Calculating GSM Wavelength in Salt Water

[Robert Wade]

Can someone please verify or correct the following calculations?

900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =
23.8cm wavelength of 900MHz in sea water.

Thanks,

Rober Wade

 

[John S]

On 10/12/2014 6:23 AM, Robert Wade wrote:

Can someone please verify or correct the following calculations?

900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =
23.8cm wavelength of 900MHz in sea water.

Thanks,

Rober Wade

Specific gravity plays no direct role.

The velocity of propagation in seawater is about 1/9 that of free space,
so your number should be 33.3cm/9 or about 3.7cm.

 

[John S]

On 10/12/2014 6:23 AM, Robert Wade wrote:

Can someone please verify or correct the following calculations?

900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =
23.8cm wavelength of 900MHz in sea water.

Thanks,

Rober Wade

You might find this pdf article useful:

<http://tinyurl.com/n7yyoyy>

 

[Jan Panteltje]

On a sunny day (Sun, 12 Oct 2014 22:23:10 +1100) it happened Robert Wade
<rwade@santos.com> wrote in <took3adqj0l86l26mp1nrgsmp8el6u405v@4ax.com>:

Can someone please verify or correct the following calculations?

900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =
23.8cm wavelength of 900MHz in sea water.

Thanks,

Rober Wade

Personally I would no expect 900 MHz RF to work in (conductive) seawater.
But I have not tried my cellphone underwater yest for other reasons .

 

[RobertMacy]

On Sun, 12 Oct 2014 05:42:16 -0700, Jan Panteltje <panteltje@yahoo.com>
wrote:

On a sunny day (Sun, 12 Oct 2014 22:23:10 +1100) it happened Robert Wade
rwade@santos.com> wrote in <took3adqj0l86l26mp1nrgsmp8el6u405v@4ax.com>:


Can someone please verify or correct the following calculations?

900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =
23.8cm wavelength of 900MHz in sea water.

Thanks,

Rober Wade

Personally I would no expect 900 MHz RF to work in (conductive) seawater.
But I have not tried my cellphone underwater yest for other reasons .

depending on saltiness the skindepth into sea water is in the range of
60 mils to 0.2 inches

However, the 'mechanical' energy of launching 900 MHz...you'd get a lot of
attenuation compared to 1-10MHz used in ultrasonic scans.

 

[RobertMacy]

On Sun, 12 Oct 2014 04:23:10 -0700, Robert Wade <rwade@santos.com> wrote:

Can someone please verify or correct the following calculations?

900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =
23.8cm wavelength of 900MHz in sea water.

Thanks,

Rober Wade

electrical wavelength in free space is around 33.3cm

conductivity of sewater is somewhere beteen 10-100S/m 40? which places the
skin depth at around 3 cm, which is so lossy, the term 'wavelength' no
longer has much meaning.

However if you're looking at the mechanical energy, do a search in
ultrasonice basice, they use 1-10MHz You'll get a lot of attenuation at
900MHz, but not so much attenuation that the meaning of wavelength is
still there. From memory, resolution at 2MHz is around 50mils?, or 0.1 to
0.2 inches ?? so 450 times better is a lot better! But do that search, it
will show you how the wavelength of mechanical energy is calculated.
relates to elasticity and mass/volume is that specific gravity?

plus everything I've seen is related to sqrt() of something else in this
stuff.

apologies for vagueness, but been a while, and haven't looked at this
stuff in a loooong time.

 

[Jeff Liebermann]

On Sun, 12 Oct 2014 22:23:10 +1100, Robert Wade <rwade@santos.com>
wrote:

Can someone please verify or correct the following calculations?
900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =
23.8cm wavelength of 900MHz in sea water.

Bad question. The wavelength (or frequency) of the RF signal does not
change when you submerge the cell phone under water. If it did, your
cell phone would change frequency/channel/wavelength when submerged
and would not be able to communicate.

What does happen is that the velocity of propagation is slowed down by
the dielectric properties of the medium (water). This causes delays
in transmission lines to increase and antenna lengths to shorten. Free
space wavelength (as measured in a vacuum) shortens to become
electrical wavelength (as measured in your salt water medium).

Velocity_Factor = 1 / e^-0.5
VF is expressed as a percentage of the speed-o-light.
e = dielectric constant or relative permittivity.

The dielectric constant of water varies with temperature and
frequency. At 1 GHz and 25C, my guess(tm) is about 60.

VF = 1 / 60^-0.5 = 0.13
Electrical_wavelength = Free_space_wavelength * VF
Electrical_wavelength = 33.3 cm * 0.13 = 4.3 cm

Google for "electromagnetic aquametry" or "microwave aquametry" if you
want to dig deeper.

Also, GSM, the cellular modulation protocol, has no effect on the
velocity of propagation or wavelength and does not change in any
manner by immersion in salt water.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Robert Wade]

On Sun, 12 Oct 2014 08:59:10 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Sun, 12 Oct 2014 22:23:10 +1100, Robert Wade <rwade@santos.com
wrote:

Can someone please verify or correct the following calculations?
900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =
23.8cm wavelength of 900MHz in sea water.


What does happen is that the velocity of propagation is slowed down by
the dielectric properties of the medium (water). This causes delays
in transmission lines to increase and antenna lengths to shorten. Free
space wavelength (as measured in a vacuum) shortens to become
electrical wavelength (as measured in your salt water medium).

Velocity_Factor = 1 / e^-0.5
VF is expressed as a percentage of the speed-o-light.
e = dielectric constant or relative permittivity.

The dielectric constant of water varies with temperature and
frequency. At 1 GHz and 25C, my guess(tm) is about 60.

VF = 1 / 60^-0.5 = 0.13
Electrical_wavelength = Free_space_wavelength * VF
Electrical_wavelength = 33.3 cm * 0.13 = 4.3 cm

Thank you for your concise explanation.

If I understand correctly then, a structure measuring 4.3cm within a
water-filled vessel would be resonated by a 900MHz signal.

What would happen if the vessel itself was a 4.3cm diameter sphere?

The dielectric constant of sea water is around 80. In my OP I confused
this with specific gravity, and the 1.4 figure was incorrect anyway.
It should be around 1.02.

Robert Wade

 

[RobertMacy]

On Sun, 12 Oct 2014 18:43:09 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

...excessive snip...

The same thing will happen to your cavity. In fresh or distilled
water, the system is a good low loss dielectric and will work just
like a cavity resonator, but resonate at a lower frequency. With
polluted or salt water, the dielectric will start to dissipate energy
and render your resonator rather useless.

Thanks for the tutorial AND the URLs!

 

[Jeff Liebermann]

On Mon, 13 Oct 2014 10:07:04 +1100, Robert Wade <rwade@santos.com>
wrote:

On Sun, 12 Oct 2014 08:59:10 -0700, Jeff Liebermann <jeffl@cruzio.com
wrote:

On Sun, 12 Oct 2014 22:23:10 +1100, Robert Wade <rwade@santos.com
wrote:

Can someone please verify or correct the following calculations?
900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =
23.8cm wavelength of 900MHz in sea water.


What does happen is that the velocity of propagation is slowed down by
the dielectric properties of the medium (water). This causes delays
in transmission lines to increase and antenna lengths to shorten. Free
space wavelength (as measured in a vacuum) shortens to become
electrical wavelength (as measured in your salt water medium).

Velocity_Factor = 1 / e^-0.5
VF is expressed as a percentage of the speed-o-light.
e = dielectric constant or relative permittivity.

The dielectric constant of water varies with temperature and
frequency. At 1 GHz and 25C, my guess(tm) is about 60.

VF = 1 / 60^-0.5 = 0.13
Electrical_wavelength = Free_space_wavelength * VF
Electrical_wavelength = 33.3 cm * 0.13 = 4.3 cm

If I understand correctly then, a structure measuring 4.3cm within a
water-filled vessel would be resonated by a 900MHz signal.

Correct. However, the losses created by the very lossy water
dielectric would result in a resonator Q that is so low as to be
useless. In effect, all the energy in the resonant structure would
end up being dissipated by the water. This is one reason why
underwater RF communications has such limited range and really only
works at very low frequencies (used for submarine communications).

>What would happen if the vessel itself was a 4.3cm diameter sphere?

The same thing. The "vessel", which I assume means either a boat or
bottle is in itself a structure, which can be resonant. Please note
that 33.3 cm would be a full wave resonant cavity, which is not
particularly useful. Multiples of 1/4 wavelength tend to be more
common.

It would be helpful if you would kindly disclose what you are trying
to accomplish, and what you have to work with. Your questions are far
too simplistic to supply a specific answer.

The dielectric constant of sea water is around 80. In my OP I confused
this with specific gravity, and the 1.4 figure was incorrect anyway.
It should be around 1.02.

The difference in dielectric constant between fresh water and sea
water isn't that different. Sea water is about 81, while fresh is
about 80. Both vary with temperature and frequency, although not
exactly at the same rate. What is radically different is the
conductivity. Sea water is about 5 Siemens/meter, while fresh water
is about 0.001 S/m. Also see the loss tangent and dissipation factor
(and note the frequency at which they're specified).
<http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm>
<http://www.microwaves101.com/encyclopedias/951-coax-loss-due-to-dielectric-conduction>

A resonant cavity is build very much like a coax cable. One of the
demonstrations I give at the local radio club meetings is what happens
when you fill a length of coaxial cable with water. I cheat a little
and clean out the inside of a length of Heliax (all copper) before the
test. I then fill it with distilled water. The impedance goes down
to about 30 ohms(?), but with proper matching, the loss is about the
same as it would be with an air filled length of Heliax. I then drop
a "pinch" of salt into the coax cable. The losses climb dramatically.
Given enough power, I could probably boil the salt water.

The same thing will happen to your cavity. In fresh or distilled
water, the system is a good low loss dielectric and will work just
like a cavity resonator, but resonate at a lower frequency. With
polluted or salt water, the dielectric will start to dissipate energy
and render your resonator rather useless.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jasen Betts]

On 2014-10-12, Robert Wade <rwade@santos.com> wrote:

Can someone please verify or correct the following calculations?

900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =

closer to 33.2cm

the specifiy gravity of sea water is about 1.04, but you want the
refractive index. which is the square root of the dielectric constant,

> 23.8cm wavelength of 900MHz in sea water.

probably something like that.


--
umop apisdn

 

[Robert Wade]

On Sun, 12 Oct 2014 18:43:09 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

Correct. However, the losses created by the very lossy water
dielectric would result in a resonator Q that is so low as to be
useless. In effect, all the energy in the resonant structure would
end up being dissipated by the water. This is one reason why
underwater RF communications has such limited range and really only
works at very low frequencies (used for submarine communications).

What would happen if the vessel itself was a 4.3cm diameter sphere?

The same thing. The "vessel", which I assume means either a boat or
bottle is in itself a structure, which can be resonant. Please note
that 33.3 cm would be a full wave resonant cavity, which is not
particularly useful. Multiples of 1/4 wavelength tend to be more
common.

The same thing will happen to your cavity. In fresh or distilled
water, the system is a good low loss dielectric and will work just
like a cavity resonator, but resonate at a lower frequency. With
polluted or salt water, the dielectric will start to dissipate energy
and render your resonator rather useless.

Thank you. I will save your replies for future reference.

Just wondering. My Dad expresses concerns about holding a cell phone
next to his head. Does the same resonant wavelength principle you
described apply to human brain tissue as well? He can't afford to
loose any more ;-)

Robert Wade

 

[Robert Wade]

On 13 Oct 2014 07:04:47 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

Can someone please verify or correct the following calculations?

900MHz = 33.3cm. Divide by 1.4 (specific gravity of sea water) =

closer to 33.2cm

the specifiy gravity of sea water is about 1.04, but you want the
refractive index. which is the square root of the dielectric constant,

23.8cm wavelength of 900MHz in sea water.

probably something like that.

Now I am a little confused. How does this relate to what Jeff is
saying?

Is the wavelength then actually 23.8cm as I originally posted, based
upon a refractive index of salt water of 1.4.

Sorry, I confused this with specific gravity in my OP. Possibly
leading some people astray.

So what is the _dominant_ determining factor of resonant wavelength
for a 900MHz signal when passing through a container of salt water ...
dielectric constant, conductivity or refractive index?

Robert Wade

 

[Michael A. Terrell]

Robert Wade wrote:

Thank you. I will save your replies for future reference.

Just wondering. My Dad expresses concerns about holding a cell phone
next to his head. Does the same resonant wavelength principle you
described apply to human brain tissue as well? He can't afford to
loose any more ;-)

How loose are his brains?


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

 

[Jeff Liebermann]

On Mon, 13 Oct 2014 19:52:46 +1100, Robert Wade <rwade@santos.com>
wrote:

Just wondering. My Dad expresses concerns about holding a cell phone
next to his head. Does the same resonant wavelength principle you
described apply to human brain tissue as well? He can't afford to
loose any more ;-)

Robert Wade

Here's my take on cell phone RF causing brain and CNS cancers.
<http://802.11junk.com/jeffl/crud/Cellular and cancer.pdf>

A better graph:
<http://802.11junk.com/jeffl/crud/brain-CNS-cancer.jpg>
Looks like I need to update the graph. Maybe later. If you want to
grind your own graphs, start here:
<http://seer.cancer.gov>

Note that the incidence rate of new cases of brain and CNS cancers is
nearly flat over the 1975 to 2011 range of the data. During this
time, cell phone usage increased dramatically starting in about 1995.
If there was any causal connection between cell phone use and brain
cancer, it would have appeared as a rise in the incidence rate.
Instead, it has gone down slightly (caused by improved early
diagnostics using positron emission tomography).

Also note that the rubbish about growing young minds being more
susceptible to RF isn't true:
<http://802.11junk.com/jeffl/crud/brain-CNS-cancer-by-age-1992-2006.jpg>
Most of the new brain cancer cases appear among seniors. Cell phone
use by seniors is far less than that of teenagers. Again, if there
was a causal relationship, I would expect to see far more cases among
the younger, high cell phone use, populations. The bad news is that
as a senior, your fathers risk of getting cancer increases with age,
which requires no alleged assistance from cell phones.

I hope this helps.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Tim Williams]

"Robert Wade" <rwade@santos.com> wrote in message
news:rq4n3apjao9ouogqrjh3h2fn09uoam6027@4ax.com...

So what is the _dominant_ determining factor of resonant wavelength
for a 900MHz signal when passing through a container of salt water ...
dielectric constant, conductivity or refractive index?

Yes.

....Dielectric constant can be expressed in complex form, where the
imaginary part represents loss (conductivity).

Ideally -- actually, not even ideally, but by definition from theory: n ~=
sqrt(e_r). BUT, this is e_r at a given frequency, and in general it
varies, even for well behaved materials.

Probably the best behaved examples are materials like polyethylene and
teflon, which are simple chemically, and low loss. But even these exhibit
atomic and molecular resonances in the IR band.

Water contains anything from rotational resonance in the GHz (I think it's
36GHz, for vapor; of course, it's not going to be exactly the same in
liquid form, but still something), to rotational and translational
resonances between THz and near IR. Throughout the range, the dielectric
constant is changing, from ~80 near DC, to, I think it drops off in the
10s of kHz or maybe it's MHz, due to molecular diffusion phenomena. All
the while being somewhat conductive, or if doped with ions, fairly
conductive. Which will act to increase |e_r|, but also significantly
decrease the transmission length characteristic.

So, figuring out what's going on at any arbitrary frequency isn't very
obvious (one of those wonderfully enigmatic aspects of water's physics and
chemistry). You might measure it yourself, or find data from someone else
who did...

(And by the way, if you consider the complex permittivity of metals,
you'll end up with a tranmission length or depth that's oddly similar to
the skin depth of that material. Not at all a coincidence, of course!)

Tim

--
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com

 

[Robert Wade]

On Mon, 13 Oct 2014 08:41:20 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

Note that the incidence rate of new cases of brain and CNS cancers is
nearly flat over the 1975 to 2011 range of the data. During this
time, cell phone usage increased dramatically starting in about 1995.
If there was any causal connection between cell phone use and brain
cancer, it would have appeared as a rise in the incidence rate.
Instead, it has gone down slightly (caused by improved early
diagnostics using positron emission tomography).

As with all "science" the outcome depends partly on who funds the
studies and what methodology is used. There is evidence on both sides,
which only encourages selective reporting depending on which side of
the debate you want to support.

http://www.telegraph.co.uk/health/8606104/Mobile-phones-cause-five-fold-increase-in-brain-cancer-risk.html

Everyone asserts the other side's research is "flawed". There is also
alot of outdated industry propaganda floating around. Like reps who
claim there is no evidence of biological effects.

One might ask why manufacturers now advise in their literature to hold
the cell phone a few cm's away from the head. Better reception?

The best we can say is that the extent of the problem or the precise
mechanisms involved are not well enough understood.

Excerpt from the linked article:

People who started using mobiles as teenagers, and have done so for at
least 10 years, were 4.9 times more likely to develop astrocytoma,
compared to controls.

Worringly, the comparable figure for cordless home phones - which are
very similar to mobiles in terms of radiation emission - was almost as
high, at 3.9.

Looking at the whole group, regardless of age of first ise of mobile
or cordless phone, they found that usage for more than 10 years
increased the risk of all malignant tumours by 30 per cent, and
astrocytomas in particular by 40 per cent.

Robert Wade

 

[miso]

RobertMacy wrote:

plus everything I've seen is related to sqrt() of something else in this
stuff.

I did some sonobouy. They use a 6db/octave boost, but I have no idea if that
was to compensate the sea water or the hydrophone.

 

[Jeff Liebermann]

On Tue, 14 Oct 2014 09:07:27 +1100, Robert Wade <rwade@santos.com>
wrote:

http://www.telegraph.co.uk/health/8606104/Mobile-phones-cause-five-fold-increase-in-brain-cancer-risk.html
Everyone asserts the other side's research is "flawed".

Everyone lies, but that's ok because nobody pays attention.

One might ask why manufacturers now advise in their literature to hold
the cell phone a few cm's away from the head. Better reception?

If a brain cancer victim arrives with their attorney and claims that
the cell phone manufacturer is responsible for their brain cancer
because they failed to provide suitable warnings, the manufacturer can
claim that the user failed to follow the recommendations in the
manual.

The best we can say is that the extent of the problem or the precise
mechanisms involved are not well enough understood.

You can say that about literally any technology, science, disease, or
phenomenon. Complete understanding is almost impossible and research
continues. Just look at all the areas of research that have not been
fully beaten to death. Here's a partial list:
<http://en.wikipedia.org/wiki/List_of_Ig_Nobel_Prize_winners>

People who started using mobiles as teenagers, and have done so for at
least 10 years, were 4.9 times more likely to develop astrocytoma,
compared to controls.

Sure. Presumably before ubiquitous cell phones, people didn't get
brain cancer. The big rise in cell phone use started in the early
1990's. Please show me where that increase appears in the statistics:
<http://802.11junk.com/jeffl/crud/brain-CNS-cancer.jpg>
4.9 times the pre-cell phone rate of about 7.0 cases per 100,000,
would be about 35 cases per 100,000. Show me that increase in the
general population here:
<http://seer.cancer.gov>

Worringly, the comparable figure for cordless home phones - which are
very similar to mobiles in terms of radiation emission - was almost as
high, at 3.9.

The typical cordless phone handset transmits at about a 5 milliwatt
average power level. The typical cell phone can run up to about 250
milliwatts, but usually operates at a much lower level in strong
signal areas to conserve battery power. I'm not 100.0% certain of
these numbers and can dig out more accurate numbers if you want.

Looking at the whole group, regardless of age of first ise of mobile
or cordless phone, they found that usage for more than 10 years
increased the risk of all malignant tumours by 30 per cent, and
astrocytomas in particular by 40 per cent.

That probably correct if you don't consider the age of the cell phone
user. See graph at:
<http://802.11junk.com/jeffl/crud/brain-CNS-cancer-by-age-1992-2006.jpg>
and notice the drastic increase in incidence with increasing age. For
example, if I selected a population of 40 to 50 year olds, which have
a brain cancer incidence rate of 6.0 per 100,000, and compared it with
a group of 50 to 60 year olds, 10 years later, then the incidence rate
would increase to 11.0 per 100,000 or almost double the initial rate.
What interesting is that it will almost double even if there is no
cell phone exposure involved. I'm surprised that they only were able
to show an increase of 30-40%. By carefully cherry picking the ages,
I can probably produce an 80% increase, without ever involving a cell
phone.

Actually, RF exposure does cause physiological effects. When I first
got into 2way radio and mobile phones, I had a full head of hair, a
steady hand, a positive attitude, and a full bank account. After
about 45 years of continuous exposure to various forms of RF, the hair
is almost gone, the hand is somewhat shaky, the attitude is
depressing, and the bank account is depleted. Obviously, all these
symptoms were caused by RF exposure. Correlation is not causation.
<http://www.latimes.com/business/hiltzik/la-fi-mh-see-correlation-is-not-causation-20140512-column.html>
<http://www.tylervigen.com>

I almost forgot the traditional ending tag line:
More research is necessary. Send funding.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Robert Wade]

On Mon, 13 Oct 2014 17:10:55 -0700, miso <miso@sushi.com> wrote:

RobertMacy wrote:


plus everything I've seen is related to sqrt() of something else in this
stuff.


I did some sonobouy. They use a 6db/octave boost, but I have no idea if that
was to compensate the sea water or the hydrophone.

Or to keep the dolphins from humping it.

Robert Wade