"Spin" wrote in news:tanvk.364$1a2.205@trnddc04:

I would like to make/experiment with a longwire antenna
specifically for the two meter fm band. Is there an optimum length to
try & still keep an omnidirectional pattern? Also the optimum amount
of radials and will i need a matching unit?




I am guessing that you want vertical polarisation, and omni directional
pattern in the H plane (azimuth).

As an end fed unloaded vertical wire over perfect ground is lengthened
than about 60% of a wavelength, the low angle major lobe splits and
significant power is radiated in higher angle lobes. You probably don't
want that.

So, in the sense that a longwire is an endfire antenna, it is not suited
to your need for a vertically polarised omni antenna for FM operations.

A 5/8 wave ground plane isn't a bad antenna, and about as long as is
useful in a straight radiator. It is an example of a good antenna that is
not resonant, debunking the myth that resonant antennas always work best.
It does not have a 50 ohm feedpoint, and is reactive, so some impedance
matching is needed for 50 ohm line, but it is not difficult.

For higher gain with omni pattern, you should consider a colinear array.
They are very popular, but mostly of commercial manufacture.

Owen