w2co
join:2003-07-16
Longmont, CO | reply to w2co
Interference to PLC systems Interference to PLC systems from Amateur Radio Operation
Interference is a two-way street, and PLC systems are at significant risk from amateur HF operation. In the US, amateurs are limited to 1500 watts PEP RF output, but there is no limit to the antenna gain. As a practical matter, few amateur antennas exceed 13 dBi on HF. This means, however, that the EIRP from amateur stations can exceed 20,000 watts. These stations can have antennas that are as close as about 10 meters or so the the electrical distribution systems.
Here is an estimate of the interference potential of a more modest HF station on 7.15 MHz:
Those unshielded overhead power lines are not great antennas, but they can and will pick up our signals. Here is a quick calculation:
Transmit power: +26 dBW (400 watts)
Transmit frequency: 7.15 MHz
Distance between antenna and power line: 20 meters
Path loss: -15.6 dB
Transmit antenna gain (with ground reflection): 6 dBi
Power-line antenna gain: -10 dBi (estimate)
Power picked up on power line:
+26 dBW
-15.6 dB
+6 dBi
-10 dBi
-------
+6.4 dBW (4.4 watts)
The total power of their signal inside the line is going to be about 10 milliwatts, and when we transmit, PLC wiring may pick up 4 watts of our power right inside the frequencies PLC is using. It is unlikely that PLC systems will continue to function in the presence of these signal levels. And this example is of a completely legal operation of an amateur radio station on 40 meters. Now on 20, 15, and 10 meters it will be possible to have much higher eirp because of the directional antennas in use there, many of which are on an even level with the power lines and many of which are using horizontal polarization. This will ad a few more db to the "gain" of the system into the power lines. |
