[Lf] Little and Large antennas]

[Andre' Kesteloot]

vernall wrote:

> g3kev wrote:
> >
> > Avoid large antennas if possible because to date I have blown the front
> > ends of two TS850'S, one TS50 and one FT890. The static collected and
> > discharged by large vertical antennas must be seen to be believed. The
> > normal precautions like gas discharge devices do not always work. I have
> > seen the sparks jump some inches across from the antenna to the nearest
> > ground/earth. Maybe an auto spark plug suitably adjusted would be
> > better.
>
> Many commercial stations use a "static drain" in the form of a large
> value RF choke, from the base of the antenna to ground.  Of course, the
> choke has to be a high impedance at the band of transmission, with no
> self-resonances, etc.  If there is a direct lightning strike then it is
> goodbye choke, and probably more, but for other times an RF choke drains
> off incidental static.
>
> Experience in New Zealand is that receiving off a large antenna can
> invite local QRM from near fields, making received S/(QRM+QRN+N) worse
> than using a smaller antenna such as an active whip.  Usually the
> receiver noise figure is not the limiting condition, and a small
> receiving antenna can perform very well.
>
> If a big antenna is used for receive, an external 20 dB attenuator could
> save a blow up inside a TS-850 or equivalent receiver, and still not
> miss a QSO in terms of system sensitivity?
>
> Bob ZL2CA