Antena Asas


Beberapa kali pertanyaan mengenai antenna sampai kedalam peti emel saya, tiada perkataan atau ayat yang boleh menerangkan sehingga faham dan boleh membayangkan rupa bentuk antenna tersebut. Amat kecewa rasanya jika apa yang terangkan itu menjadi satu satu kesilapan dan kesalahan yang besar kesan atau akibatnya. Pada rakan-rakan yang terus mencuba dengan penuh kesabaran sehingga berjaya, tahniah itu adalah bonus untuk anda. Dengan kejayaan itu anda dapat memahami prinsip asas antenna dan membuat satu antenna yang berkualiti sebagai seorang ahli radio amatur yang sentiasa ingin kehadapan. Beberapa petikan yang pernah saya cetak dari internet berkisar tentang asas antenna seperti berikut:-

The basic antenna

The most basic antenna is called “a quarter wave vertical“, it is a quarter wavelength long and is a vertical radiator. Typical examples of this type would be seen installed on motor vehicles for two way communications. Technically the most basic antenna is an “isotropic radiator“. This is a mythical antenna which radiates in all directions as does the light from a lamp bulb. It is the standard against which we sometimes compare other antennas.

This type of antenna relies upon an “artificial ground” of either drooping radials or a car body to act as ground. Sometimes the antenna is worked against an actual ground.”

Asas untuk anda memahami tentang antenna ialah panjang gelombang🙂 (Wavelength) ada formula yang boleh digunakan sebagai panduan untuk mendapatkan ukuran antena yang akan anda bua, berikut petikan yang terdapat dalam buku catatan saya;

WAVELENGTH

Originally in radio, the frequency of signals was not mentioned. The custom was to refer to the ‘wave length’.

This is easily computed from:

 

300,000,000 / Frequency (cycles) or 300 / Frequency (Mhz)

In reality this indicates, from a purely technical standpoint, that a wavelength is determined by dividing the speed of light by the signal frequency in cycles per second. The underlying reason here is that radio waves do travel at the speed of light. This is approximated as 300 million metres-per-second (and no correspondence will be entered into on that point).

Just how the custom of talking in wavelength originated I have never been able to establish. I suspect it had a lot to do with transmitting antennas where the calculation is quite critical.

As frequencies increased by about the 1930’s the wavelengths diminished in physical size to the point the term ‘short-wave‘ came into vogue.

To understand radio waves etc. visualize a pebble dropped into a pond. At the point where the pebble hits the water the transmitting antenna is situated. Waves then radiate outward from that antenna.

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