A simple kit for temporary, lightweight, wire tactical antenna systems is essential for any field Ops including EMCOMM work. 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 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 while camping. 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. 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 wire antenna“
The focus of these antennas is generally on my portable Ops for regional comms with my buddies and EMCOMM groups on the Low HF bands and local comms on VHF:
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.
This will clearly out perform any expensive, short, loaded, lossy “leaky tuned circuit” or loop contraptions, particularly during “receive” due to the tiny capture area of those severely compromised antenna designs. This wire arrangement 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:
“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….
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.
I see that there is now a company marketing a stripped-down clone of this kit for partial functionality. However, if you build a kit you will probably better understand its design and usage. “The easy way is always mined” Murphy’s Law of Combat
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, 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.
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. These will also work very well on the 27 Mc “CB” band if you need it to in a pinch.
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 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.
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 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 go 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. 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 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.
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 – look at www.eham.net too. The G5RV is an acceptable “base” antenna that performs somewhat 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….
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.) 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. Not even close. Not optimum – but it will produce contacts…It’s just a bunch of wire in the air.
Here’s the ladder line – dipole connection – a no-brainer.
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!
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 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 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, 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.) 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.
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.)
A “general purpose” end fed half-wave wire antenna can work well* and is very simple to deploy in the field. They radiate well* 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 – if I am lazy, in a hurry or only have one support available. They are very simple to rig.
However with a radio designed for “50 Ohm” loads, it will require a matching device (not a balun – it is not a balanced dipole/doublet) 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 or more. 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 (49:1 impedance ratio) or more will be “helpful”. And one end of that transformer secondary must be tied to a reasonably good ground for consistent results, even though the current flow is low at that point. Why? Because 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. Something to worry about when using a “high powered” transmitter (or fingers). 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.)
* However as a practical matter, a half wave end fed wire is generally going to be deployed as a “sloper”. Radio on the ground, wire end suspended up to some support. Max radiation is perpendicular to the wire – not much goes “up” for NVIS and not much goes “out” for low angle DX. About half hits the ground and is absorbed or somewhat re-radiated. So it is pretty much a loosing proposition for either types of service. But they will make contacts.
For local and regional HF comms, NVIS system techniques are in order (which includes time of day, operating frequency relative to the Critical Frequency and antenna radiation pattern). You want to radiate most of your signal straight up towards the ionosphere so the signal “sprays” back down within a few hundred km radius. To do that you want the high-current portion of the wire to be horizontal to the ground, about 0.1 to 0.2 wavelengths up. This is difficult with any end fed wire or sloper unless you are up in a tree with the transmitter. But it is easy with a center fed dipole or inverted Vee. Hence my favorite configuration for this application. Dipoles/InVee’s are also very good for long distance work (greater than say 1000 km) but then they need to be a half wave above ground to keep the takeoff angle low. *The “sloper” halfwave antenna is a compromise – not particularly efficient at either short of long ranges. But they will work.
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!
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, 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 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 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 or 1452 (male) BNC/Banana terminal adapter. 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.
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. 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 modes, radios, antennas and additional fixed HV capacitors which 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.
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.
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. I then worked 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. In this case, the 18″ metal tent stake with the paint sanded off; keep it wet and add a little salt 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 stiff wire “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…
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, as deployed. 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.
For more information about using this kit for building practical field antennas, see Field Expedient Antennas
For more ideas on how to employ stealthy antennas, take a look here:Stealthy/Covert Antennas