ELF radio needs more watts than MW radio?

[Green Xenon [Radium]]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

MW and ELF are forms of electromagnetic radiation in the RF spectrum.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.

Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?

So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?


Thanks,

Radium

 

[Jamie]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

MW and ELF are forms of electromagnetic radiation in the RF spectrum.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.

Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?

So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?


Thanks,

Radium

I know this is the BASIC channel how ever, All I can say is WOW!



--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

 

[Sjouke Burry]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

MW and ELF are forms of electromagnetic radiation in the RF spectrum.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.

Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?

So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?


Thanks,

Radium

I know this is the BASIC channel how ever, All I can say is WOW!

What do you expect from radium trolling?

 

[Eric Gisse]

On Jul 24, 4:31 pm, "Green Xenon [Radium]" <[email protected]>
wrote:
[snip]

This kid suffers a terminal case of "doesn't know what he is talking
about".

 

[[email protected]]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

Then your memory isn't worth a crap or what you read was wrong.

<snip crap>

 

[Sam Wormley]

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to[o] much power.

That's bullshit.

 

[Michael Black]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

True and not true.
Maybe this will help shed some ELF light on the subject.
http://en.wikipedia.org/wiki/Extremely_low_frequency

Of course, that's not an inefficiency of spectrum.

And the inefficiency of the long antennas means nothing since
such low frequencies are used for specific purposes where such
low frequencies are the only choices. Given that, the only
choice is to use such low frequencies, or not communicate
at all.

Michael

 

[Androcles]

| Hi:
|
| I remember reading somewhere than ELF [Extremely Low Frequency] radio
| transmission is inefficient because it requires to much power.
|
| If that is the case, wouldn't MW [Medium Wave] radio transmission
| require even more power?
|
| MW and ELF are forms of electromagnetic radiation in the RF spectrum.
|
| An photon [or electromagnetic wave] of a higher-frequency has more
| energy than a photon of a lower-frequency.
|
| Let's say there are there are two radio transmitters, one emits 2 GHz
| waves while the other emits 2 kHz waves. If the two radio transmitters
| use the same modulation scheme [AM/FM, etc.] and emit the same amount
| of photons-per-second-per-square-meter, the 2 GHz transmitter will be
| using more watts than the 2 kHz transmitter -- because a 2 GHz photon
| requires more power to generate than a 2 kHZ photon. Right?
|
| So how would transmitting a lower-frequency radio wave require more
| power than transmitting a higher-frequency radio wave?
|
|
| Thanks,
|
| Radium

You are making the classic mistake of confusing quality with quantity,
energy with power.
Which has more pressure, a 55,000 psi water jet or Niagara Falls?
http://www.laserfab.co.uk/cnc_water_jet_cutting.htm


A cigar tip is red hot and will painfully burn your skin. Can you heat a
cup of coffee with it?

How big is this ELF photon?
http://www.crystalinks.com/solarnews.html
Now that's extreme.

 

[[email protected]]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

MW and ELF are forms of electromagnetic radiation in the RF spectrum.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.

Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?

So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?

Thanks,

Radium

There is the modulation method - AM or FM. FM is more efficient - at
least narrowband FM. That's why we use FM for mobile transmitters. You
could use supressed-carrier AM of course but that is a sod to
demodulated.

The higher the frequency the shorter the distance it can travel for a
given power. Therefore VLF can travel round the world and back again!
trouble is you may need for ELF an aerial the size of a mountain
range!
For a 10 Gig frenquency you would need to pump out a heluva lot of
power for it to go any distance. Inverse square law.


Would help of you went to study engineering at Uni - then most of your
questions would be answered.

K.

 

[[email protected]]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

I suspect what you actually read about was the US military scheme to
communicate with submerged submarines using high-power VLF that could
penetrate seawater.  At one point there were plans to use huge
underground ore veins in Michigan's Upper Penninsula as the
transmitter antenna.  That might have been a tad inefficient!

There's also the issue of low carrier frequencies not supporting high
symbol rates.  I seem to recall that the submerged subs would get only
code, at rates so slow even the rankest beginning amateur operator
would have had no trouble keeping up... <g>

Best regards,

Bob Masta

              DAQARTA  v4.00
   Data AcQuisition And Real-Time Analysis
             www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
           FREE Signal Generator
        Science with your sound card!

Shush Bob, you're deliving into 100% reliable long distance
communications techniques first discovered and exploited in the 1950s
and which have remained classified ever since. As you point out, the
information transmission rate is incredibly low, but extremely
reliable and nearly impossible to block or jam, and it reliably
reaches every location on earth, surface, underwater, or underground,
at extremely low baud rates.

Now what would anyone imagine what purpose such a limited system might
be used for? This is precisely why VLF systems of this type remain
highly classified. Yes, correct. They have only one practical
application. Let's simply call it the Fed Ex principle, which applies
to things that must be reliably delivered on schedule.

Harry C.

 

[[email protected]]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

MW and ELF are forms of electromagnetic radiation in the RF spectrum.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.

Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?

So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?

Thanks,

Radium

There is the modulation method - AM or FM. FM is more efficient - at
least narrowband FM. That's why we use FM for mobile transmitters. You
could use supressed-carrier AM of course but that is a sod to
demodulated.

Nonsense.

FM is common because it is intrinsically immune to impulse noise
and cheap to implement.

Supressed carrier is trivial to demodulate these days but more
expensive to do.

The higher the frequency the shorter the distance it can travel for a
given power. Therefore VLF can travel round the world and back again!

Nonsense.

Most long distance terrestrial communication is done on HF.

trouble is you may need for ELF an aerial the size of a mountain
range!

About the only thing you got right.

For a 10 Gig frenquency you would need to pump out a heluva lot of
power for it to go any distance. Inverse square law.

Nonsense.

At 10 Ghz, it is all line of sight and all in the antenna. It doesn't
take much power to hear your own signal bounce off the moon at 10 Ghz.

All space communications take place in the Ghz.

 

[Igor]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

MW and ELF are forms of electromagnetic radiation in the RF spectrum.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.

Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?

So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?

Thanks,

Radium

I'm not sure about output power, but I do know that the lower the
frequency, the longer the wavelength, and hence the longer the
transmitting antenna. ELF requires a humongous antenna.

 

[[email protected]]

Hi:
I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.
If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?
MW and ELF are forms of electromagnetic radiation in the RF spectrum.
An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.
Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?
So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?
Thanks,
Radium

There is the modulation method - AM or FM. FM is more efficient - at
least narrowband FM. That's why we use FM for mobile transmitters. You
could use supressed-carrier AM of course but that is a sod to
demodulated.

Nonsense.

FM is common because it is intrinsically immune to impulse noise
and cheap to implement.

It's cheap but not immune to noise and suseptable to multipath big-
time.

Supressed carrier is trivial to demodulate these days but more
expensive to do.

Do tell how...It's not in any text book so maybe we can learn with
your advanced knowledge.

Nonsense.

Most long distance terrestrial communication is done on HF.

You have never heard of the inverse square law obviously. High
frequencies are line of site only and can go long distances
because you pump out more power. You need to compare apples with
apples.

About the only thing you got right.

The only thing we agree on - you must be a physicist - no idea about
engineering.


As for your moon thing - it's line of site again!! Try communicating
from London to New York at 10GHz.


Idiot.


K.

 

[Wim Lewis]

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

ELF can be inefficient because the wavelength is so large that it's hard
to build an efficient antenna for it. On the transmitting side, this
means that only a small amount of the current sloshing around in the
antenna gets coupled out into free-space radiation; as a result you need
higher currents in the antenna to get the same radiated output, and that
means more losses to things like resistive heating.

If you can build an antenna that's appropriately sized for the ELF
wavelength (hundreds or thousands of kilometers) then you can avoid this.
The US used to have a couple of giant ELF antennas in the Midwest; Wikipedia
says they were disassembled earlier this decade. I don't know how submarines
are signaled these days.

Anyway, MW has a shorter wavelength than ELF, so it's easier to build a
good antenna for that band.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency. [....]

The important thing is usually not how many photons can be emitted, but
how much energy can be picked up by the receiver compared to the amount
of noise it's also picking up. The amount of energy per photon really
isn't significant, at least not for radio. The energy of a single photon
is insignificant compared to the power of the Force ... errr ... I mean,
it's tiny compared to the amount of energy you need to be heard over the
background noise.

 

[[email protected]]

On Jul 25, 12:31 pm, "Green Xenon [Radium]" <[email protected]>
wrote:
Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

MW and ELF are forms of electromagnetic radiation in the RF spectrum.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.

Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?

So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?

Radium
There is the modulation method - AM or FM. FM is more efficient - at
least narrowband FM. That's why we use FM for mobile transmitters. You
could use supressed-carrier AM of course but that is a sod to
demodulated.

Nonsense.

FM is common because it is intrinsically immune to impulse noise
and cheap to implement.

It's cheap but not immune to noise and suseptable to multipath big-
time.

I never said supressed carrier wasn't immune to noise.

As for multipath, all modulation methods are susceptable to it. FM has
a slight advantage there with discriminator capture.

Do tell how...It's not in any text book so maybe we can learn with
your advanced knowledge.

See any current amateur radio transceiver. There have been IC's to do
it for decades.

You have never heard of the inverse square law obviously. High
frequencies are line of site only and can go long distances
because you pump out more power. You need to compare apples with
apples.

The inverse square law applies to isotropic radiators. No real world
RF antenna is an isotropic radiator.

Define "high frequencies".

Things don't become line of sight until about 50 Mhz. Most long distance
terrestrial communications is done between about 5 Mhz and 30 Mhz, which
is HF.

The typical amateur radio transceiver puts out 100 W max in the HF
bands.

My log books, and the logs of 100s of thousands of amateur operators
are full of contacts around the globe with far less power than 100 W
in the 1.6 Mhz to 29 Mhz range.

The only thing we agree on - you must be a physicist - no idea about
engineering.

No, I'm a BSEE and an amateur radio operator for 40 years.

Have you ever seen a HF transmitter much less operated one?

As for your moon thing - it's line of site again!! Try communicating
from London to New York at 10GHz.

That's exactly the point. You can't communicate anywhere that isn't
line of sight much over about 100 Mhz no matter how much power you
run unless you use some reflective technique such as tropo scatter.

You know nothing about RF communications.

 

[Michael Black]

Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

MW and ELF are forms of electromagnetic radiation in the RF spectrum.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.

Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?

Sure; for constant photon rates, one transmitter is outputting, say, 1
million watts, and the other is doing 1 watt. But broadcasters don't
pay for photons, they pay for watts.

So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?

Any transmitter can run at any power level, and photons don't matter.
The problem with ELF is that an efficient antenna is enormous, and elf
waves don't bounce off the ionosphere like mw waves do, so most of the
energy cruises right out into space.

Huge elf rigs were/are used for loran-C, WWVB, and communicating with
atomic subs. They use inefficient ground-wave propagation, so need
huge power levels. The loran-C station north of San Francisco is about
100 KHz at some megawatts peak power.

Not really. They use frequencies that will have good penetration, and
which don't suffer much from radio conditions.

Because the frequencies are so low, that ground-wave will be considerable,
while higher frequencies need to bounce off the ionosphere and such to
get the same sort of distance. But that is unreliable, and of course
often is dependent on the time of the day.

Those frequencies are terribly reliable, interference aside.

Once that choice is made, then they have to live with the inefficiencey.
They have decided there is no other choice for their needs, and then
compensate with the high power to overcome the inefficiency of the
antennas.

As an example, there's a broadcast station in Ottawa on 580KHz that
comes in fine during the day. But at night, they are required to
cut back on their power, so the station goes away, not enough power
for ground wave to Montreal, while bouncing off the ionosphere
results in a bounce too far away. They have to cut back their power at
night so the better propagation at night does not leave them with
a booming signal bouncing off the ionosphere to interfere with all
the other stations on that frequency. I'm sure there are plenty of
locations much further away that can receive the station at night,
that can't receive it at night (after all, I can hear plenty of AM
broadcast stations at night from much further away that I could never
hear during the daytime). I did receive the Ottawa station at night
during one period a decade ago, when an emergency situation allowed
them to run full power at night; ground wave reception was fine.

So they run WWVB and such at low frequencies so the reliable ground
wave is used for really long distances (I can receive it fine here
in Montreal, I've had an "atomic clock" for almost five years and
rarely does it not sync up at night). One can argue that their
high power is not just because of the inefficient antennas at 60KHz,
but so it is receivable so far away, just like that Ottawa station
where the ground wave signal disappears when they lower their power.

Michael

 

[[email protected]]

In sci.physics [email protected] wrote:
On Jul 25, 12:31 pm, "Green Xenon [Radium]" <[email protected]>
wrote:
Hi:
I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.
If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?
MW and ELF are forms of electromagnetic radiation in the RF spectrum.
An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.
Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?
So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?
Thanks,
Radium
There is the modulation method - AM or FM. FM is more efficient - at
least narrowband FM. That's why we use FM for mobile transmitters. You
could use supressed-carrier AM of course but that is a sod to
demodulated.
Nonsense.
FM is common because it is intrinsically immune to impulse noise
and cheap to implement.

It's cheap but not immune to noise and suseptable to multipath big-
time.

I never said supressed carrier wasn't immune to noise.

As for multipath, all modulation methods are susceptable to it. FM has
a slight advantage there with discriminator capture.

Do tell how...It's not in any text book so maybe we can learn with
your advanced knowledge.

See any current amateur radio transceiver. There have been IC's to do
it for decades.

You have never heard of the inverse square law obviously. High
frequencies are line of site only and can go long distances
because you pump out more power. You need to compare apples with
apples.

The inverse square law applies to isotropic radiators. No real world
RF antenna is an isotropic radiator.

Define "high frequencies".

Things don't become line of sight until about 50 Mhz. Most long distance
terrestrial communications is done between about 5 Mhz and 30 Mhz, which
is HF.

The typical amateur radio transceiver puts out 100 W max in the HF
bands.

My log books, and the logs of 100s of thousands of amateur operators
are full of contacts around the globe with far less power than 100 W
in the 1.6 Mhz to 29 Mhz range.

No problem there.

No, I'm a BSEE and an amateur radio operator for 40 years.

Have you ever seen a HF transmitter much less operated one?


That's exactly the point. You can't communicate anywhere that isn't
line of sight much over about 100 Mhz no matter how much power you
run unless you use some reflective technique such as tropo scatter.

You know nothing about RF communications.

Amateurs are the worst kind! There is not way to demodulate double
side-band supressed carrier (esp at low SNRs).
The only way (for analogue that is) is to recover the carrier and this
cannot be done since the carrier aint there in the first place!

Try locking a PLL into supressed carrier. So you are talking complete
rubbish.

Here is the basic euqation

m.cos(wmt)cos(wct) where wm and wc are the modulating and carrier
frequencies and m is the amplitude. Actually what you are probably
thinking of is where a BFO is multiplied into this. However this is
not stable and not phase-locked to the carrier either.It needs
constant adjustment though its a lot better than it was because of DDS
and stable crystals that we didn't have a long time back. If you try
and limit the signal to recover the carrier then it will work at high
SNRs but not at low SNRs.

K.

 

[Michael Black]

On Jul 26, 11:05 am, [email protected] wrote:
In sci.physics [email protected] wrote:
On Jul 25, 12:31 pm, "Green Xenon [Radium]" <[email protected]>
wrote:
Hi:

I remember reading somewhere than ELF [Extremely Low Frequency] radio
transmission is inefficient because it requires to much power.

If that is the case, wouldn't MW [Medium Wave] radio transmission
require even more power?

MW and ELF are forms of electromagnetic radiation in the RF spectrum.

An photon [or electromagnetic wave] of a higher-frequency has more
energy than a photon of a lower-frequency.

Let's say there are there are two radio transmitters, one emits 2 GHz
waves while the other emits 2 kHz waves. If the two radio transmitters
use the same modulation scheme [AM/FM, etc.] and emit the same amount
of photons-per-second-per-square-meter, the 2 GHz transmitter will be
using more watts than the 2 kHz transmitter -- because a 2 GHz photon
requires more power to generate than a 2 kHZ photon. Right?

So how would transmitting a lower-frequency radio wave require more
power than transmitting a higher-frequency radio wave?

Radium
There is the modulation method - AM or FM. FM is more efficient - at
least narrowband FM. That's why we use FM for mobile transmitters. You
could use supressed-carrier AM of course but that is a sod to
demodulated.

FM is common because it is intrinsically immune to impulse noise
and cheap to implement.

It's cheap but not immune to noise and suseptable to multipath big-
time.

I never said supressed carrier wasn't immune to noise.

As for multipath, all modulation methods are susceptable to it. FM has
a slight advantage there with discriminator capture.

Supressed carrier is trivial to demodulate these days but more
expensive to do.

Do tell how...It's not in any text book so maybe we can learn with
your advanced knowledge.

See any current amateur radio transceiver. There have been IC's to do
it for decades.

The higher the frequency the shorter the distance it can travel for a
given power. Therefore VLF can travel round the world and back again!

Most long distance terrestrial communication is done on HF.

You have never heard of the inverse square law obviously. High
frequencies are line of site only and can go long distances
because you pump out more power. You need to compare apples with
apples.

The inverse square law applies to isotropic radiators. No real world
RF antenna is an isotropic radiator.

Define "high frequencies".

Things don't become line of sight until about 50 Mhz. Most long distance
terrestrial communications is done between about 5 Mhz and 30 Mhz, which
is HF.

The typical amateur radio transceiver puts out 100 W max in the HF
bands.

My log books, and the logs of 100s of thousands of amateur operators
are full of contacts around the globe with far less power than 100 W
in the 1.6 Mhz to 29 Mhz range.

No problem there.

No, I'm a BSEE and an amateur radio operator for 40 years.

Have you ever seen a HF transmitter much less operated one?


That's exactly the point. You can't communicate anywhere that isn't
line of sight much over about 100 Mhz no matter how much power you
run unless you use some reflective technique such as tropo scatter.

You know nothing about RF communications.

Amateurs are the worst kind! There is not way to demodulate double
side-band supressed carrier (esp at low SNRs).
The only way (for analogue that is) is to recover the carrier and this
cannot be done since the carrier aint there in the first place!

Well there's a garbling, since it's far more common to see SSBsc, ie
Single Sideband with suppressed carrier. Either someone started with
a more complicated example for the sake of it, or it's suddenly
been reinforced to support a false notion.

A single sideband, and before going on this tangent the talk was of
ELF so if any voice modulation is going to go on down there it's going
to be SSBsc, is really easy to demodulate. Beat a signal against it,
and the sideband translates down to audio. No problem with mistuning,
you simply live with an odd sounding signal, a little retuning will
fix that.

Note that even if you started with a DSBsc signal, there are plenty
of SSB receivers out there perfectly capable of stripping off the unwanted
sideband and then the rest of the receiver treats it like it was an SSB
signal. Indeed, the only difference is that you wasted the power
used for the extra sideband. Sometimes that's fine, since it makes
the transmitter simpler.

But even if the discussion truly was DSBsc, demodulation is easy, and
has been well described for 50 years.

You don't look for the highly suppressed carrier, you get the information
about where to place the locally placed carrier at the receiver by
looking at the sidebands. Simple detectors of thirty years ago would
take the IF signal in the receiver, and double it in frequency, giving
a constant frequency, and divide it down by two to get the needed
frequency and it's right there in the middle, derived from the sidebands.

More complicated methods use a dual channel arrangement, with the VCO
locked to the outputs of the product detectors. Webb described a
practical circuit in CQ magazine about 1957 or 58, and while it used
a lot of tubes, it wasn't excessive. With solid state devices, it's
far easier.

A lot of portable shortwave receivers made in the past thirty years use
a synchronous detector, just what we are talking about, that work
just like that 1957 circuit.

Michael

 

[[email protected]]

In sci.physics [email protected] wrote:

Amateurs are the worst kind! There is not way to demodulate double
side-band supressed carrier (esp at low SNRs).

Nonsense but irrelevant as virtually no one uses double side band
supressed carrier and it has nothing whatsoever to do with the previous
discussion.

Double side band was played with about 40 years ago and essentially
abandoned as ssb is more efficient both in bandwidth and power.

Most all supressed carrier is done single side band.

Vestigial sideband is used extensively as in analog TV broadcast.

<snip babbling nonsense>

 

[[email protected]]

WWVB and Loran-C use low frequencies for phase stability. Ionosphere
bounce has bad fading and erratic prop delay; ground wave is very
lossy but is much more amplitude and phase stable. Both are being
killed by GPS.

Not quite; the decommisioning of the Loran system has been indefinetly
delayed and the implementation of a new generation Loran system as
a backup for GPS is under study.

1000 watts is enough for SSB communications halfway around the world.
You can't do that with a megawatt of ELF.

Much less than 100 W is enough for SSB communications halfway around
the world.

And depending on the state of the sun, 1 W is often more than enough.