TAMPEREEN TEKNILLINEN YLIOPISTO
TAMPERE UNIVERSITY OF TECHNOLOGY
TLT-5500, TLT-5506
83950
Telecommunication Laboratory Course
Basics of RF-measurements
E-mail: ivi@cs.tut.fi
Room: TG208/ Ismo Viitaniemi
Lab:TG205
INTRODUCTION
First we go through pre-lab assignments and some basic things on different
connectors and cables, accessories and measurement equipment.
When starting measurements make sure that you are familiar with
different functions in different equipment and that you WILL
DEFINALTELY NOT EXCEED THE ALLOWABLE INPUT POWER LEVEL.
Use attenuators always when necessary, until you are sure that the signal
level is OK. Note specially that you
shouldn’t under any circumstance (not
even accidentally) connect external signals to the RF-output of the
generator, and that the DC level of the signal connected to spectral
analyzer must be exactly zero.
1. PRE-LAB ASSIGNMENT
General information about RF technology concepts: voltage, current,
power
1.1
Why do we usually measure power and not current or voltage in RF
technology? What does dBm
mean?
Calculate:
Which absolute power equals 33 dBm?
What is 100 mW in dBm?
What would be the voltage generated by 0 dBm on a 50 load?
Impedance and matching
1.2
Consider several cases (power loss, voltage gain, digital electronics
terminations, noise properties, EMC(electro magnetic compatibility))
why and when is impedance matching necessary?
What kind of matching should be used in each case?
1.3
Define and calculate reflection coefficient, SAS and return loss,
when a 50  transmission line is terminated by a 25  impedance.
Calculate or find out graphically what is the impedance
appearing
over a /8 transmission line, (Z0 = 50), when it is terminated by a
25 impedance.
Connectors,
adapters,
cables
and
how
to
handle
them
1.4
Recognise different types of RF connectors
N-type connector?
SMA-, K- and APC-3.5 -connectors?
BNC
APC 7 (=PC 7)
Notice also difference between 75 and 50 connectors.
1.5
In RF technology you should pay special attention to the cleanness
of the connectors, their tightness, compatibility, bending, and the
quality of the cables and the connectors. Why?
Attenuators, power splitters, directional couplers
1.6
What kind of component is power splitter/combiner, i.e. where power
splitters/combiners are mainly used?
Difference between resistive- and other types (reactive) of signal
(power) splitter/combiner?
1.7
What kind of component is directional coupler?
If we feed 0dBm to the input port of a directional coupler and from
the incident port power is measured –20 dBm and from the
reflection port power -50 dBm.
Assuming that directional coupler output port is terminated ideally,
i.e. reflection to be zero, calculate the coupling, directivity and
isolation of the directional coupler.
Generators
1.8
Draw a simple block diagram of a signal generator. Explain operating
principle and what are the most usually needed control signals?
Spectrum analyzer measurements
1.9
Explain operating principle of the sweeping spectrum analyzer by help
of the simple block diagram of a spectral analyzer.
What kind of measurements can be done by spectrum analyzer?
What are the following concepts when speaking about spectrum
analyzers: span, resolution bandwidth (RBW), center frequency, video
bandwidth (VBW), sweep time, reference level (ref lev), attn? What
does MEAS UNCAL mean? Also try to figure out how these concepts
affect different blocks.
Oscilloscope
1.10
An oscilloscope is not actually an RF measurement device therefore,
what should be considered when measuring RF signals with an
oscilloscope? What if the oscilloscope is digital?
Go through the notes (pages 15-30, 5th part) before starting the lab
and find out what the following concepts are in a digital oscilloscope:
* Probe capacitance/ its compensation
* Time base/horizontal resolution
* Sampling rate/different sampling methods (real time sampling,
random sampling)
* Record length
* Glitch capture
2. MEASUREMENTS
The measurement results obtained by the spectrum analyzer and
oscilloscope are captured by HP BENCHLINK software, so make sure that
you have a floppy disk with you to save your results.
In this lab, we use the following instruments:
Signal generator Rohde & Schwarz SMY02
Spectrum analyzer HP ESA-L1500A
Oscilloscope HP
Directional coupler HP 778D
Different fixed attenuators, adapters etc.
2.1
Measure mixer output spectrum (RF 71MHz -30dBm, LO 70MHz
+7dBm) and observe what RES BW, VIDEO BW, ATTN
etc are in
practice.
2.2
Measure the coupling and directivity of the directional coupler in the
following frequencies: 100 MHz, 500 MHz, 1.2 GHz. Set output level
of the generator to -30 dBm and measure FORWARD COUPLED and
REVERSE COUPLED powers.
Measure also continuous frequency response of the directional
coupler. Use the tracking generator of the spectrum analyzer.
Set SOURCE
AMPTD -30 dBm, REF LEVEL 0 dBm, START
FREQUENCY 90MHz and STOP FREQUENCY 1.20 GHz,
2.3
Evaluate shortcomings of digital oscilloscopes. Measure the signal out
of the test card, which includes glitches. Try to demonstrate a
situation in which oscilloscope doesn’t show anything reasonable at
the beginning and how difficult it can be, especially with a digital
oscilloscope, to examine an unknown signal.
3. POST-LAB ASSIGNMENTS
Write down the answers to pre-lab assignments neatly and return it along
with the post-lab assignments. (Hopefully now, after performing the
measurements, you have a deeper understanding of the concepts).

What are the following concepts when speaking about spectral
analyzers: resolution bandwidth, input attenuation, etc (considering
your observations during the lab).

Calculate what are coupling, isolation and directivity of the directional
coupler, based on your results. Compare them with those given in the
specifications of the directional coupler’s.

Print the figures you got form the spectrum analyzer and also those
from the oscilloscope with:
Low sampling rate/ short record length, long record length/low
sampling rate, long record length/high sampling rate and also in glitch
capture mode.

In your opinion, what are the shortcomings of a digital oscilloscope when
measuring fast phenomena? Also think what the benefits of
digitalization of an oscilloscope can be.
REFRENCES

A. Lehto, A. Räisänen: MIKROAALTOMITTAUSTEKNIIKKA

Pekka Eskelinen: NYKYAIKAISEN RADIOTEKNIIKAN MITTAUKSET
KÄYTÄNNÖSSÄ

A. Räisänen, A. Lehto: Radiotekniikka

Hewlett & Packard: BACK TO BASICS

Fluke: The ABC´s of OSCILLOSCOPES

Mini-Circuits: RF / IF DESIGNER´S HANDBOOK

Fundamentals
of
Rohde&Schwarz
Spectrum
Analysis,
Christoph
Rauscher;