From: > Thanks, Jay, for the message. It's very informative. > Pardon my ignorance, but what is a Yagi ?? A Yagi antenna is named after its inventors H Yagi & S Uda of Tohoku university - invented in 1924 !!! The typical long boom TV antenna is a Yagi. It consists of a dipole radiator (two wires at 180 degrees fed by a 2 wire (balanced feed) in the centre plus a series of parallel reflectors and directors supported (usually) on a boom. There is usually one reflector opposite the direction of gain and a number of directors in the direction of gain. It works (approx) by adding the fields induced in the various non driven elements such that they add with the driven field in one direction and cancel in the other. From top view it looks like a pedestrian "zebra" crossing except the "stripes" vary in length and spacing. --- Reflector / \/ -- driven element / | | | ! i -------------- --> direction of gain | | ! i | It has the characteristics of having "gain" along the direction of the boom, (much less gain in the reverse direction, reasonable immunity to variations in mechanical dimensions, all elements except maybe the driven element * may be DC connected to the boom leading to ease of construction, and relatively good gain and pattern per cost. (* - driven element too with certain conditions and feed methods) In a amateur rocket it is probably not practical - it would be fairly deal IF you can build one that points down along the axis of the rocket. For small rockets the size available implies a VERY high frequency and for large rockets there is liable to be metal in the path which would distort the radiation pattern fatally. If pointed out sideways it would be useful ONLY if the rockets roll was stabilised and its absolute roll pointing could be guaranteed (due to its directionality). The driven element is ABOUT 150/F metres long F in MHz eg for a 450 MHz transmitter element length is about 150/450 = 0.333 metres or about 1 foot ! Element length CAN be reduced by loading the elements (winding coils as part of each element) but this is very unusual with a Yagi. regards, Russell McMahon _____________________________ What can one man* do? Donate food daily free !!! - http://www.thehungersite.com/ Donate Vitamin A! http://www.thechildsurvivalsite.com/ www.rawa.com - one perspective on Afghanistan www.changingourworld.com www.easttimor.com www.sudan.com (* - or woman, child or internet enabled intelligent entity :-)) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.