Kerry D. Wong's Simple Tracking Generator Add-On Unlocks a New Feature in the TinySA Ultra

Engineer Kerry D. Wong has added a new feature to the tinySA Ultra pocket-friendly spectrum analyzer: a tracking generator, designed to aid frequency response measurement.

"[A] Tracking generator is useful for determining the frequency response of filters. Without a tracking generator, the frequency sweep across the device under test (DUT) is independent of that of the spectrum analyzer," Wong explains.

"A common technique for capturing the frequency response using this method is to put the spectrum analyzer on maximum hold mode so that the result can accumulate over time. The main drawback, obviously, is the amount of time it would take to capture the complete characteristics. This method is usually fine when the filter is static, but it would not work if the filter response is time-varying."

A scalar or vector network analyzer (SNA or VNA) offers its own tracking generator for fixing this problem, but the tinySA Ultra — for all its other features as what Wong calls "quite a capable spectrum analyzer" — lacks such a feature. That's where Wong's add-on comes in. "Basically, to add a tracking generator, all you need is an external mixer and a 977MHz signal source," Wong explains.

"LO output is enabled on the tinySA Ultra and the LO [Local Oscillator] signal is outputted from the CAL port. The LO's signal is connected to the LO port on the mixer," Wong continues. "The RF port on the mixer is connected to the 8642B RF signal generator which is outputting a 977MHz 0dBm signal. Finally the DUT is connected between the IF port of the mixer and the RF port of the tinySA Ultra."

While the result isn't perfect — "it is actually pretty difficult to find a suitable passive mixer for this tinySA Ultra," Wong admits — the resulting add-on gives the device a new capability, suitable for what Wong says is "looking at a small frequency span, say a few hundred [megahertz]."

Wong's full write-up is available on his website.