The tape measure radio direction finding antenna is a popular design for Fox hunting and rescue. The antenna is inexpensive and very compact with its elements folding to 21” for easy transport. The kit contains all the parts you will need to make a 3 element 2 meter band Yagi from a tape measure and PVC sch. 40 pipe and fittings. A length of RG-58 is also included. You will need only a flat screw driver or a 5/16” nut driver, PVC cement and a coax. connector that will fit your receiver.
Equipment and tools for assembly - PVC Cement.
- Flat file and/or sand paper.
- 5/16” nut driver or flat blade screw driver.
- Pliers and wire cutter or a wire tie tool.
- Crimping tool or solder for antenna connectors.
- Coax. connector for RG-58U that is compatible with your receiver.
Cautions
Some of the ends of the cut measuring tape may be sharp and a small piece of electrical tape or “liquid” tape could be added.
- The kit includes a “hairpin” wire to increase the impedance to approx. 50 ohms.
- Do not use the antenna to transmit unless you carefully adjust the “hairpin” and element length to give a low VSWR and impedance very near 50 ohms.
- The “hairpin” is not crimped into the two ring connectors and can be easily de-soldered to make adjustments.
Visual
A finished antenna is shown in the following figure (I)
Note that an adjustable mount for a receiver is attached to the handle of the antenna. In place of the receiver a compass could be mounted to give your heading. The receiver shown in the photograph is the VK3YNG sniffer 4.
Figure I
PVC parts are shown in an exploded view in Figure (II). The skeleton of the antenna is made from ½” schedule 40 pipe. There are 6 couplers of ¾” PVC that have been bored out to fit over the ends of the ½” fittings. Two of the special couplers have been cemented to the feed section and drilled to accept a # 10 sheet metal screw (provided) to hold the driven elements, “hairpin” and coax. connections. The ¾” couplers are nearly the same curvature as standard 1” wide tape measures and thus the tape is not deformed when secured with nylon wire ties (provided).
Figure II
Construction
- Cement the ¾” couplers onto the “T” and “ +” fittings.
- Cement the end cap to the handle section.
- Cement the 10 ½ “ and 7” sections into the pre-drilled Driven Element mount.
- Cement the end of the 7” section into the reflector mount. Make sure the DE and REF mounts are aligned! Using a flat surface makes this task easier. Also, inserting some scrap ½” pipe into the fittings makes alignment easier.
Remember: PVC cements work very quickly and an alterative cement would be a thin CA glue which you can purchase from most hobby shops. If you accidentally miss-align the fittings a simple fix is to cut the ½” pipe and insert a straight coupler.
- Repeat step 4 and cement the DE fitting to the Director fitting. Again carefully align the elements!
- Cement the handle and end cap then cement the handle into the DE fitting. This completes the PVC skeleton for the antenna.
Installing the Elements
- Find the center of the Director and REF elements. Fasten the two element with two nylon wire ties and cut off the tag ends.
- File or sand the coating off the back side of the DE elements around the mounting hole.
- Fasten the DE elements to the center mount using the two sheet metal screws. Use two wire ties to secure the DE elements.
Refer to Figure I, and Figure III
Figure III
- Remove the two sheet metal screws and install the “hairpin”.
- Strip 1” of insulation from the coax and install the two ring connectors. Stack the “hairpin” and coax connections and reinsert the sheet metal screw.
- Install a coax. connector (usually a UHF, BNC or SMA) that is compatible with your receiver.
- Your antenna is now ready for reception. Caution: Do not use for transmission unless you carefully fine tune the antenna for acceptable VSWR and impedance very near 50 Ω.
- Time to find the fox!
| 
