Technique to enhance radio broadcasts
The Technical Manager
asymmetrical modulation distortion is applied to the radio broadcasts in
the medium wave band. This technique allows up to 150% modulation of the
audio signal without producing hard non-linear distortion in the
demodulation stage of the radio receiver. Therefore it gives a greater
audio output for a given RF input. In other words it makes a particular
radio station with a given field strength at the receiver antenna sound
louder than that for another radio station with exactly the same field
strength that uses standard amplitude modulation.
It is said to work by relocating energy from close to the carrier
towards the edges of the sidebands. It also has another subjective
effect. If one tunes to the station with a radio with a manual tuning
control, when approaching the station it sounds louder than if standard
AM were used.
Could anyone offer me more information on this devious technique ? When
was it invented ? Where was it deployed ? Was it ever used in the UK ?
Serge Auckland
processor, for example, an Optimod AM, incorporates a phase rotator that
will keep the higher amplitude of the positive or negative excursions always
positive. This allows you to ensure that maximum negative mod never goes to
clipping, and positive mod goes up to 125-150% . It's not all that devious,
just exploits the AM potential.
Serge
"The Technical Manager" <tec...@niobiumfive.co.uk> wrote in message
news:3DCFB963...@niobiumfive.co.uk...
Harry Conover
> This technique is common in the US, but not permitted in the UK. The air
> processor, for example, an Optimod AM, incorporates a phase rotator that
> will keep the higher amplitude of the positive or negative excursions always
> positive. This allows you to ensure that maximum negative mod never goes to
> clipping, and positive mod goes up to 125-150% . It's not all that devious,
> just exploits the AM potential.
>
> Serge
First, what exactly is a "phase rotator" with respect to AM
broadcasting? What phases are rotated, and why?
Second, it would seem to me that unequal excursions of the modulation
envelope would result in audio distortion, and consequently failure of
FCC mandated "proof of performance" certification with respect to
audio sine wave distortion?
Unless this is a "pirate radio station" kludge device that cannot meet
legal commercial broadcasting standards, what's the entire story?
(Other than violating commercial broadcasting standards, it sound like
the end function of this device would be the production of loud yet
horribly distorted audio. Is there any market for this?)
Harry C.
Stephen
news:7ce4e226.02111...@posting.google.com...
> "Serge Auckland" <sergioa...@aol.com> wrote in message
news:<aqopod$8p3$1...@helle.btinternet.com>...
> > This technique is common in the US, but not permitted in the UK. The air
> > processor, for example, an Optimod AM, incorporates a phase rotator that
> > will keep the higher amplitude of the positive or negative excursions
always
> > positive. This allows you to ensure that maximum negative mod never goes
to
> > clipping, and positive mod goes up to 125-150% . It's not all that
devious,
> > just exploits the AM potential.
> >
> > Serge
>
> First, what exactly is a "phase rotator" with respect to AM
> broadcasting? What phases are rotated, and why?
I guess it's a phase inverter, and a short audio delay which allows the
device to see an asymmetrical peak in advance, and flip the polarity if
required before it gets sent to the peak limiters and transmitted.
> Second, it would seem to me that unequal excursions of the modulation
> envelope would result in audio distortion, and consequently failure of
> FCC mandated "proof of performance" certification with respect to
> audio sine wave distortion?
I guess it only works on waveforms which are asymmetrical to begin with, so
it would have no effect on sine waves and these would not exceed 100%
modulation. What I don't understand is how it could suddenly invert the
phase without making an audible click.
Chuck/KE4ETH
"Harry Conover" <hhc...@yahoo.com> wrote in message
news:7ce4e226.02111...@posting.google.com...
Have you listened to Music lately
--
73,
Chuck
KE4ETH
Remove the obvious from Email.
Flingle Bunt
Hi All.
From what I remember of the Optimod AM details the "Phase
Scrambler"/"Phase Rotator" was an all-pass-filter that altered the
phase of each sin and cos component in the incomming signal, this
altered the shape of the wave form (for complex signals, but not sine
waves) but not the energy level of each component. I'm not too sure
how all-pass-filters behave to be 100% accurate on this.
Optimod also use these in the stereo FM units, when these are switched
in they do alter the sound and make any stereo image that the
programme content had even more vauge. If your playing with the phase
of the signal in anyway this is inevitable.
Cheers
John
Reg Edwards
bill. It allows the final amplifier to be run at a higher average
efficiency.
In effect, the AM carrier level is increased on loud passages and decreased
on soft passages. But it is done at an audio frequency rate.
After all, when there's no music and nobody is speaking you don't really
need any carrier at all. There's nothing to carry.
The overall effect is to run the power amplifier at greater than 100%
modulation without a significant increase in distortion.
The result at the receiving end is a little bit extra audio distortion and a
little worse signal to noise ratio. Hardly noticeable when swamped by the
distortion always present in the receiver's loud speaker.
Probably been used for the last 60 years by low-fidelity broadcasters who
are always trying to increase their service areas at lower cost. The
advertisers' are in there somewhere.
British AM broadcasters do it. Some do it more than others. Tune over the
medium wave band and ask why some very strong stations (AGC fully operative)
appear to be louder than others.
Dave Plowman
Harry Conover <hhc...@yahoo.com> wrote:
> it sound like the end function of this device would be the production of
> loud yet horribly distorted audio. Is there any market for this?)
Oh yes. Optimod have been doing it for years.
--
*The statement above is false
Dave Plowman dave....@argonet.co.uk London SW 12
RIP Acorn
North Green
Careful Reg. Asymetrical modulation wont effect the AGC on your radio
only AMC
which is what the BBC use.
Asymetrical modulation is were the peaks of the modulating audio is
made more
positive with respect to the normal symetrical audio AC signal, but
the
negative peaks must remain the same.
In the USA they run to 125% modulation as a attempt increase loudness
of a
station and even possibly improve the potental coverage of a
transmitter, it
can be said that a increase in power has occured by running to 125%
mod but the
transmitter is still running the same power a specified by the
licence.
In the UK the rules don't allow anything beyond 100 % mod.
In theory there is no limit on how positive the modulating audio can
be made
other than the maximum modulation level the transmitter can achieve,
but the
negative peaks must remain within 100 % or over modulation will occur.
Asymetry of the audio is done within the Optimod processor, while at
the receiver everything is made normal, except the programme sounds
louder with a
minor increase in distortion.
AMC = Amplitude Modulation Companding and is a method of reducing the
output
power of the transmitter has it reaches 100 % mod. Thus causing your
radio's
AGC to compensate. The BBC run 3dB AMC which means that a 150 kw
transmitter
with no modulation the output will be 150 kw while at 100 % mod the
peak mean
power will be 112.5 kw instead of 225 kw. The idea is save the BBC
money on the
electricity bill, BBC Radio 5 runs this.
AMC can sometimes be called DCC which the BBC World Service run, very
similar.
Brian Howie
electricity
> bill. It allows the final amplifier to be run at a higher average
> efficiency.
>
> In effect, the AM carrier level is increased on loud passages and
decreased
> on soft passages. But it is done at an audio frequency rate.
>
I used a technique similar to this on Ham Radio about 30 years ago. It was
called "series gate modulation". The AM modulation was applied to the screen
of the PA Valve (tube) in such a way that the PA anode (plate) current and
hence carrier level followed the speech waveform. It meant I could run the
PA Valve a bit over its ratings. It sounded a bit strange at the receiver
end because it "pumped" the AGC.
Not as good as plate-screen modulation, but saved on the big transformer.
I understand that modern broadcast AM Transmitters use some form of RF-AF
quadrature technique to produce AM.
Brian GM4DIJ
Harry Conover
I suspect you're speaking of the RCA "Ampliphase" broadcast
transmitter of the middle 1960's. It did work this way, but was a
commercial failure. To my knowledge no one has since emulated its
example.
Harry C.
Brian D
hhc...@yahoo.com (Harry Conover) wrote:
> "Brian Howie" <brian...@baesystems.com> wrote in message
> news:<3dd211b3$1...@baen1673807.greenlnk.net>...
[snip]
> > I understand that modern broadcast AM Transmitters use some form of RF-AF
> > quadrature technique to produce AM.
> >
> > Brian GM4DIJ
>
> I suspect you're speaking of the RCA "Ampliphase" broadcast
> transmitter of the middle 1960's. It did work this way, but was a
> commercial failure. To my knowledge no one has since emulated its
> example.
>
More likely to be Doherty Modulation.
--
Brian D | RiscPC600 | StrongARM 233Mhz RISC OS 4 66Mb
Linux PCs on RISC OS network |
Darlington Dolphin Masters ASC | <www.darlington-masters.org>
Philip de Cadenet
>> it sound like the end function of this device would be the production of
>> loud yet horribly distorted audio. Is there any market for this?)
>
>Oh yes. Optimod have been doing it for years.
You are joking right?
You haven't listened to Heart 106.2 in London. I'm told with an Optimod,
they really do sound good.
--
Philip de Cadenet G4ZOW
Transmitters 'R' Us
http://www.transmittersrus.com
Stephen
"Brian Howie" <brian...@baesystems.com> wrote in message
news:3dd211b3$1...@baen1673807.greenlnk.net...
> quadrature technique to produce AM.
>
> Brian GM4DIJ
>
constant amplitude square wave at carrier frequency. The sharper the edges
of the square wave, the higher the efficiency of the transmitter. The square
wave has it's mark to space ratio modulated with the program audio, i.e.
pulse width modulation is used, and it is only the filters and antenna
tuning unit on the final output of the transmitter which change this
constant amplitude pulse width modulated square wave into a sinewave carrier
with true Amplitude Modulation.
Philip de Cadenet
Check out the rest of his website:
http://www.w3am.com/8poleapf.html
Brian Howie
That seems reasonable. The quadrature technique was mentioned to me by the
Engineer showing a group of us round the Westerglen MF site;maybe I was not
listening properly, probably still stunned by the sight of him drawing the 1
foot arc off the spare Medium wave antenna.
Brian
Serge Auckland
Serge
"Philip de Cadenet" <Philst...@thebbc.fslife.co.uk> wrote in message
news:5xONtqDR...@fslife.co.uk...
Dave Plowman
Philip de Cadenet <Philst...@thebbc.fslife.co.uk> wrote:
> >> it sound like the end function of this device would be the production
> >> of loud yet horribly distorted audio. Is there any market for this?)
> >Oh yes. Optimod have been doing it for years.
> You are joking right?
If only I was.
> You haven't listened to Heart 106.2 in London. I'm told with an Optimod,
> they really do sound good.
When a pop 'CD' is sent for mastering, they'll spend a vast amount of time
and money making it sound as loud as possible using any equipment or
tricks that are available. And may (or maybe not) improve on the job the
recording engineer has done.
Then along comes Mr Optimod or another of his family and says:-
"I can do this job even better without even listening to the music first"
Or not. And no 'maybe' this time.
--
*Why are a wise man and a wise guy opposites?
North Green
> > You haven't listened to Heart 106.2 in London. I'm told with an Optimod,
> > they really do sound good.
>
> When a pop 'CD' is sent for mastering, they'll spend a vast amount of time
> and money making it sound as loud as possible using any equipment or
> tricks that are available. And may (or maybe not) improve on the job the
> recording engineer has done.
>
> Then along comes Mr Optimod or another of his family and says:-
>
> "I can do this job even better without even listening to the music first"
>
> Or not. And no 'maybe' this time.
The Optimod is alot better than those old delay line limiters the BBC used
to use in all it audio circuits. Those things could realy distroy the audio
when put on the wrong setting (8dB or something silly) and the Optimod isn't
much different, when properly setup it can work well.
Philip de Cadenet
>>
>> "I can do this job even better without even listening to the music first"
>>
>> Or not. And no 'maybe' this time.
>
>The Optimod is alot better than those old delay line limiters the BBC used
>to use in all it audio circuits. Those things could realy distroy the audio
>when put on the wrong setting (8dB or something silly) and the Optimod isn't
>much different, when properly setup it can work well.
I have to agree with the last paragraph.
It's all in the setting up.
--
Philip de Cadenet
Dave Plowman
North Green <norr_...@hotmail.com> wrote:
> The Optimod is alot better than those old delay line limiters the BBC
> used to use in all it audio circuits.
A limiter is there to limit maximum level or modulation. It may, or may
not, come into active use depending on many things. No sober sound person
I know would rely on it improving his work after the point where he's
monitoring.
> Those things could realy distroy the audio when put on the wrong setting
> (8dB or something silly) and the Optimod isn't much different, when
> properly setup it can work well.
Yes 8dB is silly. Or not. Please don't quote technical terms you don't
understand. Unless you're an Optimod salesman. Then it's obviously ok.
--
*Don't sweat the petty things and don't pet the sweaty things.
Serge Auckland
includes Optimods should be sold without a knowledge of what they do and
how.
As some of you may know, I have been involved in Broadcast equipment sales
for the past twenty five years, and with our customers, snake-oil or just
plain ignorance doesn't go down terribly well, and we wouldn't continue in
business if we didn't know what we were doing.
Consumer hi-fi is another thing, ever tried asking a Dixon or Currys
salesman what Dolby noise-reduction does?
Serge
--
Sergio Dalmazzo-Auckland
Preco (Broadcast Systems) Ltd
Direct Tel: +44 (0) 1359 232647
Direct Fax: +44 (0) 1359 232948
www.preco.co.uk
"Dave Plowman" <dave....@argonet.co.uk> wrote in message
news:4b9683369c...@argonet.co.uk...
North Green
> > The Optimod is alot better than those old delay line limiters the BBC
> > used to use in all it audio circuits.
> A limiter is there to limit maximum level or modulation. It may, or may
> not, come into active use depending on many things. No sober sound person
> I know would rely on it improving his work after the point where he's
> monitoring.
> > Those things could realy distroy the audio when put on the wrong setting
> > (8dB or something silly) and the Optimod isn't much different, when
> > properly setup it can work well.
> Yes 8dB is silly. Or not. Please don't quote technical terms you don't
> understand. Unless you're an Optimod salesman. Then it's obviously ok.
If you wish to come out with insulting remarks then don't bother, I for one
understand and work with RF and Audio equipment on a daily basis and if your
so professional then you would have understood without asking this newsgroup
why Radio and TV stations want to use Optimod processing and not just limiters.
May I suggest you read the manual for the Optimod 8100 or 9100 that can be
downloaded for Orban's web page and do yourself a big favour and find out how
this equipment works before you make your usual insulting remarks.
If you cannot be bothered to do such a simple task then get out of broadcasting
and take up re-wiring councils houses or something similar which doesn't push
your technical aptitude.
Dave Plowman
Serge Auckland <sergioa...@aol.com> wrote:
> It's not OK, even, or especially for an Optimod salesman. Nothing, and
> that includes Optimods should be sold without a knowledge of what they
> do and how.
Sorry to be flippant. I'd certainly expect the supplier of such things to
be fully conversant with what they do and how they do it. My complaint is
more with the buyers and users of such devices. No matter how clever such
a device is, it cannot possibly genuinely improve *all* program material
passed through it regardless. It might well improve audibility of that
material for in car or portable use, and will also make a transmitter so
equipped sound louder than one not so at a casual listen as when spinning
through the waveband. But it will also spoil many of the parameters of the
source material when listen to on even half decent equipment.
> As some of you may know, I have been involved in Broadcast equipment
> sales for the past twenty five years, and with our customers, snake-oil
> or just plain ignorance doesn't go down terribly well, and we wouldn't
> continue in business if we didn't know what we were doing.
True.
> Consumer hi-fi is another thing, ever tried asking a Dixon or Currys
> salesman what Dolby noise-reduction does?
Another much misused term these days is NICAM - often just used to mean
stereo.
When Dolby first arrived, there was a fair amount of confusion even with
pros.
A good question to ask was "What effect would Dolby A have, when used
with a multi track recorder, on a noisy microphone in the studio?"
--
*Hard work has a future payoff. Laziness pays off NOW.
Richard Lamont
> In article <6905f95c.02111...@posting.google.com>,
> North Green <norr_...@hotmail.com> wrote:
>
>>The Optimod is alot better than those old delay line limiters the BBC
>>used to use in all it audio circuits.
>
> A limiter is there to limit maximum level or modulation. It may, or may
> not, come into active use depending on many things. No sober sound person
> I know would rely on it improving his work after the point where he's
> monitoring.
>
>>Those things could realy distroy the audio when put on the wrong setting
>>(8dB or something silly) and the Optimod isn't much different, when
>>properly setup it can work well.
>
> Yes 8dB is silly. Or not. Please don't quote technical terms you don't
> understand. Unless you're an Optimod salesman. Then it's obviously ok.
Before it used Optimods, the BBC used simple soft-knee
compressor-limiters on its AM transmitters. These were lined up so that
low-level signals had 12 dB of gain on the domestic services, and 16 dB
on external services.
--
Richard Lamont
ric...@stonix.demon.co.uk
Gareth Rowlands
"North Green" <norr_...@hotmail.com> wrote in message
news:6905f95c.02111...@posting.google.com...
> if your so professional then you would have understood without asking this
> newsgroup why Radio and TV stations want to use Optimod processing
> and not just limiters.
Just out of interest, which UK TV broadcasters are using this dreaded
device ? My mate Nigel 'next door' wants to know if he's a bit behind
the times.
Cheers,
Gareth.
P.S. There are compressor/limiters too !
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J.L.E
in article news:ar84f7$fk4$1...@venus.btinternet.com
sent us these words of wisdom…
<snip>
>
> Consumer hi-fi is another thing, ever tried asking a Dixon or Currys
> salesman what Dolby noise-reduction does?
>
Ask some of them what Mono is and you get blank looks !.. :~(
--
If replying by E-mail, mind the Spam trap.
Location: West Sussex. United Kingdom.
Dave Plowman
> one understand and work with RF and Audio equipment on a daily basis and
> if your so professional then you would have understood without asking
> this newsgroup why Radio and TV stations want to use Optimod processing
> and not just limiters.
Well, I know that +8 dB relative to the nominal '0' level is regarded as
the peak level to be sent to a transmitter, and has been for many years.
Strange you don't appear to since you work with RF and audio equipment on
a daily basis.
> May I suggest you read the manual for the Optimod
> 8100 or 9100 that can be downloaded for Orban's web page and do yourself
> a big favour and find out how this equipment works before you make your
> usual insulting remarks. If you cannot be bothered to do such a simple
> task then get out of broadcasting and take up re-wiring councils houses
> or something similar which doesn't push your technical aptitude.
I dislike them because they frequently spoil the efforts of my colleagues
and myself. Is that too hard to understand?
--
*Caution: I drive like you do.
Rob Stampfli
How are AM radio station regulated with respect to power limits?
Power into the final? Carrier power? PEP?
Rob
Dave Plowman
Paul Martin <p...@zetnet.net> wrote:
> > Well, I know that +8 dB relative to the nominal '0' level is regarded
> > as the peak level to be sent to a transmitter, and has been for many
> > years.
> Otherwise known as PPM4 and PPM6.
I seriously doubt that anyone who loves these 'Optimod' devices would know
a PPM if it bit them in the arse.
--
*Women who seek to be equal to men lack ambition.