Service manual

Service Manual SD170E Series

Page 15 of 44

Sub-audio squelch system

The SD-170E Series can operate singly or with optional modem boards. Even if user wants to use

sub-audio SQ system, the radio will permit this SQ option according to some cases to avoid

confliction between sub-audio and data.

Contrary to general-purpose two-way radio, the input of the radio is data or audio. In case of

audio, its frequency spectra are limited to 300 ㎐ ∼ 3 ㎑ by internal BPF. So, the division of this

and sub-audio is possible on the frequency spectra because sub-audio has under 300 ㎐

frequency. But, Data has wide frequency spectra compared with audio. Normally, that has 30 ㎐ ∼

4.8 ㎑ frequency (except harmonic freq.) at 9600 baud rate. Accordingly, the conflict of sub-audio

and data are inevitable and so broken data or SQ error is unavoidable. To solve this problem, the

radios can use the FFSK modulation which converts data into two different continuous audio tone

according to their logic levels. Therefore, available cases of sub-audio SQ system are Audio and

FFSK signal. But, it‟s not permitted to FSK (FM direct modulation of data) and GMSK signal.

Note: SD-170E Series provides the connection of external modems to receive and

transmit external modulated data which can be inputted and outputted through

pin 1 and 2 of DB-15 connector, respectively. In this case, the external signals

are referenced to ground and may be A.C. or D.C. coupled depending on the

user requirement. Especially, if the type of external modem is AFSK or FFSK,

Sub-audio Squelch (SQ) System can be applied by dealer programming. For

reference, its related parameter is “TX Tone Generation for Data Input” of “TX

option” group on the “System Option / GPS” tap window of ACC-916E.