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Repeater CTCSS Setup

posted Sep 1, 2015, 11:58 AM by Mills County Amateur Radio Club   [ updated Oct 26, 2016, 11:17 AM ]


Don Steinbach, AE6PM, has a website with many useful tutorials for the beginner in ham radio. The following is his explanation of duplex, simplex, and CTCSS (tone squelch).

Duplex, Simplex, and CTCSS (Tone Squelch)

Duplex

Our Saratoga weekly net is normally conducted using the K6SA repeater.  You’ll recall that a repeater receives and transmits at the same time.  It can’t possibly receive and transmit simultaneously on the same frequency, so we use an operating mode known as duplex.  When operating duplex, you are listening on the repeater output frequency and transmitting on the repeater input frequency.  Your handheld transceiver or your base station is normally configured to operate this way.  The difference between the two frequencies is called the offset and is either positive (+) or negative (-) depending on where you are in the particular amateur radio frequency band.  If you have a radio less than 10 years old, it will figure out the offset and direction for you and you don’t need to be concerned with the details although you can take over manually at any time.  For the K6SA two-meter repeater, you will be listening on 146.655 MHz and when you transmit you will be on 146.055 MHz.  Here, the offset is 600 kHz (0.600 MHz) and the offset is negative (-).

Simplex

When operating without a repeater, we typically use a mode known as simplex. When operating simplex, you transmit and receive on the same frequency.   Unlike the repeater, you are never receiving and transmitting at the same time. 

Here in Saratoga, our emergency communication planning is that we use simplex if the K6SA repeater fails or is otherwise unavailable.  When we switch to simplex we intend to transmit and receive on the K6SA two-meter repeater output frequency of 146.655 MHz.  We could pick a different frequency for simplex operation, but just staying on the K6SA repeater output frequency eliminates reprogramming your radio to a different frequency, thus there is one less change to deal with.  You simply take your radio out of ‘repeater’ mode or set the offset to ‘none’.  See the notes at the end of this dissertation.

CTCSS (Tone Squelch)

Aside from telling the radio to operate duplex or simplex, There’s another setting that needs to be programmed and that’s called ‘Tone squelch’ or ‘CTCSS’ or ‘PL’.  These terms are used loosely and interchangeably to refer to the same thing.  CTCSS stands for Continuous Tone-Coded Squelch System and is the correct international term for all systems using 67.0 to 254.1 Hz sub-audible signaling.  PL stands for Private Line, a Motorola trademarked term.

Tone squelch is implemented by sending a low-frequency audio tone along with your voice when you transmit.  At the receiving end, the radio remains silent (squelched) unless the transmitted audio tone matches what the receiver is expecting.

The use of tone squelch is optional. Businesses and public agencies often use tone squelch so that several users can share the same radio frequency without having to listen to chatter from other users on the same frequency since each group of users would use a different tone frequency.  Ham radio uses tone squelch somewhat differently.  Ham radio repeater owners coordinate among themselves so that multiple repeaters are not assigned to the same local radio frequency. However, unwanted signals from distant stations may occasionally be received, or interference from local sources may be received, and tone squelch provides a means of silencing the audio from these unintended interferors.  Note that tone squelch does not eliminate the radio frequency interference; it only suppresses the audio output (in the case of your radio) or prevents the local repeater from keying up and rebroadcasting the interfering signal.

The tone squelch concept is simple, but the programming can be confusing.  Setting up your radio to use tone squelch involves just two actions: (1) setting the tone squelch  mode and (2) setting the tone squelch frequency

There are only three possible tone squelch modes:

(1)   OFF:   The tone squelch feature is not used.

(2)   CTCSS Encode:   The tone will always be transmitted by your radio.  Although not obvious, it also means that your radio doesn’t care if it receives a tone or not.

 (3) CTCSS Encode/Decode:   The tone will always be transmitted by your radio and your radio expects to receive a tone and will ignore (squelch) any received signal that does not include the tone.

There are 54 possible tone squelch frequencies.  Not all frequencies are available on every radio, but there are usually 30+ to 50 available.  Your equipment manual will have a table if you’re really interested. The transmitter and receiver must both use the same tone frequency in order for tone squelch to work.  The tone frequency for the Saratoga K6SA 2–meter repeater on 146.655 MHz is 114.8 Hz.

In order to use the repeater, either CTCSS Encode or CTCSS Encode/Decode must be selected because the repeater requires that the tone be present (encoded) on your transmitted signal. OFF is not usually a viable option when using a repeater. If CTCSS Encode/Decode is selected then your radio also requires that the tone be present on the signal that it receives.  Be aware that if you are using CTCSS Encode/Decode you will not hear someone trying to contact you that is not using CTCSS Encode or CTCSS Encode/Decode as well, because your radio will not respond to a signal that does not have the tone encoded.

CTCSS Encode is my preference since you will be able to hear anyone trying to contact you regardless of how they are configured (OFF, CTCSS Encode, CTCSS Encode/Decode) because your radio doesn’t care if there is a tone encoded on the received signal or not.   You will still be able to use the repeater in duplex mode since the tone will always be encoded on your transmitted signal.  Also, anyone else will hear you in simplex mode regardless of whether they are expecting the tone or not.

You can use CTCSS Encode/Decode if you are experiencing annoying interference from some distant repeater or even from some local source such as your computer or your household local area network.  Weigh this against the possibility of not hearing someone trying to contact you because they aren’t transmitting the tone your radio is expecting. 

Notes

1.     For the Yaesu FT-60, press and release the FW key, then the 4/RPT key.  Rotate the tuning knob.  You’ll see RPT. -, RPT. + or RPT.OFF.  Leave the setting at RPT.OFF and press the FW key again.

2.     For the Yaesu (Vertex) VX-150, press and release the F key then the 4/RPT key.  Rotate the tuning knob.  You’ll see –RPT, +RPT or SIMP.  Leave the setting at SIMP and press the F key again.

3.     For the Kenwood TM-V71A, press the F key then the REV key.  A + or – or nothing will appear in the display.  Repeat the key presses until the + or – disappears.