[time-nuts] Best location for a GPS antenna...?

Bob Bownes bownes at gmail.com
Wed Apr 11 14:19:40 UTC 2012


I do like the optical isolation suggestion. While less than optimal,
perhaps the easiest solution is not to put the isolation between the t'bolt
and the antenna, but to put the isolation between the t'bolt and the
distribution amplifier.

For example, locate the antenna as suggested. Locate the t'bolt in a
suitable enclosure/location either at the building entry or even at the
bottom of the tree. Protect it as well as you can, take best practices for
grounding, etc, but expect to loose one every few years. Maybe put one in
the spares collection. Then take the output of the t'bolt, run through
appropriate electrical to fiber conversion, and feed that to the
distribution amplifier. don't use metal jacketed fiber or metal conduit. A
mistake I have seen made, to great expense.

The issue is that this treats the t'bolt as a sacrificial item. I would
contend that, at a cost of $80-90, you could spend far more time and effort
trying to isolate, amplify, correct, and bias the antenna than that is
worth. Effort and gear that would need to be replaced every time it gets
blown up. My admittedly small direct experience is that lightning arrestors
don't protect from near or direct strikes, just from 'close' strikes.

Just $0.02 from a part of the world that doesn't get zorched nearly as
often. :)

Bob
KI2L

On Wed, Apr 11, 2012 at 8:50 AM, Michael Baker <mpb45 at clanbaker.org> wrote:

> Time-Nutters--
>
> My workshop is surrounded by tall trees (70 to 80 ft).  There
> is no easy way to place my T-Bolt antenna above the tree-top
> foliage.   Since choke-ring antennas do not provide much benefit
> for dealing with multi-path that originates from directly above
> the antenna I have considered putting the antenna on a 10-ft
> pole and mounting the pole in the top of the nearby trees so
> as to have the antenna just above the tree-top foliage.
>
> However, here in north-central Florida lightning is a serious
> problem.   In the 12 years we have lived here, 3 trees have
> been hit within 75 meters of my workshop building behind
> my house.
>
> Here is a DropBox link to a map of lightning-strike-days
> in USA locations:
> http://dl.dropbox.com/u/**60102282/Lightning%**20Isokeraunic%20map.JPG<http://dl.dropbox.com/u/60102282/Lightning%20Isokeraunic%20map.JPG>
>
> I have a number of VHF and UHF antennas mounted on my
> workshop building but when not in use, they are kept
> disconnected where they enter the building.
>
> I have thought about finding some way to bring the GPS
> RF signal into my workshop via an optical fiber interface
> and sacrifice the RF to optical fiber interface if lightning
> strikes it in a treetop but have not found a way to implement
> this idea.
>
> Two years ago lightning struck a neighbor's TV antenna
> mounted on a pole attached to the side of his house and
> started a fire in one of their 2nd floor bedrooms which
> did a lot of damage before it was put out.  The tower
> was well grounded and the coax leading into the room
> was fed through a grounded lightning protector but none
> of these precautions prevented the fire from the lightning
> strike.
>
> Any list folks have ideas on this?
>
> Mike Baker  WA4HFR
> Gainesville/Micanopy, Fla
>
>
>
>
>
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