SGC SG-500 SmartPowerCube™ User’s Manual, Page 4
SGC, 13737 SE 26
th
Street Bellevue, WA 98005 USA • Ph: 425-746-6310, Fx: 425-746-6384, Email: [email protected]
www.sgcworld.com
SGC RESERVES THE RIGHT TO CHANGE SPECIFICATIONS WITHOUT NOTICE
Copyright SGC 2007
4.0 Antenna and Feedline Tips
The quality of your transmission is directly related to how efficiently you transfer the power from the
amplifier to antenna (via the transmission line), and how effectively your antenna radiates your signal into
space. Keeping those two facts in mind, we offer the following advice for your station installation.
4.1 Antenna Characteristics
Connect your station antenna to the coaxial connector marked RF OUT on the SG-500. Ensure that your
antenna is rated to handle a minimum RF power level of 500 Watts PEP or greater, and is resonant at the
intended band or frequencies of operation (or being used with an appropriate coupling or tuning device to
minimize VSWR). The output impedance of the SG-500 is 50 ohms. Your antenna’s characteristic
impedance should present a VSWR of 2.0:1 or less at all desired operating frequencies.
When installing the SG-500, you should be absolutely certain that your antenna will handle the power.
Because some antenna manufacturers over-rate their antennas, ensure your antenna system is designed for
at least 1kW of power. Small antennas that are rated at 500 Watts or less are likely to fail. Also, small
antenna systems are subject to component overheating. If this occurs when using the SG-500,
immediately investigate and resolve the problem.
The antenna system used should have no sharp edges to reduce the possibility of corona discharge, a
condition that causes the area around the antenna to glow with bluish-white light. Corona is a very
dangerous condition and may lead to fire, destruction of the antenna and damage to the SG-500. When
using a wire or metal antenna that has pointed metal parts, please take the time to coat the portions with
‘corona dope’, which is frequently used in the high voltage section of televisions where similar high
voltages can occur.
The antenna (radiating) wire used with the SG-500 amplifier should be AWG # 8 or heavier, because
during transmission high currents exist at certain points on the antenna. These currents may exceed 20
amps (depending upon the impedance at a particular point on the antenna). Electrical theory states that if
you try to force 20 Amps through smaller diameter wire, such as AWG # 14, the wire will heat up. Heat
translates into lost power. We strongly emphasize that if you have any component heating, you must
resolve that issue in order to have the best possible signal. Heat loss = signal loss.
4.2 Transmission Feed Lines
You will need to construct or purchase a coaxial jumper cable to connect the transceiver output to the SG-
500 RF input. Use high quality 50 Ohm foam dielectric cable such as RG-8, RG-8X, or their equivalent.
Standard UHF connectors (known as PL-259 plugs) need to be installed at each end. Small diameter RG-
58 can be used if cable runs are less than three feet. Never use 75 Ohm RG-59 (CATV) cable for this
purpose.
Use feedline having the lowest loss (per foot) for your application. Although you may use RG-58 type
coax for short runs, you should use large coax for lengths over 25 feet. The smaller type of coax cable
should not be used because it is subject to the same heating losses as described above.