Afar AR24027, Руководство оператора

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AR24027 Operator’s Manual
2-4
The problem is that when you co-locate two or more radios they can become the source of self-
interference, even if they are set to non-overlapping channels. The reason for this is explained in the
following section.
2.3.2 Co-located radios self-interference
The self-interference situation is illustrated in Figure 2.1, that shows radio A transmitting on channel
f1 while a co-located radio is trying to receive on channel f2. Because the antennas are in close
proximity, antenna B will pick up a significant portion of the signal transmitted by radio A.
Figure 2.1also shows a block diagram of the radio front end circuitry. It includes an RF filter to reject
out of band signals, followed by a Low Noise Amplifier (LNA), a second RF filter, Mixer and finally
the Intermediate Frequency (IF) filter. Channel selection occurs at the Intermediate Frequency (IF),
where the narrow band IF filter blocks out the other channels. This means that if the interferer (radio
A) is in close proximity, and is transmitting while radio B is trying to receive, it may saturate the
LNA or the Mixer of radio B. This results in radio B making errors even when it is set to a different
channel than radio A.
Radio
A
Radio
B
f1
f2
RF
Filter
LNA
RF
Filter
IF
Filter
Local
Osc.
IF
(undesired coupling)
freq
f2 f1
freq
IF
Figure 2.1– Co-located radio interference
The traditional approaches to reduce this self-interference include:
•
Separate the antennas of the two radios further apart.
•
Use different antenna polarizations.
•
Lower the transmit power of the interfering radio.
These approaches are limited and, at most, may allow you to co-locate three of four radios. The Afar
PULSAR technology implements a synchronization scheme that completely eliminates this self-
interference allowing you to co-locate a much large number of radios. This is explained in the
following sections.