LBVM920 Series 1.2 GHz Indoor High Output Optical Node
Installation & Operation Manual
Page 3 of 4
OPTICAL, RF & POWER CONNECTIONS CONT'D.
FORWARD & REVERSE SETUP GUIDELINES
1.
Please note that LBVM920 uses JXP attenuator pads for output/input level control (forward/reverse pad) and for setting forward tilt (slope) in the
forward equalizer plug-in.
2.
For the forward path setup, make sure that the forward optical input level to the LBVM920 is within range as shown in the table in section OPTICAL, RF & POWER
CONNECTIONS above. If the optical input is higher than +2 dBm, receiver overload may occur. If the optical input is < -8 dBm, the LBVM920 loses AGC tracking,
RF output will not be as per specification and the output will drop a further 2 dB with every 1 dB drop in optical input. The LBVM920 delivers optimum performance
at -1 dBm optical input level.
3.
The specified RF output level of 50 dBmV at 1.2 GHz is only guaranteed at optical input within AGC range and with OMI ≥ 3.5% on the downstream optical signal.
The output will drop a further 2 dB with every 1 dB drop in optical input, outside the -8 to 0 dBm optical AGC range.
4.
To compensate for RF cable losses, the forward equalizer plug-in comes with a 15 dB JXP attenuator pad installed from the factory. This results in a 15 ± 1 dB
slope on the RF output of LBVM920 from low frequency to high frequency. The forward slope (tilt) can be changed by changing the forward equalizer plug-in value.
Use only JXP pad (attenuator) in the forward equalizer plug-in.
5.
Connect a signal level meter at the RF OUT port to measure the RF output from the LBVM920. You can also use the forward output -20 dB TP to measure the RF
output.
6.
If the output level is too high or low, the forward pad plug-in can be changed to adjust the output of LBVM920. The forward pad plug-in takes a JXP attenuator pad.
7.
Verify the RF output levels from the LBVM920 are as expected.
8.
This completes the forward path setup for the LBVM920 ONU.
9.
The LBVM920 is also available in a downstream only model. If using a receive only LBVM920 node, then ignore the reverse (upstream) path setup.
10.
For the reverse path setup, make sure that the reverse input level to the LBVM920 is not too high or damage to the ONU may occur. The -20 dB forward TP is a
bi-directional TP and can also be used to inject the upstream test carrier. Compensate 20 dB if using the forward TP to inject the upstream test carrier. The injected
upstream test carrier can be measured on the -20 dB reverse input TP of the LBVM920.
11.
The upstream transmitter in the LBVM920 is a continuous ON laser transmitter and is always active. The LASER ON LED on the laser diode indicates the status of
the laser transmitter and will be illuminated when the LBVM920 turns ON (irrespective of upstream RF input).
12.
Make sure the upstream RF input is within the upstream frequency and input level range. The upstream RF input range for LBVM920 is 10-30 dBmV per channel
(digital channel level) for 42/54 MHz LBVM920 and 10-27 dBmV per channel (digital channel level) for 85/102 MHz LBVM920. These upstream levels are assumed
with the condition that a 42/54 MHz split unit will have 4 equally loaded channels in the upstream band, and the 85/102 MHz split will have 8 equally loaded
channels in the upstream band. If using a different number of channels from what is mentioned above, compensate for total RF power. The total RF input level to
the LBVM920 (for all channels combined) should not exceed more than 36 dBmV (digital channel level). More than 36 dBmV (digital channel level) total upstream
RF input may cause laser clipping and saturation on the LBVM920. Use the following formula to calculate total RF power: Total RF power = RF power per c
[10* log (# of channels)].
13.
Refer to the NPR plot below to better understand the RF input levels to the LBVM920.
NOTE: The RF levels mentioned in this manual are analog channel levels, unless specified. For digital channels assume 6 dB less to that of
analog channels.
13.
The F-port labeled "RF" is the bi-directional RF input and output port for the LBVM920 optical node.
14.
There are separate forward output and reverse input -20 dB TPs labeled “FWD TP” and “REV TP” respectively. When not in use, please terminate these -20 dB
TPs with a 75 ohm terminator.
15.
When using the -20 dB TP to measure the RF input/output levels, make sure the RF port is terminated to 75 ohm. Please note the levels from -20 dB TP will be 20
dB lower than the RF port.
V (DC) on 1 mW/1V O.P. TP
DC Test Point of ONU
Optical Level (mW)
Optical Level (dBm)
OPT ON LED
Notes
0.25
0.25
-6
ON
Optical AGC
0.20
0.20
-7
0.16
0.16
-8
0.13
0.13
-9
OFF
No optical AGC
0.10
0.10
-10
< -10
Out of limit
