What is UHF

UHF stands for Ultra High Frequency Radio, this is a service cost free civilian radio frequency and is commonly found on 4WD’s, semi-trailers, construction and mining equipment and other land based vehicles.

There are many different types of UHF radio, but all transmit and receive in specified frequencies(477 MHz band). Radio waves in the UHF band travel almost entirely by line of sight and are easily blocked by geological features such as hills and canyons and will also be blocked by trees and buildings.


Built in vs Handheld

When shopping for a UHF you typically are presented with 2 options, one is a system usually designed to be run off a 12v power source and mounted inside a vehicle.an example would be the Oricom UHF380PK  a handy unit that contains all controlls in the handle great for vehicles that are not fitted with a spare “DIN” space for a UHF unit.  The other style is a more portable unit that is easily transported and can be easily carried on a belt clip or in a backpack. These are referred to as “handheld” radios and can be bought with a smaller budget. a great example of a good quality Handheld unit is the Oricom UHF2190, a twin pack of units allows portable remote communication.

Both Handheld and vehicle mounted UHF radios are limited by a legal maximum transmission power of 5 watts, this means they both have the potential to be  ‘as powerful’ as one another, however in common practice vehicle mounted units are mostly 5w offer more range and clearer signal, due to larger antennas with higher gain and higher antenna mounting location. Whilst handheld devices choose more power economical wattages like 0.5w, 1w and 2w, with some 5w units also having a 0.5w low power mode for shorter range transmissions.


What is gain

All antennas take advantage of a scientific principle called gain. The best way to think of an antenna is as if the radio waves were to propagate away in a sphere like a beach ball away from the antenna. A 0dBi has no gain, and the antenna would maintain a spherical transmission of signal.

However if you were to step up the gain to a typical 4.5dBi or 6dBi  antenna found included with many vehicle mounted UHF units the transmission pattern becomes more like a disc, which extends the plane of radio transmission to much further down the track, however the angle of incline of the vehicle when you are transmitting will dramatically affect whether or not the receiver falls within the area of transmission.

Gain can be your best friend or your enemy depending on your circumstance and terrain.

CHANNELS

With recent developments the Australian government has opened up an additional 40 UHF channels with 80 possible channels on most modern UHF devices. Older devices will still function on the first 40 channels, however with new restrictions the first 9 channels and 31-39 are dedicated to duplex mode, with channel 5 being restricted for emergency transmissions only with older units you are left with only channel 10-30.

Channel 11 is reserved as a calling channel used to find friends, to be polite once you have found your friends, move to a free channel to leave 11 for others to use.

LEGAL RESTRICTIONS

Make sure you do not use either channel 5 or 35 when you are not in a real emergency, if you are not in a real emergency you can face a 2 year jail term, and if you are interfering with a real emergency the penalty can be up to 5 years imprisonment.

So make sure you only use the emergency channels when you need them!

DUPLEX vs SIMPLEX

Duplex function transmits on one channel and receives on another, it allows the use of a repeater station which is a base station that picks up on the transmission output by your device and re-sends the transmission from an elevated high-power antenna resulting in a much further transmission.

We know of a situation where people were using Duplex via a repeater station to transmit between 2 locations that had no line of sight but were approximately 4kms or 5kms away with a large hill in between and using duplex reached a repeater 20km away from them and could read each other loud and clear!

CODED SQUELCH

Despite the word coded in the title, coded squelch systems such as CTCSS and DCS are not private transmissions, and when activated simply mutes all other radio transmissions except for ones coded the same system and it will not prevent other people from hearing your transmission.

Many UHF radios, like the Oricom UHF380PK and the Oricom UHF2190 are fitted with both DCS, and the CTCSS, depending on the circumstances you

These systems are handy for busy areas so you can clearly understand transmissions from others within your party.