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2018

Basic function generators generally can generate basic periodic waveforms such as sine wave, square wave, triangle wave, ramp wave, pulse wave and so on. Modern function generators nowadays have a very important feature called modulation. With the advent of radio wave telegraphy in the 19th century by Guglielmo Marconi and later the wide band FM radio in the 20th century by Edwin Howard Armstrong, radio waves are generally modulated by its carrier waves for efficient, long-range transmissions.


AM (amplitude modulation) and FM (frequency modulation) have been and are still very important electrical transmission techniques for radio communications. They have also evolved into sophisticated techniques such as QAM (quadrature amplitude modulation), FSK (frequency-shift keying) and more, that are used in short range wireless links such as Wi-Fi to long-range telecommunications networks.


Advanced modulation features in modern function generators


Here in this blog, let us explore some advance modulation features on a modern function generator.

 

AM (Amplitude Modulation)

Amplitude modulation by a carrier sine wave is by far the most common in terms of usage. Figure 1 shows the graphical settings of a function generator modulated by sine wave with AM Depth of 100% and AM Frequency of 100 Hz. The original data sine wave has a frequency of 1 kHz.

 


Figure 1. AM function generator setup (left) using a Keysight 33600A and an oscilloscope display of AM (right).


Modern function generators can do more than just generate sine wave as carrier signal for waveform modulation. Figure 2 shows some examples of other types of signals that are used as carrier signals for waveform modulations (other than sine wave).

 


Figure 2. Various carrier signals used for waveform modulations (other than sine wave).


Modern function generators can be quite versatile. You can also choose the source of your AM modulation from another channel of your function generator without any external connections or from an external source. For example, you can use waveform from Channel 2 to modulate your waveform from Channel 1.

 

FM (Frequency Modulation)

Frequency modulation has been the best-known analog modulation method for radio broadcasting for more than half a century. Its applications have grown into video broadcasting, critical medical monitoring systems, radar and more.

 


Figure 3. FM function generator setup using a Keysight 33600A.


Here is an example of how to setup a function generator to simulate FM signal. Figure 3 above shows frequency modulation on a 1 kHz sine wave. The modulation method used is also a sine wave with FM frequency of 10 Hz. Its peak frequency deviation is 100 Hz.


PM (Phase Modulation)

Phase modulation is widely used in digital data transmissions through digital modulation techniques such as PSK (Phase-shift keying), BPSK (Binary phase-shift keying), QPSK (Quadrature phase-shift keying) and more. It is used in Wi-Fi, GSM and satellite broadcasting transmissions.

 


Figure 4. PM function generator setup using a Keysight 33600A


Here is an example of how to setup a function generator to simulate PM signal. Figure 4 above shows phase modulation on a 1 kHz sine wave. The modulation signal used is also a sine wave with PM frequency of 200 Hz. Its phase deviation is 180°.


FSK (Frequency-shift keying) / BPSK (Binary phase-shift keying)

There are many types of digital modulation techniques available today. The common ones are FSK (frequency-shift keying) and BPSK (binary phase-shift keying). These digital modulation techniques are used in many applications such as digital radio transmissions, RFID, Bluetooth and more.

 


Figure 5. FSK function generator setup using a Keysight 33600A


Here is an example of how to setup a function generator to simulate an FSK signal. Figure 5 above shows frequency-shift keying modulation on a 1 kHz carrier sine wave. The hop (or alternate) frequency is set at 100 Hz. The FSK rate is set at 10 Hz, which is the rate at which output frequency "shifts" between the carrier and hop frequency.

 


Figure 6. BPSK function generator setup using a Keysight 33600A


Here is an example of how to setup a function generator to simulate BPSK signal. Figure 6 above shows binary phase-shift keying modulation on a 1 kHz carrier sine wave. The BPSK rate is the rate at which the output phase "shifts" between the carrier and offset phase. The BPSK phase setting in this case is 180° (phase shift in degrees). Typically, you have the option to set the phase shift from 0° to 360°.


SUM (Sum modulation)

Sum modulation adds a modulating signal to any carrier waveform; it is typically used to add gaussian noise to a carrier. The modulating signal is added to the carrier as a percentage of carrier waveform amplitude.

 


Figure 7. Sum modulation function generator setup – adding noise into sine wave carrier signal.


Figure above shows how we can use sum modulation to add measured noise to the carrier signal. This figure shows noise with an amplitude of 30% (referencing to carrier amplitude) and a noise bandwidth of 100 kHz was added to the sine wave carrier signal.
The Keysight 33600A series function generator accepts both internal and external modulation sources. On a two-channel instrument you can modulate one channel with the other. When using internal source as modulation, we can select sine, square, triangle, up ramp, down ramp, noise, PRBS and arbitrary waveforms as source of modulation.

 

Conclusion


We have just explored some advance modulation features and how intuitive the configuration setup can be using a Keysight 33600A.
If this blog helps provide you with more insight into generating modulated signals, please give it a ‘like’. If you have further questions on this topic, you can always reply to this blog.
For more information about Keysight’s 33600A Trueform function generators, please go to: http://www.keysight.com/find/function-generators
Thanks for reading!


Traditionally, digital multimeters (DMMs) have been single-measurement instruments. When engineers want to measure more than one parameter on their signal, they need to have two multimeters to measure two different measurements at the same time. This is not time and cost efficient.


With the right architecture and design, DMMs can make multiple measurements. This advanced feature can help you save cost and analysis time and finish your analysis faster!

 

Two measurements in a single screen

Secondary measurements are defined as auxiliary measurements that augment information provided by a main primary measurement function. Depending on the function, you can measure complementary data that traditionally would have taken two different operations to acquire. The table below illustrates all secondary measurement capabilities of the Keysight’s Truevolt DMMs.

 

Primary measurement function

34460A secondary measurement function

34465A/70A secondary measurement function

DCV

ACV

ACV, peak, pre-math

ACV

Frequency

DCV, frequency, pre-math

2-wire, 4-wire resistance

-

Pre-math

DCI

ACI

ACI, peak, pre-math

ACI

Frequency

DCI, frequency, pre-math

Frequency

Period

Period, ACV, pre-math

Period

Frequency

Frequency, ACV, pre-math

Temperature

Sensor

Sensor, pre-math

Ratio

Input/Ref

Input/ref, pre-math

Capacitance

-

Pre-math

Continuity

-

None

Diode

-

None

 

An example of a common secondary measurement would be the ability to measure the frequency of an AC signal, as shown in Figure 1.

 

0.398
Figure 1. AC voltage with frequency.

 

The secondary measurement provides more information than is possible with other digital multimeters because of the advanced secondary features in Keysight’s 34465A and 34470A DMMs. As an example, Figure 2 shows the primary measurement of DC voltage (DCV) with a secondary measurement of AC voltage (ACV). This is an especially important measurement if your signal has both an AC and DC component.

 

+00.780
Figure 2. DC voltage (primary) and AC voltage (secondary) measurements.

 

In DCV mode, there are two additional secondary measurements that can be made to provide insight into your signal: Peak and Pre-Math. The Peak measurement, as shown in Figure 3, keeps track of the minimum and maximum DCV readings read by the DMM.

 

+04.991
Figure 3. Peak measurement of DCV.

 

The Pre-Math is a very valuable measurement because it allows you to see modified readings and raw readings in one screen (Figure 4). You can also modify your primary display by applying useful math functions to your data (e.g., a null value or scaling) or filtering your data (Figure 5). See Adding Math Enables Faster Analysis section for more information on applying a math function.


Once you have applied the desired math function, the secondary display will display the raw reading without the math. This is useful for determining if the applied math is correct and if the readings are within the expected range.

 

-0.165 DB
Figure 4. A DCV signal with dB scaling with the Pre-Math measurement

 

+11
Figure 5. A with the null value applied with the raw measurement on the secondary display.

 

You have seen the benefits of the secondary measurement capability. Below you will see how to do this without changing the instrument’s configuration.

 

Example 1

A test engineer wants to monitor the temperature inside of an environmental chamber and needs a high level of confidence that the measurements are accurate. A 34465A DMM is selected due to its ability to log data and provide simple trend charts. A 5-KΩ NTC thermistor is used to spot check for accuracy. The engineer notices that the thermistor has a temperature error of a few degrees. To understand the error, the secondary display on the Truevolt DMM is turned on and temperature and resistor readings are read at the same time. According to the datasheet for the thermistor, it should read 25 ºC at 5 KΩ. The engineer’s probe is put inside of a calibrated chamber set to 27 ºC, but the probe reads 25 ºC with a 5-KΩ resistance reading, a two-degree error. After a bit of characterization, the engineer decides that he can simply add an offset value to adjust for the offset of his thermistor.

 

Example 2

A system designed to apply a linear force to a small structure can provide an oscillating force with an AC signal and a constant force with a DC signal. The system designer wants to keep track of both signals concurrently to characterize how much force is being applied. Using a Truevolt DMM with its ability to make secondary measurements, he can read both the DC and AC components of his control signal at the same time.

 

Summary

Advanced dual-screen measurements not only allow you to get more information concurrently, they also allow you to check your raw data compared to your adjusted measurements. This saves you measurement time.

To learn more, download the Simultaneous Measurements with a Digital Multimeter application brief.