Tektronix 1L30 Instruction Manual page 9

Phase lock— The frequency synchronization of the local
oscillator with a stable reference frequency.
Resolution— The a b ility of the spectrum analyzer to re­
solve and display adjacent signal frequencies. The measure
of resolution is. the frequency separation (in Hz) of two
equal amplitude signals, the displays of which merge at the
3 dB-down point. The resolution of a given display depends
on three factors; sweep speed, dispersion and the bandwidth
of the most selective, (usually last IF) amplifier..
Resolution bandwidth— The — 6 dB bandwidth (with Gaus­
sian response) of the analyzer, with the dispersion and sweep
time adjusted for the minimum displayed bandwidth of the
C W signal. Resolution and resolution bandwidth become
synonymous at very long sweep times.
Optimum Resolution— The best resolution obtainable for a
given dispersion and a given sweep time. Theoretically or
mathematically:
Optimum resolution —
Optimum resolution bandwidth— The bandwidth at which
best resolution is obtained for a given dispersion and sweep
time. Theoretically and mathematically:
0.66
ution bandwidth
Sweep time (in seconds)
Safe power level— The upper level of input power that the
spectrum analyzer can accommodate v^ithout physical dam­
age (usually in units of dBm).
Scanning velocity— Product
repetition rate (units of H z/unit time).
Sensitivity— Rating factor of spectrum analyzers' ability
to display signals.
1. Signal equals noise: That input signal level (usually
in dBm) required to produce a display in which the sig­
nal level above the residual noise is equal to the residual
noise level above the baseline.
noise = twice noise.
2. Minimum discernible signal: That input signal
(usually in dBm) required to produce a display in which the
signal is just visible within the noise.
Skirt selectivity— A measure of the resolution capability
of the spectrum analyzer when displaying signals of un­
equal amplitude. A unit of measure'(usually in dB) is the
bandwidth at some level below the 6dB down points. For
example 10 dB, 20 dB or 40 dB down.
Spurious response (spurri, spur)— An
or signal which does not conform to the indicated fre­
quency or dial reading. Spurri and spur are the collo-
quiaisms used to mean spurious responses (plural) or spurious
response (singular) respectively.
the following type:
1. IF feedthrough— Signal frequencies within the IF pass-
band of the spectrum analyzer that are not converted in
the first mixer but pass through the IF amplifier and pro­
duce displays on the CRT that are not tunable with the RF
center frequency controls.
2. Image response— The superheterodyne process results
in two major IF responses, separated from each other by
©
Dispersion (in Hz)
Sweep time (in seconds)
Optimum resol­
Dispersion (in Hz)
o f dispersion and sweep
Expressed as: Signal +
level
erroneous display
Spurious responses are of
O p eratin g Instructions— Type
twice the IF. The spectrum analyzer is usually calibrated to
only one of these two responses. The other is called the
image.
3. Harmonic conversion— The spectrum analyzer will re­
spond to signals that mix with harmonics of the local oscil­
lator and produce the intermediate frequency.
trum analyzers have dials calibrated for some of these higher
order conversions. The uncalibrated conversions are spurious
responses.
4. Intermodulation— In the case of more than one input
signal, the myriad of combinations of the sums and differ­
ences of these signals between themselves and their multiples,
creates extraneous response known as intermodulation. The
most harmful intermodulation is third order, caused by the
second harmonic of one signal combining with the funda­
mental of another.
5. Video detection— The first mixer will act as a video
detector if sufficient input signal is applied. A narrow pulse
may have sufficient energy at the intermediate frequency to
show up as intermediate frequency feedthrough.
6. Internal— A spurious response on the display .caused
by a signal generated within the spectrum analyzer that is in
no way connected with an external signal.
7. Anomalous IF responses— The filter characteristic of the
resolution-determining amplifier may exhibit extraneous pass-
bands. This results in extraneous spectrum analyzer re­
sponses when a signal is being analyzed.
8. Zero frequency feedthrough— (zero pip)— The response
produced when the first local oscillator frequency is within
the IF passband. This corresponds to Zero input frequency
and is sometimes not suppressed to act as a zero frequency
marker.
Sweep repetition rate— The number of sweep excursions
.per unit of time. Approximately the inverse of sweep time
for a free-running sweep.
Sweep time— The time required for the spot in the refer­
ence coordinate (frequency in spectrum analyzers) to move
across the graticule. (In a linear spectrum analyzer system,
sweep time is Time/Division multiplied by total divisions.)
CONTROLS A N D CONNECTORS
The following is a brief description of the operation or
function of these controls and connectors on the front panel.
See Fig. 2-3. A more detailed description is provided later
in this section under general operating information.
Selects the range of the DISPERSION con­
DISPERSION
RANGE trol; M H z/C M
quency dispersion range from 10 M Hz to
0.2M H z/cm .
frequency dispersion range from 500 kHz/
cm to 0 dispersion.
DISPERSION Selects the dispersion (frequency width) of
the display in conjunction with the DISPER­
SION RANGE switch.
from lO M H z/cm to 1 kHz/cm in a 1-2-5
sequence, plus an additional position of
approximately zero dispersions are pro­
vided. When the DISPERSION selector is
H 3 0
Most spec­
.
position provides a fre­
kH z/C M position provides
Dispersion ranges
2 -3