Thursday, December 10, 2020

4-Element Yagi for 40 MHz (8-metres) by YU7EF

Thanks to Dragan, 9A6W for sending on this YU7EF design for a 4-element Yagi antenna for the new 40 MHz (8-metre) band.

The design with dimensions is shown below.

The calculated gain in free space is about 6.2dBd and has a front to back ratio in excess of 20dB.

This is a version of the same antenna but with tapered elements...

The antenna is designed for the Industrial, Scientific & Medical (ISM) band from 40.660 MHz to 40.700 MHz and the VSWR is very flat over a 300 kHz span.

With 15mm elements, it's likely that the VSWR 1:1.5 bandwidth is well over 1 MHz.

The forward gain is very level at just over 8.0dBi over a 300 kHz span.

The polar diagram shows a -3dB beamwidth of about 60 degrees. The -6dB beamwidth is in the region of 85 degrees.

The front to back ratio is in excess of 20 dB at the design frequency.

The antenna feed is a simple dipole with a RF choke in the feed line. 

The example above shows the coax passing through three ferrite cores which will prevent RF from flowing on the outside of the feed cable.

If this antenna is mounted horizontally and well above ground level then it should offer good performance for the 40 MHz (8-metre) band. 

More details about YU7EF Yagi antennas can be found here...

For more information about the 40 MHz band, you can find more information here...

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