Best location for a GPS antenna...?
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
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@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.JPGhttp://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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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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and follow the instructions there.
Hi
The simple / stupid approach to the feed lines:
Put up the tower away from all structures
Put the antennas up on the tower.
Ground the tower well.
Run the feed lines down the tower
Ground the feeds both at the antenna and at the base of the tower
Put in a good arrestor at the base of the tower
Run the feed lines underground to where ever you are going to need them
Put in a separate ground at the outside wall of the destination
Bond all the lines to that ground
Protect the lines again with good arrestors
Run them off to where ever you need to use them
Plan on checking / replacing the removable cartridges in the arrestors a few
times a year.
Yes that's a lot. Fires are no fun.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Michael Baker
Sent: Wednesday, April 11, 2012 8:50 AM
To: time-nuts@febo.com
Subject: [time-nuts] Best location for a GPS antenna...?
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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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and follow the instructions there.
On Wed, Apr 11, 2012 at 5:50 AM, Michael Baker mpb45@clanbaker.org wrote:
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.
I always preface my antenna comments with "unless you live in
Florida..." I think the way to use fiber is to place the t-bolt
inside a weathertight box mounted to the antenna mast and then run the
PPS, 10MHz and re-232 out on fiber cables.
Also you don't really need to have the GPS above the trees. Maybe you
can find a compromise locations such that the GPS is NOT the tallest
target in the area.
I was looking to use fiber for something like this too. I found the
best parts to use were those designed for consumer audio s/pdif like
you might have on a home theater recover or flat screen TV. The jacks
are wired up directly to logic level and you can buy the fiber cable
at Best Buy (or cheaper at monoprice.com)
Chris Albertson
Redondo Beach, California
On Wed, Apr 11, 2012 at 7:19 AM, Bob Bownes bownes@gmail.com wrote:
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
I thought of that right after I suggested using fiber data lines.
You'd loose a few expensive t-bolts. But I think there is a better
and cheaper way to go: Buy a cheap Motorola Oncore receiver. The
Oncore UT costs all of about $18 on eBay, buy four of them. The
only signal you need to bring into the workroom from an Oncore is PPS
and that is "way easy" to do using fiber. The other signals (rs232)
can be connected as needed and that is not often. Then you build a
"standard" GSPDO in the workshop. The initial cost is lower and the
engineering is simple (because only the PPS has to go over fiber)
The Oncore and GPSDO can give as good of result as the t-bolt. It
mostly depends on how good the OCXO is, maybe even you build two
GPSDOs running off the same PPS the second one being Rubinium based.
My $35 Rb can holdover for many weeks (at the level I need) if GPS is
down.
Then you can install the t-bolt with an antenna you can disconnect and
only use the t-bolt now and then during good wearer to double check
the GPSDO that you can leave running 24x7
Chris Albertson
Redondo Beach, California
Don't forget to tighten the fiber connectors and correct for the length of
the fiber or you'll be off by 60ns! ;)
On Wed, Apr 11, 2012 at 1:17 PM, Chris Albertson
albertson.chris@gmail.comwrote:
On Wed, Apr 11, 2012 at 7:19 AM, Bob Bownes bownes@gmail.com wrote:
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
I thought of that right after I suggested using fiber data lines.
You'd loose a few expensive t-bolts. But I think there is a better
and cheaper way to go: Buy a cheap Motorola Oncore receiver. The
Oncore UT costs all of about $18 on eBay, buy four of them. The
only signal you need to bring into the workroom from an Oncore is PPS
and that is "way easy" to do using fiber. The other signals (rs232)
can be connected as needed and that is not often. Then you build a
"standard" GSPDO in the workshop. The initial cost is lower and the
engineering is simple (because only the PPS has to go over fiber)
The Oncore and GPSDO can give as good of result as the t-bolt. It
mostly depends on how good the OCXO is, maybe even you build two
GPSDOs running off the same PPS the second one being Rubinium based.
My $35 Rb can holdover for many weeks (at the level I need) if GPS is
down.
Then you can install the t-bolt with an antenna you can disconnect and
only use the t-bolt now and then during good wearer to double check
the GPSDO that you can leave running 24x7
Chris Albertson
Redondo Beach, California
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On Wed, Apr 11, 2012 at 10:19:40AM -0400, Bob Bownes wrote:
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.
By the way, would it be possible to retransmit the GPS signal to isolate it?
I mean, rx external antenna -> preamp -> tx directional internal antenna -> big
air gap -> rx directional internal antenna -> receiver.
The preamp would not be so power hungry as the full thunderbolt and maybe
it could be powered via a magnetic link (or a little solar panel with a
lamp illuminating it).
Best regards,
Andrea Baldoni
I suspect that would make the multipath problem even worse.
On Wed, Apr 11, 2012 at 4:06 PM, Andrea Baldoni erm1eaae7@ermione.comwrote:
On Wed, Apr 11, 2012 at 10:19:40AM -0400, Bob Bownes wrote:
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.
By the way, would it be possible to retransmit the GPS signal to isolate
it?
I mean, rx external antenna -> preamp -> tx directional internal antenna
-> big
air gap -> rx directional internal antenna -> receiver.
The preamp would not be so power hungry as the full thunderbolt and maybe
it could be powered via a magnetic link (or a little solar panel with a
lamp illuminating it).
Best regards,
Andrea Baldoni
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On Wed, 11 Apr 2012 22:06:06 +0200
"Andrea Baldoni" erm1eaae7@ermione.com wrote:
On Wed, Apr 11, 2012 at 10:19:40AM -0400, Bob Bownes wrote:
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.
By the way, would it be possible to retransmit the GPS signal to isolate it?
I mean, rx external antenna -> preamp -> tx directional internal antenna -> big
air gap -> rx directional internal antenna -> receiver.
The preamp would not be so power hungry as the full thunderbolt and maybe
it could be powered via a magnetic link (or a little solar panel with a
lamp illuminating it).
Yes it would be. What you basically would need is to have a LNA,
a bandpass filter and something that converts the voltage into
light with very little noise. I think it would be easiest to down
mix it first to 100MHz or so, then modulate a laser diode. In the
house you'd have to mix it up to 1.5GHz again, of course.
I have no clue whether that is feasible from the noise this whole
circuitry will add or whether it would add so much noise that the
receiver would have no chance...
Attila Kinali
--
Why does it take years to find the answers to
the questions one should have asked long ago?