Best location for a GPS antenna...?
Hi
GPS is pretty close to the noise "as received". A fully passive system with
significant cable loss and low / no gain antennas does not sound like it's
going to do a very good job.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Jim Lux
Sent: Thursday, April 12, 2012 9:52 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] Best location for a GPS antenna...?
On 4/12/12 2:09 AM, Rob Kimberley wrote:
There are commercial "re-radiators" for GPS. I found these on Google:
http://www.gps-repeating.com/?gclid=COTV88D6rq8CFcwTfAodhSKvmQ
http://gpsnetworking.com/GPS-re-radiating-kits.asp
One of my old suppliers in the UK was marketing a range of these, but I
seem
to remember some problem in getting approval in the UK, and they had to
drop
them. Things may have changed as this was a few years ago.
Interestingly I've just been looking into this... Why would you need
anything special to reradiate.. It's not like you need a particular
antenna pattern or constant gain or something. What about something like
a fat monopole against a ground plane, with a attenuator at the feed to
provide a good terminating impedance for the LNA/Line driver.
If it's L1 only, you don't even need particularly wide bandwidth (<1%)
Yes, I've seen setups at JPL where they reradiate with D&M or Ashtech
chokering antennas (or even helibowls), but that might be because we've
got a bunch of them sitting around, so why not use it.
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On Wed, Apr 11, 2012 at 3:08 PM, Bob Camp lists@rtty.us wrote:
Hi
If the antenna is no higher than your house, it's no more likely to get hit than the house.
If it's higher than the house by a few feet, the increase in hit probability is vanishingly small.
Antenna do not have to be directly hit to destroy the receiver. Let's
say that something 100 feet away is hit. The nearby strike is
thousands of amps of current in a brief pulse. What you have is
a strong electromagnetic field pulse. This will induce current in any
nearby conductor, including your antenna mast, power lines, phone
lines and even the copper traces on a PCB. The effects vary based on
the geometry. One does not even worry about a direct hit. It is
rare and if it happens your equipment is vaporized. But near hits
happen all the time you can expect them and they are mostly the cause
of damaged equipment and it is actually posable to protect against a
nearby hit.
Think of lightening like a 1,000 pound bomb. If one falls from the
sky on a city and hits you on the head you are dead. But most of the
people effected by the bomb did NOT get hit on the head and were
varying distances from it and for most of them various protection
measures can be very effective.
Redondo Beach, California
On Thu, 12 Apr 2012 12:41:51 -0400
"Bob Camp" lists@rtty.us wrote:
GPS is pretty close to the noise "as received". A fully passive system with
significant cable loss and low / no gain antennas does not sound like it's
going to do a very good job.
GPS is pretty much under the noise "as received" :-)
At least in urban regions with lots of noise around, the GPS signal is
burried deep within the noise. In rural areas the signal of a single
satelite is still below thermal noise. The combined signal of all satelites
can be above noise though.
Attila Kinali
--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
Hi
Some of the people posting to the thread seem to be concerned about the
house burning down because they put up a GPS antenna...
Receivers can die from a lot of causes. A TBolt like GPS being killed by
input overload from a strike 100 feet away would not be very high on my list
of likely problems.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Chris Albertson
Sent: Thursday, April 12, 2012 12:50 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Best location for a GPS antenna...?
On Wed, Apr 11, 2012 at 3:08 PM, Bob Camp lists@rtty.us wrote:
Hi
If the antenna is no higher than your house, it's no more likely to get
hit than the house.
If it's higher than the house by a few feet, the increase in hit
probability is vanishingly small.
Antenna do not have to be directly hit to destroy the receiver. Let's
say that something 100 feet away is hit. The nearby strike is
thousands of amps of current in a brief pulse. What you have is
a strong electromagnetic field pulse. This will induce current in any
nearby conductor, including your antenna mast, power lines, phone
lines and even the copper traces on a PCB. The effects vary based on
the geometry. One does not even worry about a direct hit. It is
rare and if it happens your equipment is vaporized. But near hits
happen all the time you can expect them and they are mostly the cause
of damaged equipment and it is actually posable to protect against a
nearby hit.
Think of lightening like a 1,000 pound bomb. If one falls from the
sky on a city and hits you on the head you are dead. But most of the
people effected by the bomb did NOT get hit on the head and were
varying distances from it and for most of them various protection
measures can be very effective.
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
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https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Thu, 12 Apr 2012 18:41:43 +0200
bg@lysator.liu.se wrote:
Rerad-systems are getting controlled in Europe too.
http://www.etsi.org/deliver/etsi_en/302600_302699/302645/01.01.01_60/en_302645v010101p.pdf
Any reports on how quick this is going? Where I live, there are rules, but
not many are aware of them.
Interesting, I thought that repeaters were covered by the standard
frequency regulation: ie they are forbidden (or in long: you are not
allowed to make radiations in a frequency band you are not licensed to
send). Unless of course, these repeaters do not fall under the
"radio devices" category, which then the radiation would be simply EMI :-)
Attila Kinali
--
Why does it take years to find the answers to
the questions one should have asked long ago?
Michael,
There is a very effective fix: move!
:)
I live in NW Florida and I believe I have found a good solution to the lightning problem.
Since lightning never strikes the same place twice (or so goes conventional wisdom), I built my 60' antenna tower a few feet from the exact spot where a tree had been destroyed by lightning 5 years prior. That was 20 years ago, so far, so good...
Didier KO4BB
Sent from my BlackBerry Wireless thingy while I do other things...
-----Original Message-----
From: Michael Baker mpb45@clanbaker.org
Sender: time-nuts-bounces@febo.com
Date: Wed, 11 Apr 2012 08:50:24
To: time-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
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
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Not good Didier!
Rob K
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of shalimr9@gmail.com
Sent: 13 April 2012 17:32
To: Time-Nuts
Subject: Re: [time-nuts] Best location for a GPS antenna...?
Michael,
There is a very effective fix: move!
:)
I live in NW Florida and I believe I have found a good solution to the
lightning problem.
Since lightning never strikes the same place twice (or so goes conventional
wisdom), I built my 60' antenna tower a few feet from the exact spot where a
tree had been destroyed by lightning 5 years prior. That was 20 years ago,
so far, so good...
Didier KO4BB
Sent from my BlackBerry Wireless thingy while I do other things...
-----Original Message-----
From: Michael Baker mpb45@clanbaker.org
Sender: time-nuts-bounces@febo.com
Date: Wed, 11 Apr 2012 08:50:24
To: time-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
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
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
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