Radio specifications.

Antenna impedance
The impedance that the antenna you connect to the radio should be. For transmitters and transceivers, this is usually 50 Ohms. For receivers, such as broadcast radio and TV equipment, the usual is 75 Ohms.

Audio power
The maximum amount of power into the speaker, the manufacturer may also state the required speaker impedance.
Any speaker connected must have the same impedance, and must be able to take the power level without being damaged.

Adjacent channel rejection
How well the receiver can reject a signal on the channel above or below the one you are using.
For communications equipment, a reasonably good figure is 60dB. A figure of 50dB is common, but can lead to trouble blocking out other nearby signals which you are not tuned to.

Channels
Usually states how many channels are available on the radio. This may include details of the frequency range covered and how the frequencies are generated.
PLL Synthesized means that the radio creates the frequencies from just one reference crystal, rather than separate crystals being used for each channel.

Conversion system
This is the type of receiver used, with Superhet being the standard type used now. Some old communications equipment used single conversion Superhet, but dual conversion is now the usual standard.

Current drain
The amount of electrical current used by the radio. This information is useful when deciding what power supply to get for a mobile radio or what size fuse to fit.

Deviation
This applies to FM transmitters, and states how much your transmit frequency is shifted by your outgoing sound. The maximum level for any specific service is set by law.
With PM transmitters, this may refer to the level of phase shift, in degrees or Radians. As PM also causes frequency shift, deviation may be stated as for FM and stated as Frequency Deviation in KHz.

Dynamic range
A measure of how well the receiver handles signals of different strengths.
This could be quoted as a minimum and maximum signal, in which case a wider range is better. It could also be quoted as a single dB figure, in which case higher is better.

Emission
Method used to place your voice onto the radio signal. Types of emission include AM, FM and SSB.
These may also be stated by the use of standard emission classes, such as A3e and F3e.
Depending upon the service and your location, laws will state which types of emission may be used.

Frequency deviation
See Deviation, above.

Frequency range
Details of the upper and lower limit of frequencies covered by the radio.

Frequency response
How well the sound circuits respond to the different audio frequencies. This may apply to a transmitter or receiver. A wider range is usually better, although there is a limit to the range that humans will hear.
For transmitters, there will usually be a legal limit. This is necessary to limit bandwidth and reduce the chances of interference.

Frequency tolerance
This is the amount by which the radio may be off frequency. For transmitters and transceivers, the maximum tolerance is set by law and manufacturers must meet that standard.
This may be quoted as a percentage, but 'ppm' may be more practical. A lower figure is better.

IF
Intermediate Frequency (see Conversion system), the frequency which the 27MHz signal is converted down to. For a dual conversion superhet, there will be two intermediate frequencies. Common standards for communications equipment are around 10.7MHz and 455KHz.

IF rejection
How well the receiver can reject a signal on the intermediate frequency. A higher dB figure is better.

Image rejection
How well the receiver can reject a signal on the image frequency. A higher dB figure is better.

Low power
For transmitters and transceivers, this will refer to the RF output power when switched to 'low'.

Modes
Method used to place your voice onto the radio signal. Types of emission include AM, FM and SSB.
These may also be stated by the use of standard emission classes, such as A3e and F3e.
Depending upon the service and your location, laws will state which types of emission may be used.

Modulation modes
See modes, above.

Power source
Type and voltage of the supply required to run the radio.
Some radios may state "reversible ground" or "floating chassis". This means that the case of the radio is NOT connected to either positive or negative - it is floating.

RF power attenuator
See low power.

RF power output
This applies to transmitters and transceivers, and refers to the amount of radio frequency power transmitted. The maximum power is usually set by law, and will depend upon the service and country.

Selectivity
How well the radio can reject a signal at a set distance from the frequency you are tuned to. Higher dB figures are better.

Sensitivity
How well the receiver picks up weaker signals.
For FM radios, this will be measured as a signal level and how noisy that signal will be. The signal may be shown in dB or microvolts and the noise will usually be shown as a dB level compared to the level of the wanted sound (SINAD or, sometimes NQ).
As long as the two sets being compared use the same measurement (SINAD or NQ) and at the same level (20 or 10dB), then:
If the signal level is in -dB, higher is better. If the signal is in microvolts (µV), lower is better.

Spurious emissions
How much signal the radio is likely to transmit on frequencies outside of the band it is designed for. This is an issue regarding interference to other services, such as radio and TV.
The maximum figures for these are usually set by law, but lower levels are better.