In article ,
Marc Heusser d wrote:

Because of an antenna unfriendly neighborhood and limited space I am
considering using a Diamond antenna either with or without radials,
specifically X-50 vs SE-100.
They are the same length, but the SE-100 is a "marine" antenna without
radials. Nominally they both sport the same gain etc.

What are the tradeoffs?
Without radials it would certainly look less conspicious.

In an antenna of this sort, I believe that the primary function
of the radials is to act as a sort of feedline choke... they minimize
any tendency of RF coming up the inside of the feedline shield to flow
back down along the outside of the feedline. Such RF on the feedline
can cause radiation which will disturb the pattern of the antenna to
some extent.

A radial-less version of the antenna has no such choking, and there
might be some RF flow on the feedline as a result. This might cause a
slight reduction in gain in some directions, due to changes in the
antenna pattern.

If there's a *lot* of RF current flow on the outside of the feedline,
it might tend to couple into nearby conductors, and might (in some
installations) be the cause of QRM (e.g. TVI).

Is this likely to present a problem? In most installations I'd tend
to doubt it. If it is, you might be able to correct it by (1)
insulating the antenna from its mast, and (2) adding some sort of
choke to the feedline, just below the antenna feedpoint... either wind
a foot or two of the coax into a coil, or clamp a ferrite or two
around the coax.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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