Advantech ABDNA-ER-DP551 handleiding
Handleiding
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To minimize the impact of the factors above, the following things need to be considered during the
development process:
▪ Minimize the distance between the radio and the location of the antenna. The coaxial cable
between the two impacts Transmit Power and Receive Sensitivity negatively.
▪ Minimize the locations where metal surfaces come into contact or are close to the location
of the antenna.
▪ Avoid locations where RF noise, close to or overlapping ISM bands, may occur. This
includes microwave ovens and wireless telephone systems in the 2.4GHz and 5.0GHz
frequency range. Mount the antenna as high on the equipment as possible.
▪ Locate the antenna where there is a minimum obstruction between the antenna and the
location of the access points. Typically, access points are located in the ceiling or high on
walls.
▪ Keep the main antenna’s polarization vertical, or in-line with the antenna of the access
points. 802.11 systems utilize vertical polarization and aligning both Transmit and Receive
antenna maximizes the link quality.
Even addressing all of the above factors does not guarantee a perfect connection. However, with
experimentation, an understanding of the best combination will help identify a preferred.
PERFORMANCE
Performance is difficult to define as the appropriate metric changes with each application or may indeed be a
combination of parameters and application requirements. The underlying characteristic that, in most cases,
needs to be observed is the link quality. This can be defined as the bandwidth available over which
communication between the two devices can be performed. The lower the link quality, the less likely the
devices can communicate.
Measurement of link quality can be made in several ways: Bit Error Rate (BER), Signal to Noise (SNR) ratio,
Signal Strength (SS), and may also include the addition of distortion. The link quality is used by the radio to
determine the link rate. Generally, as the link quality for a given link rate drops below a predefined limit, the
radio will drop to the next lowest link rate and try to communicate using it.
The reciprocal is also true. If the radio observes good link quality at one rate, it will try to move up to the next
rate to see if communication can be sustained using it. It is important to note that, for a given position, the
link quality improves as the link rate is reduced. This is because, as the link rate drops, the radio’s Transmit
Power and Receive Sensitivity improve.
From this it can be seen that looking at the link rate is an indirect way of assessing the quality of the link
between the device and an access point. You should strive to make the communication quality as good as
possible in order to support the best link rate. However, be careful not to over specify the link rate. Consider
your application’s bandwidth requirements and tailor your link rate to optimize the link quality. For example,
the link quality for a location at 6Mb/s is better than it would be for 54Mb/s. If the application only needs
2Mb/s of data throughput, the 6Mb/s rate would provide a better link quality.
Aside from the radio performance, there are a number of other things that contribute to the link quality.
These include items discussed earlier and choices made when looking at the overall antenna gain. The
antenna gain contributes to the Equivalent Isotropically Radiated Power (EIRP) of the system. This is part of
an overall measurement of the link quality called “link margin”.
Link Margin provides a measure of all the parts of the RF path that impact the ability of two systems to
communicate. The basic equation looks like this:
EIRP (dB) = TxP + TxA – TxC
Link Margin (dB) = EIRP – FPL + (RxS + RxA – RxC)
Where: TxP = Transmitter output power (dBm)
TxA = Transmitter antenna gain (dBi)
TxC = Transmitter to Antenna coax cable loss (dB)
FPL = Free Path Loss (dB)
RxS = Receiver receive sensitivity (dBm)
RxA = Receiver antenna gain (dBi)
RxC = Receiver to Antenna coax cable loss (dB)
This is a complex subject and requires more information than is presented here. Advantech recommends
reviewing the subject and evaluating any system at a basic level.
It is then possible, with a combination of the above items and an understanding of the application demands,
to achieve a link quality optimized for the application and host design. It is important to note that this is
established with a combination of hardware selection, design choices, and configuration of the radio.
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Productinformatie
| Merk | Advantech |
| Model | ABDNA-ER-DP551 |
| Categorie | Niet gecategoriseerd |
| Taal | Nederlands |
| Grootte | 15499 MB |
