Tuesday, February 22, 2011

Build an Indoor FM Antenna With These Plans


The easiest way to improve your FM reception is to build an indoor FM antenna, instead of using your FM stereo’s internal FM antenna. This indoor FM antenna is easy to build, and cheap. It works every bit as good as other FM antennas that you can buy for as much as $100.

In order to build this indoor FM antenna, all you need is two 3/8” dowel rods 48” long, 10 ft. of 20 ga. wire, and some 75 ohm RG-59 or RG-6 coax (for TV’s). All of this can be picked up at your local hardware store. However sometimes hardware stores don’t have dowel rods 48”. If you can’t find any that long, you can always take two 36” dowel rods and tie them together with cable ties to the correct length.

This FM antenna is what is called a Full Wave Loop antenna. The diagram below shows the design of this indoor FM antenna:


The red is the wire, which is to be 30” on each side. The brown represents the 3/8 inch dowel rods. Also notice that the coax is fed from the side. This is not necessary, as typically full wave loops are fed from the bottom. I was interested in receiving one particular station that transmits a vertically polarized signal. Almost all FM stations transmit circularly polarized, which is both vertical, and horizontal polarization. Also feeding the Fm antenna from the side seemed to be a stronger, more reliable means of connecting the coax to the FM antenna.As far as construction of the FM antenna, the first thing to do is cut 4 inches off each dowel rod. This will then make each dowel rod 44 inches long. Next cut a slit aprox. ½ inch on each end of the dowel rods. These slits will be how you mount the wire to the dowel rods of your FM antenna.

Here is a photo of what I am talking about:


This not only shows the slot cut in the dowel rod, but also the wire, as well as the use of a cable tie to secure the wire to the end.

On the last end, where we will attach the coax to the FM antenna, put both ends of the wire into the slot leaving about an inch extending past. Next strip off the insulation and attach one end of the loop to the center conductor of the coax, and the other end of the loop to the shield of the coax.

Here is a photo of the coax being attached to the FM antenna.

build indoor fm antenna plans

Next, secure the coax to the dowel rods with it coming off the bottom dowel rod. Lastly, take a couple of cable ties and put one on the top of the vertical dowel rod to create a loop to attach a string to hang the FM antenna.

The photo below shows the completed FM antenna:

build indoor fm antenna plans


2 Meter Turnstile Antenna For Amateur Satellite Communication


Here are construction plans of a Turnstile antenna that I use for space communication on the 2 meter amateur radio band. Specifically for 145.80 mHz.

A Turnstile antenna with a reflector underneath it makes a good antenna for space communications because it produces a circularly polarized signal pattern and also has a broad, high angle pattern. Due to these characteristics, there is no need to rotate the antenna.

My design goals were that it had to be cheap (of course!) and made from easily available materials. In looking at other turnstile antenna designs, one thing that has always bothered me is that they use coax (un-balanced feedline) and directly feed the antenna (balanced load). According to the antenna books, this situation tends to cause the coax to radiate, and upset the overall radiation pattern of the antenna.

The Antenna
What I decided to do is to use "folded dipoles" instead of traditional ones. Then feed the turnstile antenna with a 1/2 wavelength 4:1 coaxial balun. This type of balun also takes care of the "balance-to-unbalance" problem usually encountered as well.
The drawing below shows how to make a turnstile antenna. Please note, this is not to scale.

2 Meter Turnstile Antenna

Construction of a turnstile reflector antenna consists of two 1/2 wavelength horizontal dipoles that are oriented 90 degrees from each other (like a big X). Then feed one dipole 90 degrees out of phase of the second one. One problem with Turnstile Reflector antennas is that the structure to hold up the relector part can be cumbersome. Fortunately (some might disagree) I decided to build my turnstile antenna in my attic. This solves another problem in that I also don't have to concern myself with is weatherizing the antenna.
For the folded dipoles I used 300 ohm TV twinlead. What I had on hand was low loss "foam" type. This particular twinlead has a velocity factor of 0.78. You will also notice in the above drawing that the lengths ot the dipole aren't what you would expect for 2 meters. This is the length I ended up when I was finished adjusting for minimum SWR. Apparently the velocity factor of the twinlead figures into the resonance of the folded dipole. As they say, "Your mileage may vary" on this length. I would also like to point out that in the drawing above the feedpoint of the folded dipoles is actually in the center of the folded dipole. I made the drawing this way for clairity.

The Reflector
In order to get the radiation pattern in the upward direction for space communications the turnstile antenna needs a reflector underneath it. For a broad pattern the antenna books recommend 3/8 wavelength (30 inches) between the reflector and the turnstile. The material I chose for the reflector is ordinary window screen you can pick up at a hardware store. Make sure it is metal screen as there is a non-metal type of window screen they sell as well. I purchased enough to lay out an 8 foot square on the rafters of my attic. The hardware store couldn't give me one big piece for all of this, so I overlapped pieces of screen by about a foot on the seam. From the center of the reflector, I measured up 30 inches (3/8 wavelength). This is where the center, or the crossing point of the folded dipoles are located.


Monday, February 21, 2011

2M + 70cm Open Sleeve Vertical Dipole


Johnny Pedersen (LA3AKA)

I was playing around with the MMANA Antenna analysis software and wanted to design a 2m/70cm vertical antenna. I tried different antenna models, J-pole, half wave dipoles, Ground Planes …. I then remembered a chapter in the 18. edition of the ARRL Antenna Handbook covering Open Sleeve antennas to make Broad band antennas. I thought that this might be useful for making a dual band VHF/UHF antenna.

0x01 graphic

The Antenna is planned built using 6mm aluminium rods. According to MMANA this will with a distance of 3.2cm between driven element and sleeve elements give an Feedpoint Impdance of 75 ohms on 2 meter and 50 ohms on 70cm. One nice thing with this antenna is that you get a good gain on 70 cm (approximately 3dB over a g Gain:


A Magnetic Loop Antenna for Shortwave Listening (SWL)

Now that we’re on the downward slope of sunspot cycle 23 (2004) you may have noticed that some of your favorite broadcast stations don’t come in as strong as they did a few years ago. This is especially apparent on weaker DX stations. The whip on your shortwave receiver used to be sufficient to pull in some good DX, but now you find yourself looking for something better.

Maybe you have been thinking, or even have already tried, putting up a wire antenna. This may be a great solution if you live in a reasonably quiet area, noise wise, and your shortwave receiver doesn’t easily overload in the presence of strong signals. Perhaps you live in an apartment or are situated where installing a wire antenna is simply not feasible. Or maybe you’re looking for something that offers a bit more mobility so you can take it into different rooms of your house. Consider the small single turn magnetic loop antenna if any of the above situations apply to you.

The small single turn magnetic loop (SSTML) antenna consists of a single winding inductor, about 3 feet (1 meter) in diameter, and a tuning capacitor. A second loop, which is one fifth of the diameter of the large loop, is connected to the feedline and this small loop is positioned in the large loop on the opposite side of the tuning capacitor.

Magnetic Loop Antenna

More at…… http://www.kr1st.com/swlloop.htm

Simple 1/4 Wave Ground Plane


If you are just starting out or have the desire to build an antenna here is a simple and fun project. This antenna is perfect for those hams living in the primary coverage area of the .075 repeater. The radials can be made of no. 12 copper wire. The vertical radial (A) should be soldered to the center connector of the SO239. The four base radials (B & C) and (D & E) can be soldered or bolted to the SO239 mounting holes using 4-40 hardware. The four base radials then should be bend downward to a 45 degree angle. The antenna can be mounted by clamping the PL259 to a mast or even passing the coax through a 3/4 ID PVC pipe and compression clamping the PL259. Either way let your creativity flow. If you plan on mounting it outside experience teaches to apply RTV or sealant around the center pin to keep water out of the coax.

Make each radial a 1/4 wave of your desired frequency. Sometimes it helps to add a little extralength to the radials. This will give you some snipping room when you adjust the SWR.
example calculation:

Freq (mhz)    A (inches)    B&C;/D&E; (inches)
146 mhz            19-5/16            20-3/16

A Tree Friendly 2 Meter Halo Antenna


Having purchased an all-mode, all-band (160m - 70cm) transceiver, I became curious about what 2-meter weak signal operations have to offer. I have a 5/8th over 5/8th vertical collinear antenna hanging in a tree at some 30 odd feet high, but I never heard anything on it, except on FM. The reason for that, I learned, is most 2-meter weak signal operations take place using horizontal polarization. Cross polarization is good for about 20 dB attenuation, which easily translates into the difference between perfectly good copy and inaudible signals. So I decided I needed a horizontal polarized antenna.

As is usually the case with antennas, there are a bazillion designs to choose from and none of them really fulfills all your requirements. I do not have a mast or tower, and I love to use trees for supports, so I wanted something that I could hang from a tree branch. Since I have no means to rotate the antenna, I required that the new antenna have an omnidirectional radiation pattern. It didn't have to be the best performer, because I just wanted to get my feet wet in this new mode of operation. There are few designs that would fit that bill. I settled on the Halo antenna because of its small footprint. This is important because larger designs would require a longer branch, with sufficient clearance in all directions, to hang from. The Halo I describe here has a diameter of only about 12 inches and can be hung virtually anywhere in a tree.

Halo stands for "HAlf wave LOop". The antenna is in fact nothing else but a half wavelength dipole with the legs bent in the shape of a circle. However, the ends do not meet, (especially near the end of the month) so technically it's not a loop. This loop can be fed with coaxial cable using a gamma match.

The Halo is certainly not a new design. Laurence M. Leeds and Marvel W. Scheldorf obtained a patent for this antenna in 1943. You can find their design at the U.S. Patent Office under Patent Number 2324462. Click on the "Images"-button to view the patent. You'll need a special browser plugin to access the patent. See the U.S. Patent Office website for more information on this.

Most Halo designs you find on the internet have moving parts. Often they require some sort of tuning capacitor and have a capacitor in the gamma match along with a slider construction that connects the gamma arm to the radiator. I prefer a design without moving parts so that the antenna doesn't get detuned easily when a bird decides the antenna makes a good resting place. I found the design that I describe here in a German antenna book "Antennen Buch" by Karl Rothammel, Y21BK.

Basic Design

The design of this antenna is very simple and straightforward. It basically consists of a half wavelength piece of copper tubing bent into a circle. Between the ends of the tube there needs to be a gap of at least 1 3/16". This is to minimize capacitive coupling between the ends. This antenna is fed by a coax feed line through a gamma match. The gamma match is constructed from 6 1/4" #4 or #6 copper wire. This wire is bent into an L shape. The short end of the wire is soldered on the inside of the loop at the point where the long end of the gamma arm aligns with the halfway point of the loop. See below:

Basic 2m Halo Design




Interested in ultra low cost 2 meter antennas that are easy to build using cheap parts; that require no tedious matching and adjusting; that are almost invisible; that are portable, compact, quickly assembled; and that can be converted into a beam? These antennas are somewhat based on the "V" designs in other projects on this site.

They include the Ultra-simple wire version in figure 1
The Table Top version in figure 2
The 2 element beam version in figure 3

Fig. 1 Ultra-simple "wire" version above made on an SO-239 connector.Designed for hanging from any handy support and can be hung from trees, used inside motel rooms or as a "stealth" antenna.

Fig 2. Table top "wire" version above using a dowel or other simple base.Upper and lower elements must be self supporting. Use aluminum or copper tubing. Disregard the reference to the upper insulator in figure 2

Fig 3. Yagi or Beam version above

This is a variation of the designs above.By adding the extra reflector element about 16 inches behind the driven element and increasing it's length to 20 inches each side (5%), some gain can be realized! According to the article, this version had not been tested but should work with a bit of experimentation. It's no more than a standard dipole with a reflector added to come up with a 2 element yagi with all elements bent forward at a 90 degree angle.


In all of these designs, please note that the center conductor from the coax connection is connected to the element in the "down position". According to the article from which these designs were taken, this helps in adjusting swr!

Simply change the angle and or trim each half a very small amount for best swr. Remember on these antennas that the driven elements have to be insulated from each other and also their support.

The beam version can be made in a "T" shape with an insulated boom between the driven element and reflector and the "T" portion for the support mast. Small diameter PVC would be a good choice.You will have to use your ingenuity for the mounting of the elements to the support so the antenna will maintain the approximately 90 degree configuration. Experiment.

An alternate version of each antenna can be built with all elements either vertical or horizontal instead of in the form of a sideways “V”.These designs can be used from HF up thru 440 or above with a little experimentation.Just dig out that old formula you should have learned for a starting point for the lengths......468/freq = half wave dipole (driven element) and add 5 percent to the length for the reflector.

The spacing should be a little less than .25 wave lengths from driven to reflector.(According to the article, using a director and driven element arrangement would cause problems with a poor match and the spacing would be a lot closer.)Using an MFJ 259b or equal would help with tuning the antenna for your particular choice of frequency, but if you're not that lucky, then just use the old swr meter and very low power while testing. As always, start with longer elements and trim down. It is very difficult to add length!

HF VHF UHF active antenna electronic project


A very simple and efficiency active antenna electronic project can be designed using this electronic schematic circuit that is based on transistors. This active antenna electronic project is useful for a wide range of RF frequencies covering three RF bands HF , VHF and UHF . This simple active antenna is designed to amplify signals from 3 to 3000 MegaHertz, including three recognized ranges: 3-30Mhz high-frequency (HF) signals; 3-300Mhz veryhigh frequency (VHF) signals; 300-3000MHz ultra-high (UHF) frequency signals.

This HF VHF UHF active antenna contains only two active elements : Q1 (which is an
MFE201 N-Channel dual-gate MOSFET) and Q2 (which is an 2SC2570 NPN VHF silicon transistor). Those transistors provide the basis of two independent, switchable RF pre-amplifiers. Two DPDT switches play a major role in this circuit , switch S1 used to select one of the two pre-amplifier circuits (either HF or VHF/UHF) and switch 2 is used to turn off the power to the circuit, while coupling the incoming RF directly to the input of the receiver.

S2 is useful to give to receiver nonamplified signal access to the auxiliary antenna jack, at J1, as well as the on-board telescoping whip antenna.This circuit must be powered from a simple 9 volt DC power circuit ( or a 9 volts battery) and is very useful for use as an indoor antenna .

HF VHF UHF signal booster active antenna electronic project

Sunday, February 20, 2011

HF Dipole


A very basic program for calculating the length of each leg of a 1/2 wave wire dipole antenna. Program good for 1 - 500 MHz, although intended for MF - HF useage. This app does nothing more than the standard 468/freq (MHz) type calculations. It was written for DOS many years ago and ported to Windows. The output shows the 1/2 wavelength and 1/4 wavelength design wire length in feet and meters. This app is probably of no help to experienced antenna designers.

Style: GUI, File size: 46K, zipped, 22K.

Update : Minor improvements made Feb 9, 1999

Current Version is:  2 / 9 / 1999

Download the hf_dipole.zip file

Outdoor MF and HF Antenna


VE7BPO Antenna System

The schematic to the left summarizes the outdoor VE7BPO MF and HF receiving antenna system for summer 2007. Although modest for a big city lot, this antenna seems to pull in the DX and is relatively free of RFI. This antenna was just a case of "putting as much wire in the sky as possible" and the dimensions are indicated for interest sake only. The 27 meter long horizontal section is supported between 2 trees at a height of about 14 meters high. The weight of the vertical element wire plus slack in the horizontal wire droop it to about 13 meters high in the center. The vertical section is soldered to the horizontal wire 6 meters from the nearest anchoring tree and runs straight down to the antenna feed point which is about 1 meter off the ground. The feed point is a piece of copper-clad PC board (with isolated sections created with a hobbyist motor tool) and is bolted to a long copper pipe which serves as the first station earth-grounding stake. A transformer (T1) configured as a UNUN (unbalanced-to-unbalanced) is used to interface the antenna with 50 ohm coax that runs through the house and into the radio shack. Some rudimentary experiments with the UNUN and the earth-grounding system were undertaken.
The methods I used to potentially lower unwanted RFI to my antenna system are as follows:

  1. The receiver and power supply are independently connected to a single, central ground point (ground buss) in the radio shack.
  2. 6-10 gauge wire is used for my ground system (not including the radials which are bare 12 gauge wire).
  3. The ground wire connecting to my first earth stake to the station ground buss is just outside the shack window and is short as possible to provide a low impedance and low inductance path for MF and HF frequencies.
  4. There is a second ground stake located 1 meter from the primary ground stake (I will add 2-4 more in time).
  5. I have a large piece of steel buried underneath the soil tied in to my system as well as 3 bare copper radials. The radials are 3 - 7 meters in length.
  6. New RG58/U coax was used as the feed line.
  7. All wire splices in the grounding system are soldered and taped up. I used conductive grease (to prevent oxidation at the wire-stake interface) on any clamps connected to ground stakes. My ground stakes are ~ 2 meters long.
  8. The earth grounding area soil is moist and peat-laden and is watered regularly.
  9. I plan to maintain this ground system every 2 years.

Friday, February 18, 2011

The G5RV multiband dipole


Figure  shows the popular G5RV antenna. Although not without some problems, this antenna is very popular. It can be used either as a horizontal dipole, a sloper, or an inverted-vee antenna (which is how I used it). The dipole elements are each 51 ft long. The feedline can be either 300- or 450-Ω twin lead. For 300-Ω cases, use 29 ft of line, and for 450-Ω line, use 34 ft. One end of the parallel transmission line is connected to the antenna, and the other end is connected to a length of 50-Ω coaxial  cable. Although most articles on the G5RV claim that any length of 50-Ω line will work, J. M. Haerle (HF Antenna Systems: The Easy Way) recommends that the  50-Ω segment should be at least 65 ft long.

Off-center-fed nonresonant sloper antenna


Nonresonant off-center-fed sloper (OCFS) antenna  consists of a wire radiator that must be
longer than 3λ/2 at the lowest frequency of operation. The feedpoint is elevated at least λ/4 above ground at the lowest operating frequency. The antenna is fed with 75-Ω coaxial cable. The shield of the coax is connected to a  λ/4 resonant radial (counterpoise ground). There should be at least one radial (more is better) per band of operation.

The far end of the radiator element is sloped to ground, where it is terminated in a 270-Ω noninductive resistor. The resistor should be able to dissipate up to one- third of the power level applied by the transmitter.

Tubing coaxial vertical VHF antenna


The sleeve is a piece of copper or brass tubing (pipe) about 1 in in diameter. An end cap is fitted over the end and sweat-soldered into place. The solder is not intended to add mechanical strength, but rather to prevent weathering from destroying the electrical contact between the two pieces. An SO-239 coaxial connector is mounted on the end cap. The coax is connected to the SO-239 inside the pipe, which means making the connection before mounting the end cap.

The radiator element is a small piece of tubing (or brazing rod) soldered to the center conductor of a PL-259 coaxial connector. An insulator is used to prevent the rod from shorting to the outer shell of the PL-259. (Note: an insulator salvaged from the smaller variety of banana plug can be shaved a small amount witha fine file and made to fit inside the PL-259. Alternatively, the radiator element can be soldered to a banana plug. The normal-size banana plug happens to fit into the female center conductor of the SO-239.

Demiquad single element one wavelength quad antenna.


The demiquad is a single-element  one wavelength quad antenna. The length of the antenna is, like the cubical quad beam antenna , one wavelength. Figure shows a type of demi-quad based on the tee-cross type of mast.

The impedance-matching section is a quarter-wavelength piece of 75-Ω coaxial cable (RG-58/U or RF-11/U). The length of the matching section is determined from:


L is the overall length, in feet
FMHz is the frequency, in megahertz
V is the velocity factor of the coaxial cable (typically 0.66, 0.70, or 0.80)

True longwire antennas



Figure  shows the true resonant longwire antenna. It is a horizontal antenna, and if properly installed, it is not simply attached to a convenient support (as is true with the random length antenna). Rather, the longwire is installed horizontally like a dipole. The ends are supported (dipole-like) from standard end insulators and rope. The feedpoint of the longwire is one end, so we expect to see a voltage antinode where the feeder is attached. For this reason we do not use coaxial cable, but rather either parallel transmission line (also sometimes called open-air line or some such name), or 450-Ω twin lead. The transmission line is excited from any of several types of balanced antenna tuning unit (see Fig.). Alternatively, a standard antenna tuning unit (designed for coaxial cable) can be used if a 4:1 balun transformer is used between the output of the tuner and the input of the feedline.

Six-element 2-meter Yagi beam antenna


Figure 18-8 shows the construction details for a six-element 2-meter Yagi beam antenna. This antenna is built using a 2 X 2-in wooden boom and elements made of either brass or copper rod. Threaded brass rod is particularly useful, but not strictly necessary. The job of securing the elements (other than the driven element) is easier when threaded rod is used, because it allows a pair of hex nuts, one on either side of the  2 x 2-in boom, to be used to secure the element. Non threaded elements can be secured with RTV sealing a press-fit. Alternatively, tie wires (see inset to Fig ) can be used to secure the rods. A hole is drilled through the 2 x 2 to admit the rod or tubing. The element is secured by wrapping a tie wire around the rod on either side of the 2 x 2, and then soldering it in place. The tie wire is no. 14 to no. 10 solid wire.

Mounting of the antenna is accomplished by using a mast secured to the boom with an appropriate clamp. One alternative is to use an end-flange clamp, such as is sometimes used to support pole lamps, etc. The mast should be attached to the boom at the center of gravity, which is also known as the balance point. If you try to balance the antenna in one hand unsupported, there is one (and only one) point at which it is balanced (and won’t fall). Attach the mast hardware at, or near, this point in order to prevent normal gravitational torques from tearing the mounting apart.

The antenna is fed with coaxial cable at the center of the driven element. Ordinarily, either a matching section of coax, or a gamma match, will be needed because the effect of parasitic elements on the driven element feedpoint impedanceis to reduce it.

Inverted-vee dipole half-wavelength antenna


The inverted-vee dipole is a half-wavelength antenna fed in the center like a dipole.By the rigorous definition, the inverted-vee is merely a variation on the dipoletheme. But in this form of antenna (Fig. 6-7), the center is elevated as high as possible from the earth’s surface, but the ends droop to very close to the surface. Angle a can be almost anything convenient, provided that a > 90 degrees; typically, most inverted-vee antennas use an angle of about 120 degrees. Although essentially a compensation antenna for use when the dipole is not practical, many operators believe that it is essentially a better performer on 40 and 80 m in cases where the dipole cannot be mounted at a half-wavelength (64 ft or so).By sloping the antenna elements down from the horizontal to an angle (as shownin Fig. 6-7), the resonant frequency is effectively lowered. Thus, the antenna will need to be shorter for any given frequency than a dipole.

There is no absolutely rig-orous equation for calculation of the overall length of the antenna elements. Although the concept of “absolute” length does not hold for regular dipoles, it is even less viable for the inverted-vee. There is, however, a rule of thumb that can be fol-lowed for a starting point: Make the antenna about 6 percent shorter than a dipole for the same frequency. The initial cut of the antenna element lengths (each quarterwavelength) is

After this length is determined, the actual length is found from the same cut-and-try method used to tune the dipole in the previous section. Bending the elements downward also changes the feedpoint impedance of the antenna and narrows its bandwidth. Thus, some adjustment in these departments is in order. You might want to use an impedance matching scheme at the feedpoint, or an antenna tuner at the transmitter.220

sloping dipole or slipole antenna


The sloping dipole  is popular with those operators who need a low angle of radiation, and are not overburdened with a large amount of land to install the antenna. This antenna is also called the sloper and the slipole in various texts. The author prefers the term “slipole,” in order to distinguish this antenna from a sloping vertical of the same name. Whatever it is called, however, it is a half-wavelength dipole that is built with one end at the top of a support, and the other end close to the  ground, and being fed in the center by coaxial cable. Some of the same comments as obtained for the inverted-vee antenna also apply to the sloping dipole,

Some operators like to arrange four sloping dipoles from the same mast such that they point in different directions around the compass  A single four- position coaxial cable switch will allow switching a directional beam around the compass to favor various places in the world.

SWL Receiving longwire antenna


Figure  shows the common receiving longwire. The antenna element should be 30 to 150 ft in length. Although most texts show it horizontal to the ground (and indeed, a case can be made that performance is better that way), it is not strictly necessary. If you must slope the wire, then it is doubtful that you will notice any re- ception problems. The far end of the wire is attached to a supporting structure through an insulator and a rope. The support structure can be another building, a tree, or a mast installed especially for this purpose. Chapter 28 deals with antenna construction practices.


Thursday, February 17, 2011

The 10-meter "Hentenna" loop



This clever little antenna developed by JElDEU of Sagamihara City, Japan. Local hams were amused by the loop; hence the name - "hen" means curious in Japanese. "Henantenna" was quickly shortened to "Hentenna." It's shown in Figure 1. This antenna's virtue is that it has very little "wingspread"

The array has two one-sixth wave radiators separated vertically by a half wavelength. To feed them, connect the tips and tap the vertical wires with a coax feedline. Polarization is horizontal. Hentenna construction is simple. You use a single mast; try a TV-style pushup one. Make your horizontal sections out of 518-inch diameter aluminum tubing bolted to a mounting plate, and attach the plate to the mast with Ubolts. Use enamel-coated copper wire for the antenna's vertical sections. Feed the Hentenna with a balun and coax line. Run your feed wires from the balun to the vertical wires. Adjust for lowest SWR by moving the feed wires up or down the vertical wires. Copper alligator clips are ideal for this; you can remove them and make joint solders when you find the correct points. The points should be about 36 inches above the bottom tube for 10 meters. The Hentenna provides a figure eight pattern at right angles to the antenna plane. Gain is estimated at about 2.5 dB over a dipole. Bandwidth is very broad. By changing the length of the vertical wires, you can move the design frequency to any point in the 10-meter band.

Receiving loop antenna for 160 meters



Height of loop above ground is 10 feet. Illustration A is view from above. Illustration B shows 4:l balun and antenna tuner.

One of the problems in working DX on 160 meters is the high level of background noise. Many DXers have found that they cannot use their transmitting antenna for reception - the noise level is overpowering. Paul McClure, KDBSO, met this problem head on and evolved a horizontal receiving loop that provides good signal-to noise ratio. The loop's signal pickup isn't as good as that of a larger antenna, but noise drops off sharply. By adjusting audio gain of the receiver, you can bring the resulting signal up to the original level. Paul says that, out of the noise, he can pull weak signals that didn't seem to exist under normal circumstances. He says the antenna is comparable to a good Beverage wire. The loop, however, takes up less space and there are no terminating resistors to replace after a thunderstorm. The above-ground height of the loop is about 10 feet. It's fed with a random length of 300-ohm ribbon line. Paul twists the line to balance it to ground.

"Quickie" antennas for 18 MHz



The delta loop in fig. 1 is a good 18 MHz "first" antenna, It has slight gain over di-pole and user friendly

The feedpoint impedance of the loop is about 120 ohms .Use a 75-ohm quarter-wave transformer to provide a reasonable match to a 50-ohm coax line. The transformer is wound into a coil to choke off RF currents that might flow on the outside of the coax shield.


The feedpoint of the loop terminates in an SO-239 coax connector mounted on a small insulator plate. The transformer has PL-259 plugs on both ends. Make the splice between the transformer and the 50-ohm line with a PL- 258 splice adapter. After making the connection, weatherproof the plugs and adapter with coax tape or heat shrink tubing. The loop is supported at the apex and the side insulators are tied off to objects nearby. The radiation pattern is similar to that of a dipole and is horizontally polarized.

The bi-square array for 18 MHz



The diamond-shaped bi-square beam is much larger than the delta loop, but provides about 3-dB gain. This is a great antenna to try if you have the space. It's shown in fig. The loop is a half wavelength on a side and open at the top. The feedpoint impedance at the bottom of the loop is about 2900 ohms; I use a twowire 600-ohm quarter-wave stub to provide a more reasonable impedance value of about 122 ohms. Match it to a 50-ohm coax line by adding a quarter-wave transformer made of 75- ohm coax. Wind the 75-ohm line into a coil about 6 inches in diameter to reduce RF currents flowing on the out-side of the coax. Resonate the loop and stub to 18.1 MHz with a dip meter. Temporarily close the stub at the bottom using a movable short with a I-turn loop in the middle.

Portable 3 element 2M beam antenna



In April 1993 QST, Nathan Loucks, WB0CMT, described the 2-m beam shown in Fig. The boom and mast are made from 3/4-inch PVC plumber’s pipe. The three pieces of PVC pipe are held together with a PVC T joint and secured by screws. Elements can be made from brass brazing or hobby rods. (If you can’t find a 40-inch rod for the reflector, you can solder wire extensions to obtain the full length.)

Drill holes that provide a snug fit to the elements approximately 1/4 inch or so from the boom ends. Epoxy the director and reflector in place after entering them in these holes. A pair of holes spaced 1/4 inch and centered 16 inches from the reflector hold the two-piece driven element. The short ends of

the element halves should extend about 1/4 inch through the boom. Solder the 50-Ù feed line to the driven element as shown in Fig

Loucks used a pair of 4-inch pieces held in place by #12 or #14 jam screws (electrical connectors) toextend and adjust the driven element to allow for operation in various parts of the 2-m band. You can trim the driven element to length for operation in the desired portion of the band if you prefer. The figures show the beam assembled for vertical polarization. You may want to turn the boom pieces 90° for horizontal polarization for SSB or CW operation.

The 1.8-MHz inverted L.


Overall wire length is 165 to 175 ft. The variable capacitor has a maximum capacitance of 500 to 800 pF.


The antenna shown in Fig is simple and easy to construct. It is a good antenna for the beginner or the experienced1.8 MHz DXer. Because the overall electrical length is greater than 1/4 ë, the feedpoint resistance is on the order of 50 Ù, with an inductive reactance. That reactance is canceled by a series capacitor, which for power levels up to the legal limit can be a air-variable capacitor with a voltage rating of 1500 V. Adjust antenna length and variable capacitor for lowest SWR. A yardarm or a length of line attached to a tower can be used to support the vertical section of the antenna. (Keep the inverted L as far from the tower as is practical. Certain combinations of tower height and Yagi top loading can interact severely with the Inverted-L antenna—a 70-ft tower and a 5-element Yagi, for example.) For best results the vertical section should be as long as possible. A good ground system is necessary for good results.

10-m rectangular loop antenna.



With the large number of operators and wide availability of inexpensive, single-band radios, the 10-m band could well become the hangout for local ragchewers that it was before the advent of 2-m FM, even at a low point in the solar cycle.

This simple antenna provides gain over a dipole or inverted V. It is a resonant loop with a particular shape. It provides 2.1dB gain over a dipole at low radiation angles when mounted well above ground. The antenna is simple to feed— no matching network is necessary. When fed with 50-Ù coax, the SWR is close to 1:1 at the design frequency, and is less than 2:1 from 28.0-28.8 MHz for an antenna resonant at 28.4 MHz.

The antenna is made from #12 AWG wire (see Fig ) and is fed at the center of the bottom wire. Coil the coax into a few turns near the feedpoint to provide a simple balun. A coil diameter of about a foot will work fine. You can support the antenna on a mast with spreaders made of bamboo, fiberglass,

wood, PVC or other nonconducting material. You can also use aluminum tubing both for support and conductors, but you’ll have to readjust the antenna dimensions for resonance. This rectangular loop has two advantages over a resonant square loop. First, a square loop has just 1.1 dB gain over a

dipole. This is a power increase of only 29%. Second, the input impedance of a square loop is about 125 W. You must use a matching network to feed a square loop with 50-Ù coax. The rectangular loop achieves gain by compressing its radiation pattern in the elevation plane. The azimuth plane pattern is slightly wider than that of a dipole (it’s about the same as that of an inverted V). A broad pattern is an advantage for a general- purpose, fixed antenna. The rectangular loop provides a

bidirectional gain over a broad azimuth region. Mount the loop as high as possible. To provide 1.7 dB gain at low angles over an inverted V, the top wire must be at least 30 ft high. The loop will work at lower heights, but its gain advantage disappears. For example, at 20 ft the loop provides the same gain at low angles as an inverted V.

Wednesday, February 16, 2011

A Quick and Simple 2 Meter Ground Plane Project!

If you are just getting experience in building antennas or you are an old pro,here is a simple and fun project! This antenna is perfect for those hams living in the primary coverage area of the repeater for 2 meter use. This antenna is nothing more than the old standby "Droopy Groundplane" and can be used on any band where it's physical size does not pose a problem. Remember that the vertical radiator is 1/4 wavelength long at your operating frequency.

It has no gain but makes an excellent small antenna that can be mounted just about anywhere and with a little planning, can be used mobile on a short mast from the bumper!! Adding a small attachment loop at the tip of the radiator will enable it to be suspended from above for inside use.

The vertical element and radials can be made of #12 copper wire or welding rods, coat hanger, etc. The vertical radiator (A) should be soldered to the center connector of the SO239.The four base radials (B & C) and (D & E) can be soldered or bolted to the SO239 mounting holes using 4-40 hardware. The four base radials then should be bent downward to a 45 degree angle.

The antenna can be mounted by clamping the PL259 to a mast or even passing the coax through a 3/4 ID PVC pipe and compression clamping the PL259. Either way let your creativity work for you. If you plan on mounting it outside,  apply RTV or sealant around the center pin and PL259, and TAPE WELL,  to keep water out of the coax.

Make each radial a 1/4 wave of your desired xmit frequency. Sometimes it helps to add a little extra length to the radials and radiator. This will give you some adjusting room when you adjust the SWR.(If adjustment is needed, clip all radials equally about 1/8 inch at a time while checking SWR, USING LOW POWER). Center the lowest swr on your transmit operating frequency.

Example Calculation:

Freq (mhz)       146
A (inches)         19 5/16 (Note "A" length is to the SO-239 insulator but not critical)

B THRU E (INCHES)   20 3/16




simple antenna for 40 Meters


Making a simple antenna for 40 Meters is not very difficult. That is, if you have the space. A standard center fed dipole dipole for 40 Meters needs around 67 Feet of space. But, what if you only have space for a 20 Meter dipole, 33 Feet? If this is case, than you have several options.

  1. You could just forget about 40 Meters and work the higher frequency bands, 20 Meters on up.

    What? And miss out on all the fun dodging the the short wave broadcasters in the evening.

  2. You could create a Inverted-V type of antenna and raise the feedpoint on a mast.

    This is a possible alternative, but for this particular case, you would need a 28 Foot center mast and the apex angle would be less than optimum. This may cause some signal cancelation and give you a radiation pattern that you don't want.

  3. You could shorten the dipole arms to fit the space and use a loading/matching coil in the center.

Item number 3 is what this page is about. Jact Sobel, W5VM (which is now assigned to Vernon Dyer), had at one time described a shortened dipole center fed with a loading/matching coil at the feed point. A drawing of which is below.

Initially, this seems to be a different approach than the shortened dipole designs, detailed on my Short Dipole page. But it's really not. If you tilt your head, and cross your eyes a little bit, you might start seeing it as two coils, very close together. In fact, the coils are so close to the center, that they touch..

Assuming that the two coils are an equal number of turns, and that the wires attached to each side are equal in length, the center of an antenna should be a zero current point. this makes a handy place to tie your coax shield. You could wrap several turns of wire around the coil in the center and feed it that way. But I couldn't begin to tell you how many turns to use or what the feed impedance would be. Each turn of the coil, as you move away from center, provides you with a different impedance and a possible match. By attaching the center of your coax to one of the coils turns, you should be able to find a good 50 Ohm feed point. This then gets around the balanced to unbalanced conversion effort (balun), that would be required and you were center feeding or link feeding..

Each element arm is 18 Feet 6 Inches (5.029 M) long. The loading/matching coils consists of 30 turns of 12 SWG enamelled copper wire wound on 2.5 inch (63.5 mm) diameter PVC tube 6 inches (152.4 mm) long. The winding pitch should be about 6 turns-per-inch (25.4 mm). Although the picture doesn't show it very well, the shield of the 50 coaxial cable is connected to the center of the coil. The coax center conductor is connected to a point 2 or 3 turns away from the center, to a point which gives the lowest SWR. This point may take some experimenting, depending on which section of the band you wish to operate in.

Making a slim jim


made one of thease on me foundation course thease are the smae plans we used.slim jim using both 300 and 450 Ohm Feeder and have found the 450 feeder to be easier to SWR..

TO swr the Slim jim simply hang the antenna in free space away from metal objects and make sure the Coax runs straight down below the antenna.Then simply move the feed point up or down slightly until best swr is achieved..

The slim jim is Basicaly a Half wave vertical with a quarter wave matching stub so you can calculatefor any band by simply working out a halve wave length for the Longestlenghth, 468/f in mhz,and for the quarter wave length 234/f in mhz and answers in feet.To match simply adjust the feed point as on the 2m version.also worth consideration is the J-POLE seen below

A Slim Jim for 4m


This antenna is made from a length of 300-ohm ribbon cable, which makes it easily portable, but you have to devise some method of suspending it!  The dimensions quoted in the diagram have been used successfully by some constructors, whilst others have found it to be off-frequency by a few megahertz. This may be due to a parasitic capacitance in the gap between the half-wave and quarter-wave sections, so be prepared to experiment a bit..

Dimensions of 4m Slim Jim.

2 Meter Slim Jim antenna using 300 Ohm Twinlead


300Ohm slim jim antenna diagram plan

Due to popular searches, I’ve included a diagram to make a flexible slim jim antenna. This antenna is useful to increase the range of your portable radio or as a simple QRP mobile antenna for emergency situation.

Basic Slim Jim conceptual plan

In order to proceed with this project you need

  • about 165 cm (64 inch) 300 Ohm twinlead cable
  • RG-58 coax cable (RG-8, RG-213 might be too big for soldering), any length but keep it shorter than 7 meters for portable radio
  • Soldering iron
  • Wire cutter
  • Connector to your Rig (usually BNC type or UHF Male)
  • insulating tape

This is an ideal antenna for first timers to build. It is powerful yet simple to construct, once you get the hang of it you would certainly have no problem to construct other variants of Slim Jim antenna using different material.

This exercise would also prepare you in the world of Amateur Radio where real hams homebrew their own antennas.

Important Notes

  • Make sure you solder the center conductor to the longest part of the antenna, and the outer conductor (braid) at the shorter side of the antenna
  • If you use this on mobile rig, keep transmission power lower than 50watt to avoid the antenna from being burned away.
  • Make sure the antenna is held straight for best transmission and reception. Best way to make sure of that is to hang the antenna at a higher place or strap it to PVC pipe or other non-conductive pole

Advantages of 300ohm Twinlead Slim Jim Antenna

  1. Easy to construct
  2. Has radiation angle almost parallel to the ground which makes your transmission goes farther than 5/8 or ground plane antennas
  3. Wideband
  4. Portable; Easy to carry, store and deployed
  5. Can be use during emergency situation
  6. Light and flexible

Moxon Antenna Plan for 27MHz CB and Freeband Operation


Here’s another 11 meter Moxon Antenna plan suitable for 27MHz CB, Freeband and lower 28MHz Amateur Radio operation band.

10 meter moxon

27MHz CB Moxon Antenna

A- 392.09 cm (154 3/8 inch)
B- 58.62 cm (23 1/16 inch)
C- 11.25 cm (4 7/16 inch)
D- 73.4 cm (28 7/8 inch)
E- 143.27 cm (56 7/16)

Gain, Radiation Pattern (mounted at approx 30feet)

Gain : Approx 10-11dBi (30 feet above the ground)
Freq range : 27.300 MHz – 28.300 MHz

>11 meter 27MHz CB Homebrew Moxon Antenna

The main advantage of Moxon rectangle antenna are :

  • Compact and Small
  • Has considerable gain
  • It can eliminate noise on HF band
  • Easy to construct
  • Suitable for HF operation (mid-low radiation angle)

Refer here for 10 meter Moxon Antenna Plan for Amateur Radio operation (28.2MHz-28.8MHz) : 10 Meter Band Compact directional antenna, Moxon

Hamradio Homebrew 2 Meter Square Dipole Plan


Here is a plan for homebrewing a 2 Meter Square Dipole plan. The advantage of this antenna is that it is unidirectional, and it takes less space than the regular 2 meter dipole. The calculation included on the diagram below is for building the antenna using copper tubing, you should use MMANA-GAL or other antenna simulation software to come up with new dimension for other materials (aluminium, wire, etc).

2 meter square dipole plan

2 meter square dipole plan

Click on the diagram to enlarge it. Hopefully this will help you in brewing new antennas! Original plan taken from KOFF website

VHF or UHF Yagi BALUN Calculator.


For the VHF/UHF frequencies, a 4:1 impedance ratio coaxial balun is normally used. Two sections of identical coaxial cable are needed. One section (A) has a convenient length to reach between the antenna and the transmitter.  Its characteristic impedance is Z.

The other section (B) is a half-wavelength long at the center of the frequency of interest.
The "physical" length is found from: 5904/F = L.  The complete formula is:
        L = 5904 * V/ F  in MHz
L is the cable length, in inches F is the operating frequency, in megahertz
V is the velocity factor of the coaxial cable. 
The result is found by multiplying L by V.
To find the "Electrical" length, divide this result by F.
The velocity factors of common coaxial cables are shown in the following table.
Coaxial cable velocity factors
Regular polyethylene 0.66
Polyethylene foam 0.80
Teflon 0.72

Both radio signals and light travel almost 300,000,000 meters (186,363 miles) per second.

When designing a matching or phasing BALUN for a VHF or UHF Yagi, the quarter wave transformer is where these calculations will come to life.   Most coax cables we use in HAM radio have varying velocity factors (VF).  That is; RF signals travel at different speeds through these coaxial cables, depending on the cable type we use.   For example, the coax cable you are using has a velocity factor of .80%.  This indicates that the electrical length is actually 80 percent of of its "free space length".  When making a VHF or UHF BALUN or phasing transformer we must be sure we have included the velocity factor in our computations.

Slim Jim (J Integrated Match J-Pole)

 Slim Jim (J Integrated Match J-Pole) is probably the most easiest and powerful 2 meter antenna to build provided you have the exact measurement and material to build it.

This how to will show you how to build a 2 meter slim jim antenna from ordinary insulated copper wire commonly used for carrying AC (alternate current) electricity in your household.

Slim Jim construction basic
I am not only going show you the measurement of slim jim antenna for specific frequency, but I’m going to show you how to calculate slim jim antenna by your own using the basic formula below.

Basic Slim Jim Idea

The figure above shows that the longest side of slim jim is 3/4 wavelength long and the shorter side of the slim jim consist of 1/2 wavelength and 1/4 wavelength long seperated by a gap.

The feedline (coax cable) is normally connected 1/20 wavelength from the bottom of the slim jim antenna with the center conductor connected to the longest side and the shield/braid is connected to the shorter side.

Building the Slim Jim antenna
This guide assume you want to build a slim jim antenna that centered on 146MHz.

The formula for calculating wavelength in metric system is 300/(freq MHz)

Using the formula from the figure, we have :

300/146 = 2.055 M
Wavelength = 205.5 cm

Wavelength x copper wire velocity factor = 205.5 cm x 0.94
= 193.17 cm

3/4 wavelength = 193.17 x 0.75
= 144.88 cm (57″)

1/2 wavelength = 193.17 x 0.5
= 96.585 cm (38″)

1/4 wavelength minus gap = 193.17 x 0.25 – 2.6 cm
= 45.69 cm (18″)

Coax tap = 193.17 x 1/20
= 9.6 cm (3 3/4″)

Building Materials

  • 3/4″ diameter PVC (20mm) – 6 feet (180 cm)
  • ordinary insulated copper wire for carrying altenate current (AC) – 11 feet (3.40 meter)
  • Cable ties


  • Soldering iron
  • Glue gun
  • Somthing to make a hole on PVC pipe

Wire Slim Jim Building Steps

  • First take the PVC pile and measure it according to the 3/4 wavelength formula above (144.88 cm).
  • Make two holes at the opposite side of the pipe. This hole is used for putting the copper wire through the pipe. Repeat this step 144.88 cm away from the top hole. Both of these holes will hold the copper wire.
  • Insert the wire through the hole until both end reaches each other on one side of the PVC pipe. Then measure the length of the wire and cut the wire on that side so the setup resembles the figure above.
  • Cut the wire insulation (but leave the wire uncut) 1/20 wavelength away (9.6 cm) from the bottom of the PVC pipe, again refer the figure above.
  • Solder the center of the coax cable at the longest side of the slim jim (3/4 wavelength part) and the braid/shield at the shorted part of the antenna.
  • Test the antenna using SWR meter to ensure that its SWR is at minimum or within acceptable level.
  • There you go, you’ve build yourself your own 2 meter Omnidirectional Slim Jim antenna for less than USD2 (RM 6.00)

2 Meter Wire Slim Jim Antenna in action


mypapit homebrew 2 meter slim jim


The 2 meter Omni Samurai Antenna