RadioBanter - Is AM Radio Harmful?

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There is still no commercially-available equipment for the 902 MHz amateur
band that I am aware of.

Using commercially-available equipment is cheating anyway. What does it
take to modify PCS cellular phone firmware for digital communication on
902? Is it just a matter of firmware or isn't the RF section able to tune
that far out of band?

Think of it this way. When you have an FM broadcast antenna and transmitter, it
makes quite a difference when switching within the same band from 88 Mhz to 100
Mhz. (only 12 Mhz)

Now you want to take something from around 850 Mhz to 902 Mhz (52 Mhz
difference)

Plus the higher up you go, the more critical the circuitry. Even in the 440
band you are already dealing with microsurgery when using the miniature surface
mount components.

Besides, working with microwaves is never a good idea. Might as well just take
up smoking cigarettes instead.

I would play with mercury and use lead paint in my home no problem, but I would
not ever build a transmitter and use microwave frequencies.

Go to http://tx.mb21.co.uk/gallery/ and look at some of their AM/MW
sites. Not only do many of them still use those cool T-shaped
horizontal wire antennas, but in some shots you can see sheep grazing in
the fields very close by. The RF foes in the USA should consult with
veterinarians in the UK and see what their research comes up with

GTT

Truth wrote:
Yes, but researchers can also sift through 80 years of public health
records. The people who have, or had, leukemia are known. It shouldn't be
hard to find out who lived near a radio transmitter and for how long. It
might be interesting to ask veterinarians about animal leukemia, since many
transmitters are located in rural areas.

(snip)

"Truth" wrote in message ...
On the other hand, the FM signal is radiated from an antenna atop the
tower. Stand at the base of a 300' FM tower, and you're 300' from the
thing that radiates.

This is the same theory in which people claim using their cell phones are
safe,
because the power they put out is so low.

They are powerful enough to transmit to cell towers miles away!

and that proves? ... nothing

Now put that
power inches from your head and how more concentrated is that power?

why not look it up?

you will find that a 5 watt transmitter operating on 450 MHz with a 1/4 wave
antenna might produce enough heating to damage the cornea of the eye IF the
tip is placed within one CM of the eye.

In rec.radio.shortwave Truth wrote:
I don't doubt that high levels of RF can be dangerous. The first two chief
engineers I worked with both died of cancer in their 50s.

Wouldn't FM broadcast antennas be an even greater concern? The height of
most adults would make them resonant somewhere near, or in, the FM broadcast
band.

Comparing wavelengths of "people" based on their height is ridiculous.
Microwaves are a much shorter wavelength and cause much more damage to the human
body, so the wavelength of people based on their height theory needs to be
thrown out right away.

To oversimplify a bit: Low frequencies (like AM broadcast) pass through
the body without being absorbed. Microwave frequencies bounce off the body
without being absorbed. It's the frequency range between 30 and 300 MHz
where maximum absorption takes place.

Art H.

And the government exposure limits are more stringent at the FM
frequencies (30 to 300 MHz).

Every government has different limits, rules and laws. So this is MEANINGLESS!

As if moving to a different country somehow makes the exposure more or less safe
than being in another country.

Never go by government information.

One road along side homes in my area is 55 mph, while another road with no homes
or buildings on it is 25 mph.

What does that prove? That the government is made up of bozos and idiots.

What if the government issues a statement that smoking cigarettes is good for you
and gets rid of cholesterol? Would you start smoking?

"Bob Haberkost" wrote
Huh? AM stations essentially always have vertical radiators,
especially in Europe where there are so many high powered
stations. In general, AMs don't work very well otherwise.

H-Pol radiators have little to no ground wave.

H-pol would not be used on VHF and above (FM/TV broadcast etc) if that was
true. A linear, horizontal dipole antenna at MW or any other band generates
its maximum field strength at all angles perpendicular to its longitudinal
centerline -- which includes all angles from below the antenna out to the
radio horizon; i.e., a "ground" wave. [Free-space radiation with respect to
the dipole itself is the same whether its axis is horizontal or vertical.]

The reason h-pol is not used for MW is because path losses are much higher
for h-pol than v-pol in that part of the radio spectrum.

This is why a vertical radiator is sometimes called a "ground plane"
antenna, snip for those installations on the ground, this counterpoise
is usually buried.

The radial ground system used with MW broadcast antennas reduces antenna
system losses (I^2R), and keeps maximum radiation directed more toward the
the horizontal plane, rather than at some elevation angle above the
horizontal. The FCC defines the minimum efficiency of radiators licensed
for MW broadcast in terms of producing a field strength of so many mV/m at 1
km from the antenna, per kW of antenna input power. These efficiencies
cannot be met without using a good ground system.

Those familiar with 11-meter Citizens Band know this antenna
in its 27MHz form, snip the reason why this particular configuration has
these radials at a 45-degree angle from the horizontal is because a ground
plane
antenna has an intrinsic impedance of about 30 ohms....the farther towards
being
vertical, the more it's like a dipole, with a dipole's characteristic 72
ohm
impedance. Thus, at 45 degrees or so, the ground planes typically used
for C-Band
are about 50 ohms without the need for a matching network.)

Possibly more important is the point that drooping the radials also tends to
lower the angle of maximum radiation, which can improve field strength for
receiving antenna sites at/near ground level.

The nice thing about the low radiating impedance of a vertical radiator is
that the
high base current necessary for a given power means that the magnetic
vector is
bigger than the electrostatic vector, and since ferrite loops used in most
AM radios
respond to the magnetic vector, the "connection" is more intimate.

?? The table below shows the efficiencies for MW vertical radiators with a
good ground system. The self-impedance of a 90 degree vertical is about 50
ohms, and for a 180 degree vertical it is over 100 ohms. So for the same
input power, base current is lower in a 180 degree radiator than in a 90
degree radiator. Yet the efficiency of the 180 degree radiator is higher --
the opposite of the above quote statement.

The ground wave field strength of a MW vertical radiator per kilowatt of
input power is related only to the current distribution in the radiator, not
its base impedance. Whatever the base impedance is, it can be matched to 50
ohm line at the tower base, using the right network. But the network doesn't
affect the relative field radiation pattern of that radiator.

AM Radiator Efficiencies, 1kW input
(for equal distances)

Twr Hgt, Deg Effic
70 182mV/m
90 190
100 195
180 237
190 246
225 274

Note here that "efficiency" is the FCC definition for MW broadcast.
Efficiency falls for short radiators because the ohmic loss even in the best
ground system becomes a bigger percentage of the resistive term of the
radiators base impedance.

RF

Visit http://rfry.org for FM broadcast RF system papers.

"Truth" wrote in message ...
There is still no commercially-available equipment for the 902 MHz
amateur
band that I am aware of.

Using commercially-available equipment is cheating anyway. What does it
take to modify PCS cellular phone firmware for digital communication on
902? Is it just a matter of firmware or isn't the RF section able to
tune
that far out of band?

Think of it this way. When you have an FM broadcast antenna and
transmitter, it
makes quite a difference when switching within the same band from 88 Mhz
to 100
Mhz. (only 12 Mhz)

Now you want to take something from around 850 Mhz to 902 Mhz (52 Mhz
difference)

yes but 88 to 100 = 12 percent of final freq

850 to 902 is only 5.765 per cent

Plus the higher up you go, the more critical the circuitry. Even in
the 440
band you are already dealing with microsurgery when using the miniature
surface
mount components.

Besides, working with microwaves is never a good idea. Might as well
just take
up smoking cigarettes instead.

I would play with mercury and use lead paint in my home no problem, but I
would
not ever build a transmitter and use microwave frequencies.

"Truth" wrote in message ...
There is still no commercially-available equipment for the 902 MHz
amateur
band that I am aware of.

Using commercially-available equipment is cheating anyway. What does it
take to modify PCS cellular phone firmware for digital communication on
902? Is it just a matter of firmware or isn't the RF section able to
tune
that far out of band?

Think of it this way. When you have an FM broadcast antenna and
transmitter, it
makes quite a difference when switching within the same band from 88 Mhz
to 100
Mhz. (only 12 Mhz)

Now you want to take something from around 850 Mhz to 902 Mhz (52 Mhz
difference)

Plus the higher up you go, the more critical the circuitry. Even in
the 440
band you are already dealing with microsurgery when using the miniature
surface
mount components.

pretty might the same for all hand held electronics these days

Besides, working with microwaves is never a good idea.

everyone has to have a hobby... 900 MHz are NOT microwaves (we call it
microwave in brroadcast, but it is a slang term for high UHF)

Might as well just take
up smoking cigarettes instead.

I would play with mercury and use lead paint in my home no problem, but I
would
not ever build a transmitter and use microwave frequencies.

gunplexers are friendly... bi-directional line-of-sight audio