HF Telsiz

Giriş
High Frequency (HF) için açıklama burada. Muhabere cihazları genellikle 0 - 2 Ghz arasında çalışır. Radarlar ise 2 - 50 Ghz arasında çalışır

Radardan farklı olarak muhabere cihazları yansıyan sinyali okumaya ihtiyaç duymaz.

Gökdalga
HF Telsizler muhabere için gökdalgayı kullanabilir. Açıklaması şöyle

HF propagation over long distances is by skywave propagation, the reflection and refraction of radio waves between Earth's surface and the ionosphere. The ionosphere is a consequence of radiation from the sun ionizing Earth's atmosphere, so it changes significantly with time of day and sunspot activity.

Gökdalga'dan defalarca sekme yapılabilir. Açıklaması şöyle

Unlike VHF and higher bands, which travel mostly via line of sight and therefore have limited range depending on altitude, HF radio relies on skywave propagation. This means the radio waves travel up, bounce off a layer in the upper atmosphere and then travel back down to the receiver. They may even bounce up and down between layers several times, allowing one to receive signals from the other side of the planet. You may be able to talk to stations far away but not nearby, or the bounces may not work the same in both directions. It’s unpredictable.

All of this odd bouncing depends on atmospheric conditions, which vary from place to place and even from hour to hour. Worse, different parts of the HF band will behave differently at the same time and place, so it has been broken up into several sub-bands of frequencies that tend to behave similarly.

That is why oceanic flights are given two HF frequencies in different sub-bands: at least one of them will probably work. Probably. And which one (if any) may change over the course of a long flight!

Worst of all, because of this long-range behavior, every station on the planet needs a unique frequency, and there isn’t a lot of bandwidth to go around, which is why it is chopped up into very narrow channels that give horrible sound quality. So, HF is only used when absolutely nothing else will work (or is available).

İyonosfer en iyi gece çalışır. Bazı dalga boylarının açıklaması şöyle

6m- Randomly opened, in random directions. I think this happens more in the day, but I'm not a 6m expert. Strictly speaking this is VHF, not HF, but it's often included on HF rigs.
10m- This is more consistently opened, especially in times of higher solar activity. Evening tends to be the best time, at least that's what I've found, but this is a daytime band.
12-17m- These are traditional daytime bands, usually opened. The longer the band in this window, the more reliable it is, and the more likely it is opened night or day.
20m- Can be opened day or night. This is the most reliable band for dx.
40m- Daytime is opened in a "local" area, give or take 500 km or more with a good set up. Night time opened worldwide.
80m- Similar to 40, but even more extreme.
160m- This one is only opened at night, and tends to be a more local area. Not unlike 6 meters, strictly speaking this is MF rather than HF, but it's often included on HF rigs.

HF Anten
Genellikle büyük antenlerdir. Açıklaması şöyle

At lower frequencies a wavelength is longer, making it more difficult to design antennas to fit into small devices. The signals travel farther which makes coverage easier and less costly.

HF ve Dijital Muhabere
Yüksek hızlara çıkmak pek mümkün değil. Açıklaması şöyle

Digital communication on the HF bands is inherently more difficult than on VHF, UHF, and higher bands, due to noise, fading, and many other issues; the bit rate varies according to the signal-to-noise ratio.

HF ve Video
Video göndermek için yeterli bant genişliğine sahip değildir. Açıklaması şöyle

In general, the HF bands (1.8 MHz through 30 MHz) do not have sufficient bandwidth to support live transmission of a video signal. In the US, the FCC does not authorize an emission mode for live video on HF. The lowest available band in the US that supports live video is 70 cm (~440 MHz).

Bandwith İçin açıklama şöyle

10 MHz of bandwidth contains the same amount of information, regardless of whether it's centered at 900MHz or 2600MHz, or any other center frequency.

Yani frekansın ne kadar yüksek veya düşük olduğu önemli değil. Bandwidth daha önemli. Açıklaması şöyle.

By quick analogy (the other answers are sufficient in their detail):

If you own a hotel where all the rooms are the same size (bandwidth), it doesn't matter how high a floor (frequency) they're on--they all hold the same amount of stuff. If you have some larger rooms (more bandwidth), they'll hold more stuff, whether they're on the 2nd floor or the 26th.