Question: A copper wire of length and diameter cm has what modulus of impedance at MHz?

A radio transmitter at a frequency of MHz and power kW creates what electric field strength, assuming an isotropic antenna and free space, at a distance of metres?

Faraday's Law is:

Two circuits, each about 25cm long and 5mm apart, are screened from each other by an aluminium foil 10μm thick which is grounded to one circuit's 0V reference by 10cm of 16/0.2mm wire. The circuits carry broadband analogue signals up to 100MHz in bandwidth, and by chance it is found that when the foil is removed, the interference from one to the other goes down by 10dB. What is happening?

Measurements show that an RF field at 100MHz within a few cm of a radiating source has an electric component of 10V/m and a magnetic component of 0.66A/m. How does this compare with the field that the source would produce 3m away?

A 2kW variable speed drive is driven from an inverter at 5kHz with a 380V peak output via an unscreened cable. Running 10cm from this cable for a distance of about 1m there is a twisted pair audio line-level signal of 0dBm (1mW) into 600 ohms. The audio circuit expects a signal-to-interference ratio of at least 40dB at 5kHz. Will it achieve it?

In the circuit opposite a "single point ground " is implemented at G in the apparatus. However, the opening and closing of switch S is found to produce flicker due to a change of voltage across the light bulb, as measured between points B and G. Wire size 32/0.2mm (50-metres long) connects V_N and G, and the same wire size and length connects V_L and A. A 1m length of 7/0.2mm wire connects A and B. The resistance of 32/0.2 wire is 19.1Ω/km and of 7/0.2 is 88Ω/km. What is the change of voltage across the light bulb when the switch is opened and closed, neglecting inductive effects?

In the circuit of Q7, the 32/0.2 mains wires are separated by (on average) 5mm. In the steady state and assuming that the supply is an undistorted 50Hz sinewave, will their inductance significantly affect your answer?

Because of the flicker, the circuit of Q7 has been modified to reduce the length of the supply wires from 50m to 5m. You want to control the heater to half power by pulsing it on and off at a 50 duty cycle. The flicker requirement of IEC 61000-3-3 for this kind of waveform is shown opposite, which gives the maximum allowable voltage variation in percent versus number of voltage changes per minute, where 1200 per minute give 10Hz flicker. What switching frequency limits apply to the heater to comply with this requirement?

A product in a plastic case of about 10x15x30cm has several ports, connected to cables of 1-2m length. It is tested for RF susceptibility and shows an unacceptable effect at the test level over the frequency range from 80 to 150MHz. Are you going to concentrate on:

A clock generator at 25MHz creates a fifth harmonic current of 5mA on a straight PCB track of length 5cm which sits 1.5mm over a ground plane. Will the radiated emission at this frequency directly from the PCB breach the 3m Class B limit of 40dBμV/m (47dBμV/m above 230MHz)?

The same circuit current and frequency as in Q11 creates a voltage across the ground plane due to its impedance of 300mΩ. This voltage feeds into a 24cm length of wire which has an impedance at this frequency of 150 ohms. Again, will the radiated emission at this frequency breach the 3m Class B limit of 40dBμV/m (47dBμV/m above 230MHz)?