The Portable Random Wire Vertical is a multi-band antenna for the QRP enthusiast! This antenna was designed to cover 10M through 40M, be free-standing and quickly installed/ removed by one person. It's just a random wire going straight up..........but an "RWV" meets the requirements and makes those contacts! THE FEED SYSTEM The key to this multi-band design is a transmatch based feed system. The line is a 28' run of RG-58 with one major difference! While it's connected to an unbalanced output with a PL-259, the shield is allowed to float at the antenna's feed point. This method allows the braid to serve as a tunable counterpoise within a limited range. It apparently provides an adequate RF ground at modest input powers. The coax is terminated in a small alligator clip. The line should be waterproofed after first tinning the stranded center conductor to prevent wicking. A hose clamp positioned about 3" above the base serves as a feed point. The T-match, Z-match or L-match may be used interchangeably in this application. THE RADIATOR The radiator for a basic RWV is 33 1/2' of graduated an- tenna tubing. The outside diameters are 1 1/4", 1 1/8", 1". 7/8", 3/4" and 5/8". The overall length was chosen to achieve a full quarter-wave on 40M. With hose clamps in place the antenna collapses to less than 6 1/1'. This size fits the interior of mid-size cars and most compact sedans. Heavy-duty type 6061-T6 extruded aluminum tubing in .058 wall is recommended. This grade is very strong, flexes in windy conditions but will not take a set. Other grades of tempered aluminum are probably suitable but have not been fully researched. Slot across the top of each section with a fine tooth hacksaw blade to a depth about the same as the tubing diameter. Slotting produces an excellent compression joint but leaves sharp burrs on the tubing. The burrs may be eliminated using a round metal file and the surface finished with steel wool. Any metal chips left behind must be removed before the radiator is assembled. This will prevent scoring of the aluminum and possible jamming when the close tolerance sections are assembled. A cloth attached to the end of a stiff cord and pulled through the tube works well for the interiors. Circle sections two through five with a permanent marking pen, six inches from the un-slotted end. This serves as an important visual warning to stop extending a section prior to re-tightening the hose clamp. Those desiring absolute maximum height may use less overlap bur for structural integrity not less than two and one-half tubing diameters. The radiator is now ready to be assembled. The stainless steel hose clamps are installed at the feed point and at the top of the first five sections. Recommended sizes are: 38 mm (2). 32 mm (1), 25 mm (1) and 22 mm (2), all with standard 5/16" heavy-duty hexagonal screw heads and wide clamping bands. Position the clamps on the tubing so the screws can be reached from the same side of the mast. A guying ring is added at the 6' level as discussed in the following sections. THE MOUNTlNG SYSTEM The collapsed radiator is socketed in a heavy-duty 1 1/4" diameter rubber crutch tip which insulates metal from the earth. The crutch tip is tightly pinned to the ground with a screwdriver passed through a drilled center hole. Select a screwdriver handle with a minimum shaft length of 6". The handle should fit snugly inside the base tube. A Phillips-type head is preferred for easy insertion into the earth by hand pressure alone. The completed radiator is then pressed firmly into the socket. This mounting system supports the nested tubing while the guys are being attached and expedites installation by one operator. THE GUYING SYSTEM The three point grounding system is connected to a 1 1/8" inside diameter steel or brass washer installed between the first and second sections. Drill three equidistant holes in the washer to accept small S-hooks as described below. The correct guy length for a basic RWV is 9'. Select 1/8" or 1/16" diameter solid plastic clothesline with a stranded nylon core. This line is strong, will not stretch or unravel and contains no metal to absorb RF. The guys should be carefully attached to 1 1/4" or 1 5/8" steel S-hooks with securely locked knots. S-hooks are available in hardware or variety stores. Check to insure they will pass the largest screwdriver being used as a guying stake. A hook used at the guying ring is closed on one side with a pliers. The open side of that hook is attached to the guying washer. A hook on the earth end of a guy is pressed closed on both sides. The earth end of each guy is held in place with a 6" or longer screwdriver set at a forty-five degree angle. A sharp Phillips-type head is again recommended for easy insertion in hard earth. After several practice sessions a new user will have little trouble setting the nested antenna perfectly straight. The guys should be taut but need not be overly tight. he three-point system coupled with a pinned base is remarkably stable, even in windy conditions. The basic RWV antenna and guying system has unintentionally survived 30 mph storm gusts in portable use without difficulty. EXTENDING AND LOWERING THE ANTENNA The fully assembled radiator weighs just under six pounds and is very manageable. Antenna installation takes one experienced person an unhurried five to seven minutes! Lowering the antenna is the reverse of the installation procedure and takes less than two minutes. What happens to performance with longer or shorter feedlines? Other feedline lengths up to 50' have been substituted with no significant changes noted in performance characteristics on 10M through 40M. The 28' run of RG-58 was actually chosen at random from coax already on hand. Since it seems to work well there has been no serious investigation to date into feedline alternatives. A longer shield braid appears to provide a better artificial ground, particularly on 80M, but at the expense of increased feedline losses. What about higher operating powers? The basic antenna and feed system load easily and have handled 100 watts input during informal tests. No unusual SWR changes or coax healing were observed. The impedance is non-critical in this application so either 50 ohm or 72 ohm coax may be used. It should be noted that the shielded feedline tends to keep stray rf out of the station at all power levels. Does the RWV require any maintenance? During installation the friction between sliding tubing sections (.009 clearance) assures good electrical contact at all times. The withdrawal warnings on each section will have to be re- marked periodically. Check the feedline waterproofing and locked knots occasionally. At least annually disassemble the radiator, clean the tubing and wipe each section with a cloth lightly sprayed with WD-40. At the same time a little lubricant should be placed on the hose clamp screws. How else can this design concept be utilized? Replace the aluminum radiator with a wire! It should be at least a quarter-wave length on the lowest operating frequency. Ideally, The wire should hang straight down from an insulated support or tree branch. Backpacking hams can exchange the RG-58 for RG-174 to reduce weight but should anticipate additional feedline losses. WHAT'S THE BOTTOM LINE? The RWV is a compromise design and not particularly efficient electrically. Nevertheless, in eight years of active use this simple portable antenna has consistently worked states. provinces and DX from 10M to 40M. Any 33 1/2' vertically polarized antenna in the clear and resonant is going to make contacts. even when running QRP! CLOSING COMMENTS With this design the QRP portable enthusiast has wide latitude in choosing operating locations. It's a major advance from being totally dependent upon trees or other supports when utilizing otherwise excellent wire antennas. The self- supporting radiator and accessories are relatively light thus easily carried from a vehicle to nearby picnic benches or campsites. Finally, the convenience with which a single operator can install a RWV means more air time is available when running portable. Just for fun, put the receiver on line before extending the radiator. Then tune a weak CW signal and listen for that inevitable increase in signal strength. Height is still every thing when it comes to antennas! Good luck and have fun in the field with your own RWV! Hope to catch you QRP portable soon!
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