9
10.0 Reverse Path Set-up:
LBN200 RFoG ONU
User Manual
1.
The LBN200 reverse input is designed to have a wide dynamic range to accommodate most
system design levels. Your design input should be matched to align with the optimum operating
point for the node, and it can be adjusted with the controls available in the reverse path.
2.
The Total RF return level at the LBN200
NODE
INPUT
should be 20 to 40dBmV
for NPR≥38dB.
See Figure 8. The default configuration of the node (ATT3/4=2dB, ATT5=10dB, EQ2=0dB, 2-
port). The node input level can be checked at the RETURN TEST1 or RETURN TEST2 test
points adjacent to ATT3/4. See Figure 10.
3.
For ANY configuration of the node the optimum
LASER INPUT
should be 40-60dBmV. This
level can be checked at the RETURN TEST 3 test point following ATT5.
4.
If operating with a total node input of 35-40dBmV (total laser input of 55-60dBmV) then the
ATT3/4 attenuators should be changed from 2dB to 7-10dB in order to keep the operating point
to the left of the NPR peak and well way from the down slope of the curve (Figure 9).
5.
When the node is first powered switch the Laser Mode switch to “NORMAL”. This will set the
laser to continuous-on mode and will let you measure its output level at the laser output test
point. Measure and verify the power in mW
(1Vdc=1mW) then switch back to “BURST” mode if
you are setting up an RFoG system. If the RFoG system is already in operation then skip this
step since NORMAL mode will cause laser collisions.
6.
On a default configured node, and with no RF signal present at the RF inputs you can verify the
RF signal path within the node. Using a portable RF signal generator inject a +40dBmV CW
return carrier into one of the external forward RF test points. Then measure the level at the
RETURN TEST3 test point (laser input). It should be 20dBmV at the test point, indicating
40dBmV at the laser input. And the laser LED should be on.
7.
When measuring levels at the test points please remember to allow for the test point loss of
20dB. When Return verification and set up is completed make sure the Laser Mode switch is
set to “BURST” for RFoG operation.
Hints:
-
For optimum operation plan to apply a total RF input level that is 2 to 4dB to the left of the peak
on the NPR vs. Input Level curve (Fig 8). This is the “operating point”. Doing so will allow
variations in the composite input power while at the same time it positions the total level safely
below the clipping region and above the thermal noise.
-
Take an account of all the upstream services going into both ports of the LBN200 so that the total
lands at the Operating Point. The following equation can be used for the calculation:
Operating Point (dBmV) = 10Log(10
(S1/10)
+ 10
(S2/10)
+ …. + 10
(Sn/10)
)
(Where: S1, S2, … Sn are the dBmV levels of each upstream service)
- To help with this calculation, or to set the levels based on an equal power per Hertz basis,
www.lindsaybroadbandinc.com
Resources Tab
for a spreadsheet calculator.
LBN200 April 2013_rev1
