This 98.5' (32.349 m) long  portable antenna was designed by VE7BQH for W0PT.  This high gain (19 dbd) antenna is relatively lightweight, inexpensive, and very portable - it can be rolled up for transport.  It also has an unusually high Front/Back ratio, which makes it especially good for receiving weak signals when pointed out over a quiet direction toward the moon (such as out over the ocean), and facilitates an operating/equipment position very close to the rear of the antenna (with a very short feedline). The forward gain of this antenna compares very favorably with arrays of four good 13 element yagis; depending on the type of terrain over which it is mounted (near a beach overlooking salt water is the absolute best!), 2m EME contacts with 10-20 stations should be possible - EVEN WITH ONLY 100 WATTS!  W0PT indicates that he built this antenna for
approximately $30.

This design uses .125" (3.175 mm) diameter aluminum elements, which are to be supported on two parallel non-conducting lines that will not stretch, such as dacron, Phyllistran or polypropylene (will not work if the antenna is to be left out in the sun for an extended period of time); the lengths shown for the antenna elements will only be correct if .125" diameter rods are used.  If you need to aluminum rods of a different diameter for the elements, please contact me or VE7BQH so proper element lengths can be provided.  The antenna is meant to be suspended between two end supports, with the two support lines tightened to remove antenna sag.  The yagi can be made more horizontal by hanging a third line above the antenna and extending several vertical support lines (such as in the middle and between the middle and ends) down from it to hold the antenna up.  However, W0PT reports very satisfactory operation by simply pulling the antenna tight at the two ends (without any further support from above).

W0PT connected his elements to polypropylene support ropes with plastic cable ties, and then the mechanical connections was sealed with "Plastic Rubber" to make sure the element locations would remain fixed. The intended use of this antenna is to provide gain in a specific direction, such as over a fixed tropo path or toward a particular azimuth where the moon is intended to rise or set.  It can be steered somewhat (to adjust for the changing moon declination and corresponding change in azimuth of moonset or moonrise) by moving one end of the yagi (such as moving the end support point between two trees).  In an ideal situation, the transmission line to the Driven Element can be kept very short, with the yagi extending out away from the operating position.

NOTE: Be sure to mount the rope yagi at least 12' above the ground.  Mounting it lower than this will cause excessive ground absorption, and loss of gain.
 
 

*The driven element used by W0PT was constructed as a "T Match" as follows:  Overall length of the 1/2" (12.7 mm) diameter driven element was 37.598" (955 mm); each of the two 3/8" (9.525 mm) diameter T-match sections was 15.197" (386 mm) long; center-to-center spacing between the driven element and T-match rods was 1.575" (40 mm); the driven element was fed with a standard half-wavelength balun 29.528" (750 mm) in length (RG-303 coax was used by W0PT).  It may be necessary to slightly re-adjust the T-match if the antenna is set up in a substantially different place (or different amount of sag, height, etc.) than where initially tuned.

Below is a photo of the 51 element 2m rope yagi used by N7BHC in V5 to try to make contact with ZD8BI.  The wind was blowing 80 km/h, with gusts to over 100 km/h when this picture was taken.  The wind was deflecting the middle of the antenna about 50 cm even with more than 200 kg of tension on the antenna. N7BHC used 3mm Kevlar for the boom wires to minimize stretch and keep element spacing accurate over a wide range of tensions. The Kevlar rope was obtained from West Marine.  The yagi has a 40m boom.

This page last revised on 18 March, 2009