Below is a drawing for the practical construction of a VHF/UHF discone antenna I have built and have been using with great success: <-----------D------------> u N J========================== V i V G c F x F c c I i I c c I i I c c I i I c TABLE c I i I c MEASUREMENTS(Lengths) D = Diameter Of Disk Tc c c c c cI i Ic c c c c cT D = .67-.70 Of 1/4 J = Jumper(Used Only I i I Wave Of Desired Freq. With Dbl. Side CopperClad) I i I S = 1/4 Wave Desired V = Insulating Disks I i I Freq. i = Threaded Brass/Copper Rod I i I c = 1/4 Wave Desired Center Conductor. I i I Freq I = Wall Of 1/2 Wave Length I i I I = Copper Pipe 1/2 Copper Pipe F x F Wave length Of Desired T = Edge Of Cone Skirt N Freq N = Female N, BNC, or SO-239 G = .3 To .5 Of Diam- Connector <-------------S-------------> eter Of Cone At Top F = Pipe Cap x = Insulating Spacer THEORY OF OPERATION = The Discone antenna is N = Nut To Match Thread Of an omnidirectional, multi-band vertical with Center Conductor i a very low angle of radiation, lower than a u = Protruding Length Of 5/8 wave vertical. The SWR ratio is 1.5:1 over Center Conductor i If 1/4 a 10 to 1 range from the lowest desired freq Wave Vertical Is Desired the antenna is designed for. (See Theory Of Operation) First determine the lowest operating freq you G = Gap Between Disk And wish to transmit from. This is the foundation Cone. Very Important!!! for your measurments. A discone designed for 140 MHz will consistently perform to 1400 MHz (10 x 140 MHz). For operations below the design frequency, a simple quarter wave vertical may be added, as long as it maintains electrical contact with the disk/center conductor, and is insulated from the cone. Gain is accepted as 0 to low. SALIENT CONSTRUCTION POINTS = I have tried to make the schematic as readable as possible. Space prohibits a step by step instruction, yet an explanation of several important points follow: GAP BETWEEN DISK AND CONE = This, with the cone length, determines the SWR. 1/4 wave length of c responds best with a distance of .30 of the diameter of the cone at it's apex. No more than .50 if the length of c is 1/2 wave or more. DISK CONSTRUCTION = A solid disk may be used, this will increase wind load. I used double sided CopperClad circuit board material for discones of 200 MHz or higher. Circuit copper has the fiberglass center layer and adds rigidity over sheet metal. Be sure to jumper the top and bottom layers to maintain electrical contact. A spoked disk may be constructed, a rim of heavy gauge copper wire may be added, as the rim of a wagon wheel, for rigidity. INSULATING THE GAP(V) = This is the platform the disk rests on. This may be cut from PVC and epoxied in place. Remember height/gap G above! I found some rubber disks at a local surplus parts store that I layered till I got the right gap. INSULATING CENTER CONDUCTOR(i) FROM END CAP AT APEX OF CONE = Choose your coax connector, drill the end cap to take the connector, then solder the threaded center conductor(i) to the center of the coax connector. I silver- brazed this assembly to the bottom of the 1 inch copper spine(I). The other end-cap must have a plastic or wood dowel inserted in order to insulate the center conductor(i) to remain remote from the spine and cone. I found some plastic disks at my suplus store that worked as if made for this project. CONE CONSTRUCTION = The classic discone has a cone made of solid sheet metal. I used brass rods(c) bent perpendicular to the spine(I). Solid copper wire attached at T (in a rim configuration) will add strength and stability. Crimp 1/4-1/2 inch of the ends of c and bend to appropriate angles, silver- braze in place. GENERAL HINT = Solder/braze all assembly points, copper/brass gives best electrical connection if soldered. This discone is a reproduction of of one I observed at PATRICK A.F.B. in Florida, I estimated the size to be around 150 MHz. Basic discone measurements are: a) DISK = .67-.70 1/4 WAVE OF LOWEST DESIRED FREQ. b) CONE LENGTH = 1/4 WAVE OF SAME c) CONE DIAMETER AT SKIRT = 1/4 WAVE OF SAME d) CONE DIAMETER AT APEX = VARIABLE, DETERMINED BY b) & c) Please feel free to direct all inquiries to me here at W8BI. 73 Corny N8TQJ@W8BI