Equipment – Page 2 – WB3GCK QRP Amateur Radio

The Raddy RF760 Shortwave Radio

A while back, I purchased the Raddy RF750 Multimedia Music Player and did a blog post reviewing that remarkable little radio. The folks at Radioddity reached out to me recently to see if I would be interested in taking a look at their latest offering. A week or so later, I received the Raddy RF760.

[Disclaimer: In the interest of full disclosure, this radio was sent to me free of charge to evaluate and review. This was with the understanding that I would write an honest and unbiased review.]

What It Is

The seller refers to the RF760 as a “full-band radio”. That’s an apt description, since it covers everything from the AM broadcast band up through the UHF range.

Here are the specs from the iraddy.com website:

FM 1: 64.0-108MHZ
FM 2: 76.0-108MHZ
FM 3: 87.5-108MHZ
AM: 520-1710KHZ
SW: 2.00-30.00MHZ
CB: 25.00-28.00MHZ
AIR: 118.00-138.00MHZ
VHF UHF: 20.000-520MHZ
VHF: 30.00-223.00MHZ
VHF: 144.00-148.00MHZ
VHF: 156.025-163.275MHZ
UHF: 430.00-520.00MHZ
WX: 162.400-162.550MHZ
Product dimensions: 4.37 x 2.36 x 0.79’’ / 11.1 x 6 x 2CM
Lithium battery: BL5C 1000mAH 3.7v 3.8WH
Loudspeaker: Ф40MM 8Ω 1W
Headphone output: 3.5MM stereo input
External antenna hole: 3.5MM
Storage Capacity：700 stations in total（FM: 100, MW: 100, SW: 100, AIR: 100, CB: 100, VHF/UHF: 100, UBD: 100)

With the battery installed, the RF760 weighed in at a mere 3.8 ounces (108 grams) on my kitchen scale.

The box includes:

RF760 radio
1000MAH 3.7V Lithium battery
Earbuds
USB-C cable for charging
External antenna wire (approx. 10 feet)
Wrist strap
Storage pouch
User manual

RF760 vs RF750

It’s clear from the specifications that the RF760 is not an upgraded RF750. The RF750, with its Bluetooth and ability to play MP3 files, is more of a multimedia player. The RF760 does not have those capabilities, but, rather, provides expanded frequency coverage.

The Raddy RF760 (left) and the Raddy RF750

In my view, the RF760 is aimed more towards shortwave listeners and scanning enthusiasts. It includes features like selectable bandwidths, selectable demodulation modes on certain bands (AM/USB/LSB/NFM), and adjustable squelch.

The RF760 also includes a headphone jack (earbuds included) and a connection for an external wire antenna. These features are lacking on the RF750. The RF760 also has a digital display, which the RF750 does not. Both radios are charged via a USB-C connector.

The RF760’s additional features come with a higher price tag. As of this writing, it was selling for $99.99 USD

My Impressions

The RF760 is one small radio. It’s roughly about the size of an Altoids tin and weighs next to nothing. (It weighs about 0.65 ounces less than the RF750.) You can fit the RF760 in a shirt pocket, and you might even forget that it’s in there.

There’s a lot going on with the RF760. Even with the power off, a press of any button will light up the display showing time and temperature. Oh yeah, did I mention this thing even has a built-in thermometer? It even includes an alarm clock and a sleep timer. If you can think of a function, the RF760 probably has it.

The user manual does a decent job of covering the myriad of features in this radio. The small size of the printed manual, however, is a little tough on my old eyes. Fortunately, the Raddy website has a PDF version of the manual for downloading. The softcopy manual allows me to search for specific functions, which is handy. I also stored a copy on my cell phone, so I always have it available. As is typical of manuals for Chinese products, some of the wording is not always clear. For example, a section covering how to delete a station that has been saved to memory is titled “Delete the radio.”

The various configuration options (e.g., bandwidth, demodulation mode, tuning increments) vary according to the band you are on. Once you get the hang of it, navigating through the options and selecting specific values becomes an easy task.

In the FM mode, the sound quality is reasonably good, considering the RF760’s diminutive size. In all honesty though, I think the RF760’s audio lacks the richness and fullness of the RF750. When using the included earbuds, however, the RF760’s audio is greatly improved. On FM, make sure you have the radio set for the proper de-emphasis (75 microseconds here in the U.S.).

The weather alert function is one of the more important features for me, and I had the opportunity to give it a “real world” test. My area was under a tornado watch, and we had multiple severe thunderstorm warnings. While tuned to the weather band, a long press of the “SET” button places the radio in the “SCAN” mode. When NOAA issues an alert, the radio comes on with a brief tone followed by the weather station’s audio. There’s no loud siren like the RF750 has, but that’s fine with me. After an alert, you need to long-press the “SET” button to go back into the “SCAN” mode. During the storms, the RF760’s weather alert function worked flawlessly, going off three or four times.

Tuning is interesting in that it uses a combination of two methods: up/down tuning buttons on the front panel and a rotary “shuttle tuning” knob on the right side of the radio. You can select the tuning increments for the buttons, which is helpful. You can also select the digit of the displayed frequency that is adjusted by the rotary knob. Now, I’m an old “knob spinner” from way back, so I’m generally not a big fan of using buttons for tuning. However, once you get the hang of using the shuttle tuning knob, you can tune to a specific frequency quickly. You can also scan the selected band by long-pressing the “up” or “down” tuning buttons.

There’s a lot of information shown on the display panel. On such a small radio, though, I find a few of the smaller items hard to read with my old eyes. Fortunately, these are items that I don’t have to deal with often. You folks with better eyes probably won’t have a problem.

I haven’t done any formal measurements on battery life, but you should be able to go for days before recharging. The USB-C charging port is handy; I can charge the radio with the same chargers I use for my phone.

Bottom Line

The RF760 is a small, lightweight, and feature-packed radio. For camping or in my emergency go-kit, I’d go with the versatility of the RF760. It’s like the Swiss Army knife of radios. I especially like how the NOAA weather alert feature is implemented on this radio. However, If I want to listen to music while working around the house, I’d go with the RF750 and it’s superior audio.

73, Craig WB3GCK

The Raddy RF750 Multimedia Music Player

My (far) better half and I like to keep a radio in our little travel trailer. When we’re camping, we often listen to baseball games in the evening (go Phillies!) while sitting around the campfire. It’s also handy to have a weather radio on hand, when the cell service is unreliable or non-existent. I bought this little radio to see how it compares to the old radio we’ve been using for years.

The Raddy RF750 is sold by the folks at Radioddity. When I went out to their website to buy one, it was showing “sold out.” They had some in stock, however, on Amazon, so I placed my order there. The same radio is also available at a lower price from Chinese sellers branded as the HanRongDa HRD-700. Being the impatient sort, I went with Amazon Prime at a slightly higher price than the $34.99 price tag on the Radioddity website. (When I checked a few days after receiving my radio, Amazon was showing it as “currently unavailable,” and Radioddity was still “sold out” in the U.S. These things must be selling like hotcakes.)

What It Is

The Raddy RF750 is a compact multimedia player with a radio that covers the AM, FM, shortwave, and the NOAA weather bands. It has a Bluetooth mode, so it will play audio from your smartphone. The RF750 will also play MP3 files from a micro SD memory card (up to 256GB) you can insert into the unit. It’s powered by a 1000mah Li-ion battery, which you can recharge via a USB-C port on the radio.

When playing audio via Bluetooth or SD card, the RF750 has an audio equalizer with six preset configurations to choose from. You can also set the radio to scan a band automatically and store the stations it finds (up to 20 stations each on FM and AM, 10 stations on each of 7 shortwave bands). This can be useful when you’re traveling. There is also a sleep timer that will shut off the radio after a user-selected time (10 to 70 minutes).

Here are the specifications from the Radioddity website:

FM: 87.5-108MHz
AM: 520-1720KHz
SW: 5.7-17.9MHz
WB: 162.400-162.550MHz
Memory: Support TF card, Max 256GB
Audio format: AV, WMA
Power supply: replaceable 3.7V 1000mAh BL-5C lithium battery included
Charging: DC 5V, Micro USB-C interface
Size: 3.5″ x 2.4″ x 1.5″
Weight: 0.22lbs

My Impressions

When I first unboxed this thing, the first thing that struck me was the small size. The descriptor, “compact,” is an understatement. It’s smaller than an Altoids tin and just a bit thicker. Weighing in at less than 4 ounces, it won’t add much weight to your go-kit or backpack.

Along with the radio, the box included the Li-ion battery, USB charging cable, wrist strap, a rubberized drawstring storage pouch, and a user manual. The battery was easy to install and charge up.

I powered it up and tuned to a local FM station. Frankly, I was blown away by the sound coming out of this little radio. Apparently, it uses DSP filtering to provide that sound clarity. Given the radio’s small size, tuning can be a little touchy for an old guy with clumsy fingers. Fortunately, there’s a tuning indicator that makes it easy for me to lock in on a station.

I was particularly interested in the weather band capabilities. In addition to covering the 7 NOAA weather channels, the RF750 also includes a weather alert function. In this mode, the audio is silenced, and the radio appears to be scanning the 7 weather channels. I haven’t been able to test this out yet, but I plan to see what happens during NOAA’s next weekly test.

[Update: I set up the RF750 in the “Alert” mode for the NOAA weekly weather radio test, and the RF75o’s alert went off as expected. The only issue is that the siren sound it makes is excruciatingly loud. On a positive note, when a weather emergency happens, you will definitey know about it!]

When I tested the Bluetooth mode, it paired easily with my smartphone. Although my phone’s audio played through the RF750 was nice and clear, I don’t see myself using this function much.

To test the “Music Player” mode, I copied a few MP3 files to a 2GB micro SD card, which I inserted into the RF750. The sound quality coming out of the tiny speaker really impressed me. I plan to load more of my music collection onto a larger memory card, which I’ll leave installed in the RF750.

I was a little surprised that the RF750 doesn’t include an earphone jack. I would have expected one on a portable radio like this.

The user manual provided is typical of low-cost Chinese products. The English isn’t always clear, but it was enough for me to figure out how to use the various functions.

I have to say, I’m impressed with this little unit and all the features packed into it. It will be a handy item to have around, especially while camping or during emergencies. In fact, during a recent snowstorm, we lost power for a while. The RF750 allowed us to check the local NOAA weather forecast, listen to local news on the AM band, and enjoy some music on FM.

Disclaimer: I have no financial interest in this product. I purchased it with my own funds, and I’m merely a satisfied customer.

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

Old Tuner to the Rescue

According to the weather prognosticators, today is the start of a 4- or 5-day heatwave here in southeastern Pennsylvania. So, I wanted to get out early for some antenna testing before things heated up too much.

I planned to play around with the speaker wire end-fed halfwave antenna I built recently. To do this, I went back to my favorite antenna test range—my daughter and son-in-law’s property.

I set up the formerly 66-foot wire (now about 63 feet) in an inverted-V configuration. Since the last time I used this antenna, I trimmed off a couple of feet to see if I could get my little Hendricks SOTA tuner to load it on 20M.

I started with the SOTA tuner on the 40M band and worked a POTA activator in Indiana. I moved up to 20M, but the SOTA tuner wouldn’t tune below a 2.2:1 SWR.

Before I left the house today, I had the forethought to pack an old antenna tuner I built about 25 years ago. I used it extensively years ago, but I relegated it to the shelf when fancier equipment came along. I switched to the old tuner, which I configured as an L-match. It loaded up nicely on 40, 20, and 15 meters. As a bonus, the old-school tuner gave a good match on 30 and 17 meters.

My 25-year-old homebrew antenna tuner. It doesn't look like much, but it did a nice job with my end-fed halfwave antenna cut for 40M. — My 25-year-old homebrew antenna tuner. It doesn’t look like much, but it did a nice job with my end-fed halfwave antenna cut for 40M.

After I finished experimenting with the antenna, I set out to make a few contacts. It was a busy day for Parks-on-the-Air (POTA) activators. I worked 10 of them in 8 states plus Puerto Rico. Three of the QSOs were on 17 meters. It was nice to hear POTA activity up there.

All in all, I was pleased with how my old homebrew antenna tuner performed. I don’t think it will be spending as much time on the shelf in the future.

73, Craig Wb3GCK

My HT Go Bags

I mentioned in a previous post my obsession with bags and cases for equipment. Well, this post is further evidence of that.

Over the past year or so, I purchased a couple of new HTs. It was a long-overdue upgrade. I first acquired a Kenwood TH-D74. About six months later, I came across a deal on an AnyTone AT-D878UV I couldn’t resist. Accessory-wise (batteries, chargers, antennas, etc.), these radios are very different. So, I wanted a way to organize these accessories and pack everything for travel and ARES-RACES events.

After looking at available options, I settled on an electronics travel organizer from a company called Bagsmart. They weren’t very expensive, so I bought one for each HT. I purchased my bags on Amazon for well below the list price shown on the manufacturer’s website. The specific models available on Amazon, however, seem to come and go.

The bag measures 9.4″L x 7.5″W x 2.8″H and is constructed of water-resistant—not waterproof—nylon. It weighs a mere 0.25kg/ 0.55 pounds. There three padded partitions that attach with Velcro that can be repositioned or removed. The bag also has a zippered mesh compartment under the lid that is great for storing cables, adapters, etc. There’s also a small compartment intended for memory cards or thumb drives. Despite its small size, it has sufficient room for everything I use for each radio.

My HT "go bags." Several items were left out of the open bag, for the sake of clarity. I often pack a desktop charge, roll-up J-pole, a couple of spare batteries, and a hotspot for digital voice modes. — My HT “go bags.” Several items were left out of the open bag, for the sake of clarity. I often pack a desktop charge, roll-up J-Pole, a couple of spare batteries, and a hotspot for digital voice modes.

These bags have been perfect for my needs, but they do have their limitations. While they offer some protection for your radios, we aren’t talking Pelican cases here. If you need something water-tight that you can bang around on a rock, these bags aren’t for you. These are light-duty bags, to be sure.

My only complaint with these bags is that the partitions are somewhat flimsy. Something a bit more rigid would be more to my liking. They do, however, keep things separated inside the bag.

There’s nothing earth-shattering here, but if you need an inexpensive way to organize your gear, this bag (or something similar) might do the trick. The usual disclaimer applies: I have no financial interest in this company or their products. I’m just a satisfied customer.

73, Craig WB3GCK

My Hotspot is Back From the Dead

While trying mobile DMR last month, my (relatively) cheap hotspot experienced an untimely death. I set the hotspot aside as a future troubleshooting project.

While the Pi-Zero board appeared to be working, the MMDVM board was dead as a doornail. The OLED display was blank, and the RF side of the hotspot was non-responsive. It also wasn’t interacting with the Internet at all.

The other day, I came across a posting on a Facebook MMDVM page that shed some light on my problem. Some users reported shorts between the internal boards and the aluminum case. This tidbit of information prompted some further investigation.

I removed the top of the case, reinstalled the antenna, and applied power. To my surprise, the hotspot booted up and came back to life.
I let it run for a while without the case to verify that all was well. It was.

I noticed a solder connection that extended a little beyond the edge of the MMDVM board. It appeared to be a power connection, so I suspect that might have been what shorted. I also noticed that a single screw and the header pins are all that secure the top board. I’m guessing the board shifted a small amount while mobile causing the short.

My disassembled hotspot. If you look closely, you can see the electrical tape I added inside the top cover.

To remedy this, I applied electrical tape inside the top cover of the hotspot. Not being 100 percent certain where the problem was, I covered everything except the vent openings. I used a razor blade to trim the tape around the OLED display and antenna jack openings. I also took a file to the little solder blob I had noticed. (I exercised extreme caution in doing this since I’m sometimes prone to creating new problems.)

I reassembled the case and powered it up. Voila! It still worked. Hopefully, this fix will avoid any reoccurrences and make it withstand the vibrations of mobile use.

Although you’re far more likely to find me on CW on the HF bands, I do monitor Brandmeister TG-3142 (Pennsylvania State-wide) on DMR. And, on occasion, I listen to D-Star REF20A.

73, Craig WB3GCK

K1EL WKmini Morse Interface

I haven’t bought any new ham radio toys lately, so I decided to upgrade the homebrew passive CW interface I use for contesting. I had been looking at the K1EL WKmini USB keyer for a while. I recently bought one, and it fit my needs exactly.

I’m not a big contester, but for Field Day, Winter Field Day, and some POTA activations, I key the radio using macros in the logging software. For years, I used a passive interface built into a DB-9 connector, along with a USB-to-RS-232 adapter. The interface consists of a resistor and a 2N2222 transistor. It served me well, but occasionally, there were some hiccups. With this simple interface, the logging software on the laptop is doing all the CW work. Once in a while, I noticed some timing issues in the code sent.

The WKmini is based on the WinKeyer 3 chip and designed for use with contesting logging software. The WKmini takes on the work of generating the CW, so it eliminates those timing issues. The logging software sends commands and data to the keyer, and the keyer does the rest.

The other nice feature is the paddle input. This feature allows me to instantly send CW manually when needed. I was able to do this in my previous setup, but it was a bit more complicated. The WKmini keyer is a more simple, elegant approach. Its small form factor makes it ideal for portable operating.

The WKmini Morse Interface from K1EL Systems. This compact device measures 2.25" W by 1.75" D by .5" H. — The WKmini Morse Interface from K1EL Systems. This compact device measures 2.25″ W by 1.75″ D by .5″ H.

The WKmini was incredibly easy to set up. I connected the keyer to my laptop, and Windows immediately recognized it. I used the free K1EL WKscan utility to determine which COM port the keyer was using. I connected the keyer to my KX3 using a stereo patch cable with 1/8-inch connectors. Using the K1EL WK3demo utility, I was successful in keying up the radio and sending some code.

The last thing I needed to do was to configure my N3FJP logging programs to use the WKmini instead of the old passive interface. The WKmini doesn’t have any external controls; the logging software provides the necessary settings. There is a long list of software that supports WinKey keyers, including the N3FJP suite of software. The User Manual covers the N3FJP software, which was helpful. So, with a few mouse clicks, I was in business. All of this testing and setup took less than 15 minutes.

Like other K1EL keyer products I own, the WKmini is a solid performer. I’m hoping to give this little gem a workout during Winter Field Day later this month.

73, Craig WB3GCK

Water Bottle and HT Holder

My XYL says I’m obsessed with bags, cases, and containers. She might be right.

During normal years, I participate in several public service events with my local ARES-RACES group. For a couple of those events, I’m often out on foot away from my truck with an HT. I wanted a convenient way to carry a few essentials for those situations.

I put together this little kit last Winter, but it hasn’t seen much use. Sadly, the pandemic forced the cancellation of our public service events this year. This year has been anything but normal.

My water bottle carrier with HT pouch attached on the side

I wanted something to carry the following items:

Water bottle
HT
Spare battery for the HT
Small notepad and pencil
Minimal first aid kit (a few antiseptic wipes and bandages)
A few snacks

To carry everything, I bought a no-name water bottle carrier on eBay for about $13. I looked at lots of bottle carriers, but this inexpensive one was best suited to my needs. I’d provide a specific link, but these eBay offerings tend to quickly come and go. A search for “tactical military molle system water bottle bag” should should yield lots of options. I found some for less than $10. Of course, there are name brands out there that cost much more.

Here are the particulars of the one I bought:

The bag is constructed of 600D nylon. The specs say it’s waterproof, but I haven’t verified that.
The main compartment is 10.6″ tall and 4.3″ in diameter. It’s large enough to hold a 2-liter bottle. If I use a smaller water bottle, there’s room in this compartment for some other gear, too. It also has a zippered lid that will keep your gear from falling out.
There’s a 5.9″ x 4.3″ x 2″ gadget pouch on the front. This pouch is large enough for a couple of HT batteries, notepad, pencil, first aid kit, etc.
It has plenty of MOLLE webbing. A couple of them have Velcro for attaching patches. You could use the straps on the rear of the bag to attach it to another larger bag or your belt.

This bag certainly has room enough to carry everything I plan to carry in it. Heck, I’m sure I could carry a complete HF QRP station in it.

To hold my HT, I tried out several MOLLE-compatible pouches. The one I plan to use is a no-name item I bought from a Chinese seller on eBay. It only cost me about $4.00 (shipping included), but it works well with my current collection of HTs. I attached it to the side of the bottle carrier using the MOLLE webbing. An Internet search for “radio pouch” will bring you a dizzying assortment from which to choose.

As a final touch, I added a patch with my callsign on it. I ordered the 4″ x 1″ custom embroidered Velcro patch from a shop on Etsy. This little bit of vanity cost almost as much as the bag, but it looks good.

So far, I’ve only used this bag for a few short hikes. I haven’t used this bag for its intended purpose yet, but I’m hoping that will change next year. (Fingers crossed)

73, 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.

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.

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

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
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!

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.

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