We had a #tornado last night.
-All my #antennas have survived.
-The #solar panels are still in one piece.
-The only damage seems to have been some knocked over trash cans (it's trash pick-up today) and a few shingles from somewhere in my yard. I say "from somewhere" because the shingles are a different color than the ones on my roof.
-Freeways are flooded in the area.
Mother #Nature is angry about something... Guess we need to figure out what and un-fuck it.
A Linear-Loaded Monopole antenna for hiking
There is a lot of information online about Linear-Loaded Dipoles, but I haven’t found anything at all about cutting a Linear-Loaded Dipole in half to create a Linear-Loaded Monopole worked against ground. The legendary L.B. Cebik (W4RNL, SK) published a design philosophy for an 80m Linear-Loaded Monopole, but it didn’t match what I had in mind. So I decided to build one for the purpose of experimentation. Maybe I could make it into a compact, lightweight antenna capable of rapid deployment while hiking – maybe.
What is Linear-Loading?
According to my search engine’s “Search Assist”, “Linear loading is a technique used in antenna design where a portion of the antenna wire is folded back on itself to reduce its overall length while maintaining good electrical performance. This method allows for a shorter antenna that can still operate effectively on the desired frequency.”
Sounds very simple doesn’t it? In the real world, where the RF hits the ether, it gets a little more complicated – especially when venturing outside the box. I could have made life nice and simple by building a Linear-Loaded Dipole; there are lots of designs available online that I could have used. But a dipole is too large for agile, rapid deployments; it needs a taller pole which, in turn, requires pegging into the ground and guy wires. I could use a tree limb for support, but only if suitable trees are available; often they are not. No, my requirement for a very simple hiking antenna implies a vertical antenna – a short vertical antenna.
Short antennas are easy to build; simply add a loading coil at the base and Bob’s your uncle. But that won’t qualify for my purposes. Short loaded antennas have a reduced radiation resistance and ohmic loss in the coil – they are inefficient. So how to shorten an antenna while maintaining efficiency? That’s where linear loading comes into play. A linear-loaded antenna is almost as efficient as a regular version.
How to build a Linear-Loaded Monopole?
It should have been “EZ-PZ”. Just take the dimensions from any of the online designs for a Linear-Loaded Dipole and cut them in half. That’s where I started. For a 20 meter antenna, a length of around 11 feet of window line, shorted at one end, is a good starting point. I hauled it up the mast in my newly glacier-free backyard, attached a counterpoise wire and started trimming. Between snips the resonant frequency was monitored on my RigExpert antenna analyzer. I use the term “resonant frequency” loosely in this context. The expected impedance of a quarter-wave vertical is around 37 ohms which implies there will be some reactive component to the impedance. I searched for a dip in SWR over a wide frequency range until it was possible to locate where the antenna was “resonant”.
Home made ladder line. The separators are made of shrink wrap heated with a Weller soldering gun with plastic welding tip. Lots of work and not very elegant, but practical and cheap!So long John?
A low SWR in the region of the bottom end of the 20 meter band was the target, but the dip in the curve was below the bottom of the band – way below. I snipped and snipped until that dip fell where it was needed. Then the counterpoise length was adjusted until the lowest SWR was obtained. How long was my ladder line? A large pile of snipped ladder line lay on the grass beneath the pole. When I took the antenna down, laid it out on the ground and measured its length it was quite a surprise to see the ladder line radiator was only 8.67ft (2.64m) long. And the counterpoise length was 18ft (5.5m).
Jingo-la-ba!
Will it QSO? I fired a smidgen less than five watts into it and received a response from a station somewhere in the US with an encouraging signal report. Well, at least it “works”. But now came the next step. That pesky 18ft counterpoise had to go, to be replaced with the 2T2C (Tuned Tank Circuit Coupler) described in the last post.
A new challenge
The 2T2C ground coupler was directly connected to the ground side of the short coax feedline and a further wire was added to connect to a small capacitance plate on the ground. Life is complicated and then you die, so why do I insist on adding more complications? It’s called experimentation – experiment and learn! I learned. I learned that my choice of inductance and capacitance for the 2T2C resulted in impossibly sharp tuning of the ground circuit. The 2T2C needed a design modification to reduce the inductance and increase the capacitance. Spreadsheet modeling suggested this would make the 2T2C easier to adjust. I needed to confirm that before rebuilding the 2T2C, but how?
L-match innovation
The answer came in the form of a variable L-match that I built quite recently. It has switch selectable inductors and a variable capacitor. It could be adapted to fit this bill very nicely.
This idea was inspired by VK3YE who published a YouTube video about it some time ago. At one terminal of the L-match a connection is made to the BNC center conductor. At the other terminal, a connection is made to the shield side of the BNC. If you trace the signal path through the device it can be seen that the inductors and capacitor are in series. Now we have a Ground Tuning Unit (GTU) and can use binary selection of the inductances, together with rotating the variable capacitor, to determine the combination of inductance and capacitance for easiest tuning of the ground connection.
The inductances available on my L-match are 0.5, 1, 2, 4, 8 microhenries, allowing the inductance to be varied up to 15.5 microhenries in 0.5 microhenry increments. The variable capacitor is a 30-160pF polyvaricon.
Now, with the 8.67ft linear-loaded vertical erected and the “L-match GTU” making the ground connection via a capacitance plate on the ground, it was easy to select values that would allow smooth adjustment of the antenna SWR. It was found that 1 or 1.5 microhenries worked best. With these values selected the polyvaricon could be adjusted around mid-range to easily select best SWR.
A caution!
There’s a gotcha with this technique. My L-match has a switch to connect the top end of the variable capacitor to either the input or output. This is used to enable fast selection of either high or low impedance antennas. Referring to the diagram above, if the switch (not shown) is set to connect the variable capacitor to the left side of the inductors, this technique will not work. The inductors will be out of circuit and only the variable capacitor will be in circuit.
Will it still QSO?
My low-band QMX was dug out of its field pack and hooked up to the revised antenna (8.67ft of vertical window line with the “L-match GTU” providing the “other half” of the antenna. Using the “Tune SWR” feature of the QMX, the best SWR of 1.36:1 was obtained by a very small adjustment of the variable capacitor in the L-match GTU. Then it was time to go hunting. My best contact was in the state of Arizona (the “Arid Zone”?) almost 3000km away from my station in Southern Ontario. Signal reports were 599 each way. My sent report was a genuine 599 suggesting the antenna has good ears. The 599 report I received may have been genuine or perhaps it was just a “contest report”. In any event a good solid contact was made. A second contact into North Carolina only yielded a 549 signal report, but perhaps the low angle radiation pattern favored longer distance contacts.
Notice that the L-match GTU has no RF current meter. I could perhaps have inserted my home brewed RF current meter in circuit, but it wasn’t really necessary. Adjusting the ground current also regulates the radiating element current. Simply adjusting for lowest SWR indication on the radio peaks the radiated energy.
For practical outdoor use while hiking through the woods and rapidly deploying the antenna in clearings, the L-match GTU will be replaced with a much smaller series L-C coupler (2T2C). A 13ft Crappie pole is used to support the antenna. It collapses to the perfect length for carrying inside a fishing pole bag (no surprise there then) and is very lightweight.
There’s another gotcha
When the current distribution on the antenna was viewed in EZNEC it was discovered that the current maximum is in the ground circuit instead of in the radiator. Just like any ground-mounted antenna, this can lead to ground losses and inefficiency. However, the primary design objective was not to seek a Nobel Prize in antenna physics, but to come up with a design that meets the objective of a rapid deployment, simple antenna for hiking through the woods. The Linear-Loaded Monopole may just meet that requirement, but I have other ideas to try first. Stay tuned.
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!
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Amazon reveals aviation antenna as LEO inflight connectivity race intensifies
The “tootie-toosie” and the Hiking Antenna
My favorite way of operating is to hike into the woods, find a clearing, set up a quick and easy antenna, make one or more contacts and move on. Well, to be honest, I might pause long enough at a back country waypoint to get out my Aeropress and brew up a refreshing cup of Joe.
To do this my antenna must be simple, compact, lightweight and (hopefully) efficient. The simplest arrangement that meets those criteria is an end-fed wire, but quite often the trees are not tall enough, or contain dense brush in which wires can become entangled. I needed something compact and self-contained that is easy to carry into and set up in a dense wooded area.
I came up with a couple of ideas. First up to bat was a Linear-Loaded Monopole (LLM: no, not a Lunar Landing Module). The LLM is a recent bizarre invention that escaped from my basement skunk works lab and made its virgin QSO in the outback (out in my backyard). But I also had another idea on deck – a converted photo lighting tripod with short whip that I used very successfully out in the field last summer.
Hiking antenna 01: a Linear-Loaded Monopole Hiking antenna 02: 13ft tripod/whipOther craft ale inspired ideas may enter the fray during the course of the coming weeks and months but, for now, let’s discuss these two strange RF launch systems.
A rapid deployment hiking antenna does not share the same design imperatives as other less temporary antennas. The efficiency – the proportion of energy radiated compared to the amount delivered to the antenna by the transceiver – is obviously important, especially since my transient operating base will be primarily QRP. Rapid deployment is the key objective; it must be very fast to set up and tear down. Hiking expeditions often take me well away from my vehicle and any road. I operate in areas that are heavily forested and patrolled by sometimes aggressive black-coated guardians with big teeth and long sharp claws.
Another requirement that factors into the design is a small ground footprint. Trails in these parts are often shrinkingly narrow, rocky, uneven and sometimes covered in mud or pools of rainwater. Laying out a system of radials on the ground is not an attractive proposition and sometimes it is next to impossible. In a recent post (Link: Be gone pesky radials!) we introduced an alternative using a Ground Tuning Unit (GTU). Well, that’s all fine and dandy but the GTU I had built is a a little big and heavy for carrying down a trail. I challenged myself to come up with an alternative.
Most of my outdoor operating time is spent on one band: 20 meters, so I wondered whether it would be possible to design and build a much simplified alternative to the GTU that would be very small, very light and serve the same purpose. I came up with something that met those criteria very well indeed.
Enter the “tooty-toosie”
The “tootie-toosie”, or 2T2C is a Tuned Tank Circuit Coupler. The idea involves a tank circuit designed to resonate at a desired frequency. The frequency I targeted was 14.060 MHz which is the CW calling frequency in the 20-meter band. This L-C circuit is actually a series connected resonator so maybe not strictly a “tank” circuit but I liked the “tootie-toosie” name anyway.
It is actually quite difficult to wind an inductor and select a capacitance for resonance on a specific frequency. Instead I targeted the bottom end of 20m (I am a CW op). Component tolerances limit the accuracy so I gave it my best shot and the end result was quite good. A simple L-C resonant circuit will have a fairly low Q and that will give some leeway in the frequency response. I measured the finished project on a nanoVNA and the peak in the curve showed a useful bandwidth at the bottom end of 20m.
I had already designed a great little tool to assist in a project like this. It is a LibreOffice Calc spreadsheet that will compute the resonant frequency of an L-C tank circuit, or the capacitance required with a known inductance to resonate at a desired frequency; or the inductance required with a known capacitance to resonate at a desired frequency.
I plugged in some parameters to come up with component values needed then began construction.
20m 2T2C ground couplerJust like with previous projects I didn’t have the correct toroidal cores in my component drawer. And just like with those previous projects I leaned on my inner MacGyver to find a solution. T37-2 powdered iron cores were the best I could find and, just like before, I stacked multiple cores together to make a bigger aggregate core. As I understand it, inductors wound on toroidal cores perform best when as much of the winding as possible lies within the core. That gave me an idea. If I built a MacGyver version of a binocular core most of the winding will be inside the core. Could that work?
MacGyver inspired binocular coreHere is how it came together. Two tightly stacked sets of three T37-2 powdered iron cores were put together and secured with electrical tape. Then thin enameled copper wire was wound through the cores until the cores were full of wire. [By the way, the enameled copper wire was scrounged by unwinding old surplus transformers I had in my junque drawer]. I had no idea whether this would work but I gave it a try anyway. The inductance measured on my L, C meter was 29 microhenries.
The tuned circuit calculator told me that was probably too much inductance, but it would be easy to reduce it by unwinding a few turns of wire. I wanted to use a 10pF ceramic capacitor (I have hundreds of them) so I needed only about 13 microhenries in the inductor.
After carefully unwinding the cores and measuring the inductance I got it down very close to 13 microhenries. The capacitor and inductor were quickly soldered together in series to create my tuned circuit.
About that capacitor
A tiny ceramic disc capacitor looks a little dodgy in this application. It has to carry the full AC current flowing in the ground circuit of whichever hiking antenna is chosen. Operating QRP puts less stress on the capacitor so I am hoping it can carry the load. As a backup a short length of thin speaker wire, or maybe even coax can be substituted in place of the ceramic capacitor.
[UPDATE: the ceramic capacitor has now been replaced with a compression trimmer. The only value I had available is 3-30pF so I reduced the number of turns on the coil so that the trimmer could be adjusted near its top end. Adjustment is quite coarse but it gives some flexibility to peak the ground current fairly accurately.]
First field test
Most of the winter snow that was in my backyard has now melted so I was able to set up the tripod/whip antenna shown in the picture at the top of this post. Last summer this antenna was used with either two raised radials, or four ground radials. Will it work with the 2T2C ground coupler? On the day of the test there was a major solar storm and the bands were silent, but at least it would still be possible to see if the antenna would tune up with the radials replaced by this new arrangement.
This antenna has a radiating element only 13ft long made up of a 9ft Buddipole whip with the remainder coming from the tripod main tube itself. It requires a 4:1 unun and a tuner but has the advantage of operating on multiple bands from 20m up to 10m (but used as a fixed 20m antenna in this experiment).
The test was successful in demonstrating that the antenna with this new fixed, tuned ground system would deliver a low SWR (1.3:1) to keep the transceiver happy. The next step, when the bands cooperate, is a full magic smoke test.
Ham Radio Outside the Box will report back when the hiking antenna options have been exposed to full field conditions. I am looking forward to getting back into the woods with my radio gear after another long, snowy winter!
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!
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I'm intending to put up a horizontal 40m full wave loop. Dimensions will be approx 2x sides of 16m and 2x sides ~6m for a total length of 43m.
I can feed with with a 4:1 balun, or put a SG-239 remote tuner at the feed.
Anyone done something similar and have good reasons for one over the other?
I was not expecting this new throw line cube to be so tricky to unfold. I take this as confirmation I need to work on my line skills. ⬛
#ThrowLine #Throwing #AmateurRadio #HamRadio #Meshcore #portable #antennas
Isn’t every quarter-wave antenna really a half-wave antenna?
It’s a bit early for April Fool’s jokes so this is a perfectly serious discussion. Just maybe, the distinction between a quarter-wave and a half-wave antenna is a bit more obscure than we thought. Which is better; a quarter-wave or a half-wave antenna? Does it even matter if indeed every quarter-wave antenna really is a half-wave antenna? The answer is not straightforward and we will explore why in this week’s post.
Let’s all use our noddles
An expert could be defined as somebody who knows at least a little more about a subject than most other people. I am not an expert, but I do have a very inquiring mind. Don’t accept anything you read here without question. Science is the process of submitting a hypothesis which can be challenged, refuted, updated or even discarded. New hypotheses can replace old ones as further studies are completed. Treat everything you read here as a hypothesis; it might be completely wrong, partially right or even brilliantly correct. Challenge it with your own critical thought because I thought I was wrong once – but I was mistaken 😉
How to improve the efficiency of an antenna by burying half of it in the ground
Sounds ridiculous doesn’t it? But isn’t that exactly what we do when we erect a ground-mounted quarter-wave whip with a set of radials? What role do the radials play? Do they reflect the signal away from the ground? “Experts” say no, so my hypothesis suggests that an efficient set of radials establishes a ground plane that is better (or worse) than the actual ground itself.
Current in a ground-mounted quarter-wave antenna. Green line represents ground.The Good Earth
The problem with “the good Earth” is that it isn’t always. It depends on the conductivity of whatever our antenna is mounted on. Seawater could be considered the best ground plane but it has an unfortunate habit of being a slightly unreliable support for antennas. Moving inland a little we have sand, nice firm sand. The sea is still close by and helps with antenna efficiency and directionality, that is if you wish to send your signal in the direction of where the sea is.
Unfortunately for me, the closest sea (James Bay in the near Arctic) is over a thousand kilometers to the north and is frozen for much of the year. So I have to rely on the conductivity of the soil in my area. I live in the Great Lakes region and I am surrounded on three sides by the waters of mighty Lake Huron. Pure freshwater is almost a perfect insulator, but I have the advantage of living on the Niagara Escarpment and water from my well contains over 2000 parts per million of dissolved solids. That may improve my soil conductivity for ham radio purposes but it cost me a small fortune in water treatment equipment to get rid of those dissolved solids to make the water drinkable.
Whenever I wish to deploy a ground-mounted antenna I have to rely on ground radials because sometimes my portable operations take me to locations where I set up on the ancient bedrock of the Canadian Shield, or sandy lakeside beaches where the ground conductivity is not so good.
How do ground radials really work?
I hypothesized earlier that radials establish a ground plane. Their purpose is to give the antenna – and it’s image in the ground – a zero reference point. If this ground plane is efficient (i.e. lots of radials) the current in both the ground and the antenna will increase. Higher current in the antenna means more signal is radiated. And what about that higher current in the ground? The earthworms will thank you for the extra warmth.
By the way, counterpoise or radials?
The two terms are often confused. When I use the term “counterpoise” I use it to mean “the other half of the antenna” which may be made up of a set of radial wires, or a blanket of Faraday cloth, or AA1AR, Bruce’s copper mesh.
End-Fed Half-Wave antenna current distributionWhat’s to be done?
If half our signal is warming the winter nightcrawlers what can we do to redirect the crown joules in a more useful direction? First, let’s examine the current distribution in a half-wave antenna wire.
Let’s call it a “voltage-fed” antenna because a lot of half-wave antennas are end-fed. It could equally be a center-fed dipole which is also a half wavelength long. There are several different ways to erect an End-Fed Half-Wave antenna:
Notice that however we erect it, the entire antenna remains above ground. Some online advice suggests the ends of the wire can be placed close to the ground because there is almost no current there. Others disagree and note that the ends of a half-wave wire are high voltage points and should be kept above head height. And it isn’t just for safety reasons. What are the effects of placing a high voltage point close to ground? Could there be some ground interaction that affects the antenna performance. Any experts care to comment?
Enter the Dipole
A dipole or an EFHW can be erected vertically. Let’s talk about the dipole. It is a center-fed half-wave (a CFHW if you like acronyms). A vertical dipole could be described as a quarter-wave vertical antenna with a quarter-wave counterpoise. Can’t see it? Suppose the counterpoise section is tilted away from vertical. Now it looks more like quarter-wave with a counterpoise. But, the whole antenna is still a half-wave, isn’t it?
Bifurcate that counterpoise
A bifurcated counterpoise is a fancy way of saying split it in two, or in other words, duplicate it. Why? Well again, this is my personal theory. The lower half of a vertical dipole may come close to ground unless it is raised high enough. Ground effects may distort the radiation pattern. If we add an extra wire to the counterpoise section the antenna looks like an Inverted-Y and the current in the counterpoise is split between two conductors. If the current in each conductor is half that of a single conductor the resistive loss in the counterpoise section will be lower, and any ground interaction may be mitigated.
I have occasionally used an Inverted-Y for many years. It was one of the earliest antennas I ever built and performs well. An Inverted-Y built for 20m has to be erected at a height of at least 30 feet (~10m). At that height the feedpoint sits about 13ft above ground and the two radials must be spread at quite a wide angle to remain clear of the ground. I wonder whether we could make this antenna more stealthy? A 30ft mast in a busy public place tempts unwelcome attention from passers-by and park officials. Some ideas rattling around in my old, grey noddle are:
Any other ideas from readers would be most welcome. Let me know what you think in the comments.
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.
Allpoints
Jake Averill
Eh Eye Ate Dub Yah ✡︎ 
Ham Radio Outside the Box
SpaceNews
Dr David Mills
Mäh W.
Mike K3LOE