G8MNY > ATV 22.03.95 21:56 88 Lines 3789 Bytes #9 @EU BID : 61154_GB7HSN Subj: A 23cm Flat Plate ant design. Sent: 950319/2311Z @:GB7HSN.#32.GBR.EU [Mottingham] #:61154 $:61154_GB7HSN From: G8MNY@GB7HSN.#32.GBR.EU To : ATV@EU Flat Plate Aerial ================= This design is simple & offers 10dB gain over the whole 23/24cm band or it can be centred on 23 or 24cm (*) ends of the band. A detailed design can be found in UHF Compendium, but I have found simpler constructions work just as well, & on tests are better than some of the ATV long yagis on offer! FIGURE "8" ELEMENTS Two elements are construction from mains 2.5mm Cable with the inner insulation left on. Each compound element is bent into a a figure of "8" from 2 wave lengths 2x 24.5cms (* 23/24) long (2x49cms for both & leads), and equates to 4 dipoles (8 for both elements). The start & stop of the two 8s are at the top & bottom respectively, and the "8" centre cross over points are left insulated. Stalk Mounting V ----- ! ! ! ! Cross over ===== ! ! ! ! Feed point -\ /- COAX BALUN To make the feeder balanced a balun using 6cm (1/4Wave) of insulated dead coax alongside the feeder coax is used. Solder the end of dead piece braid to the coax braid outer 6cm from the feeder end. Solder the feeder inner to the dead piece braid. ___ ---------------------/ Balanced Coax Feeder ], 50 OHM ------*============= ! Feed ! DEAD COAX !*--- * = solder ------------- REFLECTOR The reflector can be sheet metal, hardboard & foil, or chicken wire mesh, at least 23x32cm in size. Plastic stalks (UR67 Polythene, or Wallplugs) will be needed to support the ends of the 8s about 2.5cm in front of the reflector. Make a hole for the feeder, and also holes for mounting the aerial. Re-usable Cable ties make quick test mounting. --------------- ! o o ! Cable tie mounting holes ! x ! Stalk ! 8 ! ! ! ! oo ! Balun Feeder Holes ! ! ! 8 ! ! x ! Stalk ! o o ! Cable tie mounting holes --------------- ASSEMBLY Push Balun feeder though reflector, & glue (heat glue?) in place. Solder the two 8s one going up & one down, in place so that the feeds are paralleled & in phase. Fix the 8s to the stalks (glue). Test with RF for SWR & if needed adjust the reflector spacing (bend 8s). POLAR DIAGRAM The aerial produces horizontal polarization when the 8s are vertically above each other, and corresponds to 8 stacked & phased dipoles with reflectors. In this mode it has a 90deg coverage angle. But there is a very narrow vertical aperture, so it must be mounted in a vertical plane. - _ / \ ! ____ ! / \ !8 __ -- \ ==!* 90ø ! ==! * __ 10ø ) ! \ / !8 -- ____ / \ _/ ! - ATV USE GB3HV Repeater uses 4 of these on TX to produce 360deg coverage around its mast, and another 4 with power switched individual preamps on Rx. 73 de John, G8MNY @ GB7HSN