3
Positioning the Antenna
This antenna has a directional ‘Figure Eight’ pattern with two deep 25- 30 dB nulls as shown in the diagram in
Figure 1
,
so for maximum daytime low-angle ground wave reception of a desired signal it should be oriented so that the
imaginary plane in which the loop rests should be vertical to the ground and should, if extended, pass through the
general location of the signal’s transmitter. There is a label on the antenna’s upper junction box that shows the
proper pointing directions for maximum signals and the nulls. At night, for reception of high- angle sky waves
this antenna is less directional and the nulls are far less prominent.
For best results it should be located as far away as possible from any metal objects that could distort or shield the
antenna’s reception like gutters, downpipes, metal plumbing and aluminum foil backed thermal insulation. It can be
positioned indoors or outdoors at least 5 feet above ground level, but for best results it should be as far as possible
from sources of interference such as AC power cables, cat 5 network cables, fluorescent lights, light dimmers,
computers and flat panel TV’s. If located outdoors it can be camouflaged with shrubbery. Ideally a location outdoors
at least 20 feet away from any buildings will yield superior results. It can be mounted to any pole up to 2 inches in
diameter or attached to a flat surface or wall via the included L-bracket.
Use with Near-By Transmitting Antennas
The antenna’s low-noise preamplifier will withstand RF input levels of at least 30 dBm without failure. In tests with a
1,500 Watt transmit amplifier and a ¼ wave vertical transmitting antenna we found that the worst- case loop output
power into the preamp was 10 dBm when the antenna was located 25 ft from a vertical radiator and adjusted for
maximum coupling. This would indicate that at 25 ft separation there is a 20 dB safety margin. The other factor to
consider however is that with this kind of input signal (+10 dBm) the preamplifier’s 27 dB gain will cause it to saturate
and output 1.3 watts into the connected receiver. This high saturated output level is a byproduct of the excellent
intermodulation distortion performance of this preamplifier, but while most receivers have some sort of input protection
and possibly an internal transmit / receive switch that disconnects or shorts the input when transmitting, we cannot be
sure of what the radio’s protection limits are and we don’t want to be responsible for any damage that may result.
Hence included in the loop’s power inserter is a relay that can be actuated by the “KEY” output of a typical
transceiver. When actuated, the relay disconnects power from the antenna’s preamp. A green LED on the power
inserter is illuminated when power is applied to the preamp. An RCA-plug to RCA-plug cable is included with the
accessories to connect the KEY output of your transceiver to the RCA jack on the side of the power inserter. An RCA
Y-adapter is also included to enable connecting the KEY signal from your transceiver to other equipment.
(See
Figures 2 and 3
).
The relay’s actuation circuit is designed to operate with a typical transceiver’s 12 VDC “KEY” signal. The power
inserter has internal DIP switches that can be programmed to harmonize relay actuation with the proper state of the
transceiver’s KEY signal. The default setting is such that when the KEY output is “low” (less than 0.7 VDC) the relay
turns on and disconnects the preamp’s power and the connection to your receiver is grounded through a resistor. If
the KEY signal is “high” or greater than 1.2 VDC the relay is not actuated and power is applied to the amplifier and
connection is made to your receiver. If the KEY input to the power inserter is left open or disconnected, then power is
always applied to the preamp. If your transceiver has a “KEY” output that goes high on transmit, then you can reverse
the polarity of the power inserter relay actuation by removing the power inserter’s base plate and programming the
DIP switches on the PC board in accordance with the table shown in
Figure 4
.
A simplified schematic of the relay interface circuit is shown in
Figure 5
. Note that the KEY input is pulled up internally
via a 10K ohm resistor to the “high” state. If your transceiver’s KEY output is not compatible with this interface circuit
and does not operate the power inserter relay, please contact our customer service (303 526 1965,
[email protected]) for assistance.
