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

[Dale J. Robertson]

It seems to me (and I would be more than happy to hear any differing 
opinions) that your GPS antenna only needs to be high enough to be able 
to see a reasonable slice of sky. i.e. if your workshop were in the 
middle of a circular clearing 80 feet in diameter in a forest with an 80 
foot tree canopy, 40 feet of elevation gives you a 90 degree slice of 
sky. It makes no sense (again, to me) to elevate your antenna in order 
to make your choke ring antenna effective against horizontal multipath. 
Below the canopy there would be no horizontal multipath to deal with. 
Consider your forest as a 'poor mans choke ring antenna upgrade'
As far as fiber isolation of the GPS RF, I have seen many commercial 
installations like that, and judging by the cost and complexity of the 
equipment used, I would say that solution is pretty non-trivial. Fiber 
isolation of the thunderbolt reference clock output and serial control 
would be far easier. You might even be able to rig up rudimentary solar 
power  for the remote portion of the system. That would effectively 
eliminate any ground path for lightning.
My 2 cents
Dale Robertson
NV8U

On 4/11/2012 8:50 AM, Michael Baker 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
>
> 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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