Speed of waves
 

"Wimpie" napisal w wiadomosci
...
On 25 mar, 10:17, "Szczepan Bialek" wrote:

I am simple asking if radio people have trouble with the fact that the
speed
of waves are frequeny dependent.
I am interesting with the real radio waves in the real media. Here is an
example: "Pulsars are spinning neutron stars that emit pulses at very
regular
intervals ranging from milliseconds to seconds. Astronomers believe that
the
pulses are emitted simultaneously over a wide range of frequencies.
However,
as observed on Earth, the components of each pulse emitted at higher radio
frequencies arrive before those emitted at lower frequencies. This
dispersion occurs because of the ionised component of the interstellar
medium, which makes the group velocity frequency dependent".

S

Try to find document "Descanso4--Voyager_new.pdf" (very likely the
first result in google). This describes the Voyager communication
system. It is now more the 10 light hours from us (as far as I
know).

As far as I know, they don't equalize to correct for in band
dispersion (due to wave propagation). Maybe other people have better
info on this.

They used the "Ultrastable oscillator".
They measure the ions and electrons density in the interstellar medium. So
the band dispersion is obvious and the only remedy is the "Ultrastable
oscillator".

So AM and FM are quite opposite. It seems to me that FM is not the best for
the long distances.

It seems to me that here is a confirmation of that: ""Because of the low
signal-to-noise ratio, as with amateur-radio practice,
EME signals can generally only be detected using narrow-band receiving
systems. This means that the only aspect of the TV signal that could be
detected is the field scan modulation (AM vision carrier). FM broadcast
signals also feature wide frequency modulation, hence EME reception is
generally not possible. There are no published records of VHF/UHF EME
amateur radio contacts using FM." From:
http://en.wikipedia.org/wiki/TV_and_FM_DX

I do not understand this but guess.

Best regards,

S*

Speed of waves
 

Szczepan Bialek wrote:

I am simple asking if radio people have trouble with the fact that the speed
of waves are frequeny dependent.

No, they are not because the speed of electromagnetic waves is NOT frequeny
dependent, the speed is media dependent, you babbling, ignorant, trolling,
moron.



--
Jim Pennino

Remove .spam.sux to reply.

Speed of waves
 

On Mar 24, 10:42*am, "Szczepan Bialek" wrote:
*"Wimpie" napisal w ...



On 24 mar, 10:53, "Szczepan Bialek" wrote:
"This finding had practical applications for telegraph communications.
For
example, Heaviside actually solved one of the biggest problems affecting
long distance telegraph and telephone communication in 1887 -distortion.

Speed of waves
 

On Mar 25, 5:54*am, Wimpie wrote:
On 25 mar, 10:17, "Szczepan Bialek" wrote:



Uzytkownik "Wimpie" napisal w ...
On 24 mar, 18:42, "Szczepan Bialek" wrote:

"Wimpie" napisal w
...

On 24 mar, 10:53, "Szczepan Bialek" wrote:
"This finding had practical applications for telegraph communications.
For
example, Heaviside actually solved one of the biggest problems
affecting
long distance telegraph and telephone communication in
1887 -distortion.
It
was known that different frequencies travel with different speeds on a
long
cable. For example, the low bass frequencies in a voice signal travel
faster
than the high treble frequencies. When the cable is long enough, the
frequencies smear, and both voice and telegraph signals become garbled
noise. Heaviside used his equations to show that if inductances (i..e.,
a
small coil of wire) were added along the length of the cable, the
distortion
could be reduced."
From:http://www.ieeeghn.org/wiki/index.php/Oliver_Heaviside

" It was known that different frequencies travel with different speeds
on
a
long cable".

Is the same in air and space?
S*

Hello Szczepan,

Search for the effective permittivity of media with free electrons
(plasma). You will see that the effective permittivity changes with
frequency, hence the phase velocity. Don't look strange to find
apparent permittivities below the value for vacuum.

Just ignore DC magnetic field as this complicates that math
significantly.

Hello Wim,

So you confirm that in plasma is the same as in metal.

No

But what with the space. The AM should be better than FM to communicate
with
the Mars.
Is/were FM used for long distances?

As power is limiting factor, a modulation scheme with coherent
detection and digital decoding will give best performance (best Eb/N0
ratio for certain BER) I think. So it is not just a question of AM or
FM/PM, but more how it is processed at the receiver. *Processing power
changed over time, so theoretically the best method may not be used
because of technical limitations.

Were done the proper experiments in the early years of radio?
S*

Best regards,

Wim

I am simple asking if radio people have trouble with the fact that the speed
of waves are frequeny dependent.
I am interesting with the real radio waves in the real media. Here is an
example Pulsars are spinning neutron stars that emit pulses at very regular
intervals ranging from milliseconds to seconds. Astronomers believe that the
pulses are emitted simultaneously over a wide range of frequencies. However,
as observed on Earth, the components of each pulse emitted at higher radio
frequencies arrive before those emitted at lower frequencies. This
dispersion occurs because of the ionised component of the interstellar
medium, which makes the group velocity frequency dependent

S

Try to find document "Descanso4--Voyager_new.pdf" (very likely the
first result in google). This describes the Voyager communication
system. It is now more the 10 light hours from us (as far as I
know).

The DESCANSO web site (http://descanso.jpl.nasa.gov/) has a variety of
reports and books available for online/download/free use that discuss
a lot of this stuff. Pretty much all the missions JPL has done in the
past few decades have a "design and performance" report out there that
describes the radio system and how it works. The monograph series has
a bunch of books on some general aspect (like large antennas or
autonomous radios).

the IPN progress reports (which has had various names over the years)
is more a peer reviewed journal of record for various work in space
communication, and all of it is freely downloadable, too.


As far as I know, they don't equalize to correct for in band
dispersion (due to wave propagation). Maybe other people have better
info on this.


No compensation is made for dispersion.. the bandwidth of the signal
is so narrow compared to the carrier frequency that dispersion in
propagation isn't a factor. The bumps in the group delay
characteristics of the radio components are orders of magnitude
greater. To minimize that, we tend to use designs that keep the
signal in the nominal center of the IF passband.

Where dispersion becomes interesting (and is actually measured) is
when comparing signals at two separated frequencies, e.g. 8.4 GHz and
32 GHz. Or, for a closer to earth example, L1 & L2 for GPS (separated
by a couple hundred MHz at 1500 MHz) allow for compensation for
ionospheric delays.

Speed of waves
 

On 25 mar, 15:52, "Szczepan Bialek" wrote:
*"Wimpie" napisal w ...
On 25 mar, 10:17, "Szczepan Bialek" wrote:





I am simple asking if radio people have trouble with the fact that the
speed
of waves are frequeny dependent.
I am interesting with the real radio waves in the real media. Here is an
example: "Pulsars are spinning neutron stars that emit pulses at very
regular
intervals ranging from milliseconds to seconds. Astronomers believe that
the
pulses are emitted simultaneously over a wide range of frequencies.
However,
as observed on Earth, the components of each pulse emitted at higher radio
frequencies arrive before those emitted at lower frequencies. This
dispersion occurs because of the ionised component of the interstellar
medium, which makes the group velocity frequency dependent".

S
Try to find document "Descanso4--Voyager_new.pdf" (very likely the

first result in google). This describes the Voyager communication
system. It is now more the 10 light hours from us (as far as I
know).

As far as I know, they don't equalize to correct for in band

dispersion (due to wave propagation). Maybe other people have better
info on this.

They used the "Ultrastable oscillator".
They measure the ions and electrons density in the interstellar medium. So
the band dispersion is obvious and the only remedy is the "Ultrastable
oscillator".

Sorry, I don't see the link between "ultrastable oscillator" and
dispersion. Good oscillators in both transmitting and receiving
equipment are required to get the lowest possible Eb/No for your
digital modulation scheme.


So AM and FM are quite opposite. *It seems to me that FM is not the best for
the long distances.

It seems to me that here is a confirmation of that: ""Because of the low
signal-to-noise ratio, as with amateur-radio practice,
EME signals can generally only be detected using narrow-band receiving
systems. This means that the only aspect of the TV signal that could be
detected is the field scan modulation (AM vision carrier). FM broadcast
signals also feature wide frequency modulation, hence EME reception is
generally not possible. There are no published records of VHF/UHF EME
amateur radio contacts using FM." From:http://en.wikipedia.org/wiki/TV_and_FM_DX

I do not understand this but guess.


Low bit rates, result in low required power, so it is true that with
the advent of low bitrate digital schemes, EME is within the reach of
more radio amateurs. As these modes use narrow bandwidth, dispersion
effects are negligible when looking to the demodulation of the
received signal (as far as I know). Even amateurs using satellite
communication with analog voice, don't have to modify their
demodulators.

Wim
PA3DJS

Speed of waves
 

On Mar 25, 7:52*am, "Szczepan Bialek" wrote:
*"Wimpie" napisal w ...
On 25 mar, 10:17, "Szczepan Bialek" wrote:





I am simple asking if radio people have trouble with the fact that the
speed
of waves are frequeny dependent.
I am interesting with the real radio waves in the real media. Here is an
example: "Pulsars are spinning neutron stars that emit pulses at very
regular
intervals ranging from milliseconds to seconds. Astronomers believe that
the
pulses are emitted simultaneously over a wide range of frequencies.
However,
as observed on Earth, the components of each pulse emitted at higher radio
frequencies arrive before those emitted at lower frequencies. This
dispersion occurs because of the ionised component of the interstellar
medium, which makes the group velocity frequency dependent".

S
Try to find document "Descanso4--Voyager_new.pdf" (very likely the

first result in google). This describes the Voyager communication
system. It is now more the 10 light hours from us (as far as I
know).

As far as I know, they don't equalize to correct for in band

dispersion (due to wave propagation). Maybe other people have better
info on this.

They used the "Ultrastable oscillator".
They measure the ions and electrons density in the interstellar medium. So
the band dispersion is obvious and the only remedy is the "Ultrastable
oscillator".

The USO has nothing to do with the dispersion. It's just something
that lets you make the measurement, because you can integrate over
100s of seconds, and know that the signal being transmitted didn't
change (much) during that time, so any changes are due to the
propagation.


So AM and FM are quite opposite. *It seems to me that FM is not the best for
the long distances.

It seems to me that here is a confirmation of that: ""Because of the low
signal-to-noise ratio, as with amateur-radio practice,
EME signals can generally only be detected using narrow-band receiving
systems. This means that the only aspect of the TV signal that could be
detected is the field scan modulation (AM vision carrier). FM broadcast
signals also feature wide frequency modulation, hence EME reception is
generally not possible. There are no published records of VHF/UHF EME
amateur radio contacts using FM." From:http://en.wikipedia.org/wiki/TV_and_FM_DX


I don't know that I'd use a wikipedia article as my primary reference
on this particular topic.

The reason hams don't do EME FM or EME TV is more a matter of link
budgets than propagation characteristics. amateurs are limited in the
maximum output power (e.g. 1500W PEP in the U.S.), and particularly if
they're using amateur antennas (no 300m dish at Arecibo), you don't
have enough radiated power density to send a wideband signal and have
it arrive back at earth with decent SNR. So, hams use narrow band
transmissions and narrow band receivers (so that they get the minimum
noise power in the detection bandwidth). (also, there's a cultural
thing.. the hams that are interested in TV aren't the same hams
interested in moonbounce, so there's not necessarily and motivation to
even try what would be a fairly difficult and expensive stunt)

If you're not limited by amateur budgets or regulatory power limits,
there's no reason you couldn't send FM or TV to the moon and back.
Apollo used FM in their Unified S-band system (granted, one way from
the moon, not a moonbounce). I haven't run the numbers, but maybe if
you had a big enough transmitter, and used something like Arecibo, you
could do moonbounce tv.

We send several MHz bandwidth back from Mars with a 100W transmitter,
a 3 meter dish, and receive it with a 34 meter dish on earth at
greater than 0dB SNR.

A big advantage of AM is that it has simple and cheap transmitters (a
modulated amplifier) and receivers (a diode). If you're spending
billions of dollars to send a probe to Mars, saving (relatively) small
amounts on the radio isn't worth it, especially if you have to spend
large amounts more on solar panels to get the additional DC power
needed.

That said, for short range links in space, FM, FSK, and AM are
considered as viable alternatives, especially where you are looking
for very small, very low mass. The Muses CN rover (which was about
the size of a pack of cards and was going to drive around an
asteroid's surface) was proposed to use a FSK data link, as I recall.
AM for astronaut backup voice comm is also a possibility.

Speed of waves
 

napisa³ w wiadomo¶ci
...
Szczepan Bialek wrote:

I am simple asking if radio people have trouble with the fact that the
speed
of waves are frequency dependent.

No, they are not because the speed of electromagnetic waves is NOT
frequency
dependent, the speed is media dependent,

"In optics, dispersion is the phenomenon in which the phase velocity of a
wave depends on its frequency,["

S*

Speed of waves
 

"Jim Lux" napisal w wiadomosci
...

Where dispersion becomes interesting (and is actually measured) is
when comparing signals at two separated frequencies, e.g. 8.4 GHz and
32 GHz. Or, for a closer to earth example, L1 & L2 for GPS (separated
by a couple hundred MHz at 1500 MHz) allow for compensation for
ionospheric delays.

It is what I was looking for.
Speed of all waves are frequency, amplitude and temperature dependent.
I realize that for radio waves the effects are small. It seems that for
radio amateurs too small.
GPS is extremely precise and there the effects must be measured.
Thanks you very much.

Best Regards,
S*

Speed of waves
 

On 25 mar, 16:46, wrote:
Szczepan Bialek wrote:
I am simple asking if radio people have trouble with the fact that the speed
of waves are frequeny dependent.

No, they are not because the speed of electromagnetic waves is NOT frequeny
dependent, the speed is media dependent, you babbling, ignorant, trolling,
moron.

--
Jim Pennino

Remove .spam.sux to reply.

Hello Jim,

Given a certain medium, both phase and group velocity can be frequency
dependent (example: ionosphere).

DRM uses OFDM to achieve very low baudrate to mitigate the dispersive
behavior of ionospheric propopation. A least 88 subcarriers are in 10
kHz bandwidth.

Wim
PA3DJS
www.tetech.nl

Speed of waves
 

In message , Szczepan Bialek
writes
"This finding had practical applications for telegraph communications. For
example, Heaviside actually solved one of the biggest problems affecting
long distance telegraph and telephone communication in 1887 -distortion. It
was known that different frequencies travel with different speeds on a long
cable. For example, the low bass frequencies in a voice signal travel faster
than the high treble frequencies. When the cable is long enough, the
frequencies smear, and both voice and telegraph signals become garbled
noise. Heaviside used his equations to show that if inductances (i.e., a
small coil of wire) were added along the length of the cable, the distortion
could be reduced." From:
http://www.ieeeghn.org/wiki/index.php/Oliver_Heaviside

" It was known that different frequencies travel with different speeds on a
long cable".

Is the same in air and space?

Yes in air , and no in space.

B
--
Brian Howie