Frequency Generator voltage. - Page 1
Forum section: electronics / beginners

author: yalect
author_rank: Regular Contributor
timestamp: August 20, 2025, 10:58:21 am
content: Hi,I would like to ask you, the frequency generator is it working onVppvoltage or thier outputs voltage measured with Vpp voltage?.- If there are some images of devices or Equipment for frequency generator and the Oscilloscope connected together explain the signal waveform?.Thank you.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 20, 2025, 01:12:19 pm
content: Typically pk-pk rather than RMS.The RMS value of a complex waveform that changes over time cannot be defined.It may also depend on the load.Many HF cheap generators will often have an optional 50R output impedance to match a coaxial cable.You'd load that with 50R at the far end. The Vpp would then be half that shown on the generator.On a professional gen it would create the full pp voltage in the terminated load.A generator might have its output defined in dBm, a power level into a fixed impedance load.

author: radiolistener
author_rank: Super Contributor
timestamp: August 20, 2025, 08:40:22 pm
content: Most laboratory signal generators specify their output amplitude in Vpp (volts peak-to-peak). However, this value is referenced to a matched load.- In most lab instruments, the output impedance is 50 Ω, so when you set, for example, 2 Vpp, this corresponds to the amplitude measured across a purely resistive 50 Ω load (no inductance, no capacitance).- In audio-related equipment you may encounter outputs with 600 Ω impedance, or even multiple outputs with different nominal impedances.- Be careful with many low-cost Chinese generators: their settings often show the amplitude for an open output (high-Z load). This means that if you connect such a generator to a 50 Ω load, the actual amplitude will drop to half the set value. For example, setting 2 Vpp on the panel will result in only 1 Vpp across the 50 Ω load. To compensate, you would need to set double the desired amplitude.This factor-of-two difference arises because with matched impedance, the generator and the load form a voltage divider, so the voltage across the load is halved compared to the open-circuit value.Also note: when you change the “output impedance” option in many generators’ menus, it usually does not change the real hardware output impedance (which remains 50 Ω). Instead, it only changes the displayed amplitude so that the value corresponds to the selected load type.On an oscilloscope you will typically see:- With the input set to 50 Ω termination, the displayed Vpp matches the generator setting (assuming the generator follows the lab convention).- With the input set to high-Z (1 MΩ), the waveform amplitude will appear twice as large, because the scope is not loading the generator.Keep in mind that when using the oscilloscope’s high-impedance input at higher frequencies (typically from 1-3 MHz and above), the measurement becomes unreliable: the high-Z input causes signal reflections, and the observed amplitude depends on the standing wave pattern in the coaxial cable. In such cases the displayed voltage will vary with cable length and frequency, and you may not see the true generator amplitude. For accurate results at RF, always use proper 50 Ω termination at the scope input or with an external feed-through terminator.

author: TimFox
author_rank: Super Contributor
timestamp: August 20, 2025, 10:03:17 pm
content: Most laboratory sine-wave generators display the rms value into the specified impedance.Digitally-controlled units such as the Wavetek 98 can switch output units from V rms to dBm to V pk-pk to V pk.Especially true for RF generators.Other laboratory function generators usually display the pk-pk voltage, again into a specified impedance.My favorite pulse generator, the -hp- 8012A, uses a pulsed current source to the output BNC, with an internal 50\$\Omega\$ load that can be switched out.The output control has two scales, one for 25\$\Omega\$ (both external and internal) and the other for 50\$\Omega\$ load (one of external or internal).

author: MrAl
author_rank: Super Contributor
timestamp: August 21, 2025, 12:35:22 am
content: Quote from: yalect on August 20, 2025, 10:58:21 amHello,The best way to tell is to look at the owners manual for that frequency generator. They should tell you what it is. Another model may be different so you have to look at the owners manual for that one too.When you say "working" that's not exactly a very good description anyway. If you have a scope you can always measure it too.