www.RFM.com
Technical s1.678.684.2000
Page 23 of 82
©2009 by RF Monolithics, Inc.
E-mail:
DNT2400 - 08/18/09
frequencies, because of their close proximity, the transmitting base can reduce the receiving base’s ability
to hear distant remotes. The EX_SYNC input has the following characteristics:
1. Base radios trigger on the rising edge of the pulse applied to their EX_SYNC input.
2. All co-located bases must use the same hop duration and the period of the pulse train applied to
the EX_SYNC input must be within ±10 µs of this hop duration.
3. The co-located bases must use different network IDs but the same frequency subband, which as-
sures they are using different hopping patterns.
4. A
“narrow” pulse of 50 to 800 µs triggers base beacon synchronization. A train of narrow pulses
as described above will synchronize a group of co-located base stations after a period of time.
5. An
optional
“wide” pulse of 1 to 2 ms triggers a hopping pattern reset. Note: a wide pulse
can only be used in ETSI applications. It is not allowed under FCC and Canadian IC
regulations. The benefit provided by the wide pulse is to keep co-located networks from ever be-
ing on the same frequency at the same time. When the wide pulse is not used, it is possible that
co-located networks may occasionally try to transmit on the same frequency at the same time.
This can slightly reduce the network throughput. Where a wide pulse can be used, it should be
sent to reset all base patterns to their first frequency following the reset or power-up of any of the
co-located bases. Thereafter a cycle of N -1 narrow pulses and then 1 wide pulse should be sent,
where N is the number of frequencies in the subband being used. For example, if the frequency
subband contains 15 frequencies, a repeating cycle containing 1 wide pulse followed by 14 nar-
row pulses should be used.
