- power
- The power of an electromagnetic wave is measured in watts. It can be
produced by a transmitter, or received by an antena. P = I
^{2}R where I is the current in the antena and R is the Impedance of the antena material. - Frequency Band
- Section of the radio spectrum in which channels are usually used for a similar purpose. Eg. 300 - 3000 Mhz is used for mobile phones.
- out of band transmitting
- The erroneous transmission of a signal outside the desired channel, created in the transmitting equipment.
- stability
- The property of a transmitter to transmit a signal that remains within the desired frequency channel.
- envelope (information) distortions
- distortions caused by the modulation process such that the signal
is not what we wanted it to be.
The envelope function of a rapidly varying signal is a smooth curve outlining its extremes in amplitude. There is a technique to predistort a signal so that the inherent distortion generated by the transmitter will be compensated for and thus the desired signal will be produced after tranmission. This is termed Envelope Feedback transmission.

- peak factor
- Also called Crest Factor, it is calculated from the peak amplitude of the waveform divided by the RMS (root mean squared) value of the waveform. It is useful in determining how much the wave form is being affected (distorted) by noise.
- power efficiency
- how much of the power source is usefully applied to the amplifier's (transmitter's) output.

- Frequency range
- the range of frequencies over which a receiver (or any system) is considered to provide a useful level of signal with acceptable distortion characteristics. Signals outside the range will be too distorted or faint to be useful.
- Impedance
- As an electro-magnetic wave travels through the different parts of the antenna and receiver system it may encounter differences electrical impedance in the medium. At each interface, depending on the difference in electrical impedance, some fraction of the wave's energy will reflect back to the source. Similar to optical refraction.
- Noise Figure
- How much noise the receiver introduces compared to an ideal receiver having the same impedance and same bandwith reception capacity. Measure in dB.
- Signal to Noise Ratio
- power of signal / power of noise. Both signal and noise power must be measured at the same or equivalent points in a system, and within the same system bandwidth. If the signal and the noise are measured across the same impedance, then the SNR can be obtained by calculating the square of the amplitude ratio.
- amplification
- process of increasing the power of a signal using an external energy source, ideally without introducing noise. The gain of an amplifier is the ratio of output to input power or amplitude, and is usually measured in decibels.
- dynamic range
- Output dynamic range is the range, usually given in dB, between the smallest and largest useful power or current output levels. The lowest useful level is limited by output noise, while the largest is limited most often by distortion. The ratio of these two is quoted as the amplifier dynamic range. More precisely, if S = maximal allowed signal power and N = noise power, the dynamic range DR is DR = (S + N ) /N More generally, DR is the measurement of the ratio between the strongest un-distorted signal on a channel and the minimum discernable signal, which for most purposes is the noise level. SNR measures the ratio between an arbitrary signal level (not necessarily the most powerful signal possible) and noise. Measuring signal-to-noise ratios requires the selection of a representative or reference signal. In audio engineering, the reference signal is usually a sine wave at a standardized nominal or alignment level, such as 1 kHz at +4 dBu (1.228 VRMS).
- bandwidth
- range of frequencies that a reciever is designed to accept or an amplifier is designed to give satisfactory output for. It is a set of channels.
- adjacent frequency rejection
- a goal of filter building is to block out neighboring signals to the desired signal. For example you might want to reject neighboring signals at a rate of 30-40 dB and to reject alternate channels at the rate of 60 dB.
- spurious channels
- aliasing occurs when the sample rate is slower than the Nyquist rate for the input. When this occurs undesired or spurious signals will be accepted. An anti-aliasing filter should be used to remove any frequencies out of the acceptable nyquist rate determined by the sample rate. I.e. the input to an ADC must be low-pass filtered to remove frequencies above half the sampling rate.
- Image Rejection
- In a heterodyne receiver, a received signal is added to or subtracted from a LO frequency. If this reaches the IF (intermediate frequency)it is accepted by the receiver. Mathematically, there are two RF which can produce the IF. The one of these two which is not desired is the image. It must be rejected by the receiver. See Image response
- Cross modulation
- The first transistor (before the filter) receives all signals and can
be affected by them all. A stong (undesired) signal can affect the hardware
of the machine (circuits) such that that signal appears in a different frequency range and can thereby get past the filter.
in a high frequency amplifier, because of non-linear gain, errors are caused. Modulation of one frequency may bring it into the range of another frequency.

- blocking effect
- Radio waves can be blocked by physical objects like mountains.
- AM Suppression
- In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency,
containing power as a result of the modulation process. The sidebands consist of all the Fourier components
of the modulated signal except the carrier (baseband). All forms of modulation produce sidebands. In some forms of AM,
the carrier may be removed, producing double sideband with suppressed carrier (DSB-SC). An example is the stereophonic difference
(L-R) information transmitted in stereo FM broadcasting. The carrier may be regenerated directly from the sidebands by a
Costas loop or squaring loop. This is common in digital transmission systems such as BPSK where the signal is continually present.

See Sideband - Total Harmonic Distortion
- In a receiver or transmitter, a measurement of the harmonic
distortion present and is defined as the ratio of the sum of the
powers of all harmonic
components to the power of the fundamental frequency.
It is virtually impossible to measure since many harmonics are out of the frequency range and are filtered out.
THD is used to characterize the power quality of electric power systems. When a signal passes through a non-ideal, non-linear device, additional content is added at the harmonics of the original frequencies. THD is a measurement of the extent of that distortion. When the input is a pure sine wave, the measurement is most commonly the ratio of the sum of the powers of all higher harmonic frequencies to the power at the first harmonic, or fundamental, frequency.

- Intermodulation
- Since THD cannot be accurately determined, engineers can determine the distortion inherent in a transmitter or receiver by sending two close signals. If the output differential of the two siganls is equal to the input differential (impossible) then you have no noise. Any variance from the expected ideal output is therefore noise. This method of determining machine noise is called intermodulation. See also Intermodulation
- Subjective sound quality
- a Person may feel the sound is better on a theoretically worse receiver. This is because the distortions can actually improve the subjective sound quality. After you manufacture some equipment, give it to people to listen to.
- heterodyne radiation
- The receiver itself may produce electromagnetic radiation which distorts the received signal.

- Δf * Δt = 1
- a filter needs more time to accurately measure small changes in frequency. As the difference in frequency become smaller, you need more time to detect it in a filter.
- I - Q modulation
- You make a graph where one axis is Q and the other is I (I is for imaginery number). Now I and Q represent Phase and Amplitude. Then you can chart out different symbols that you can send. When computing the Ber for schemes other than 4QAM, you need a longer vector to maintain the same distance betewwn points. YOu can compute that geometrically.
- Sound Signal FFT (slide 31)
- If you sampled a signal and you don't have enough density in the frequency domain, how can you increase your density? You can take a longer sampling time. This will increase your frequency density after FFT. (Alternatively, Nachum says you could increase the sample rate. But assuming that is not practical, that you would have to increase teh time of the sampling.)
- Symbol Rate
- The number of symbol changes (waveform changes or signalling events) made to the transmission medium per second using a digitally
modulated signal, measured in baud (Bd) or symbols per second. The sending device places symbols on the channel at a fixed and known
symbol rate, and the receiving device has the job of detecting the sequence of symbols in order to reconstruct the transmitted data.
The symbol duration time T
_{s}can be calculated as:T

where f_{s}= 1/ f_{s}_{s}is the symbol rate. See Symbol rate - Gross bit rate
- If N bits are conveyed per symbol, and the gross bit rate is R, inclusive of channel coding overhead,
the symbol rate can be calculated as:
f

_{s}= R / Nor put more logically, the gross bit rate, R = f

_{s}* NNow, let's define M as the maximum number of distinct messages passable per T

_{s}. M is also called the alphabet since it represents all the different frequencies we might need to send.It turns out that M = 2

^{N}. For example, if our baud rate is 1000 and N is 3 then our gross bit rate is 3000 and our alphabet of frequencies (M) is 8. Furthermore, in a 64QAM modem, M=64.By taking information per pulse N in bit/pulse to be the base-2-logarithm of the number of distinct messages M that could be sent, Hartley constructed a measure of the gross bitrate R as:

R = f

where fs is the baud rate in symbols/second or pulses/second. M becomes important because it determines the S/N ratio required. The larger our alphabet becomes within a finite channel, the harder it becomes to distinguish between out alphabet letters._{s}log_{2}( M ) - Quantization Noise
- Quadrature amplitude modulation
- see QAM
- Shannon Hartley Theorem
- See Hartley Theorem
- frequency
- See frequency and frequency range