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

[Bruce Kerney]

All,
I have been in contact with GME and they are more than happy to have one of their sales reps attend a club meeting to explain radios and everything related. I have pasted their phone number on to Reg for him or someone on comittee to follow it up.
It would be an interesting club meeting to attend but would be a let down if organised and not backed up or supported by members. Anyway out of my hands now, let me know how or if it goes ahead.
Bruce

[casey]

with the desert trip being on the agenda for the next meeting - i think most the people interested in setting up a good permanent UHF system will be there for the GME guys :)

[Steve F]

The next meeting we have Chris coming to talk to us about helping out at Tuff Truck, maybe the meeting after for GME?

Cheers
Steve

[jeepthing]

this is good timing. ive been thinking about buying a proper UHF....

[Bruce Kerney]

Was doing some homework regarding 477MHz UHF Base Station Antennas for a mate and came across the MobileOne web Page. It has goo basic explanations of different antenna types you might like to read about before April meeting.

http://www.mobileone.com.au/antennas/default477.htm

[jeepthing]

So I probably should have asked the GME lady these questions, but I only thought of them as I was driving home last night... so hopefully someone else might be able to answer them

If I have 2 antennas with the same dB gain but different lengths/heights, whats the difference?

The difference between the fibreglass antennas and the thinner flexible antennas is purely strength for different driving conditions e.g. corrugations or tree branchs, etc, and both types have pros and cons over each other- correct?

And what are 'unity gain' antennas?

[sbadman]

And what are 'unity gain' antennas?



Unity gain is 0 gain, what goes in is what comes out.

Not sure about the length question though, might have something to do with quater wave/half wave/etc. Two quarter wave antenas of different formates ie UHF and AM would be different lengths though.

[Bruce Kerney]

Be careful when reading about "Gain" , Proper gain is amplification, which takes power in the form of an amplifier, Db "Gain" in Antenna, is what I call actually "less loss", a better aerial just picks up signals that lesser antenna can't but are in the air anyway. On transmit it does convey the electrical signal to radio more efficiently but not in amplification just more effectively.

[casey]

i was filling out my door prize card when they were explaining the different kinds of aerials at ARB the other night, so i wasn't giving my full attention :P

from what i think i heard, the fibreglass ones were good for corrugated roads, but bad for thick bush - if they hit a tree, they snap.

the steel whips are good in thick bush, but weren't so good for corrugations because their tendency to bend generates heat in the whip when being constantly bending, causing it to eventually snap.

- is this correct?

[Steve F]

That was pretty much it, although I think it was only the smaller of the stainless ones that was prone to cracking on corrugations. In saying that mine has done 110,000km now and there's a few long distance trips in there with plenty of corrugations and it's no worse for wear. She also said something about only the ute muster guys getting the big fiberglass ones and there was no real need for them.

Cheers
Steve

[casey]

cheers.
any idea what the difference between the barrel and parallel spring bases are?
im guessing one is stiffer than the other?

[casey]

i got the answer just in case anyone else was interested:
parallel springs are less flexible than barrel springs.

[Cpage66]

i got the answer just in case anyone else was interested:
parallel springs are less flexible than barrel springs.


Have you seen the barrel spring mount on the HEEP?

[TK421]

Since we are on the subject - does anyone want to part with their old radio? I am interested in buying a second hand unit, try them out, and then decide what to buy - new.
I like to try and test things before I spend considering they are exactly cheap.
Any suggestion would be welcomed.
TK

[casey]

to start off with, we just bought a $30 handheld from jaycar, after a year or so its still going fine, although we're looking to get a UHF installed in the jeep after coffs.

[jeepthing]

Yeah i just started off with 2 1W handhelds. Ive had them for a few years and still going strong.

having said that though i just bought a fixed unit. the handhelds did all that i asked of them but I wanted to give a fixed unit a go.

[TK421]

Hey, that is so strange... I am the Jaycar Engineering catalogue designer... and I have never looked inside. That is so stupid... I do the designs, the photo shoots, the product selection for the sections, the type concepts, the marketing lines, and I have never ever looked inside for a CD radio.
I can even buy them cheap - hell, I am so stupid. I'll go and get the latest catalogue... and open one up for once!
TK

[TK421]

I'll just spend the next two hours browsing in the catalogue for things - and tell my manager I am doing research - and I won't get into trouble... how cool.

[TK421]

OK... this is what I found out after reading - there is a difference between UHF and HF radios... but, what do we use and what is the preferred radio for what we do?
I have the opportunity to buy a 5 watt HF 40 Channel CB - but the model is very old - works well, but, it's not the UHF kind that we all talk about.
If I get it, can I tune in to the channel we use at t he club?
TK

[Steve F]

OK... this is what I found out after reading - there is a difference between UHF and HF radios... but, what do we use and what is the preferred radio for what we do?
I have the opportunity to buy a 5 watt HF 40 Channel CB - but the model is very old - works well, but, it's not the UHF kind that we all talk about.
If I get it, can I tune in to the channel we use at t he club?
TK


HF is totally different to UHF and no use on trips where you just want to chat with the rest of the group. HF runs at 3Mhz to 30Mhz, UHF is 300Mhz to 3000Mhz so nowhere near each other. HF is typically for long range stuff like 3000km and UHF short range like 0-10km. So we use UHF, cheap and free usage etc.

Cheers
Steve

[jeepthing]

Do many people use HF much these days? I thought for city folk that do the outback trips once every few years, it was more cost (and weight) effective to use a sat phone instead?

[Dave]

Some commercial operators still run HF, and people who go very remote - eg tour operators, Hema mapping people etc. They are expensive, cost to run, and you need to know how to use them (not simple). On the plus side, you can use them for phone contacts through Telstra Radphone, and to contact the Flying Doctors or other emergency services.

These days even the tour operators prefer Sat Phone as they are cheaper and easier to use, and can reach anyone that an HF can reach without needing a big instruction book and luck.

[casey]

my Dad used to have an HF radio in his Landcruiser when he started doing sandalwood harvesting in outback WA in the late 90's.

The RadPhone feature was pretty cool (and was pretty much the only reason he had it). You could call phone numbers over the radio. Eventually he switched to a satphone, it was easier to use, much more portable, and your communications were secure.