Avitec AB FD-3100A ユーザーズマニュアル
and the contribution to the
RF loss is 0.8 dB. In a real
installation, two optical
connectors will add
approximately 0.5 dB of
optical loss.
The laser and, to a much
lesser degree, the
photodiode, add noise and
distortion to the RF signal.
This RF performance is
characterized just as any
RF link in terms of dB loss,
noise figure, third order
intercept, etc.
The fiber path itself can
contribute noise and
distortion. In the
FiberDAS, the laser used is
a Fabry-Perot (FP) laser
instead of a Distributed Feedback (DFB). The DFB has a single spectral component. The FP laser has
multiple spectral components which can contribute noise and distortion for longer fiber runs. For the
distances used in the FiberDAS, this effect is not significant. Also, optical backscattering back into the
laser from less than perfect connections can cause additional noise and distortion. The FP lasers used in the
FiberDAS are much less sensitive to this than are DFB lasers. DFB lasers are also considerably more
expensive. However, if optical reflections are severe enough from a bad connection, the resulting optical
reflection may cause performance degradation even with FP lasers. To minimize this, SC/UPC optical
connectors with a return loss > 50 dB are used. Following standard practices in cleaning of the removable
optical connectors (see procedure outlined below) will keep the connections in spec and will avoid the
problems of performance degradation.
RF loss is 0.8 dB. In a real
installation, two optical
connectors will add
approximately 0.5 dB of
optical loss.
The laser and, to a much
lesser degree, the
photodiode, add noise and
distortion to the RF signal.
This RF performance is
characterized just as any
RF link in terms of dB loss,
noise figure, third order
intercept, etc.
The fiber path itself can
contribute noise and
distortion. In the
FiberDAS, the laser used is
a Fabry-Perot (FP) laser
instead of a Distributed Feedback (DFB). The DFB has a single spectral component. The FP laser has
multiple spectral components which can contribute noise and distortion for longer fiber runs. For the
distances used in the FiberDAS, this effect is not significant. Also, optical backscattering back into the
laser from less than perfect connections can cause additional noise and distortion. The FP lasers used in the
FiberDAS are much less sensitive to this than are DFB lasers. DFB lasers are also considerably more
expensive. However, if optical reflections are severe enough from a bad connection, the resulting optical
reflection may cause performance degradation even with FP lasers. To minimize this, SC/UPC optical
connectors with a return loss > 50 dB are used. Following standard practices in cleaning of the removable
optical connectors (see procedure outlined below) will keep the connections in spec and will avoid the
problems of performance degradation.
I
bias
I (mA)
I (mA)
P (
m
W
)
out
I
th
RF
Input
Input
RF
Output (ac coupled
to remove dc component)
Output (ac coupled
to remove dc component)
Optical
Output
Output
Optical
Input
Input
P (
m
W
)
in
LASER DIODE
CHARACTERISTIC
PHOTODIODE
CHARACTERISTIC
Figure 1-1. Laser and photodiode characteristics.
1.2.2 Functional Description
The FiberDAS Fiberoptic Antenna System connects to the mobile coverage RF ports of a repeater or base
station as an extended coverage antenna. The Hub Shelf mounts in a standard 19 inch rack close to the
repeater or base station transmit and receive RF ports. Generally, the appropriate configuration of the Entry
Shelf is used for convenience in combining multiple BTS channels, duplexing the signals to separate
Transmit and Receive, combining, setting the proper RF levels and routing the combined Tx and Rx
signals to and from one or more Hub Shelves, as necessary. The Hub Shelf RF connections are made via
the RF connectors on the rear panel. Inside the chassis, the transmit signal is split and routed to the Hub
Transceiver Plug-Ins. Each plug-in is a dual fiberoptic transceiver. The Hub Shelf holds up to eight plug-
ins. Each plug-in interfaces with up to two Remote Transceivers by way of fiberoptic connections on the
Hub Shelf rear panel.
Transceiver optical output is the green connector. The Remote Transceiver units are generally mounted
above the false ceiling on a bulkhead or post. Each Remote Transceiver is connected to an indoor coverage
antenna by way of a customer-supplied flexible RF cable. Some indoor antennas are available with flexible
RF cable pigtails and an SMA connector termination. These units are distributed throughout the building or
campus as necessary to get full coverage. After installation, the transmit power from each Antenna Unit
may be adjusted manually by way of a rotary dip switch on the unit. This switch is indented in 2 dB steps.
This is a one time adjustment. For dual band units, there is a separate adjustment for each band.
1-3