80 channel UHF

80 channel radios receive 40 channel radios distorted and broken and 40 channel radios receive 80 channel radios with low audio.

So much for they were meant to be compatible to each other.

Ah, there you go . . . hadn't bothered as yet to test out how this went.

Explains why my noise inducted hearing loss is further aggravated by these inconsistencies, especially the distortion.

Firstly "old" means one of the original 40 channels.
"new" means one of the recent 80 channels.

We think of channels as one being next to the each other in numeric sequence. No gaps and just a sequence of channels. And such is the case with the "old" 40 channels being phased out.

But with the new UHF CB channel/frequency allocation that is not case.
channel allocation frequencies. The top half of the "new" channels is slotted in between the "old" channels.

Channel 18 on both the "old" and "new" are the same. But what screws the compatibility is that the "new" channel 58 is slotted in between "old" channel 18 and "old" channel 19. Stuffing up transmissions on both radios.

That means anyone on 58 will stuff anyone on 18 and vice versa. Similarly signals on ch 50 will screw anyone on 10 and any signal on 80 will screw 40. Anyone on 41 to 80 will play havoc with anyone on the "old" 1 to 40.

Volumes or voice tones will still be okay but their volumes will differ.

I hope that helps the non technical people.

Phil

Almost right but good enough.

This:
"Anyone on 41 to 80 will play havoc with anyone on the "old" 1 to 40."
Should read:
"Anyone on 41 to 80 will play havoc with one adjacent "old" 1 to 40."

That's a bit better but the brain is not with it today. I hope you get the idea.

Phil

I was communicating with one friend who had 40 channel UHF. We were using channel 14. We could hear each other fine, but she could also pick up clearly someone else that I couldn't hear and they couldn't hear me either. She was chatting to this person and I had no reception of them at all or them of me.

That sounds like they were on the "other" side of her to you and thus much farther away from you. UHF does nit have a very big range.

That is quite normal and a regular occurrence. You may hear "tail end charlie" in a convoy calling the leader and someone in the middle having to relay the message.

Phil

Twinkles, or she could have been on sel-call

Just changed to a 80 channel unit as the 40 was playing up.

Fellow travellers using 40's were complaining of my lack of volume, yet I could hear them loud and clear.

Out with the book, there is a auto volume compensation for received transmissions which explains their clarity and volume possible.

Next step was to get it all tested, passed with flying colours, SWR? was 1.1 I think and output was just under 5 watts with each different antenna I have. so that's all OK too.

Also in the book it says hold the mike 2 - 5 cm from mouth which I am having trouble doing after all the years holding it 30cm away. Must be a background noise cancelling thing.

And finally he said the 80's don't talk to the 40's real well as noted above.

If that dont work I'm getting the 40 fixed and it can go back in LOL, put the new one away until a few more have them.

We were travelling close to each other and the area was around Goolwa, SA, fairly flat. I've been 4wding for many years in groups and never had problems like this. The 80 channel just doesn't seem to have the distance.

The limit of all radio communication is signal to noise.

the 80 channel has half the frequency deviation, there for half the signal of the 40 channel.

Therefore it will be more subject to noise than the 40 channel thus the range will be reduced.

If ya jamming 80 channels in where there where 40...there is no free lunch.

cheers

Quote"the 80 channel has half the frequency deviation, there for half the signal of the 40 channel."

What gives you that idea? The emission designation of the 25 kHz channels is 16K0F3E and the designation of the 12.5 kHz channels is 10K1F3E.

Yes! You are correct.

And if I had said that the audience that I was talking to wouldn't have had a clue what I was on about and completely written off my whole post.

What I said would give them something that they understand would make the 80 ch appear (note "appears") weaker on the 40 ch radio.

But if you want to feel free to explain to them what the two emission standards that you quoted to mean. And without getting technical.

Phil

Please tell me more Ross. My 80 channel has all the problems mentioned above. Are you suggesting that the aerial could be placed in a better position to improve performance?

Yes, get it above the roof of the vehicle. Antennas on the bull bar have very distorted patterns. There were some tests done with model cars with the wave length of the carrier scaled to suit. When the antennas were mounted on a mudguard the direction of strongest radiation was across the turret of the car (don't ask for an explanation of the reason for that strongest direction, the answer is too complicated.) The only way to get good radiation in all directions is a center of the roof mounting.

Thanks Peter
I guess mounting the aerial in the centre of the roof rack would be a little impractical. Do you think fitting it on the front edge above the windscreen would be ok? Will have to be a little careful with low hanging boughs and carry a few spare aerials!

An antenna on the edge of its ground plane will have its maximum radiation across that ground plane. One way od mounting it near the middle would be to use one ladder bar and mount a ground independent antenna on the middle of that.

remember most of our UHF antennas are ground independent.....thus the ground plane will have far less influence on the radiation pattern.

AND

the wave length is small in comparison to the size of the body of the vehicle.......a half wave radius ground plane on UHF would be about the size of a bread and butter plate.

many things change as we move to different frequency bands....some things may be exactly opposite.

What is true for VHF 27Mhz CB radio may not be true for 400 ish Mhz CB radio.

On 27Mhz, the vehicle is smaller than a minimum ideal ground plane....that would be 9 foot radius......and 27Mhz vehicle areials are almost invariably ground plane dependent............thus the shape of the vehicle and the location of the aerial on that vehicle will have a significant effect on the radiation patter....the signal will tend to radiate stronger in the direction of the greater area of the ground plane.

Its all to do with having an inadequate ground plane.

As I have mentioned on UHF.....most aerials we use are ground independent...and even if using the vehicle as a ground plane...it is many times larger than required.

The predominating factor.....for direction of radiation on UHF is line of sight.......if the aerial is partly or totally obscured by the vehicle body....radiation in that direction will be dramatically reduced.


The single most important thing to consider for good UHF radio reception is mounting the aerial high and clear.

High and clear predominates over every other consideration.

Anywhere on the roof will be fine......being mounted on the edge will make very little difference.

cheers

Quote "Each of the old channels 1 to 40 has been effectively cut to half bandwidth"

Only the channel spacing is cut in half. The occupied bandwidth is cut from 16 kHz to 10.1 kHz. Things are not as bad as you blokes are making out.

No the bandwidth has been reduced from 25Khz to 12.5khz. The bandwidth has been cut in half. This means the emissions have reduced from 16Khz to 10.1khz, this is referred to as narrow band and allows the channel spacing to be halved. If the bandwidth wasn't reduced then the spacing could not be reduced without overlap.

I agree things are not as bad as people make out but generally a new narrow band radio may sound a little faint to an old 40ch radio which may sound a little distorted to a close by 80channel radio.

Boobook, you know not of what you are talking about. The necessary bandwidth (or occupied bandwidth) of a modulated radio signal is different to the channel spacing.

DownloadRadiocommunications (Citizen Band Radio Stations) Class Licence Variation 2011 (No. 1) and you will see the following:

In - Part 2 UHF – 25 kHz channels you will see the following-
(a) Operation of a CB station must only employ F3E or G3E with a transmitter power not exceeding 5 watts pZ and with a necessary bandwidth not exceeding 16 kHz.

In - Part 3 UHF – 12.5 kHz channels you will see the following-
(a) Operation of a CB station must only employ F3E or G3E with a transmitter power not exceeding 5 watts pZ and with a necessary bandwidth not exceeding 10.1 kHz.

In an earlier posting in this thread I mentioned that the designation of emission for 25 kHz spaced channels is 16KF3E and that for 12.5 kHz channels is 10K1F3E. I have also used the terms "necessary bandwidth" and "channel spacing." I see that these terms are used in the
Radiocommunications Licence Conditions (Amateur Licence) Determination No. 1 of 1997. I see you have an amateur radio call sign and you thus should have a copy of that document. You should therefore have researched those terms and know what they mean. If not then I suggest you do some research and explain to the others what the terms mean.

I apologise, you are quite correct.

regardless of the proportions...and we can argue the detail all day.....a reduction in modulated band width on FM will result in poorer signal to noise performance

There is no free lunch... 80 channels where there where previoulsy 40....poorer performance.

cheers

as I originall said...all radio reception is limited by signal to noise considerations.

As we use more advanced methods of modulation the point where loss of service occurs becomes more dramatic.

with crude old "continuous wave" modulation...just turning the carrier on and off...( morse code)...the signal can be very noisy and still be read for a very wide margin near the limits of range.....except in very short range conditions the signal will always be read thru fairly obvious noise.

AM...amplitude modulation where we vary the size of the carrier ( as we use in AM radio and old 27Mhz CB radio gives us a clearer in range reception...but there is still a wide margin where the signal is read thru fairly obvious noise near the margins of reception.

FM..Frequency modulation....where we vary the frequency of the carrier while keeping its size constant has far better in range noise performance and noise immunity...but the margin of readbility thru obvious noise is considerably narrower.

When we get into the current digital modulation methods like are used in digital television and mobile phones......the in range readbility is near perfect...but there is very little margin at the limits of readbility thru noise...it will be near perfect..suddenly become unreliable and then its gone.




what the OP and other will be experiencing with the new 80 channel CB is a combination of factors.
Starting with a radio system that is intentionally range limited.

A combination of the frequencies used, the modulation system, and power restrictions very effectivly limits the range of UHF CB.

It is intended to be pretty well line of sight and only a few Km.

A hell of a lot of what is done with UHF CB is pushing it right in to that bleeding edge where the signal is read thru the fairly narrow noise tolerance margin.

Reducing the signal to noise ratio by only a few db will mean that margin of readability thru noise will be dramaticall reduced.

the regulators will have known damn well that this will occur, and they will have considered that the range reduction is a positive result.
because it will allow the system to carry more users over a wider area.

some of us argued that this would not benifit anybody outside of a few very busy locations and would in general be not worth the trouble....but the regulators did not care.

SO...with 80 channel UHF CB is is even more important to understand that it is line of sight and good antenna positioning is imperative.

Selecing a good aerial with a reasonable amount of gain and having it well located will predominate ove all other considerations.

there have been some..."spirited" discussions about the near fradulent marketing that goes on with CB radio aerials..and a number of things people believe that simply are not true....like the "gain for terain" idea and the notion that a big white (or black) stick mounted on the bull bar is a good choice.

The difference between what actually works and that that does not will become more obvious with this chnage to an 80 channel system.

Persnally I'll be hanging onto my 40 channel radios as long as I can....even if I do buy 80 channel.


cheers

There have been significant improvements in noise performance and sensitivity in generally available radio electronics in recent years ( the earlier part of last 10 years)...but to say the new 80 channel radios have better sensitivity is just not a reliable statement.

Most of the good radios have been running near best theoretical performance for years now...and they wont get any better without the use of exotic technologies like super conductors.

Many of the current 80 channel radios are near identical if not completely identical to the recent 40 channel units with little more than a softwear change.

Companies like GME and ICOM that actually design and manufacture radios and have a large commercial radio market have been selling radios with varios band witdth options for quite some time.....because commercial UHF radio has been going narrow band for some years.

the top manufacturers will have had to do practically no new design work to accomodate the 80 channel band plan.

this suposed improvement in performance will have been put forward to justify the change to narrow band, but it will only hold tru if the new 80 channel radio is compared to a prervious generation 40 channel radio or a cheapy built on older generation technology.


As for the power density argument.......this is FM not broadband.....the power density argument is weak.

The published noise specs as posted earlier prove the point.

Don't expect your 80 channel radio to go as far as a good 40 channel did...there IS no free lunch.

cheers

Hi Bantam

Its fundamental to radio transmissions that potential sensitivity is related directly and inversely to bandwidth and the bandwidth of 80 channels is smaller by definition and hence less noise is contained in the smaller bandwidth.

I'm pretty sure I'm the only professional radio engineer of this site and have designed some of the things we are talking about so you can take that comment as well founded.

Its for this reason that I did not say 80 ch is more sensitive - I said all else being equal they are and that in practise they can be less because in practise the front end sensitivity is not more but less these days for the reasons I gave above.

Check out the actual published Sinad figures for radios like I mentioned and you can see that they have dropped off by a db or 2 , not the opposite.

For those interested in a practical example of drop off in Radio receive performance when they could theoretically be actually better , I enclose figures for two radios I own.


TX3220 1/2 size 40ch radio Its sensitivity is less than -122dBm for 12dB SINAD

UHF058 Standard size 80ch radio Its sensitivity is less than -118dBm for 12dB SINAD

-122 is a weaker signal than -118 by 4dbm.

4dbm is a little less than 1/2 power.

So the TX 3220 picks up a signal at 1/2 the power of the UHF058 for the same level of noise.

However radio transmission power drops off at the square of the distance, so a rough approximation of the range difference between those two radios is square root of 2 or 1.4

So this means that if conditions were such that the 40ch TX3220 would hear a signal 2km away, the 80ch UHF058 could only hear the signal as clearly when it was 1.4km away.


The base reason for this lesser performance is simply cost.

ya not comparing apples with apples.

Lets talk about a TX3220 running on 40 channles and another identical unit running on 80 channels....they have been making several of these models spanning the 80 channel conversion..the later versions the change from 40 to 80 channles was software alone.

Same for the modern ICOM radios..particularly the commercial units programmed for legal operation on CB.

So if I power up a machine on 40 channles and read the output on my power meter, then power the same machine on 80 channels the meter will read more......I don't think so.

lets look at this another way..if I fire up a unit on 40 channel and input a sinewave then read the power output in the most complicated manner you like...then power up the same rig on 80 channels with the same sinewave...will the power output read any different......I think not.

the noise figures of the reciever will be the same, the deviation is less therefore the actual total system noise performance will be poorer on 80 channels.


I don't know what theory you are talking about...but 80 channles in the same space as 40 channles with the same equipment...there Is no free lunch.

That is before you account for increased noise floor due to closer adjacent channel operation....not that that will bother a lot of people.


sorry but theory don't always work out in practice.

cheers