CB radios

[Cpage66]

Okay, as the foreigner here can somebody explain the diff in the UHF CB radios and the AM CB radios? Are they two seperate systems that act wholly independent of each other? (Can I use a UHF channel 12 to talk to someone with AM channel 12 as an example?)
I've been checking on different systems and now I'm confused...I'm wanting to use a linear booster but they work on AM and I'm not sure if they work on UHF as well as use a linear boosting antenna.

Can someone help

[chrispy]

Chris

Their frequencies are wildly different.

AM CB operates on the 27MHz band and UHF on the ~470MHz FM band.

The higher frequency and FM (Frequency Modulation) system that UHF CB radios use means a clearer signal - at the expense of distance - which is typically line of sight depending on the terrain. FM modulation changes the frequency around a tight band close to the carrier band frequency to carry the message.

AM CB radios use Amplitude Modulation (same base carrier frequency which is modulated (or changed) in signal strength (amplitude) to modify the carrier and transmit a message.

They are totally exclusive of each other.... and you will need one of each to talk to people that have either.

[Cpage66]

Okay...gotcha. So I need to find out if anyone builds boosters for UHF but I knda doubt it...

[AussieCJ7]

Okay...gotcha. So I need to find out if anyone builds boosters for UHF but I knda doubt it...

5W is the max legal transmit power through Australia unless it is for professional registered use eg fire police defence etc

If you know what you are doing you can aquire UHF radio capable of upto approx 25 watt's but you 'must' reprogram them to 5W

Chris I am planning on having a communications discussion at one of the upcoming club meetings so watch this space for further details

[Bruce Kerney]

As far as I know Codan make a brilliant 477MHz UHF set that can transmit on a higher power if required in emergency conditions but is outside normal 5W legal operating parameters.
A good quality single side band AM 27 MHz set does come in handy if you intend traveling into remote areas, but without the the performance of a RFDS set operating on even better performance.
A lot of UHF 477MHz set come with a scan mode that samples the channel range in either a group mode ( you chose what channels you want to monitor) or open scan where it can scan all 40 channels in the set. The UHF set can make use of "Repeaters" that use base stations to retransmit over a larger range.
Whatever you do in choosing a set put good money into a good antenna, too many times people buy a good radio and then a really cheap antenna, the antenna is the means that the electrical signal is propagated to the air and really the most important part, also antenna position on the vehicle, sometimes it can be better to buy a reasonable radio and good antenna then the other way around.
Sorry for sounding enthusiastic about this but have worked with radio comms. for 20 years and am frustrated at the amount of times people buy cheap or are advised wrongly.

[tim]

Hi Bruce,

good timing on this post.
I am looking at at GME 3220 or the 3420.
On those models what aerial would you recommend?

Are there better/more suited aerials for different terrain ?

Cheers
Tim

[Bruce Kerney]

GME make a really good range, to a degree it depends on where you are going to travel, if a lot of wooded over grown tracks you aren't going to bash an expensive aerial, naturally in a lot of cases people forget to fit a spring base to the aerial, these can be purchased in soft to hard tension. The more expensive have springs built in, also a deciding factor is the base itself, that is the lead that goes from the back of your radio to the external mounting point, most are cheap basic ones then the good ones and the plugs that go into your set, there are two types , when you look in the end if it is brown its a bakerlite one , the best, if a off pink plastic, plastic melts and not as good an insulator, are you going to fit yourself, professional or someone in club, remember ALWAYS "Tin" the inner conductor, make soldering easier.
And we still aren't to the aerial, keep in mind the longer the aerial the flater it propargates, a bit like a wave in water, a small aerial works like a "point source" and more rounded waves that can "bend" over hills in mountainous areas where a long aerial transmitts a flat long signal that bounces off hills. Remember 477MHz is basically line of sight, what type of vehicle do you have,Yeh OK I now a Jeep but what model, hard or soft top, do you have a bullbar etc....Send me a PM with more info and how desperate you are to get it in your truck, time wise....I have the GME catolugue and a Comms folder here at home but it depends on you(or the Mrs) your budget and what you expect.....

[tim]

Thanks Bruce.

I have a XJ 94. hardtop.
you might remember it from the menai clean up..
I have removed the factory roof racks, and have a stock front bar at the moment.
But i will most likely mount the aerial on the front bar.
budget = $400

cheers
tim

[Bruce Kerney]

Tim, I can't believe I'm going to ask this........what colour Jeep was it..........remember metal works for and against radio, it helps as a "ground plain" to transmit.... sorry for getting technicial, so theroetically the best place is in the middle of a metal roof, hey theres no way I'm drilling the roof of my vechicle, if you mount it like some on the rear wheel carrier, it uses the metal area in front to transmit marginally better forward in a lobe , metal surfaces work like a driving light you can spread or focus the radio transmission,
If you are going to mount on Bumper bar, the distance from the base on the bar to the top of your bonnet if sort of nullified , there are aerials designed to compensate for this though, but you certainly don't put a small whip 1/4 wave on a bumper as you kill it.
Again, you can buy a good Mobile One or GME "normal" thin black aerial,good everyday rugged aerial...... I have tried the GME "Loaded coil" ones, solid hard wire with blue loading coils in them, my experience avoid them, will explain later, or the GME big white aerials, the best being one with a rugged heavy duty base and a stronger screw in for aerials youcan change for flat or mountain country use.
Again, the money you are talking will get the best, but are you doing Canning stock route or Kurrajong back roads, remember I only have a Mobile One thin black, mounted on the channel of my bull bar so not ideal but practical,
Please remember your passanger when you mount too, or it could be you in the gate opening seat, do you want a big white thing in your view or a smaller big thin aerial that after a while you hardly notice, in that case mount near edge and you can use as an indicator for tight tricky tracks but again damage

[Bruce Kerney]

Tim, I'm going to give Steve F or T, and Reg the details of the boys at GME, they are only down the road, they may come out to one of your club meetings with a desplay of aerials, I'm sure if a request comes from the club they would assist and explain without getting too in depth everything from radio, connector, base and aerial sellection.Cheers Kern