GAOTek DDS Function Generator

Operating Instructions

 Operation Common Rules

1.1.1 Menu Selection

If there is a triangle displayed on the right side of the menu, it means this menu has several options. Otherwise, this menu has only one option. Press one option key to select the corresponding option in this menu. The first line on the right side of TFT is function menu. This instrument has ten functions which are selected by the corresponding five function keys: [Channel], [Sweep], [MOD], [BURST], and [SK]. The second to the sixth lines are option menus, which can be selected by pressing one of the five blank soft keys located on the right side of the TFT. The selected menu will turn to a green color.

1.1.2 Parameter Display

The area under the waveform display is for parameter display. The contents in this parameter area are divided into two parts. One is the name of parameter displayed in the 8×16 size text. The other is the parameter value displayed in various colors. These setups make the TFT display more beautiful and easier to recognize.

The parameter display is divided into the five areas:

• “Frequency” area: display the frequency or period value.
• “Amplitude” area: display the output amplitude value. The frequency and amplitude parameters are displayed in a larger font size because of frequent use of these parameters.
• “Offset and Other Parameters” area: display all other parameters except frequency and amplitude parameters. The bottom line in the TFT displays the units of parameters. The unit is selected by the corresponding blank keys under the TFT, and it changes according to variation of parameter values. The input data is validated only after selecting a correct unit.
• “Parameter of Channel A” area: display the current waveform, function and the other parameters of the channel A.
• “Parameter of Channel B” area: display the current waveform, function and the other parameters of the channel B.

1.1.3 Numeric Keypad Input

If a parameter is selected, the color of this parameter changes to yellow. It means this parameter can be modified. There are ten numeric keys for data input. The input method is the shift input from left to right. The data can have only one decimal point. If one data input has more than one decimal point, only the first one is valid. In the offset mode, the negative sign can be input too. After input a new value, press unit key to validate it. If the input data has an error, there are two ways to correct it.

Method 1: If the destination side of the output signal can receive the wrong signal, press any unit key to terminate the current operation. Input the correct data, and press the unit key to validate the input.

Method 2: If the destination side of the output signal can not receive the wrong signal, the wrong input is not validated because of no any wrong signal at the output. Reselect the operation, input correct data, and press the unit key to validate the input.

Although there are a variety of combinations of the decimal point and the unit key for data input, the instrument always displays the input data in a fixed format.

1.1.4 Knob Adjustment

In some applications, it requires to adjust the output signal continuously. Using the rotary knob can complete this task. When a parameter is selected, the color of this parameter changes to yellow. One digit in this parameter which is located by cursor changes to anti-color. Press key  [] or [] to move the cursor left or right. Rotate the knob to the right to continuously increase the cursor-located digit by 1 and make the carry to a higher unit position. Rotate the knob to the left to continuously decrease the cursor-located digit by 1 and make the carry to a lower unit position. When you use the knob to modify a specified data, the modified data is validated instantaneously without pressing the unit key. A coarse adjustment is made by moving the cursor to the left; and a fine adjustment is made by moving the cursor to the right.

1.1.5 Frequency and Amplitude Step

In practice, a set of frequency or amplitude value with same interval is commonly used. It is complicated and time consuming to input this kind of data by repeatedly pressing the numeric keypad and unit key. It is very convenient to use the step input method. Set the frequency interval as the “step frequency” value, every press on key [] makes the frequency increase by a step value, every press on key []  makes the frequency decrease by a step value. The modified data is validated automatically without pressing the unit key.

For example, to generate a series of frequency with interval 12.5 kHz, press the keys sequentially as follows: select “Step Freq” by the corresponding soft key

Press keys [1] [2] [.] [5] and the soft key corresponding to [kHz]; Select “CHA Frequency” by the corresponding soft key

Press key [] to increase the frequency by 12.5 kHz or press key [] to decrease the frequency of 12.5 kHz. Repeat this operation, a series of waveform with equal interval frequency difference can be generated. The same procedure can be used for the amplitude operation. This method is only used on the frequency and amplitude of channel A.

1.1.6 Input Mode Selection

 It is convenient to input the known data through the numeric keypad. It makes the input be set at only one step without the intermediate transition data. For the partial modification of the input data or at the situation of monitoring the variation process of the input data, the rotary knob is usually more useful. For a series of equal interval data input, the step input method is the most efficient. Users can use the different data input methods according to different situations.

 1.2 Setup of Channel A

 Press key [Channel] and select “CHA Alone” function.

1.2.1 Set the Frequency of Channel A

Select “Frequency” option by the corresponding soft key. The current frequency value changes to yellow. Input a new frequency data here by numeric keypad or rotary dial. Press the key corresponding to the frequency units to confirm the new data input. The function generator outputs the specified frequency at CHA Output.

1.2.2 Set the Period of Channel A

The frequency of the channel A can also be set and displayed in the way of period. Select “Period” by the corresponding soft key. The current period value changes to yellow. Input a new period data here by numeric keypad or rotary dial. Press the key corresponding to the period time units to confirm the new data input.

However, the instrument still uses the frequency synthesis internally and the input data are just converted to the correct value when it is input and displayed. Due to the limitation of the lower resolution at low frequency, when the period is too long, the function generator can only generate the frequency points with the longer period interval. Although the preset and displayed period is precise, the actual period of the output signal has the relatively big variation. Users shall pay attention to this point.

1.2.3 Set the Amplitude of Channel A

 Select “Vpp” or “Vrms” by the corresponding soft key. The current amplitude value changes to yellow. Input a new amplitude data here by numeric keypad or rotary dial. The function generator outputs the desired signal at the CHA Output.

The input and display of the Channel A amplitude value have two formats: Vpp and Vrms. Press key [Vpp] or [mVpp] after numeric input to input and display amplitude peak-to-peak value. Press key [Vrms] or [mVrms] after numeric input to input and display amplitude true RMS value.

Although the amplitude value has two formats, the instrument still uses the peak-to-peak format internally and does the format conversion on the data input and the data display. Due to the limitation of the amplitude resolution, there is a difference between the format conversions. For example, if the Vpp of the sine wave is 1Vpp, the Vrms conversion value is 0.353 Vrms. If the Vrms of sine wave is 0.353Vrms, the Vpp conversion value is 0.998Vpp. In most of cases, this difference is within the error range. If the square waveform is selected, the conversion factor is 2. The Vrms format can only be used at the “CHA Alone” mode and the waveform selected as sine or square wave. For other operations and waveforms, only peak-to-peak format can be used.

1.2.4 Amplitude Attenuation

Select “Offset” by the corresponding soft key, next select “Attenuation” by the corresponding soft key. Input a new attenuation value here by numeric keypad or rotary dial. Press the soft key corresponding to [dB] to confirm the new data input.

After instrument power on or reset, the attenuation is default in “Auto” mode. In “Auto” mode, the instrument automatically selects suitable attenuation ratio according to preset amplitude values. When the output amplitude is at 2 V, 0.2 V, or 0.02 V, the instrument switches between attenuation ratios. In this situation, the instrument generates a waveform of high amplitude resolution, high signal & noise ratio, and low distortion, regardless of signal amplitude values. However, during  an attenuation ratio switch, there is instant hopping in the output signal, which is not allowed in some practices. That is why the instrument has preset with fixed attenuation mode.

Select “Attenuation” by the corresponding soft key. An attenuation data can be input here by numeric keypad or rotary dial. There are five ranges of attenuation: 0dB, 20dB, 40dB, 60dB and AUTO, which can be input from numeric key 1, 2, 3, 4 and 0 respectively plus the soft key corresponding to [dB]. The attenuation mode can also be selected by rotary dial. One step in rotary dial tuning goes to one range. If a fixed attenuation mode is selected, the attenuation is fixed and does not change according to amplitude value changes, which make a continuous variation of the output signal in full amplitude range. But in the range of 0 dB, if the signal amplitude value is too small, there will be higher waveform distortion and the signal & noise ratio cannot be so good.

1.2.5 Output Load

The default amplitude value is calibrated when the output is open circuit. The real voltage on the output load is the default amplitude multiplying the dividing ratio of the load impedance and the output impedance. The output impedance of the instrument is about 50 Ω. When the load impedance is big enough and the voltage dividing ratio is close to 1, the loss on the output load impedance can be ignored. The voltage on the load is close to default amplitude value. When the load impedance is too small, the loss of the output load is significant and cannot be ignored. The voltage on the output load is not same as the default amplitude value. Please pay attention to this point.

The output of channel A has the over voltage and over current protections. The instrument cannot be damaged if the output is short-circuit for a few minutes or the transient inverse voltage is less than 30 V. However, this kind of operation should avoid in case of potential damage to the instrument.

1.2.6 Amplitude Flatness

If the output frequency is lower than 1 MHz, the amplitude and frequency characteristics of the output signal are very flat. If the output frequency is over 10 MHz, due to the characteristics of the output amplitude and load matching, the amplitude and frequency characteristics of the output signal will not be so good. The maximum output amplitude is also affected. The higher frequency is, the higher amplitude and the more distortion will be in the output waveform.

1.2.7 Set the Offset of Channel A

Select “Offset” by the corresponding soft key. The current offset value shown on the TFT display changes to yellow. Input a new offset data here by numeric keypad or rotary dial. Press the key corresponding to the offset units to confirm the new data input. The function generator outputs the desired signal at the CHA output.

Please note that the sum of half of the signal output amplitude value and the offset value should be less than 10 V, so as to make sure the offset signal peak value is less than ±10 V. Otherwise, there will be amplitude distortion. Besides, when Channel A is at AUTO attenuation, the output offset attenuates as per amplitude attenuation. When the amplitude Vpp value is above about 2 V, the actual output offset is the preset offset value. When the amplitude Vpp value is approximately between 0.2 V~2 V, the actual output offset is 10% of the preset offset value. When the amplitude Vpp value is approximately less than 0.2 V, the actual output offset is 1% of the preset offset value.

When adjusting the DC offset value of the signal, the rotary knob is more frequently used than numeric keypad. As a common rule, tune the rotary knob to the right to increase DC offset level, while to the left to decrease the DC offset value, regardless of the DC offset value as positive or negative. When the rotary knob, tune across zero, the offset value changes automatically between positive and negative signs.

1.2.8 DC Voltage Output

When the attenuation of channel A is set at 0 dB, the output offset is the preset offset value, regardless of amplitude values. If the amplitude value is set at 0 V, the offset value can be set at any value between -10 V and – 14 – +10 V. In this situation, the instrument becomes a DC power source, which can output preset DC voltage signal.

1.2.9 Select the Waveform of Channel A

The channel A can output three kinds of waveforms: sine wave, square wave, and pulse wave. Press function key [A-], [A- ] to select the corresponding waveform. When the square wave is selected, the duty cycle is defaulted to 50%.

1.2.10 Set the Duty Cycle of Channel A

Press function key [A- ] select “Duty” by the corresponding soft key. The current duty cycle value changes to yellow. A new duty cycle data can be input here by numeric keypad or rotary dial. The duty cycle value can be set at any value between 0.1%~99.9%. When the converted duty cycle value is less than 0.1%, the duty cycle value is displayed as 0.1%. When the converted duty cycle value is greater than 99.9%, the duty cycle value is displayed as 99.9%.

1.2.11 Set the Phase of Channel A

Select “Phase” by the corresponding soft key. The phase value changes to yellow. Input a new phase data here by numeric keypad or rotary dial. The phase can be adjusted at any value between 0~360 degree. The phase resolution is 11.25 degrees.

1.2.12 Set the Output Impedance of Channel A

Select “Impedance” by the corresponding soft key. The impedance value changes to yellow. The function generator is default as high impedance. The impedance value can be set by numeric keypad or rotary dial and the output impedance is 50Ω.

1.3 Setup of Channel B

Press key [Channel] and select “CHB Alone” function.

1.3.1 Set the frequency of Channel B

Select “Frequency” by the corresponding soft key. The current frequency value changes to yellow. Input a new frequency data here by numeric keypad or rotary dial. There will be corresponding frequency output in the CHB output terminal. Same as channel A frequency, channel B frequency can also be set and displayed in the way of period.

1.3.2 Set the Amplitude of Channel B

Select “Vpp” by the corresponding soft key. The current amplitude value changes to yellow. Input a new amplitude data here by numeric keypad or rotary dial. Press the soft key corresponding to the amplitude units to confirm the new data input. The function generator outputs the desired signal at CHB Output. The amplitude unit of Channel B can only use Vpp but not Vrms. The channel B does not have the amplitude attenuation or DC offset functions.

1.3.3 Select the Waveform of Channel B

The waveform of channel B is represented by the index number. Select “Wave” by the corresponding soft key. The index number of current waveform changes to yellow. Enter the index number by using the numeric keypad or rotary knob, press the soft key corresponding to [No.] to confirm the index number input. The function generator outputs the selected waveform at the CHB Output. The channel B has 32 kinds of waveforms. The index number and name of the 32-waveform are shown in the table below.

 1.3.4 Set the Harmonic Wave

The frequency of channel B can be set and displayed as multiple times of channel A frequency. That is, channel B signal becomes the multiple N times harmonic of channel A signal. Select “Phase” by the corresponding soft key next select “Harmonic” in the same way. Input harmonic times via numeric keypad or rotary dial. Press the soft key corresponding to [Time] to confirm the new data input. Channel B frequency becomes the set multiple times of channel A frequency. That means, channel B signal becomes the multiple N times harmonic of channel A signal. The frequency of channel B varies with the harmonic number simultaneously.

1.3.5 Set the Phase of Channel B

Select “Phase” by the corresponding soft key. The phase value changes to yellow. Input a new phase data here by numeric keypad or rotary dial. The phase can be adjusted at any value between 0~360 degree. The phase resolution is 1 degree.

1.3.6 Sum of Channel A and Channel B

Signals After power on the instrument, the signals of channel A and channel B are completely independent. Signals from the two channels can be summed together. Select “A B ADD” mode with the corresponding soft key. The output signal on CHA output becomes the linear sum of channel A and channel B signal. In this situation, frequency and amplitude of channel A and channel B are still in independent mode and can be set independently. This function is very useful in the applications of filter experiment and waveform analysis. To return to independent channels, select “A B Alone” mode with the corresponding soft key. The sum of signals of channel A and channel B can only apply in the mode of CHB Alone. In other working mode, channel A and channel B signals are completely independent.

1.4 Frequency Sweep

Press key [Sweep] to select “CHA Sw Fr” function by the corresponding soft key. The function generator outputs the frequency sweep signal at the CHA Output. The sweep mode of output frequency is step sweep. The output frequency automatically increases or decreases by a step value in a certain interval time. Start frequency, stop frequency, sweep time, sweep mode and trigger mode are free to be set by the users.

1.4.1 Set the Start and Stop Frequency

Select “Start Freq” option by the corresponding soft key. Input a new start frequency data here by numeric keypad or rotary dial. Press the soft key corresponding to the frequency units to confirm the new data input. To set the stop frequency, press the same soft key to select “Stop Freq” option. Input a new stop frequency data here by numeric keypad or rotary dial. Note: the stop frequency must be greater than the start frequency. Otherwise the sweep can not operate.

1.4.2 Select the Sweep Direction

Press the corresponding key to select one of the three sweep directions below:

Up Sweep (key [Up Sweep]): the output signal sweeps from the start frequency to the stop frequency at the preset sweep rate.

Down Sweep (key [Down Swe]): the output signal sweeps from the stop frequency to the start frequency at the preset sweep rate.

Up-Down Sweep (key [UpDownS]): the output signal sweeps from the start frequency to the stop frequency of the preset sweep rate, then sweep from the stop frequency to the start frequency at the same sweep rate.

1.4.3 Select the Sweep Mode

Press the corresponding key to select linear sweep or logarithmic sweep.

Linear sweep: the output signal changes linearly during the duration of sweep.

Logarithmic sweep: the output signal changes logarithmically during the duration of sweep.

1.4.4 Set the Sweep Time

After the start frequency and the stop frequency are set, the sweep time can be determined according to frequency step. The shorter sweep time is, the bigger frequency step will be. The long sweep time is, the smaller frequency step will be. The minimum frequency update time is the software execution time. Select “Sweep Time” option by the corresponding soft key, the sweep time changes to yellow. Input a new sweep time here by numeric keypad or rotary dial. Press the soft key corresponding to the time units to confirm the new data input.

1.4.5 Manual Sweep

After the “CHA Sw Fr” mode is selected, the sweep mode is default as auto mode. In auto sweep mode, the sweep parameters and sweep mode can be modified at any time. Select “Manual Sw” option by the corresponding soft key, the sweep process stops at once. The output signal will keep at the stop state without any changes. The current frequency value is shown on the TFT display. After the sweep process stops, press key [CHA Output/ Trigger] once, the sweep process goes on by one step. The frequency of Channel A will sweep according to the desired sweep mode.

1.4.6 Auto Sweep

Select “Auto Sweep” option by the corresponding soft key. This operation ceases the manual sweep and starts auto sweep. Users can have dynamic monitor of the sweep process. Frequency of channel A changes simultaneously according to the sweep process. The refreshed frequency values are displayed on the TFT. In auto sweep mode, setting up other parameters will stop the current sweep process.

1.5 Amplitude Sweep

Press key [Sweep] to select “CHA Sw A” option. The function generator outputs the sweep signal on CHA Output. All operations of sweep parameter, sweep mode, single sweep, and sweep monitor apply the same operation procedures as explained in section Channel A frequency sweep. To have continuous amplitude variations, user shall firstly set attenuation of channel A. In the sweep process, the generator attenuates according to channel A fixed attenuation, so as to avoid frequent relay switch during auto attenuation.

1.6 Frequency Modulation (FM)

Press key [MOD] to select “CHA FM” option. The function generator outputs the frequency modulation signal on the CHA Output.

1.6.1 Set the Carrier Frequency

Select “Carrier Freq” option by the corresponding soft key. The carrier frequency changes to yellow. A new carrier frequency data can be input here by numeric keypad or rotary dial. Press the soft key corresponding to the frequency units to confirm the new data input. In the frequency modulation mode, the signal of Channel A is used as the carrier signal and the carrier frequency is the frequency of Channel A. In this mode, the clock signals of DDS synthesizer are switched from the fixed reference clock to the programmable reference clock, the accuracy and stability of the carrier frequency may decrease.

1.6.2 Set the Modulation Frequency

Select “Mod Freq” option by the corresponding soft key. The modulation frequency value changes to yellow. A new modulation frequency data can be input here by numeric keypad or rotary dial. Press the soft key corresponding to the frequency units to confirm the new data input. In the frequency modulation mode, the signal of the Channel B is the modulation signal and the modulation frequency is the frequency of Channel B. Generally, the carrier frequency should be at least 10 times higher than the modulation frequency.

1.6.3 Set the Frequency Modulation Deviation

Select “FM Deviation” option by the corresponding soft key. The frequency modulation deviation value changes to yellow. A new frequency modulation deviation data can be input here by numeric keypad or rotary dial. Press the soft key corresponding to [%] to confirm the new data input.

Deviation shows the variations of the carrier signal frequency during the frequency modulation. It is more intended to show the variation in the way of carrier waveform period variation. Variation in the frequency of modulated waveform is shown as the equation below:

DEVI% = 100×SHIFT/PERD DEVI is the modulation frequency deviation;

SHIFT is the peak variation;

PERD is the period of the carrier signal at the zero frequency deviation.

In the modulation demonstration, to have clear observation of the frequency variation, a bigger frequency deviation should be set. In practice, to reduce the bandwidth of the carrier signal, the frequency deviation is usually less than 5%.

1.6.4 Set the Modulation Waveform

Since the signal of channel B as the modulation signal, the Channel B waveform is actually the modulated waveform. Select “Mod Wave” option by the corresponding soft key. The index number changes to yellow. Input the correct index number of numeric keypad or a rotary dial to select the corresponding waveform. Press the key corresponding to [No.] to confirm the index number input. The function generator outputs the desired modulated signal.

1.6.5 External Modulation Source

The frequency modulation can use the external modulation signal. There is a “Modulation In” connector on the rear panel to import external modulation signal. The external modulation signal frequency should be compatible with the frequency of a carrier signal. The amplitude of the external modulation signal should be adjusted according to the frequency deviation. The bigger the amplitude of the external modulation signal is, the bigger the frequency deviation will be. In the external modulation mode, the frequency deviation should be set to 0 and turn off the internal modulation signal. Otherwise, it will affect the external modulation process. Similarly, in the internal mode, the frequency deviation should be set, and the external signal connection should be disconnected. Otherwise, the internal modulation will be affected.

1.7 Amplitude Modulation (AM)

Press key [MOD] and select “CHA AM” option. The function generator outputs the modulated signal on the CHA Output.

1.7.1 Set the Carrier Frequency

Select “Carrier Freq” option by the corresponding soft key. The carrier frequency value changes to yellow. Input a new carrier frequency data here by numeric keypad or rotary dial. Press the soft key corresponding to the frequency units to confirm the new data input. In the amplitude modulation mode, the signal of Channel A is the carrier signal and the carrier frequency is the frequency of Channel A.

1.7.2 Set the Modulation Frequency

Select “Mod Freq” option by the corresponding soft key. The modulation frequency value changes to yellow. Input a new modulation frequency data here by numeric keypad or rotary dial. Press the soft key corresponding to the frequency units to confirm the new data input. In the amplitude modulation mode, the signal on Channel B is the modulation signal and the modulation frequency is the frequency of Channel B. Generally, the carrier frequency is at least 10 times higher than the modulation frequency.

1.7.3 Set the Amplitude Modulation Depth

Select “AM Depth” option by the corresponding soft key. The amplitude modulation depth value changes to yellow. Input a new modulation depth data here by numeric keypad or rotary dial. Press the soft key corresponding to [%] to confirm the new data input. In the amplitude modulation mode, the amplitude of the carrier signal varies periodically with the modulation signal. The modulation depth represents the variation in the carrier signal.

For example, the 100% modulation depth represents that the maximum amplitude of modulation signal is 100% of the set value, the minimum amplitude of modulation signal is 0% of the set value, i.e. 100% – 0% = 100%. The 0% modulation depth represents that both maximum and minimum amplitude of modulation signal are 50% of the set value, i.e. 50% – 50% = 0%. Similarly, the 120% depth is 110% – (-10%) = 120%. The modulation depth has another expression: If the maximum modulation peak-to-peak value is A, the minimum peak-to-peak value is B, then the modulation depth is expressed as:

DEPTH% = 100× (A-B) / (A+B)

Actually, these two kinds of expressions are the same. However, the second one is easier to understand. In the amplitude modulation demonstration, in order to clearly observe the amplitude variation, the modulation depth is set to a relative big value even greater than 100%. But in the practices, in order to avoid the distortion of the modulation signal, the modulation depth is generally set to less than 50%. This kind of modulation carrier is called the double-side carrier. Most of the middle-wavelength radio stations use this modulation.

1.7.4 Set the Modulation Waveform

Since the signal of channel B as the modulation signal, the Channel B waveform is actually the modulated waveform. Select “Mod Wave” option by the corresponding soft key. The index number changes to yellow. Enter the correct index number of numeric keypad or a rotary dial to select a waveform. Press the key corresponding to [No.] to confirm the index number input. The function generator outputs the desired modulated signal.

1.7.5 External Modulation

The amplitude modulation and frequency modulation can use the external modulation signal. There is a “Modulation In” connector on the rear panel to import external signal. Select “Mod Wave” option by the corresponding soft key, press the same key again to select “External”. The internal modulation is automatically shut off. The frequency of the external modulation signal should be compatible with the carrier frequency. The amplitude of the external modulation signal should be adjusted according to frequency modulation deviation or amplitude modulation depth. The bigger amplitude of the external modulation signal is, the bigger frequency modulation deviation or the bigger the amplitude modulation depth will be. In external modulation mode, the keypad operation is not valid for frequency modulation deviation or amplitude modulation depth. In this mode, if “FM Deviation” or “AM Depth” is selected by the corresponding soft key, the instrument turns to internal modulation. “Modulation In” connector on the rear panel should be disconnected, otherwise there will be significant effect on the internal modulation.

1.8 Burst Output

Press key [BURST] to select “CHB Burst” option. “CHB Burst” is displayed in the upper-left portion of the TFT. The function generator outputs a waveform with a specified number of cycles at the burst frequency continuously at the CHB Output. Each set has a preset burst count and there is a time interval between each burst.

1.8.1 Set the Frequency of Channel B

Since channel B signal is the burst source for burst output, frequency and amplitude of the channel B signal should firstly set up. The settings of the frequency and amplitude are introduced in the above section.

1.8.2 Set Burst Count

Select “Cycles” option by the corresponding soft key. The burst count changes to yellow. Input a new burst count number here by numeric keypad or rotary dial. Press the key corresponding to [CYCL] to confirm the new data input. If the burst frequency is fixed, the maximum value of the burst count is limited. The lower burst frequency is, or we say the longer burst period is, the bigger the burst count number can be set. Vise visa, the smaller burst count number is. If the burst frequency is not set, the burst count can be set firstly and then the burst frequency value is adjusted in order to keep an appropriate time interval between each burst.

1.8.3 Set the Burst Frequency

Select “Burst Freq” option by the corresponding soft key. The burst frequency changes to yellow. Input a new burst frequency data here by numeric keypad or rotary dial. Press the soft key corresponding to the frequency units to confirm the new data input. The burst frequency is determined by the Channel B frequency value and the burst count number. The multiply of channel B signal period value and the burst count number is the time needed for a set of burst. In order to keep an appropriate time interval between each burst, the burst period should be greater than the time of a burst. Otherwise, all bursts are connected to each other and the waveform is not the burst signal anymore.

1.8.4 Burst Start Phase

The start phase of each set of burst waveforms is fixed to 0 degree.

1.8.5 Set the Single Burst Mode

Select “Single” option by the corresponding soft key. The function generator turns off the continuous burst mode and signal output is 0. In the single burst mode, press key [CHB Output] once, the burst process executes once and the function generator outputs, one burst waveform according to the preset value of the burst count. If the burst count number is set to 1, the single burst can be operated manually. If the “Int Burst” option is selected, the burst process is back to the continuous burst mode. If the “TTL Burst” option is selected, use “Count In” connector to import the burst signal. In this case, a frequency counter input function should be equipped with the instrument. Burst count can be used to test the dynamic characteristics of the audio equipment and calibrate the counter.

1.9 Frequency Shift Keying (FSK)

In the digital communication and remote measurement systems, the transmission of the digital signal uses the Frequency Shift Keying (FSK) or Phase Shift Keying (PSK) method to encode the frequency or phase of the carrier signal. At the receiving station, the received signal is decoded and recovered to the original digital signal. Press key [SK] to select “CHA FSK” option. The function generator outputs the FSK signal on the CHA Output. The upper-left portion of the TFT displays the FSK waveform. The frequency of the output signal is the alternative variation of the carrier frequency and the hop frequency. The interval time of alternation is adjustable.

1.9.1 Set the Carrier Frequency

Select “Carrier Freq” option by the corresponding soft key. The carrier frequency value changes to yellow. Input a new carrier frequency here from the numeric keypad or a rotary dial. Press the key corresponding to the frequency units to confirm the new data input. In the FSK mode, the signal of the channel A is the carrier signal. The carrier frequency is the first frequency value of channel A.

1.9.2 Set the Hop Frequency

Select “Hop Freq” option by the corresponding soft key. The hop frequency value changes to yellow. Input a new hop frequency here from the numeric keypad or rotary dial. Press the key corresponding to the frequency units to confirm the new data input. The hop frequency is the second frequency value of the channel A.

1.9.3 Set the Interval Time

Select “Interval” option by the corresponding soft key. The interval time value changes to yellow. Input a new interval time data here by numeric keypad or rotary dial. Press the key corresponding to the time units to confirm the new data input.

1.10 Amplitude Shift Keying (ASK)

Press key [SK] to select “CHA ASK” option. The function generator outputs the ASK signal on the CHA Output. The upper-left portion of the TFT displays the ASK waveform. The amplitude of the output signal is the alternative variation of the carrier amplitude and the hop amplitude. The interval time of alternation is adjustable.

1.10.1 Set the Carrier Amplitude

Select “Carrier Amp” option by the corresponding soft key. The carrier amplitude value changes to yellow. Input a new carrier amplitude data here by numeric keypad or rotary dial. Press the key corresponding to the amplitude units to confirm the new data input. In the ASK mode, the channel A signal is the carrier signal. The carrier amplitude is the first amplitude value of channel A signal.

1.10.2 Set the Hop Amplitude

Select “Hop Amp” option by the corresponding soft key. The hop amplitude value changes to yellow. Input a new hop amplitude data here by numeric keypad or rotary dial. Press the key corresponding to the amplitude units to confirm the new data input. The hop amplitude is the second amplitude value of the channel A signal.

1.10.3 Set the Interval Time

Select “Interval” option by the corresponding soft key. The interval time value changes to yellow. Input a new interval time data here by numeric keypad or rotary dial. Press the key corresponding to the time units to confirm the new data input.

1.11 Phase Shift Keying (PSK)

Press key [SK] to select “CHA PSK” function by the corresponding soft key. The function generator outputs the PSK signal on the CHA Output. The upper-left portion of the TFT displays a PSK waveform. The phase of the output signal is the alternative variation of the reference phase and the hop phase. The interval time of alternation is adjustable.

1.11.1 Set the Hop Phase

Select “Hop Phase” option by the corresponding soft key. The hop phase value changes to yellow. Input a new hop phase data here by numeric keypad or rotary dial. Press the key that corresponds to [°] to confirm the new data input. The resolution of the hop phase is 11.25 degrees. If users enter the phase value by using the numeric keypad, the instrument will round the input value to the number of times of 11.25 degrees.

1.11.2 Set the Interval Time

Select “Interval Time” option by the corresponding soft key. The interval time value is shown in yellow on the TFT display. Input a new interval time here by numeric keypad or rotary dial. Press the key corresponding to the time units to confirm the new data input.

1.11.3 PSK Observation

Due to the phase variation caused by PSK signal, it is hard to have synchronization on the oscilloscope, and therefore cannot observe a stable waveform. If the frequency of the channel B is set at the same value of carrier frequency, and use channel B signals as synchronization burst signals, a stable PSK signal waveform can be observed. However, the PSK waveform displayed on the TFT is just an extreme special case for the purpose of direct and easy explanation of PSK process. There are conditions for operating the special case: the carrier signal period should be exactly same as the interval time of two alternative phase signals, hop phase at 180° and hop at the phase value of 0°. In practice, it is very difficult to meet the conditions required. If we set the carrier frequency at 1Hz, interval time as 1s, hop phase at 180°, we can observe a similar waveform on the oscilloscope. But the waveform can only stay for a very short time, because the actual interval time is not exactly same as carrier frequency period. Adjust the interval time to make it as close as possible to the carrier frequency, period so as to have a longer display of the waveform.

1.12 Measure External Frequency

This function is available only when the user chooses to install the frequency counter. Press key [COUNT] to go to the external measurement mode. The TFT display shows the external measurement interface. In this mode, the instrument can be used as a frequency counter and measures the frequency value of the external signal.

1.12.1 Frequency and Count Measurement

Select “Measure Freq” option by the corresponding soft key. The instrument can measure the frequency of an external signal. The measured result is displayed in the purple text on the upper-left of the TFT display. During the measurement, the measured signal must be continuous. But the measurement process is intermittent. It samples the signal using the preset gate time as a period, calculates the measurement result, and updates the display.

1.12.2 Set the Gate Time

Select “Gate Time” option. The gate time changes to yellow. Input a new gate time data here by numeric keypad or rotary dial. Press the key corresponding to the time units to confirm the new data input. The instrument usually adopts average periodical measurement. The longer gate time is, the more cycle numbers to be collected from the testing signal, the more stable the average value will be, the more valid digits to get in testing results, but the slower tracking to the frequency variation will be. The shorter gate time is, the less valid digits to get in testing results, the faster tracking to the frequency variation will be, which is suitable for frequency testing requiring a short time of stability.

1.12.3 Low-pass Filter

In the measurement of the external signal, if the signal frequency is relatively low and has high frequency noise, the measured data have bigger error and is not stable. The low-pass filter is the default as OFF. Select “LPF On” option by the corresponding soft key. This adds a 100 kHz low-pass filter to the input signal. The low-pass filter filters out the high-frequency noise and makes the measured result much more accurate. If the frequency of the testing signal is relatively high, the low-pass filter may attenuate the signal, decrease the sensitivity of the measurement, and even result in the wrong testing data. In this situation, Press the key corresponding to “LPF On” once more to select the “LPF Off” function to remove the 100 kHz low-pass filter. For the low frequency of square signal, because of the steep edge of the signal, the trigger error is not significant. Therefore, the low pass filter is not necessary here.

1.13 System Setup

Press key [SYS] and select “System” option. The system interface is displayed. Users can select operations of storage and recall system setup parameters, set up remote control interfaces. This operation is valid only on software operation via PC, but not valid for rotary dial operations.

1.13.1 Store Parameters

Select “Store” option by the corresponding soft key to store preset parameters into the memory of the instrument. The instrument provides 40 index numbers (0-39) for the parameter memories, starting from index number 0 to 39. Memories of index number 1~39 are available for user defined setting storage, except the memory of number 0. Memory index number 0 is for the storage of default parameters setup.

1.13.2 Recall Parameters

Select “Recall” by the corresponding soft key. Input recall index number 0 to 39 to recall the stored settings in each memory. Input number 0 recalls the default parameter setting of the instrument. After the parameters are recalled, the instrument outputs the signal based on the recalled parameters. In some applications, it is required to frequently use a set of certain parameters, such as frequency, amplitude, offset, waveform, etc. It is very easy and convenient to store and recall these frequently used parameter settings. After input a set of parameters, press soft key [SYS] to select “Store”, input the memory index number of the numeric keypad, press the corresponding soft key of [No.] to store this set of parameter setting in the corresponding memory. Apply the same stored procedure to store up to 40 sets of parameter settings. The parameter memory uses a non-volatile memory, which can store the settings, even the instrument is powered off. If you need to use the stored parameter later, select “Recall” by the corresponding soft key, input the recall index number and press the soft key corresponding to [No.]. The stored parameter setting is recalled. Select “Recall”, then press the key [0] and the soft key corresponding to [No.] to recall the default parameter settings.

1.13.3 Remote Address

Select “Address” option by the corresponding soft key. The remote address changes to yellow. The remote address can be entered by numeric keypad or rotary dial. After power on, the instrument remote address is default as 88. If the instrument is connected to other equipments with RS232 interface to make an auto testing system, each equipment in the system should have a different remote address for PC recognition. If the instrument is connected to other equipments with USB interface, the PC has a way to recognize it and the remote address is invalid here.

1.13.4 Beeper

Select “Beep On” option by the corresponding soft key. The beeper can be turned on or off here. After power on the instrument, the beeper is default as ON, the key sound is on. Every press of a key, there is a sound going with. To turn off the beeper, press the soft key “Beep Off”.

1.13.5 Select a Language

Select a language. There are three languages available in the system: English, Chinese (simplified), Chinese (traditional).

1.14 Parameter Calibration

The parameter errors listed in the technical specification are the factory calibrated specifications. Long-term use or drastic changes in ambient temperature may enlarge the parameter errors. When the instrument is used as a precise testing instrument, a calibration should be carried out periodically. Press key [CAL] to select “User CAL” option. This function uses the calibration software to calibrate the three parameters through the keypad.

1.14.1 Calibration Code

Select “CAL Code” option by the corresponding soft key. The calibration code value changes to yellow. Input a calibration code 666666 and press the soft key corresponding to [No.]. The “CAL Code” changes to “CAL On”, which means the instrument is ready for parameter calibration.

1.14.2 Calibrate the Frequency of Channel A

Select “CHA Freq” option by the corresponding soft key. The frequency value of channel A changes to yellow. The instrument outputs a sine wave at fixed 2MHz. Use a frequency counter of at least 6 digits to test the frequency of channel A. In the mean time, rotate the knob to change the calibration code to change channel A frequency until channel A frequency has an accuracy of 10-6 . Since channel A frequency and Channel B frequency use the same fixed reference clock, after channel A frequency is calibrated, channel B applies the same accuracy.

1.14.3 Calibrate the Carrier Frequency

In the frequency modulation mode, the carrier frequency uses a programmable clock as its reference clock. Although the carrier frequency is the frequency of the channel A, it still needs to be calibrated. Select “Carrier Freq” option by the corresponding soft key. The carrier frequency value of channel A changes to yellow. The instrument outputs a sine wave at fixed 2MHz. Use a frequency counter to measure the frequency of channel A and adjust the calibration code by the rotary knob until the accuracy of channel A frequency is calibrated to 10-3.