Specifications

PL 3120/PL 3150/PL 3170 Power Line Smart Transceiver Data Book 199
If either of the -72dB LEDs is on solid or if either of the -66dB LEDs flash or if the PKD LED flashes more than once
per minute, then excessive noise or interference is present. This could be caused by one or more of the following
sources:
• The UUT is generating unwanted noise internally. This is most often associated with on-board switching power
supplies. If the UUT includes a switching power supply, verify that the power supply noise masks of Chapter 5
have been met.
• Power line communications signals present on the power input side of the isolator are not sufficiently atten-
uated. Ensure that no other power line signaling equipment is operating on the power mains when performing
this test.
• The isolator is not completely isolating the test set-up from noise on the power mains. Verify the effectiveness
of the isolator as described earlier.
The source of this noise or interference must be identified and eliminated before proceeding with verification testing.
Excessive Loading Verification
The procedure described in this section is used to determine if the receive mode impedance of the UUT is greater than
approximately 100
Ω at its primary communication frequency (as it should be). A receive mode impedance of less than
100
Ω could cause excessive signal attenuation resulting in impaired reception by both the UUT and its neighboring
nodes. For applications which require an even higher receive impedance, refer to discussions in Chapters 5 and 6.
The 10Vp-p output capability of the PLCA-22 analyzer is used to increase the sensitivity of the test. The higher output
signal allows the 0dB, -3dB, and -6dB LEDs of the PLCA-22 analyzer signal strength meter to be used for observing
signal strength. These LEDs, unlike the other LEDs in the signal strength meter, are only 3dB apart allowing for better
measurement resolution.
A series impedance circuit (Figure 7.4) in the output path of the transmitting PLCA-22 analyzer is used to increase its
effective output impedance, thereby preventing its normally low transmit output impedance from overshadowing the
receive mode impedance of the product under test.
The recommended verification procedure is as follows:
1. Set a first PLCA-22 analyzer (referred to as the Recv PLCA-22 analyzer) to use the same band of operation as the
UUT. Set it for Recv and UnackPri modes of operation and configure it for Internal and Line-to-Neutral coupling
as shown in Figure 7.7.
2. Set a second PLCA-22 analyzer (referred to as the Send PLCA-22 analyzer) for the same band of operation as the
UUT. Set it for Send and UnackPri modes of operation and configure it for External coupling. Connect the
impedance circuit (88.7Ω resistor of Figure 7.4) and the coupling circuit as shown in Figure 7.7. This test is best
conducted with the CENELEC protocol (an option for C-band operation) turned off in order to provide uninterrupted
LED illumination (select this option on the send unit's setup screen if testing in C-band).
3. Verify that Attn on the Send PLCA-22 analyzer is set to 0. Set the number of packets to be transmitted to 9999k on
that unit and set the packet length to 13 bytes. Set TxVpp: 10.
4. Without the UUT connected, press START on the Send PLCA-22 analyzer. A test should begin and the receive
packet count on the Recv PLCA-22 analyzer should increment with a packet error rate very close to 0%. The signal
strength meter on the Recv PLCA-22 analyzer should have the LEDs up to and including the -3dB primary signal
strength LED illuminated. The 0dB primary LED may or may not be flashing.
5. Next, connect the UUT as shown in Figure 7.7. The -3dB primary signal strength LED on the Recv PLCA-22 ana-
lyzer either should be flashing or illuminated continuously. If the -3dB primary LED is extinguished, then the input
impedance of the UUT is excessively low (<100Ω). The impedance of the UUT must be corrected before
proceeding; refer to the node checklist of Appendix B for assistance.
6. Record the results of Step 5 in Table 7.1 at the end of this chapter.