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February 23rd 05, 02:47 AM

On 22 Feb 2005 06:38:53 -0800, wrote:

I'm tracking a high altitude balloon on 2m via a handheld scanner, and
in the past have used the standard rubber-duck antenna that the scanner
came with. However, reception isn't too great at times. What kind of
gain increase could I expect to see if I were to replace the current
rubber-duck antenna with a quarter-wave antenna (designed for 2m and
70cm)?

Thanks in advance for any insight!
Dave

Hi Dave,

Well, I see you got advice, but unrelated to the problem you offered.

The standard rubber duck and a quarterwave are going to have the same
failings: they both have the same response curve in space. Basically
they both are designed to work with transmitters located at right
angles to them. And if you stand in the conventional upright manner
of a biped, then those antennas are going to be vertical with the
favored direction lying along the horizon.

Now, if your balloon is tracking along the curve of the earth's limb,
some several hundred miles out, then this might work admirably (it
doesn't take all that much power to hear this distance when nothing is
in the way). However, as balloons go, they are generally above you
and your antenna is pointed toward them, or nearly so (certainly more
so than at the horizon). This is NOT a favored direction for
communication and antennas when they are small (and a rubber duck, a
quarterwave, or a halfwave easily meet that dismal prospect).

To obtain overhead coverage for communication (and this presumes that
the balloon antenna is also vertical - which means it will suffer from
the same geometry); then you need an antenna that is at least one
wavelength long, or longer (1¼ wavelength would be a nice way to go).

Long antennas have more sensitivity in the direction along their
length.

Now, if your tracking pastime includes all angles from the horizon to
directly above, then you need to consider designs that are more
isotropic (and none of the suggestions offered by everyone, including
me, come anywhere close).

73's
Richard Clark, KB7QHC

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