possible tg workaround ?. - Page 1
Forum section: electronics / rf-microwave

author: ME
author_rank: Frequent Contributor
timestamp: July 26, 2025, 10:08:24 am
content: I have a waveteksi4015 , It has a spectrum analyser but no tracking generator , can the nanovna be used to do a cw sweep and be used with the spectrum analyser to align transceiver band pass filters as a work around?

author: tggzzz
author_rank: Super Contributor
timestamp: July 26, 2025, 10:13:15 am
content: Quote from: ME on July 26, 2025, 10:08:24 amEr, a VNAisa tracking generator plus spectrum analyser with two inputs.

author: radiolistener
author_rank: Super Contributor
timestamp: July 26, 2025, 12:38:02 pm
content: Technically, yes - you can use the NanoVNA as a CW sweep generator to work with your spectrum analyzer for aligning transceiver bandpass filters. However, there are at least two important limitations to consider:1) The NanoVNA generates a square wave (meander) signal, so the output contains not only the fundamental sweep frequency but also its odd harmonics.2) Performing a smooth, continuous frequency sweep above ~100 MHz is challenging because the Si5351 synthesizer inside the NanoVNA requires a PLL reset when changing frequency. This causes phase discontinuities and breaks in the sweep signal, which may be undesirable for certain alignment tasks. At lower frequencies, sweeping can be performed without requiring a PLL reset.If you can tolerate the presence of harmonics and phase breaks during sweeping, then using the NanoVNA as a sweep source is feasible. But if you need a clean, continuous CW sweep without these artifacts, NanoVNA is not ideal for that purpose.I have tested using the Si5351 as a sweep generator for BPF analysis on an oscilloscope at frequencies below 100 MHz, and it works, although the signal quality is somewhat noisy. At higher frequencies, the PLL requires resetting, which introduces phase discontinuities that negatively affect the waveform on the oscilloscope.I’m not sure exactly what tasks you plan to solve on the Waveteksi4015 using a sweep generator, but if it’s filter testing, you should consider connecting the NanoVNA input to the filter output. This way, you can measure the filter’s frequency response directly on the NanoVNA without needing the Waveteksi4015. If your tasks differ, keep in mind that the sweep signal from the NanoVNA output is not very clean and contains harmonics, at higher frequencies, it also exhibits phase discontinuities and brief pauses.

author: ME
author_rank: Frequent Contributor
timestamp: July 26, 2025, 05:27:35 pm
content: I wanted to allign my hf transceiver bandpass filters, The guy who sold me the 4015 told me it had a tg so i am trying to find a way to do this with the kit i have, the seller lied!.

author: tggzzz
author_rank: Super Contributor
timestamp: July 26, 2025, 05:48:48 pm
content: Quote from: ME on July 26, 2025, 05:27:35 pmWhy can you not use your NanoVNA to do that?

author: ME
author_rank: Frequent Contributor
timestamp: July 27, 2025, 12:28:29 am
content: Quote from: tggzzz on July 26, 2025, 05:48:48 pmI didnt know its possible with a vna.Thought i needed a spec analyser with a tg?.

author: radiolistener
author_rank: Super Contributor
timestamp: July 27, 2025, 02:11:30 am
content: A spectrum analyzer is indeed very useful for examining and adjusting transmitter output signals, especially when monitoring harmonics, spurs, or overall spectral cleanliness. However, if your goal is simply to align bandpass filters, a VNA is actually better suited for the task -that's exactly what it's designed for. It allows you to directly measure the filter's frequency response (S21), making it easier to tune for optimal performance. With VNA you can see picture more detailed.A tracking generator is not needed in this case, as the VNA has its own built-in signal source. More importantly, the VNA receiver is phase-synchronized with its own internal generator, allowing for much more accurate and reliable measurements. This setup is inherently less sensitive to harmonics, spurious signals, and external interference compared to using a separate signal source with a spectrum analyzer.A VNA is the tool of choice when precise tuning of passive RF circuits is required, particularly when no active signals are present. In contrast, a spectrum analyzer is intended for measuring the characteristics of active signals - those generated by a circuit during operation.

author: ME
author_rank: Frequent Contributor
timestamp: July 27, 2025, 07:58:43 am
content: It was the radio's rx bp filters that i wanted to align, The service manual says a tg+sa is neeted, with a diode detector if i remember?.

author: radiolistener
author_rank: Super Contributor
timestamp: July 27, 2025, 09:05:33 am
content: just connect your bpf to nanovna (input and output ports) and you will see detailed frequency and phase response of your bpf in realtime, then you can tune it