Vertex Standard FT-1000MP manual Accessory Installation

ACCESSORY INSTALLATION

DIGITAL MODEM (TNC, WEATHERFAX, ETC.) INTERFACING

NOTE: COMPUTER-GENERATED RFI

When using a TNC connected to your transceiver, or even having a PC located in the shack, the possibil- ity exists that you may experience computer-generated RFI (Radio Frequency Interference).

The CPU in a personal computer operates with a crystal-controlled oscillator (clock) and timing circuits. Common clock frequencies include 8, 12, 16, 20 and 25 MHz. In addition, high-speed digital data switching uses square waves, which produce odd-order harmonic frequencies.

Computer-generated RFI may appear at seemingly random frequencies (usually right where a rare DX sta- tion is calling CQ!) throughout the range of your trans- ceiver, and may sound like constant ticking or buzzing that may change as you type or work within a program. Severe RFI may have S-meter indications as much greater than S-9, making copy of voice signals difficult and data signals virtually impossible.

Computer-generated RFI is usually a result of in- adequate shielding of the PC’s cabinet or I/O and pe- ripheral connections. While computer equipment may

comply with RF emission approval standards, this does not ensure that sensitive amateur radio receivers will not experience RFI from the device.

There are a few steps you can take to reduce or eliminate computer-generated RFI. The first step is to ensure that only shielded cables are used for TNC-to- transceiver connections, carefully check RF ground connections and re-orient your station equipment in relation to the computer. Try moving your PC and pe- ripherals slightly and see if it has any affect on the RFI, in some cases, this alone may be enough to correct the problem.

If not, several additional steps to try include install- ing AC line filters on the power cord(s) of the suspected equipment and inserting decoupling ferrite toroidal chokes on interconnecting patch/data cables and smaller ferrite beads on single wires.

As a last resort, you can try installing additional shielding within the PC case, using appropriate con- ductive mesh/screening or conductive tape. Especially check RF “holes” where plastic is used for cabinet front panels. For further information, consult amateur radio reference guides and publications relating to RFI sup- pression techniques.

page 18 MARK-V FT-1000MP Operating Manual