Portable Field Antenna Kit

N6CC – by Tim

UPDATED 7/26/14

A simple kit for temporary, lightweight, wire tactical antenna systems is essential for any field Ops.  No “Rocket Science” here, just proven, simple, efficient systems that work very well in a field environment.

Here’s 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 decades and it supports almost any kind of field 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, fed in parallel from the same coax feedline. This covers both day and night time freqs without having to change anything. 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 29 MC and 51.0 MC plus a twin-lead J-Pole vertical for 2 meters. No Rocket Science here – 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.

The focus of these antennas is generally on my portable Ops for regional comms on the Low HF bands: 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. Put out a quarter wave wire to the nearest support, even if it’s just laying on top of some 3 foot scrub. With another quarter wave wire on the ground or laying atop more scrub, it will clearly out perform any short, loaded, lossy “leaky tuned circuit” contraption.
Wire HF antennas are simple, lightweight, cheap, compact, easy to deploy andEFFICIENT! It’s basic physics. If its long RANGE (> 2000 KM) that you are after, mount the horizontal wire antennas 1/2 wavelength high.

But my Buddipole has a 1:1 SWR !

So does a dummy load…..
Sorry – Flame Shields Up….

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 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  ground wire 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 length of ground braid (keep it short!) with alligator clip
M-1956 Canvas Butt Pack to contain the entire kit.

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 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 its RF losses are low and acceptable. It is flexible, tolerates rain, rolls up into a compact kit, “connectorizes” 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.

Above: the Jungle Antenna deployed for 51 MC operation. 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 29 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.

Keeping a “low profile”: 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 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.

I have found that 8 Ounce fishing sinkers are the optimum weight for slinging up into the trees. They are light enough to throw and 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. 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.

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

I can “sling” a wire up over 30 meters into a tree usually with just 1 or 2 attempts. Takes a little practice but is easily mastered. Forget the bow & arrows, compressed air mortars, fishing rods etc. 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 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 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. Even a 6 oz sinker can 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. With any technique you use, place about 6 feet of “hot pink” or fluorescent orange leader on the weight first. That will help you see it dangling from the tree.

Above: The slingshot antenna halyard launcher. It works, but doesn’t fit into my kit. Note the fluorescent leader on swivel. I’ll go with the hand-slung weight using the KISS method in the field.

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 45 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.  Throw that G5RV away as a “field” antenna unless you exclusively run 20 meters and need a little directional gain there, 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 “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 – look at www.eham.net too. The G5RV is an acceptable “base” antenna that performs efficiently and predictably only on 20 meters for which it was designed (and that does not include multiband service). Elsewhere, it can be made to work 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 just as well from the perspective of the guy on the “receiving” end. A simple, resonant dipole is even better….

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 feedpoint. Good engineering practice. However I have rarely used them and no-balun 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….

Of course for wire antennas, 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, highly visible and generally impractical for a portable, field antenna. Works great at fixed installation though.

Further, resonant dipoles generally outperform the purpose-designed “long” wire antennas supplied with military field radios such as the AT-101, “Hank” or other Inverted L antennas. Both 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.

End fed half-wave wire antennas can work well – primarily since 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 and local absorption losses near the ends. I carry sufficient wire to intentionally deploy them occasionally – they are very simple to rig. However with a radio designed for “50 Ohm” loads, it will require a matching device to transform that very high antenna impedance into something much lower (and that transformation incurs losses and complexity). An end fed half wave wire can present a feedpoint impedance of over 2500 ohms. That’s a 50:1 impedance mismatch for a 50 ohm output radio (2500/50=50:1). A transformer with a 7:1 turns ratio or more will be “helpful”. And one end of that transformer secondary must be tied to a good ground, even though the current flow is low at that point.

The end fed half-wave antenna will necessarily have high voltages at its feedpoint – and the matching transformer must withstand every volt! Something to worry about when using a transistorized transmitter (or fingers); vacuum tube radios are more “understanding”. The GRC-9 and GRC-109 work well with half-wave wires – their output coupling network is designed to efficiently handle high impedance antenna loads relative to the high plate impedance of a vacuum tube PA. Of course if you initially deploy a quarter-wave sloper wire for 80 meter operation and then decide to use it on 40 meters – it instantly becomes a half wave end fed antenna. The GRC-9 and GRC-109 will be quite happy with that setup. (When using a half wave end-fed antenna, make SURE you ground the radio to avoid RF burns from the chassis!)

Also, 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. 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!

Resonant dipoles deliver high performance, are cheap, simple, lightweight and easily “home made”. 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.  “I’m just here camping”….

So “What’s the Best Antenna?”
It depends…….

Above: The PRC-74 dipole assembly. Ready made insulator, terminal strip and wind-up fixture as deployed from trees. Simple, works great on the GRC-9, RS-6 or GRC-109’s when in the field. (Can’t afford a PRC-74 radio!).  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 is 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 material will work as the center insulator. 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: 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.

Switching between modes, radios, antennas and additional fixed HV capacitors is accomplished with knife switches that can handle the high RF voltages and currents. As such it 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.

http://www.n6cc.com/field-antenna-kit