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NPX138N Series Panel Mount FM Transceiver
SM41 Installation and Operation Manual
Section 3 Rev: 1.00
Issue 4
Page 3-14
ENG-FORM: 806-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
3.11.3
Turning Tones On and Off
The NPX138N radio also has the capability to have tones enabled or disabled globally. By editing the
TONES status line, the operator can set all the tones ON, OFF or to TX ONLY.
TONES=ON enables all the tones programmed into the individual channels. (Remember that some
channels may have no tones programmed.) Both the frequency and tone of incoming signals must be
correct to hear the receive audio. If the incoming frequency is correct, but the incoming tone does not
match the tone set in the radio, the radio will not produce any audio. The RX indicator lights whether the
logic is correct for audio or not, to warn the operator that the channel is active with radio traffic of some
kind.
TONES=OFF disables all tones. The radio will still display the individual tones on the RX and TX channel
display lines, but only for reference purposes. All incoming transmissions on the RX frequency will be
heard.
TONES=TX ONLY enables all transmit tones but disables all receive tones. This is used on U.S. Forest
Service contracts, for example, where the tones are needed only to open the repeater and serve no RX
squelch function.
3.12
Scanning{tc "1.4.10
Scanning"}
3.12.1
General
Scanning is an automatic internal function that rapidly samples a selected group of channels. It is very
useful for checking radio traffic on one or more channels, while still working a ‘home’ or monitor channel.
When scanning is active, the radio ignores all CTCSS/Sub-audible Tones. It does not test for these
conditions when determining whether or not to lock on to a channel (although tones do remain active for
squelch control). This is because the delay to test for tones is so long (compared to the channel lock-up
time), that it would seriously compromise scanning. It takes almost half a second to provide tone
decoding, which would result in virtually useless scanning of 2 channels per second.
The radio will stop on any flagged channel that has a correct RF signal present, but there may be no
audible signal if the tones do not match those set in the radio. To avoid any confusion, set tones to OFF
(via the status edit mode) during scanning so that all channels will be audible.
In order to be detected properly, a signal needs to be slightly stronger when the radio is scanning than
when the radio is in ‘Normal’ operating mode.
The document reference is online, please check the correspondence between the online documentation and the printed version.