You misunderstand modern (post 1950) SW transmitter design.

Class-B, PDM and PSM (and hybrids of the two) modulators produce an AM
waveform, no matter what.

Some Russian Class-B transmitters can handle transmitting FM, but these are
very pure analog beasts.

Only the modern PDM / PSM / Hybrid transmitters are being put into service
for DRM, no Class-B modulators.

CODFM (as DRM uses it) in the SW bands is a PSUDO-CODFM; the audio of the
CODFM signal is imposed on an AM waveform for transmission. The BSEE
electronics is a lot simpler, and it is backwardly compatible with the
installed base.

Thankfully this DRM AM-CODFM design is so simple that it is totally
misunderstood, and you can't tell the difference at the receiver end.

PSUDO-CODFM aka AM-CODFM
-- CODFM signal is of Audio bandwidth, 10 kHz or 20 kHz
-- Most modern SW transmitters can accept 20 kHz audio with only minor
retrofits
-- Most modern SW transmitters are "linear" up to about 40 kHz, based on 90
kHz PDM / PSM clock rates
-- Most modern SW transmitters only know how to transmit AM +SSB (but not
FM)
-- SW DRM transmitters universally get their PDM / PSM clock rates increased
to 100 kHz + (Continental, retrofit infos)
-- A true wideband CODFM signal of 1 MHz would not work on SW, ITU
allocation issues aside ... the installed transmitters base cannot handle
it, only PSUDO-CODFM is workable
-- VHF / UHF CODFM transmitters are real CODFM transmitters, as there is no
PDM / PSM / etc involved.

There are no true CODFM transmitters in the SW band with powers above 2kw
(or maybe 10kw), as the electrical engineering is just too hard to do.

DRM,
the new standard for DAB over SW uses AM modulation with CODFM content.
=======
DRM, Digital Radio Mondiale, uses COFDM, as does the European VHF and L-band
DAB system and the US HD Radio. COFDM, in its multiple subcarriers, does not
use AM. Instead, each subcarrier is modulated with an orthogonal QAM. So
that's a modulation in which both amplitude and phase are varied at the same
time, to carry twice as much information as an AM signal of the same
bandwidth can carry.

Max Power wrote:
You misunderstand modern (post 1950) SW transmitter design.

Class-B, PDM and PSM (and hybrids of the two) modulators produce an AM
waveform, no matter what.

Some Russian Class-B transmitters can handle transmitting FM, but these
are very pure analog beasts.

Only the modern PDM / PSM / Hybrid transmitters are being put into
service for DRM, no Class-B modulators.

CODFM (as DRM uses it) in the SW bands is a PSUDO-CODFM; the audio of
the CODFM signal is imposed on an AM waveform for transmission. The BSEE
electronics is a lot simpler, and it is backwardly compatible with the
installed base.

Thankfully this DRM AM-CODFM design is so simple that it is totally
misunderstood, and you can't tell the difference at the receiver end.

PSUDO-CODFM aka AM-CODFM
-- CODFM signal is of Audio bandwidth, 10 kHz or 20 kHz
-- Most modern SW transmitters can accept 20 kHz audio with only minor
retrofits
-- Most modern SW transmitters are "linear" up to about 40 kHz, based on
90 kHz PDM / PSM clock rates
-- Most modern SW transmitters only know how to transmit AM +SSB (but
not FM)
-- SW DRM transmitters universally get their PDM / PSM clock rates
increased to 100 kHz + (Continental, retrofit infos)
-- A true wideband CODFM signal of 1 MHz would not work on SW, ITU
allocation issues aside ... the installed transmitters base cannot
handle it, only PSUDO-CODFM is workable
-- VHF / UHF CODFM transmitters are real CODFM transmitters, as there is
no PDM / PSM / etc involved.

There are no true CODFM transmitters in the SW band with powers above
2kw (or maybe 10kw), as the electrical engineering is just too hard to do.

DRM,
the new standard for DAB over SW uses AM modulation with CODFM content.
=======
DRM, Digital Radio Mondiale, uses COFDM, as does the European VHF and
L-band DAB system and the US HD Radio. COFDM, in its multiple
subcarriers, does not use AM. Instead, each subcarrier is modulated with
an orthogonal QAM. So that's a modulation in which both amplitude and
phase are varied at the same time, to carry twice as much information as
an AM signal of the same bandwidth can carry.

My head hurts.

In article ,
Dave wrote:

Max Power wrote:
You misunderstand modern (post 1950) SW transmitter design.

Class-B, PDM and PSM (and hybrids of the two) modulators produce an
AM waveform, no matter what.

Some Russian Class-B transmitters can handle transmitting FM, but
these are very pure analog beasts.

Only the modern PDM / PSM / Hybrid transmitters are being put into
service for DRM, no Class-B modulators.

CODFM (as DRM uses it) in the SW bands is a PSUDO-CODFM; the audio
of the CODFM signal is imposed on an AM waveform for transmission.
The BSEE electronics is a lot simpler, and it is backwardly
compatible with the installed base.

Thankfully this DRM AM-CODFM design is so simple that it is totally
misunderstood, and you can't tell the difference at the receiver
end.

PSUDO-CODFM aka AM-CODFM -- CODFM signal is of Audio bandwidth, 10
kHz or 20 kHz -- Most modern SW transmitters can accept 20 kHz
audio with only minor retrofits -- Most modern SW transmitters are
"linear" up to about 40 kHz, based on 90 kHz PDM / PSM clock rates
-- Most modern SW transmitters only know how to transmit AM +SSB
(but not FM) -- SW DRM transmitters universally get their PDM / PSM
clock rates increased to 100 kHz + (Continental, retrofit infos) --
A true wideband CODFM signal of 1 MHz would not work on SW, ITU
allocation issues aside ... the installed transmitters base cannot
handle it, only PSUDO-CODFM is workable -- VHF / UHF CODFM
transmitters are real CODFM transmitters, as there is no PDM / PSM
/ etc involved.

There are no true CODFM transmitters in the SW band with powers
above 2kw (or maybe 10kw), as the electrical engineering is just
too hard to do.

DRM, the new standard for DAB over SW uses AM modulation with
CODFM content.
======= DRM, Digital Radio Mondiale, uses COFDM, as does the
European VHF and L-band DAB system and the US HD Radio. COFDM, in
its multiple subcarriers, does not use AM. Instead, each subcarrier
is modulated with an orthogonal QAM. So that's a modulation in
which both amplitude and phase are varied at the same time, to
carry twice as much information as an AM signal of the same
bandwidth can carry.

My head hurts.


Stop snorting the CODFM then.

--
Telamon
Ventura, California

Telamon wrote:

Stop snorting the CODFM then.

Far better that than a Cod Piece.



mike


--
__ __ __ __ __ __ __ __
/ /\ / /\ / /\ / /\ / /\ / /\ / /\ / /
/ /\ \/ /\ \/This space for rent/\ \/ /\ \/ /
/_/ \/_/ \/_/ \/_/ \/_/ \/_/ \/_/ \/_/

Densa International©
'Think tanks cleaned cheap'

Due to the insane amount of spam and garbage,
I block all postings with a Gmail, Google Mail,
Google Groups or HOTMAIL address.
I also filter everything from a .cn server.

http://improve-usenet.org/

In article ,
"Max Power" wrote:

You misunderstand modern (post 1950) SW transmitter design.

SNIP

And you do?

There are no true CODFM transmitters in the SW band with powers above
2kw (or maybe 10kw), as the electrical engineering is just too hard
to do.

Tell that to NZ then. They will be surprised.

DRM is crap.

Why don't you read up on the transmitter requirements on the consortium
web site and stop cross posting this nonsense.

I'm going to rename you Max Headroom.

--
Telamon
Ventura, California

On Aug 17, 8:46*pm, "Max Power" wrote:

CODFM (as DRM uses it) in the SW bands is a PSUDO-CODFM; the audio of the
CODFM signal is imposed on an AM waveform for transmission.

Sorry, but that's simply not the case. It is true that DRM can be used
along with AM, or along with FM, exactly the same as HD Radio does. In
a simulcast, where the DRM COFDM spectra can be placed on either side
of the analog spectrum. But the DRM signal per se is COFDM, modulated
either QPSK, 16-QAM, or 64-QAM. Not AM.

All of this is readily available information:

http://www.drm.org/uploads/media/ETS...980_v2.3.1.pdf

Check out in particular Annex K, which I think is what's confusing
you.

PSUDO-CODFM aka AM-CODFM
-- CODFM signal is of Audio bandwidth, 10 kHz or 20 kHz

DRM can use 9, 10, 20, 50, or 100 KHz bandwidth. Maybe more. The
bottom three are when it's used in the LW, MW, or SW bands. The upper
two are for the new extension of DRM into the VHF band (up to 120
MHz). Those bandwidths are chosen specifically so that DRM can coexist
with analog spectra in those RF bands.

The bandwidth of the signal is not directly related to the max audio
frequency here, as it is in AM. It's related to the max bit rate, at
different levels of robustness, like any other digital transmission.
In turn, that max bit rate can be related to the max audio frequency.
But with digital, you can trade off the audio frequency limit against
the bits used in quantizing each sample.

In short, DRM could have been used as the basis for the new HD Radio
service in the US, instead of the Ibiquity system we have here.
Functionally, they are similar.

Bert

Shortwave band PDM, PSM and hybrid modulators can't modulate true CODFM --
only AM variants.
http://www.contelec.com/pdf%5CDRM_Requirements.pdf
"DRM Transmitter Requirements and Applying DRM Modulation to Existing
Transmitters"

High power SW transmitters are not linear, in spite of the advent of PSM &
PDM and Hybrid modulators.
High power MW transmitters have some of the same linearity problems.

A kit usually is needed to fool or coax most modern AM (be they on SW or MW)
transmitters into transmitting CODFM -- without it most AM transmitters
would not be able to handle CODFM with any linearity whatsoever. This is
CODFM limited to the audio band only, not wideband CODFM.

CODFM on SW (and MW too, same kind of technology) rides on top of a "primary
carrier wave" with sidebands that carry the other "pseudo carriers" at
energies nearly equal to the primary carrier wave. The pseudo-carriers are
just audio tones, not true carrier waves in the modulator.

DRM demodulators on SW and MW are based on PLL and Sync detection ... of a
primary carrier wave. The slightly increased power of the modulator's
primary AM carrier helps hold recover sync for non-ground wave reception.
The AM sidelobes are still there, it is just that they are at 100% duty
cycle.

With true VHF / UHF etc ... CODFM, there is no primary carrier wave at all
in the modulator -- and the modulator is not PDM or PSM or a hybrid of
them -- and the energy distribution of the carriers is linear. You can't
really do this on MW or SW, or no one has bothered to create a modulator to
do so.

With CODFM over SW (and MW), one of the carrier waves in the carrier group
rides on primary carrier wave (and it probably has ~1.5db ... 3db more
energy in it to help with the link margin, due to fading margins this does
not disturb linearity).

-- You can switch to analog "AM" mode service with a "flick of a switch", as
CODFM is imposed on an AM waveform. A true CODFM modulator could never be
switched into AM modulation service due to the electrical engineering
impossibility of such.
-- With AM modulators it is difficult (or even impossible) to make the
primary carrier have the same amount of energy as the sidelobes ... but this
is also a energy saving issue for analog transmission.

How you managed to confuse HD Radio and VHF DRM (more or less totally
unrelated technologies to DRM on MW and SW) is a mystery to me. Masking (and
simulating) is even not my DRM radar, albeit it works for VHF service. There
is no DRM for VHF yet, only SW and MW. DRM over VHF will probably resemble
HD Radio.

===============
CODFM (as DRM uses it) in the SW bands is a PSUDO-CODFM; the audio of the
CODFM signal is imposed on an AM waveform for transmission.
===============
Sorry, but that's simply not the case. It is true that DRM can be used
along with AM, or along with FM, exactly the same as HD Radio does. In
a simulcast, where the DRM COFDM spectra can be placed on either side
of the analog spectrum. But the DRM signal per se is COFDM, modulated
either QPSK, 16-QAM, or 64-QAM. Not AM.

All of this is readily available information:

http://www.drm.org/uploads/media/ETS...980_v2.3.1.pdf

Check out in particular Annex K, which I think is what's confusing
you.

On Aug 18, 8:52*pm, "Max Power" wrote:

Shortwave band PDM, PSM and hybrid modulators can't modulate true CODFM -- *
only AM variants.http://www.contelec.com/pdf%5CDRM_Requirements.pdf
"DRM Transmitter Requirements and Applying DRM Modulation to Existing
Transmitters"

Nowhere in the paper you pointed out does it state that DRM is
transmitted "over AM." Check it out again, paying attention to the
discussion on amplitude *AND* phase signals that must be generated.

-- You can switch to analog "AM" mode service with a "flick of a switch", as
CODFM is imposed on an AM waveform. A true CODFM modulator could never be
switched into AM modulation service due to the electrical engineering
impossibility of such.

Come now. Think of the ideal transmitter as being a box that generates
a perfectly flat RF spectrum within a well defined channel bandwidth.
Whatever input you feed that box modulates the RF carrier to create an
exact replica, as high power RF emission, of the input signal to the
transmitter. And nothing is emitted outside the desired frequency
channel.

COFDM exciters are what create all the subcarriers of COFDM, and which
modulate the signal in phase and in amplitude. The transmitter must
simply pass this on through, perfectly unchanged (ideally). The paper
describes problems that transmitters optimized for analog AM have in
transferring that COFDM waveform, and work-arounds. The main issue is
that AM transmitters are made more efficient by being designed to be
non-linear. This is because for analog AM, they don't need to be
perfectly linear in phase.

Nowhere does the paper claim you aren't transmitting amplitude and
phase variations, multple subcarriers, or anything else required by
DRM. The main thrust is, if you want to use your current AM
transmitter, here are a set of compromises and workarounds. The
underlying message being, the next tranmsmitter you buy should be
linear.

Ultimately, sure, you can describe the COFDM subcarriers as being
audio tones. Just as the telephone industry does, when they call their
version of COFDM "discrete multitone" (DMT). Calling it "multitone" in
no way changes the fact that these are multiple subcarriers of COFDM.

http://en.wikipedia.org/wiki/Discret...one_modulation

Bert