What about the NWT-500 on e-bay?

[dzseki]

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?

[cellularmitosis]

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.

 

[GEOelectronics]

" 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 Dowell
K0FF

[ogden]

Perhaps all you need is a noise source and tuned detector....

What you mean by tuned detector?

[GEOelectronics]

What you mean by tuned detector?
[/quote]

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

[Andreas]

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.

In 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-specifications

https://www.picotech.com/library/picoapp/frequency-response-analyzer-with-bode-plots

with best regards

Andreas

[dzseki]

" 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 Dowell
K0FF

They 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.

[GEOelectronics]

"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