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The Telecom Digest for July 02, 2011
Volume 30 : Issue 162 : "text" Format
====== 29 years of TELECOM Digest -- Founded August 21, 1981 ====== |
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Date: Thu, 30 Jun 2011 17:07:04 -0500
From: GlowingBlueMist <glowingbluemist@truely.invalid>
To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org.
Subject: Re: NETTALK VOIP SERVICE
Message-ID: <4e0cf392$0$2634$892e0abb@auth.newsreader.octanews.com>
On 6/26/2011 3:19 PM, GlowingBlueMist wrote:
> I along with a friend are considering getting a VOIP service called
> NETTALK. He will use in place of his current Magic Jack, which he has
> several problems with recently. If you are a user of NETTALK, I would
> like to ask a favor of you. Magic Jack blocks calling to many
> locations here in the USA. We are trying to see if NETTALK does the
> same thing. We would like for someone who has NETTALK to call a few
> phone numbers I will send to you and make a few test calls for us.
> Please contact me if you have NETTALK.
>
> Thank you
>
> GEORGE "SKIPPER" THURMAN
>
>
> ***** Moderator's Note *****
>
> If this is a scam, it's a good one: Google didn't turn up any hits on
> various phrases from the above post, so it's not velveeta AFAICT. Of
> course, all the usual caveats apply.
>
> Bill Horne
> Moderator
For what it's worth, I just completed a small list of test calls for
George and with few exceptions the calls were answered.
Some of these test calls were to organizations in small communities that
might not have someone waiting to answer a call all the time like
Historical Society or Chambers of Commerce so I tried similar calls to
the same area code and exchange. The alternate calls were to libraries,
banks, or hospitals. Those numbers did get answered indicating that
calls to the small communities that were being tested did get through
when I use my NetTalk line.
Date: 30 Jun 2011 09:53:02 -0400
From: kludge@panix.com (Scott Dorsey)
To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org.
Subject: Re: Battery power support today
Message-ID: <iuhv3u$3h8$1@panix2.panix.com>
AES <siegman@stanford.edu> wrote:
>In article <BANLkTikg3_jasxgAbPLuJ5WqtABxNZVHKg@mail.gmail.com>,
> Bruce Bergman <brucebergman@gmail.com> wrote:
>
>> You can walk around under an AM Broadcast antenna holding a fluorescent
>> light bulb that's glowing in the RF field, especially at a 50KW Clear
>> Channel blowtorch like KFI.
>
>Could you give your take on how this relates to currently on-going and
>often very fervid debates over the (alleged) health hazards for people
>and especially children caused by the r-f fields from cell towers in
>residential neighborhoods, in church steeples, in close proximity to
>schools, and so on?
Well, the primary argument is, considering that we have had high power AM
broadcast in the US for ninety years now, and a whole lot of people have
worked in very strong RF fields, that if there was going to be a substantial
health risk it would have been noticed almost a century ago.
>Speaking for myself, based on my own technical and physical (though not
>explicitly medical or biological) knowledge, I'm pretty damn sure that
>cell phones simply do not ญญ and in fact physically can not ญญ cause
>brain cancers, no matter how long you hold one against your skull.
The OTHER side argument is that since the wavelengths are so much shorter
than AM wavelengths that the effects are different. In reality, this means
actually less current induced in tissues due to the skin effect. But, there
might be something different.
>But that said, would you yourself want to linger for very long "under an
>AM Broadcast antenna holding a fluorescent light bulb that's glowing in
>the RF field" as you describe above?
I did for about twenty years, working in the broadcast industry. I've had
plenty of offices where the desk lamp flickered brightly with the transmitter
modulation when it was turned off.
>Are there published standards for
>acceptable rf field levels for humans working in close proximity to
>high-power broadcast antennas?
There are now OSHA standards for allowable RF levels. However, they are not
really based on any biological evidence and mostly seem to be random numbers
picked out of a hat. Most of the transmitter sites from a decade ago would
not pass the current OSHA standards.
> What's the field intensity in that
>situation, compared to living next door to a cell tower with 8 or 10 or
>even 20 antennas on it? Do the r-f intensities in your "glowing
>fluorescent" situation approach levels where nonlinear effects, over and
>above just simple heating, may start to appear in human flesh?
You get two main effects, first of all simple heating, and also currents
induced in the flesh. Most of the current is on the surface due to skin
effect; you can get very serious looking electrical burns from careless
tower work, but which turn out to be just surface damage.
>And how does this all relate to cataract formation or visual clouding
>effects associated with eyeball exposure to low-level microwave
>radiation? -- Effects which I take it are well document[ed] to occur,
>leading to stringent standards for microwave oven leakage. Can r-f
>fields down in the few hundred MHz range cause similar visual damage?
The cataract formation is a side-effect of tissue heating. The eyeball
heats up, the cornea gets damaged.
Lower frequency fields can cause these effects but they need to be at
much higher levels in order to get substantial energy into the tissue.
>Do normal telecom or WiFi/WiMax signals in the 1 to 2 Ghz range pose
>threats comparable to a leaky microwave oven.
Probably, which is to say very little.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Date: Thu, 30 Jun 2011 18:36:01 -0500
From: bonomi@host122.r-bonomi.com (Robert Bonomi)
To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org.
Subject: Re: Battery power support today
Message-ID: <9PidnRDXzef8lZDTnZ2dnUVZ_gqdnZ2d@posted.nuvoxcommunications>
In article <siegman-D89C20.12231829062011@bmedcfsc-srv02.tufts.ad.tufts.edu>,
AES <siegman@stanford.edu> wrote:
>In article <BANLkTikg3_jasxgAbPLuJ5WqtABxNZVHKg@mail.gmail.com>,
> Bruce Bergman <brucebergman@gmail.com> wrote:
>
>> You can walk around under an AM Broadcast antenna holding a fluorescent
>> light bulb that's glowing in the RF field, especially at a 50KW Clear
>> Channel blowtorch like KFI.
>
>Could you give your take on how this relates to currently on-going and
>often very fervid debates over the (alleged) health hazards for people
>and especially children caused by the r-f fields from cell towers in
>residential neighborhoods, in church steeples, in close proximity to
>schools, and so on?
The frequencies involved are very far apart, thus the putative mechanisms
involved are radically different.
Anybody worried about _cell_tower_ radiation should be _far_more_worried_
about air traffic control, and weather, radar installations. Those units
produce megawatts of output, and use highly directional antennas,
producing effective signal strengths something like one hundred million
times stronger than the cell tower. This translates to an 'equivalent RF
strength at 10,000 times the distance from the transmitter. In other
words, if you are 50 ft from the cell-tower, a high-power radar installation
roughly 100_miles away will produce the same strength of signal.
Admittedly, it only hits you every 10-30 seconds, while the cell-cite is
more or less a constant.
>Speaking for myself, based on my own technical and physical (though not
>explicitly medical or biological) knowledge, I'm pretty damn sure that
>cell phones simply do not -- and in fact physically can not -- cause
>brain cancers, no matter how long you hold one against your skull.
As far as I know, nobody has identified anything that is 'absolutely
guaranteed' to cause cancer. That is, where 100% of the people exposed
to it contract cancer. Similarly, I don't believe that any identified
'mechanism' whereby a 'carcinogen' triggers cancerous growths exists.
There is 'statistical evidence' that certain things increase ones
'susceptibility' to cancer. For some carcinogens, and particular forms
of cancer, the 'statistical correlation' is high enough that it makes
good sense to avoid those carcinogens. The 'statistical evidence' for
cell-phones is VERY tenuous, to put it charitably.
>I'd also be pretty confident the r-f fields associated with any standard
>telecom or computer devices or installations that you'll encounter in
>everyday life are extremely unlikely (or in fact unable) to cause any
>kind of negative health effects, even after prolonged exposure.
Computers sold for residential use are required to meet "Class B" radiation
emission standards. Those standards are designed to prevent interference
with other electronic devices, but effectively eliminate human health risks
from radiation as well.
THE possible exception is a CRT display. Regardless of whether it is
a computer monitor, a TV set, or 'something else'. the electron gun
spits stuff at high enough velocities, that the impacts on the phosphor
generate various 'high energy' leptons, including X-rays. There's a
-reason- CRTs have a 'leaded glass' faceplate. :)
>But that said, would you yourself want to linger for very long "under an
>AM Broadcast antenna holding a fluorescent light bulb that's glowing in
>the RF field" as you describe above?
It's a non-issue. I've put time in, in a 'transmitter shack' near the
base of a 50KW AM station. Regular building lighting was 'unpowered'.
Only the emergency lighting was connected to the mains (and batteries).
> Are there published standards for
>acceptable rf field levels for humans working in close proximity to
>high-power broadcast antennas?
There undoubtedly are -- I don't know where to find them, however.
I'll note that 'big' transmitting towers -- those 1500-2000' (or more)
tall ones -- are routinely serviced (things like changing the marker
lamps) while all the transmitters are in full operation. The elevator
ride up one of those towers is typically 20-30 minutes. And that long,
again, coming down. You're "somewhat" shielded, by being 'inside' the
skeletal tower, but only "somewhat". <wry grin>
People have been doing this kind of work on live towers for many decades.
> What's the field intensity in that
>situation, compared to living next door to a cell tower with 8 or 10 or
>even 20 antennas on it?
A 'high power' AM broadcast station, in the U.S., will be running no more
than 50,000 watts of RF into an omni-directional antenna. If they're using
a directional antenna assembly, the transmitter power output will be lower.
A broadcast FM radio, or _television_, station often uses a 'gain'
antenna, which 'amplifies' the effective strength of the transmission.
"Effective Radiated Power", after accounting for the 'gain' of the
antenna can be in the multi-megawatt range for TV stations. IIRC, one
network TV station, locally, used to claim an ERP of around 8 megawatts.
Certain stations in Mexico, just across the border, and catering to a U.S.
audience, were known to run much higher output -- 'famous' locations include
just across the border from Del Rio, TX, and Tijuana and Juarez MX.
In comparison, a cell site has an output measured in watts. There are
possibly 64 (56 voice + 6 'control') discrete transmission 'channels'
in use. Absolute "worst case" is a few watts ERP on each channel.
In practice, especially in urban areas, 'typical' transmit power is
a few hundred milliwatts, possibly less -- somewhere around 10 watts ERP
per cell cite. "More" antennas at a single cell site simply means that
the cite can operate at lower _actual transmitter power to get the =same=
"Effective" Radiated Power (ERP).
> Do the r-f intensities in your "glowing
>fluorescent" situation approach levels where nonlinear effects, over and
>above just simple heating, may start to appear in human flesh?
At 'VHF' frequencies, or below, it takes high power levels, at practically
'contact' distances, to be an immediate threat to humans.
'Microwave' heating occurs when the radiated wavelength 'resonates" with
water molecules in the object irradiated. They 'vibrate', and the ensuing
friction generates heat. AM broadcast radio has wavelengths in the 200-500
meter range., FM radio is around 3m, and UHF TV can be a mere .3m wavelength.
None of these are anywhere near short enough to trigger molecular resonances.
>And how does this all relate to cataract formation or visual clouding
>effects associated with eyeball exposure to low-level microwave
>radiation?
Due to the frequency difference, there is virtually no relation to
microwave effects.
> Effects which I take it are well document[ed] to occur,
>leading to stringent standards for microwave oven leakage. Can r-f
>fields down in the few hundred MHz range cause similar visual damage?
>Do normal telecom or WiFi/WiMax signals in the 1 to 2 Ghz range pose
>threats comparable to a leaky microwave oven.
A 'standard' microwave oven generates 700-1000 watts of RF. "compact"
microwaves are generally 500 watts, with a few as low as 350 watts.
WiFi signals are in the tens of _milliwatts_. Call it 1/10,000 to
1/100,000 of the RF level inside a microwave.
Microwave oven safety standards limit leakage to 5milliwatts per cm2 at 5cm
from the outside of the oven.
RF energy levels diminish as the square of the distance from the transmitter.
Assuming a WiFi signal of 50mw (typical units are around 20mw, 'legal limit'
is 100mw), at a distance of 10 cm from the antenna, the energy density is
0.08mw/cm2. At 2cm from the antenna, RF energy approaches the allowable
leakage (measured at 5cm) from a Microwave oven.
To put things in perspective, the signal from a WiFi node is about 1/6 the
"allowable" leakage from a microwave oven. Or around 3x the leakage of
a typical microwave oven in 'good working order'.
Date: Thu, 30 Jun 2011 07:16:46 -0700
From: AES <siegman@stanford.edu>
To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org.
Subject: Re: Trials of 'super WiFi' to begin in Cambridge
Message-ID: <siegman-5AA66D.07164630062011@sciid-srv02.med.tufts.edu>
In article <alpine.GSO.2.00.1106291355250.2523@nyx3.nyx.net>,
John Mayson <john@mayson.us> wrote:
> "Trials of a new breed of 'super WiFi' that uses the white space between
> TV channels are set to begin in Cambridge. Microsoft, the BBC, BSkyB and
> BT are among the tech giants investigating how the gaps in frequencies
> between TV broadcasts can be used to transmit broadband."
If these spectral bands are currently empty of deliberate signals (in
most locations anyway), are they "white space" or "black space"?
[Are "dark fibers" full of "white light"?]
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