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- Thread starter AJorge1219
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Not sure why they’d appear confusing except for the black finish….

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Thanks!

Ha, then I re-read the initial post…the longer is VHF, the shorter is UHF.

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Thank you so much for the information and easy explanation!

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"148 mhz is 16 inches" I think you have a typo there as that is too short for a simple whip.

According to that a 1 meter long antenna would be for 2953 MHz. That is not correct.For antennas simple whips like this (not for rubber ducts and not for antennas with a loading coil), use the formula 2953/L where L, the length is in meters to find the *approximate* frequency in MHz

The common way to calculate a straight 1/4 wave antenna (or one half of a dipole) at a known frequency is:

L=2808/F

L = electrical 1/4 wavelength in inches (not the free space 1/4 wavelength based on the speed of light in a vacuum)

F = frequency in MHz

It also works with the other way around by swapping L and F to figure the unknown frequency of a known length 1/4 wave antenna.

F= 2808/L

If you need feet instead of inches then use 234 (2808/12)

If you need meters instead of inches then use 71.32 (2808/39.37)

VHF quarter wave on the left and UHF quarter wave on the right.Looking for some help - one of these is "VHF" and one is "UHF". Any idea which is which?

Extra bonus points for an explanation, but not necessary Thanks in advance!

View attachment 148999

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Oops! I meant for my formula for the length to be in inches and in a hurry (I should not have posted then (Note: I am not correcting for different materials nor antenna thickness, which is why I said it is approximate--good enough for the purpose.) My 2953 comes fromAccording to that a 1 meter long antenna would be for 2953 MHz. That is not correct.

The common way to calculate a straight 1/4 wave antenna (or one half of a dipole) at a known frequency is:

L=2808/F

L = electrical 1/4 wavelength in inches (not the free space 1/4 wavelength based on the speed of light in a vacuum)

F = frequency in MHz

It also works with the other way around by swapping L and F to figure the unknown frequency of a known length 1/4 wave antenna.

F= 2808/L

If you need feet instead of inches then use 234 (2808/12)

If you need meters instead of inches then use 71.32 (2808/39.37)

(3x10^8 [cm/s]/ (f [MHz]*10^6))/4)*39.37 [inches/meter]=L [inches]. I used 146 MHz. ND5Y's formula is the commonly used one and gives a little bit different [5%] answer. I remember once knowing where this difference comes from.

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CORRECTION: Length above should be in inches (not meters). This formula ignores the material composition and diameter and is only approximate. ND5Y gives the different formula that is commonly used that gives a little different answer--likely it is due to the material of the antenna.

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It uses a velocity factor of approximately 95% which approximates the speed of RF on the surface of wire or very small diameter (tiny fraction of the wavelength) antenna radiating elements.ND5Y's formula is the commonly used one and gives a little bit different [5%] answer. I remember once knowing where this difference comes from.

The other formula assumes the speed of light in a free space vacuum rounded to 300,000,000 meters per second.

STI-CO's ROOF-FT-NITI-M 136 – 1000 MHz flexible Nitinol whip and base for roof mount antenna.

www.tessco.com

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Yes, I new that 299,792.458 m/s exactly due to recent re-definition of the meter). Your explanation is the one I hinted at. But not knowing the material of diameter of the wire I go with the other formula for approximating. And using the other formula to space elements (in air) would be more of an error--something do without realizing it. The speed of light (radio waves) in air is closer to that in free space than that of RF in the surface of a conductor. Of course, either formula puts us close enough for estimated whip lengths etc. which have probably been cut only approximately for the intended frequency if trimmed at all.It uses a velocity factor of approximately 95% which approximates the speed of RF on the surface of wire or very small diameter (tiny fraction of the wavelength) antenna radiating elements.

The other formula assumes the speed of light rounded to 300,000,000 meters per second in a free space vacuum.

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