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UHF Radios – Are You Receiving?

During some of our recent 4WD Training Courses, it became apparent that there are some myths and ideas out there that aren’t quite right regarding UHF radios, antennas and installations, and it became clear that perhaps an article about them might be well timed.

UHF Radios are a great accessory in our 4WD vehicles enabling us to contact others in our group or convoy, other road & track users, truck drivers and possibly someone who can come to our aid, especially in remote regions and if we can contact them because we have a well set-up UHF radio.

So, if your UHF CB radio reception is patchy and unreliable, that is often due to its poor set-up.

A UHF radio transmits best in a line of sight – in other words, if your antenna can ‘see’ a point, your radio can potentially transmit to it. Therefore, antenna location and type have a huge influence on a radio’s performance.

What Radio type to get?

Whilst a small hand-held CB radio might be convenient don’t be fooled into thinking it’s all you need. From our experience we’ve found that they generally only cover a radius of about 1 to 2 kilometres, to maybe 5 kilometres at best and that depends on conditions including dust. Having said that, in recent years’ hand-held models have improved and you can now get 0.5 watt to 5 watt units, 5 watts being the maximum legal power output, which do get slightly better coverage, but they are limited by a very short aerial. Some of the better hand-held models can be switched from 1 watt, 3 watt to 5 watts allowing the user to conserve battery life when in close range, by setting the unit to 1 watt, but being able to switch the unit up to 5 watts to help increase its transmission range when you’re further away from others. Of course, being on 5 watts reduces the battery time available before it needs to be recharged. Some units can also be connected to an external antenna via a coax cable (RG 50 or RG 58). Hand-held units are ideal for close quarters communication such as from a spotter directing a driver through some tricky terrain, to helping with reversing a caravan or camper or for general camp communications.

Standard in car units are legally 5 watts and there are several reliable brands to choose from. GME (Australian owned), Uniden (made in Vietnam) and Oricom (made in Korea) are all well regarded brands and there are other new players on the market now too. You also have a choice of a traditional larger unit with all the controls on the face of the unit or a smaller one with the controls on the hand-piece with an extended lead and a slimline head unit that can be installed out of the way.

It is also important to consider where you will install your UHF radio. Traditionally (years ago) the radios were commonly installed on the side of the gearbox tunnel or at the bottom of the dashboard with the microphone clipped within easy reach. Some also installed them under one of the front seats with the microphone clipped to the centre console. Whilst the lower locations seem good, some people have discovered that their door seals leak in water crossings and as a result the units have been drowned and are beyond repair or salvage.

As UHF units have become smaller and more streamlined in more recent years, it has become fashionable and practical to install them with the Radio/CD Player higher up in the dash itself. Overhead consoles provide the ultimate solution because your radio/s can be installed above your head with no impact on the dashboard at all and the microphones are still within easy reach.

Antenna Type and Coax Cabling

Your choice of antenna is also particularly important. For close convoy-style touring, where you only wish to talk to and hear from vehicles within a few kilometres in front of or behind you, a short, rubberised antenna, between 150mm and 300mm, is fine. These low gain antennae are less likely to strike overhead foliage but for long distance work, a higher gain antenna is much better.

Gain refers to an antennae’s ability to improve reception and transmission and is measured in decibels (dB).

It refers to its radiation pattern with low dB in the shape of an apple and better for hilly terrain and as dB increases so does distance and the transmit pattern becomes more the shape of a flat dish.

One important thing to consider and often not understood is that coiling excess antenna coax cable in the engine bay or under the dash is also a problem. It causes the cabling to become an inductor which can produce a voltage spike down the cable and back into the transmitter and blow up the output stage transistors.

The Solution:  Shorten the antenna’s coax cable at one end to the desired length, (either aerial base or radio end), fit the plug to the coax and then plug the coax into the UHF radio. This will not damage the antenna or its signal regardless of what ‘dB’ the aerial is. If you are not able to or don’t want to shorten the coax, the next best option is to run it in long loops under the dash, to help avoid it possibly creating that inductor issue.

Antenna Location

Location is really a compromise of best transmit location compared to where you can mount it on the vehicle.  The best position is in the middle of the roof, but who wants to drill a hole in their roof. For ease of fitting, traditionally many people attach their CB aerial to their bull bar, but in doing so their vehicle creates an uneven radiation pattern spreading out behind the car and to one side if fitted to one side of the bull bar. Your signal forwards can also be shadowed by any vehicles in front of you. Ironically, poor antenna location means that only a low percentage of user’s realise their radio’s full potential. Even an expensive high gain antenna projecting above the roof level from a bull bar suffers because antenna tips radiate very little energy. The general rule of thumb is to place the bottom half of the aerial at a point where it can ‘see’ the greatest distance, even to the horizon if possible. In other words, the ideal place to achieve this is up on the vehicle’s roof line or roof racks. If you’re at ground level, on flat terrain, the horizon is about 5 km’s away. If there is nothing between your antenna and the visible horizon, that would be the limit of your transmission range, but if you raise your antenna by just 1 m (i.e. from your bull bar up on to your vehicles roof) you may increase the range over that visible horizon.

The antenna pictured is a 6.6dB mounted on a hinged mounting system. It also has an artificial ground plane in between the spring and the aerial, which evens out its radiation pattern. This style of antenna is designed for roof mounts and on truck mirrors and not for bull bars.

If having an aerial high up on your vehicle is a concern, you can get hinged mounting systems so the aerial can be folded down going into a shed or carport and when it encounters overhanging foliage. Even a short antenna higher up that can take the knocks of overhanging branches works much better than a long antenna mounted low down. Aerial mounts with an artificial ground plane can help improve transmissions by evening out signal radiation patterns. With more modern technology in recent years, some aerials are now ‘Ground Independent’ and don’t require a metal ground plane to help transmit and receive signals. These aerials are very robust and designed for vibrations from corrugated roads.

It’s also best to fix your antenna vertically, this sounds obvious but the closer the antenna is to vertical, the more effective it will be. A UHF antenna that bends as you drive may lose performance when travelling but should be fine when you are stopped. A sloping unit may look good, but its efficiency will suffer because an antenna’s broadcast is largely flat, like a dinner plate, radiating out from a central point at the base. If you tilt the antenna, one edge of that ‘imaginary plate’ rises into the air, while the opposite slopes down towards the ground, impeding its efficiency.

With a higher altitude and a clear line of sight, your UHF CB radio can have a range of more than 100km, greatly enhancing your chance of finding someone to come to your aid.

From our in vehicle unit, I once spoke to a bloke with a 5W hand-held unit and we managed to stay in contact with him more than 120km away from a high point in the Flinders Ranges, but our altitude (over 600m) was an important factor.

                   A ‘Ground Independent’ 2 dBi aerial designed to be mounted on Bull Bars and tolerate corrugated roads

So, in an Emergency Situation, one option to optimise your transmit capability is to drive up onto higher ground if its available. Of course, all of this is ignoring the benefits of the repeater station network, which will often give you further coverage also. There are a lot of repeater stations in the Australian Outback operated on or by station properties. Only use these repeater channels in case of emergency as they are used for property operations. This is a gentlemen’s agreement not to operate on the repeater channels.

With Duplex transmission (let’s say Ch 8/Ch 38), the lower number is your receive frequency and the higher number is your transmit frequency. The radio does this automatically when duplex mode is chosen. So, the Duplex repeater will receive on the high channel number and transmit on the low number.

If you are in Simplex mode, then the transmit/receive frequency is the channel you’ve selected for both transmit and receive.

 

 

Radio transmissions are emitted from the centre of an aerial, not the tip as some people believe. So, the higher the aerial can be mounted the better the signal and the further the distance you can send and receive transmissions.

In hilly or mountainous terrain radio transmissions can be missed by others depending on the type of aerial gain you have. A 2dBi or 3dBi aerial is much better in these terrains as it has a rounder signal, and you have a better chance of contacting someone in your vicinity.

A 6dBi aerial is a good ‘all purpose’ aerial for touring when you might be in more open country and want to be able to send and receive transmissions over a greater distance.

A 9dBi aerial is excellent for more open station country and is what you typically see on farm Utes, etc. as it’s a taller aerial that pushes a signal over greater distances but in a flatter plane.

Personally, I use a 2dBi and a 6dBi aerial which are easily interchangeable, so I have the signal flexibility depending on the terrain we’re operating in.

Alternatively, some people have two UHF radios mounted in their vehicles, one connected to a 2dBi aerial, and one linked to a 6dBi or 9dBi aerial. This is why you’ll sometimes see 2 aerials on their bull bars or perhaps one up on a roof rack or gutter mount. We use a 5 watt handheld UHF as a secondary radio in the vehicle as we already have and use these for our 4WD Training anyway. So, you have a few options depending on what your needs are.

 

Where to in the future?

About 10 years ago, the UHF service was expanded from 40 channels (wide band) to 80 channels (narrow band) utilizing the same 477MHz spectrum by slotting 40 more (new) channels in between the existing 40 channels. (e.g. Ch41 frequency is between Ch1 & Ch 2, Ch 57 sits between Ch 17 and Ch18, Ch 67 sits between Ch 27 and Ch 28, etc.

This has created a small problem many are not aware of but is noticeable when you are communicating with others using the old 40 channel units when using your 80 channel unit. Because the band width has been halved it equates to an audio lower in volume, which is why reception sounds softer or louder depending on who’s transmitting on what units. It becomes a pain in the proverbial when you have to constantly adjust the volume to compensate when two different aged radios are being used in a conversation. With my old 40 channel unit I find that I receive 80 channel transmissions with lower volume than for 40 channel transmissions. The converse doesn’t seem to apply, but there is light at the end of the tunnel.

The Australian Communications Authority (ACA) had mandated a phase out 40 channel UHF radios by around 2022, so that all UHF radios would have to be 80 channel units and the current ‘volume issue’ will then be resolved. However, it seems they have backed down from that stand for now. If offered a second hand 40 channel unit for sale or free, it might be a wise idea to politely refuse the offer.

 

 

Our UHF Radio Channel – Quick Reference table

CHANNEL USAGE UHF   80 Channel General information
 Emergency channel  (LD)  5 and 35  Legally Designated – Do NOT use this channel for general transmissions
 Call channel  (LD)  11  Call channel – to locate friends or a meeting point if comms are lost, before moving to another channel
 4WD / Outback Travellers  (R)  10  4WD Clubs or Convoys, Outback Tracks (e.g. Oodnadatta, Strzelecki, Birdsville & Simpson Desert) and National Parks
RV / Caravanners channel  (R) 18 Caravanners and RV Campers Convoy Channel
 4WD / Outback Travellers  (R)  29  Road Safety Channel – Pacific Motorway (NSW & QLD)
 Road channel  (R)  40  Truckies & Oversize loads channel
Channel 5 (& 35) is the Emergency Channel – You should NOT be on this channel for general voice transmissions. Only use it if you have an Emergency or are helping someone in an emergency situation.

 

Channels 22 & 23 are Data (Telemetry) Channels and are NOT to be used for voice transmissions.

 

Channels 61, 62 & 63 on the 80 channel UHF are reserved for future Data Channels and have not been assigned frequencies and can NOT to be used for voice transmissions.

 

Channels 1 to 8 and 41 to 48 are Duplex or Repeater channels (output).

 

Channels 31 to 38 and 71 to 78 are Duplex or Repeater channels (input).  

      

General use channels:  9,12-17, 19-21, 24-30 & 39. 49-60, 64-70, 79 and 80

 

 

…. and to finish off …. A couple of Handy Hints.

If you have thin steel aerials on your vehicle, corrugated roads have a tendency to shake the aerials to the point that they snap off at the base (particularly aerials mounted on bull bars). These aerials are actually designed to be mounted on truck mirrors etc., where vibration is not a real issue.

The Solution:  Try using self-vulcanising tape wrapped around the aerial base and part way up the aerial. It seems to limit the whip affect at the aerials base that creates the right harmonics to shake the steel until it breaks and falls off.

The antenna pictured is a 6dB with the self-vulcanising tape covering the locking grub screw and only a short distance up.

The tape could be wound further up the antenna, if desired.

 

 

UHF Radios & Operational Etiquette

Always listen before transmitting, as the channel may be in use by other persons. This helps avoid people talking over each other which leads to a squawking noise and can be quite annoying.

Always wait for 1-2 seconds after you’ve pushed the microphone button in, before talking. This helps avoid those listening, missing the first part of your conversation or reply.

Always leave a three second break between “overs”. This allows others in the group, or other parties, to put in a “breaker”. The “breaker” may only be to add comment to the discussion, or it may be because of an emergency situation.

When in convoy – Always get someone in the middle of the convoy to give a double tap (with a 1 second gap in between) of their microphone button, after someone makes a statement that doesn’t require an answer. This ensures the sender that their message is getting through the group.

For larger convoys or if your group has become spread out over some distance because of bulldust or its just slow going in soft sandy terrain, etc., on our tours we get our Tail End Charlie to give a triple tap (with a 1 second gap in between) of their microphone button after we make a statement that doesn’t require an answer. This ensures us as the sender that our message is getting through the entire convoy. If we don’t hear the triple squawk, then we get the middle vehicle to relay the message back through the second half of the convoy. Our Madigan Line Tour is a good example of this, as we often get spread out over 2 or 3 dunes (3 – 5km’s apart) and it can be hard to hear the last few vehicles.

So, enjoy your UHF radio contacting in the future, over & out!

 

By Norman Bee

© Pindan Tours and 4WD Training

*Original blog March 2017 has been updated – July 2021

If you have any questions about UHF Radios, or you’d like to speak to us about our 4WD tag along tours or even a 4WD course, contact us today.

9 Comments

  1. Lyn on 18 April 2017 at 10:12 pm

    Hi, if calling on a 27MHz CB radio can UHF radio listeners hear?

    • Steve on 31 August 2017 at 8:57 am

      27mhz is vhf not uhf so no it wont.

      • Andy on 21 January 2018 at 3:13 am

        27Mhz falls in the hf band

    • EskyVX on 25 October 2017 at 7:36 pm

      Nope , AM / SSB cb is like u said , 27 meg … while uhf is 477 meg , Worlds apart.

    • Norman Bee on 21 November 2017 at 10:25 pm

      Hi Lyn,

      No 27MHZ is the old AM CB radio and UHF operates on different bandwidth and frequencies.

  2. Tom on 27 April 2017 at 3:36 am

    Thanks for the very helpful summary. Was about to instal my areal on my roobar and will not do that a result !!

    • Norman Bee on 21 November 2017 at 10:23 pm

      No worries Tom, happy to help.

  3. Syd Poole on 27 September 2017 at 5:31 pm

    Great read, thankyou. Re: length of lead, my UHF Shop tech says lead length is tuned to aerial. Your thoughts please?

  4. Peter on 4 April 2021 at 7:11 pm

    I agree great read many thanks, I had my radio fitted by mechanics at work from what I now understand it was not correct Mmm there is a lot of unknown in what seems to be simple installation I have looked further at the installation whilst it’s very neat well installed plenty of cable ties and yes a coil of antenna wire very close to the unit I corrected this and I have moved the antenna to the roof seems to work better very hard to compare I guess I have talked to more people on my local roads I guess it has worked thanks.
    Peter

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