A Homebrew Z-Match Transmatch

[This is an updated version of an article that originally appeared on my QSL.NET website. Although it’s twenty years old, I still occasionally hear from people who have built similar tuners.]

Antenna tuners (more accurately referred to as “transmatches”) make great homebrew projects; they are reasonably simple to build and, when finished, provide a useful piece of equipment. Every shack should have (at least) one. I built this one a couple of decades ago, and it’s still in use.

WB3GCK Z-Match Tuner - front panel
WB3GCK Z-Match Tuner – front panel

For this project, I decided to try my hand at building a Z-Match tuner from scratch. This type of tuner has been around for a while. While the Z-match can take on several variations, what distinguishes it from other circuits is that it is a resonant circuit that uses a fixed inductor. 

WB3GCK Z-Match Tuner - rear panel
WB3GCK Z-Match Tuner – rear panel

Z-Match tuners became very popular within the QRP community years back, thanks primarily to articles in QRP journals by Charlie Lofgren W6JJZ and the emergence of Z-Match tuners in kit form. Emtech sold its wildly popular ZM-2 kit commercially and the NorCal QRP Club began selling their BLT tuner kit (a W6JJZ design) like hotcakes.

Some Pros and Cons

Why the popularity? Here are some advantages that the Z-match design offers:

  • Matches balanced loads without the use of lossy baluns.
  • Being a parallel resonant circuit, the Z-match can provide some band-pass filtering for your receiver and harmonic attenuation for your transmitter.
  • A well-designed Z-match tuner has a high Q and is more efficient (less lossy) than other types of tuners.
  • The fixed inductor simplifies construction (no taps or rollers needed).
  • Using a toroid inductor and some small poly-film variable capacitors, the Z-match can be built into a very compact package. This sort of thing usually appeals to QRPers.

There is, of course, no free lunch here. Here are some disadvantages of the Z-match design:

  • Tuning is usually very narrow and can be a bit touchy sometimes to tune up
  • The range of impedances that can be matched is not as great as in other designs, such as the “T” configuration.

Design and Construction

I make no claims of originality for anything in my version of the Z-match. I based it on a classic design which was first appeared in SPRAT #84 (see the G3YCC web site for a schematic of the original design). This design, by the way, is similar to the one used in the Emtech ZM-2.

I incorporated a few modifications in my version, based on an article by W6JJZ (“The Z-Match: An Update”, QRP Quarterly, July 1995, pp 10-11). First, instead of the T-200-2 toroid specified in the SPRAT article, I used a T-200-6 core. W6JJZ recommends the Type-6 core over the Type-2 because it provides a higher Q over most of the HF range. The number of turns has to be adjusted for the Type-6 core, due to differences in permeability. Here again, I went with W6JJZ’s suggested turns count. Another reason for choosing the T-200-6 core was that I happened to have one in my junk box. How convenient!

Z-Match Tuner Schematic
Z-Match Tuner Schematic

The coil was wound using some #22 solid hookup wire (from Radio Shack) which I had laying around. The secondary winding is wound between the turns of the primary to ensure tight coupling. I added a toggle switch to ground one side of the secondary winding to accommodate single-ended loads (like a random wire). A piece of styrofoam was glued to the bottom of the enclosure to provide some support for the toroid and to keep it away from metal surfaces.

WB3GCK Z-Match Tuner - Inside view
WB3GCK Z-Match Tuner – Inside view

Another W6JJZ modification I used was the inclusion of a DPDT (center off) toggle switch to provide some flexibility with the input capacitor. Using this switching arrangement, I can select between one section of the capacitor, both sections in parallel, or both sections in parallel with a fixed 470pF mica capacitor. The extra input capacitance can sometimes be helpful on the lower frequencies.

The capacitors are poly film variable capacitors (2 sections @ 365pF each), which were originally purchased from Mouser Electronics. Unfortunately, Mouser no longer carries them, and I don’t know of another commercial source. I should have purchased a truckload of them when they were available! Similar capacitors with smaller values are still available if you look around.

The SWR bridge I used is a Dan Tayloe LED SWR indicator from a kit that was offered years ago by the Arizona scQRPions. It uses a resistive bridge circuit with a single LED to indicate a null when the bridge is balanced. For the 50-ohm resistors in the bridge, I substituted 2 100-ohm, 1-watt resistors. The bridge will handle a typical 5-watt QRP rig without flinching and could probably handle a bit more than that.

SWR Bridge Schematic
SWR Bridge Schematic

The whole thing was packaged in an enclosure which measures 3 x 5 x 2 inches. It certainly could have been built into a smaller package, but I had this enclosure on hand and decided to put it to use.

On the Air

To use the Z-Match, adjust the capacitors for a null in the background noise in your transceiver. That will get you close to a match. Then, switch in the SWR bridge, apply some RF, and tweak the capacitors for minimum brightness on the LED. There may be some interaction between the two capacitors, so you might have to go back and forth between them a time or two.

For an initial test, I hooked it up to the famous—in my mind, at least—WB3GCK Downspout Antenna. The little Z-match loaded up the downspout on 40 through 10 meters with no problems. On most bands, I could get the LED indicator to go completely out. On one or two bands, I couldn’t get it completely extinguished but it did give a definite null. Double-checking with a second SWR bridge indicated that the SWR was 1.5:1 or less in this condition. While tuned up on 40 meters, I had a quick QSO with a station near Chicago from here in southeastern Pennsylvania with 3 watts.

Wrap-Up

This little Z-Match tuner was one of my favorite—and most useful—projects. It’s a great accessory for QRP rigs that lack an internal tuner or SWR meter.

73, Craig WB3GCK

©2000-2020 Craig A. LaBarge

My Favorite Apps for Portable Operating

I do the majority of my HF operating while out at portable locations. Like most people these days, I always have my cell phone handy. While I have a bunch of apps installed, there are a few that I use most often to figure out where to go and where I am.

Before I begin, I should mention that I use an Android phone. Some of these apps may be available for the iPhone or there may be similar apps available for you.

I should also point out that I do most of my hiking and biking on well-established trails. Suburban Philadelphia is not exactly a wilderness area. Wilderness and backcountry folks will likely have different needs.

Having said all that, here are the non-ham-specific Android apps I use most often in the field.

Where Am I?

This appropriately-named app by Ejelta LLC does exactly what it says. Using your phone’s location services, it shows where you are in the world. It shows your city, zip code, phone area code, sunrise and sunset times, elevation, and GPS coordinates. It also identifies the county you’re in, which is useful for setting up a new location in the TQSL software for Logbook of the World (LoTW).

Where Am I? Screenshot
Where Am I? Screenshot

The sharing feature is also important to me. When I’m out alone, I use Where Am I? to text my location to my (far) better half. I can send her the location of where I parked my truck and where I stopped along the trail to play radio.

Maidenhead Grid Locator

Another piece of information I need for LoTW is the grid square I’m in. For years, I used (and still use) an app with the simple title, Locator. As I started writing this post, I found that this particular app is no longer available in Google Play. No worries; there are lots of other apps to determine your Maidenhead grid square. Here are a few:

  • Ham Locator (by OH5GQF) shows your grid square (6 characters) on a map. You can toggle between street view and satellite view.
  • If you use HamLog (from Pignology) for portable logging, check the “Tools” tab. There’s a grid locator tool there. You can navigate around a map to find the grid square anywhere on earth.
  • HamGPS (by EA4EOZ) is a grid locator on steroids. It shows your current grid square out to 10 characters, along with your coordinates and compass heading. It also shows the location and status of the GPS satellite constellation. That can be fascinating to watch.

Ham Locator Screenshot
Ham Locator Screenshot

TrailLink and AllTrails

These are two similar apps that I use for planning trips to new trails. The Rails to Trails Conservancy produces TrailLink, while AllTrails is from AllTrails, Inc. They both give you maps, directions, reviews, and more. Both apps have paid versions that will let you save maps to your phone. That’s handy if you are in an area with poor cellular coverage.

AllTrails map display. You can zoom in and navigate around the map to see a detailed view. With the paid version, you can save maps to your device for offline use.
AllTrails map display. You can zoom in and navigate around the map to see a detailed view. With the paid version, you can save maps to your phone for offline use.

Storm Radar

Last but not least… There’s no shortage of weather apps for your phone. I have one that I use for the usual weather forecasts: daily, hourly, and so forth. I also use Storm Radar (The Weather Channel) and it has saved my bacon on a few occasions.

Storm Radar. Fortunately, there was no rain in view when I captured this screenshot.
Storm Radar. Fortunately, there was no rain in view when I captured this screenshot.

Of course, Storm Radar‘s radar display lets you see exactly what’s coming your way. What I really like, though, is the real-time rain and lightning alerts. Even if I don’t have the radar display up, Storm Radar gives me a heads up on nasty weather headed towards me. There have been times when this app helped keep me and my gear from getting rained on.

Wrap-Up

So these are some of my favorite apps for portable operating. I didn’t cover any apps that are specific to ham radio but I may do that in a future post.

Do you have any must-have apps for outdoor operating? Let me know in the comments.

72, Craig WB3GCK

 

Links

[My usual disclaimer: This blog is not monetized in any way. I have no financial interest whatsoever in any of these products.]

OK. With that out of the way, here are links to the apps mentioned in this post:

 

Adjustable Bungee Cable Ties

This is another one of those little hacks that takes longer to describe than to build. Some time ago, I stumbled on a clever idea online that has been useful in my ham radio activities.

I used to use ball bungee fasteners in a variety of sizes as temporary fasteners. While they are handy, they have limitations for my uses. On occasion, I found that the sizes I had available were either too small or too large for the task at hand.

A year or two back, I found a great video on the MOD YouTube Channel. The video described how to make these simple, adjustable cable ties. I made up a few and found them handy for several ham-related applications.

A completed bungee cable tie, along with one of the two-hole cord locks I used.
A completed bungee cable tie, along with one of the two-hole cord locks I used.

These little devices have a multitude of uses but my main use is for antennas in the field. I use them to fasten a BALUN or UNUN to a telescopic pole for portable verticals.

I also found they are also handy for lashing odd items to the MOLLE loops on my backpack. In a recent post, I showed how I use them to secure a 19-foot telescopic pole to my sling pack.

I use one of the bungee ties to attach the 19-foot vertical matching box to the fiberglass pole.
I use one of the bungee ties to attach my 19-foot vertical matching box to the fiberglass pole.

Of course, they make great cable ties. Their ability to adjust allows them to fit a wide variety of cables.

You only need 2 things to make these: some shock cord and some double hole cord locks. (If you watched the MOD video, you already know all this.)

I use 4mm diameter shock cord most often to make these. For some smaller, light-duty applications, I have used a thinner 2.5mm shock cord. I have found that the cord locks seem to hold better with the larger 4mm shock cord.

Construction is super simple.

  • Cut the shock cord to the desired length. Be sure to singe the cut ends with a lighter to prevent fraying.
  • Put the two ends through the holes in the cord lock.
  • Holding the two ends together, tie a simple overhand knot and snug it down.
  • To use them, place the bungee around whatever you need to fasten. Place the loop end over the cord lock to hold it. Press the button on the cord lock and pull the ends to cinch it down.

That’s all there is to it. In the time it took to write and edit this post, I could have made a ton of these things. It’s not an Earth-shattering thing but sometimes it doesn’t take much to amuse me.

Thanks to MOD YouTube Channel for sharing this great idea.

72, Craig WB3GCK

[Disclaimer: I have no financial interest whatsoever in Amazon or any of these products.]

Links:

Sling Pack for My QRP Stuff

My XYL has accused me of being obsessed with bags, backpacks, and storage containers of all sorts. She’s an excellent judge of character.  This one, fortunately, wasn’t very expensive.

A few years ago I bought a backpack with ham radio in mind. I wanted one big enough to carry my Alexloop antenna, along with my QRP rig, battery, and, assorted emergency and survival-type gear. (I could survive a zombie apocalypse with all the stuff I put in that pack.) Although it continues to serve me well, at 35 liters it’s a bit overkill when I don’t need to carry all that stuff. I wanted something a bit smaller and lighter for short hikes and casual outings.

After looking at a dizzying array of small packs, I settled on the Rambler sling pack from Red Rock Outdoor Gear. It’s a bit larger than most other sling packs but I needed one that would accommodate my essential radio gear. It measures about 10 inches x 16 inches x 4 inches and has lots of compartments and MOLLE webbing.

The main compartment comfortably accommodates the box that holds my KX3 and accessories. I also carry a LiFePO4 battery and my antenna wires in this compartment. I use one of the outer compartments to hold safety and comfort items, e.g., first aid kit, sunblock, insect repellent, emergency poncho, etc. In the remaining outer pocket, I keep a headlamp, emergency whistle, compass, a copy of my Amateur Radio license and a notepad and pencil. There’s a compartment on the back of the pack that’s perfect for carrying a folding sit pad and a large contractor garbage bag that I use as a ground cloth. With the water bottle pouch on the side of the pack, I don’t have to use up space inside the pack to carry water.

My Red Rock Rambler sling pack. My 19-ft fiberglass pole is attached to MOLLE webbing on the side of the pack. The HT pouch I added is on the lower left of the pack.
My Red Rock Rambler sling pack. My 19-ft fiberglass pole is attached to MOLLE webbing on the side of the pack. The HT pouch I added is on the lower left of the pack.

The Red Rock Sling Pack also does double-duty for public service events with my local ARES-RACES group. I just remove the QRP gear from the main compartment and replace it with my HTs, spare batteries, emergency vest, etc. Oh, did I mention snacks? Yeah, lots of snacks.

With all the MOLLE webbing on the pack, I couldn’t resist adding a few things. On the back of the pack, I added a pouch for my HT. I added a cell phone holder in the front on the shoulder strap. I use the webbing on one side of the pack to carry my telescopic fiberglass pole, which I fasten with some adjustable bungee cords. And just for the heck of it, I added some molle-compatible velcro strips for attaching a morale patch.

The back side of the Red Rock Rambler sling pack. There's a pouch behind the padded back of the pack that holds a folding sit pad. The small strap at the bottom of the picture helps to stabilize the pack but can be tucked away if not needed. My cell phone pouch is at the bottom of the shoulder strap.
The back side of the Red Rock Rambler sling pack. There’s a pouch behind the padded back of the pack that holds a folding sit pad. The smaller waist strap at the bottom of the picture helps to stabilize the pack but can be tucked away if not needed. My cell phone pouch is at the bottom of the shoulder strap.

In use, I find it very comfortable. The padded strap is non-reversible and goes over my left shoulder. That’s my preference anyway. The zippers on this bag have all worked smoothly without a lick of trouble. (Nothing frustrates me more than balky zippers!)

After nine months of use, the sling pack is holding up well and has fit my needs exactly. It provides a handy and comfortable way of carrying my radio stuff out into the field. There certainly are more expensive packs available but, for less than $50.00 USD, the Red Rock Sling Pack has been money well spent.

Now, all I need is to find some time to get back out into the field for some QRP fun.

72, Craig WB3GCK

[Disclaimer: I have no financial interest in Amazon or any these products. I’m just a satisfied customer.]

Links:
Red Rock Outdoor Gear Rambler Sling Pack
Tactical MOLLE Smartphone Holster
OneTigris MOLLE Radio Holder
Del Molle Strips for Attaching Tactical ID Patches

A “Cooler” Idea

When I was in need of a container to transport my QRP rig, my XYL came up with an inexpensive solution. The answer was as close as the nearby grocery store.

A few years ago, I was using a plastic food container to keep my little YouKits HB-1B and accessories organized and protected in transit. It had enough room for the radio, a Li-Ion battery, keyer, paddles, K1 tuner, earphones, my clipboard/paddle mount, and assorted cables and connectors. Life was good until I cracked the plastic box while out in the field for a QRP Skeeter Hunt contest. I started searching for a replacement.

I mentioned my dilemma to my XYL. She came back into the room carrying a nifty insulated lunch box that she was using for a first-aid kit. I emptied out the first aid stuff and found that it could hold all of my radio stuff. I was particularly happy that my clipboard/paddle mount fit in there perfectly. I made a trip to the grocery store where she found the container and bought one for myself.

Arctic Zone Upright HardBody® Lunch Box. This one has seen years of use and now holds my KX3 and accessories.
Arctic Zone Upright HardBody® Lunch Box. This one has seen years of use and now holds my KX3 and accessories.

The box my XYL found was the Upright HardBody® Lunch Box made by Arctic Zone. The outer material is padded for insulation and it has a rigid plastic liner that provides some extra protection. It also comes with an adjustable divider, which might be useful in some cases. There’s an outside pocket that I use to hold a notebook and pencil for logging. At the time, I paid less than $10 USD for it.

Last year, when I bought my KX3, I went through the same trial and error with the lunch box. I was able to get the KX3, Palm Mini paddles, MS2 straight key, microphone, earphones, clipboard and assorted cables and adapters in there. It holds everything but my LiFePO4 battery and antenna. (These items can vary from trip to trip, so this isn’t much of an inconvenience for me.)  So, off to our local KMart store I went. I bought two of the lunch boxes this time — one for the KX3 and one for a first-aid kit for in my truck.

This is the lunch box with the KX3 and accessories packed up. Out of sheer paranoia, I normally wrap the KX3 in a layer of bubble wrap for extra protection. When placed on top of everything, the clipboard provides another rigid surface for even more protection.
This is the lunch box with the KX3 and accessories packed up. Out of sheer paranoia, I normally wrap the KX3 in a layer of bubble wrap for extra protection. When placed on top of everything, the clipboard provides another rigid surface for even more protection.

When I load up the KX3 box, the other items keep the radio for shifting around while in transit. Out of sheer paranoia, I put a layer of bubble wrap around the KX3. I’m not really sure that’s necessary though. When I’m ready to head out to the field, I just grab the KX3 box, my battery, and antenna of choice for the day and I’m all set.

There are certainly better, more expensive containers available. For the price, it’s hard to beat these lunch boxes. Maybe I should buy another one to hold my lunch and a couple of cold ones when I go into the field.  Hmmm…

73, Craig WB3GCK

Clipboard Keyer

I purchased a set of Palm Mini paddles for portable operating a while back. I love the magnet base, which attaches nicely to the side of my little YouKits HB-1B transceiver. However, in some situations — like sitting on the ground or operating from inside my truck — that isn’t always the most convenient arrangement for me. Here’s a little hack I came up with to solve that problem.

clipboard-1
Figure 1. Washers attached to clipboard

clipboard-2
Figure 2. Paddles attached to clipboard

I purchased an inexpensive 6-inch by 9-inch, acrylic clipboard at my local office supply store. I used some GOOP adhesive to attach two steel washers to the clipboard, as shown in Figure 1. I made sure that the washers lined up with the magnets on the base of the paddles. Figure 2 shows the paddles attached to the clipboard. Figure 3 shows the clipboard in use during a recent outing. For transport, the little clipboard fits in the small plastic container I use for the HB-1B and accessories.

clipboard-3
Figure 3. Clipboard & paddles in use

For less than $2.00, this little accessory makes portable operating a bit more convenient.

73, Craig WB3GCK