Outdoor or indoor antenna? To buy or to do?

11.03.2015 by: lz3ai

Making of antenna is a simple job that describes three activities:

– Cutting of rods and cables;

– Rasp, etc.;

– Turning screws and nuts.

(The book also wrote by the same way – press the keys in determined sequence.)

lz5ug_ant_dig_tv

The Faraday cage 64 channel

Why the large antennas are external and “very cool catch”? (And also they are more expansive, ’cause they do most Western’.)

  1. Because there is a very long rail on them and thus cannot her tours in the kitchen, so for this – out.
  2. You try to pick the most highly that person still wants to get the burning of Everest, Botev, Black Peak or at least Kopitoto (restaurant). If you drive – perfect.
  3. “Cool catch ” because in the greatest possible lifting ensures signal reception with better detection of Fresnel zones and thus the signal is better intensity than if the antenna is seven or eight or more meters down .
  4. Much of the proposed corporate-made antennas are with amplifier exactly on the vibrator and from there goes feeder vessel to the TV. Infinitely right decision. However, the amplifier is subjected to all the wonderful outdoor conditions and thus will not be his very long life.

Why the big TV antenna structures more please the eye than to do the work in the advertised frequency band – example of 21-69 channel? Because:

  1. If the vibrator has a wave resistance approximately 75 ohms on 650 MHz, the same vibrator (the antenna is the same) on 490 MHz is about 35-40 ohms and on 818 MHz is 110-115 ohms. The example of the 490 and 818 MHz is real Sofia broadcasting and goes to show that when you read the inscription on the box for 75 ohm-volume TV antenna, this is true for mid-range or knows where on it. More here coordination and trying to make a go to …
  2. All distances between vibrator, directors and reflector are frequency dependent (as defined) and thus, the antenna will be directed to one and one to two adjacent frequencies, but for other frequencies in the range will only work as an ordinary vibrator one-dipol antenna (and with a vague wave resistance). Salvation comes from lifting high.

Yes, I’ve done seven-element antenna, however, it was for only 145 MHz and there fell a great fight and a setting. Range is simply unthinkable. There are devices with coordinated steps filled with capacitors and coils for electrical shortening or lengthening, but TV you certainly do not have them.

  1. The logo-periodic antennas really work in a wider range, but they hardly work more than two to three units for different frequencies, because alas and apply to them the laws of physics. For comparison, a good to excellent set 3-element “Yagi” antenna gives about 5-6 dB gain. However, if someone has a tendency to disregard laws can earn from 12 to 18 log periodic decibels. If parliament votes to repeal these laws, then things will come into place, but they do not want!

A major influence on the phenomenon has taken interference waves which occurs in all cases where the path of the signal distribution has ground obstacles and objects (even if not closed) along the lines of block, house and even iron barrel to collect rainwater . This brief I have described in Methods of finding a location of an indoor “antenna for digital TV“. It has been reported in the title are easily available.

The other important thing is that the cable (feeder) must be a multiple of a length half the wavelength (λ) multiplied by the coefficient of shortening and the condition is satisfied for all frequencies are taken TV – in most places in Bulgaria they are three. What if this is not met? Obtained excellent results (ideal) or accept anything regardless of the antenna, cutting or adoption of a canal and the others are worse.

Such examples – so many as you like.

The case of the length of the feeder multiple of λ / 2 is valid when the shoulder/arms have dipole length λ / 4 (for the accurateness – 0,253 λ to be 75 ohms). However, this dipole is for one frequency and higher long (i.e., resonant length) and a lower frequency will be too late at resonant. So what – when the dipole is longer feeder needs to be shorter for the thus produced configuration, and, when the dipole is shorter – feeder needs to be longer. When good is “disordered” these three cases, the output of work done already antenna feeder device must signal out of the three (or as calculated) frequencies with maximum possible amplitude of the voltage induced in the antenna. Solution of the problem is easy. Personally, I took about two or three months ahead of time.

Adopting a scruffy signals can be created fullwave dipole, i.e., shoulders a length of λ / 2 and then feeder vessel must have a length n * λ / 2 -(+) λ / 4 and not to forget ratio shortening. And I work on top the logic in shorter arms longer feeder or vice versa, and all these conditions are met in one configuration (one antenna feeder unit).

I personally made my passive (no amplifiers) antennas have achieved the following results (with the permission of my wife, of course!):

– Village Padesh near Blagoevgrad. In this village is not accepted terrestrial TV and the news was reporting that people preen for “rebellion” for having been deprived of this option. Made respectively device and went there – came three multiplexes. God willing.

– Village Kremenik near Dupnitsa, which is located above the dam Dyakovo. Also people do not watch broadcast television due to impossibility. Went there and channels of the three multiplexes.

– Village Zhivkovo near Ihtiman. Neighbor methodological my head in fishing trial version with lifting heights of big antenna with technical assistance digital team. The result is a pass to an alternative provider (cable, satellite), together with some profanity. At the same time, the fishing guru watching me with my passive antenna fabrication, which is located in the room.

– Village Beli Iskar near Samokov. “Crummy” place with over 70 meters of excess land mass in the middle of the 3.5 km route through which excess does not pass and the third Fresnel zone (i.e., whatever touches of fifth). Had erected a new external logo-periodical antenna, but did not accept a package of BNT, which is taken to 722 MHz, and the package of bTV, Nova TV and TV7 of 626 MHz was accepted with periodic interruptions. After placing the amplifier (amplification max) fix adoption. The situation does not satisfy me. Some efforts already taken with indoor antenna without amplifier.

– And I cannot even remember how many seats village Vladimir in the lowest part, Kocherinovo, Gorni Dabnik near Pleven, Varvara (between Tsarevo and Ahtopol) in the lower part below the center and so on.

From Sofia and surroundings also there are not reception problems, whether first or last floor, overlooking or the reverse side to the transmitter and show work in a workshop (auto workshop) which in practice is pure “Faraday cage” – all inside a metal structure with a corresponding bonding (all metal columns in the ground). Acceptance is a 64 channel – TV vest.

If you think incredibly written here, re-read the article.

Otherwise, the proliferation of VHF is “God willing!”

sv

Svetoslav Stoyanov, LZ5UG

lz5ug@dir.bg

Filed under: Antenas,HAMs
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Comments

One Response to “Outdoor or indoor antenna? To buy or to do?”
  1. Димитър Радев says:

    Пич, та дрънка!!! И това за жената е вярно… Разрешава му да лови сигнали и риба, но само толкова!!!!!

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