Hello dear authors, journalists, readers!
I was prompted to manufacture this device by an egregious case. I was watching TV, suddenly the image completely disappeared, and a low-frequency sound with the frequency of the mains went from the speakers, and intermittently. Apparently it was electric welding. Someone in our block of flats has cheated. Several years ago, a friend's antenna cable in his apartment even melted under similar circumstances. How this can happen – there are several options. For example, the cable was led through a metal structure, and they began to cook it. As a result, there was a powerful pickup on the cable.
It's good that I have a connector available, I quickly managed to disconnect it, otherwise both of my TVs would probably be out of order.
To protect my equipment once and for all from such cases, I made this protection device. And this task is not as simple as it might seem at first glance. Firstly, it is necessary to ensure reliable protection of the cable along the central core and along the screen (braid) from a voltage of at least 220 V. Secondly, the device should not give a noticeable attenuation of the signal. Thirdly, it should be easy to connect to the existing cable network.
I considered two options for the protection device. Based on transformer or capacitive decoupling. I decided to stop at a capacitive junction. Here is a schematic diagram of the device.
It's very simple. The role of protective elements is performed by high-voltage ceramic capacitors of relatively small capacity. They practically do not have resistance to high-frequency currents, which television signals are, and accordingly do not weaken the signal. But for a mains frequency of 50 Hz, they represent a high resistance. Thus, when the mains voltage hits the antenna cable, the current will be limited to a level that is safe for TV equipment.
For some time I thought about the design of the device. Namely, how to do to enable it without reworking the existing cable network. I came to the decision to install F-connectors of the “male” type at the input and output of the device, this will allow you to connect the device to the splitter and the supply cable through the connector. As shown in the photos.
Details and materials: < br> 1) Ceramic capacitors 680 pF 1 kV – 2 pcs.
2) F-connectors “male” – 2 pcs.
3) Connector for F-connectors
4) Coaxial cable with a characteristic impedance of 75 Ohm, length 0.5 m
6) Solder, rosin, active flux, alcohol wipes
This set of parts:
These are high-voltage ceramic capacitors. They can be dropped from an unusable computer power supply unit or office equipment. I dropped out of an old copier. The capacity can be from 470 to 1000 pF, the operating voltage is 1-1.5 kV.
STEP 2. Fitting parts (cutting the leads of cables and capacitors so that the circuit fits into corpus).
STEP 3. Prepare the cable. I cut the cable into 2 equal lengths. Stripped the ends and screwed on the connectors.
Stripped other ends and tinned it. I must say that this process has its own characteristics. The central core is tinned without problems, but the braiding of such cables in most cases is not soldered with rosin. Therefore, an active flux had to be used. Here's a
Service cable ends
STEP 4. Soldering parts. To do this, I fixed the cables on the device case with electrical tape, and then I unsoldered the circuit. Then I carefully removed the circuit from the case and thoroughly cleaned it and the case from the remnants of active flux using alcohol wipes.
STEP 5. The assembly put the circuit in the case and connected the halves of the case with screws. So I was not sure of the good insulating properties of this case at high frequencies, so I wrapped the circuit with a thin fluoroplastic tape.
STEP 6. Checking with a multimeter. I believed that there were no short circuits between the contacts of the input and output connectors. Then I checked for no contact between the inputs and outputs of the device. By the way, his entrance and exit are equivalent. Finally, switching the device to measure the capacitance, I checked the capacities between the inputs and outputs. They should be around 680pF. After making sure everything was in order, I started testing.
STEP 7. Testing the device. I connected it to the splitter and to the input cable.
No deterioration in image quality was observed. Moreover, the amount of low-frequency interference from various power tools, such as a drill or a hammer drill, has decreased.
Thank you for your attention.
I hope this article will be interesting and useful to you.
I will be glad to your comments and wishes.
Best regards , R555
Hello dear authors, journalists, readers!