What about the NWT-500 on e-bay? - Page 1
Forum section: electronics / general

author: dzseki
author_rank: Frequent Contributor
timestamp: May 02, 2018, 09:40:20 pm
content: I am considering to buy some sort of instrument(s) which would enable me to measure frequency response of my hobby circuits: linear amplifiers up to 500MHz.So far I was investigating the circuits with a fast pulse generator (tr~470ps) and an (275MHz) oscilloscope, and calculated the upper freqency limit from the slew of the rise time on the output. This was good so far, but I want something different as well, because with this method it is difficult to peel out the "waviness" of the frequency response...I know ideally this should be done with a VNA or SNA, but factory instruments are "too good" for my requirements, and by coincidence they fall out of my budget too.I found surprisingly few hits on this forum (and those were not very promising, either...) about the chinese NWT-500 "VNA", does anyone have first hand experience with those?Also I'd be insterested in other methods for the goal, like using a VHF generator (like HP 3200B) or signal generator (many choice..) and measuring the response with either an RF voltmeter (like HP 3406A) or even a vector voltmeter (like HP 8405A).Honestly, I have more faith in old HP gear than in this chinese VNA, what is your opinion?

author: cellularmitosis
author_rank: Unknown
timestamp: May 02, 2018, 10:59:39 pm
content: Subscribed. I'd love to be able to characterize some simple low-pass filters, but I'm not (yet) willing to shell out $$$ for an ebay spectrum analyzer or network analyzer.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 02, 2018, 11:52:25 pm
content: " linear amplifiers up to 500MHz"Can you be more specific? Power amplifiers? Preamplifiers? Instrument amplifiers?Perhaps all you need is a noise source and tuned detector....George DowellK0FF

author: ogden
author_rank: Super Contributor
timestamp: May 03, 2018, 12:16:48 am
content: Quote from: GEOelectronics on May 02, 2018, 11:52:25 pmWhat you mean by tuned detector?

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 03, 2018, 12:25:21 am
content: What you mean by tuned detector?Specifically a FSVM = Frequency Selective Voltmeter.I use a CRT type spectrum analyzer with a tracking generator now.Basically is it a CRT version of the NWT-500, but mine came before computer control (bummer).George Dowell

author: Andreas
author_rank: Super Contributor
timestamp: May 03, 2018, 04:28:55 am
content: Quote from: cellularmitosis on May 02, 2018, 10:59:39 pmIn which frequency range? up to 20 MHz my Oscilloscope (with function generator) does the job with 3rd party software.https://www.picotech.com/oscilloscope/5000/picoscope-5000-specificationshttps://www.picotech.com/library/picoapp/frequency-response-analyzer-with-bode-plotswith best regardsAndreas

author: dzseki
author_rank: Frequent Contributor
timestamp: May 03, 2018, 07:28:35 pm
content: Quote from: GEOelectronics on May 02, 2018, 11:52:25 pmThey are for CRT projectors, so in fact these are high bandwidth video amplifiers.I have interest in these and developed a series of preamplifiers those I want to characterize deeper.They take an input signal of 0.7V and can output 2V max, and I want to ensure reasonably flat bandwidth up to 300MHz (hence my requirement is 500MHz)I also have interest in the CRT driver amplifiers, as those are the real bottle neck in terms of bandwidth. Those however take 0.7-2V signals (depending on type) and output 100Vpp with 3.5ns rise time or less. Now this is hard nut to feed to any off the shelf instrument, but I have active FET probe with 100:1 divider that I can using interfacing to the "detector".Honestly I've never considered having a noise generator and a tuned detector, how would that work?PS.: At work I have access to serious RF instruments like multi GHz VNA and SA, So I can characterize whatever I build, I mean any homebrew generator or detector.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 03, 2018, 08:53:02 pm
content: "They are for CRT projectors, so in fact these are high bandwidth video amplifiers."Understood, broadband + linear. Is there a need for a differential front end to cancel hum and noise?Is the load Hi-Z or Low-Z (power requirements). Just curious. Mini-Circuits makes a 50 Ohm MAR-8A DC-1 GHz monolithic amplifier chip that has 20+ dB gain and 12 dBm output capacity.The item you referenced on eBay looks really interesting not o mention handy..Hmmm\What I suggested as a possibility was an RF Noise Generator, which fills the spectrum with "white noise energy", then you investigate the output one frequency or frequency segment at a time with a tunable detector to determine the frequency response of the amplifier and its gain-bandwidth-product. Old-school. Much better to use a real Spectrum Analyzer/tracking generator.George Dowell