Boschveldt Field Day 2020

This year has presented some challenges, but the members of the Boschveldt QRP Club were up for those challenges. We adapted to the current situation and held our annual Field Day outing—with suitable precautions, of course.

The sign at the entrance to the Boschveld QRP Club (W3BQC) Field Day site

We convened at the same location we’ve used for the past few years. A local businessman graciously allows us to camp on a section of his property for the weekend. We had the following members in attendance this year: Ed WA3WSJ, Glen NK1N, Ed K3YTR, Ron WA8YIH, John NU3E, and me. 

Now, here’s where things changed a bit. Due to the COVID-19 pandemic, we implemented some guidelines:

  • Tents had to be at least 10 feet apart—no problem, given the large field we were on.
  • No central food preparation area. Each member was responsible for providing and cooking their food.
  • No sharing of radio equipment
  • Maintain social distancing, especially around the campfire.
  • No outside visitors

This year we operated in the 4A Battery category—using QRP, of course. We ran 4 HF stations, plus a satellite station and a VHF/UHF station. 

As usual, I ran CW on 40M and 80M, with my tent serving as both my sleeping quarters and radio shack. I ran my KX3 into a 53 foot inverted L. I used a 17-AHr gel cell for my rig and a deep cycle battery to charge my laptop. 

Yours truly, WB3GCK, operating CW from my tent. (Photo by WA3WSJ)
Yours truly, WB3GCK, operating CW from my tent. (Photo by WA3WSJ)

Glen NK1N worked the satellites and had a slick setup for his Jeep. The Jeep also served as his sleeping quarters. There’s a lot of tree cover at this site, so Glen set up in an open spot near the entrance to the property. As a result, he had his best year ever from this site. 

NK1N working the satellites
NK1N working the satellites

Glen NK1N took a break from the satellites to tune into the W1AW digital broadcasts to copy the Field Day Bulletin. He also checked into the paNBEMS on Sunday morning to pass our Field Day radiogram to the EPA Section Manager. 

Not far from the satellite station, Ed K3YTR operated the VHF/UHF station from his car. Like last year, Ed slept in a slick, little teardrop trailer he rented for the weekend. 

K3YTR working VHF and UHF from his car.
K3YTR working VHF and UHF from his car.

Ron WA8YIH operated both digital modes and phone from his tent/sleeping quarters. He also used a KX3 with an inverted L. Ron supplied the firewood for our evening campfires, which is a traditional feature of a Boschveldt Field Day.

WA8YIH operating FT8 from his tent
WA8YIH operating FT8 from his tent

John NU3E has been a member of this group for a long time, but this was his first Field Day with us. John operated CW on 15M and 10M using a KX2 with a dipole. John used his backpacking tent for lodging. 

NU3E operating CW. This was John's first Field Day with the Boschveldt QRP Club.
NU3E operating CW. This was John’s first Field Day with the Boschveldt QRP Club.

Ed WA3WSJ operated CW on 20M, using his KX2 and an inverted L. Ed spent the first night on a cot underneath a tarp. He also had a neat sleeping setup in his car. He used that on Saturday night, due to the weather forecast. 

WA3WSJ taking a break. Ed's station is in the background.
WA3WSJ taking a break. Ed’s station is in the background.

Field Day for the Boschveldt QRP Club is by and large a social event; we aren’t in it for the score. Sure, we operate, but there are lots of breaks and plenty of socializing. We had a campfire each night and exercised our tradition of roasting marshmallow Peeps®. (If you haven’t tried roasting Peeps®, you haven’t lived!)

The initial weather forecast for Saturday looked dire. We were under a severe thunderstorm watch for Saturday afternoon and evening. Instead, we only had some light rain on Saturday morning. The rest of the weekend was dry and storm-free. 

Despite our social distancing protocols, we had a fun weekend. It sure was great to be out of our homes and camping with old friends again. 

72, Craig WB3GCK

Rough Start to the Camping Season

After months of closed state park campgrounds due to the pandemic, I was finally able to go camping in our little trailer. I was expecting a relaxing and peaceful weekend, but what I got was something different.

Back before the pandemic shut everything down, I made a reservation at Elk Neck State Park in Maryland for Father’s Day weekend. So we headed out on Friday for the delayed start of our camping season. 

We had a great campsite; it was large, private, and surrounded by woods. The site didn’t have electricity for the camper, but we often camp that way. Propane and battery power are all we need for a weekend of camping in the camper. After getting situated, we had dinner and enjoyed a relaxing campfire. And, of course, my antenna went up, and I set up the radio. 

Our campsite at Elk Neck State Park in Maryland. This was literally the calm before the storm.
Our campsite at Elk Neck State Park in Maryland. This was literally the calm before the storm.

During the evening, the trailer battery started to fade. Eventually, it died altogether. It’s a 100 Ah deep cycle battery that has served us well for several camping seasons. Without it, we had no lights, the propane refrigerator wouldn’t start, and we had no water for the toilet. (I can hear the backpackers out there laughing right now.)

Fortunately, I had an extra 35 Ah battery I could press into service as a backup. After swapping a few connections, we were back in business. We used some alkaline battery-powered lights inside the camper to minimize the current draw on the smaller battery.

On Saturday, we awoke to some great weather and watched a deer pass by in the woods. Radio-wise, I started the day with a CW chat with KB4GYT in South Carolina. But, as the morning progressed, we started hearing some rumbling off in the distance. By mid-day, the storms moved in, and it continued to rain the rest of the afternoon.,

To our good fortune, the rain let up around dinner time. As we were finishing our dinner, however, we heard the propane gas detector in the trailer starting to chirp. That chirp meant we had another depleted battery on our hands. 

At that point, we could have reverted to tent camping mode, using our battery operated lights and making use of the campground bathroom facilities. (We had other workarounds for using the toilet in the trailer, but I’ll spare you those details.) We had two coolers, so we could deal with the loss of the refrigerator. Plus, we still had another battery for charging phones and running a fan. We tent-camped for many years, so we’ve done all this before.

In the end, we decided we didn’t want to spend our time implementing workarounds for our workarounds to extend our stay one more night. We had to be out by mid-day the next day, anyway. So, we took advantage of the remaining daylight to hastily pack up and head home. 

In between the thunderstorms and dealing with trailer battery issues, I managed to make a half-dozen contacts. Of those, two were Parks on the Air (POTA) park-to-park contacts. At times, the static crashes made radio reception difficult. I can only imagine what my 5-watt signal sounded like on the other end.

It was nice while it lasted. Well, most of it was, anyway. Instead of camping, I’ll spend Father’s Day getting my tent camping gear together for Field Day next weekend. Oh yeah… and shopping for a new battery.

73, Craig WB3GCK

Speaker Wire Half-Square Antenna

I’ve been intrigued by the half-square antenna for some time now. I don’t have the real estate to put one up at home, so I built one for portable use. Like my other speaker wire projects, this antenna is built from a 50-foot length of cheap, two-conductor wire.

You can think of the half-square as two quarter-wave verticals spaced a half-wavelength apart. It provides some gain over a quarter-wave vertical and has a low take-off angle. The half-square has a bi-directional pattern with lobes broadside to the antenna and nulls off of the ends.

Normally, the half-square is fed with coax at the top of one of the vertical elements and functions as a single-band antenna. The coax should be kept perpendicular to the vertical leg, to avoid interaction. That arrangement, however, would be somewhat awkward for a portable antenna.

For expediency in the field, I went in a different direction. I decided to feed it at the bottom of one of the vertical legs, which is a high impedance point. I use a 9:1 unun to reduce the high input impedance to something easier for a tuner to handle.

I designed this antenna for the 20M band, but I wanted to use it on other bands as well. By using the 9:1 unun to feed the bottom of the antenna, I’m able to squeeze some more bands out of it. A tuner is required, of course.

Speaker Wire End-Fed Half-Square Antenna
Speaker Wire End-Fed Half-Square Antenna

Materials

Here’s what I used to build it:

Construction

Refer to the accompanying diagram to help make sense of the following steps.

  • Separate the speaker wire into two 50-ft wires
  • On one of the wires, install a spade lug at one end. This will be the connection to your matching device)
  • From the spade lug, measure up 16′ 7.2″ and make a small loop using two small zip-ties. 
  • From the second wire, cut a length that is about 16′ 9″ or so. 
  • Strip and splice the smaller wire to the end of the larger wire. After soldering it, I covered the splice with heat-shrink tubing. 
  • Next to the splice, make another small loop, using two zip-ties.
  • At the end of that wire, twist the wire to form an attachment loop. When you do this, make sure you have 16′ 7.2″ from the splice to the attachment loop.
  • I applied some Goop® adhesive to the loop at the end of the wire to hold it together. I also added Goop® to each of the other attachment loops.
  • As is my usual practice, I added some Goop® to where the wire enters the spade lug to add some strain relief.
  • At this point, the antenna is finished. You can, however, cut the leftover wire in half to make two radials for 20M (approximately 16 feet, give or take). I installed a spade lug on each of these wires and twisted the other ends to make a small loop. You guessed it; I put Goop® on these wires, as well.
This photo shows the splice and one of the mounting loops used in the Speaker Wire Half-Square.
This photo shows the splice and one of the mounting loops used in the Speaker Wire Half-Square.

Matching

[Update (6/17/2020) – After initially publishing this post, I received some great feedback from readers. As a result, I have updated, clarified, and expanded this section.]

For my first couple of outings with this antenna, I used a 9:1 unun as a quick and dirty way to get it on the air. I run about 18 feet of RG-8x coax from the unun to the radio. There’s nothing particularly critical about the coax length, but I would recommend a minimum of 16-feet for 40M and up. The exact length of the radials isn’t critical either since they’re laying on the ground. In fact, you can probably use the antenna without them. In this case, you’re relying on the coax shield for the counterpoise.

While the 9:1 worked fine, there are more efficient ways to match this antenna. I plan to continue experimenting with other methods to match the high-impedance input on 40M and 20M.

I haven’t tested them myself, but the end-fed halfwave tuners from Pacific Antenna and QRPGuys should work on 20M and 40M. They use a parallel resonant circuit and are designed to match an end-fed halfwave (EFHW) antenna. 

An EFHW transformer, like the ubiquitous 49:1 transformer, should also work. You will likely need to do some pruning on the antenna to get the SWR where you want it.

Finally, a simple L-Match antenna tuner with a tapped inductor in series and a variable capacitor across the output looks like it may be the best solution for me. It should handle the high impedances on 40M and 20M, and work on other bands like a random wire tuner. This will definitely be part of my next round of experiments.

Deployment

Deploying this antenna is a snap and takes me about 5 minutes. I use two collapsible poles to support it. I attach one corner to a partially-extended 28-foot Jackite pole. The feed point of the antenna is about 3 feet off the ground. 

These are the two poles I used to support the Speaker Wire Half-Square. Unfortunately, the wire is too thin to be visible in this picture.
These are the two poles I used to support the Speaker Wire Half-Square. Unfortunately, the wire is too thin to be visible in this picture.

I use a 20-foot Black Widow pole (actual length about 19.5 feet) to support the other end. I support this pole with an appropriately-sized screwdriver shoved in the ground. The handle of the screwdriver fits snugly inside the bottom section of the pole. After attaching the other corner of the antenna to top of this pole, I extend the pole and remove the bottom cap. Next, I walk the pole back until the horizontal section is taut. Then, I just shove the screwdriver in the ground and place the pole over it.

With appropriate trees nearby, you might be able to eliminate one or both of the poles. I’m not usually that lucky.

Results of Field Testing

I was pleased with the results of my initial field tests with the half-square. The internal tuner in my Elecraft KX3 was able to load the antenna from 80M through 6M. (Since the antenna’s input impedance is low on 80M, I wouldn’t recommend using the 9:1 there.) The SWR was 1.2:1 or better on all bands with the tuner. 

During my first outing with the half-square, I was able to make contacts on 40M, 20M, and 15M at 5 watts with no difficulty. The antenna is a half-wavelength on 40M, and it appears to play well on that band. I had numerous Reverse Beacon Network spots on 40M showing a signal-to-noise of 20db or better.

I also used it in the field during a recent QRP contest with similar results. Signals were strong on 40M, and I worked Georgia and Quebec on 20M.

This was hardly a rigorous scientific evaluation, but I’m happy with this antenna so far. One of these days, I’d like to do some modeling to see what the radiation patterns look like on the various bands. In the meantime, I’ll do some more experimenting with impedance matching.

Wrap-Up

This was an easy and fun project. It certainly made good use of a roll of cheap speaker wire. After using this antenna in the field a couple times, I have officially added it to my arsenal of portable antenna options.

73, Craig WB3GCK

Cookie Crumble 2020

After some damaging storms this week, we were blessed with some great weather for the weekend. Today was a perfect day to head outdoors for the annual Cookie Crumble QRP Contest.

The Cookie Crumble is a QRP contest run by Tim Carter W3ATB and Emily Saldana WC3R. It was inspired by the cookies that Emily used to make during the 2016 National Parks on the Air event. You get bonus points for working stations designated as Cookie Monsters. What’s unique about this contest is that you lose points for working Burnt Cookie stations. In any event, it’s a lot of fun.

My set up for the Cookie Crumble QRP Contest.
My set up for the Cookie Crumble QRP Contest.

This year, I headed out to my daughter’s farm to operate from one of the fields. My setup was almost identical to the setup I used last weekend. I used a half-square antenna made from cheap speaker wire, along with my KX3. I set up my chair under a shady tree—for a while, at least.

I wasn’t out for too long, but I worked 10 stations in the contest. One of those was a Cookie Monster station. Fortunately, I didn’t encounter any burnt cookie stations. 

Some of the highlights from today included:

  • My first QSO was with my old friend, Carter N3AO, down in Virginia. It was great to hear him again.
  • I worked VE2DDZ, who was doing a joint Cookie Crumble and SOTA activation. Malcolm had a great signal into Pennsylvania.
  • Outside of the contest, I worked WD8RIF who was doing a Parks-on-the-Air (POTA) activation from Ohio.
WB3GCK hard at work (or hardly working) in the Cookie Crumble QRP Contest.
WB3GCK hard at work (or hardly working) in the Cookie Crumble QRP Contest.

After a while, I began to lose my shade and I was starting to get a little sunburned. Right before I started tearing down, I heard another old friend, Dan KA3D, very faintly. I gave him a couple of calls but, sadly, he couldn’t hear me. We were probably a little too close for 40M. Maybe next time.

It was a great day to be outside playing radio. I also got some more on-the-air experience with my homebrew half-square antenna, which I’ll document in my next post.

Thanks for Tim W3ATB and Emily WC3R for running this fun contest. 

72, Craig WB3GCK

More Socially-Distant Antenna Testing

It was a beautiful day yesterday, here in southeastern Pennsylvania. I hadn’t done any portable operating lately, so this was a perfect day to get out there to test a new antenna I built.

I headed back out to the property my daughter and son-in-law own. They are in the process of restoring an old farmhouse on a large piece of land. Like my last outing there, I had the place to myself.

I mentioned in a previous post that I had built a half-square antenna out of speaker wire. So, I set it up in what had been a cornfield and gave it a go.

My setup out in what had been a cornfield. The old barn in the background is slated to be replaced later this year.
My setup out in what had been a cornfield. The old barn in the background is slated to be replaced later this year.

The bands were wall-to-wall with participants in the CQ WW PX Contest. While I was playing around with the antenna, I worked several contest stations on 40M, 20M, and 15M. Running five watts, I was able to work most of them on the first call. Contesters, of course, have exceptional ears.

All in all, I was pleased with the half-square antenna. I used a slightly different approach to this antenna, which gave me some multi-band capabilities. The KX3 was able to load it up from 80M through 6M. A detailed post on this speaker wire antenna project is in the works.

After two months away from it, it sure felt great to be back out in the field again playing with the radio.

72, Craig WB3GCK

Delving into D-Star

I mentioned in a previous post that I was going to venture into the digital voice modes. Well, I did. I was successful in getting a hotspot up and running, although I did hit a snag along the way.

Yeah, I know; as usual, I’m late to the party on this stuff. Up until now, I’ve had only limited experience with D-Star. Years ago, I used a borrowed Icom ID-1 for 1.2GHz data during a couple of ARES-RACES exercises. I hadn’t used D-Star again until I bought a Kenwood TH-D74A six months ago. Even then, I had only used D-Star to check into a local ARES-RACES net over a nearby D-Star repeater.

My local ARES-RACES group here in Chester County, PA, held one of our monthly Tech Rallies using Zoom. Jim WA3NOA gave an interesting talk on digital voice hotspots. Inspired by Jim’s talk, I went ahead and ordered an MMDVM hotspot from Amazon.

While waiting for the hotspot to arrive, I started studying up. I found lots of great articles and videos out there. W6GPS’s videos on the TH-D74 and D-Star were particularly helpful. Following one of his videos, I picked a hotspot frequency and programmed it into my radio.

The hotspot arrived a few days later. I was immediately struck how tiny this thing is. The instructions that came with it were sparse but clear enough to get started. I was able to successfully connect my laptop to the hotspot’s internal WiFi hotspot and access the Pi-Star configuration screens.

MMDVM Hotspot in use
MMDVM Hotspot in use

Long story short… Before too long, I had the hotspot connected to my home WiFi network and had the D-Star section configured. I keyed up my radio and received the expected D-Star response from the hotspot. Then, I tried to connect to some reflectors. No matter which one I tried, I got a “reflector is busy” message on my radio. Hmmm…

I sent screenshots of my hotspot configuration screens to Jim, but he didn’t see anything out of wack. I next focused on my WiFi router. I tried connecting the hotspot to other WiFi networks. No joy.

Finally, I went out and checked the status of my D-Star registration. That showed that my registration from way-back-when was missing a Terminal ID. An email exchange with WA3NOA confirmed that was likely my issue. My D-Star registration password no longer worked, so I reached out to Jim W3BIF, the admin for the W3EOC D-Star repeater.

My faulty D-Star registration. This turned out to be the cause of my hotspot problem.
My faulty D-Star registration. This turned out to be the cause of my hotspot problem.

The next morning I had an email from W3BIF saying he had straightened out my incomplete D-Star registration. Within minutes, I was connected to a reflector and having a QSO with a ham in Georgia. He reported that my audio sounded great. 

I used to be one of those guys who thought this stuff isn’t real ham radio. I guess I’ve come around a bit. I won’t be giving up CW any time soon, but I will admit it has been fun playing around with this new (to me)mode over the past week. 

Over time, I might branch out to try some other digital voice modes. In the meantime, you can often find me monitoring D-Star reflector, REF20A or REF30C. 

73, Craig WB3GCK

My Activities of Late

I haven’t been posting much here lately. The COVID-19 pandemic and other family obligations have been cutting into my ham radio activities. Nevertheless, I do have a few projects in the works.

A few weeks ago, I started another project in my ongoing series of speaker wire antennas. This one will be a variant of the bi-square antenna. This antenna has the potential to be a little more field-friendly than the delta loop I tested last month. It’s all built; I just need to get out somewhere to set it up and see how it works.

I’ll file my next project under the category of Old Dogs/New Tricks. Back in December, I bought a Kenwood TH-D74a HT. That gave me the ability to reach a nearby D-Star repeater. This week, I purchased an MMDVM hotspot to go along with it. I plan to spend some time in the coming days getting it set up. I’m hoping to be able to eventually connect to the DMR talk groups used by my ARRL section and local ARES-RACES groups. Fortunately, my local group has some experienced hotspot users I can consult if I run into any snags. Wish me luck.

Sadly, our camping season with our little QRP Camper is off to a late start. State park campgrounds in our area have been closed due to pandemic. We have reservations at a state park in Maryland next month, however, and it looks that might be our first trip of the year. I’m looking forward to a little QRP-portable operating from the camper.

My local QRP club has started making plans for Field Day. We have a set of social-distancing guidelines we’ll be following this year. We’ll be limiting the number of participants, keeping our tents at least 10 feet apart, and eliminating common eating areas. Also, we won’t be sharing stations and equipment. This year’s Field Day will be different, for sure. 

Other than that, I’ve been active on our local ARES-RACES nets, and I have been checking into the Pennsylvania NBEMS Net on Sunday mornings. 

You can also find me on 40M or 80M CW in the evening. I usually hang out around the SKCC watering holes.

I’ll be posting more on all of this stuff in the coming weeks. Until then, stay safe, and I’ll see you on the air. 

73, Craig WB3GCK

USNTC Bainbridge Fire

I came across a news item posted in one of the U.S. Navy Facebook groups I follow. There was a fire at what is left of one of my duty stations from back in the early 1970s. It was where I went through Navy Radioman School and learned the Morse Code.

Here’s a link to the article: Historic Naval Training Center Burns Down on Susquehanna River

The fire at the former Bainbridge U.S. Naval Training Center in Port Deposit, Maryland. I don't recognize the building in this picture. (Photo: Maryland State Fire Marshal/ Facebook)
The fire at the former Bainbridge U.S. Naval Training Center in Port Deposit, Maryland. I don’t recognize the building in this picture. (Photo: Maryland State Fire Marshal/ Facebook)

I was stationed at the U.S. Naval Training Center, Bainbridge, in Port Deposit, Maryland, from November of 1970 through April of 1971. The base was very old then, but there was some history to it. Bainbridge first served as a Navy training center for new recruits (aka boot camp) during World War II. After that, it was home to a variety of Navy schools, including the Radioman School that I attended.

The old wooden barracks were pretty decrepit, by the time I got there. While the accommodations at Bainbridge weren’t the best, I still have some good memories of the short time I spent there.

The Navy deactivated the base in 1976, and the expansive property has been mostly vacant and over-grown since then. Fortunately, the Bainbridge Museum is just down the road in Port Deposit, Maryland. They have captured a lot of old photographs and items from the old base. I paid a visit to the museum back in 2009. It was a walk down Memory Lane for sure.

The Bainbridge Museum in Port Deposit, Maryland
The Bainbridge Museum in Port Deposit, Maryland

So, thanks to Bainbridge Naval Training Center for getting me formally trained in radio and CW. Almost 50 years later, I’m still using much of what I learned there.

73, Craig WB3GCK

Morse Code Day 2020

It’s that time of year again. Today is Morse Code Day. Celebrated each year on April 27th, Morse Code Day coincides with the birth of Samual F.B. Morse (1791-1872).

Samuel F.B. Morse circa 1840 (Open-source image)
Samuel F.B. Morse (circa 1840)

Morse contributed to the development of the single-wire telegraph and developed the encoding method, which bears his name. But, of course, you probably already knew that.

I’m always amazed that I still use a means of communication that was first used in 1844. CW has been my favorite mode since I learned the code in Navy Radioman school nearly 50 years ago.

So, have a happy Morse Code Day. I hope to hear you on the air today!

73, Craig WB3GCK

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

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