Simplex communication refers to the configuration such that only one person can communicate at a time. When a station is transmitting and receiving on the same frequency, the operator can either send or receive, but not both. For amateur radio, simplex communication means that a single frequency is used for both transmitting and receiving.

Transmitting and receiving on the same frequency is the simplest mode of communication, thus the term Simplex.

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CTCSS - Continuous Tone Coded Squelch System

Originally invented by Motorola and called Private Line (PL), the repeater access tones 'open' the squelch of the receiver. This allows different users to share a repeater without hearing other conversations, as the other tones will not 'open' their receiver. This technique is also known as subaudible and privacy codes/tones.

The use of CTCSS tones also prevents people from accidentally using a repeater unless they've properly programmed their radio specifically for a particular repeater. Yes, it makes the programming a little more complex, but it also ensures that repeaters remain as quiet as possible, since common radio noise and interference can't activate the repeater (remember, the repeater won't activate unless that CTCSS tone is present). This makes life much easier for all who might be monitoring a repeater, since it will remain quiet unless a human really does want to use it.

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Pay particular attention on this question. Many people answer this one incorrectly as either CTCSS or Tone Squelch, which are the same thing, or rather, CTCSS squelch and Tone Squelch actually are. They refer to the muting of receiver audio controlled by the presence or absence of a subaudible tone in the signal.

This question is asking specifically about muting of receiver audio (squelch) controlled solely by the presence or absense of an RF signal... meaning any RF signal, not just one with a special tone on it. That is called Carrier squelch, because it squelches the audio whenever a Carrier is not present.

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Many repeaters experience problems with picking up RF "noise" from nearby powerlines, buildings, other transmitters, etc. In order to avoid having the repeater retransmit this noise, various methods are used to be certain that only intentional and/or authorized signals are retransmitted.

1. The first method is to have the repeater only open its squelch and retransmit a signal that begins with a tone burst. This is also called Selective Calling, and is much more common in Europe than it is in America. SelCall tone bursts usually consist of 5 in-band DTMF audio tones at the beginning of the transmission.
2. The second method is to have the repeater use DCS (Digital Code Squelch). With DCS enabled the repeater will only open up if the signal contains specific DCS tone sequence, which most modern radios can be configured to output.
3. The third, and probably most common, method is to use a CTCSS (Continuous Tone-Coded Squelch System) subaudible tone; if the tone is not present, the repeater will not retransmit the signal.

If any of these features are in use on the repeater and you do not have your radio correctly configured, the repeater will simply ignore you.

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The amplitude of the modulating signal is converted to frequency variations of the FM (Frequency Modulation) signal. These variations are referred to as carrier deviation or deviation.

A question pool committee member has clarified that PM as used here refers to Phase Modulation

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Deviation for FM refers to the amount of frequency variation. As deviation increases, so does the variation of the frequency. An increase in deviation implies that the signal occupies more bandwidth..

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Frequency Modulation sends a voice signal by "modulating" the frequency -- in other words, it varies the frequency of the transmitted signal as the audio signal changes.

Louder noises require a larger variation in frequency, so if your mic gain is too high it can cause the variation to be large enough to interfere more with stations on frequencies close to yours.

High SWR would simply reduce your effective power output, which would actually be less likely to interfere since it wouldn't go as far. CTCSS tones only affect whether or not a station "listens" to you, so obviously neither of those options are relevant.

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No amateur radio operator has an absolute right to any amateur frequency. When you sign your license application, you're reminded of that and agree to it.

The Strongest or weakest signal or length of time on a frequency does not give you a greater claim to that frequency.

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Phone means voice. The phonetic alphabet is generally understood by operators in all countries, so using it enhances communication in identifying your station.

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Hams use all sorts of Q codes to convey quick messages. QRM means interference from other stations, QTH means location, QSL means 'a conversation', QSY means changing frequency or channel, etc.

In practical use, if you hear another ham say "I'm hearing a little QRM on your signal", it means there's interference from other station transmissions. They might also say "I hear some Q-R-Mary", which means the same thing.

The "M" in QRM means man-made interference, as opposed to the "N" in QRN, which means natural, or atmospheric, interference.

Q - Radio Messy

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This is one of the most commonly used Q Codes. QSY means to change frequency. For example:

"Please QSY to 147.34."
"Copy that, this is KD7BBC, QSY to 147.34"

Or

"Shall we QSY to 146.52 simplex?"

Here is a memory aid:

If you got Q uea SY about a frequency, you would change to a different one.

Or, (S)ee (Y)ou at a different frequency.

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As a general rule, repeaters are a valuable resource. If you can communicate directly with another station and don't need a repeater then you should often consider using simplex operation and keeping the repeater free for other use.

It is possible to go too far on this, of course -- repeaters are intended to be used and if nobody uses them nobody will know if they work. No special permission is ever needed to use simplex; third party traffic can be passed on any ham radio frequencies.

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Amateur radio operators have some portion of all amateur bands above 50 MHz where they are permitted to use SSB.

SSB is an abbreviation for Single Side Band, a type of amplitude modulation.

"Phone" means "voice."

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