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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 |
#2
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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 |
#3
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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 |
#4
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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 |
#5
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From OP: Scanner Antenna Lenth Tuning to 1/4 Wavelength Question ?
Hi, Just a quick thanks for explanations. Appreciate it. Bob (Sudbury, Mass.) |
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