Doublets I Have Known and Loved

In a recent post, I covered some (very) basic information about the venerable doublet antenna. This time around, I’ll cover some practical examples. These are antennas I have used and one unique design I know of.

Doublet Fed with TV Twinlead

My go-to portable antenna for several years was a simple doublet fed with 25 feet of that cheap, brown TV twin-lead. For the radiating elements, I used some #22 stranded hookup wire.

I first built the antenna as a 40M dipole fed with RG-174 coax. After a while, I wanted to cover multiple bands, so I removed the coax and replaced it with the twin-lead. I used a small piece of fiberglass perf board for the center insulator.

I have often used my homebrew Z-match tuner to load it up, although a 4:1 balun and a short run of coax to my rig’s internal tuner works fine, too. The whole antenna weighs next to nothing, and fits in a sandwich-sized Ziplock® bag.

Nothing fancy but it works great.

This is the center connector for my 66-foot doublet. The feedline is the old, cheap TV twin-lead.
This is the center connector for my 66-foot doublet. The feedline is the old, cheap TV twin-lead.

Up and Outer

The Up and Outer is simply a doublet with one vertical leg and one horizontal leg. I had done some experimenting with this old-time antenna and decided to build one to use while on vacation in the Outer Banks of North Carolina. 

I planned to support the vertical leg with a 28-foot Jackite pole, so I made a simple modification to a 44-foot doublet I had on the shelf. I spliced 6 feet of additional wire to each of the elements down to 28 feet each, and I was in business. Like my 40M doublet, the Up and Outer is fed with TV twin-lead and uses a perf board center insulator.

This antenna always goes with me on our annual Outer Banks vacation. I’ve used it from numerous beach rental houses, and it’s perfect for use on a second story deck. I used it last summer with great results, connecting it directly to my KX3. And, if I need to, I can use it as a normal horizontal doublet.

Appalachian Trail (AT) Dipole

This design is the brainchild of my friend, Ed Breneiser WA3WSJ, and goes back about 20 years. Rich Arland K7SZ, wrote about it in his QRP column in QST [1] back in 2001 and devoted a few pages to it in one of his books [2].

In simplest terms, it’s a 40M doublet made from #26 copper-clad stealth wire. Ed used a 3/4-inch PVC end cap for the center insulator (see photo). After soldering wires to an SO-239 socket and routing the wires through the end cap, the inside of the end cap is potted with epoxy. This makes it pretty much bomb-proof. 

The antenna is fed with 300-ohm ladder line, which is soldered to a PL-259 UHF connector. The PL-259 probably causes a slight imbalance, but in the field, you’ll never notice it. You can also feed it with coax and use it as a normal 40M dipole. Pretty cool, huh? 

When I built mine, I went with some #22 stranded hookup wire I had on hand. Although I departed from Ed’s design a bit, this doublet has been a reliable portable antenna over the years. 

My version of the WA3WSJ AT Dipole. The discoloration on the PVC end cap is from a mishap I had while potting it with epoxy. On the right is a PL-259 connector used with 300-ohm ladder line. As you can probably tell, this antenna has seen years of heavy use.
My version of the WA3WSJ AT Dipole. The discoloration on the PVC end cap is from a mishap I had while potting it with epoxy. On the right is a PL-259 connector used with 300-ohm ladder line. As you can probably tell, this antenna has seen years of heavy use.

WV0H Park Doublet

Myron WV0H designed a unique doublet that he dubbed The WVØH Park Portable DoubletHe uses two 50-foot pieces of wire to create a 60-foot doublet fed with a built-in open-wire feeder. I won’t attempt to offer a detailed description here; Myron’s blog post provides all the details you need to build one. Go check it out.

While I’ve never used Myron’s unique antenna, I can vouch that it works. I worked Myron a few years back while he was out in a park with his doublet. I can attest that it puts out a great QRP signal.

Wrap-Up

Well, that’s about it. If you need a reliable, easy-to-build, multi-band antenna, give the time-tested doublet a try.

73, Craig WB3GCK

References:
[1] Arland, R. (2001, July). QRP Power – Antenna Time. QST, p. 100.
[2] Arland, Richard K7SZ, Low Power Communication – The Art and Science of QRP, The American Radio Relay League, 2nd Edition, 2004, Chapter 6, pp. 6-36, 6-37

The Doublet – Revisiting a Classic Antenna

I was recently going through my stash of portable wire antennas and came across one of my old favorites—the doublet. I don’t see too many references to this type of antenna these days, but the doublet provides a great portable antenna option.

What is it?

The doublet, simply put, is just a dipole. The difference is that you feed it with a balanced feeder, rather than coax. 

Hams have been using doublets for many years. The earliest reference I could find in the ARRL QST archives was from September of 1929.[1] In this write-up, Clair Foster W6HM describes a 40M doublet fed with twisted wire lamp cord used for receiving. 

Advantages of the Doublet

The balanced feeder provides some advantages. Depending on how it’s constructed, it can withstand higher SWR with lower losses than coax. Because of the low losses at high SWR, you can use the doublet as a multi-band antenna. 

As a portable antenna, it’s hard to beat, especially as an inverted vee. Use a tree branch or telescopic pole to hoist up the center, tie off the ends, and you’re in business. [2]

Some Disadvantages

This multi-band capability comes with some disadvantages, though. Fortunately, none of them are insurmountable.

First, you’ll need a transmatch that can handle balanced feedlines. Typical commercially-available feedlines have either 300 or 450-ohm characteristic impedances. For open-wire feedlines, the impedance can sometimes be 600 ohms or more.  

I’ve had success using a homebrew Z-match tuner. Companies like Pacific Antenna and QRP Guys sell Z-match tuner kits that will handle balanced lines. They offer tuners that are small and light enough for QRP-portable use. 

You can also use a balun to transition from the balanced feedline to 50-ohm coax. While this isn’t an optimum approach, it works. Textbooks often recommend a 4:1 balun, and that’s a good starting point. If you go this route, I recommend keeping the coax as short as practical. If you run into matching problems on some bands, try another balun ratio (e.g., 1:1), or change the length of your feedline. 

The second drawback is that you need to be careful of how you route balanced lines. You need to avoid getting it too close to metal or laying it on the ground. Both can upset the line’s balance. This can cause it to radiate or introduce losses. If you have excess line, don’t coil it up. Operating outdoors, I found these restrictions aren’t very difficult to work around; you just need to be mindful of them. 

Construction

Building the doublet is pretty simple. Many folks suggest making the doublet a half-wavelength long at the lowest band you intend to use. I’ve built one for 40M and it worked well on 40M and higher. Depending on your tuner, it may also be usable on the next lower band.

L. B. Cebik W4RNL (SK) popularized the 44-foot doublet for 40M-10M. According to Cebik’s analysis, this length produces a more consistent radiation pattern across the bands. 

Doublet diagram. One rule-of-thumb suggests avoiding combinations of feedline electrical length (L1) and one leg of the radiator (L2) that are odd multiples of an eighth-wavelength.
Doublet diagram. One rule-of-thumb suggests avoiding combinations of feedline electrical length (L1) and one leg of the radiator (L2) that are odd multiples of an eighth-wavelength.

Regardless of the size of the doublet, you should try to avoid certain feedline lengths. One rule-of-thumb suggests avoiding combinations of feedline electrical length plus one leg of the radiator that are odd multiples of an eighth-wavelength. [3] If you run into matching problems, you can try adjusting the length of either the feedline or the radiating elements.

Feedline Options

You have several options here:

  • Commercial 450-ohm or 300-ohm ladder line. These are commonly available, and they work great. 
  • Homebrew open-wire feeders. This is the most efficient option. If you do some Internet searching, you’re likely to find lots of ways to build open-wire feeders. SOTABEAMS has a great example on their website.
  • TV twin-lead. I’ve used the cheap, brown stuff quite a bit for portable doublets. Unfortunately, it’s nearly impossible to find these days. If you come across it somewhere, stock up!
  • Lamp cord or speaker wire. This works and I’ve seen folks use it for portable antennas. However, it can be lossy, compared to window line or open-wire feeders.

More Later

If you want more technical details on this antenna, information abounds on the Internet and in antenna books. In particular, Cebik wrote some great articles that are worth searching for. 

In a future post, I’ll cover some practical examples that I have come across or used in the field.

73, Craig WB3GCK

References:
[1] Foster, C. W6HM (1929, September). Experimenters’ Corner: The “Doublet” for Receiving. QST, p. 39.
[2] DeMaw, D. W1FB (1991). Technical Bits & Pieces. In W1FB’s QRP Notebook (2nd Ed., pp. 157–161). Newington, CT: QST.
[3] Heys, John D., G3BDQ (1989). Center-fed antennas using tuned feedlines. In Practical Wire Antennas. Bedford, UK: Radio Society of Great Britain, p 7.

No-Name CW Paddles

Once a day, I receive an email from eBay showing the latest listings for CW keys. In one of those emails, a small and inexpensive set of 3D-printed paddles caught grabbed my attention. My curiosity got the better of me, and I ordered some.

The primary reason for my interest was the size. I normally use Palm Mini paddles attached to a clipboard, when I’m out operating portable. The eBay listing offered paddles that were a bit smaller than my Palm Mini paddles. The Palm paddles are no longer available (much to my chagrin), so I was curious if these cheap paddles might be a viable alternative. Given the low price (around $15, shipping included), I had no delusions that the no-name paddles would be as good, though.

The paddles are “unbranded” and listed on eBay under the awkward title, “Cw key automatic key short wave automatic key double paddle radio report NEW.” There are numerous listings for these paddles. Most of them ship from Hong Kong but there are some U.S.-based sources. Some are available in kit form.

They are available in 3 sizes. The two larger paddles have magnetic bases. I bought the smallest one (3x8x2 cm), which had the potential to work with my clipboard setup. They are intended for two-handed operation but I figured I could improvise some sort of magnetic base for them.  

Unbranded, 3D-printed paddles from eBay. The screw (one on each side) adjusts the paddle contact spacing.
Unbranded, 3D-printed paddles from eBay. The screw (one on each side) adjusts the paddle contact spacing.

As mentioned earlier, they are 3D-printed. The seller cautions: “Can’t work in high temperature environment!” The term, “high temperature,” is undefined. I’m sure I would start to wilt in the heat long before the paddles.

It took a couple of weeks to receive my paddles from Hong Kong. Besides the paddles, the package contained a 3-foot patch cable with 3.5mm stereo plugs. There was no documentation but none was needed. 

Read view of the small, un-branded, 3D-printed paddles from eBay. The rear connector is a standard 1/8-inch stereo jack.
Read view of the small, un-branded, 3D-printed paddles from eBay. The rear connector is a standard 1/8-inch stereo jack.

Out of the box, I found the contact spacing to be much wider than I’m accustomed to. Fortunately, the paddles have access holes on each side to adjust the spacing. A few tweaks with a Phillips screwdriver got the spacing closer to my liking.  

It was easy to fashion a magnetic base. Using some two-sided foam mounting tape, I added two strong magnets to the bottom of the paddles. The magnets didn’t line up exactly with the washers on my clipboard but they held pretty well. 

You’re probably wondering how they work. Well, they are about what you’d expect from $15 paddles. For sure, they lack the solid, precise feel of my more expensive Palm paddles. The paddle arms have what I call, “vertical slop.” By that I mean you can wiggle them up and down. Also, the paddles’ contacts aren’t the greatest. They are just the threaded ends of two machine screws contacting the threads of a vertically-mounted machine screw. 

With the “vertical slop” and the rough contacts, you don’t always get clean contact closure. To me, it feels like the contacts sometimes “scratch” when they close. The left paddle also sticks occasionally. At higher speeds (20+WPM), they can be challenging. That said, I am able to coax decent-sounding code out of them at moderate speeds—if I’m careful.

As they say, you get what you pay for. These paddles won’t be replacing my Palm Mini paddles anytime soon. They don’t have the smooth, quality feel of my Palm paddles—or any other paddles I own. Not by a long shot. I concede, however, that comparing these $15 paddles to more expensive products is not entirely fair.

CW keys and paddles are always subject to personal preferences; however, if you are on a limited budget, these paddles might work for you. It certainly won’t cost you a lot to find out. 

73, Craig WB3GCK

[Disclaimer: I have no financial interest in these products whatsoever.]

The K0MBT Mini-Mini Key

OK, I admit it. I have a fascination with tiny straight keys and paddles. With the proliferation of 3D printers, there are a lot of neat, innovative products available these days. This unusual little key from Dave Balfour KØMBT is a good example. [Update 3/16/2020: Dave recently changed his callsign to ADØB.]

Dave got started in 3D printing as a hobby a few years ago. A while back, he started sharing his straight key designs with his fellow SKCC members on the SKCC mailing list. That generated some interest and, before long, Dave was offering his keys for sale. As of this writing, Dave is offering straight keys in two sizes and a single lever paddle that can be used as a sideswiper (aka cootie) key.

I ordered the smaller of Dave’s straight keys, which he calls the “Mini-Mini.” Dave promptly shipped one and I had it a few days later. When I opened the box, I was immediately intrigued by this little key.

K0MBT "Mini-Mini" Key
K0MBT “Mini-Mini” Key

When I say “little,” I mean “little.” Overall, it measures approximately 2-1/4″ L x 1″ W x 3/4″ H and weighs in at a minuscule 0.7 oz. (19g). Instead of a traditional knob, Dave uses a novel indentation on the keying lever. The other unique thing is the switch he uses instead of the contacts. A little computer mouse switch provides both the contact closure as well as the return spring. As a result, there are no adjustments for contact spacing or tension. It doesn’t get much simpler than this.

On the rear of the key, there are two terminals for connecting the wires of your choice. There are holes on each side of the key, that meet at the two terminals. You can route your wires in from the side, providing a little strain relief.

Rear view of the K0MBT "Mini-Mini" key
Rear view of the K0MBT “Mini-Mini” key

When I first grasped the key, my forefinger instinctively went into the indentation and it felt very natural. Despite the lack of adjustments, the key has a nice feel to it. With it just sitting on my desk, I can send code without the key sliding around too much. With the cable I’m using, though, it can sometimes feel like “the tail wagging the dog.” It’s not a huge issue, as long as I’m careful.

Kudos to Dave KØMBT for this unique and fun little key. If you’d like more information on Dave’s keys, look him up on QRZ.com or download Dave’s PDF file describing his offerings.

73, Craig WB3GCK

[Disclaimer: I have no financial interest in this product whatsoever.]

Westclox Canadian Military Key

While puttering around the shack this morning, I came across an old key I had all but forgotten. It’s a Westclox Canadian military key that I acquired back when I was first licensed. It has been tucked away in the back of my desk drawer for most of the past 44 years. I can’t remember ever using it on the air, so I figured it’s time to give it a fresh look.

Westclox Canadian military key. According to the original box, it was manufactured in May 1949.
Westclox Canadian military key. According to the original box, it was manufactured in May 1949.

It seems like I’ve had this Westclox key forever. I remember buying it from a mail-order military surplus house around 1975. It was in excellent condition and appeared to be unused. The label on the box reads: Z1 ZA/CAN 0977. The box also shows a manufacturing date of May 1949. An identical key is shown on the W1TP website. The PA3EGH website also shows some similar keys.

Original box for the Westclox Canadian military key. The label reads Z-1 ZA/CAN 0977 and shows a date of May 1949.
Original box for the Westclox Canadian military key.

I don’t remember what I paid for it, but it wasn’t very expensive. I took a quick look at eBay this morning and I saw these keys listed anywhere from $80 to an outrageous $750.

One of the reasons it hasn’t seen much use is its “feel.” Unlike the J-38 style keys I used in the Navy, the contacts on the Westclox key are behind the fulcrum. This results in a “feel” that was a bit unusual to my taste.

The other issue with this key is that it’s somewhat loud. At one time I considered using it for portable operating while camping. However, I don’t think it would be a good choice for early morning operating when others are still sleeping.

Having said all that, there’s still something about this key that fascinates me. I spent some time re-adjusting it and it now feels better than I remembered. I also mounted it on a wooden base for some additional stability.

Frankly, I don’t think I gave this key a fair shake back when I bought it. So, I think I’m going to put this 70-year-old key on the air this week. If it really was new/unused when I bought it, this will be the first operational use in its 70-year existence.

73, Craig WB3GCK

A Slippery Sloper

I spent the weekend with my grandkids out near Harrisburg, Pennsylvania. My XYL and I watched the kids while my daughter and son-in-law took a little anniversary get-away. Of course, there was some time for ham radio, too.

By the time I got around to setting up an antenna on Friday, it was dark and the temperature was well below freezing. Oh yeah, there was about 4 inches of snow in the backyard to boot. So, I was in need of a real quick and dirty antenna.

I decided to toss a 29.5-foot wire out of a 2nd-floor window. I then went out to the backyard to secure the other end of the wire. I used some shock cord to tie it off to the top of a 6-foot wooden fence. My total time outside in the cold and dark was about a minute.

Back inside, I fed the wire through a homebrew 9:1 UNUN with 18 feet of RG-8X coax. This particular wire and UNUN served me well as a vertical during many National Parks on the Air (NPOTA) activations. I commandeered one end of the dining room table for my KX3 and powered up for a test. The KX3 was able to get a match on 80M through 10M.  Then, I went back to hanging out with the kids.

My impromptu sloper's feedpoint. The wire from the 9:1 UNUN is just pinched in the window.
My impromptu sloper’s feedpoint. The wire from the 9:1 UNUN is just pinched in the window.

By now I’m sure you’re wondering where the “slippery” part of the this post’s title comes in. Well, the next morning I looked out the window and saw that some ice had accumulated on the wire. The wire was dragged through the snow during installation and it froze overnight. The KX3 didn’t mind at all; the internal tuner loaded up the frozen wire without problems.

I got on the air for a bit on Saturday afternoon.  On the air, my impromptu antenna far exceeded my low expectations. I started off working N2CX on 40M. Joe was activating a park on the Eastern Shore of Maryland. I followed that up with a nice two-way QRP chat with WK2J in North Carolina.

My dining room table set up.
My dining room table set up.

I worked a couple of QRPers in the FYBO contest sponsored by the Arizona ScQRPions. I also worked some Minnesota and Vermont QSO Party contesters. An assortment of SKCC, POTA, and SOTA stations also made it into my log over the weekend. The best “DX” of the weekend was VE7ST in the British Columbia QSO Party on 20M.

I didn’t expect much from this quickie antenna configuration but I was happy with the way it got out. Plus, set up/tear-down was easy and only took a few minutes. This sloper will likely be my go-to antenna for future visits to see the Harrisburg grandkids.

72, Craig WB3GCK

Revisiting the Rybakov 806 Vertical

Some recent Internet discussion got me thinking about the Rybakov 806 Vertical antenna. This easy-to-build antenna has served me well over the years. So, I went back and revisited some of the ways I’ve used it.

What the heck is a Rybakov anyway?

The Rybakov 806 Vertical appears to be the brainchild of Enrico IV3SBE from Italy (now 5Z4ES in Kenya). The term, Rybakov, is Russian for “fisherman.” That’s right… It’s an antenna with a Russian name designed by an Italian who lives in Africa — truly an international creation. From what I could glean from exhaustive Internet searches, this design dates back to the mid to late 2000s. I found numerous references to it from 2009.

The classic Rybakov configuration is a 7.6m or 8m (~25 or 26 feet) wire fed through a 4:1 UNUN. The length isn’t critical, as long as you avoid resonance on the bands of interest. It’s often supported by a telescopic fishing pole (hence, the name, “Rybakov”). Being a non-resonant antenna, you need to use an antenna tuner to make it work. You also need to use radials or some other type of ground.

The antenna can cover 80M through 6M (the “806” part of its name, I suppose). The band coverage depends on the wire length used and the capabilities of your tuner. With a 7.6M wire, you can cover 40M and up without problems. For 80M coverage, plan on using a longer radiator.

The only thing you need to build is the 4:1 UNUN. The IW7EHC website provides detailed instructions for building one. Beyond that, you just need to cut some wire to length for the radiator and radials. Easy peasy!

My experience with the Rybakov

I had been using this type of antenna before I even knew it had a name. Rick KC8AON had a version of this type of antenna he called, “The Untenna.” That’s where I found it.

My first experiment with it was in a “stationary mobile” setup. I rigged up a 26-foot vertical wire and grounded the UNUN to the body of my truck. My Z-817 tuner was able to load it up with no difficulty. I had no problem making contacts and I liked the multi-band coverage.

I next used the Rybakov at a Boschveldt QRP Club Field Day. I set up a 26-foot ground-mounted vertical and used about six 16-foot radials with it. Again, the performance seemed decent and I remember doing well on 10M that year. The only shortcoming was that it wouldn’t load up on 80M.

The next year, I solved the 80M problem by using a 50-foot wire in an inverted L configuration. For the ground, I used six 16-foot radials and two 33-foot radials. This configuration gave me full coverage from 80M to 10M and it worked great. This antenna configuration became my “go to” Field Day for several years. In later years, I used a 53-foot radiator.

My typical implementation of the Rybakov 806 antenna. A length of 25 to 27 feet does well from 40M and up. I go with a 53-foot radiator for 80M coverage.
My typical implementation of the Rybakov 806 antenna. A length of 25 to 27 feet does well from 40M and up. I go with a 53-foot radiator for 80M coverage.

I used another version of the Rybakov with the pop-up camper that I used to own. I strapped a 31-foot Jackite pole to the camper and used it to support a 27-foot wire. I grounded the UNUN to the body of the camper. This antenna worked great on 40M to 6M and, best of all, I didn’t need to go outside at night to change bands. I used this antenna with good results for several years until I sold the camper.

I also built a Rybakov that I use as a backup antenna in the field. I built a small 4:1 UNUN that I use with a 26.5-foot radiator and a 26.5-foot radial. The antenna, along with a short length of coax, is easy to carry in my pack.

The bottom line (for me, at least)

I’ve had good luck with the Rybakov Vertical over the years. Is it the best antenna? Nope. Purists will argue about UNUN, ground, and coax mismatch losses. Yep, there are those. Yet, its simplicity and “no gap” band coverage are hard to beat. It’s easy to deploy in the field and it really does work.

If you’re in the market for a simple portable antenna project, the Rybakov 806 is an easy one.

[Update 4/3/2019: I’ve always wondered about the rationale behind the 25-foot radiator often used with the Rybakov antenna. An article in QST [1] by Joe Reisert W1JR shed some light on that for me. Joe’s article discusses the 3/8-wave vertical antenna. According to the article, the 3/8-wave antenna has a low take-off angle and its 200-ohm feedpoint is easily matched with a 4:1 transformer. Its higher radiation impedance provides good performance with just four 1/4-wave radials. For 20M, a 3/8-wave radiator is about 25-ft. Similarly, for 40M, it would be 50-feet. So, my guess is that’s the concept behind the Rybakov design.]

73, Craig WB3GCK

Reference Links:

Reference Articles:

  1. Reisert, Joe W1JR, “The 3/8-Wavelength Vertical — A Hidden Gem,” QST, April 2019, pp. 44-47.