Do you recognize this situation:
You designed a system which uses a Radio Frequency application, using one or more
between a transmitter and a receiver.
Examples: Garage door openers, Wireless door chimes, wireless headphones,
communication receivers, RFID tag systems, broadcast receivers, wireless
Are you sure that your receiver is only sensitive for the wanted signals?
The answer is: NO!
Each receiving system is not only sensitive for the wanted signals, but
also for unwanted
signals, even when these signals are present at completely different
This is an important quality issue of radio receiver specifications.
See this list of specifications which will influence the quality of the
Determines what's the lowest signal level which can be received
above the noise floor.
2. Selectivity (bandwidth). Represents the bandpass characteristic for the wanted signal.
3. Selectivity (image rejection). Applicable for superheterodyne
4. Selectivity (desensitization). Represents how large an
unwanted signal may be, before the
sensitivity for weak wanted signals becomes worse (blocking).
5. Selectivity (Intermodulation, crossmodulation). Represents
how large a combination of two or
more unwanted signals may be, before a weak wanted signal is
being interfered by these large unwanted signals.
6. Intermodulation free dynamic range. Is a quality figure which,
in combination with the applicated
distribution of gain and selectivity inside the receiver circuit, is a
property to distinguish the quality of different receiver circuits.
7. Whistles (birdies).
Are generated inside the receiver circuit, will make the receiver
insensitive or unusable at certain reception frequencies.
8. Harmonic mixing.
Causes reception of unwanted signals, related to harmonics of the
local oscillator frequencies.
9. Distribution of gain and selectivity. When this is done at a
wrong way, poor quality of the
receiver is the result. For each receiver design, an optimum for
this issue exists.