Hal Communications CWR6850, Instruction Manual

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CHAPTER 5 PAGE 42
5.9 RF-Induced Problems
The CWR6850 is designed to operate in close proximity to radio frequency transmitting and receiv-
ing equipment. However, under certain conditions in an RF-saturated environment, the CWR6850
may be susceptible to HP-induced interference. This may manifest itself in any of a number of
ways, such as partial or complete lack of response to switches or keyboard operations, or erratic
behavior of the video display.
The first thing that should be checked if RF problems are suspected is the GROUND system. The
transmitter should be properly grounded for RF (in addition to an electrical safety ground) and all
other station equipment grounds should be connected to the transmitter chassis. The RF ground
should consist of a short length of heavy copper wire or braid terminated at a good earth ground
(ground rod, cold water pipe, etc.). If a water system ground is used, be sure that the pipes are
100 percent metal from the connection point to the water mains - plastic plumbing will break the
ground path. If the distance between your transmitter and ground connection is more than a quar-
ter wavelength at the highest operating frequency, make the ground wire an integral number of
half-wavelengths long. If you plan to operate 10 and 15 meters, you may need to run separate
ground wires for each band.
Stations located on the second floor of wood frame houses can present special problems for RF
grounding. One technique that has worked well when none of the usual ground returns work is to
spread copper screen material on the floor of the room under the operating position. The equip-
ment ground is then attached to the screen with one or more low inductance leads. The screen
creates an "artificial" ground plane in the studio. A carpet is usually placed over the screen to im-
prove the appearance of the room! Consult any of the amateur handbooks or antenna books for a
more in-depth discussion of grounding techniques.
The best way to confirm that a problem is caused by RF-induction is to temporarily eliminate the
source. This may be done in stages, starting with a partial reduction in exciter drive, and ending
with transmitter shut-off. Since RF energy may be induced in the CWR6850 through several paths,
connecting the transmitter to a dummy load may not eliminate all RF related problems, although
this is an excellent first step in verifying RF problems.
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