The Upright V Dipole

For Limited Space / Lanai Use

The concrete lanai of a condo is about as bad, technically, as it gets for limited space antennas. In addition, there are usually house rules and condo bylaws. However, there should be some provision for antennas. Most condos have had to contend with the direct TV satellite dishes and the rules for those should also cover Ham antennas. There may be restrictions on things like visual impact and especially attachment to common areas.

40 Meter V With 54 Inch Masts

The above photo shows one workable method. Any antenna must be exposed as much as possible. In this case condo rules say it must be self supporting, not attached to any common area structure and low visual impact. This design also attacked the problem of reinforcing rod in concrete surrounding on many sides. It is designed to be at an angle to everything, not parallel to anything. I have managed to get it working well on most bands except 20 meters. I suspect the lanai railing to be resonant on 20 meters, but there is some kind of local black hole for 14 Mhz. energy.

Latest Center Support

All types of wires running about on the lanai were tried and worked OK in a few cases, but the upright V proved to be the big breakthrough in getting signal out. My DX record is not great but it does allow me to work stations on the Mainland, Oceana, NZ and AU, and Asia on 40, 30, 17, 15 and 10 meters. For 10 meters I use a pair of Radio Shack 102 inch Stainless Steel whips which bend outwards like swan wings and give very good results and excellent broad band characteristics.

The basis of the upright V antenna is a pair of mobile whips. They are installed as a dipole, but as an upright V dipole. Like giant rabbit ears. Many other things were tried on this small urban lanai, but after years of experimenting this was found to be the best. Also the corner of the lanai where the sticks can get maximum exposure was found to be best. The SS Whips used for 10 meters clearly show how superior a full size element with no loading coil is. The bandwidth decreases dramatically as soon as even a small loading coil is added to a design.

Closeup of New Center

Hustler makes a good line of whips, and fittings are available for the 3/8 inch NF thread that is used on the base of these sticks. There are other designs which do not use separate loading coils but which are more helical like in design. The most important part is the center support.

The center support must be incredibly strong. The eight foot whips at an angle put huge amounts of strain on the center insulator. The parts are from Radio Shack who has a line of supports for CB antennas. Two designs have proven practical over the years. One used a balun and was feed with RG8 coax. But recently a new design to revive the idea of twin lead feed was created when a Johnson Matchbox was acquired. It seems to be significantly more efficient, but the Matchbox has problems matching low impedance loads.

New Center

A recent modification mated the top two concrete blocks together with a wooden wedge designed to produce an 11 degree outward tilt, moving the ends of the antenna a bit more into the clear without unstabilizing the stack of blocks used as the base very much. It seems to have helped significantly, and of course changed all the tunings. It also was designed super strong. It uses construction adhesive and large lag screws with holes drilled in the concrete blocks to secure everything together, plus some giant cable ties for good measure. Anything designed to hang over the edge of a lanai needs to be super strong and stable.

A major problem with lanai antennas is proximity effects. The antennas are so close to everything that their feed point impedances are unpredictable and affected significantly by movements of just inches. Bouncing in the wind easily produces bounding of the needles on the SWR bridge, but not severe enough to matter much.

Coax feed worked well but I was concerned about loses in the balun. It is hard to avoid the balun as proximity effects make it hard to get any balance without some kind of forcing. The tuner is fitted with a set of counterpoise wires. These are 9 feet, 19 feet and 35 feet long with the ends very heavily insulated since high RF voltages appear at the end of these 1/4 wave resonant wires. I tried and MFJ ground tuner and finally just settled on a set of 1/4 wave wires as equally satisfactory. They need to be a bit longer than .25 wave to compensate for the detuning of being laid on the floor around the condo and need to be well insulated along their entire length. Lately I have gone back to coax, but used ferrite chokes on the coax to attack common mode currents.

Original Center + Balun

For such applications you cannot have too much tuner horsepower. All such experimenting is going to require extensive matching capability. I have taken an MFJ roller inductor tuner and used one of its two switched coax outputs to feed a Johnson Matchbox. This gives the best of both worlds. The MFJ provides an antenna switch, SWR bridge, dummy load and an unbalanced T-match. The Matchbox provides a balanced link coupled tuner. This is an extremely flexible setup.

For twin lead feed it is important to float the line off the concrete deck. I have used blocks of wood with the standoffs available for TV twin lead at Radio Shack. I managed to get some 72 ohm transmitter twin lead and some 300 ohm special windowed twin lead as well.

The major problem with the Johnson Matchbox is that it was designed for high impedances. It has trouble matching below about 50 ohms and such limited space designs often have feed point impedances down in the 25 ohm range. For such low feedpoint impedances the MFJ and coax feed is just better. Some nice antenna analyzer such as the MFJ or the Autek is a major plus for setting up such atypical antennas in tight spaces.

Tuner Stack, MFJ and Matchbox

In Urban Honolulu the RF background is enormous. I have found that a standard Low Pass Filter is virtually required. It is surprising how it improves the front end performance of many HF rigs by blocking out the several volts of TV, FM, beeper and cell phone RF that the area swims in. From my lanai I can see the tops of Waikiki hotels which sport 100 Kw plus transmitting antennas for local TV and FM stations. Commercial stations seem to have some special exemption from RF exposure rules.

Just because something loads or even shows a good SWR does not mean it is going to work. It has to radiate. The energy can be lost easily in the tuner. I have found it worth while to try to resonate the antennas at the antenna itself as much as possible. Leave the tuner to do resistive to resistive impedance transformations as much as possible. I am firmly convinced you should try a balanced antenna design if at all possible, vs an end feed wire, unless you have superb ground.

A good tuner also helps stretch the narrow working bandwidth of the heavily loaded whips on the lower bands, though by the time 80 meters is reached, there is little that can be done to get more than about 50 Khz out of such a limited space setup. I have an 80 meter version of the upright V and I am lucky to get it to work from 3880 to 3895 Khz.

40 Meter V + Stubby 22 Inch Masts

This is a photo of the stubby version, using 22 inch MO4 Hustler steel whips. It has amazingly good statewide coverage in spite of its compact size. It also is very rugged and can be used when high winds whip across the lanai and make the larger sticks too scary to deploy. The strain on the center insulator is great when the long sticks and the big Hustler 40 meter resonators start bouncing up and down violently.

The Upright V design has worked very well. Much of the mainland USA is blocked to me by the condo and a mountain to make matters worse. But I have still managed to work New England and along the bottom part of the USA into places like Florida and Arizona, plus the West Coast. There seems to be little hope for the central USA, however. But to the west things are quite good and all around the Pacific works well. The antenna does a satisfactory job on 40 meters for the local statewide SSB net.

The V has done quite a bit of QRP and RTTY as well. I have worked most of the DXpeditions to the Pacific area, often netting a response on one call in a pileup using only 5-20 watts. The 10 meter version collects lots of stations during contests. True the lanai is a disapointment when someone in the middle latitudes of the US wants a FIST sked right in the area most blocked by condo and mountains. But the V sure beats not trying because everyone tells you "you'll never get an antenna up there that will work".

Return to UH Ham Club Home Page

12/99