8-Element High Frequency Log Period Dipole Array: The 8-element HF LPA antenna was placed in service on 8 June 2010 (see pictures below). It replaced a 3-element Yagi described here.
The 8-element LPA is model KMA1832, a custom design for the Reeve Observatory by KMA Antennas (www.kmaantennas.com/). It has a 14 ft double-boom made from 1 in. square aluminum tubes. The elements are stepped and made from round aluminum tube varying in diameter from 7/8 in. to 3/8 in. The characteristic impedance of the antenna is about 50 ohms (see VSWR and impedance charts below). A choke balun made from ferrite beads reduces common-mode currents on the transmission line.
The LPA antenna installation includes an antenna support structure, antenna rotator, and transmission line. Because of the overriding need to preserve local foliage, mainly for aesthetic reasons, the antenna installation is surrounded by deciduous trees and conifers and is far from optimum. The antenna site elevation is approximately 13 m AMSL and is about 200 m from the shore of Cook Inlet. Click here for a description of the antenna supporting structure (tower).
The LPA is a directional antenna with an a gain of approximately 7 to 10 dBi and 3 dB beamwidth of approximately 60 degrees, both determined from antenna models provided by the manufacturer. It is mounted on a rotatable shaft at the top of the tower approximately 13.8 m above ground level (AGL). The coaxial cable transmission line is 10 mm diameter Times Microwave LMR-400-DB (direct burial) and is approximately 50 m long.
The four images below are from the antenna model (Nittany Scientific Products NEC-Win Plus). An animation of the azimuth patterns from 18 to 32 MHz also is provided below.
Animations showing how the azimuth and elevation patterns change with frequency are here:
- Azimuth pattern of main lobe in 1 MHz steps from 18 to 32 MHz
- Elevation in 1 MHz steps from 18 to 32 MHz
The rotator is a Yaesu G-450A, which is mounted on the tower at approximately 12.5 m AGL with a plate-mounted bearing located above it to provide lateral support. The rotator is controlled by an MDS RC1-G Digital Rotor Control through 50 m of 6-conductor outdoor control cable. The RC1-G serial port is connected to the laboratory Ethernet LAN through a B&B Electronics ESP901 EIA-232-to-Ethernet converter. This converter's virtual COM port mode allows the rotator to be controlled from a station PC using Ham Radio Deluxe software or YO3DMU PstRotatorAz software. Click here for a rotor control diagram.
Antenna before being placed on tower
Front of antenna showing choke balun connection to the boom transmission line
Inductive short circuit at rear of antenna to terminate the boom transmission line
Antenna on tower with gin pole and hoisting ropes. Antenna is in position and clamped
Installation completed June 8, 2010
Antenna is above trees in immediate area
View against a partly cloudy sky pointed south