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MX165C

Low Voltage CTCSS Encoder/Decoder with TX/RX Filters

MX-COM Inc  

Low Voltage CTCSS Encoder/Decoder

7

General Description

MX165C

Description

Voice on shared radio channels are multiplexed with a subaudible CTCSS (Continuous Tone Controlled Subaudible

Squelch) tone as a means of directing messages among user groups sharing the same RF frequencies. CTCSS

modulates the transmitter with a discrete tone, from 39 standard CTCSS tones in the range (67.0Hz to 250.0Hz)

according to TIA/EIA-603. There are an additional eight CTCSS tones not specified in TIA/EIA-603 that the MX165C will

encode and decode. They are : 159.8Hz, 183.5Hz, 189.9Hz, 196.6Hz, 199.5Hz, 206.5Hz, 229.1Hz, and 254.1Hz, for a

total of 47 CTCSS tones plus Notone.

The MX165C also incorporates TX/RX on chip speech filters. In early CTCSS designs, TX speech was not filtered from

the CTCSS tone, rather the filtering was dependent upon the host transmitter’s pre-emphasis network. At only

6dB/octave, the attenuation of speech components at higher CTCSS tones was only a few dB which resulted in talk-off

(low frequency voice components unsquelching the receiver audio).

I/O Conditions

D0-D5

Input Pins Condition

RX / TX

PTL

Decode Comparator In

Output Pins Condition

RX TONE DETECT

RX TONE DECODE

Result / Function

Tone Transmitter Enabled

TX Audio Path Enabled

Tone Decode Enabled

RX Audio Path Enabled

Notes

Tone

0

0

X

0

1

Yes

Yes

No

No (Bias)

1

No Tone

0

X

X

0

1

No (Bias)

Yes

No

No (Bias)

2

Tone

1

0

0

0

1

No (Bias)

No

Yes

No (Bias)

3

Tone

1

1

0

0

1

No (Bias)

No

Yes

Yes

4

Tone

1

X

1

1

0

No (Bias)

No

Yes

Yes

5

No Tone

1

X

X

X

0

No (Bias)

No

Yes

Yes

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Notes:

1. Normal tone transmit condition.

2. Notone programmed in TX mode, tone transmit output set to VDD/2. TX audio path enabled.

3. Normal decode standby.

4. Normal decode standby with PTL used to enable audio.

5. Normal decode of correct CTCSS tone condition, PTL has no effect.

6. Notone programmed in RX mode, tone transmit output (Bias). RX audio path enabled.

7. X = don’t care

Table 3: Combinations of Input / Output conditions

© 1997 MX•COM Inc.

www.mxcom.com Tele: 800 638-5577 910 744-5050 Fax: 910 744-5054

Doc. # 20480102.008

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

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