| General > General Technical Chat |
| A spectrum analyzer for measuring linearity |
| << < (4/4) |
| SilverSolder:
Is it an option to use a notch filter of some kind, to get rid of the fundamental, so you can measure the device using less esoteric equipment? |
| TimFox:
That’s the normal method for audio distortion measurement, where the residual harmonics (after nulling) can be analyzed further in a SA. Perhaps a passive RLC bridged-tee filter would work in his frequency range? There is a reasonable amount of literature on this subject. |
| xzswq21:
my brother told me Siglent SA is new, light weight, with USB port, LCD and etc and it's lovely! but if your are concerned about the distortion, HP8560E is a reference Spectrum Analyzer and has better Second harmonic distortion, I wanted to buy Siglent SA tonight but I'm skeptical to buy it! just look at: SSA3021X distortion: HP8560E distortion: |
| Wuerstchenhund:
--- Quote from: xzswq21 on March 29, 2021, 07:34:09 am ---I analyzed all the circuits in theory and then simulated and built the sensors. In simulation the SFDR is from 70dBc to 90dBc. the results are very good for my application. For example if the input signal is 0dB the second harmonic distortion is 80dB or 85dB or something similar (it depends on the frequency). One of my sensors covers from 10KHz to 50MHz but another sensor can cover from 10KHz to 100MHz and all the outputs are 50 Ohm, 1Vp-p and the SNR is from 75 to <87 (it depends on the bandwidth). now I want to measure the HD2, HD3, THD, AC response (magnitude of the bode plot) of my sensors. --- End quote --- Simulation is fine, as it gives you some idea as to what performance you can expect, but especially in the world of RF just using simulation has its limits. But leaving that aside, you'd be looking at a signal source which can deliver SHD of better than 95dB for your measurements to gain any realistic results. And as other members said, finding a suitable low distortion RF source will be more difficult than a suitable SA. --- Quote from: xzswq21 on March 29, 2021, 02:29:10 pm --- --- Quote from: SilverSolder on March 29, 2021, 02:26:37 pm ---In theory, practice doesn't matter. In practice, it does! --- End quote --- In practice I need a low distortion Spectrum Analyzer :) --- End quote --- Yes, you do. And neither the Siglent SSA (an entry-level device designed for low costs) nor the HP 8560E (a quarter of a century old SA designed for portable operation) are low distortion analyzers. Since your budget seems to be a secret, have you considered just renting proper test equipment? |
| Shiv:
--- Quote from: xzswq21 on March 26, 2021, 02:30:25 pm ---Hello I have designed a new sensor in 2018 so I need to have a spectrum analyzer to measure the harmonics and noise of the sensor. Unfortunately I haven't accessed to a Spectrum Analyzer yet! I analyzed all circuits in theory and then simulated and built the sensors. In simulation the SFDR is from 70dBc to 90dBc. the results are very good for my application. For example if the input signal is 0dB the second harmonic distortion is 80dB or 85dB or something similar (it depends on the frequency). One of my sensors covers from 10KHz to 50MHz but another sensor can cover from 10KHz to 100MHz and all the outputs are 50 Ohm, 1Vp-p and the SNR is from 75 to <87 (it depends on the bandwidth). now I want to measure the HD2, HD3, THD, AC response (magnitude of the bode plot) of my sensors. I apply 10KHz to my sensor and check the output response to measure HD2 (second harmonic distortion), HD3 (third harmonic distortion), THD then I will increase the input frequency upto 100MHz step by step (for example 100KHz, 200KHz, 300KHz,...., 1MHz,...) to plot HD2, HD3, THD over frequency axis, another test is only to plot magnitude of the bode plot of the sensors, this is all of I want :) finally I will publish the results in a journal. I see most of good spectrum analyzers have Amplitude accuracy better than 1dB and it's very good for me, 90dBc/Hz of phase noise is very good, which spectrum is good for me? Old HP8560a, HP856x, E440x series or etc? Plus I've found HP3588a dynamic signal analyzer as an interesting choice but it's boatanchor!!: https://accusrc.com/uploads/datasheets/4629_3588A.pdf Thanks --- End quote --- -70 to -90 is a big difference. What about the signal generator? To measure -90dBc you should use a very, very clean signal ... Y our cal lab some time ago, we needed to use filters to help cleaning the input signal and reducing the carrier on Analizer. Maybe you could do this: Very clean signal @ 10 MHz (<90dbC is very hard to find...or HP + LP filters to make it clean) Low Span measurement at 10 MHz HP filter 15 MHz before the analyzer. Low Span measurement at 20 MHz Calibrate the HP filter response Discount filter response to harmonic measurement. So you don´t deal with Analyzer generated harmonics and dynamic range and just matters the noise floor. BUT: if you want to check it at some frecuencies you will need a trailer full of attenuators. (We only take 2 or 3 special measurements) I would go for external calibration or equipement rental And trully I don´t know what to use to get so clean MHz. |
| Navigation |
| Message Index |
| Previous page |