My radio is tiny. So why is my POTA backpack so heavy?

We have mountains in Ontario. We call them mountains, but they are really just small hills. So I have never had to actually hike for miles up steep slopes carrying a backpack with all my radio gear, plus anything else I might need for a mountaintop activation. To all those who operate in this fashion, you have my sincere admiration.

Get your kicks on fourteen zero six

At the other end of the scale we have what has been called PLOTA (Parking Lots On The Air) activators. These operators perform their activations while sitting in their vehicles. It is tempting to think they probably grab their morning coffee at the a drive-thru en route to the activation. I confess that I have done this too, but only when the temperature drops down to double digits with a minus sign in front. I imagine that, in southern states, when it gets hot enough to cook eggs on the sidewalk, operating in air-conditioned comfort is almost a necessity. If this style of operating works for you, or is necessary in your environment, then you are doing your part to keep outdoor radio operations alive and thriving.

Mr Blue Sky

In between hiking up an inhospitable mountain, exposed to the elements, and being welded to a car seat is another option. Maybe this is the true expression of operating outdoors – leaving your vehicle and carrying your station into the back country, or even a local park. This is my personal choice. It combines a love of the great outdoors with a love of radio – what I have dubbed operating in the Big Blue Sky Shack.

There are options even within that. Do you carry your gear from your vehicle to the nearest picnic table, or do you backpack everything you need (seat and table included) down a trail, blatting the bugs that are intent on drinking your blood, admiring the wildlife while avoiding large mammals intent on eating you, to find a clearing in the trees where you can set up.

Oh Yuck!

Let me tell you a story about picnic tables that may discourage you from regarding them as a comfortable, convenient place to operate. I used to be an RV camper; it was fun but for several reasons I eventually sold my trailer. During one camping trip a neighboring camper was packing up his giant fifth wheel. I watched as he laid his sewage hose out to dry on a picnic table. For those who have never owned an RV (or caravan as it is known in many parts of the world), a sewage hose is used for emptying the contents of the “black tank” at the “dump station” on the way out of the campground. But I am sure you always use a plastic table cloth, don’t you? Well consider this, your table cloth is going to pick up millions of bacteria from the picnic table surface and transfer them to your food. Yuck!

Little boxes

Going back to the supremely fit, energetic types who climb real mountains to operate. They tend to carry extremely lightweight radios; often the whole station packs away into a tough, rugged plastic case that slips into the pocket of a backpack. I have often thought of emulating this idea. But instead, not being quite as fit as I could be, and with age-related physical limitations, I have chosen a different approach. My backpack station is a little on the heavy side (not to be confused with the Heaviside which is a layer of the ionosphere that makes our hobby possible).

Say, friend, I got a heavy load

At the heart of it all is a QRP-Labs QMX transceiver. This tiny device is so light it almost defies gravity – but it is not a complete portable radio station. So I built a backpack frame that can carry everything I need – and it is surprising what that includes when you can’t pop back to your vehicle to grab something else. Here is a list of what I carry:

• Transceiver – QRP-Labs QMX (low band version)
• Talentcell 6500 mAh LiFePo4 battery
• Drok buck converter to regulate the voltage fed to the transceiver
• Putikeeg CW paddle key
• Earbuds
• Ham made line isolator (common mode current choke)
• Selection of RG-316 coax cables
• Rite in the Rain log book, pencils
• UTC wristwatch
• Reading glasses
• Selection of wire antennas and radials
• 18.5ft telescoping stainless steel whip
• Lightweight tripod for supporting the whip on rocky ground
• Spiderbeam 7m telescoping fiberglass pole
• Telescoping plastic seat
• Multitool
• Small tarp
• Selection of cordage

Of course there are even more things that must be carried such as water, bug spray, snacks etc. Those little hardened plastic boxes with a tiny radio, key and wire antenna are impressive to behold, but they are not a complete and independent station incorporating everything needed for personal comfort and survival far from shelter and the means of egress.

Experience has taught me not to rely on commercial backpacks to carry all my gear. Most are intended to carry the typical range of items needed by a hiker. I bought a rugged, military style, cotton canvas backpack from a local supplier and was disappointed when I tried to use it to carry my radio equipment. There was no padding, no frame; it was very uncomfortable to carry. Clearly it was made for lighter, softer loads than mine.

Another alternative is real backpacks made for the military. They are built tough but are also very tough on the budget. I just couldn’t justify spending many times more on a backpack than the radio equipment inside it.

Just in case

The solution involved a little bit of work in my garage workshop using many items I had already hoarded ready for future project ideas. I had to purchase two 30-cal steel ammo cases, but they were very inexpensive. One was sold for storing hunting ammunition, but the other was a bona-fide military surplus case with markings indicating it was intended for storing 200 cartridges of 7.62mm rounds and other items. I plan to repaint it sometime before it gets me into trouble. Why steel ammo cases? They are built tough for protecting delicate equipment, they are cheap, and they provide sufficient heft to create a firm operating platform.

Both steel cases are stacked vertically on a modified aluminum backpack frame. The bottom case holds antennas, cables etc. The top case holds radio, battery, key etc. Everything is pre-assembled inside the radio case – just pop the lid, insert the earbuds, turn on, tune in and go.

My Putikeeg CW key has very strong magnets on its base and holds very securely to the steel case. I use it in vertical fashion, with the paddles peeking up above the rim of the steel case. The assembly sits at a very comfortable height for operating the radio without the need for a table. My seat is a lightweight, plastic, telescoping thing with a padded cushion on top. It is an ingenious design with many latches holding it up. I was very cautious about trusting my posterior atop this perch at first, but it supports my weight just fine. The pictures tell a lot more than many more words can convey.

Whatever style of outdoor operating you prefer you are helping keep amateur radio alive. This post describes the way I operate and is not meant to be judgemental about any other style. There is room enough in our hobby for whatever way you like to operate. In fact, I invite you to comment or send me a description of your outdoor radio equipment – even if it is mounted on a set of four wheels 😉

My POTA gear is constantly evolving so what you see and read here may not be what you see if we meet on a trail sometime. I like to experiment and try out different ideas. Some call me nuts; maybe they are right but I’m having fun.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#CW #OutdoorOps #Portable #POTA #QMX

Mic in purple so I can get appropriately funky in QRP SSB. Now I have to get serious about updating the QMX+ firmware to add SSB functionality.

These two *little* mics were printed and assembled by AD7OV based on the K6ARK plan...so close to cost that it's being allowed under the non-commercial CC license 😂. Info is in the https://groups.io/g/QRPLabs archives.

3D model: https://www.printables.com/model/320559-mini-microphone-for-qmx-trusdx-usdx-kx2-and-kx3

#prince #QMX #3dprint #SSB #QRP #microphones #RigPix #KeepSSBfunky

Adding 4x SMD 10nF to remove Rotary encoder glitch on my #QMX #HamRadio

Trying some 20m during the g4 magnetic storm. Deck-mode with my #doggo #qmx #baesus #bamakey #cw #qrp #pota #dota. Not making it too far from what I can tell on the web-sdr radios out east. #amateurradio

2/2

Based on the hard work of Adam, K6ARK I designed a PCB which does all the work of the connections and designed a case for it.

I think it looks like a Turret from the game Portal, hence its name.

https://shop.g7ufo.radio/products/assembled-g7ufo-turret-mini-microphone-for-qmx-trusdx-usdx-fx-4cr-zbitx-kx2-and-kx3

#Elecraft #KX2 #KX3 #QRPLabs #QMX #truSDX #uSDX #FX4CR #zBitx

@bgarfoot if I can have only one, then it must do everything.

The IC-705 never appealed to me but the #ftx1 does.

If I can bring along an HT, then I would opt for the #lab599 #tx500 because of its ruggedness, and it being light weight and having a very low RX current draw.

If I want to go realy light weight, I grab the #qrplabs #qmx. Very high quality radio for small a price.

#hamradio #radioamateur
Beta firmware for #QMX transceivers. It should now better works in SSB. Very interesting video :

https://youtu.be/bsDBcFXgHbY

Just finished building my #CW practice kit. Also nicely turns into my #POTA / #SOTA travel kit for CW. I designed the cases for the BaMaTech - BaMaKeY TP-III and the HAMCUBE Mini so that they provide more ergonomics and comfort while in use.

Whatcha think?

#bamatech #bamatechtpiii #cwmorse #hamradio #amateurradio #radio #icom #yaesu #qmx

Made some micrphones for my #qmx setup. I think Josh KI6NAZ is going to make the same ones tonight! Many thanks to Adam Kimmerly for designing these and allowing a ludite like me to make them at home! I figured I'd make 2 just in case one was a dud! All good though, both work! #pota #sota #qrp #hamradio #amateurradio

https://www.printables.com/model/320559-mini-microphone-for-qmx-trusdx-usdx-kx2-and-kx3

https://youtu.be/EQwLx5BpdFw?si=IDOaza2vzz9f76dR
#hamradio #amateurfunk #qmx #qmxplus

First test with the QMX and SSB.

https://dl6joe.de/first-test-with-qmx-and-ssb/

#qmx #ssb #retevis

Finally got round to getting acquainted with my #QRPLabs #qmx. For reasons known only to her, Pippi the #whippet has decided to get involved and is currently “helping”.
#AmateurRadio #HamRadio #dogsofmastodon

EFHW matching: 49:1 Impedance Transformer or L-Network?

What is the best way to match the very high impedance of an End-Fed Half-Wave antenna to the 50 ohm impedance of a transceiver? There are various ways to do this but this week’s post is going to focus on just two – a 49:1 impedance transformer (or UNUN if you prefer) and an L-network.

We are dealing with QRP devices but the same issues arise with QRO devices. In fact some of the complexities may be exacerbated at higher power – especially core overheating.

49:1 impedance transformer

This is by far the most widely used matching device but many claim it is inefficient. I have used an “Outside the Box” winding method that I have seen described as “Fuchs style”. The primary and secondary windings are entirely separate instead of being twisted together. This method isolates the windings and is said to prevent static from traveling back down the coax to damage the transceiver. But it also requires a separate 0.05WL counterpoise connected to the bottom of the secondary winding.

Pros

• Broadband operation
• Easy to construct
• No calculations needed

Cons

• Lower efficiency claimed
• Can be used on even harmonics but the antenna is only a half-wave on its fundamental frequency
• Potential for losses due to core overheating
• Leakage flux due to poor coupling between windings
• May require capacitance across primary and/or secondary to compensate

L-network

Some claim that an L-network is more efficient than an impedance transformer. While I don’t dispute the claim I would respond “show me the math”. An L-network is usually constructed from a fixed value serial inductor and a fixed value parallel capacitor (although there are other topologies depending on the matching parameters involved). I built one using a slug-tuned variable inductor and a ceramic trimmer capacitor.

Pros

• Higher efficiency claimed
• Easy to construct
• Avoids complex issues with transformer cores and winding coupling

Cons

• Single band only
• Calculations required to establish correct values of L and C

The Ham Radio Outside the Box laboratory (a grand name for my basement workbench) has built many 49:1 impedance transformers for both QRP and QRO operation. The QRP units are deployed in backpack portable operations and the QRO units have seen service both in the field and in the home shack. Both the conventional “twisted” coupling method and separate windings have been used.

Which winding method is best?

One of the issues with 49:1 transformers is “leakage flux” which means not all of the energy in the primary winding is coupled to the secondary. The conventional winding method is to twist the first two turns of the primary and secondary together to improve coupling. The remaining turns are only coupled to the primary by the flux in the core. Furthermore, there is often a “crossover” turn to bring the far end of the secondary out on the opposite side of the core from the primary. This may further reduce the coupling efficiency.

An alternative method is to wind the secondary, without a crossover turn, around the core. The separate primary is then wound around the center of the secondary. Should the secondary be spread around the core, or closely spaced? Opinions vary on this. I now favor keeping the secondary turns closely spaced. The reason? A closely spaced secondary winding should improve inter-winding coupling and reduce leakage flux.

What about the turns ratio?

Should it be 49:1, 64:1 or …? There is an easy answer to that: just divide your antenna impedance by 50 and bingo, there’s your answer. Oh, but what is the impedance of your antenna, 2000 ohms, 2319.647 ohms, 3000 ohms? We don’t actually know and it may vary depending on how the antenna wire is erected (which for portable operators may be different every time). A ratio of 49:1 provides a good enough match to most every value of End-Fed Half-Wave (and multiples) we are likely to experience.

Or just build an L-network!

We have seen that 49:1 impedance transformers have many variables that impact efficiency. Leakage flux has been discussed so it is relevant to note that placing a small capacitor (typically 100pF) across the primary winding is recommended to somehow compensate. Conventional 49:1 transformers are wound as autotransformers, so we have a series inductor between the antenna and the radio, and a parallel capacitor. Doesn’t that sound very similar to one of the topologies of an L-network?

My initial experiments with building L-networks involved a fixed series coil and a parallel capacitance made from a short length of thin coax – like RG-174. I experienced the problem that the calculated values of L and C did not provide the best possible match to 50 ohms. I still needed a “touch-up” tuner to bring the SWR down to a safe level for my QRP Labs QMX transceiver. I realized that a field portable antenna was going to need slightly different component values depending on whether my temporary station was setup on exposed ancient bedrock, or over the moist ground at the edge of one of the Great Lakes. What I needed was an L-match “tuner”, i.e. an L-network with variable inductors and capacitors.

42 years ago …

A long, long time ago (42 years to be precise) I was a penniless SWL foraging for food in the forest – alright that’s an exaggeration, but I had a young family and couldn’t spare the cash to buy a decent shortwave receiver. A friend told me about a design in Practical Wireless magazine for a shortwave converter that would work with a regular domestic AM receiver. I had the components shipped over from the recommended UK suppliers and built the converter. It worked splendidly and I spent many happy hours listening to the busy shortwave bands. Then I became fabulously wealthy (i.e. I could at last afford shoes and to eat every day of the week), bought a real HF radio and the converter was relegated to the back of a closet.

The point of the story is that I was able to scavenge that converter for the components I needed to build an L-match for an End-Fed Half-Wave antenna. The inductor shown in the picture above is wound over an adjustable slug-type ferrite core of unknown mix. The capacitor is a ceramic trimmer with a couple of fixed ceramic capacitors in parallel to bring its value into the range that was needed. The only comment I can make on the efficiency of that unknown core is that it didn’t get hot (or even warm) after an extended period of transmitting at 5 watts. Tuning is quite sharp but I was able to get a 1.5:1 SWR from my Shortened Sloping End-Fed Half-Wave antenna (see last week’s post). I probably could have obtained an even lower SWR by adjusting the length of the high Q top section of the SSEFHW.

QSO’s?

As a recent convert to L-networks I have only made enough QSOs to be countable on fingers and toes. On the other hand, over the years, I have made thousands of QSOs with a 49:1 impedance transformer. Both the devices shown in the pictures above accompany me on every field portable outing so I have options and can compare their performance.

Does it matter, really?

Sometimes I give my head a shake and tell myself to put the physics textbooks back on the shelf and just enjoy the experience of being out in the Big Blue Sky Shack with my radio. At other times, after calling CQ ’til the cows come home and getting no responses, I ponder the question of whether my antenna is doing its job or, as sailors used to say, is idly “swinging the lead”.

What are your experiences with either impedance transformers/UNUNs or L-networks? Your opinions are very welcome either by adding a comment below, or if you prefer, by email (QRZ.com).

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#AmateurRadio #Antennas #Counterpoise #OutdoorOps #Portable #QMX

SSEFHW – Another Shortened End-Fed Half-Wave Antenna for 20m

I was browsing through ham radio videos on YouTube recently as I often do (daily!) when I came across one from Peter Waters G3OJV on the Waters & Stanton video channel. The title of the video immediately caught my attention: “Shortened Vertical Half Wave Antenna”. End-fed antennas are a favorite of portable operators because of the ease with which they can be erected. End-Fed Half-Wave antennas have the added advantage of needing a counterpoise that is 5 times shorter than required by an End-Fed Random Wire.

Another attribute that is appealing to portable operators is a small station footprint, so a vertical antenna, combined with a very short counterpoise, results in a stealthier station that is less likely to interfere with other people using the same park or trail, or attract unwelcome attention.

I achieved this already with the 20m CLEFHW (Coil-Loaded End-Fed Half-Wave) which has performed very well, although it has also attracted consternation from antenna physics experts. Sometimes we just have to shrug and accept the principal that “if it works, it works” and move on.

When I watched Peter’s video I realized I had overlooked another very simple way of shortening a half-wave antenna. Peter took a commercial helically loaded quarter-wave antenna and put it at the top of a pole. Beneath it he connected a full-length quarter-wave wire to create an electrical half-wave fed at the bottom through a 49:1 impedance transformer.

I realized I had used this technique once before to fit an 80m EFHW into the restricted space of a campsite. I built a 40m EFHW, added a coil and then a short pigtail wire. The 40m EFHW comprised one half of an 80m EFHW while the coil and short pigtail made up the other half. Yes, it was a compromise with lower efficiency than a full-length 80m EFHW but it got me into my weekly CW rag chew with friends who are often over a hundred miles away when I am traveling.

A Shortened Sloping End-Fed Half-Wave antenna

I built the G3OJV shortened EFHW for 20m using the same loading coil I had built for the CLEFHW with a 57-inch whip from an old hamstick as the radiating element. A 17ft wire was added below it to make up the other half of a 20m EFHW. It worked – well to be precise, I made contacts with it using just 5 watts.

I did make one change to the G3OJV design. The whip, loading coil and mounting arrangement are a little too heavy for my 29ft fiberglass pole (a damaged MFJ 33ft pole repaired with sections of a Crappie fishing pole). So I erected a kludge pole that was only 15ft tall and routed the bottom wire out an angle to a point a few feet away from the pole. This resulted in a strong front-to-back gain ratio at elevation angles above 35 degrees, but also, unfortunately, expanded the footprint on the ground. From my QTH in southern Ontario, the front-to-back ratio is an advantage since most of my contacts are to the south. I point my wire at Texas to cover most of CONUS.

But, this arrangement resulted in a set of gear that is not very convenient to carry down a trail. I had to come up with a better idea. So I built SSEFHW version 2.

SSEFHW version 2 is a Shortened Sloping EFHW made entirely of one single length of 26ga silicone coated wire, wound around a short section of 2-inch diameter PVC built-in vacuum cleaner pipe, 57 inches from one end. Approximately 28 feet of wire was used in its construction.

The coil section is approximately 7.7 microhenries to match the original heavier coil used in version 1. The whole antenna is so light it almost defies gravity and fits in a small plastic freezer bag.

Another kludge 17ft pole was made from the remains of two 13ft Crappie poles (after being scavenged to repair my damaged MFJ pole) and a short piece of half-inch Schedule 40 PVC plumbing pipe. It all fits over, and is supported by, a driveway marker pole stuck in the ground.

You may notice the dramatic difference in weather between the two pictures taken only a day apart. The image to the right was electronically color enhanced to improve its contrast.

Side note: Kludge is cheap and cheerful but a Spiderbeam pole is now on order from Vibroplex. Spiderbeam poles, engineered in Germany, have a good reputation for strength and robustness. Ham Radio Outside the Box will review the product when it has been received.

I was entirely unsure how Version 2 would perform and was pleasantly surprised when the SWR, measured using my RigExpert antenna analyzer, turned out to be 1.8:1 at the output of the 49:1 impedance transformer. That is already an acceptable SWR but, to preserve the legendary immortality of the PA transistors in my QRP Labs QMX transceiver, I added my “Old Barebones” ham-made Z-match and brought the SWR down further to 1.05:1.

Does it QSO?

No, absolutely not. I make the QSOs; the antenna is just a dumb bit of wire [smile]. My first contact using the SSEFHW was with a station in Kansas about 900 miles away. He gave me a 559 RST report and I received him at 599. Not bad for a QRP CW contact and typical of the kind of reports I have been receiving using other antennas. The SSEFHW (sounds like the name of a ship doesn’t it) can be supported by a pole, or even a low tree branch. My feeble throwing skills will not be overly challenged launching this antenna into a tree.

Kudos where it belongs

I cannot claim originality for this antenna, that belongs to Peter Waters G3OJV. I simply massaged Peter’s idea to suit my own backpack portable operating style.

You will find me in remote clearings at the end of a trail on the Bruce Peninsula or elsewhere along the Niagara Escarpment.

The Bruce Peninsula is approximately 100km long and forms part of the Niagara Escarpment which runs from Niagara Falls at the border between Ontario and New York State to Tobermory, Ontario at the top left of the map.

The west coast of the peninsula is bounded by Lake Huron while the east coast runs along Georgian Bay and comprises dramatic scenery with tall cliffs plunging down to the lake. With scenery like this who would want to sit inside a vehicle to play radio?

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#AmateurRadio #Antennas #CW #MorseCode #OutdoorOps #QMX

@passthejoe #zbitx is not a good portable QRP radio until it has more efficient finals though. Over 30 watts in for less than 5 watts out!?! come on. You run down your batteries too fast, just to overheat the radio and its insufficient flat-plate heatsink. I added a fan to mine to try to cope with that. But yeah, the rest of it is pretty cool. As with most things, there are disadvantages to be an early adopter, that's all. I ordered a #qmx+ kit in the meantime; too bad it's not open source.

Played some radio, but oh boy am I unfit. 23km on the bicycle and I am absolutely shattered. How do people do 150km a day? Steroids?
https://youtu.be/g56AFGz2zhI?si=4XpkEy2KJRi5vx4_
#hamradio #amateurfunk #qmx

Received my #QMX and printed some bits and bobs to make it mine. My world consists of lots of Velcro and 3D Printed Goods :D What else should I print for this rad radio? #qrp #hamradio #amateurradio #sota #pota #3dprinting #3dprint #3dprinted #velcro

25 Years a Ham and Still Learning

I actually got my “ticket” a little late in life. I spent many years as an SWL, then college, career and a family took priority. By the time my wife and I became empty-nesters I had combined my passion for radio and Space “the final frontier” by chasing satellites; military satellites mainly. I formed the HearSat group dedicated to monitoring Low Earth Orbiting satellites. My account of a unique method of decoding the signals from Russian navigation satellites was kindly published by Monitoring Times magazine. At the time I felt there were so many fascinating signals flying around that there was nothing of value I could contribute by adding my own. However that feeling didn’t last long and eventually I bought a study guide, passed the written test and became a ham.

Now, I am into my 25th year in this great hobby. Frankly I was never satisfied with using a radio just to rag chew; I felt an urge to experiment – to contribute something useful to the science of radio communications. I didn’t fully realize it at the time, but I was at the bottom of a steep hill that I am still climbing, learning with every step. As my personal lifelong learning journey progresses I am proud to share knowledge gained here at Ham Radio Outside the Box.

“In times of change, learners inherit the earth; while the learned find themselves beautifully equipped to deal with a world that no longer exists.” – Eric Hoffer

Several weeks ago Ham Radio Outside the Box introduced a rather unique antenna idea, called the Coil-Loaded End-Fed Half Wave (CLEFHW). It is a telescopic whip that is inductively base-loaded to become an electrical half-wave. What is the purpose? To create a backpackable antenna with a very small footprint achieved by eliminating the need for a long counterpoise or system of radials. It worked very well – for a while. Then I began tinkering with it; I call it “continuous improvement” and it stopped working properly.

“If it ain’t broke …”

The antenna started to experience unstable SWR. Then the great snowstorms of February 2025 arrived and I could no longer get outside to investigate. Undaunted, I set up a wire in my basement “lab” to simulate the whip and was able to adjust the antenna to get a good SWR again. All was good – until an unusual warm spell hit and I was able to get out to a local park to do a POTA activation. Suddenly, the good SWR was gone again. Abandon the activation? No, improvise and adapt! I pulled my ham-brew “Old Barebones” Z-match out of my pack and finished the activation.

Back at the shack I was determined to find out what had gone wrong. The park I had visited sits on shale stone rock just beneath the soil and is right alongside one of the Great Lakes. Previous activations at that park had given spectacularly good results.

It ain’t gonna work John, give up and go have a beer

The snow still lay deep and crisp and even on my backyard but I managed to shovel my raised wooden deck clear and continue the investigation. That was the start of a very frustrating series of antenna trials. It can be tempting at times to quit – “it ain’t gonna work John, give up and go have a beer”. But, I remembered my college physics training: experiment – document the results – change one thing at a time – document the new results – make further changes as required and repeat until success is achieved.

The most important part of that process is to document the results at each and every step. I keep a small spiral bound notebook and a pencil nearby while I tinker in my basement lab. That makes it easier to review what went wrong and when. Yes, it’s tedious to put down the soldering iron and pick up the pencil, but it does make a big difference in the end.

So what was learned? It seemed a fair assumption that an 18.5ft whip, replaced with an 18.5ft wire would perform pretty much the same. But oh, no John, no John, no! There was another parameter involved that hadn’t been considered. The lab experiment with the wire took place in the nice, warm environment of my basement replete with space heater and a constant supply of hot beverages. But the basement lies 6 feet below grade – could that be an issue?

The carefully adjusted antenna with the 1.2:1 SWR was then carried up, up and away to the deck, out into the cruel Big Blue Sky Shack where the temperature was hovering around freezing. The 18.5ft wire was replaced with the telescopic stainless steel whip which, with all 13 sections extended, was also 18.5ft long. I confidently powered up my rig and set the mighty micro QMX to monitor SWR. “Should be pretty close to the same SWR I got in the basement” methought. But then disappointment haunted all my dreams. The lilliputian radio gave me the bad news: SWR 2.6:1.

A bit of a stretch

Previous learning experiences had taught that any physically short antenna that is artificially extended to it’s electrical full length by means of a loading coil tends to exhibit a very high Q. The CLEFHW uses a base loading coil to extend its physical length of 18.5 feet to an electrical length of approximately 33 feet which is a half wavelength on 20m. If the inductance of the loading coil isn’t right in the bullseye of the required value, the electrical characteristics can be subject to unexpected change.

But perhaps the unexpectedly high SWR out on the deck was influenced by another factor. Yes, the basement lab is 6 feet down below ground while the deck is 2 feet above the ground. How to compensate for this? Is the CLEFHW going to need a custom coil for each and every deployment? Maybe it will, but there is a solution that we will get to in a moment.

“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
― Nikola Tesla

Back in the lab the loading coil was rewound with nearly enough inductance to earn a place in Nikola Tesla’s lab.

The idea was that turns could be removed until the SWR settled down to an acceptable level. The target was less than 1.5:1. It worked! The SWR out on the deck came down to 1.10:1.

Just a cotton pickin’ minute Einstein…

The victory dance had to be put on hold as another doubt surfaced. The SWR measured out on the shale stone ground in the park was different to the SWR measured on the hardwood over concrete floor of the basement lab. The SWR out on the deck had been different again. A pause and a little stroking of the chin while the old gray matter overheated with intense thought. This deck, said the voices inside my head, is 2 feet above the ground. Do we have another variable to throw into the equation here?

The base of the antenna is at the top of the backpack frame and when the pack sits on the ground, as intended during outdoor operating sessions, it is only about a foot and half above the ground. The antenna is an almost vertical shortened End-Fed Half-Wave (it is sloped to give it some directionality). So is proximity to ground another factor to consider?

The whole backpack rig, antenna and all, was beamed over to an area of grass just beyond the deck. Here we go again, with everything exactly as it was up on the deck, the SWR grew legs and climbed up over 2:1 again.

The Ultimate Lossless Tuner?

The simple solution would have been to pull out “Old Barebones” (Z-match) again and bring those pesky standing waves under control. But I had another cunning plan. By leaving some extra turns on the coil I could increase the inductance beyond what is required to load the whip and use the whip itself to adjust the SWR.

Brilliant! It worked. The final iteration of the coil (nothing is ever really final) involves three taps near the top of the coil to leave some inductive flexibility to accommodate persnickety ground conditions. An SWR of 1.09:1 was obtained with the pack out on the grass. But, it was necessary to collapse two sections of the whip to get there. Interestingly, adjusting the whip length retunes the antenna without introducing any further loss; it simply restores the electrical length of the loaded whip to a half-wave.

So now, once again, the Ham Radio Outside the Box Coil-Loaded End-Fed Half-Wave antenna is ready for action. Lessons learned. Oh, and – Note to Self – move onto another project John – don’t tinker with things that work already!

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#Antennas #CLEFHW #Ground #OldBarebonesZMatch #POTA #QMX

Really enjoyed this thorough presentation "Introduction to the QRP Labs QMX+ Transceiver" by @kp4md for the River City Amateur Radio Communications Society.

https://youtu.be/l7s7_-zT2vQ?feature=shared&t=2710

Carol, what would name the category of radios you discuss in the QMX geneology at 1:10:15? Low cost, independent manufacturer radios? I'm writing something for the @hamchallenge week HC51 challenge and would like to cite your presentation. I'm writing about cost accessibility for #NewHams

#QRPlabs #QMX+ #HamRadio

A Ham with One Voltmeter Always Knows the Battery Voltage

There is a popular old saying about a man with one clock always knowing what time it is, but a man with two clocks is never sure. Well doesn’t that also apply to voltmeters and any other kind of meter in a ham’s kit bag?

The Ham Radio Outside the Box QRP field portable kit is powered by a Talentcell 3000mAh Li-Ion battery. It’s a nice little battery, but it has one rather annoying feature – an on/off switch. I am going to guess that the function of the switch is to prevent battery drain due to the LED capacity gauge on the battery. Problem is, I forget to switch the battery off when I have finished operating. Until recently the battery was buried deep in the bowels of my rapid deployment backpack radio kit – out of sight and out of mind.

To overcome this failing of the operator’s gray matter I connected one of those tiny LED voltmeters found at many hamfests, or online via the usual suspects. If the voltmeter is lit up, the battery is still turned on. It works fine business but how accurate is it? Should I care? It was just a quick and easy way to remind me to fish inside the radio box and turn off the battery when I’m done operating. Perhaps I should have used a simple LED instead.

During a recent outdoor operating session at a local park I found myself obsessing about the battery voltage. When I turn on the radio the tiny voltmeter shows a drop of one decivolt (cute word, means one tenth of a volt). Ok, the radio is drawing current so that’s to be expected. So what’s the problem?

Too much information?

The radio is the mighty but microscopic QMX from QRP Labs although these observations could equally apply to any other QRP radio with a restricted DC supply range. The QMX is a tiny little package that packs a powerful punch. It has proved it’s worth on a lot of POTA activations over the last year. The QMX has a small LCD screen that displays a lot of information – maybe too much in fact. Yes, some of the info displayed can be turned off in the user settings but who wants to keep fiddling with the settings when we could be pounding brass to get more contacts?

The paranoids are chasing me again!

The QMX tells me my frequency, signal strength on send and receive, ALC level, SWR and among other distracting data, the battery voltage. It can also decode and display the incoming CW but I turned that off. Call me paranoid, but if the radio can replace the need for the operator to copy CW, how long before a future firmware update incorporates AI and does the sending for me too?

Now here’s the problem: when this ham had just one voltmeter he was happy in the knowledge that all was well. But now there are two voltmeters – one on the QMX and another one whose job is to remind me to turn off the battery before packing up. The two voltmeters do not agree – which one is right? Are they both right but measuring the supply voltage in different places? Is it important?

There is much discussion in the QMXverse about the sensitivity of the PA transistors to excessive voltage, or high SWR, or both. In the world of big radios 12 volts means well alright, try to keep the DC supply voltage down below maybe 15 volts. Twelve volts, 13.8 volts, what’s the difference? But in QMXville, 12 volts means 12 volts. How strictly must we QMXheads adhere to 12 volts? No guarantees there and no hard and fast rule. Those four eensy-weensy BS170 transistors that pump power into the big, blue sky are as unpredictable as the weather.

Here comes my 19th nervous breakdown

So maybe you can understand why the obsession with the state of the battery. Which voltage is the one that is going to fry the finals – the voltage at the battery terminals, the voltage displayed on the QMX in receive mode, the voltage during transmit?

And … after sending out CQs for a half hour or so, the QMX display tells me the radio is no longer pumping out a full gallon. OMG, will the battery outlast the activation or will it die on me before I get “my ten”?

Don’t worry, be happy

Before “running for the shelter of mother’s little helper” anxiety can be overcome through understanding the discharge curve of a typical Li-Ion battery. But before we delve into that let’s talk about how to wrap our QMX baby in electronic swaddling clothes.

A freshly charged 3S (3 cells in series) Li-Ion battery will have a voltage of 12.6 volts which represents 4.2 volts per cell. The nominal voltage is a little less at 11.1 volts or 3.7 volts per cell. As the battery discharges it will hold its voltage fairly steady in the Goldilocks Zone of 10.8 to 12 volts. Eventually, when the battery is nearly fully discharged, the voltage will drop precipitously and the internal BMS (Battery Management System) will shut it down to prevent damage due to over-discharging.

The only external protection needed is to curtail the excess voltage at the start of the discharge. This can be achieved by series diodes or (as I and others have adopted) a Buck Converter. The job of the buck converter is to limit the voltage to a preset value, for example 12.0 volts. When the battery voltage depletes to lower than the preset value the buck converter has no effect (except perhaps a very small voltage drop across the device). A buck converter is preferred over diodes because the latter will reduce the voltage by 0.6V per diode even in the Goldilocks Zone.

That makes the job of the buck converter very easy. With reference to the discharge diagram above, the buck converter only plays a role during the first 10% of the battery discharge cycle. A Talentcell 3000mAh battery has a nominal capacity of 36Wh. So the excess voltage is only a problem during the first 3.6Wh of operations. In theory that represents about three quarters of an hour of operation at 5 watts, although my own experience is that the battery voltage drops more quickly. I suspect this may be due to improper charging. Although I have been using the charger supplied by Talentcell, I have been leaving the load (i.e. the buck converter) connected. This creates a small “parasitic load” which may confuse the charger.

Is battery voltage regulation really necessary?

Are the radio’s final transistors in jeopardy at 12.6 volts? Some users have reported using an unregulated 12.6 volts with no damage to the radio. Perhaps the magic smoke is waiting for a later time to be released – who can tell? It’s a gamble.

What is the impact of operating the radio at 11.1 instead of 12.0 volts?

When I received my QMX a year ago, it came with a test sheet from the factory. The lab results showed my radio produces 4.8 watts on 20m with a 12 volt DC supply. Since the output power is proportional to the square of the voltage we can calculate the expected output power at any supply voltage. A quick and dirty back-of-an-envelope calculation suggests that at 10.8 volts (at the end of the yellow/orange Goldilocks zone in the diagram) the expected power output will have dropped to 3.9 watts. Let’s round that number to 4 watts.

So, after discharging the battery until it is almost fully depleted we can expect to lose less than 1 watt of output power. Even that could be compensated for by replacing the buck converter with a buck/boost converter. A buck/boost converter will ensure a constant voltage right up to the point where the BMS turns off the lights and says goodnight.

Is it really necessary to become paranoid about battery life, or output power? Before reaching for the “little yellow pill” prescribed by Messrs Jagger and Richards, maybe we should just relax and enjoy playing radio out in the Big Blue Sky Shack. It doesn’t matter if we run out of battery power, or our puny signal gets eaten by the D-layer on its round trip into space because QRP is such fun (isn’t it?).

Addendum: I have recently made a couple of small changes to my kit to overcome the issues identified above. First, I relocated the battery to make the on/off switch more accessible and allow the load to be disconnected during charging. Second, I eliminated the tiny voltmeter since I have convinced myself not to become paranoid about the supply voltage. Third, I have invested in a CC/CV (Constant Current/Constant Voltage) bench power supply to charge the battery. Now I can see the changes in charge voltage and current and verify that the battery is indeed reaching full charge.

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#AmateurRadio #Battery #OutdoorOps #Portable #POTA #QMX