Scanner Antenna Lenth Tuning to 1/4 Wavelength Question ?
 

Hello,

Will be purchasing a scanner, and like most scanners these days, has a range
of about 30 MHz to 1.2 GHz.

If I obtain a telescopic antenna for the unit, and wish to stick with just
this antenna realizing it will always be sort of a compromise, the following
question arises:

If I leave the antenna extended to its longest length, will this
"automatically" provide me the best possible
broadband coverage on "all the frequencies (particularly at the low end), or
is this long length negated by the fact that the antenna wouldn't be tuned
to exactly 1/4 wavelength most of the time ?

I guess the question would relate mainly to what happens on the really low
30 - 50 MHz frequencies.

Must the antenna in that range "really" be tuned to exactly a 1/4 wavelenth
to be effective, or you gain so much by
having a quite long length that exact tuning isn't all that necessary ?

Thanks,
Bob

Scanner Antenna Lenth Tuning to 1/4 Wavelength Question ?
 

On Fri, 9 Nov 2007 12:24:09 -0500, "Robert11"
wrote:

If I leave the antenna extended to its longest length, will this
"automatically" provide me the best possible
broadband coverage on "all the frequencies (particularly at the low end), or
is this long length negated by the fact that the antenna wouldn't be tuned
to exactly 1/4 wavelength most of the time ?

Hi Bob,

The longest length will make your scanner deaf at the high
frequencies. This is because the long antenna (longer than 5/8ths of
a wave) wants to turn its focus along the line of the antenna itself,
instead of broadside. This trend gets progressively more focused
along the length as the length grows in relation to the wavelength.
(Or contrariwise, as the wavelength gets smaller for the same size
antenna.) As such, a one antenna for all bands (using just one wire)
is a poor choice.

I guess the question would relate mainly to what happens on the really low
30 - 50 MHz frequencies.

You stand to get good enough reception for antennas that are as short
as a tenth of a wavelength.

Must the antenna in that range "really" be tuned to exactly a 1/4 wavelenth

No.

to be effective, or you gain so much by
having a quite long length that exact tuning isn't all that necessary ?

Use a variety of antennas, notably thick ones, to obtain a frequency
range of up to a couple of octaves. Overlap them to extend the range
further. If the term octave throws you, consider:
30-60
60-120
120-240
240-480
480-960
960-1920
Your scanner covers 5+ octaves. You probably need as few as 3
antennas, probably more.

73's
Richard Clark, KB7QHC

Scanner Antenna Lenth Tuning to 1/4 Wavelength Question ?
 

Robert11 wrote:
Hello,

Will be purchasing a scanner, and like most scanners these days, has a range
of about 30 MHz to 1.2 GHz.
...
Thanks,
Bob



Best scanner antenna I ever found was a discone mounted high, ~40 ft.
above ground.

I was able to pick up much traffic from even surrounding towns and
cities ... not perfect but provided more than was needed.

Regards,
JS

Scanner Antenna Lenth Tuning to 1/4 Wavelength Question ?
 

Best scanner antenna I ever found was a discone mounted high, ~40 ft.
above ground.

I was able to pick up much traffic from even surrounding towns and
cities ... not perfect but provided more than was needed.
=====================
Agree with that . I even use my discone antenna for transmitting on
144 -146 MHz (local repeater + Packet BBS)

Advice : If you live near salt water get a discone anttenna in stainless
steel to prevent corrosion.

Frank GM0CSZ / KN6WH

From OP: Scanner Antenna Lenth Tuning to 1/4 Wavelength Question ?
 

Hi,

Just a quick thanks for explanations.
Appreciate it.

Bob (Sudbury, Mass.)