Here's a post that's mostly for my own studies, but I hope others will find it useful. Today's topic is basic operation of a transmitter and receiver.
A
dual-band transceiver works on the 2-meter and 70-cm bands. A
multi-band transceiver works on higher HF bands. In either case, the first thing the operator does is to select the band over which he is to transmitter or receive. From inside the band, the operator uses the
variable frequency oscillator (VFO) to select the frequency. The
tuning rate may be adjustable on a radio so that discreet movements in the VFO change the frequency more or less quickly. Some radios have a keypad to punch in the desired frequency.
On multi-mode radios, the operator must also select the
signal mode - AM, SSB, USB, LSB, FM, CW, Data. Most wideband rigs are
multi-mode.
Memories or
memory channels allow the operator to store settings for later use. These settings include frequency and mode but may also include power level and access tones.
The
RF power control changes the maximum transmitter output power. Some handhelds include a set of fixed levels for recall. The
microphone gain control also affects transmitter output though adjusting the sensitivity of the microphone. Frequency or amplitude can be
overmodulated to cause distortion in the signal.
The
speech compressor or
speech processor raises the low levels of transmit signal more than the strong parts. This makes for a more uniform waveform that improves reception. Too much compression can cause distortion or loss of interference.
Peak envelope power (PEP) measures the loudest that speech gets on an AM or SSB signal.
A
dummy load absorbs all the energy from a station so that adjustments can be made to the radio without actually broadcasting.
A transmitter only transmits if it is keyed through a
push-to-talk (PTT) or
voice-operated transmission (VOX) function. Since VOX automatically keys the transmitter, several controls are available to adjust the level of sensitivity --
gain,
delay,
anti-vox.
Overmodulation can cause distortion or
spurious outputs on adjacent frequencies. In general, this is called
splattering. Speaking softly often reduces overmodulation.
Automatic level control (ALC) automatically reduces power output when a certain output power limit is reached.
The
AF gain is the volume control on a receiver. The
RF gain on an HF rig controls the sensitivity of the receiver. The
squelch circuit mutes the audio if no signal is present so that you're not listening to static.
Band-pass filters allow the receiver to only listen to certain frequencies. A
notch filter removes a narrow range of frequencies.
Noise blankers remove sharp noises and mute them.
Noise limiters attenuate the sound so you don't get blasted with sound if lightning strikes and other spikes.
S-units measure the signal strength and is measures from S-1 to S-9.
Sweeping looks through presets for activity.
Scanning jumps through frequencies.
Repeaters have a standard
offset (or
shift) between output and input frequencies. This means you only have to remember the output frequency to know what the input frequency is. Offsets can be positive or negative for 2-m and 70-cm bands. Repeaters are referenced by their output frequency.
Repeaters also have
access tones that tell it that the signal needs to be retransmitted. These tones are called
continuous tone coded squelch system (CTCSS),
private line (PL), or
subaudible. GMRS and FRS radios have the same thing called
privacy codes. Radios have
tone keys that automatically send the CTCSS tones when the mic is keyed.
Data conversion can often be done with software and a sound card, though some sort of radio control interface is required for the computer. An
Internet gateway connects the radio network to the Internet. No money-making over the radio network; this includes ads on webpages!
