Last winter I made a design for a hobby spectrum analyser and the main stumbling block was a suitable low phase noise oscillator. Most of the RF sources that I came about have terrible spurs from pll adjusts when they are used for sweeping. I’ve been thinking about buying a YIG on ebay and do it that way but that approach would devalue the project for open source.

I’m eager to look at that lmx2594 you use, thank you for the article.

Just wondering how the frequency range of VNA is up to 15 GHz when you're using the receiver chip ADL5802 with frequency up to 6 GHz not the more expensive ADL5961 with much higher frequency ranges up to 26.5GHz?

If you're looking a kind of learning kit for building your own 2-port VNA this one from Mini-Circuits is excellent although it's bit more expensive (USD2000++ when launched, now USD3000++) [1].

Fun facts, VNA is called small-signal network analyzer utilizing s-parameter and it's the special case of LSNA (see later). For the four receivers architecture with complete real-time transmitted and reflected waves availability of a1, a2, b1, b2, you can build a comprehensive large-signal network analyzer or LSNA utilizing X-parameter, of course with elaborate RF/Microwave components for signal flow control [2].

More fun facts, with advent of high bandwidth and high frequency direct RF ADC and DAC popularized by ADI, TI and AMD, this will turn RF and Microwave measurements into its head [3]. Essentially you don't need separate and dedicated specialized RF signal generator and receiver. The RF ADC and DAC are your sources of generic synchronized signal generators and receivers of the a1, a2, b1, b2 waves for building the next generation LSNA based on RFSoC.

But for now anyone building a VNA (or any RF/Microwave instrument for that matter) can utilize the newly release high frequency ADL5961 for a very low cost but very capable RF/Microwave system. For USD200 per unit, it's not a bargain it's a steal. Anyone looking for motivation (I saw one asking for motivation), this one is your motivation. Just build a RF/Microwave instrument for below the ground object detector looking for freely available expensive exotic foods for examples bamboo shoot if you're in Japan or truffle if you're in France, you can thank me later.

ADI is probably the most underrated US company, if you have money just buy their stocks, period.

[1] UVNA-63 | DIY Vector Network Analyzer Kit:

https://www.minicircuits.com/WebStore/uvna_63.html

[2] X-parameters:

https://en.wikipedia.org/wiki/X-parameters

[3] AMD adds RF-sampling data converters to Versal adaptive SoCs (2024) (21 comments):

https://news.ycombinator.com/item?id=42899304