Which equipment is required to test the no radio device for compliance with electromagnetic compatibility (EMC)?
This is called precompliance testing. It is useful, and recommended, because while less accurate and precise, it can detect design mistakes earlier than otherwise.
First of all you need a book you can trust. A book like Electromagnetic Compatibility Engineering by Henry W. Ott specifies exact requirements for European, American and Canadian regulations, recommended procedures, advises on design and contains in depth chapter on precompliance testing. It is from the reputable author and has many positive reviews in Amazon. Of course you also need to read it but there is nothing there impossible to understand. All other suggestions in this answer are from this source.
Antennas are not recommended in this kind of testing: they are large, sensitive to nearby reflections and interact with metal objects. It is more reliable to measure some parameter that is proportional to the radiated emission. Instead, small probes just few inches size are used. The shielded room is also not required and can introduce huge errors if wrongly implemented. It is possible to verify the source of EMC inference (our device or something external) by simply powering the device under testing down.
Cables are usually the major source of emission so clamp on probe around the device cable (if it has any) should be tried first. Most cable radiation occurs below 250 MHz. All cables must be measured for inference, regardless of they function. This is called common mode radiation. These measurements require the HF current probe clamped on the cable. The devices mentioned in the book cost unfortunately $2000+ even if used. Here is an innovative device below $1000 from Tektronix, wonder what it could do.
Another kind of inference results from current flowing around loops in PCB. This is called &quot;differential mode radiation&quot; and needs another probe. The source mentions probes with the range up to 500 MHz as useful. &quot;Professional&quot; probe set may cost about $1000 but they are actually very simple devices and can be hand made from several pieces of high frequency cable (the book contains the drawing). Anyway they cannot give numeric results for saying how much is the device compliant, but can help to find the source of the RF noise and would tell if you have a lot of it.
The most expensive part of equipment is the spectrum analyzer. The book source calls $15000 analyzer &quot;ok&quot; but there are more bearably priced devices on Alibaba.com. Some of them may be good enough for precompliance testing.
You can also do the noise voltage measurement on various power circuits. This can be done with high frequency oscilloscope. They are helpful in pinpointing the source of emission.
A simple precompliance testing for the radiated immunity can be done with some power tool containing a brushed electric motor. The arcing that occurs on brushes emits very broad range of electromagnetic noise. Move it 1 m from the PCB across the board and observe the behavior of your device.
A simple device for ESD (electrostatic discharge) tests can be made from pjezoelectric fire lighter.
Finally, if you really want to measure real radio emissions, pack your antenna, spectrum analyzer, device, portable power source and go somewhere deep into the woods where mobile phones are unlikely because there is no coverage.
Most of the approaches to achieve the EMC are not any secret and can be found in the literature. The problem is that in some cases simply adding ferrite bead or decoupling capacitor in a wrong way may even worsen the problem. Even rather approximate measurements would show if the situation has improved or getting worse.