Introduction to Quarter Wave Antennas and SWR Relationship on the FT991A

This video is a collection of learning notes and materials I been collecting from various You Tube Channels and books. The focus is to share with newer HAM’s some of the things I find interesting and to encourage more interests into the various topics by sharing my personal experience.
I have learned and am starting to grasp the world of RF and how things work with a focus on Antennas and Feed Lines. I find this very interesting and with the knowledge on the internet will allow HAM’s to build their own antennas or at least know what to look for when shopping to obtain the best antenna delivery system.

The purpose of the video is to review basic ¼ wave Antenna’s and some of the characteristics of their feed point impedance and how this interacts with the SWR on your FT991A

There are a wide variety of ¼ wave Antenna’s covering 70cm all the way up to 160 meters.

Some of the ground planes antennas for 20 through 160 meters are so large that they require to be mounted on the ground surface and use a base plate with screw holes where you attached physical wires that act as a ground plane.

We also look at the vertical ¼ wave and the horizontal ½ wave Dipole Antenna and see the relationship as to orientation and some common observations I found that were interesting.

The purpose is to show why a relationship between the 50 Ohm impedance of the FT991A radio antenna connection should match as close as possible to a resistive impendence match of the antenna feedline system.

With a good impedance match there will be a minimal reactance (capacitance and inductance) in the feed line system. The result is lowest SWR possible and a very happy transmission feedline and radio.
The antenna Vertical Radiator length is typically ¼ wavelength, there can be cases where the vertical can be 5/8 wave vertical is used and others, the ¼ wavelength is the most common. The ¼ wave is a self-resonant link which makes it a popular choice.

The ¼ wavelength vertical antenna can have up to 3 to 4 Ground Radials, each at a ¼ wavelength mounted at the base of the vertical and are horizontal or sloped down at an angle, depending on the ground radials angle will determine the antenna feed point impendence, these radials act as ground surface to radiate the signal in all directions when the base of the antenna is at or close to ¼ wavelength height or more above the surface of the earth.

The ¼ ground plane antenna for example 20 to 80 meters can also be mounted directly on the ground, use of Ground Wire Radials along the ground typically are buried just below the surface, I have seen many examples where up to 16 wire radials and are common.
The length of the buried ground radial wires is not restricted to the ¼ wavelength length as shown in previous slides on radial at the base of the vertical ¼ wavelength so you can have different lengths of wire radials buried just below the ground surface. A common connection point is a steel plate that also supports the vertical radiator.

The below shows the formula to calculate the length of a ¼ wave ground plane radiator for use on the 2-meter band.
234 ÷ 27.335 MHz = 8.56’
8.56’ x 12” = 102.7”
Links:
Arrow Antennas 2m, 6m, 70cm
https://www.arrowantennas.com/

Hustler Antenna G-2537 DXE Engineering Web Link:
https://www.dxengineering.com/parts/h...

COMTEK COM-20VA DXE Engineering Web Link:
https://www.dxengineering.com/parts/c...

DXE-40VE-1 DXE Engineering Web Link:
https://www.dxengineering.com/parts/d...

DXE-7580FS-VA-1 DXE Engineering Web Link:
https://www.dxengineering.com/parts/d...

DXE-160VA-1 DXE Engineering Web Link:
https://www.dxengineering.com/parts/d...

DXE-VA-PIVOT-3 - DX DXE Engineering Web Link:
https://www.dxengineering.com/parts/d...

DXE-RADP-3 DXE Engineering Web Link:
https://www.dxengineering.com/parts/d...

'73 from KI5JUF