tinySA Spectrum Analyzer for Hams: What It Can Measure

A tinySA is a small, battery-powered spectrum analyzer that costs a fraction of a traditional bench instrument, and for many radio amateurs it is the first test device that shows what is really happening on a frequency instead of what the radio claims. Where a wattmeter gives a single number and an SWR meter tells you about the match, a spectrum analyzer draws a picture: signal level on the vertical axis, frequency on the horizontal axis. You can see your own harmonics, the noise that a cheap charger puts on 40 metres, the response of a filter you have just built, and the carrier of a nearby transmitter that is overloading your receiver. This guide explains what the tinySA family can do, how to use it for typical station jobs without damaging it, and where its limits are.

What a Spectrum Analyzer Actually Shows

A swept-tuned spectrum analyzer works like a very patient receiver. As the Wikipedia article on spectrum analyzers explains, it converts a slice of the input spectrum down to the centre frequency of a narrow band-pass filter, records the power that comes through, and then moves the slice a little higher in frequency, again and again, until the whole span has been drawn. The width of that filter is the resolution bandwidth, usually shortened to RBW. A narrow RBW separates two close signals and lowers the displayed noise floor, but it makes each sweep slower. A wide RBW is fast and good for a first look, yet it smears neighbouring signals together.

That trade-off is the one idea you need to use any such instrument well. Choose the span first (for example 1 to 30 MHz to see the HF bands), then choose the RBW so that the sweep takes a sensible time, and only then look at the levels. The vertical scale is normally in dBm, which is decibels relative to one milliwatt. Our guide to antenna gain in decibels introduces the decibel scale, and the same arithmetic applies to dBm, where 0 dBm is 1 mW, 30 dBm is 1 W and 50 dBm is 100 W, which is the arithmetic you will use every time you attach a pad in front of the analyzer.

The tinySA Family in Brief

The manufacturer’s wiki, at tinysa.org, describes two main lines. The tinySA Basic has a 2.8 inch screen and two inputs: a high quality input for 0.1 MHz to 350 MHz and a lesser quality input for 240 MHz to 960 MHz. Its switchable resolution filters run from 2.6 kHz to 640 kHz. The tinySA Ultra and Ultra+ models have a 4 inch screen and cover 0.1 MHz to 800 MHz or 900 MHz in their normal mode. With Ultra mode switched on the range reaches 5.3 GHz, with calibrated levels up to 6 GHz according to the wiki, and the resolution filters go from 200 Hz to 850 kHz. The Ultra models add a built-in optional 20 dB low noise amplifier, a microSD card slot for saved traces and screenshots, and a step attenuator at the input on the larger versions.

The same page contains two warnings that are worth repeating. The maximum input level is +10 dBm, which is only 10 milliwatts, and the page says plainly not to destroy the instrument. It also warns about low quality copies and tells buyers to use the “where to buy” page. Both points matter more than any feature list: buy from a listed seller, and never connect a transmitter directly.

Where It Fits Beside a NanoVNA

Many amateurs already own a NanoVNA, and the two devices are often confused. They answer different questions. A vector network analyzer sends a known test signal into an antenna or filter and measures what comes back, so it tells you impedance, SWR and filter response. A spectrum analyzer only listens: it measures what other things produce, such as a transmitter, an oscillator or a noise source. Our NanoVNA guide covers the first job. The tinySA covers the second, and the small generator inside it lets you do simple tests of the type described below.

Checking Transmitter Harmonics Safely

This is the classic job, and the one where a mistake is the most expensive. A transmitter that produces 5 watts is putting out about 37 dBm, and 100 watts is 50 dBm. The tinySA input can take only +10 dBm, so you need an attenuator that brings the level well below that limit with a margin for mistakes. Do not guess. The method is as follows.

1. Use a dummy load path, not an antenna. A load that can take the full power goes after the attenuator, or the attenuator itself is rated for the power. Our guide to the dummy load explains the choices.
2. Calculate the level at the analyzer before you key the transmitter: output power in dBm minus the total attenuation in dB. For a 10 watt output (40 dBm) and 40 dB of attenuation, the analyzer sees 0 dBm, which is safe with 10 dB to spare.
3. Start with the lowest power your transmitter allows, a carrier at a single frequency, and look at the screen. Then raise the power in steps and keep checking the level of the strongest peak.
4. Set the span to cover the fundamental and at least the second to fifth harmonics. On 14 MHz, the second harmonic is at 28 MHz and the third at 42 MHz.
5. Read the harmonic levels as the difference in dB between the fundamental and each harmonic. This difference is what matters. If the second harmonic is 50 dB below the carrier, then it is 50 dB below, however much attenuation you use.

A small instrument has limits of its own. Its input stage can produce harmonics of a strong signal, which then look like harmonics from the transmitter. The way to find out is to add 10 dB more attenuation: a true harmonic of the transmitter will fall by exactly 10 dB together with the carrier, while a harmonic created inside the analyzer will fall faster than 10 dB. This simple test removes most doubts. For the filter that may be needed afterwards, see the guide to the low-pass filter for harmonics. The limits on spurious emissions are set in your national licence conditions, so check them before you decide what counts as acceptable.

Finding Noise and Interference

A spectrum analyzer is excellent at making noise visible. Connect a small whip or a wire as the antenna, set the span to the band that is troubled, choose a narrow RBW such as 3 kHz to 10 kHz, and look at the trace. Interference from switching supplies often appears as a comb of evenly spaced lines. Light dimmers show up as broad humps that vary with the mains cycle. A shared pattern across several bands tells you that the source is wideband and local.

The portable form of the instrument is its strength here. You can walk through the house with it, in a way that a bench analyzer does not allow, and watch the level rise when you approach the guilty charger or the LED lamp. Compare this with the receiver method in our guide to finding and killing RF noise: the analyzer adds a number and a picture to the search, and you can save a screenshot to document the problem for the neighbour or the supplier of the device. The tinySA wiki mentions an optional 20 dB LNA in the Ultra models, which helps with weak sources, but remember that an amplifier also raises the risk of overload when a strong station is nearby.

Testing Filters and Cables

The generator in the tinySA can produce a sine wave across the lower frequency range, and the wiki states that it cannot be used as a tracking generator, since the analyzer and the generator do not work at the same time. That sounds like a disadvantage for filter work, and for a swept measurement it is. A practical alternative is to feed a known signal from a separate source or from a second tinySA, and to measure the level with the analyzer through the filter, point by point. For the shape of a filter, a NanoVNA is faster. For a quick check, such as whether a band-pass filter blocks the neighbouring band by the expected number of decibels, a single frequency test is often enough.

Another use is to check a mixer or an oscillator you have built. A local oscillator should be a single, clean line. Extra lines on both sides show spurious products, hum or poor power supply filtering. The instrument also lets you check the frequency accuracy of a crystal oscillator, although for a precise measurement you want a calibrated reference, which is discussed in the guide to the transceiver frequency calibration.

Limits to Keep in Mind

A low-cost analyzer is a very good teacher and a poor reference standard. The maker publishes a list of limitations for each version, and it is worth reading before you rely on a number. Some general points apply to every device of this class. The level accuracy is a few dB, not a fraction of a dB. The dynamic range is limited, so a weak signal next to a very strong one can be hidden by the analyzer’s own distortion. The high frequency input of the Basic model is described as being of lesser quality, and the screen has a limited number of points, which the wiki gives as 290 for the Basic and 450 for the Ultra, so a very wide span shows less detail. These points do not make the instrument useless. They mean that you should use it to compare, to find and to understand, and not to prove compliance with a legal limit.

Practical Tips for First Use

• Charge it and update the firmware following the instructions on the maker’s wiki, which also has a first-use page and a PC control page.
• Run the self-test and calibration that the device offers, using its built-in calibration signal, before you trust any level.
• Keep a labelled attenuator kit with a 10 dB, 20 dB and 30 dB pad, and add them up on paper before connecting anything.
• Use a good coaxial lead and ferrite on the cable when you measure near a transmitter, so that the cable shield does not pick up and re-radiate RF.
• Save screenshots to the microSD card on the Ultra models, or a photo of the screen on the Basic, so that you can compare before and after a modification.

The Bottom Line

The tinySA is a pocket spectrum analyzer that turns invisible radio problems into a picture. The Basic covers 0.1 MHz to 350 MHz on its main input and 240 MHz to 960 MHz on a second input, and the Ultra family reaches into the gigahertz range. It can check harmonics, hunt for noise, test an oscillator and compare filters, but the input can take only +10 dBm, so an attenuator is part of the instrument. Calculate the level before you key the transmitter, keep a dummy load in the path, and treat the readings as good to a few decibels. Used that way, it is one of the most useful additions to a station workbench.

Frequently Asked Questions

What is a tinySA used for in ham radio?

It is used to see the spectrum of signals: checking the harmonics of a transmitter, finding sources of noise, testing oscillators and comparing the response of filters.

Can I connect my transmitter directly to a tinySA?

No. The maker gives the maximum input level as +10 dBm, which is 10 milliwatts. Use a suitable attenuator and a load, and calculate the level before you transmit.

What frequency range does the tinySA cover?

According to the maker, the Basic covers 0.1 MHz to 350 MHz on its main input and 240 MHz to 960 MHz on the second input. The Ultra models start at 0.1 MHz and reach up to 5.3 GHz or more in Ultra mode.

Is a tinySA the same as a NanoVNA?

No. A NanoVNA sends a test signal and measures reflection and transmission, so it is best for antennas and filters. A tinySA listens and shows the signals that are present.

Is a tinySA accurate enough to prove my signal is legal?

Not by itself. It is accurate to a few decibels, which is good for finding problems and comparing changes, but compliance measurements need a calibrated instrument.

Can the tinySA be used as a tracking generator?

No. The maker states that the generator function cannot be used as a tracking generator because the analyzer and the generator do not work at the same time.