Some good detective work there, Sig!
Ken
R. Sigismonti wrote:
> >The problem is not noise caused by the motor. The noise filter at
> >the motor does a good
> >job, except when the capacitors blow (which has only happened on my
> >10 meter tower).
> >
> >N3RS verified that there is significant noise caused when the ring
> >turns, even when turned manually (take the motor off the tower).
>
> Not only is the noise not caused by the motor, it is even there when
> there is no motor action at all. We have a very aggravated case of
> this noise problem here at N3RS. We have a 3 stack of 20M 5 element
> yagis on TIC rings and a 3 element 40M yagi just 127 feet away. When
> the 40M yagi is pointed at the 20M TIC rings we get a wideband noise
> on 20M that is centered on the harmonic of the 40M signal. The 40M
> station has all sorts of filtering and is not the cause of the noise.
> This has also been verified by K3WU, who lives less than a mile from
> me. He listened to both the fundamental and second harmonic of the
> 40M signal and it is absolutely clean. The second harmonic was very
> weak as well.
>
> Two weeks ago we determined that the noise is not being generated by
> anything on the antennas themselves. This was done by shaking the
> elements while transmitting on 40M. We also checked all RF
> contacts/connections at the same time. We did notice a very strong
> correlation between noise generation and gentle rocking of the TIC
> rings. We believe that we are getting reasonably substantial
> currents in the circuit comprised of the 20M yagi/TIC ring/tower
> system. This is induced current from the 40M near field signal.
> This current is flowing through a rather poorly connected and
> weathered set of surfaces, some of which may be generating the
> harmonics.
>
> Noise is also generated when we transmit on 20M and turn the rings at
> the same time. The assumption here is that there is current induced
> in the rings by the 20M signal itself. This noise can be heard on
> other bands as well.
>
> ASAP we plan to insulate the 20M yagis from the ring assembly,
> thereby reducing the current that is likely to flow through the
> rotating mechanism in the ring. There are several metal-metal
> surfaces that are not in good contact at all times in the assembly
> and some of the galvanized surface on the rings has become quite
> tarnished. We will post any results we get as a result of
> introducing the insulation between the ring cradle and the 20M booms.
>
> 73's de Sig, N3RS
>
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