5
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 RF amplifier and a ¼-wave vertical transmitting antenna
it was 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 for the preamplifier. The other factor to
consider is, 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.
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 the radio’s
protection limits and DX Engineering cannot be responsible for any damage that may result.
Therefore, included in the loop’s power inserter is a relay “KEY” jack that can be actuated by the
amplifier keying output of a typical transceiver. When actuated, the relay disconnects power to the
antenna preamplifier. A green LED on the power inserter is illuminated when power is applied to
the preamplifier. 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. It is the user’s responsibility to ensure proper keying line connections.
The diagram below shows an Icom IC-7600. Your radio set may differ. Consult your radio
instruction manual for details when using a separate receive antenna input.
