The VHF Monopole Transmitting Aerial Radiation Pattern

Monopole Aerials operate against ground, they are unbalanced and so need no Balun. Unlike the Centre Fed Half Wave Dipole, they usually feed in at the base which can be handy! These aerials are used for Low Power FM Broadcasting and Mobile PMR. The Quarter Wave Vertical Groundplane Monopole Aerial is a Gift for the mobile operator, usually requiring just a 70cm steel whip into a magnetic roof mount base. a good 50-ohm match is assured! The pictures show what you can expect from your FM Broadcasting Transmitter when used with an End Fed Transmitting Aerial.

The Antenna types described are all Omni-Directional vertical end fed types. This means they transmit a signal throughout a horizontal 360 degree arc. However, we want the signal out in all directions, but parallel to the ground. Upward radiation to the sky is wasted transmitter power! With a perfect high performance antenna, we are looking for zero angle radiation level (the take off angle) and a zero angle of vertical spread as the radio wave propagates from the transmitting antenna. In practice this is impossible, but good results are possible and high gain omni-directional antenna's do have low and narrow angle of radiation.

A High Gain Aerial needs good height to realise it's full potential!