Electrical hum at home

The coexistence of equipment of different technologies coupled with poor installations facilitates the emission of electromagnetic energy and this can cause EMC problems.

The topology and distribution of the wiring, the types of cables, the protection techniques are factors to be considered to minimize the effects of EMI. Do not forget that at high frequencies cables work as a transmission system of crossed and confused lines, reflecting energy and diffusing it among all circuits. Keep connections in good condition, as connectors that are inactive for too long can develop resistance or become RF detectors.

Many times the reliability of a control system is put at risk due to poor installations. Generally, users are compromised and, after more thorough analysis, problems involving cables and their routing and packaging, shielding and grounding are discovered.

It is of utmost importance to have the awareness of all participants and above all, the commitment to reliability and safety of operation of machines and people in a plant. This article provides information and hints on grounding systems, emphasizing that local regulations always prevail in case of doubt.

Electrical noise solutions

The result can be erratic circuit performance, reduced resolution and accuracy, and increased bit error rate (BER), at best. At worst, it can cause total system malfunction or frequent or intermittent performance problems, both of which are difficult to debug.

Switching DC/DC regulators and their output rails present two main noise problems: ripple and radiated noise. The noise generated in a circuit is subject to electromagnetic compatibility (EMC) regulatory mandates and must be below specified levels in the various frequency bands.

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The easiest noise to observe, and the one that has a direct impact on circuit performance, is the ripple at the switching frequency. This ripple is typically on the order of 10 to 20 millivolts (mV) (Figure 1). Although not random in nature, it is still a manifestation of noise that affects system performance. The millivolt level of this ripple is not usually a problem for high-voltage digital integrated circuits operating on rails of 5 volts or more, but it can be a problem for low-voltage digital circuits operating at less than 3 volts. Ripple on power rails is also a major problem in precision analog circuits and components, so specification of the power supply rejection ratio (PSRR) for these devices is critical.

Is it normal for the light box to make noise

I am looking for recommendations on how to reduce noise in this preamp circuituser103218I have a circuit that uses MMBT3904T-7-F parts, running at 100uA collector current, which is quite noisy. This is a preamplifier for the 475 kHz ham band.

Your test circuit (grounded emitter) has no ability to reject power supply noise. Stick 1Kohm on that VDD line and place a limit of 1,000uF. Your 0.16Hz F3dB promises 60dB of attenuation at 160Hz, 58dB at 120hz and 52dB at 60Hz. Now you can rely on what you see in the scope as random noise.

glen_geekI’m not familiar with LTspice noise analysis (I use a different tool). I was curious how your GUI works, and ran most of your circuit. Your circuit is not bad at all, but keep in mind that SPICE models of transistors are generally not meant to characterize noise sources correctly (they are optimistic). But you do get a picture of the noise source contributions from the resistor.

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Types of telecommunications noise

FinbarrIt depends on what type of noise you are talking about. I suspect, given the configuration of Q3, that you are getting a very distorted output because Q3 is not biased to work in your linear region.

You may want to consider a push-pull output stage: read about class AB amplifiers. You may also want to investigate some of the free online circuit simulators: you can feed your circuit a test waveform and observe the points around it with a virtual oscilloscope. It will become painfully obvious where the problems are.S. BrokenThank you very much, the situation improved a lot! There is definitely a lot of static left, but it’s much clearer now.

1) Power supply. I’m not going to calculate a PSRR for this, but for any amplifier without feedback it is likely to be poor. To eliminate this noise, start by powering it with batteries. (USB power supply units are not suitable for this).