# Antenna Engineering Question

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#### Tim-B

##### Member
If I want to make my own antenna for a handheld to recieve VHF frequencies and I want to make it half wave but coil the antenna so it is shorter then is there a formula for what pitch and diameter the coils need to be to work best with a given frequency or does it not really matter?

#### prcguy

##### Member
There are formulas but at VHF there will still be a lot of experimenting to get the coil and whip lengths working together. The placement of the coil along the whip also makes a noticeable difference in the coil specs. Here is a link to a loading coil calculator for 1/4 antennas as an example: https://m0ukd.com/calculators/loaded-quarter-wave-antenna-inductance-calculator/

Even at HF frequencies where the calculator is intended to be used, there will still be a lot of tinkering with the coil windings to get the antenna to resonate where you want.

A 1/2 wavelength end fed antenna like your whip idea is a very high impedance antenna and you first need a circuit to match the roughly 3,000 ohm impedance of the 1/2 wave whip to your 50 ohm radio, which is not easy. Then you want to shorten the half wave antenna with a coil, which will reduce its efficiency and probably not make it worth using a half wave at that point.

Its much easier to just use a full size 1/4 wave whip, which is around 15 to 20 inches long depending on what part of the VHF band you want. Shortening a 1/2 wave antenna to a similar length will not work any better than a 1/4 wave whip of the same length due to all the efficiency problems you introduce with the coil and a shorter antenna. A full length half wave antenna with a proper 3,000 ohm to 50 ohm matching network will work noticeably better than a full length 1/4 wave if done right, but its going to be at least 3ft long.
prcguy

#### Tim-B

##### Member
Okay thanks, I may just stick with a straight whip antenna. Does the diameter of the antenna make any difference? Will a thick wire work better than a thin wire since resistance is inversely proportional to the cross sectional area of the conductor or does that not really matter much with antennas?

#### prcguy

##### Member
A thicker antenna will have more band width. For example, a 1/4 wave whip made of thin piano wire might have an acceptable match over a few MHz at VHF but a 1" diameter tube might work over 20MHz of BW or more.
prcguy

Okay thanks, I may just stick with a straight whip antenna. Does the diameter of the antenna make any difference? Will a thick wire work better than a thin wire since resistance is inversely proportional to the cross sectional area of the conductor or does that not really matter much with antennas?

#### lmrtek

##### Active Member
all you need is an 18 inch whip

you can add a wire counterpoise which will give you excellent performance

also you can easily make a 1/2 wave "sleeve dipole" and it will also work very well

18 inch radiator over a 18 inch sleeve

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