analyzer seeing near field effects- clarification

[jferg977]

Comrades,
what I was wondering was whether an analyzer would help me locate and
tune an antenna on my boat.  I was hoping to find out whether it would
"see" the capacitance and other effects of several of the large metal
structures above deck. I was hoping that I would be able to move the
antenna around, maybe tip it a bit, adjust its ground connections and
try a lot of things and have some hint of progress show up on the
analyzer. I was hoping I would be able to see whether grounding these
other structures was worthwhile or indifferent.  I am not likely to
have to deal with strong adjacent signals nor other structures.  All
"near-fiield" effects will be caused by a large radar arch (aluminum),
an aluminum jib crane (dinghy lift) and the other antennas.  As always,
I'm astonished at the knowledge available on this reflector and am
appreciative of the help I'm getting.

John Ferguson
M/V Arcadian
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[Mark J. Schreiner]

Thanks for the clarification, John.  So I think the analyzer would best
help you determine the impedance match which may be affected by those
various affects and proximities that you refer to.  It won't tell you
what your radiation pattern will be.  Certainly coupling to nearby
metalic objects can detune an antenna (and change radiation patterns)
and so the adjustment of its location to minimize those affects would be
something you could see with such an analyzer, w.r.t. impedance and
SWR.   You might best if possible find a location to mount the antenna
that has minimal affect from nearby conductors.  Presumably minimal
affect may also result in less distortion of the desired radiation
pattern as well.   However, in some cases the spacing of a vertical
antenna a given distance from a metalic object (mast, wall, etc) can
give possibly desired directional characterists as well, always
something to consider.

Mark, NK8Q
K2 4786

[hidden email] wrote:

> Comrades,
> what I was wondering was whether an analyzer would help me locate and
> tune an antenna on my boat.  I was hoping to find out whether it would
> "see" the capacitance and other effects of several of the large metal
> structures above deck. I was hoping that I would be able to move the
> antenna around, maybe tip it a bit, adjust its ground connections and
> try a lot of things and have some hint of progress show up on the
> analyzer. I was hoping I would be able to see whether grounding these
> other structures was worthwhile or indifferent.  I am not likely to
> have to deal with strong adjacent signals nor other structures.  All
> "near-fiield" effects will be caused by a large radar arch (aluminum),
> an aluminum jib crane (dinghy lift) and the other antennas.  As
> always, I'm astonished at the knowledge available on this reflector
> and am appreciative of the help I'm getting.
>
> John Ferguson
> M/V Arcadian
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

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[Rob KK4R]

John,

Another post explained that the analyzer would give you an idea of how your
antenna is affected with respect to SWR and impedance.  If you are
concerned primarily with how your antenna is "getting out", I suggest a
field strength meter.  A simple one will do the job, but you will probably
need a friend to help you make the best use of it.

As an example of how you might use a field strength meter, consider
anchoring or tying up your boat away from other boats or buildings.  Your
friend could be 50 or 100 yards away on another boat or on the dock,
equipped with the meter and a HT.  After you get a baseline measurement,
you can move or adjust the antenna, then transmit and let your friend tell
you how the change affected the field strength.  Of course, given a single
orientation of your boat relative to the measurement point, you will only
have knowledge of the pattern in one direction.  It would be better if you
could get measurements from multiple angles.

With some good help and a few measurements you should be able to figure out
a good configuration for your antenna, and you will have some idea of the
directivity.

Rob
KK4R

At 06:23 PM 8/3/2005, [hidden email] wrote:

>Comrades,
>what I was wondering was whether an analyzer would help me locate and tune
>an antenna on my boat.  I was hoping to find out whether it would "see"
>the capacitance and other effects of several of the large metal structures
>above deck. I was hoping that I would be able to move the antenna around,
>maybe tip it a bit, adjust its ground connections and try a lot of things
>and have some hint of progress show up on the analyzer. I was hoping I
>would be able to see whether grounding these other structures was
>worthwhile or indifferent.  I am not likely to have to deal with strong
>adjacent signals nor other structures.  All "near-fiield" effects will be
>caused by a large radar arch (aluminum), an aluminum jib crane (dinghy
>lift) and the other antennas.  As always, I'm astonished at the knowledge
>available on this reflector and am appreciative of the help I'm getting.
>
>John Ferguson
>M/V Arcadian
>_______________________________________________
>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.):
>http://mailman.qth.net/mailman/listinfo/elecraft
>
>Help: http://mailman.qth.net/subscribers.htm
>Elecraft web page: http://www.elecraft.com

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