Hal Communications ST-6000, Инструкция по эксплуатации

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6-2
2A shows a common bypass-filter method used in many transmitters. The drawing in Fig. 2B de-
picts a brute-force AC-line filter that can be added to transmitters or other equipment to eliminate
the flow of RF on power lines.
RF-induced problems that cannot be cured, or ones that appear not to be the fault of inade-
quate transmitter filtering should be referred to HAL factory Customer-service personnel. In cases
where this is not feasible, or where station rearrangement is necessary to affect complete elimina-
tion of RF problems, the i formation in the following section may be of some help.
2. MINIMIZING RF-RELATED PROBLEMS THROUGH ANTENNA SELECTION
In addition to the liberal use of RF bypassing capacitors on station equipment, the use and de-
ployment of certain antennas will offer reduced levels of RF in the radio room in many cases.
Whenever possible, use resonant Yagi, quad, dipole or vertical antennas. Try to achieve a good im-
pedance match at the antenna instead of relying on an antenna tuner. Random-length wire anten-
nas and others that require tuning from the shack are more likely to create high levels of RF within
the vicinity of the operating position.
The location of the transmitting antenna with respect to the radio room also has an effect on
the RF energy that is coupled into interconnecting cables. Apartment dwellers may have the most
difficulty achieving a good installation since many times an indoor antenna is the only type al-
lowed. when this is the case, locate the antenna as far away from the operating position as possi-
ble. Where outdoor antennas are allowed, they should be placed as high as practicable. Not only
will this provide optimum reception, but it will also reduce the level of RF in the shack – all other
factors being constant. Excellent antenna installation information can be found in radio & electron-
ics handbooks and antenna theory and construction booklets, as well as in articles published in
electronics periodicals.
In most situations, coaxial cable feed line is preferred over open-wire, twin-lead or single-wire
type feed systems as its self-shielding property reduces the chance of unwanted RF coupling.
RF energy may also be conducted back to the station by coupling of RF between the antenna
and the outside shield braid of the coaxial cable feed. The use of a balun on a center-fed dipole
fed with coaxial cable may also help reduce coupling, and therefore reduce interference. An RF
choke constructed by winding five or six turns of coaxial cable in a coil approximately six inches in
diameter may also help reduce the flow of RF currents on the outside of the coaxial-cable braid. If
such a choke is used, it should be wrapped with electrical tape to hold the windings together, and
be secured as close as possible to the feed point of the antenna.
Try to dress the coaxial cable feed lines so that they drop perpendicular to the antenna wire,
and not parallel to the radiating portion of an element. In some cases, it may be necessary to run
the coaxial cable straight to the ground and bury it for the run to the transmitter to reduce the
coupling between the outside shield braid of the coaxial cable and the antenna. If there is a mod-
erate SWR on the line, try adjusting the coaxial cable length so that a low impedance (high feed
current) is presented to the transmitter. This may help reduce the level of RF in the vicinity of the
transmitter.