I still have an antenna from an old TV from a foreign company, bought in the 90s of the last century. It is interesting that a circuit diagram was attached to the TV set, with which I successfully repaired the TV a couple of times. Now in the new 20th century, electrical circuits complete with goods are not offered. I wondered if this antenna can be used to receive the digital signal of modern television.
Fig. 1. Antenna from an old TV of a foreign company.
The object for modernization is an antenna of the type “symmetrical vibrator with matching transformer”, with two parallel wires in the dielectric, located at the same distance, and a connector for connecting to the antenna jack of the TV or set-top box.
Fig. 2. Close-up matching transformer.
Fig. 3. Close-up plug.
The symmetric vibrator is model from the field of theory, it consists of two conductive segments, each of which is equal to 1/4 wavelength (1/4 λ), and its total length is 1/2 wavelength (1/2 λ). λ is the designation of the wavelength in physics.
Fig. 4. Total antenna length.
The length of my antenna in the shortest form, that is, in the form for taking the shortest wavelength for this antenna, was 50 centimeters.
Fig. 5. Measuring the length of the antenna.
Fig. 6. Enlarged image of the caliper scale.
Using a calculator to calculate the dipole and pin (symmetric vibrator) on the substitution method, I determined that with the highest efficiency my antenna will receive a signal with a frequency of 284 MHz. So it should be, since this is a meter-long antenna.
Fig. 7. Print screen calculator for calculating dipole and pin.
The broadcast frequency of digital television has become more high-frequency. I found out the frequency of broadcasting in my city on the website of the Russian television and radio broadcasting network. The broadcasting frequency of digital television in the city of Buzuluk for the first package of television channels is 610 MHz, and for the second package - 626 MHz.
Fig. No. 8. Print screen of the interactive map of DEC.
So, we have an antenna with the maximum efficiency of receiving a television signal at a frequency of 284 MHz, and we need an antenna at a frequency of 610 MHz, that is, we need to shorten our old meter antenna.
To determine how much to shorten the antenna, I used a calculator to calculate the dipole and pin.
Rice number 9.Print screen calculator for calculating dipole and pin.
Fig. 10. Print screen calculator for calculating dipole and pin.
For effective reception of the first package of TV channels, the total antenna length should be 23.33 cm. But I decided to play it safe and shortened the antenna to 30 cm.
Fig. 11. The total length of the shortened antenna.
Before shortening the antenna, I tested its effectiveness with a digital set-top box. The signal intensity was 73% and there was no television reception. After shortening the antenna and checking its operation, the signal intensity was 78%, 100% quality and reliable reception of television programs appeared.
Fig. 12. The setup screen when operating a TV with an entire antenna.
Fig. No. 13. TV setup screen and antenna (total antenna length 30 cm.).
Fig. 14. TV setup screen and antenna (total antenna length 29.3 cm.)
Shortening the “horns” of the antenna, I decided to enter the results in the table:
After bringing the total length of the antenna to 23.3 cm. I was alarmed by the results. I also decided to reduce the length of the "horns." As a result of locksmith work, it turned out to reduce the total length of the antenna to 19.4 cm. And further refine the antenna to smoothly change its length. Results in the table.
Fig. 15. Details of the sliding contact of the "horns" of the antenna.
Fig. 16. Modified antenna.
Somewhere on the Internet, I read that the transmitter power for a package of RTRS-2 TV channels is less than the transmitter power for a package of RTRS-1 TV channels.
As a result of the work done, I came to the following conclusions:
- a redesigned antenna can be used in my conditions to receive a package of RTRS-1 TV channels on TVK 38;
- in the manufacture of home-made small-sized antennas for digital television, it is necessary to use an antenna amplifier.
I hope that what I wrote will be interesting to someone.
Good luck