1-Bands Frequency and Wavelength

1-The basics of bands, frequency and wavelength

This is to help you understand the basics of radio transmission modes to give an overview of what is out there.
Frequencies, wavelength and bands

Basically, wavelength is the inverse of frequency.

Frequencies

Frequency(Hz) = C (3x 10^8M/s) / Wavelength (Metres) 

where C is the speed of light, approximately 300 million M/sec.

Let’s simplify the digits for 145 Mhz

The wavelength of the 145 Mhz band is 2 Metres = 300 / 145 Mhz to the nearest whole number. 

Wavelength 

The frequency of the 2 metre band is 150 Mhz = 300/ 2 metres

Bands

A waveband is an approximation to communicate a band, not an exact measurement, and is based on the lowest frequency. 

A ¼ wave antenna at 145 MHz would be 2M/4 each element

That’s 0.5 * 0.95 velocity ratio, = 0.491379310344 so just start longer than  0.5m

Velocity ratio allows for radio waves travelling slower in a conductor than in a vacuum.

https://codingace.net/physics/frequency_cal_antenna_equations.html

All band allocations vary across the world so you may hear things that you do not expect in places you don’t expect them.

0-30 Mhz is High Frequency. There are sub-bands within especially at the low end, HF is mainly for long distance work, broadcast and amateur radio, CB. Long distances 50-5,000 miles!

Broadcast HF bands

120 meters: 2.3–2.495 MHz (overlapping upper medium frequency / lower HF)

90 meters: 3.2–3.4 MHz

75 / 60 meters: 3.9–4.0 MHz (region dependent, often shared)

49 meters: 5.9–6.2 MHz

41 meters: 7.2–7.45 MHz (shared with amateur radio globally)

31 meters: 9.4–9.9 MHz

25 meters: 11.6–12.1 MHz

22 meters: 13.57–13.87 MHz

19 meters: 15.1–15.8 MHz

16 meters: 17.48–17.9 MHz

15 meters: 18.9–19.02 MHz

13 meters: 21.45–21.85 MHz

11 meters: 25.6–26.1 MHz [1]

Amateur Radio HF bands
160 m 1.6Mhz to 2.0 Mhz

80 m 3.5 to 3.8 Mhz

40 m 7.0 to 7.20 Mhz

30 m 10.1 to 10.150 Mhz

20 m 14.0 to 14.35 Mhz

17m 18.068 to 18.168 Mhz

15 m 21.0 to 21.450 Mhz

11 m 27.60125 to 27.99125 Mhz * UK CB Radio (license free)

12m 24.89 to 24.999 Mhz

10 m 28.0 to 30.0 Mhz

https://rsgb.org/main/operating/band-plans/hf/

https://www.red-radio.co.uk/CB-Frequencies

VHF

30 Mhz to 300 Mhz, portable and hand-held radios, aviation, television, emergency services and maritime, medium distances often to High antenna base stations or repeaters 5 to 200 miles.

6 m 50.0 to 52.0 Mhz
4m 70.0 to 70.5 Mhz
2m 144.0 to 146 Mhz

UHF

300 - 1000 Mhz , portable and hand-held radios amateur radio, PMR446, emergency services, mobile to base line-of sight, medium distances 5-100 miles
70cm 430.0 to 440 Mhz

https://rsgb.org/main/operating/band-plans/vhf-uhf/

PMR446 – (The Modern CB) is license free!
PMR446 stands for Private Mobile Radio, which is a licence-exempt personal radio service operating on frequencies between 446.0 MHz and 446.2 MHz, primarily used for short-range communication in Europe and some Asian countries. It allows users to communicate without needing a license, making it popular for both recreational and business purposes.

You cannot legally use a radio that is not specifically designed for PMR446 only.
https://www.ofcom.org.uk/siteassets/resources/documents/manage-your-licence/business-radio/business-radio-guidance/ir_2009_analogue_and_digita1.pdf?v=335306

PMR – Private Mobile Radio The acronym PMR is not the same as PMR446. That refers to Private Mobile Radio and needs an Ofcom business radio license.
https://www.dcrs.co.uk/what-type-of-radio-licence-from-ofcom-do-i-need/

UHF/Microwave – uses dishes rather than antenna and is strictly line of sight

1000 Mhz (1 Ghz) to 3 Ghz UHF, but generally referred to as Microwave, drum dishes connecting other services, very focussed line of sight < 200 miles (I personally received aircraft 1090 Mhz ADS-B signal at 230 miles)

https://globe.adsb.fi/
https://radio-hobbyist.com/how-to-track-aircraft-with-ads-b-and-an-sdr/

3 Ghz to 30 Ghz - Radio astronomy, microwave devices/communications, wireless LAN.

To be honest these require specialist equipment that is often expensive, or bought send hand from clearance sales or for you to build yourself which need RF antenna design experience.

https://rsgb.org/main/operating/band-plans/