20MHz Frequency Response Analyzer for $80 - Page 1
Forum section: electronics / testgear

author: yangyao
author_rank: Regular Contributor
timestamp: June 09, 2025, 08:28:04 am
content: Do you think there is a market for a frequency response analyzer with a price of 80 USD, 0~20MHz, 0~5VPP, ±5V offset, and a 4-inch screen? I don't know why there is no dedicated frequency response analyzer on the market. There are no related products or the price is particularly expensive. I think this device is very useful. It can measure filters, amplifiers, attenuators, whether active or passive, used for measure amplitude-frequency characteristic curves and phase-frequency characteristic curves. It is still helpful for beginners.

author: tautech
author_rank: Super Contributor
timestamp: June 09, 2025, 09:00:08 am
content: Quote from: yangyao on June 09, 2025, 08:28:04 amSome scopes come with FRA as standard.

author: yangyao
author_rank: Regular Contributor
timestamp: June 09, 2025, 09:07:39 am
content: Quote from: tautech on June 09, 2025, 09:00:08 amYes, but this oscilloscope plus the corresponding options cost at least $700, there is no other way

author: Antonio90
author_rank: Frequent Contributor
timestamp: June 09, 2025, 09:10:15 am
content: It could be very useful indeed, although it would depend on the implementation. The option of exporting the plots to a computer would be quite important for storage, comparison and processing. 4" can be pretty limiting. At 80$ you are entering NanoVNA and TinySA pricing territory, with their bang per buck ratio.Also, I'm not sure about the added complexity, but maybe a couple resistors and open-short calibration could be implemented as an option to roughly measure impedance? If so, it could show LCR meter data, which might also be good for the discoverability of the device. My guess is many more people search for impedance/lcr on Amazon or Aliexpress than for FRA or Bode Plot.

author: tautech
author_rank: Super Contributor
timestamp: June 09, 2025, 09:17:02 am
content: Quote from: yangyao on June 09, 2025, 09:07:39 amActually a good bit less for just one FRAandPhase trace.4ch scopes can provide 3 FRA traces for multistage filters etc.You need analyze the existing market products better/more.

author: Antonio90
author_rank: Frequent Contributor
timestamp: June 09, 2025, 09:33:06 am
content: Quote from: tautech on June 09, 2025, 09:17:02 amThere are already cheap oscilloscopes from Hanteket alwhich can do FRA for 200 bucks or less on sale, although the generator specs are worse on amplitude and offset. I still think a solid, reasonably fast and mostly bug-free device with some kind of connectivity could be quite useful at 80 USD.

author: ptluis
author_rank: Frequent Contributor
timestamp: June 09, 2025, 10:51:54 am
content: Quote from: yangyao on June 09, 2025, 08:28:04 amYes if it's capable of plotting the whole audio spectrum and even better, starting from 1Hz even if is slow.

author: aeg
author_rank: Regular Contributor
timestamp: June 09, 2025, 09:13:19 pm
content: Quote from: Antonio90 on June 09, 2025, 09:10:15 amBut NanoVNA is an RF network analyzer. It only goes down to 50kHz. If you want an FRA for switching converters, the frequencies of interest are 100Hz-2MHz. For PFC you need to go all the way down to 1Hz.

author: Antonio90
author_rank: Frequent Contributor
timestamp: June 10, 2025, 07:13:19 am
content: Quote from: aeg on June 09, 2025, 09:13:19 pmYes, they are completely different devices. I was thinking more on the line of additional features, being able to extract data, controlling them from a computer and possibility of firmware improvement and updates.

author: nctnico
author_rank: Super Contributor
timestamp: June 10, 2025, 08:57:33 am
content: Quote from: Antonio90 on June 09, 2025, 09:33:06 amI agree. FRA on oscilloscopes tends to be slow. I have an LF network analyser from Anritsu and I tend to use that instead of an oscilloscope because it sweeps much much faster (the R&S oscilloscope I have does FRA quite fast compared to other oscilloscopes).

author: Kosmic
author_rank: Super Contributor
timestamp: June 10, 2025, 12:00:23 pm
content: 20Mhz FRA at 80$, I would get one

author: mawyatt
author_rank: Super Contributor
timestamp: June 10, 2025, 02:44:41 pm
content: The speed of the FRA is dictated by the total number of frequency points involved, the lower frequency range, and signal processing. The obvious necessary time involved in capturing the lower frequencies and total points, but not so obvious is the method and techniques involved in signal processing which tend to be "hidden" from the user.One of the important aspects of a FRA function is the ability to reject unwanted signals and noise. For example, when looking into the Open/Closed Loop Response of a SMPS where the switching behavior becomes a huge unwanted signal and the FRA is asked to accurately pull out the small injected signal from all this "noise", which requires some time for the significant signal processing involved behind the scenes. Having some user control of these signal processing routines/parameters would be a nice added feature which could be user adapted for specific applications.Some of the latest DSO FRA Bode Functions, even on entry level devices, have multiple channels, dynamic input/output signal scaling, linear/decade frequency sweeping, built-in AWG sources, LAN/USB Signal Source control and so on.The latest DSOs have useful built-in Bode (FRA) Functions, often good enough to replace a dedicated low frequency FRA, but could benefit from some extended frequency coverage and more user control to help improve measurement times.Anyway, if a dedicated stand alone FRA can be created with similar DSO features/performance for under $100 that would be impressive, however, the firmware development seems like a formidable task indeed!Best

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: June 11, 2025, 03:41:47 am
content: I think you could probably make a basic FRA for $20 which gets to 50 MHz using switching mixers.Here's my idea: the Si5351 ($1) can generate 3 different frequencies from 0-200 MHz. The first output is constantly at 200 MHz, and it is filtered into a 200 MHz sine wave. This sine wave can be attenuated using a PIN diode to control the output amplitude. The second output drives a switching mixer (based on the 3157 IC which is a few cents). The second output generates a 150-200 MHz square wave, causing the output to be a 0-50 MHz sine wave. A somewhat sharp 50 MHz filter is used to cut off any harmonics, which should produce a good sine wave. A cheapo 500MHz 20 cent op amp from LCSC can be used to increase the signal strength.On the receiving side, another pair of switching mixers downconverts the two input signals to 10 kHz (or some other low frequency). The LO of these switching mixers is powered by the third Si5351 output. At audio frequencies, this output is disabled, causing the mixer to just pass through all of the input signal straight to the ADC. The microcontroller can do all the math (or just send over the raw samples through USB).There might be some holes in my design but it does seem like no fancy ADC/DAC is needed at all, so everything should be able to be done for a fairly low price.