variations I might encounter. Now I can change bands in the time it takes to move the coil tap and hit the “tune” button on the tuner.

Despite the so-so band conditions this morning, the 12-foot whip performed well. In less than an hour of operating, I made 18 contacts. Most of my contacts were on 40 and 30. There were two park-to-park contacts I’m aware of.

The 12-foot base-loaded whip in use at K-1351

My operations were interrupted for a chat with a curious park ranger. I gave him my standard Parks on the Air spiel. He had encountered POTA activators in another state park, so he had some familiarity with the activity. After a few minutes, he left to look into a reported issue on one of the hiking trails.

So, I’m pretty satisfied with this antenna. It has a length advantage over my Gabil GRA-7350TC antenna. Comparing coil dimensions, I suspect it also has an efficiency advantage over the Gabil antenna.

Regardless, I now have another useful option in my antenna arsenal.

73, Craig WB3GCK

POTA with Repurposed Antenna Parts

While going through my stash of old parts, I came across a coil assembly I built over 20 years ago. Originally, it was part of a homebrew antenna inspired by the MFJ-1622 Apartment Antenna; but I used it over the years with a variety of whip antennas while “stationary-mobile.” As I moved on to other antennas for my portable operations, the coil was relegated to the junk box and forgotten—until now.

I also had an old MFJ-1956 12-foot telescopic whip that I haven’t used in years. It was stashed away in the basement waiting to become part of a new antenna project. Having just installed a ⅜-24 antenna mount in the bed of my pickup truck, I thought the coil and whip might work well with it.

The coil is a beast. It’s made from 1.5-inch PVC pipes and wound with bare copper wire—16 awg, I think. I used four strips of nylon grommet edging material to keep the turns evenly spaced. (I don’t remember where I got the grommet material, but it’s similar to this Panduit product.) The coil is about 5.4 inches long and 2 inches in diameter with 40 turns. Using an online calculator, I figured the coil is approximately 25.4 μH.

The homebrew coil I built more than 20 years ago.

The coil assembly weighs in at a hefty 14.1 ounces, and the overall length is 10.5 inches. The whip is 24 inches collapsed and weighs 9.6 ounces, so it wouldn’t be my choice for a backpacking antenna. However, on my truck, it should do fine.

Using another online calculator, I reckoned the coil should be more than enough to resonate the 12-foot whip on the 40M band and possibly the 60M band. Since the whip, coil, and mounting bracket all use ⅜-24 hardware; it was just a matter of slapping it all on the truck to see what how it would perform.

To test it out, I made a trip to Valley Forge National Historical Park (K-0761, KFF-0761) this morning. With a minor geomagnetic storm underway, the forecasted band conditions looked pretty dismal. I also got an early start, since we were expecting some severe storms around mid-day. So, I wasn’t expecting much, in the way of contacts.

I mounted the antenna on the back of the truck and broke out the antenna analyzer. It took a bit of fiddling to find resonance on 40M. The lowest SWR was around 3.8:1. That’s not great, but my little Elecraft T1 tuner handled it with no difficulties. On the air, I was getting some decent spots from the Reverse Beacon Network, and I made about 8 contacts before moving to 30M.

My homebrew coil and 12-foot whip mounted on the back of my truck.

The SWR on 30M was down to about 2:1. Again, the T1 made sure my TR-35’s finals stayed happy. I made one park-to-park contact on 30M before moving up to 20M

The SWR on 20M was about 1.3:1 across the band. I made another seven contacts here, before stopping to do some experimenting with the antenna.

I checked 17M and measured an SWR of about 1.2:1 across the band. I didn’t try to make contacts on 17M. Instead, I went back to 40M to pick up a few more contacts before shutting down.

I intended to bring a Sharpie® pen along to mark the coil for each band to speed up band changes. Of course, I forgot to bring one along. Oh well, I’ll do that next time. For 15M and above, I’ll need to bypass the entire coil and shorten the length of the whip accordingly.

The static crashes were getting louder, and I heard thunder off in the distance. So, I called it quits. Just as I shut the rig off, the heavy rains started. I quickly took down the antenna and packed up to leave.

Despite the lousy band conditions and heavy QRN, I ended up with 18 contacts. I had three park-to-park contacts today. And, as it turns out, this was my 20th POTA activation at Valley Forge, earning me a “Repeat Offender” award for this park.

It looks like this mash-up of antenna parts works pretty well. I’ll give it another shot in a few days. Hopefully, the weather and band conditions will be better.

72, Craig WB3GCK

Portable 4:1 UNUN

I recently came across a product on Etsy that caught my eye. It’s a 3D printed project box with an integrated antenna wire winder. I couldn’t resist, so I ordered one.

The Etsy vendor is 3dPrintedSolution, and they list the product as “EFHW End Fed Half Wave Antenna Radio Box.” While its name suggests they designed it with EFHW antennas in mind, I had a slightly different plan for it.

The box will accommodate a T-130 toroid, and the snap-on lid comes with a gasket. There is a pre-drilled hole for a BNC-F panel mount connector, and there are marks to guide drilling for the output and ground connectors of your choice. You can choose from two colors: orange or green. The vendor states that it is “UV and weather resistant.”

I like the idea of having a box to enclose the balun or transformer. My preference for portable antennas is to avoid exposed components or circuit boards.

I used mine to build a 4:1 unun for portable use in a Rybakov configuration. The unun consists of 19 bifilar turns of #24 solid hookup wire on a T130-2 toroid. You can find plans for winding the unun here and other places on the Internet. For the output and ground connections, I used #10-24×3/4″ stainless steel machine screws, along with some nuts, flat washers, and lock washers.

Inside view of the 4:1 unun. I used double-sided foam mounting tape to secure the toroid. I also use a small piece of packing foam (not shown) between the lid and the toroid for added stability.

To go along with the completed unun, I prepared two 26-foot wires; one for the radiator and one for a counterpoise. I finished up by attaching a length of 2.5mm bungee cord. This cord keeps everything together for travel. I have also used it to secure the box to a vertical support, e.g., fiberglass mast, fence post, etc.

The 4:1 unun deployed in a Rybakov vertical configuration with a 26-foot radiator and a 26-foot counterpoise

In the field, this Rybakov antenna worked as well as others I have built over the years. I tested it using my Penntek TR-35 and Elecraft T1 tuner with 18 feet of coax. It tuned up easily on 40, 30, 20, and 17 meters, and I made a couple of QSOs while testing. The integrated winder made it easy to deploy and take down.

I have a feeling another one of these boxes is in my future. Maybe a 9:1 unun next time?

73, Craig WB3GCK

Weather-Resistant 4:1 UNUN

One antenna I plan to try during my annual Outer Banks, North Carolina, vacation this summer requires a 4:1 unun. If the antenna works as hoped, it’ll be in place for the entire week. So, I need an unun that can stand up to the elements.

About a year ago, I built a 9:1 unun in a weather-resistant housing made from PVC pipe parts. I had some parts left over from that project, so I built a 4:1 unun version. The construction of this unun is like the last one, however, this one has a ground terminal.

I wouldn’t want to take this unun on a backpacking trip; it weighs in at a substantial 8.6 ounces. When I’m going to be operating from a location for an extended period, however, this should do the trick.

Parts

The parts for the housing are similar to the last one, but there are some additions for the ground connection.

About 2.5 inches of 1.5-inch PVC pipe
(1) 1.5-inch PVC end cap (slightly rounded top)
(2) 1.5-inch PVC end caps with flat tops
(1) SO-239 panel-mount connector (along with some #4 hardware for mounting)
A 4:1 unun wound on a T130-2 toroid
(2) #10-24×3/4″ stainless steel machine screw (along with some #10 flat washers, nuts, wing nuts, and lock washer)

The PVC end-caps with flat tops can be hard to find. If you search online for furniture-grade end caps, you might find some.

Construction

You can find plans for winding the unun here and other places on the Internet. The one I built for this project uses 19 bifilar windings of #24 solid hookup wire on the T130-2 toroid.

To start, you need to glue the two flat top end caps together. When dry, drill the holes to mount an SO-239 connector in the center.

The underside of the 4:1 unun. The SO-239 is recessed to provide some protection from the elements.

For mechanical reasons, I added the #10-24 stainless steel screw for a ground terminal in the lower half of the connector housing. A short length of wire runs from the ground screw through a small hole and connects to one of the SO-239’s mounting screws. I installed another #10-24 screw in the slightly rounded end cap for the antenna connection.

The final assembly was straight forward. I soldered the toroid’s input wires to the center pin of the SO-239 connector. Then, I attached the toroid’s ground wire to one of the SO-239’s mounting screws.

This is how the toroid is installed in the Weather-Resistant 4:1 UNUN.

Next, I inserted the PVC pipe section into the connector housing. I then installed a ring lug on the output wire. I left the output wire just long enough to make the connection to the output bolt in the rounded end cap. Before mounting the end cap to the PVC pipe, I added some pieces of foam around the toroid core to hold it in place. Then I press-fitted all the PVC parts together.

Testing in the Field

I tested the 4:1 unun in the field recently, and it performed as expected. I used it as part of a Rybakov vertical, with a 26-foot radiator supported by a Jackite pole, another 26-foot wire on the ground for a counterpoise, and 18 feet of RG-8x coax. My little Elecraft T1 tuner matched it with no problems on 40M, 30M, 20M and 17M, the bands covered by the rig I was using. Similar 4:1 ununs I have built worked well from 40M through 6M, so I’m confident this one will, too. While I was testing, I had a couple of nice CW rag chews on 40M and 30M.

The weather-resistant 4:1 unun in use. In this configuration, there's a 26-foot radiator and a 26-foot counterpoise wire. — The weather-resistant 4:1 unun in use. In this configuration, there’s a 26-foot radiator and a 26-foot counterpoise wire.

Wrap-up

Like its 9:1 counterpart, this unun is probably a bit over-engineered. My weather-resistant 9:1 has served me well through several camping trips and two Field Days, so I expect this 4:1 version will do likewise. So, bring on that beach weather!

73, Craig WB3GCK

Inside My Old Tuner

In a recent post, I wrote about an old antenna tuner I built about 25 years ago. Although a description of it has been online for decades, I never posted pictures of it. So, here it is.

I originally posted an article about this tuner on my QSL.net website under the title: A Simple and Flexible Tuner for QRP. Once my go-to transmatch for portable use, it had been on the shelf for quite a while. I hadn’t opened the case in 20 years, so it was a nostalgic walk down Memory Lane for me.

Schematic of the "Simple and Flexible Tuner for QRP." — Schematic of the “Simple and Flexible Tuner for QRP.”

All of the parts used for this project came from my junk box or were re-purposed from other projects. This is the second tuner to inhabit this enclosure, so the variable capacitor and rotary switch were already in place.

The coil is consists of 40 turns of enameled copper wire on a plastic 35mm canister. The wire appears to be 22 AWG. I wasn’t shooting for any particular inductance value; I just started winding turns. Based on the dimensions of the coil, the total inductance appears to be approximately 31 uH. I tapped it in 8 places and wired it to a rotary switch. I used two-sided foam tape to secure it to the bottom of the enclosure. I left the cap on the film canister so that the lid would press down slightly on it. This helps to securely hold the coil in place.

The variable capacitor was salvaged from an old radio by a friend of mine. It’s a two-section capacitor, totaling about 365 pf, according to my notes. I added a switch to select between one or both of the sections. Because the capacitor is sometimes in series with the coil, I used some thin fiberglass material to insulate it from the chassis.

Front panel of my old antenna tuner. The switch selects one or both sections of the variable capacitor.

To the best of my recollection, I purchased the aluminum box at Radio Shack back in the day. I finished off the project with some embossed labels made on an old Dymo label maker. They look tacky, but they’re still holding up after all these years.

Rear view of my old tuner. The slide switch on the left selects the confiuration. In the "LO" position, the coil and capacitor are in series. In the "HI" position, the tuner is configured as an L-match tuner. — Rear view of my old tuner. The slide switch on the left selects the configuration. In the “LO” position, the coil and capacitor are in series. In the “HI” position, the tuner is configured as an L-match tuner.

After spending 15 or more years on the shelf, this funky-looking tuner has been seeing a lot more use lately. I mostly use it as an L-Match for end-fed wires. (I’ve only used the low impedance, series connection a few times over the years.) It’s a great portable tuner for QRP when weight isn’t a consideration.

I have the parts on hand to build a lighter L-match when I need to carry a tuner in my backpack. Until I find the time to put it together, I’ll keep using this funky old tuner.

73, Craig WB3GCK