How does a handheld walkie talkie transmit without a ground
connection?  In radio antennas, a ground is usually required

Design of antenna depends on the frequency band.

Handheld amd modern devices use high freguencies
http://www.cellular.co.za/gsm-frequencies.htm

and so, have short wavelength.

Longer wavelength require bigger antenna and grounding or distance to
ground becomes more important.

example
http://deepspace.jpl.nasa.gov/dsn/antennas/70m.html
theory
http://cfcp.uchicago.edu/education/explorers/2002summer-YERKES/pdfs-sum02/background.pdf

This is a technical explanation of how Earth acts as mirror, doubling the size
of antenna dipole. For microwave devices this is not needed, as
requred dipole is short.

Hedgie
http://www.bencher.com/pdfs/00361ZZV.pdf

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Request for Answer Clarification by particlem-ga on 15 Feb 2005 10:37 PST

So are you saying that for high frequency HF range transmission, that
a ground connection is not theoretically necessary, but is very likely
practically necessary to successful transmission?  Does this mean that
a radio on an airplane cannot use low frequencies?

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Clarification of Answer by hedgie-ga on 15 Feb 2005 21:45 PST

particlem-ga

  1) Theory and practical use agree that high frequency transmission
needs smaller antenna and less of a ground. The two points were not in
opposition.
   Think of a laser or visible light emission  -- it is a very HF
electro-magnetic wave -- and one does not even think about ground.
 2) Indeed - it  is not practical to send long-wave transmission from an
airplane. I do not say impossible - modern electronics has many tricks but
long wave antenas still tend to look like this:
http://www.wireless.org.uk/gallery/z38.htm

3) It is better (for all) to rate the answer only after all RFCs
(clarifications) were closed. That way you rate  the complete answer.
 Thanks anyway.

Hedgie

AS I recall from my days at the fire department the term you are
refering to is a ground plan.  The larger the ground plan the shorter
the antenna is required to be.  Also as hedgie-ga stated the higher
the frequency the shorter the antenna is required to be.  We had some
low band radios in use in one division 46 megihertz.  This required
the entire vehicle to act as the ground plan and the antennas were
aways attached to the center of a large metel surface.  The same
radios used on vessels made of wood required different antennas with
built in ground plans.  This was acheived by making the antennas
longer by spiro wraping the antenna up a mask making it longer than
had it just went straight up.   A short answer; The higher the
frequency the shorter the antenna.  46 megahertz = about a four foot
antenna with a ground plan.  Without, the antena need about a 15 ft
antenna.  Most modern radios are VHF or UHF 800 megahertz to upto 2.3
gegahertz. requiring minamul antenna even without a ground plan.

The simplest form of aerial is a horizontal dipole (half wave being
the most amenable) -- this does not employ a groundplane. If however
one elects to design vertically using only one arm of the dipole, a
groundplane (or counterpoise) is required to emulate the other arm.
It?s not quite as simple as a straight replacement but that?s the
principle.

As you suggest, low-frequency transmitters don?t work too well on
aircraft but that?s partly a function of the aerial length
requirement. For anything above a few MHz, it?s not problem, bearing
in mind that 30 MHz is only ten metres so a standard half-wave dipole
is only 5 meters (discounting other parameters) and the single arm is
only 2.5 meters. More of a problem is the polarisation because to
receive in all directions, vertical polarisation is demanded. But you
don?t actually have to use a quarter wave arm -- in fact shorter is
better, suitably matched) because the radiation pattern is more
appropriate for high flying aircraft. There are limits though how
short you can go whilst still maintaining acceptable efficiency and
design.

Low(ish) frequency walkie talkies are not particularly efficient
because the impedance matching is somewhat variable due to proximity
effects of the body. The counterpoise in both these and mobile phones
consists in main of the internal chassis and / or conductors. They
won?t work without the ?groundplane? but the very nature of the
circuitry automatically creates this.

Mobile phones incorporate radial radiation helical antennae (to reduce
the length) which can exacerbate the problem because they are
intolerant of mis-match. Quite remarkable that the manufacturers are
able to perform such good optimisation but the counterpoise area
demands are ameliorated by the high frequency.

Don?t worry if you still find aerials a bit of a mystery -- most
engineers do too :-)

Best

Let me keep to the point.  Handheld radios usually have a 1/4
wavelength antenna (which may be "loaded" with a coil of wire so that
the antenna is an "electrical" 1/4 wavelength, even though it is
physically shorter.  A vertical 1/4 wave antenna will radiate more
efficiently when it has a ground plane.  The most efficient ground
plane is a large number of additional 1/4 wave radials, but one radial
will do.  When a 1/4 wave radial is not available, any metallic
surfice will do, like the top of your car.  If no metallic  surface is
available, then any conductor will do, like salt water, or YOU!  The
bottom line:  When using a handheld radio, you can become the rest of
the antenna.  You are inductively coupled to the radio's "ground" by
holding the radio.

And just because the frequencies are high, and wavelengths are short,
doesn't mean that the physics of antennas went out the window.  The
same physics that applies to the 80M ham radio band where a 1/4 wave
antenna is 60 ft. long applies to the aircraft band and microwaves.
And by the way, antennas don't have to be grounded to work, and
neither do the radios.

73's N4SM