Antenna for 150 up to 200 MHz..........

[Rfboy]

Hi guys,

I need an omnidirectional antenna ( l/4 or 5/8 l )......the problem is that I don't have a ground plain.....

How can it's possible to develop this type of antenna ?????

It's possible with a monopole ??????

Thak you

 

[flatulent]

You can use a vertically oriented dipole. With coax you put half of the dipole to the center conductor and extend it up. You then make the other half of the dipole out of a metal tube and put it over the coax and connect it to the outer conductor at the end where the center conductor is connected to the other half of the dipole.

You then have the problem of input impedance changing over this about 25% fractional bandwidth. You can minimize this problem if you need better impedance uniformity by making the two halves of the dipole be cone shaped with the points connected at the center. The cone can be metal sheets or can be a cage of stiff wires.

 

[divan]

You can search for J-Pole Antenna, this one no need grounding
for example
https://www.n7qvc.com/amateur_radio/copper.html