Overview - 50 MHz and Up50mhzandup.org/Advanced RF Tips and Tricks.pdf · 2016/3/2 5 RIGOL TECHNOLOGIES, INC. VSWR and reflectivity measurements For our example of an ~800MHz antenna,

2016/3/2

1

RIGOL TECHNOLOGIES, INC.RIGOL TECHNOLOGIES, INC.

Overview

Available and capable test equipment is always

important to RF design and debug whether at the

office or as a hobby.

RIGOL brings a portfolio of capable tools, but are

there ways we can do more than expected with

affordable RF test equipment?


Advanced RF Measurements

1) Filter and Amplifier tests with a Tracking Generator

2) Using mixers as paired converters

3) Testing filters and amplifiers at higher frequencies

4) VSWR and reflectivity measurements

• Antenna characterization

5) Noise Figure Measurements• Methodology for basic NF measurements without an NF meter

• Passive devices, active devices, and systems

6) System modulation tests• Testing IF modulation through your system with emulation

7) Phase measurements• Determining phase changes in your system

8) Conclusions

2016/3/2

2


Testing devices with a tracking generator

- A Tracking Generator is a synchronized swept source always

outputting power at the same frequency the detector is at as they

scan together

- This allows a clear view of the response of a device across frequency

Response of a 40 MHz Band

Pass Filter at 950 MHz

Filter and Amplifier tests

Key points and limitations

- All RIGOL tracking generators

extend to the top frequency of the

Analyzer (not all other units do)

- TGs are settable from -20 to 0 dBm

- N dB BW markers can be used to

simplify measurements

- Use traces and trace math to

compare IN and OUT of an

amplifier

hgjfghj


Normalization improves accuracy by providing an offset calibration

adjustment for the integrated source at each frequency.

This can be used for simple devices or for more complex systems

Tracking Generator Performance Normalized TG Output

Normalization

2016/3/2

3


Mixers as paired converters

Mixers can be used to extend the frequency range for many tests using

a paired upconverter and downconverter section

Example of setup for making measurements at 10 GHz

RF Signal

Source

@ 500 MHz-

1.5 GHz

LO @ 9.5

GHz

Test signal from 10-

11 GHz

RF IN

10 GHz

DUT

RF OUTSpectrum

Analyzer

@ 500 MHz-

1.5 GHz


Testing passives with mixers

Applying the converter methodology to our passive tests

- Filter after down conversion not needed since analyzer is scanning

synchronously with source. RBW filter is handling it.

LO @ 9.5

GHz

Test signal from 10-

11 GHz

RF IN

10 GHz

DUT

RF OUT

1.5 GHz

Spectrum Analyzer

Tracking Generator

Output

Analyzer input

2016/3/2

4


Testing passives with mixers

Tracking generator Normalization

- Essentially an offset calibration for power

- Normalize with a Thru connection before testing DUT

Adjust test range with a higher bandwidth Analyzer. This requires a

lower frequency LO which may be easier to achieve and increases the

range of the scan

LO @ 6

GHz

Test signal from 6-

13.5 GHz

RF IN

10 GHz

DUT

RF OUT

Tracking Generator

Output

7.5 GHz

Spectrum Analyzer

Analyzer input


VSWR and reflectivity measurements

VSWR measurements require:

- Directional coupler

- Analyzer with tracking generator

- Broader power range can be tested with a signal source

- Calibration done with a “OPEN” cal test (No antenna connected)

Calculations: The VSWR can be calculated by the following

a = Return Loss (dB)

r = Reflection coefficient of the DUT

s = VSWR

r = 10^(-0.05 * a)

s = (1 + |r|) / (1- |r|)

2016/3/2

5



For our example of an ~800MHz antenna, we have the following:

a = -26.22 dB

r = 10^(-0.05 * 26.22) = 10^(-1.31) = 0.05

s = (1+0.05) / (1-0.05) = 1.11

Math is done in the instrument and ratio is calculated at peak power

transmission frequency

Reference: http://beyondmeasure.rigoltech.com/acton/attachment/1579/f-0684/1/-/-/-/-

/VSWR%20with%20a%20DSA800%20%28includes%20VSWR-DSA800%20and%20standard%20measurement%20technique%29.pdf

Test VSWR from

DC – 7.5 GHz

RF IN

Antenna

Tracking Generator

Output

7.5 GHz

Spectrum Analyzer

Analyzer input

Directional Coupler



Using mixers to test at higher frequencies is possible, but you need a

directional coupler capable of the actual test range. The coupler should

be connected directly to the device to measure the directionality at the

device.

LO @ 6

GHz

Test VSWR from 6-

13.5 GHzRF IN

Antenna

Tracking Generator

Output

7.5 GHz

Spectrum Analyzer

Analyzer input

Directional Coupler

http://beyondmeasure.rigoltech.com/acton/attachment/1579/f-0684/1/-/-/-/-/VSWR with a DSA800 (includes VSWR-DSA800 and standard measurement technique).pdf

2016/3/2

6


Noise Figure Measurements

Noise Figure measurements using a Spectrum Analyzer can be made

using the gain method. Summarized from maxim reference document

https://www.maximintegrated.com/en/app-notes/index.mvp/id/2875

Noise Factor (F) = Total Output Noise Power / Output noise from input src

One factor is the noise power density from Brownian motion.

In spectral power density and at room temperature this simplifies to:

NF = PNOUTD + 174dBm/Hz – Gain

First, we measure the Gain of the device or system at the frequency of

interest. We can do this with the tracking generator as we did earlier

testing passives.




Second, we test the Spectral Noise Power of the system with no input

and with the input terminated with a 50 Ohm load.

50 Ohm

Termination

LO src

RF Signal

Source

Power Supply

RF SYSTEM IN LO (if applicable)

RF SYSTEM

Vcc RF SYSTEM OUT

Spectrum

Analyzer


2016/3/2

7




Accuracy:

The DSA815 has inherent noise of about -155 dBc/Hz. Measurements

should only be attempted above that. Therefore, the Noise Figure + the

system Gain should be at least 20-25 dB to make accurate

measurements. 50 Ohm

Termination

LO src

RF Signal

Source

Power Supply

RF SYSTEM IN LO (if applicable)

RF SYSTEM

Vcc RF SYSTEM OUT

Spectrum

Analyzer




Frequency Converting Noise Figure measurements

- Once you measure the gain and adjust for the offset of the mixers you

can then measure the noise. View the mixers as part of the system under

test. The noise figure of the mixers and filter is equal to their attenuation.

Reference: University of Kansas – Noise figure of Passive Deviceshttp://www.ittc.ku.edu/~jstiles/622/handouts/Noise%20Figure%20of%20Passive%20Devices.pdf

50 Ohm

Termination

RF Signal

Source

Spectrum

Analyzer

LO @ 6

GHz

RF IN

10 GHz

DUT

RF OUT

http://www.ittc.ku.edu/~jstiles/622/handouts/Noise Figure of Passive Devices.pdf

2016/3/2

8


System modulation tests

How to verify signal modulation through the system

- Use a RF signal source to emulate the 144 MHz radio output with

known modulation data

- Monitor modulated signals in zero span mode

- Measure deviation using max hold traces ->

Reference: http://beyondmeasure.rigoltech.com/acton/attachment/1579/f-059e/1/-/-/-

/-/FM%20Deviation%20with%20a%20DSA.pdf

RF IN

RF OUT

Modulated Signal

Output

Zero Span Analyzer

Time Domain Signal

TX System Under test


System modulation tests

View the modulation on carrier with a spectrum analyzer

- Time domain measurements help verify signal to noise ratio and optimal

levels for modulated source

- Important for adjusting components in the TX or RX paths

sinusoidal FM modulation slower FM with visible noise floor

http://beyondmeasure.rigoltech.com/acton/attachment/1579/f-059e/1/-/-/-/-/FM Deviation with a DSA.pdf

2016/3/2

9


Phase measurements with mixers

Phase measurements of RF signals

- Use down converters with phase linked LO signals to preserve phase

offset

- Option 1 is to convert to a frequency easily measured with an

oscilloscope

- Be careful that you have enough voltage from the mixer to view easily on

the scope

Reference: http://www.av.it.pt/nbcarvalho/docs/ci47.pdf

RF signal

Source LO

@ RF – 50

MHz

RF Signal

Source

RF IN

DUT

RF OUT

CH 1

Oscilloscope

CH 2


Phase measurements with mixers

Phase measurements of RF signals

- Option 2 is to configure the system to output DC and measure with an

RMS Voltmeter

- This method requires 3 measurements (Vrms between signals and

each signal to ground)

- Result is a DCV value related to phase. To get a absolute phase value

you would need to know the DCV at 180°offset

Reference: http://etc.unitbv.ro/~olteanu/Tehnici%20de%20masurare%20in%20tc/Phase%20Measurement.pdf

RF signal

Source LO

@ RF

(difference

= DC)

RF Signal

Source

RF IN

DUT

RF OUT

HI

DMM

LO

http://www.av.it.pt/nbcarvalho/docs/ci47.pdf

http://etc.unitbv.ro/~olteanu/Tehnici de masurare in tc/Phase Measurement.pdf

2016/3/2

10


Summary

Combining power, phase, and noise measurements across frequency to

completely characterize RF systems and components

Utilize mixers to convert to easier to measure frequencies

Use tracking generators for synchronization across frequency or add a

RF signal source for power range, modulation options, or increased

flexibility

Add directional couplers to measure reflection, determine impedance

matching, and conduct VSWR measurements

Make noise figure measurements on an RF system using the gain

method

Select an option for phase measurements based on mixer and

instrumentation requirements


Digital Oscilloscopes

- Phase and time domain

measurements

- 50 MHz – 1 GHz

DSG3000 RF Signal Sources

- 3 and 6 GHz

- AM, FM, and Phase modulations

- Pulse, pulse train, and IQ options

RIGOL Instruments

DSA800 Spectrum Analyzers

- High performance and value

- 1.5, 3.2, or 7.5 GHz

- Tracking generator to top freq

DSG800 RF Signal Sources

- 1.5 and 3 GHz

- FM, AM, and Phase modulations

- Pulse and Pulse train mod options

2016/3/2

11


References and Resources

1) http://www.microwaves101.com/encyclopedias/mixer-noise-figure

2) http://www.reeve.com/Documents/Noise/Reeve_Noise_6_NFMeas

SpecAnalyz.pdf

3) https://www.maximintegrated.com/en/app-notes/index.mvp/id/2875

4) http://www.av.it.pt/nbcarvalho/docs/ci47.pdf

5) http://www.ittc.ku.edu/~jstiles/622/handouts/Noise%20Figure%20of

%20Passive%20Devices.pdf

6) http://etc.unitbv.ro/~olteanu/Tehnici%20de%20masurare%20in%20t

c/Phase%20Measurement.pdf

http://www.microwaves101.com/encyclopedias/mixer-noise-figure

http://www.reeve.com/Documents/Noise/Reeve_Noise_6_NFMeasSpecAnalyz.pdf


http://www.av.it.pt/nbcarvalho/docs/ci47.pdf

http://www.ittc.ku.edu/~jstiles/622/handouts/Noise Figure of Passive Devices.pdf

http://etc.unitbv.ro/~olteanu/Tehnici de masurare in tc/Phase Measurement.pdf