additional ham notes

zk/Calling_CQ.md

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+---
+tags: [radio, ham-study]
+---
+
+The term "calling CQ" means making contact with other amateur radio operators.
+There is an established protocol for doing this. Below is the convention for 2m
+communications (VHF):
+
+1. Tune to the _calling frequency_ for the band. For VHF this is 145.500 MHz.
+2. Check that the calling frequency is not currently in use.
+3. If free, call for a specific call sign, or, for general contact call "CQ".
+4. Once you have found someone, find _another_ free frequency (not the CQ
+   frequency) and ask/check that it is not in use.
+5. If it is free, return to the calling frequency and direct your contact to the
+   new frequency.
+
+> Each of the main frequencies on the band plan will specify a "center of
+> activity". This is where to start listening of contacts for the frequency when
+> establishing CQ.

zk/Digital_voice_and_data_modes.md

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+---
+tags: [radio, ham-study]
+---
+
+Digital voice (DV) radios are the same as normal analog radio but the vocal
+sound wave is sampled and converted into digital information (bits) and
+transmitted in this format.
+
+This provides better audio quality for weak signals and transmits more
+efficiently than analog (i.e. using less bandwidth).
+
+There are various DV systems and generally they are not compatible with each
+other. (Examples include D-Star and C4FM).
+
+DV can only be used on certain frequencies so it is important to check the band
+plan.
+
+> DV radios often embed the call sign within the transmission. If using someone
+> else's equipment, or second-hand equipment, you need to make sure to reprogram
+> the call sign.
+
+"Data modes" means transmitting anything other than voice or CW via SSB, FM, AM.
+This is transmitted digitally like DV.
+
+21

zk/Repeaters.md

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+---
+tags: [radio, ham-study]
+---
+
+Repeaters exist in order to extend the range of mobile stations. They are
+designed to solve the line-of-sight problem associated with VHF/UHF, receiving
+your signal and re-transmitting it at much higher power, extending the range of
+low-powered portable devices.
+
+Repeaters **have an input and output frequency** so that they can receive and
+transmit at the same time. On VHF, repeaters typically transmit at 600KHz above
+their input (receiver) frequency. The difference between the transmitting and
+receiving frequency is known as the "offset".
+
+In order that the repeater can distinguish intentional communication from noise,
+it will use CTCSS tones. These are non-audible low-frequency tones that are
+transmitted along with your audio. The repeater will only activate if it "hears"
+the right tone. You have to program your radio to transmit the right CTCSS tone
+for the specific repeater. In the UK there are 9 blocks of tones.
+
+> It is important that you do not use the calling frequency of a repeater for
+> normal two-way communication (simplex). This would prevent people from using
+> the repeater. When you are agreeing on a shared frequency for CQ, ensure you
+> are not accidentally using a repeater frequency. The repeater frequency (and
+> its offsets) should only be used for repeater-relayed communication.

zk/Signal_reports.md

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+---
+tags: [radio, ham-study]
+---
+
+Signal reports are used for reporting on the quality of a given frequency.
+
+There are three values comprising **RST** (Readability, Signal, and Tone). Tone
+is only used for [CW](./Frequency_modulation.md). Each value is given its own
+score:
+
+| Signal value | Scores | Meaning                                                     |
+| ------------ | ------ | ----------------------------------------------------------- |
+| Readability  | 1,3,5  | Unreadable, readable with some difficulty, totally readable |
+| Signal       | 1,5,9  | Faint, fairly strong, very strong                           |
+| Tone         | 1,5,9  | Rough, some ripple. pure                                    |
+
+A very good signal report is therefore known as a "five and nine".