An invisible antenna farm and wire beam antenna.

Last updated Dec 2003.

Special thanks to Mr.John Van der Ryd (VE3CYC) for the original idea

Click on pictures to get the magnified view

After moving into my new house, I started the rebuilt of my antenna farm. On considering the quickly approaching winter plus potential comments from neighbors, I finally decided to limit the construction within the attic. I need a low profile but highly efficient system. My antenna inventory list includes:

    • UHF high gain antenna for VA3CTR repeater.
    • UHF/VHF dual band for local contact
    • 6m vertical ground plane antenna.
    • H.F. beam antenna for 20m and 15m.

This roof housed all the above mentioned antennas !

Design selection

The interior of an attic is made mostly of wooden frame. They are perfect for mounting antenna poles or pinning down wire elements. Since the attic is inside the roof, it is protected from outside environment. Antenna installation in this area needs very little water proofing. The only trade off is the extra attenuation after water or wet snow has coated the shingles of the roof. That might make application of precise tuning antenna designs unstable.

I already have two factory-built UHF/VHF antennas. In order to compare the lost caused by the attic, I installed both of them (Diamond X50 and its clone) inside and outside the roof for performance comparison. Based on the same design and length of cable run, the difference in performance is a combined factor of R.F. shielding and a slightly lower elevation of 10 ft. The result turned out to be a weaker performance for the antenna placed inside the attic. The difference between the two is approximately 6db. It is quite an amount of power lost but that's the cost of employing in-building hidden construction.

The outdoor X50 dual band antenna

My 6m-ground plane is another cheap built. I just soldered a piece of insulated wire (50" long) to the core of a SO-239 socket. Three insulated wires of the same length are then secured onto the mounting holes of this socket and stretched out to maximum length to form the ground plane. The length of the core conductor is then gradually trimmed in 1" intervals until the best return lost (S.W.R.) is obtained on the lowest portion of the band. The wires are just nailed onto nearest wood frame for holding. The appearance is ugly (that's why no picture) but it works fine.

The H.F. antenna is the biggest issue. I'd once seen an article in 73 magazine (by VE3CYC) which described the building of a wire beam antenna. I had been using part of that design (the single element dipole version) during the past 2 years at my old house and had obtained an amazingly good result. With the size of my new attic (35'x40' roof area with a 10'x25' patch cleared for standing up), it is fully possible to have the whole wire beam housed. The neat part is that I don't even need poles, insulators or cords to hold up the wires. All wire elements can be stapled on the plywood roof or any near by 4x 6 wood logs.

The wire beam design

The beam composed of two dual-band dipoles (20m and 15m) placed 10 ft. apart. Only one of the two arrays is being used at one time. With the other side hanging in mid air, the vacant dipole forms a parasitic element. The array is basically a YAGI composed of 2 elements. For such design, the parasitic elements are shorted and should be built longer (as reflector) then the driving element. In this wire-beam, unlike a conventional YAGI, both elements have chances to serve as a driving element. This forced them to be built with the exact same dimension. The parasitic nature has to be achieved by loading of external elements. By switching between array-A and array-B with the unused side loaded with a non-terminated feed line, a directional effect will appear. Signal will usually be stronger on the direction where the active array is in front of the parasitic array.


Circuit diagram of the wire beam antenna.


3D figure of the wire beam secured inside the attic.

The wood frame of the roof section is not shown above to prevent confusion. The boom of the beam is a PVC pipe (3" diameter and 10 ft. in length). Two RG-58U cables are routed to both opening of the boom from the center portion. R.F. chokes are required to prevent R.F. pick up to travel back down the origin and causing unexpected interference. They are made from 8 turns of tightly coiled up feed line of each individual dipole on the boom. The end of each cable is then spliced. The exposed core and braid are then secured onto two screws that are used to hook up those 20m and 15m wire elements in future.

To make it simple, starting length of 20m wire elements are 190 in. while that for 15m are 130 in. The length of all wire elements listed above are just reference. Final length will alter with different attic environment anyway. Length of each wire will have to be trimmed individually. As long as wires on the same plane are cleared from each other by distance or at a separating angle, they won't interfere with each other. In order to get the most accurate result, wires of the first dipole has to be detached temporary from the boom when dealing with tune up of the second dipole. For my case, I had to cut off nearly 24 in. of wire for the 20m and about 14 in. for 15m before I can bring both dipoles into proper resonance. The final wire length for 20m elements are 156 in./168 in.(dipole one/dipole two). The final wire length for 15m are 108 in./114 in.)


Head-piece of the boom

Working inside the attic

Working inside the attic did border me at the beginning. The floor of the attic is basically a wood frame with the ceiling boards hanging from its bottom. One can only walk on the wood frame. If you step on the dry wall, you can easily punch a hole and drop straight through. It is not funny if you made a landing on top of the open concept area and stop at the basement. What makes it worse is that the whole attic floor is sprayed with insulating material. You can imagine yourself walking in a pink snow 12" deep. The wood frame is invisible until the pink stuffs are cleared off temporary. Even with good illumination, it will be very distracting if you have to watch you steps when you are trying to work on the antenna. I got an advice from VE3HVL. It turned out to be a very good practice. I got some cheap 0.4" chip-wood boards (48"x96") and cut them up into 16" strips. The strips must be narrow enough to pass the manhole (access of the attic) but still wide enough for you to walk on. Once these strips are moved into the attic, place them on top of the wood frame and make yourself a catwalk. Moving around will then be much safer although you still have to watch for those overhead frames. It is also important to carry a dry battery torch even though you have installed temporary illumination. That prevents you from running into unexpected total darkness. For example, when the bulb is toasted or when your XYL unplugs your attic light by accident. If you have an aged house where the attic is dusty, always wear mask and air filters. Inhaling of these dust is not healthy.

Running the feed lines

In order to make the whole package neat (so that the XYL can't complain on degrading the house value), I run all R.F. cables inside the drywall. The walls of our house are all gypsum boards mounted on 6" wood frame. If the wall is not back to the exterior wall, it doesn't need insulating material. That hollow area is perfect for cable routing. I chose the wall behind my station's desk and punch a 2" hole on it. A desk light is then switched on and have the back side of the hole shined up. The distance of this hole from the nearest corner is then measured. Once back in the attic, a hole is drilled on the wood frame on top of this spot (using the distance from the corner as reference). A perfect line up is verified if the lighted spot of the inside wall can be seen. Drill another hole if the line up is not straight down. Once the holes are made, cables from the attic area can be lowered and retrieved from the 2" hole on the bottom. The bottom hole can then be closed up with a cover plate in future after all cable work is completed.

Constructing the antenna

The material for the wire beam is cheap. I spent only $50 for the boom, wire and 150ft of coaxial cable in total. The first step is to secure the boom on the highest point of the attic. Feed lines are then dropped down and brought up to the antenna switch at the console. Construct one side of the beam first. All elements of the antenna need clearance from each other. Elements hooked on the same connecting screws have to be placed 30 degree apart. Main parts of this antenna can be seen below.

Do not attempt to tune up both arrays at the same time. Due to difference in the attic condition, no two elements will have the same length. Always try to maintain close length between both sides of the same dipole and keep an eye on the cutting progress. Set up the first array and cut for lowest S.W.R. on both 20m and 15m bands. Once the length of the first array is identified, disconnect it from the boom (retaining all stabled hold points) and connect up elements for second array. Repeat the same tuning procedure. Reconnect the wires after second array is completed from cutting.

The 70ft cable length is a special value chosen to make it close to quarter multiples of both 20m and 15m. This provided the best optimization range between both bands. Such feed line length including the section forming the R.F. choke is critical for matching. More precise matching can be applied by adding and subtracting cable length from this start reference. In the original VE3CYC document, he needed 60ft only to get the match. It might be due to environmental factors. One thing for sure, length between both arrays to the antenna switch must be equal.

Test result

It is still a bit early to get to conclusion. The only comment I can make at this moment is that this wire beam works perfect for receive while directional pattern can be felt clearly. The effect is strongest when target station is located on either side of the center axis. Reception on the same station can differs by 7 S-units just by switching between both arrays. For transmission, effect is most distinguishable on weaker local station. It can be weakened from S10 down to barely readable. I also worked some stations at Calgary and Edmonton for far field evaluation. Result again indicated clearly the felt of directional change (report came back as a difference of 3 to 4 S-units). Yet the change in signal strength is not truly on the expected array combination. This might be due to the point that the beam can not be rotated. A lot of contacts came from the sides. Another possibility is that the unused array might not be a reflector to start with. Note the parasitic character is achieved by loading via a non-terminated feed line. If the effect turned out to be making it to behave shorter, it can become a director element.

I think it is safe to say that among all the contacts evaluated, 40% indicated significant signal quality changes between use of both arrays. Among these samples which shows difference, 30% of them indicated a S-unit difference of over 4 S-units. This is not as good as a 3 element YAGI, but at such a cost and being a system totally invisible, I felt I should not be picky.

I shall proceed into more detail tuning later this winter. Keep an eye on this web page for the later update.


By VE3RGW 16/Nov/97

Special thanks to VE3ZEM for taking pictures of this antenna farm :

The H.F.beam, U/V dual band and 6m ground plane (click to zoom)

 6m wire ground plane antenna

 The pole penetrating roof for mounting of outdoor X50.

Close up of H.F.beam and the wire elements

Latest view inside my attic in 1999 Summer. I have added additional components into the collection. That refers to a new pair of dipole for 20m and 40m. These new dipoles are perpendicular to the original wire beam. This provides me option to work on azimuth 90 degree off from the original focus. The new dipoles employs home brew loading coil elements which greatly reduced the over all size of the array. The trade off is a narrower operating bandwidth.

 The new 40m dipole only took a tip to tip space of 28 ft.


Detail about the loading coils of this reduced size dipole can be found inside 

As an update, I had torn down the 2 element wire beam and replace it with a tri-band 3 element design that can be steered (or flip ) via remote switching of LC elements. The construction detail had been submitted to ARRL and is now published inside “The ARRL Antenna Compendium vol.7” as article “A 3-element Ninja Wire Beam”.  Feel free to contact me if more detail required.

By VE3RGW Jan-2003