- Antennas can have high gain, high bandwidth or small size. Pick any TWO
- Every antenna is a compromise
- Put up a resonant dipole
- Have a nice day (outside!)
The Question: What do you want your portable field antenna to DO?
The employment of these antennas is generally for my portable field Ops, typically camping or otherwise vacation/road trips. My focus is on regional comms with my family, my buddies and EMCOMM groups on the Low HF bands and local comms on VHF. I’m not into chasing long distance “DX” very much but any of these horizontal wire antennas will work over very long ranges especially when elevated to around a half wavelength.
A simple kit for temporary, lightweight, deployable wire antennas is essential for any field Ops. No “Rocket Surgery” here, just proven, simple, efficient systems that work very well in a field environment. Included is my experience-driven rationale for what is in this kit and what is not, and why.
Described below is my kit as it fits in a standard US Military M-1956 “Butt Pack”. I have used the types of parts and techniques in this kit for 50+ years and it supports almost any kind of field (or home) radio installation from HF through 6 and 2 meters.
For local and regional HF, I usually use a double dipole with legs for both 40 and 80 meters (and sometimes including 60 meters), fed in parallel from the same feedline. This covers both day and night time freqs without having to change anything while camping.
Known as a “fan dipole” they have been in the Handbooks since the 1930’s; it’s the electrical basis for the military AS-2259. When deployed “low” for NVIS applications they are also known as “cloud warmers”.
The kit also includes extra wire for dipoles, half-rhombics and Vee beams on other bands. It includes pre-made Jungle Antenna ground planes cut for 28 MC and 51.0 MC plus a twin-lead J-Pole vertical for 2 meters. Just simple, effective and proven antennas. Locally customize as required, you won’t need to bring ALL this stuff if you’ve done a little pre-planning.
“It’s a brave person who can admit to using a store-bought antenna”
Unless you are set up on a 5 square foot balcony under observation, in the Sahara or on the Ross Ice Shelf (no vegetation to support at least one end of a wire), forget those “Buddipoles”, “Isotrons”, “Hamsticks” and other such marketing miracles. If you have the space, and can “pull it off”, put out a quarter wave HF wire to the nearest support, even if it’s just laying on top of some 3 foot scrub. Place another quarter wave wire in the opposite direction on the ground or laying atop more scrub. Maybe some kind of LC coupler if your radio needs it. You’ve made a Hasty Dipole. See below.
Although it won’t outperform a somewhat elevated dipole, this will clearly out perform any expensive, short, loaded, lossy “leaky tuned circuit” or transmit loop contraptions, particularly during “receive” due to the tiny capture area of those severely compromised antenna designs. (Loops are excellent for direction finding and can be very effective at nulling out local noise sources otherwise getting into a receiver. Not so much for a transmitter antenna, their efficiency is very poor.)
Those wire arrangements will also get your antenna away from all those noise sources inside and around the typical inhabited structure. VERY important. But this post is about a portable, field antenna kit.
Wire HF antennas are simple, lightweight, cheap, compact, easy to deploy and EFFICIENT! It’s basic physics. If its long RANGE (> 2000 km) that you are after, mount the horizontal wire antennas 1/2 wavelength high.
An antenna engineers’ Axiom as above:
“You can have High Gain, High Bandwidth or Small Size. Pick any TWO”.
But my Buddipole has a 1:1 SWR !
So does a dummy load…..Think about that…
Sorry – Flame Shields Up….
My portable field antenna kit:
As shown, the kit contains the following:
Lightweight HF dipole center insulator with terminals and SO-239 Coaxial connector.
Dipole 20 AWG insulated wire legs for both 80 and 40 meter dipoles. Note fishing snap swivels for far-end attachment to halyards.
One 40 foot RG-58C/U coax feedline with PL-259 connectors
Two 20 foot RG-58C/U transmission lines, one with BNC and the other with PL-259 connectors.
3 each nylon heaving lines / halyards.
Three 8 Oz fishing weights for launching into trees.
One “high visibility” heaving line / halyard.
One 1/4 wavelength insulated wire with insulator and banana plug for HF or ground wire array needs.
One coil 200 feet 26 AWG insulated wire for halfwave ground reflector wires or stealthy/halfwave antennas on other freq’s.
One 2 – meter twin lead J-Pole and coax feed line with heaving line and fishing weight.
One 6 – meter “Jungle Antenna” ground plane cut for 51.0 MHz, photo below, details seen elsewhere on this website.
One 10 – meter “Jungle Antenna” ground plane made with WD-1/T commo wire.
One 12 volt soldering iron with cigarette lighter plug, solder and electrical tape.
One lensatic compass with aviation Sectional map of my usual Op areas. (aiming antennas)
Two porcelain end insulators.
Assortment of BNC – UHF and wire adapter connectors. One BNC-UHF jumper cable.
One 20 foot (adjustable) length of ground braid (keep it short!) with alligator clip.
M-1956 Canvas Butt Pack to contain the entire kit.
I see that there is now a company marketing a very stripped-down version of this kit for partial functionality. The $200 price tag includes conventional wire-wound ( ! ) end termination resistors. (The inherent inductance of typical wire-wound resistors completely defeats their purpose as terminations for unidirectional wire antennas.) So if you build your own kit you will probably better understand its design and usage.
“There IS a way.” Murphy’s Law of Combat
“The easy way is always mined” Murphy’s Law of Combat
“There is no free lunch” The First Law of Thermodynamics
Although I carry a couple, I usually don’t use “formal” insulators at the dipole ends. I don’t run more than 100 watts (PRC-47), usually just 10-20 watts or so from the smaller field sets. The nylon halyards provide more than adequate insulation, even when wet. I use brass fishing snap swivels at the dipole ends to provide a quick connection to the halyard and these also eliminate twisting and kinking of the wire and nylon halyard while winding back up. They also “pull” more easily over a branch than a big insulator would – big insulators can get hung up on small branches. White or glass insulators can also be quite visible.
Why Coax? With the resonant HF antennas that I use, the RF transmission line losses are low and acceptable. (There is nothing magic about antenna “resonance” as far as effective radiation goes. The resonant antenna just helps keep the feedline losses to a minimum). Coax is flexible, tolerates rain, rolls up into a compact kit, “connectorizes” fairly easily, deploys and retrieves easily and is pretty hard to see.
These are all advantages over twin lead, ladder line etc. although open wire lines like those are very “low loss”. For a temporary, resonant HF dipole in the boonies, not too high up and that fits in this small kit, coax was the transmission line of choice. I use RG-58C/U.
Above: the Jungle Antenna deployed for 51 MC operation before being hoisted up to operational height. Simple, effective, long-range, lightweight and fits in your BDU pocket. Just find some local sticks for spreaders; bamboo as used here is perfect. (See the “Field Expedient Antenna Systems” post elsewhere under the Antenna Systems category for further details and variants.)
Above: A Jungle Antenna made with the older style WD-1/TT commo wire utilizing a standard BNC chassis-mount connector. The 4 radials (in this case) are soldered to the 4 mounting holes in the connector flange, the vertical radiator wire is soldered into the BNC center pin. This one is pre-cut for the 28 MC Ham radio band; each leg is about 8 feet long.
Use either 2 long sticks in a “cross” pattern or 4 shorter sticks for a “square” pattern to separate the radial wires. Connect up your coax via a BNC connector, hoist up high, expect very good range. When the “skip is in” on 10 meters, this antenna has produced cross-continent contacts with low power. These will also work very well on the 27 Mc “CB” band if you need to use it in a pinch.
On Optics: Keeping it low profile while “stealth camping” or in suburban HOA zones: I have found that brown wire is the least visible when strung through trees for dipoles or other HF wire antennas; it has less contrast than black or even green. Gray is best when out in the open, viewed against the sky. 20 AWG teflon or PVC insulated, stranded wire is hard to see, adequately strong and takes up little space.
Be sure to skuff-up the insulation with sand paper to knock down the glossy sheen – cuts down on sun reflections for even more stealthy camouflage. Interestingly, bare copper wire becomes difficult to see against foliage AFTER it has oxidized a bit. Its surface becomes non-reflective and approximately olive drab colored as well. Nothing to see here, move along…..
“Try to look unimportant – they may be low on ammo” Murphy’s Laws of Combat
Bare wire contacting wet trees or leaves can detune a system and/or increase losses, especially if the contact is near the high-impedance (and therefore high voltage) ends of the antenna or other high impedance node. Not a critical consideration but use insulated wire if you have the choice. You’ll get more consistent results. For a “fixed” installation where the wire is always entirely in the clear – doesn’t matter.
On Launching: I have found that 8 Ounce fishing sinkers are the optimum weight for slinging up into the trees. They are light enough to throw but have enough weight to fall down through the branches easily once they have flown over your target branch. If they get hung up part way down, the Arctic Orange paint job makes locating them easy (or just use a partially-filled canteen; run what you brung). When slinging, wear gloves – nylon line makes nasty “rope burns”!
For launching the dipole and for halyards, I use woven nylon line sold for duck decoy anchors; one length serves both purposes. It is low visibility, strong and just right for launching behind an 8 Oz fishing sinker. Wound up on a handle sold for carpenters chalk snap-lines, it works great.
It is much better that parachute “550” pound test line which is unnecessarily strong for temporary antennas, it is hard to launch due to its weight – and easier to see than the antenna wire itself. I have found that duck decoy anchor line to be the optimum weight for this purpose. Anything around 1/16″ / 1.6 mm is good.
Above – The Assistant Radioman helping to set up the PRC-74 dipole fixture with built-in balanced feedline.
“Teamwork is essential – It gives them someone ELSE to shoot at”
Murphy’s Laws of Combat
Here’s the PRC-74 dipole spindle assembly with transmission line and legs for 80 meters CW:
I can “sling” a wire up well over 20 meters into a tree usually with just 1 or 2 attempts. It takes a little practice but is easily mastered. For launching a temporary field antenna forget the bow & arrows, compressed air mortars, fishing rods etc. (However their complexity may make sense for a very high or semi-permanent or one-time installation – they may also be more fun!)
Just fake out a sufficient amount of line on the ground between you and the target tree after tying the wire element to it. Grab a bight of line with the sinker on the end, swing the weight around in a vertical circle (underhand) a few times to gain momentum and let ‘er rip at the right time. When using NVIS system techniques for local and regional comms I usually attach the halyards much lower, 5 – 15 meters up – very easy. Underhand slinging takes just a little practice but it works very well.
I have also used my “Hill Billy Engineering” DIY slingshot with a Zebco fishing reel – it can work OK, but like other contraptions, it is bulky and doesn’t fit in my field kit. The main problem with the slingshot is you can’t launch a heavy 8 oz sinker very high – and you need the weight to pull the line down through the branches. (It depends somewhat on the target tree species.)
A 6 oz sinker can be shot or cast higher but then get hung up and not drop. You can use very light line and a lighter sinker but then you have to splice an intermediate weight messenger line/halyard to then pull up the wire. Too many parts, too complicated, too slow for a temporary field installation.
Above: The slingshot antenna halyard launcher with a 2 ounce sinker. It works, but doesn’t fit into my kit. I’ll go with the hand-slung weight using the KISS method in the field.
With any technique you use, place about 3 feet of “hot pink” or fluorescent yellow leader on the weight first. That will help you see it dangling from the tree, especially if it is still high up. You’ll thank me later.
Both 6 and 8 (preferred) ounce “torpedo” type fishing weights painted Arctic Orange for slinging the heave lines. They fall through the branches easily. Attached to the launch halyard with 1 meter of fluorescent yellow line. Hard to miss among the branches.
Pretty easy to spot among the green clutter, Hot Pink line would be even better here.
The use of “hot pink” or fluorescent yellow nylon for entire halyards (hardware store carpenters chalk snap lines) is warranted when setting up a public display or EMCOMM station when the high visibility can prevent clothes-lining someone. Those snap lines also come on spiffy winder-upper gizmo’s to keep them orgainzed.
A case for simplicity in the boonies: I have used these types of portable antennas at home and in the woods for over 50 years of casual Ham ops/camping and also including decades of Military service. Resonant dipoles are simpler, cheaper, more efficient and have intuitive directionality when compared with “G5RV’s” etc.
G5RV Portable? Not…. They must be great – everyone is selling them!
Throw that G5RV away as a portable “field” antenna unless you will exclusively run 20 meters and need a little directional gain in 4 random directions, you want a frequency-dependent quasi-omnidirectional “scatter” radiation pattern, if you like high coax feedline transformer losses, if you like overheating a mismatched Balun or if you want to carry around a lossy, bulky “antenna tuner” to make up for its inadequacies. Better yet – bury that G5RV in the back yard and use it as part of your ground system.
See a very good article by VE2CV on the G5RV’s problems in QST, March 1994, Page 34. There are several others detailing its inadequacies and compromises – look at the work done by W5RH The G5RV Antenna System – An Analysis which is particularly good. The G5RV can be an acceptable “base” antenna that is supposed to perform somewhat efficiently and predictably only on 20 meters for which it was designed (but doesn’t work very well there either).
Elsewhere, it can be made to work (with an additional coupler) if you realize, understand and accept its compromises, feedline complexities (and cost). But a bunch of wire in the air, connected via an antenna coupler will also work “multiband” just as well from the perspective of the guy on the “receiving” end.
“The G5RV antenna system is suitable for multi-band operation, just as any wire from about 88 to 140 feet might be.” As noted by antenna design expert L.B. Cebik (Reference 89).
A practical example with a G5RV: My buddy bought a G5RV a long time ago thinking it was the “way to go”. This was the original 102 foot long version. (By the way, there is nothing engineered about that length. or even “magic”. 102 feet was the the maximum length the designer, Louis Varney, G5RV, could accommodate in his back yard. Hmmmmm.) Today, the “magic” is in the marketing….
So we installed it per the instructions, about 40 feet high, above a clear farmland area where the water table was about 10 feet down. Pretty much an ideal location. We then measured the feedpoint impedance at the coax side of the balun with an antenna network analyzer before connecting the coax to the station. The VSWR was all over the place from 3.5 to 30 Mc as expected. The lowest it produced was 1.6:1 with some reactance at 20.065 Mc. It was well into the “Red”, over 3:1, almost everywhere else, including on 20 meters, the single band for which the G5RV was “designed”.
That very high VSWR is not a particular problem per-se, since the 450 ohm ladder transmission line from the balun up to the dipole elements is very low loss and the antenna will radiate most of the power you can manage to push into the ladder line.
The problem comes when you then connect coaxial cable from the balun at the ladder line down to the equipment. The high VSWR at that junction causes big losses in the coax; the impedance is “all over the place”, so you must use an antenna coupler with its inherent additional losses and high voltages. (That random length coax then also acting as a lossy, frequency-dependent RF impedance transformer.)
Further, that balun only works as an unbalanced-balanced 9:1 impedance transformer when it is terminated with a purely resistive 450 ohm load. This is NOT what the 450 ohm ladder line in a G5RV looks like on almost any frequency when connected to the antenna elements.
Also note the big mismatch between the 450 ohm ladder line and the much lower feed point impedance of a typical dipole/doublet/G5RV. Not even close.
Not optimum – but it will produce contacts…It’s just a bunch of wire in the air. But you can buy them.
Here’s the ladder line – dipole connection.
Above: Standard stuff. (next time run the ladder line wires through the insulator holes!) If you MUST use a G5RV, ditch the balun and coax and run the ladder line directly to the transmitter and feed it with a balanced-output antenna coupler. (But now it is a generic Doublet, not a “G5RV” anymore) That will work pretty well at a fixed station – but not very practical for a portable antenna kit.. Sorry – End of engineering-details rant!
Back to effective simplicity: Another field expedient antenna is the Hasty Dipole:
Above: Even with a full kit, sometimes you are just lazy or don’t have the time to deploy a “proper” dipole at a temporary site. Then just rig a Hasty Dipole which is a halfwave dipole with no transmission line. Connect each quarter wave wire directly to the radios’ Antenna and Ground posts respectively, run the wires off to your supports. Works just fine, the TRC-77 (in this case) loads to full power output.
On Baluns in the Boonies: Of course, running a balanced antenna like a dipole and feeding it with unbalanced feedline like coax calls for a balun or at least a current choke at the antenna/feedline connection. Good engineering practice. However I have rarely used them and no-balun, coax fed dipoles seem to work as expected with respect to directionality, RF on the transmitter chassis, SWR etc.
In the boonies, unwanted feedline radiation (if there even is any) is usually not an issue; try to keep the coax at right angles to the antenna for as far as you can, to reduce that. Once again, the guy on the receiving end will not notice the difference. I like to keep it simple.
Above: Another day in the mountains….The NVIS “Cloud Warmer” as deployed.
Of course for wire antennas at a fixed installation, open-wire ladder or “window” line all the way back to the transmitter is your best choice to minimize line losses with a balanced antenna (and then it must be properly coupled to the transmitter). However that stuff is clumsy, difficult to transport in a small pack, highly visible and generally impractical for a portable, field antenna system.
Further, resonant dipoles generally outperform the purpose-designed “long” wire or vertical HF antennas supplied with military field radios such as the AT-101, “Hank”, other Inverted L antennas or verticals like the AT-1011. (Verticals radiate equally poorly in every direction and require a big, low impedance ground system to achieve any reasonable efficiency.)
Both wire types need two supports but the balanced dipoles do not require a ground or ground wire array like the Inverted L’s or slant wire antennas. Simpler setup for the same effective radiated power and the dipoles don’t waste skywave power on a vertically polarized component like an Inverted L does. Also, less probability of an interference field between each polarization mode which causes holes in your coverage pattern.
HF Verticals are great if you only have to operate while moving in a vehicle or if you don’t need to communicate within a 300 km radius or so (beyond groundwave.)
End-fed wires? They must be great; everyone is selling them! Meh.
The generic End Fed Wire and the End Fed Half Wave (EFHW) is a special case of those. They are all the rage these days, and as with any conductor up in the air, they will produce contacts. Easy and simple to deploy, they warrant some discussion.
My kit has sufficient wire for employing end-fed wire antennas occasionally – if I am lazy, in a hurry or only have one support available. They are very simple to rig but are generally my last choice especially if more than 1/4 wavelength long. Even then. Why?
A “general purpose” end fed half-wave wire antenna can work OK*. It’s only real attribute is that it is very simple to deploy in the field, especially if you only have one support available. They can radiate on multiple harmonically related Ham bands with impedance matching; and on non-resonant bands with even more help from an ATU. An “End Fed Dipole” ? – um, just no.
If you initially deploy a quarter-wave wire for 80 meter operation and then decide to use it on 40 meters – it instantly becomes a half wave end fed antenna.
A half wavelength wire in free space will radiate in the classic double-lobed pattern – regardless of where it’s fed along its length. End, center, off center etc. So:
* As a practical matter, a half wave end fed wire is generally going to be deployed as a “sloper” with significant, asymmetrical ground interaction. As an example, on 80 meters, with the radio on or near the ground, the wire end might be suspended to a support 90+ feet high; the slope angle is then 45 degrees. EZNEC computed Z=1525 + J 2064 ohms, SWR = 51:1
When deployed as above and operated at the lowest design frequency (half wave) the resulting EZNEC Model of the radiation pattern shows it to be within about 2 db of omni directional for 80 degree takeoff angle NVIS work; usable. At a 20 degree “DX” takeoff angle there are four nulls in the pattern including a 25 db null to the rear. When that antenna is used on the second harmonic there are many smaller pattern nulls at the 20 degree DX takeoff angle. Not great.
For a deliberate fixed path a lot of your RF probably goes where is doesn’t do you any good unless the wire is deliberately aimed – or if you’re lucky. But they will make random contacts on some azimuths and at some ranges.
Powering an EFHW Antenna: If you can get power into them they can radiate it well. That’s because the high current portion (the portion in the middle approximately third of the half-wave wire that does most of the radiating) is up and away from the radio, infrastructure and local ground absorption losses.
But that portion needs to be horizontal and low for effective regional NVIS, or horizontal and a half wavelength high for long distance comms. Or vertical for either local ground wave or long range omni directional comms.
It’s hard to rig an end fed wire that doesn’t simultaneously do all 3 modes like that. (Resulting in lots of “lost” or wasted RF power that doesn’t get to your target.) Especially when operated as a two or more halfwave antenna on the higher frequency bands; their azimuthal radiation and takeoff angle pattern becomes full of lobes and nulls.
With a radio designed for “50 Ohm” loads, an end-fed halfwave wire will require a matching device. Those are typically a ferrite core transformer to transform that very high antenna impedance into something much lower (and that transformation incurs losses and extra complexity in a portable field deployment).
Transformer examples abound on the Interwebs. The more I read about the topic the more I am reminded of the old saw:
“The plural of anecdote is NOT data.” Even if you can get past the Apples versus Lug Nuts comparisons. Choose wisely.
Note that many EFHW antenna users report that the transformer core gets hot at moderate power levels and the SWR begins to climb with heating towards the ferrite Curie point. Coax losses also climb correspondingly. Not good – unradiated power lost – but maybe those losses contribute to the EFHW’s potential broad band performance. Just as a dummy load is broadband.
An end fed half wave wire can present a feed point impedance of 2500 ohms or more. That’s a 50:1 impedance mismatch for a 50 ohm output radio (SWR of 2500/50=50:1). A typical ferrite core transformer with a 7:1 turns ratio (49:1 impedance ratio) or more will be “helpful”. Here’s my solution for the portable field antenna kit:
Below. An experimental 43 Mix torroidal 49:1 (Z) impedance transformer for a high impedance EFHW antenna. I’ll use an EFHW if I don’t have adequate time or supports for a better antenna. The transformer helps, if you must.
Above: Mounted in a plastic 35 mm film can (remember those?). The torroid does not get warm to the touch with my 10 watt military field sets operating on 80 and 40 meters. There is sufficient core cross-section to be adequate with low power sets. Packaging is Good to Go for Bush Ops.
One way to fine tune the transformer is to terminate the output with a 5-10K non inductive pot (rheostat). Add or delete secondary turns from “design” to yield the best match versus the resistance presented by the pot. Shoot for the best 50 ohm match @ appx 2500 ohms load over your working frequency bands. Then verify it with your installed antenna and an SWR measurement.
The alligator clip grabs the “counterpoise” wire which is run on the ground under the antenna wire.
This 132′ wire end can be plugged into the transformer output with a banana plug or a pigtail, the radio connects to the BNC connector. It’s cut for a half wavelength on the 80 meter CW band. It’s occasionally used as a hasty deployable Bush antenna that works adequately with my low power military field sets on both 80/40 meters, my primary interest in the field.
The GRC-109, TRC-77, RS-1 and RS-6 sets that I use in the field will load properly into low-to-medium impedance antennas unaided (but not into high impedance antennas such as a half wave wire). When driving a high Z antenna like the EFHW, their output power indicator lamps (series antenna current) won’t glow, therefore precluding any PA tuning adjustments – which wont have any effect in any event. Not good. This transformer is an engineered solution to get around one of the EFHW’s systemic problems.
The GRC-9 however can work adequately with higher impedance end-fed wires as part of their issued antenna kits. (Those kits also include a substantial ground radial system.) In the “REEL” antenna selection mode, their output coupling network is designed to efficiently handle higher impedance, end-fed antenna loads relative to the high plate impedance of a vacuum tube PA.
On 80 and 40 meters, and as-rigged in the field, my “film can” system has a VSWR under 2:1 depending upon the height/near-field environment. Who knows which directions or takeoff angles the resulting RF goes but it comes down somewhere. It does make contacts to random places if it’s all that I have, or all I am interested in at the time.
EFHW antennas can take power on higher, n-harmonically related bands since those are now n-half wavelengths long. They therefore also present a very high impedance to the transformer secondary on those higher frequencies.
These Fixed Ratio transformers then also transforms that high impedance into something lower that the radio output circuit/ATU can possibly match to. Or not.
Here’s another experimental version, this one with a larger FT140-43 torroid. This one will handle more power.
Awaiting packaging but it may be a little too big for my portable field kit.
In addition to 80 meters, this one also has a good match on 60, 40 and 30 meters, my other favorite CW bands. The transformer with 43 mix is quite broadband for these purposes.
Again, bench testing with a non-inductive rheostat (Pot) load, set to 2500 ohms. My 20 watt PRC-174 is awaiting some field trials with this version transformer.
Especially in higher frequency, n-half waves operation, the resulting impedance seen by the transmitter is quite sensitive to the antenna’s immediate environment. That is part of the source for the EFHW’s reputation as being “finicky”, “won’t load”, “position sensitive”, “still needs a tuner”, “RF in the shack” etc..
It’s a transformer and one end of that transformer secondary must be tied to a reasonably good ground for consistent results, even though the current flow is relatively low at that point. It is NOT zero.
Why the grounding requirement? Because RF current flow in a conductor is what causes Electromagnetic radiation (ala Mr. Maxwell) and the transmitter does not “create” current from nothing (ala Mr. Kirchhoff).
With an unbalanced antenna the power amplifier/output network essentially “pushes” current into the antenna by “pulling” an equal current from the ground system to create a complete circuit for the sinusoidal RF current to flow in the antenna. The resulting E/M field induces current flow back into the ground system. This is why ground losses must be minimized – they waste transmitter power because ground losses are in series with the antenna radiation resistance (ala Mr. Ohm).
The commercial EFHW antenna manufacturers sometimes state that a ground/counterpoise is not needed (except for safety/lightning protection; true). They rely on the uncontrolled, random capacitance of the coax feedline shield (or your body/radio) to the soil to complete the circuit. Not real good.
Also, voltage, including “high” voltage, is measured between two points: The antenna feedpoint and the chassis, ie: ground (and hopefully not via YOU, capacitively or otherwise.)
The end fed half-wave antenna will necessarily have high voltages at its feedpoint – and the matching transformer must withstand every volt.
Eg: A transmitter delivering 100 watts to the end of a 2500 ohm EFHW antenna will see about 500 volts at the output of the matching transformer to ground. Generic 600 volt rated hookup wire will work but with little design margin. How about uninsulated antenna wire? Something to worry about when using a “high powered” transmitter (or fingers).
The “sloper” halfwave antenna is a compromise – not particularly efficient at either short or long ranges. But they will produce contacts as any wire antenna will.
The Low Dipole: To enhance NVIS radiation “straight up” for regional comms, it’s useful to deploy a half wave wire in the near-field, on the ground under the half wave dipole to serve as a reflector. Theory and modeling indicates it should add 2-3 dBd gain versus a simple dipole over “average/poor” soils. Wire conducts better than dirt!
Absent an instrumented antenna test range it is difficult for me to perform an “A-B” comparison measurement due to QSB fading and the practical aspects of instantly adding/removing the wire! But definitely worth it, simple, seems to work in the field – I’ll take it! The wire should be about 5% longer than half wavelength to enhance the reflection effect.
A 2-element directional “Yagi” array pointed “up”. What’s not to like?
The ends should be insulated and away from dry vegetation. The ends are high impedance points and will see high voltage; a possible ignition point in dry grass etc if you are running high power levels. Below: Two examples of ground reflector wires; one insulated, the other bare stranded wire on an RL-29 reel with clips for the end insulators:
These are actually for laying on the ground directly under a halfwave dipole antenna to reinforce ground-bounce; in this case cut for a half wavelength + on the 3.55 mc CW band.
When the dipole is erected 0.25 wavelength (can be a little lower at the expense of gain) above ground it produces a strong signal up at high angles due to ground-bounce for regional NVIS coverage. These low-loss ground wires enhance the in-phase ground-bounce necessary for even more effective radiation at high angles.
Another significant advantage of this technique for regional comms is that the low dipole is quiet during receiving. Quiet since it has low gain at low signal arrival angles. So it can reject interference from very distant stations and especially atmospheric static crashes from distant, multi-megawatt lightning activity near the tropics. Obviously these advantages make it a poor choice for “DX” work beyond 500+ km or so. Not my target.
Verticals for regional comms? Forget those fancy military ground-mounted vertical HF antennas/tuners unless you want to work really long range, omnidirectional “DX” via F1/F2 refraction or just local groundwave stuff. Verticals are terrible for “short skip” regional comms from say, 20 miles through a few hundred miles out via NVIS. Verticals produce a NULL straight up – exactly what you DON’T want for NVIS. Verticals are also comparatively noisy since man-made noise is primarily vertically polarized as is the noise from distant, multi megawatt lightning strikes. QRN. Your worst-case antenna unless you are mobile or constrained by real estate etc. (If you want to work long-range “DX”, you are much better off with a horizontal dipole at a half-wavelength high anyway.)
However, the above observations are about effectiveness of communications on frequencies within narrowly defined limits. Specifically in my application for regional (not “DX”), few hundred mile coverage out from remote locations like campsites, vacation hideaways and even my home base. If you want to operate with strictly / only military issued gear for the sake of “the experience” or authenticity (I also do that routinely), go for it !! It’s supposed to be fun now!
Note: Some really well designed field evaluations were done by the US Army in Panama in 1963. It addressed the issue of short radio ranges in jungle environments. The HF portions of those experiments contrasted the AN/TRC-77 with the AN/GRC-19 utilizing different antenna types in different configurations.
Slant wires, verticals/whips, dipoles, inverted dipoles, wires in the tree canopy etc were carefully evaluated. Short answer: The low horizontal dipole was overall most effective. An interesting read: Interim Report on Tactical Jungle Communications Study. (Reference 87) Lessons learned also apply in tactical deployments outside of purely jungle areas.
Resonant dipoles deliver high performance, are cheap, simple, lightweight, easily “home made”and compact for storage and transport. A rare case in life where the simplest, cheapest solution is also the most effective all-around. If you have no skills, no time, no wire, no tape measure, no tools or no imagination, you can purchase a “store-bought” dipole; a last resort that will work.
Stealthy dipoles? I have never been “caught” with antennas in the woods. (Forest Rangers don’t like anything in “their” trees.) “I’m just here camping”….
So “What’s the Best Antenna?”
Above: The PRC-74 dipole assembly. Ready made insulator, terminal strip and wind-up fixture as deployed from trees. Simple, also works great on the GRC-9, RS-6 or GRC-109’s when in the field. This antenna stays packed with the GRC-109 system kit. It would be a no-brainer to duplicate this with scrap materials.
Close up view. The transmission line is about 25 feet of thin twin-lead. I’m guessing the feedline Z could be around 72 ohms. Pretty hard to see when deployed.
Above: The home made plexiglass dipole center insulator as seen in my kit above. Deployed here at a mountain campsite with legs for 80 meters CW. One wire leg ran directly over our campfire, about 40 feet up, the coax quickly disappeared into the foliage. It was there for a 4 day weekend camping trip before any of my buddies even noticed it or the RG-58C/U feedline. Pretty stealthy.
Any reasonable non-conducting scrap material will work as the center insulator; the DeLuxe version above with suitable connectors installed. Even with a 1 KW transmitter and assuming a 72 ohm antenna feedpoint impedance, the voltage between the elements at the center is less than 400 volts peak. At 100 watts it is 118 volts peak – almost anything made of plastic will work if it is strong enough. Plexiglas or lexan is ideal, dry wood will work in a pinch too. Or a dried out pine cone.
Above: Another off-the-shelf expedient, a Pomona 1296 shown here, or the preferred Pomona 1452 (female) BNC/Banana terminal adapter. The female Pomona 1452 (NSN 6625-00-102-5652) is preferred for a dipole fed by RG-58/U coax with an existing BNC male connector already attached. Otherwise you will need a “double barrel” adapter as shown above.
This can work well and is simple and small. However the RG-58/U can pull out of the BNC cable connector if the feedline is too long/heavy. The feedline may need some strain relief at the connector for long runs back to the radio. A Prusik knot is your friend.
Above: Although not really “portable”, here is my home brew mobile antenna impedance matching / patch panel unit. Built on plexiglass panels and permanently mounted in the Bronco it can select either the TS-50 Ricebox, PRC-47, the GRC-9 or any other installed HF radio for fixed-portable operation. It can also select either the 14′ (to the tip) whip on the rear bumper or an external SO-239 antenna jack for fixed-portable operation.
It uses large-spacing Mil-Spec variable capacitors and AirDux coils and is configurable as an L network or a CLC Tee network as needed. The seemingly odd knife switches are excellent for high voltage – high current RF switching tasks. Having a mobile antenna capability is important in addition to pure “portable” ops:
Above: My mobile setup when operating mobile or fixed-portable. Antennas include an AM-FM broadcast radio antenna, 1.8-30 Mc center-loaded HF whip, 51 Mc Whip, 28/27 Mc whip, GPS antenna under a radome on roof, 145 Mc 5/8 wave whip and VHF/UHF scanner whip. Also included, and connected to the impedance matching device pictured above is an HF slant wire for regional NVIS comms while stationary. That wire is seen just touching the top of the spare tire in the photo. I also have visible and infra-red strobes available for signalling. The homebrew matching circuit permits operation on any authorized frequency I could need to use. From this mountain top, I have it covered.
The “tuner” permits switching between Hi/Lo Z transformation modes, radios, antennas and additional fixed HV doorknob capacitors. This is accomplished with an otherwise odd application for knife switches that are excellent for handling the high RF voltages and currents that are present. As such the coulpler can handle more power than I can generate – but at the same time operate in thin mountain air where corona discharge and breakdown can occur. It even includes a small NE-51 neon lamp across the input terminals to indicate full power transfer as well as a modulation/carrier indicator – very handy, especially at night.
Thankfully, and by design, nothing “automatic” here, it is pretty bullet proof, and will match almost anything in my portable field antenna kit as well.
Back to simple, quick and dirty. Running a wire up into a nearby tree and two “counterpoise” wires laying on the ground makes it happen for this AN/TRC-77 CW transceiver. This configuration is “per” the TRC-77 manual. Let’s see if it works well.
Above: The radiating element here is a 25 foot long, bare copper stranded “slant wire” up into a tree. The counterpoise consists of two 50 foot pieces of WD-1/TT infantry field telephone wires connected to the set’s Ground post. The ground wires are spread about 90 degrees apart. That insulated wire has 3 steel strands for strength and 4 copper strands for high conductivity. The steel strands make it springy – it remembers how it was last coiled up. But it makes excellent antenna or radial ground wires.
Here, testing the 10 watt transmitter on the 40 meter ham band. My first contact with this antenna was KF6GC on CW, a 178 mile shot in mid-day. This antenna system goes on the air quickly with minimal effort. It works OK, even for a slant-wire; a dipole is significantly better although harder to deploy. The Wonderful World of Tradeoffs.
Above: Although the ground radial wires are necessary for the efficient operation of an unbalanced “Bush Antenna” like that, this particular deployment also needed an additional “ground” to keep RF off the chassis while working on 3560 kc. The soil was particularly dry. In this case, the 18″ metal tent stake with the paint sanded off; keep it wet and add a little salt from your C-Rats or MRE to improve soil conductivity – it cured the problem here.
Another handy (essential) device for field antennas is the “Radioman’s Helper“. This is a two-piece, 15 foot bamboo pole made by slipping a smaller diameter section into a larger one, with a hose clamp to keep them together.
A mangled piece of a wire coat hanger “S” hook on the top end is very handy for placing or routing antenna wires up into trees, around branches or connecting a halyard loop to a nail high up on a building, etc. The “S” hook allows you to push wire up or pull wire down as needed. The pole is also essential for grabbing the sling-weight which often doesn’t (rarely) make it down though tree branches to within reach…
The smaller end of the left “hook” piece slides into the larger “handle” slotted end, secured with the hose clamp. I consider this 15 foot pole to be an essential tool for stringing wire antennas in trees. Rides on the roof rack on trips.
In the below case the pole is lashed to a “support of opportunity” to hold up one end of the TRC-77 slant wire antenna. Or just jam it down a local gopher hole. Another mount is to just hammer a short piece of re-bar or concrete form-stake into the ground and slip the large (open) end of the pole over it. Self supporting, strong enough. Very handy:
Above: The Radio Man’s Helper, here deployed as an expedient mast on this tree-less hilltop. This antenna, on this site, with the 10 watt TRC-77 operating on CW is easily capable of local and cross-continent contacts. Day or night.
You can use the bamboo pole along with the usual dipole parts from the kit to build a multi band dipole antenna array suitable for NVIS propagation. The bamboo bottom section is now reinforced with duct tape. Note the color-coded wire element attachment snap swivels:
Gray = 8 for 80 meters, Blue = 6 for 60 meters, Yellow = 4 for 40 meters.
Just hammer a steel stake or piece of re-bar into the ground, slide the big end of the bamboo pole over it. This will hold it vertically after you connect and deploy the 1, 2 or 3 resonant dipoles in parallel from the feed point insulator out to the ends. Insulate and secured the far ends via nylon line and 10″ nail spikes for guy anchors. You can also run a half wave ground reflector wire under the dipole(s) to enhance the vertical gain if the soil is particularly dry/poor.
The feed point uses an old Budwig dipole center insulator hanging on the hook; it’s strong enough. Tie the wires at the insulator holes then connect them via the red/black binding posts to the SO-239 coax connector. Ready to attach the dipole legs, then stand it up.
Just slide the bamboo over this concrete-form stake. A short piece of re-bar is also good.
The bamboo Radioman’s Helper makes a handy, light weight, easy to deploy NVIS antenna mast where there are no trees or other supports available to hold up wire antennas. Here on the “antenna test range” awaiting attachment of the dipole legs for 80,60 and 40 meters.
(You can also use it to find True North, determine local time or, with a time-tick from WWV, determine your longitude! But that’s another story.)
The Antenna Atlatl: Based upon the ancient spear-launching device (the lever). Just slide the launch weight inside the foot-long hollow end of the larger bamboo pole.
As with a surf casting fishing pole, aim for your target tree and whip the end forward. You can easily throw an 8 ounce sinker 100 meters or more. With some practice it’s easy to get it 30 meters up into a tall tree. Multi-use antenna tool!
For more information about using this kit for building practical field antennas including terminated Vee’s and vertical rhombics, see Field Expedient Antennas
It includes information on making field expedient termination resistors from available materials.
For more ideas on how to employ stealthy antennas, take a look here:Stealthy/Covert Antennas