N4REE - Minimalist Ham

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QMX – High band version – kit built

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Introduction

The QMX is a tiny little multiband, multimode, software defined transceiver, from QRP Labs, that runs at QRP power, roughly 5 watts output. Mine is the “High Band” version covering 6 bands from 20 meters through 10 meters. While designed for CW, various digital modes, and SSB, my interest is (you guessed it) CW.

Mine is kit built. I like building things, and building allowed me to acquire a working QMX several months earlier than waiting for an assembled version.

This radio is one version of a series designed by Hans Summers, G0UPL / AF7BF. I am most impressed by how compactly it is packaged. The parts are packed in so densely that successful assembly requires sharp vision, tiny soldering iron tips, and a jewelers loupe. Click on any of the images and then click again to see how dense things are. My successful assembly came by working in small steps and inspecting constantly with that loupe.

Rather than writing more about the technical details of this radio, you might want to read Hans’ own description of how he developed it, a fascinating read for those who like evolution stories.

Assembly done – Let’s start testing

Jul 12, 2024 – At first, I thought it wasn’t getting power correctly.

Yes, the instructions say that when first powered connected PC sees it as a thumb drive.  It also says there is nothing displayed. Yet, somehow I still expected ~some~ sign of life and saw none … other than the bench power supply showing about 1/8 A power draw. (I had it set for 7 vDC and .250 A)  I also have an inline voltage regulator set for 7 volts. It is extra protection to avoid voltages over 12.0, but set to 7 for initial testing.

Look closer! Yes, there is a drive named “QMX” on the PC. Drag the firmware file, 1_00_020.QMX to that drive. Drop power. Power up again and be greeted by “Initializing EPROM,” and other messages. Voila! It works without emitting smoke.

Next, CONFIGURE and test …

Jul 13 – 2024 – First RX tests: After a round of thunderstorms, I connected the HS20 antenna and listened on 20M for a while. This little rig sounds ~almost~ as good as the TR-45L, but has only one CW filter*, 300Hz, which is a reasonable choice. Its audio is FAR better than the (tr)uSDX with enough amplitude that I don’t need the follow-on audio amp, and no unexpected squealing so far.

*update: More filtering options appear in firmware version 23.

So far, so good. Let’s move up to “normal” input power, 11.7v.

BandPower outputPower drawn
20M – 14Mhz4.06 watts0.582 A
17M – 18 Mhz5.61 watts0.797 A
15M – 21 Mhz5.64 watts0.903 A
12M – 24 Mhz3.93 watts0.743 A
11M – 27 Mhz4.05 watts0.772 A
10M – 28 Mhz3.63 watts0.718 A

Jul 14, 2024 – First quick TX tests (key down for 2 seconds) RF power output was with about 11.7v from a Talentcell battery, RF output goes to my QRPoMeter SWR/PWR meter, then to a dummy load. Power drawn was measured from a bench power supply.

On the air: As of Jul 31, 2024 the QMX has enabled quite a few POTA QSOs. I’m pleased with its performance and use it for those bands the TR-45L doesn’t cover.

Update: Oct 18, 2024 – Dozens of QSOs have flowed through this little radio. Yesterday, it helped drive the fun-o-meter way above max. That came from a QSO with Paul Butzi, W7PFB out in the woods in Washington state. I parked on his frequency until I started hearing very faint CW. The usual advice is to avoid trying to contact until you’re absolutely certain of 100% copy. I broke that rule, at the 99 and 44/100s mark. (Oldsters will understand the reference.) Thanks to Paul’s sharp ears, we made it work at the 229 RST level. Thanks Paul!
[fun-o-meter image “borrowed” from Paul’s QRZ page.]

Overall, the radio is a joy to use. Hans, the designer, developed a user interface that is very easy to manage, and the radio has the sensitivity and audio characteristics that obviously perform well for weak signal work. As much as people praise the TR-45L for excellent audio, I enjoy the QMX audio more. It seems to have a better SNR than the TR-45L, and recent filter updates have let me move zero-beat and sidetone frequencies to something more pleasant to my hearing.

Next… AK and HI.

T41-EP SDT “Pop-Pop” (3 of ?)

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When we last visited this radio, it was almost complete. That’s when I decided to switch out the power amplifier. The “-EP” in the name means “Experimental Platform.” Let’s experiment. The reason is because of reports of poor power output on higher bands due to the original power amplifier using transistors with a very steep output falloff above 20 Mhz. A newer power amp has a much flatter frequency response at 20 watts output. (I only want 5, but will appreciate the extra headroom.)

The semi-kit by K9HZ Bill Schmidt arrives as a PCB (Printed Circuit Board), a few semiconductors, a few transformer cores, some wire, and a BOM (Bill Of Material) for the rest of the parts. Almost all of the parts were SMD (Surface Mount Devices), giving me the opportunity to learn a new skill. 🙂 Despite needing a very good magnifying glass and a jeweler’s loupe, construction went very well.

So did initial power testing. The fun came along at the next stage, when the “bias” potentiometers are adjusted to produce the correct current flow through each of the power transistors. For that, the amp needed a signal voltage from the transceiver. So, I mounted it in the case and hooked up power.

A very quick “POP-POP” was the response on flipping the rig’s power switch. Puffs of smoke from new holes in the power transistors floated up. All electronic devices are powered by smoke and once you let the smoke out, they no longer work. ;{

What the???? User error, of course. Wrong polarity power. I tried using a new battery, a new LiFePO4. It is a very nice battery that will serve well as a base station power source. My mistake was NOT making up new power cables, but using a couple that were in the box. Hey, these two fit together. I blithely went ahead without realizing that using them in series, instead of alone, produced a polarity reversal. Stupid error! … POP-POP and along with it lesser POPs and PFFFTs inside the mostly complete T41.

As I write this, I don’t know the extent of the collateral damage. After replacing a few parts on the power board, the rest of the T41 does not come to life and there are significant voltage drops on the 5V line. It may be time for an extensive rebuild.
UPDATE: There are enough “anomalies” with the existing build that I’ve decided to rebuild completely using the V12 version of the T41. More function, refined RF specs, and known-good hardware are some of the reasons.

Meanwhile, I can easily rebuild, and correctly test the power amp. It is independent of the main radio and easily rebuilt.

P.S. Safety glasses recommended for first power. In this case, it was under a magnifying glass which stopped the remnants.

Antenna shootout: Hamsticks vs TW2010

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After taming the Hamsticks, I turned my attention to effectiveness. How do these antennas compare to another in my collection?

Contestant 1: Hamstick verticals

I have used various forms of 1/4 wave ground mounted verticals, including the Hamsticks, for quite a while. They have the attributes of being relatively low cost, easy to setup almost anywhere, and will perform. Yes, everyone calls them “compromised,” but that’s a term that can be applied to most any antenna. I use my verticals as “backyard portable” from my home QTH in the midst of an HOA community. I have no objections from wonderful neighbors, and no complaints from passers-by who probably can’t even spot the antennas.

There’s a radial field under the antenna, 16 radials of 18 feet each.

For some Hamstick variations, I use loosely deployed radials above ground. See the taming article for more details.

For almost all verticals, dragonflies are attracted to the tops. Dunno why.

Contestant 2: DX Engineering TransWorld 2010

I also use a DX Engineering TW2010 from time to time for the 20M through 10M bands. The TW2010 is a 5 band vertical dipole. Each side of the dipole is a “T” shaped section. A box between those sections contains a group of loading coils. It is about 5 feet wide and stands 8 and 1/4 feet tall. DX Engineering originally acquired the design from someone else and then set about its own manufacturing. I can confirm that it is well built, of fine quality materials, and engineered for easy set-up.

The only complaint about the physical form is that the 4 legged base occasionally spontaneously self-disassembles. (Thanks Elon for that description.)

DX Engineering describes the antenna as “portable” because they offer a carry bag about the size of the typical golf bag. Now, add to the antenna parts the 65 feet of coax that’s used for impedance matching, and the “portable” antenna becomes, in my mind, not man portable, but truck portable. … about 30 pounds.

P.S. KA3DRR, Scott Morrison, drags his TW2010 around in a wagon he calls Land Rover One. He’s not one of those strong healthy young males who grumble about the difference between a 9 ounce radio and a 14 ounce radio. 🙂

The competition

Some of the YouTube ham personalities review antennas by describing them in manufacturers’ terms, showing how they are assembled, and usually taking them outside somewhere, hooking up 100w SSB transceiver and making a few calls. “See, it works!”

Of course it does, almost everything does. If K0KLB, Kevin Behn, can loads up his grain auger or hay wagon at QRP power and make contacts, almost any other antenna “works.”

I’m more of a data person. Fifty years in the IT business, and the delight of working many of those years in a research laboratory, does that to a person. I like data to support conclusions. So, I use a ZachTek WSPR Transmitter to check out antennas. WSPR is Weak Signal Propagation Reporter, a network of radio stations that listen for specifically coded signals and file them in a searchable database.

For these tests, I set up 12 minute runs for each antenna in midday on May 27. Midday is not optimal for any particular band, so results don’t indicate the best that can be achieved during peak propagation periods. But, the results do show relative performance of each antenna compared to another. Yes, there are those who say propagation conditions vary constantly, and I agree. Running 6 tests as close together as possible is the best that I can do to mitigate constant change. I collected results using the wspr.rocks site, one of several that collect WSPR data.

There are three rounds of tests, each individual test running for 12 minutes:

  • TW2010 set for 20M vs a 20M Hamstick with a radial field in the grass
  • TW2010 set for 15M vs a 15M Hamstick with 3 loose radials on the ground
  • TW2010 set for 10M vs a 10M Hamstick with 3 loose radials on the ground
SpotsAvg SNR (dB)Max KMSpots @ Max
TW 20M190-1738081
HS 20M121-1838081
TW 15M103-1764664
HS 15M88-1864666
TW 10M72-1842513
HS 10M50-2042134

Counting spots, the TW2010 performed better than each comparable Hamstick. That’s not really a surprise since well tuned dipoles usually outperform 1/4 wavelength verticals. The margins for numbers of spots are 35% better on 20M, 15% better on 15M and 31% better on 10M.

As for reach, the Maximum Kilometer distances are almost identical, with outliers for both antenna versions. At max distance, the Hamsticks have more hits which seems a disparity from the overall spot counts. The SNR averages are only 1 to 2 dB difference, with the Hamsticks showing a stronger average. So, why is it they have a lower number of spots? Tis a puzzlement…

For the graphic record, here are 6 maps corresponding with the 6 runs.

TW2010 20M
TW2010 15M
TW2010 10M
HS 20M
HS 15M
HS 10M

Turning from data to reality, I’ve made 6 QSOs from my Florida QTH to Oregon: 1 with the 20M Hamstick, 2 with the 20M TW2010, 2 with the 20M Wolf River Coils 17’whip, 1 with the 15M Wolf River Coils 17′ whip , most on different days, different times, different RSTs. so, yes all of these antennas “work.” 🙂

In the end, a subjective question remains: Is it worth paying about 6 times more for the TW2010 than for my collection of Hamsticks?

UPDATE 10/20/24: Two recent events happened recently with the TW2010.

  • A QSO with Paul Butzi, W7PFB out in the woods in Washington state. I’ve been chasing POTA for a long time, and WA is a LONG way from FL. Paul and I made a faint QSO, via the TW2010 and my QMX on my end and 10W into a a Chelegance MC-750 on his end.
  • The next day, frequency agility worked very well on the TW2010 as I made QSOs on all of its bands, 10m, 12m, 15m, 17m, 20m. Yes, I have Hamsticks for each of those bands, but band switching was easier with the TW2010’s “U” plugs, even faster than the Hamstick quick disconnects. Good propagation days and beautiful fall weather brings out POTA activators on all bands.

Taming my Shark HamSticks

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Neighbors near me in this HOA location are very tolerant of my “backyard portable” vertical antennas. The antennas are not obtrusive in appearance, use little space and work reasonably well considering they are not multi element yagis on a 60′ tower.

For some time, I worked with Wolf River Coils verticals on 40M, 30M, 20M. I use them on a tripod sitting over a radial field of 18 radials, each about 16′ long. While reasonably effective, changing bands is really fussy. Get out the NanoVNA, adjust the coil, adjust the whip length, repeat until good enough for the transmitter to be happy. Wash, rinse, repeat…

Some will suggest a multiband vertical instead. Even though I had a good experience with a fellow ham’s 6BTV, I’m not willing to live with its equally fussy tuning and losses, esp when it’s hidden inside a flagpole and every adjustment is a sequence of: lower the pole, uncover the antenna, adjust, re-cover the antenna and re-raise the pole, quite an ordeal.

So, I had the idea that I could acquire a collection of Hamsticks (40M, 30M, 15M, 10M) tune ’em once, install quick-change adapters on them and have band changes within seconds. BZZZZZZZZZT! A couple of them worked OK above my radial field. The others wouldn’t. We read frequently that more radials are always better, and Callum tells us that up to a certain point that’s true.

More radials: It Ain’t Necessarily So

Gershwin tried to tell us… I spent a lot of time yesterday trying each of these HamSticks in different configurations. My goal was to discover the configuration of each with the lowest SWR, as indicated by a NanoVNA.

My first variable included trying them directly atop the WRC tripod and then atop 1 or 2 aluminum extensions, 24″ long, that are part of the Wolf River Coils family. Only one of the HamSticks liked to be atop the extensions. The 40M stick worked out best atop two 24″ extensions. All the rest sit directly on the tripod.

My second variable included different radial configurations: (1) the in-the-grass radial field, (2) a set of 3 radials each 33 feet long, and later (3) some shorter ones. The 40M and 20M sticks were OK with the 18x 16′ in-the-grass radial field. The others wanted shorter radials. The 15M stick liked 3×33′ radials better (1.572 vs 2.100). Next, I folded those in half and got even better results. After that revelation, I reduced the 3 radials to 1/4 wavelength for 15M, 11 feet each, and found yet better results. Same thing for 10M. Three really short radials outperform a bigger radial field. Who would’ve guessed?

Photo of one hamstick mounted on the WRC tripod and the other three leaning against a wall

Of course, these measures of goodness are simply SWR numbers from a test device. On air performance is the real test. I’ve already made on-air contacts with all of them. My next round of measured testing will be WSPR runs.

Till then, this chart sums up my test results. I’ll be using he bold entries to make band changes fast, easy and tuner-free.

BandNo radials3 x 11 ft3 x 33 ft18 x 16′ field
40M3.65n/a1.7181.387
20M3.52n/a1.0821.085
15M1.7181.1391.5722.132
10M1.5951.4831.5831.656

T41-EP SDT (2 of ??)

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Construction is well on its way. All the boards are built and the transmitter has passed an important milestone. First a look at the assembly which currently consists of three panels.

On the left is the back panel which currently is home for the 20 watt Power Amplifier board and its boost supply. The middle is the base panel which is home for 5 boards, itemized shortly. The panel on the right is the front panel which accommodates the display, four encoders and an array of pushbutton switches.

photo of the 3 main panels

Back panel

The 20W power amplifier board is the V10 original. It is claimed to be able to produce 20 watts power output across the various bands, using 4 each IRF510 transistors. For this, it also needs voltage higher than the 12 vDC used throughout the rest of the rig. That smaller board is a buck convertor that bucks 12 vDC up to 25 vDC.

Since ordering this kit, I’ve learned that the transistors used in this amplifier have a very steep frequency efficiency falloff that reduces power in the 10M band to something notably less than 5 watts. I don’t care for 20 watts across all bands, but really do want at least 5. So…. there’s another power amplifier waiting in the wings, and it is the reason for that extra open space in the back panel. It will be the subject of another post where Bob learns to handle small SMD components.

Base panel

The 5 boards attached to the base are, from the bottom of the picture to the top:

  • the 12 vDC power supply
  • the QSD, Quadrature Sampling Detector, board where RF signals are prepared for digital signal processing.
  • the Main board which holds digital signal filters, the little Tiny 41 microcontroller which handles all the signal processing, system configuration details, and menu system. This board also houses interfaces for the display, encoders and pushbutton grid, along with some audio processing
  • the Exciter board produces phase shift and SSB, Single Side Band, modulation
  • lastly a filter board includes all the pesky toroids (aka torroids, or toeroids) for RF Low Pass and Band Pass filtering

All of these functions are concisely explained in Al and Jack’s book: Software Defined Radio Transceiver: Theory and Construction of the T41-ep Amateur Radio SDT. About 500 pages which include a deep drive in Digital Signal Processing.

Note: there is now a 3rd version, which adds information for V12, version 12, of this radio.

Front panel

Self explanatory, a display board, 4 encoders, 16 pushbuttons and various other connectors.

Milestone – PA biasing

Even though I intend to replace the V10 Power Amplifier with another, I decided to complete the initialization, or biasing, of this amplifier. Maybe it can be used elsewhere sometime. The process is simple, and avoids smoke and explosions if each of the 4 blue potentiometers are first set to their lowest values (many turns counter-clockwise).

Then, an ammeter is placed inline with a 12 vDC power source and power is applied. The desired result is a base line of 50-55 mA for the board. One by one the blue potentiometers are turned up (clockwise) until the power drawn increases 200 mA for each IRF510 transistor. The end result is a current draw of about 850 mA and no smoke. Success. Done.

BTW, the finned aluminum heatsink, with no fan, reaches about 140 degrees F.

photo of the bias adjustment setup

Next …

A whole bunch of interconnects, software loading, and various adjustment / alignment processes.

photo of cables, knobs, jacks, etc.
a whole lot of jumpin’ goin on

T41-EP SDT (1 of ??)

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The T41-EP is a Software Defined Transceiver designed by Albert F. Peter, AC8GY and Jack Purdum, W8TEE. The “T41” part of the designation comes from the fact that it uses the Teensie 4.1 microprocessor for software processing. The “EP” part of the designation means “Experimental Platform.” I started building Version 10 of the radio a couple of months ago, while Jack and Albert are now well off into version 12. Experimental — evolving.

The 4SQRP version of the T41-EP uses a 5″ LCD and enough front panel controls that one doesn’t have to be constantly digging through menus. That grid of buttons on the right gives instant access to many menu pages.

The picture is from the T41 site, not my build.

My interest is not the 20W capability, but the 15M, 12M, 10M capability. I’ll strick to QRP power levels, but want the rig for the bands. Yes, I have those bands with the “quirky Lil Orange” (tr)uSDX, but I trust the T41 will have more pleasing audio quality, and much easier operation.

My T41-EP

While the designers create circuits, PCB layouts and such, it is up to builders to either collect their own parts or find groups that are collecting parts for sale. One such group is the Four State QRP Group, 4SQRP, located in the Ozarks region of the U.S. A little over a year ago, they began a kitting operation to both promote the T41 and as a fund raiser for their club attending the OzarkCon ham radio conference. One interesting aspect of their sourcing is the provision of Printed Circuit Boards (PCBs) that already have the tiny Surface Mount Devices (SMDs) installed. Buyers are relieved of needing to acquire SMD assembly techniques. It was my very good fortune to snag a kit near the tail end of their run, which I think was 150 units plus a few betas. It arrived a few months ago and has not yet self-assembled.

My first job was making a “jig” to hold circuit boards. I think there are 7 or 8 in the kit. Instead of buying a fancy-looking collection of plastic, I wandered out to my woodworking shop, picked up a 2×2 cutoff, cut a very accurate kerf with my kerfing plane, and cut it into 2 pieces. Done!!! no waiting for Amazon.

The first assembly task is the power supply regulation board. It was an easy way to start and is now done and tested. AOK!

The assembly manual, about 120 pages, is concise and includes circuit diagrams, bills of materials, suggested build sequences, and in some cases test procedures.

A more extensive document, Software Defined Radio Transceiver: Theory and Construction of the T41-ep Amateur Radio SDT, is a 497 page book by the designers, and is a full fledged tutorial on digital signal processing using the T41 radio as the basis. It too holds extensive build and test advice.