SHOULD be. But it's not what they care about.
But in America they want to be LOUD on the radio. That usually means exceeding 100% modulation.
The smarter chaps have designed/changed the circuit to increase positive peaks whilst supressing the negative peaks.
It's done in commercial AM broadcasting - not being an RF expert on this I am certain someone else could weigh in on that.
I think they stick to 125% modulation max (I think it's 125%?) as ordered by the regulatory body in the US (FCC)
Now, with CB radios the regs don't matter anymore. It's a larely abandoned band in the states with little oversight.
In order to sell a radio it has to conform to standards set forth by FCC. That's about where the oversight ends.
Once it's sold they open it up and remove any form of limiting they have, or turn the modulation up to 11.
Another thing that's done is the import of the so-called "10 meter" radio. It's a CB radio in discuise.
Remove a jumper or change a menu setting and bang, it's a CB radio as intended.
They call them "exports" but they are not exported, but imported into the states.
They also want to be WIDE. They are looking for AM broadcast quality. That means altering the BPF in the audio path.
As this is beyond the abilities of most, they do "direct injection" in chich the BPF/limiting is bypassed altogether.
The radio god in the states has a video up where this is demonstrated.
It's not the best demonstration but it does suffice. Fortunately it's short.
That's done here:
Using a spectrum analyser and sweeping would yield a much cleaner and easier to understand picture for the end user but either he doesn't know how or the instrument doesn't have max or min.
It's for testing cellphones so probably not. I have not looked in the doc to see.
Now, they worship the results of this as if it's impossible for anyone else to achieve them but this bloke.
First thing you see is the sweep of the radio. He turns on an analog signal generator and starts from pretty much zero until > 5KHz.
You see it start to roll off around 5Khz.
This is what the "hifi" CB crowd likes and since they think this is the only bloke that can change a couple of parts in a bandpass filter he is worshipped by a few cheeky buggers.
It will and does bleed into the adjacent channel but that's not shown.
At the end of the video he shows you spans of 300KHz and 100KHz and such and proclaims it "clean".
(concealing the incursion into the adjacent channel, since CB channels are on 10KHz centers.)
What the casual observer doesn't know is that you cannot see much about a narrowband AM signal at a 100KHz span.
We are talking about an AM signal that (should) be consuming less than 6KHz of bandwidth but in this case closer to 10KHz.
In the beginning of the use of the cellphone test set you see center frequency around 27Mhz and the span is probably 300MHz or so.
He reduces the span to various points declaring it "clean" which is apparently his typical showing.
According to the manual for the 8924 the resolution bandwidth and span are locked, so the RBW @ 100KHz is 1KHz.
You won't see much. the span is too wide to have a decent look at a narrowband AM signal.
This is likely done by omission. Can't show people the two sidebands and any resultant harmonics, now can we?
Or that it's now in the space occupied by an adjacent channel.
As to the audio response....
It took me longer to copy the bandpass filter from the drawings of the radio and input them into LTSpice than it did for me to compute new values.
One is "stock" and one is after the changes.
But this is how things are done on American CB.
At least when I am in England I can use the radio without hearing this rubbish all of the time about who has the loudest radio.
I think Ofcom is just as lax as FCC when it comes to CB in the UK. Still have our "tech wars" but not like the Americans.
You are not missing much mate. It's a bloody joke mate.