and magnetic fields due to several different antenna types and configurations with various antenna gains were studied. Antennas used at the stations included Yagis, Quagis, "inverted-V" dipoles, horizontal dipoles, vertical radiators, VHF-discones, and others. Primarily, HF and VHF frequencies were used for transmissions. Operating powers ranged from below 100 watts to as much as 1400 watts.
MEASUREMENT PROCEDURES AND INSTRUMENTATION
Measurements were made using instrumentation appropriate for each particular transmitting frequency. Electric field strength for frequencies of 7.2 MHz and below was measured using an Instruments for Industry Model EFS-1 field intensity meter. This instrument consists of a single short monopole on a conductive box. The box contains the readout electronics and acts as an integral part of the antenna. The instrument detects only the component of the field aligned with the monopole. In this study, the instrument was oriented until a maximum reading was obtained.
For frequencies above 7.2 MHz, electric field strength was measured using a Holaday Industries Model HI-3001 isotropic, broadband, field intensity meter. Both of these instruments were calibrated in the EPA's transverse electromagnetic (TEM) cell. An automated, narrowband instrumentation system, incorporating a NanoFast fiber- optically isolated spherical dipole (FOISD) antenna and a Hewlett-Packard spectrum analyzer, was also used in a few cases for electric-field comparison measurements.
Magnetic field strength was measured using a calibrated loop antenna connected to a Hewlett-Packard, Model 435B, battery-operated power meter. Readings were converted from milliwatts to milliamperes per meter. The loop antenna was calibrated by the manufacturer. An Aeritalia Model TE 307 broadband field- intensity meter and a Narda Model 8631 broadband probe with a Model 8621 meter were also used for comparison with loop measurements.
Measurements were made at one or two meters above ground at various distances with respect to the antennas studied. Measurements were also made at various locations inside buildings and at operator locations ("ham shacks"). All measurements were made while operators transmitted in the "key down" position, i.e., continuous wave transmissions without modulation. Although this would not be a normal operating mode, it was used in order to obtain a stable reading on the measuring instruments. Electric and magnetic field strength values were corrected for calibration error and rounded off.
RESULTS AND DISCUSSION
An attempt was made to survey as many different types of antenna installations as possible and to take measurements at frequencies commonly used by amateur operators. A summary of the various amateur sites visited is given in Table 1, along with information on frequencies and powers used. The antennas that appear to be the