RadioBanter - View Single Post

December 23rd 03, 03:07 AM

On 22 Dec 2003 17:17:02 -0800, (Art Unwin KB9MZ)
wrote:

Richard,
At the moment I am interested in Richards comment that the
tines that he has SEEN commercially were pock marked because
of flashovers. Hearing that encourages me that my choice of
doing the same thing was a good one where I was persueing
the hope that it will reduce local noise and static crashes.
I am not a long time user of the top band but it doesn't
take a rocket scientist to see that any noise reduction on
receive will help! Maybe at a later date I will try my coax
coil idea, but for now I am useing existing wheels before
thinking about inventing a new wheel.
Ofcourse, any comments on the subject are very welcome in
the event I decide to change my aproach as this is new to
me with regards to prior personal construction.
Have you personally constructed an antenna with a coupling
interface and how did it work out.
By the way the tines are already on my antenna
but it will take time to determine any advantages.
Tho it is a horizontaly polarised antenna I assume there are
vertical components that could be erased BEFORE it gets
to my radio.
You may recall that my antenna is very narrow banded so as
to prevent extranious noise getting to the radio, in that the
signal is filtered before it is amplified and removed by
the radio's filter.This is the phillosophy behind
my design and it is hoped that tines will help here also.
Best regards
Art

Hi Art,

I've worked on many shielding problems, and they are not always
intuitive, nor simple. In fact, the inappropriate "addition" of a
ground is often a cure worse than the original ill. There are also
issues of where to ground when the circuit being shielded has a
floating termination (like the coax example). In one instance the
shield is perfect, in others it is a coupling capacitor. To all
outward appearances, the circuits are identical until you come to the
question of ground.

Here the variables are manifold, but in general (unless experience
demonstrates otherwise) you always ground at the load of a signal.
For two-way communication systems, this presents something of a
paradox (which end is the load? When?). And of course, this has
NOTHING to do with lightening strikes, and everything to do with
Common Mode (which are sometimes one and the same problem).

If you are worried about received noise, the load is the receiver, but
this is not necessarily the lightning protection answer. Putting a
ground at both ends can create nightmares, and it can solve
nightmares. The creation of nightmares often comes in the form of
using the coax shield as the ground common between two points (a
serious risk to the point of death). Such a quick fix, ad hoc
solution may remove noise and yet kill you when you disconnect it for
maintenance. A separate wire conforms to code, keeps you safe, and
generally takes care of the noise and lightning.

73's
Richard Clark, KB7QHC