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daltonman

newbie question

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whats is meant by 70 cm -2 meters- 6 meters -10 meteres .another question will the handhelds outperform a 5 watt cb in range ? not using repeators just talking handheld to handheld . if so what distance will they go in flat terrain ? thanks

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quote:
Originally posted by daltonman:

whats is meant by 70 cm -2 meters- 6 meters -10 meteres .another question will the handhelds outperform a 5 watt cb in range ? not using repeators just talking handheld to handheld . if so what distance will they go in flat terrain ? thanks


 

The quick answer is that 70cm is the wavelength for the 430MHz band, 2 Metres is the wavelength for the 144MHz band, 6 Metres is the wavelength for the 50MHz band and 10 Metres is the wavelength for the 28 MHz band. A quick rundown of some other common Amateur bands is as follows.

 

160M = 1.8MHz

80M = 3.5MHz

40M = 7.0MHz

30M = 10.0MHz

20M = 14.0MHz

17M = 18.0MHz

15M = 21.0MHz

12M = 24.0MHz

10M = 28.0MHz

6M = 50MHz

4M = 70MHz (available in the UK and some European countries)

2M = 144MHz

1.3M = 220MHz (Mainly USA - Not allocated in Europe)

70cm = 430MHz

23cm = 1200MHz

and so on up through the microwave bands.

 

A quick rule of thumb is to divide 300 by the frequency to get the wavelength in metres.

 

For example, 300/144 = 2.08M but most people round it down to just "2 Metres".

 

Remember also that a resonant dipole for a particular frequency is a half-wavelength long, so you need to divide by two to get the approximate length of a half-wave dipole for a particular frequency. (It's approximate because the antenna will not be in 'free space' so it will actually need to be cut a bit shorter to resonate in the real world.)

 

The question about handhelds is a bit more tricky! If it's true flat ground, then the usual rule of thumb is that on VHF you can transmit to just beyond the horizon, due to the bending effect of the radio waves. However, another rule of thumb is that the higher in frequency you go, the shorter the effective range. So, in theory, a 2M handheld of 5 Watts would not get as far as a CB (which is a lower frequency - 27 MHz) but the problem is that the CB handheld antenna will be shorter than a quarter wavelength long (which a 2M antenna could be and still be held) plus the CB receivers are likely to be less effective (due to their being made to a lower specification) than the 2M one. (The quarter wave is because you are providing the other half of the halfwave dipole by being a 'ground' for the antenna on the handheld radio)

 

The next problem is down to propagation. In a 'lift' on 2M you may get a very long way when the CB radio seems dead. Then, on another day, the activity of the Sun may mean that the CB handheld signals get bounced to the other side of the world!

 

It's good fun this radio lark. icon_razz.gif

 

--... ...--

Morseman

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A pair of VHF (2m) walkie-talkies ought to net you about 5-7 miles in the open. The same could also be said of a pair of CB walkies. However, the noise-floor on CB is profoundly higher than on VHF and this severely limits the usable range. FRS walkies are on UHF, but at these frequencies (and above) there is much more attenuation due to foliage and terrain so the range tends to be shorter. The actual transmitter output power is always secondary to the environment the radio is used in. I work in uWave and can talk at length about this but I'll leave it here for the time being.

 

Cheers!

Coupar-Angus

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