CommScope Inc. of North Carolina AIRBRIDGE-AP ユーザーズマニュアル
10
3.0 Connectors & Configurations
3.1 AP Connection
The only required connection to the AP is made through the F-connector. Connect a coaxial cable, such
as CommScope cable F677TSVV, from the power passing tap to the F-connector on the AP. You
should use a drip loop and a coax weather boot on the connection to the AP. Note the power and
voltage requirements as mentioned in the Power Requirements section (Section 2.3).
as CommScope cable F677TSVV, from the power passing tap to the F-connector on the AP. You
should use a drip loop and a coax weather boot on the connection to the AP. Note the power and
voltage requirements as mentioned in the Power Requirements section (Section 2.3).
3.2 AP Configuration
The AP status and configuration may be monitored and modified either remotely via Ethernet or locally
via the local interface. For local control of the radio, use the 9-pin RS232 local interface located on the
base plate of the unit with settings as described in the Direct Connection section of this manual (Section
4.1.0). Since the AP is capable of providing a wide range of upstream gains and downstream transmit
levels, the setting of these levels is very important to maintain optimal performance.
via the local interface. For local control of the radio, use the 9-pin RS232 local interface located on the
base plate of the unit with settings as described in the Direct Connection section of this manual (Section
4.1.0). Since the AP is capable of providing a wide range of upstream gains and downstream transmit
levels, the setting of these levels is very important to maintain optimal performance.
3.2.1 Downstream Transmit EIRP
The downstream transmit EIRP is normally set to the maximum value of 28 dBm EIRP. For very
short distances, the transmit power should be reduced to prevent overdriving of the CM at the
customer site. When operating normally, the status will show the downstream output as
“Unmuted.” The AP automatically mutes if there is a problem, such as the internal cable modem
unable to register on the system, no valid signal for the downstream demodulator, or a hardware
problem indicated by a Hardware Failure alarm. It will indicate “Muted (Alarm)” under these
conditions. If it shows “Muted (Manual),” this indicates that the output has been manually muted
by the user. It can be unmuted in the downstream menu. The downstream power may also be
adjusted to optimize subscriber CM receive SNR (Signal-to-Noise Ratio) if desired. On all but the
longest links, reducing the transmit EIRP by a few dB may improve downstream receive SNR by
improving transmit linearity.
The downstream transmit EIRP is normally set to the maximum value of 28 dBm EIRP. For very
short distances, the transmit power should be reduced to prevent overdriving of the CM at the
customer site. When operating normally, the status will show the downstream output as
“Unmuted.” The AP automatically mutes if there is a problem, such as the internal cable modem
unable to register on the system, no valid signal for the downstream demodulator, or a hardware
problem indicated by a Hardware Failure alarm. It will indicate “Muted (Alarm)” under these
conditions. If it shows “Muted (Manual),” this indicates that the output has been manually muted
by the user. It can be unmuted in the downstream menu. The downstream power may also be
adjusted to optimize subscriber CM receive SNR (Signal-to-Noise Ratio) if desired. On all but the
longest links, reducing the transmit EIRP by a few dB may improve downstream receive SNR by
improving transmit linearity.
3.2.2 Upstream Gain
The upstream gain setting is used both to compensate for the link distances and to enable the
upstream signal to meet the required level into the tap. Note that the broadband noise level in the
18 to 42 MHz upstream band is directly proportional to the upstream gain setting, so in general, it
is desirable to operate with the lowest practical gain setting to minimize the noise level. The initial
setup of a link should be performed with the upstream mute set to “Muted,” so that excessive
noise is not injected into the plant when the AP is powered on for the first time.
The upstream gain setting is used both to compensate for the link distances and to enable the
upstream signal to meet the required level into the tap. Note that the broadband noise level in the
18 to 42 MHz upstream band is directly proportional to the upstream gain setting, so in general, it
is desirable to operate with the lowest practical gain setting to minimize the noise level. The initial
setup of a link should be performed with the upstream mute set to “Muted,” so that excessive
noise is not injected into the plant when the AP is powered on for the first time.
The CM may not be able to register with the initial gain settings. The upstream gain can be
increased in 10 dB increments until the subscriber CM registers, allowing time for registration at
each gain change. When registration is achieved, the upstream gain should be optimized by
setting it to a value that has the subscriber CM transmitting between 40 dBmV and 50 dBmV.
The optimal gain setting for a specific link will depend on both the link distance and the upstream
level required at the tap. Lower upstream gain settings will cause the CM to transmit harder to
maintain the same level at the tap. This may improve the SNR, but will also reduce margin to
compensate for gain variations in the path between the CM and the CMTS. Conversely, higher
upstream gains will cause the subscriber CM to reduce its transmit power to maintain the same
level at the tap, and this may degrade the upstream SNR.
increased in 10 dB increments until the subscriber CM registers, allowing time for registration at
each gain change. When registration is achieved, the upstream gain should be optimized by
setting it to a value that has the subscriber CM transmitting between 40 dBmV and 50 dBmV.
The optimal gain setting for a specific link will depend on both the link distance and the upstream
level required at the tap. Lower upstream gain settings will cause the CM to transmit harder to
maintain the same level at the tap. This may improve the SNR, but will also reduce margin to
compensate for gain variations in the path between the CM and the CMTS. Conversely, higher
upstream gains will cause the subscriber CM to reduce its transmit power to maintain the same
level at the tap, and this may degrade the upstream SNR.