Passive power filter for installation in cars with an on-board voltage of 12 V. The filter is designed to eliminate high- and low-frequency interference created by surrounding power devices, which can affect the operation of connected video devices (image distortion) or the audio path of connected devices (create additional sound interference ). Maximum load 2 A.

Power filter
Connection example

Attention! The filter is sold wirelessly!

Power filter
Notes

Please pay special attention to the most common error. Under no circumstances should you take the negative power pole (ground -12V) from the housing of devices connected nearby!
As a result of such a connection, a potential difference appears, which causes errors and interference in the operation of connected devices. In this case, the filter will not help.
Plus and minus must always be taken from one place, for example, from the standard radio, taking into account that the circuit to which you are connected must have a power reserve and withstand additional devices.

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DIY filter for radio

So, I decided to assemble a filter against RF interference. I needed him For car radio power supply from pulse block nutrition in one recent design. I tried a bunch of them, no matter what I did - the effect was weak. First I put large capacitors in the battery and connected 3 capacitors of 3300 µF 25 volts - it did not help. When powered from a switching power supply, the amplifiers always whistle, I installed large chokes, 150 turns each, sometimes on W-shaped and ferrite magnetic cores - it was useless.

The HF component still penetrated into the amplifier. Then I took the throttle from the radio on an iron core, there are 20 turns of approximately 1 mm wire, an electrolytic capacitor of 1000 µF was inserted in front of it and after 1000 µF 16 volts (although it is better to set it to 25), after the block there is another capacitor immediately at 0.1 µF.

It is this filter that now protects the car radio from RF interference from pulse generators 100 percent. The background has completely disappeared. Using a similar scheme, you can solder the filter into a car, or even better, make it two-section, as shown in the figures below.

Single-stage filter circuit:

Two-section filter:

Note - Filter parts It is best to twist them together closer to each other and place them in a separate box outside the device and the unit in order to avoid interference. There is no need to install too large a container, 1000 microfarads is enough, but to use this circuit in a car, the capacity can be increased several times.

In this article we will discuss how to eliminate interference on a car radio that reproduces a radio signal.

The secret of a high-quality radio signal

Despite the fact that currently there are simply an incredible number of radio stations in most populated areas of our vast country, the quality of the received signal sometimes leaves much to be desired.
The reasons causing deterioration in the quality of radio wave reception can be divided into two types:

Eliminating radio signal interference

Objective reasons

Since in this case we are not able to level the hills surrounding us, disperse the clouds and de-energize the high-voltage power line to strengthen the radio signal, there is only one way to eliminate the interference from the car radio - turn it off or switch to autonomous playback of the audio file, that is, discs (see) , flash drive, etc.

Subjective reasons

Reason #1

First of all, it is necessary to check the interference filter for the car radio, namely its presence and the tight contact of its connecting plugs.

Reason #2

As a rule, in old cars with an inexpensive car radio and on used car radios, this device is simply missing. In the case of an old car, you will not detect it due to the fact that in the recent past, car radio manufacturers did not particularly think about how to eliminate interference in a car radio using a radio interference filter.
Well, in the case of a used radio, this filter often remains in the previous owner’s car on the cut wires, and you can only wonder why, unlike it, the radio reception in your car has deteriorated so much.

Attention! When traveling far from transmitting stations (the strongest signal, as a rule, is located within the city), it is not recommended to use the “local reception” mode, which is activated by the “LOC” key. In this case, the quality of the radio broadcast deteriorates significantly, since weak and unstable radio signals are simply ignored by the car radio tuner.

Reason No. 3

As you probably already guessed, the technical part of the car radio and the terrain conditions greatly influence the quality of the conversion of the radio signal into an acoustic signal; they are responsible for approximately eighty percent of reliable radio wave reception.
This means that we cannot help but note the device that is responsible for the remaining twenty percent of the total power of the received signal - this is the radio antenna. Quality of external radio reception whip antennas and active ones inside the salon are no different. A comparison of them shows that a good indoor active antenna receives no worse than a two-meter whip antenna.
In general, it’s not the price of the antenna, but its correct installation are an important factor influencing the purity of radio signal reception. The only difference between them is that the antenna does not get in the way inside the car and does not attract attention, but unplanned adventures can happen with the rod (driving into a low garage, hooligans, etc.).

Diagnosis of faults and their causes

You can “calculate” a malfunction of the radio interference filter using the following signs:

• “Failure” of the radio wave when the car radio tuner heats up, which requires constant additional adjustments of the radio channel;
• Extraneous noise both from the running engine and generator, and from the cooling system fan, wipers, and, in principle, from all consumers of the car's current, which is provoked by improper power supply to the car radio, which is not equipped with a filter.

Advice! When purchasing an interference filter for a car radio, do not confuse it with a converter that looks similar to it, which has a completely different task - to convert the radio wave range from the Russian “VHF” (65...74 MHz) to the European “FM” (87.5...108 MHz).

Also, do not forget that the causes of radio interference can be problems in the electrical equipment of the car itself, and which cannot be removed by any filters.

A competent auto electrician will tell you how to eliminate interference in the car radio in more severe cases (checking the generator brushes, relay regulator and similar troubles).

Making a radio interference filter

Very often, when buying an interference filter for a car radio, we are, to put it mildly, not happy with the result. When opening a purchased filter, as a rule, we can observe the following picture.

That is, for a symbolic price we have a capacitor and a choke wound on a ferrite ring. It is clear that by studying this miracle of technology, we will not be able to find the answer to the question of how to eliminate interference on the car radio.
It is also clear that we will need a better filter. Well, since you and I “have a mustache ourselves,” I propose to make a radio interference filter for a car radio with our own hands.
The instructions for making your own filter are not complicated at all.

The design of the radio interference filter usually uses a T-shaped circuit:

• A fuse is installed in the positive circuit;
• Then, following the diagram, a coil with a tap is installed on a capacitor connected in turn to the housing;
• And from the same tapping point, another coil is installed on the capacitor, before connecting to the car radio; car radio speakers (crackling, clicking, etc.) precisely while the car engine is running. And until the listed malfunctions of the car’s electrical equipment are eliminated, no filter will save you from radio interference!
  Are you sure you don't have any problems with your car?

Power supply interference is a problem for many motorists who want to use communication equipment in their car. Fight them different ways and by installing ferrite rings on the power wire. Or you can install a factory product called a commercially produced power filter.

I was interested in this small box that promised to remove all reception interference. She looks completely inconspicuous. Just a box and 3 wires. As it is written on the package, we connect the red wire to the power source, connect the black wire to ground, and connect the radio station or radio to the white one.

This miracle costs 250 rubles and this is what is inside it.

To be honest, I did not imagine that there could be anything different inside, but I was more surprised by the quality of execution.

Essentially, this is a single-link G-filter consisting of inductance and capacitance. Classic.

The inductance of the inductor, measured with an LC meter, turned out to be about 0.290 mH. The capacitor capacity is 33 µF.

Without going into technical details, such a filter can effectively combat interference that penetrates the power supply into a radio station working for reception or for a car radio. For transmitting equipment we will have to come up with something more efficient.

However, the efficiency of the filter can be increased by adding an electrolyte to the filter input and a small capacitance film capacitor in parallel with it. For example, 100uF (or more) + 10nF.

Poor quality radio sound, constant wheezing and humming from the speakers, engine roar - a familiar phenomenon for owners car radio. Although we already live in the 21st century and modern car radios They have long been digital with processor control, but nevertheless, among us there are owners of old car radios who do not want to replace their old friend with a more modern and multifunctional radio.

So, first, let's make a throttle. Winding can be done on a ferrite ring, although a ring of powdered iron, which can be found in computer units food (yellow or white ring in color). A winding is wound around the ring, which consists of 10-15 turns of wire with a diameter of 1-1.5 mm. For ease of winding, you can use several strands of thinner wire, for example, 3 strands of 0.5 mm wire (each).

After winding the inductor, we assemble a simple circuit. This scheme works effectively even with a wide range of values ​​of the components used - capacitors are not critical, you can use electrolytes with a voltage of 16-100 Volts (no more sense), capacitance from 1000 to 4700 uF (the more, the better).

The circuit is not intended to completely suppress noise, since the main problems may arise due to malfunctioning of the ignition system (for example, a spark jumps from the spark plugs to the wiring, etc.) - in these cases, the filter is useless.