GPS Antenna Feed Line Decision
Hi Clay,
Intersting subject.
What design for ultra stable/clean power supply are you using please ?
Thx,
Gilles.
On Sep 2, 2017, at 22:47, Clay Autery cautery@montac.com wrote:
PCTEL GPS-TMG-HR-26NCM Antenna.
http://www.neobits.com/pctel_maxrad_gps_tmg_hr_26ncm_high_rejection_gps_p2769137.htm
Can't say what the gain tolerances are, but it appears to be a pretty
decent quality part.
The distribution amp is an HP 58516A GPS L1 Distribution Amp with the
external power supply tap which will be fed with an ultras stable/clean
adjustable linear power supply. As I understand it, this is a unity
gain amp, so there should be little to no insertion loss or distro losses.
The distribution amp will be mounted near the devices such that amp to
device jumpers will all be < 1 meter/3.28 feet. Likely a lot less. ALL
Times N-connectors until reaching a connector TM doesn't make.
Clay Autery, KY5G
On 9/2/2017 3:26 PM, Bob kb8tq wrote:
Hi
A lot depends on what comes after the feed cable. The “disto amp” will determine
a lot. You likely need 10 db of net gain in front of it to keep things running ok. For an
antenna that is really 26 db (as opposed to 26 db +/- 6 db), that would come out to
16 db of feed line loss. This isn’t a terribly surprising outcome. The antennas are designed
for installations that run 150’ or more of coax ….
Bob
On Sep 2, 2017, at 2:57 PM, Clay Autery cautery@montac.com wrote:
Having decision-making problems for the materials for my GPS main
feedline. Going to use a TM LMR stock, just can't decide how big to go
with it...
26 dB 5vdc antenna on top of a 38 foot mast. Feed will come down the
inside/center of mast and exit near the bottom, thence routed through a
window and to the GPS distro amp. Antenna will feed GPSDO, NTP Server,
Blitzortung System Blue station, and one other device TBD.
Just cannot decide how big to go with the antenna to distro amp feed...
Assuming 50 feet total (38' mast + 12 feet to amp in shack) @ 1800 MHz
(closest to 1725 MHz), here are the losses from just this piece
(ignoring the amp to device jumpers):
-240 = 5.45 dB XXX - too much loss?
-400 = 2.85 dB
-500 = 2.30 dB XXX - too hard to find
-600 = 1.85 dB
-900 = 1.25 dB
Money not necessarily a consideration as this is a short run for a
permanent installation. Don't anticipate ever moving the GPS antenna to
the tower.
For 900 and likely 600, likely would not be able to do it in one piece
as routing it out of the mast and into the shack would get complicated.
Would likely bring it out of the mast at the bottom with a right angle
connector, and then use a smaller diameter jumper for the last 12 feet.
500 is pretty uncommon stock wise and it and connectors are harder to find.
I already have the tooling for both 240 and 400... but I definitely
don't want to challenge ANY of the devices for signal gain.
So it mostly boils down to easy vs. more effort ($$ aside).... Is it
worth the additional trouble to move from -400 to -600 or -900? To NOT
lose the 1-1.6 dB additional?
I'd appreciate your recommendation and reasoning. Thanks in advance!
73,
--
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389
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On Sat, 2 Sep 2017 18:48:52 -0500
Clay Autery cautery@montac.com wrote:
Not sure why you and the other guy both recommended RG-6 75-Ohm cable
and F-connectors, when the nominal impedance of literally everything
else in the system is 50 Ohm, including the antenna and the HP GPS
Distribution Amp.... And then adding N to F adapters?
Because it doesn't matter in a receive only application.
The transmission coefficient for a 75R<->50R step is 0.8, or -1.9dB.
In return, you can get a much better cable for half the price with
less damping. Not to talk about all the other bits and pieces that
are readily available for 75R F connectors. Like lightning arrestors
and grounding blocks. And please, include at least a lightning arrestor
at the point where the cable enters the building!
Doesn't make any sense unless one has $$ as a top priority, already has
a spool of RG-6 quad shield, etc... but I specifically stated that $$
is not a top priority.... Not really even in the top 5 or 10...
If you have more than enough money, then by all means go for the 50R
solution :-)
Strain relief solution: Really depends upon which cable stock I end up
using.... Obviously, the larger the cable, the more weight will be
suspended under the antenna (approx. 38 feet, depending on where I pull
the cable out of the mast at the bottom. (The mast is on a tilt-base of
my own construction.... which brings up a valid consideration. it is
already a chore to walk the mast up manually. The more weight added at
the top and inside the mast, the more difficult a manual walk-up will
be. I'd prefer to keep this a manual tilt for now... at least until I
add the tri-band vertical dipole)
LMR-400 would be less than 4 lbs total weight... I'd likely suspend the
cable by the connector alone. (although, it wouldn't be JUST the
crimp... The connector would have at a minimum, 1 layer of
adhesive-lined shrink tube... probably 2, with the second, overlapping.
Then a nice wrap of self-fusing tape and then electrical tape over that.
Even LMR-600 could be suspended by the connector alone, at 5 lbs max in
the 38 foot max vertical section.
I do have several methods of secondary suspension within the top (and/or
second) mast section though if I decide I need it.
You do not want to have 2kg of weight on a RF connector.
Even if it will hold now, over time material creep will lead to
intermediate faults. Better use a dedicated strain relieve. This
can be something as simple as a wire wound around the cable that
holds the weight.
Attila Kinali
--
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering. -- The Doctor
On 9/2/2017 4:48 PM, Clay Autery wrote:
Thanks for the response...
Not sure why you and the other guy both recommended RG-6 75-Ohm cable
and F-connectors, when the nominal impedance of literally everything
else in the system is 50 Ohm, including the antenna and the HP GPS
Distribution Amp.... And then adding N to F adapters?
As "the other guy" (I think) let me say that the impedance mismatch is
immaterial and in my case I have one GPSDO with an SMA connector and another
with a BNC and an antenna with an SMA. So I "adapt" no matter what I do.
Because I understand the cascaded noise figure equations, I know that I don't
need an active distribution amplifier to feed just these two devices, so a $5.00
"F" connector splitter is adequate.
(https://www.markertek.com/product/201-232/2-way-2-4ghz-90db-satellite-splitter-dc-power-passing-to-one-port)
Doesn't make any sense unless one has $$ as a top priority, already has
a spool of RG-6 quad shield, etc... but I specifically stated that $$
is not a top priority.... Not really even in the top 5 or 10...
Then by all means you should use L-band waveguide. :-)
Wes
Hi
There is no need to feed the 58516 or the antenna with any sort of super power supply.
It’s just a simple RF amplifier in there. It’s designed to be feed off of the
bias supply coming out of a GPS module. If a module has a dedicated
78L05 style regulator on it, it’s one of the better ones ….
Bob
On Sep 3, 2017, at 2:55 AM, Clemgill clemgill@club-internet.fr wrote:
Hi Clay,
Intersting subject.
What design for ultra stable/clean power supply are you using please ?
Thx,
Gilles.
On Sep 2, 2017, at 22:47, Clay Autery cautery@montac.com wrote:
PCTEL GPS-TMG-HR-26NCM Antenna.
http://www.neobits.com/pctel_maxrad_gps_tmg_hr_26ncm_high_rejection_gps_p2769137.htm
Can't say what the gain tolerances are, but it appears to be a pretty
decent quality part.
The distribution amp is an HP 58516A GPS L1 Distribution Amp with the
external power supply tap which will be fed with an ultras stable/clean
adjustable linear power supply. As I understand it, this is a unity
gain amp, so there should be little to no insertion loss or distro losses.
The distribution amp will be mounted near the devices such that amp to
device jumpers will all be < 1 meter/3.28 feet. Likely a lot less. ALL
Times N-connectors until reaching a connector TM doesn't make.
Clay Autery, KY5G
On 9/2/2017 3:26 PM, Bob kb8tq wrote:
Hi
A lot depends on what comes after the feed cable. The “disto amp” will determine
a lot. You likely need 10 db of net gain in front of it to keep things running ok. For an
antenna that is really 26 db (as opposed to 26 db +/- 6 db), that would come out to
16 db of feed line loss. This isn’t a terribly surprising outcome. The antennas are designed
for installations that run 150’ or more of coax ….
Bob
On Sep 2, 2017, at 2:57 PM, Clay Autery cautery@montac.com wrote:
Having decision-making problems for the materials for my GPS main
feedline. Going to use a TM LMR stock, just can't decide how big to go
with it...
26 dB 5vdc antenna on top of a 38 foot mast. Feed will come down the
inside/center of mast and exit near the bottom, thence routed through a
window and to the GPS distro amp. Antenna will feed GPSDO, NTP Server,
Blitzortung System Blue station, and one other device TBD.
Just cannot decide how big to go with the antenna to distro amp feed...
Assuming 50 feet total (38' mast + 12 feet to amp in shack) @ 1800 MHz
(closest to 1725 MHz), here are the losses from just this piece
(ignoring the amp to device jumpers):
-240 = 5.45 dB XXX - too much loss?
-400 = 2.85 dB
-500 = 2.30 dB XXX - too hard to find
-600 = 1.85 dB
-900 = 1.25 dB
Money not necessarily a consideration as this is a short run for a
permanent installation. Don't anticipate ever moving the GPS antenna to
the tower.
For 900 and likely 600, likely would not be able to do it in one piece
as routing it out of the mast and into the shack would get complicated.
Would likely bring it out of the mast at the bottom with a right angle
connector, and then use a smaller diameter jumper for the last 12 feet.
500 is pretty uncommon stock wise and it and connectors are harder to find.
I already have the tooling for both 240 and 400... but I definitely
don't want to challenge ANY of the devices for signal gain.
So it mostly boils down to easy vs. more effort ($$ aside).... Is it
worth the additional trouble to move from -400 to -600 or -900? To NOT
lose the 1-1.6 dB additional?
I'd appreciate your recommendation and reasoning. Thanks in advance!
73,
--
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389
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Clay
LMR-400 is probably the best compromise , I doubt you will see any
useful improvement in system performance as a result of the improved
1.5db loss characteristics of the larger cables. Losses due to
atmospherics, ionospherics and multi-path will be an orders of
magnitude higher than the additional 1.5 db of signal improvement with
the larger cables. We are not talking comms with some guy in a space
suit on Mars here :-)
AS for walking the mast up I have done a number of installations of
this sort and the use of a block and tackle at the eve point is not
difficult, and will be appreciated more and more the older you get .
Mechanical multiplicative advantages are easy to implement. Don't use
block & tackles which can pivot since depending on the weave/braid of
the rope they will twist around and bind.
On 9/2/2017 7:48 PM, Clay Autery wrote:
Thanks for the response...
Not sure why you and the other guy both recommended RG-6 75-Ohm cable
and F-connectors, when the nominal impedance of literally everything
else in the system is 50 Ohm, including the antenna and the HP GPS
Distribution Amp.... And then adding N to F adapters?
Doesn't make any sense unless one has $$ as a top priority, already has
a spool of RG-6 quad shield, etc... but I specifically stated that $$
is not a top priority.... Not really even in the top 5 or 10...
The whole point of this exercise is to put up a semi-permanent SINGLE
antenna/feed-line install that will supply all 4 ports of the HP amp
with the least compromised signal within reason.... 4 now, and 8
whenever I can find the HP 8-way distro amp with external power input.
Strain relief solution: Really depends upon which cable stock I end up
using.... Obviously, the larger the cable, the more weight will be
suspended under the antenna (approx. 38 feet, depending on where I pull
the cable out of the mast at the bottom. (The mast is on a tilt-base of
my own construction.... which brings up a valid consideration. it is
already a chore to walk the mast up manually. The more weight added at
the top and inside the mast, the more difficult a manual walk-up will
be. I'd prefer to keep this a manual tilt for now... at least until I
add the tri-band vertical dipole)
LMR-400 would be less than 4 lbs total weight... I'd likely suspend the
cable by the connector alone. (although, it wouldn't be JUST the
crimp... The connector would have at a minimum, 1 layer of
adhesive-lined shrink tube... probably 2, with the second, overlapping.
Then a nice wrap of self-fusing tape and then electrical tape over that.
Even LMR-600 could be suspended by the connector alone, at 5 lbs max in
the 38 foot max vertical section.
I do have several methods of secondary suspension within the top (and/or
second) mast section though if I decide I need it.
Also prefer to keep all the connectors N-type as much as possible since
that is the station standard.
73,
Clay Autery, KY5G
On 9/2/2017 6:07 PM, Mike Naruta AA8K wrote:
Clay, you may wish to consider using a quality RG-6 with F
connectors. Grounding blocks are readily available for the base of
your mast and the entrance to your house. Also, off-the-shelf
over-voltage protectors (Zap-Tech) are available. I even found an
F-to-N adapter for the antenna on Amazon. Watch out for the ones with
metric N threads though.
For my 25 meter run I was going to use an existing one inch Heliax,
but pulled a run of Belden RG-6 instead after learning that Trimble
used RG-6.
It worked well directly connected to a Trimble Thunderbolt; now it is
connected to a Symmetricon 58535A GPS L1 distribution amplifier.
My Blitzortung System Red station has been running fine in my attic
(Michigan) on a Motorola 97 Oncore patch antenna fastened against the
roof underside. It is looking through wood, shingles, and nails (and
a tree and antennas and utility lines).
How are you planning to do strain-relief on the vertical run of coax
inside of your mast?
Mike - AA8K
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Hi
The bigger issue with unsuspended cables is wind and weather. It’s not just a static weight issue.
When the wind blows the cable jerks around. You very much want to tie it off against the mast. You
also want a strain relief loop at the antenna.
Bob
On Sep 3, 2017, at 10:44 AM, Artek Manuals Manuals@ArtekManuals.com wrote:
Clay
LMR-400 is probably the best compromise , I doubt you will see any useful improvement in system performance as a result of the improved 1.5db loss characteristics of the larger cables. Losses due to atmospherics, ionospherics and multi-path will be an orders of magnitude higher than the additional 1.5 db of signal improvement with the larger cables. We are not talking comms with some guy in a space suit on Mars here :-)
AS for walking the mast up I have done a number of installations of this sort and the use of a block and tackle at the eve point is not difficult, and will be appreciated more and more the older you get . Mechanical multiplicative advantages are easy to implement. Don't use block & tackles which can pivot since depending on the weave/braid of the rope they will twist around and bind.
On 9/2/2017 7:48 PM, Clay Autery wrote:
Thanks for the response...
Not sure why you and the other guy both recommended RG-6 75-Ohm cable
and F-connectors, when the nominal impedance of literally everything
else in the system is 50 Ohm, including the antenna and the HP GPS
Distribution Amp.... And then adding N to F adapters?
Doesn't make any sense unless one has $$ as a top priority, already has
a spool of RG-6 quad shield, etc... but I specifically stated that $$
is not a top priority.... Not really even in the top 5 or 10...
The whole point of this exercise is to put up a semi-permanent SINGLE
antenna/feed-line install that will supply all 4 ports of the HP amp
with the least compromised signal within reason.... 4 now, and 8
whenever I can find the HP 8-way distro amp with external power input.
Strain relief solution: Really depends upon which cable stock I end up
using.... Obviously, the larger the cable, the more weight will be
suspended under the antenna (approx. 38 feet, depending on where I pull
the cable out of the mast at the bottom. (The mast is on a tilt-base of
my own construction.... which brings up a valid consideration. it is
already a chore to walk the mast up manually. The more weight added at
the top and inside the mast, the more difficult a manual walk-up will
be. I'd prefer to keep this a manual tilt for now... at least until I
add the tri-band vertical dipole)
LMR-400 would be less than 4 lbs total weight... I'd likely suspend the
cable by the connector alone. (although, it wouldn't be JUST the
crimp... The connector would have at a minimum, 1 layer of
adhesive-lined shrink tube... probably 2, with the second, overlapping.
Then a nice wrap of self-fusing tape and then electrical tape over that.
Even LMR-600 could be suspended by the connector alone, at 5 lbs max in
the 38 foot max vertical section.
I do have several methods of secondary suspension within the top (and/or
second) mast section though if I decide I need it.
Also prefer to keep all the connectors N-type as much as possible since
that is the station standard.
73,
Clay Autery, KY5G
On 9/2/2017 6:07 PM, Mike Naruta AA8K wrote:
Clay, you may wish to consider using a quality RG-6 with F
connectors. Grounding blocks are readily available for the base of
your mast and the entrance to your house. Also, off-the-shelf
over-voltage protectors (Zap-Tech) are available. I even found an
F-to-N adapter for the antenna on Amazon. Watch out for the ones with
metric N threads though.
For my 25 meter run I was going to use an existing one inch Heliax,
but pulled a run of Belden RG-6 instead after learning that Trimble
used RG-6.
It worked well directly connected to a Trimble Thunderbolt; now it is
connected to a Symmetricon 58535A GPS L1 distribution amplifier.
My Blitzortung System Red station has been running fine in my attic
(Michigan) on a Motorola 97 Oncore patch antenna fastened against the
roof underside. It is looking through wood, shingles, and nails (and
a tree and antennas and utility lines).
How are you planning to do strain-relief on the vertical run of coax
inside of your mast?
Mike - AA8K
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Actually haven't settled on an exact solution yet, Gilles. The power
supply will likely become part of the observations/experiment that
prompted me to use the external supply in the first place.
-
All of the devices WANT to supply the antenna. 2 are nominal 5VDC, 1
supplies nominal 3.3VDC... so I was going to have to use DC blocking
anyway. The HP amp provides a load resistor (to fool the devices
hopefully) and DC blocking on all ports. Thus, I get to choose how I
provide the DC power to the PCTEL antenna. -
I saw in some aviation references where pilots claimed that they
achieved "better performance" by running their antennas at higher
voltages. (Overclocking the antenna amp? Who knows.) But it piqued my
interest, especially since the PCTEL antenna I have will "run" from
below 5VDC through 12 VDC and has an even higher survival voltage.
Thus was born the secondary goal of finding out if there is anything to
these reports. IF I can control the voltage supplied on a (preferably
constant) variable basis to the antenna, I can construct an experiment
to evaluate IF there are performance increase/degradation and in what
ways.... over a wide range of voltages. IF it pans out on MY antenna,
I will likely have to expand it to additional antennas.
BUT, in answer to your direct question: Right now I do not know. I do
know a FEW things.
- It certainly will not be a switching PS.
- While I would love to use a super-expensive "lab-grade" supply, I
would actually like to engineer a solution that I can integrate into the
shack/lab on a permanent basis for use in normal ops and future projects. - I'm leaning in the same direction that I am for powering everything
in my house that actually wants DC current.... some combination of
linear power supplies and batteries. - A lot of this is simply an excuse to engage in an academic exercise
in order to learn/play. <smile>
Bottom Line: I'll read/research/design and build until I come up with a
supply that meets my needs. Just off the top of my head, a linear
supply that charges a battery or batteries that provide the top voltage
or voltages in multiple ranges which are then regulated/filtered to
provide dead flat DC at the desired levels.
I am not an engineer or an expert of any kind. I'll have to go learn
all this. <grin>
73,
Clay Autery, KY5G
On 9/3/2017 1:55 AM, Clemgill wrote:
Hi Clay,
Intersting subject.
What design for ultra stable/clean power supply are you using please ?
Thx,
Gilles.
On Sep 2, 2017, at 22:47, Clay Autery cautery@montac.com wrote:
PCTEL GPS-TMG-HR-26NCM Antenna.
http://www.neobits.com/pctel_maxrad_gps_tmg_hr_26ncm_high_rejection_gps_p2769137.htm
Can't say what the gain tolerances are, but it appears to be a pretty
decent quality part.
The distribution amp is an HP 58516A GPS L1 Distribution Amp with the
external power supply tap which will be fed with an ultras stable/clean
adjustable linear power supply. As I understand it, this is a unity
gain amp, so there should be little to no insertion loss or distro losses.
The distribution amp will be mounted near the devices such that amp to
device jumpers will all be < 1 meter/3.28 feet. Likely a lot less. ALL
Times N-connectors until reaching a connector TM doesn't make.
Clay Autery, KY5G
On Sun, 3 Sep 2017 12:32:31 -0500
Clay Autery cautery@montac.com wrote:
- I saw in some aviation references where pilots claimed that they
achieved "better performance" by running their antennas at higher
voltages. (Overclocking the antenna amp? Who knows.) But it piqued my
interest, especially since the PCTEL antenna I have will "run" from
below 5VDC through 12 VDC and has an even higher survival voltage.
There are a couple of LNA chips around that work at 3.3V and 5V.
Usually they exhibit better performance (higher amplification and
less degradation with frequency) with higher voltage. You should
not run those chips at higher voltage then spec'ed, though.
An antenna with a 5V-12V rating has most likely a local LDO, thus
it will not benefit from higher voltage, beside having more heat
generated localy, which might or might not stabilize temperature.
Bottom Line: I'll read/research/design and build until I come up with a
supply that meets my needs. Just off the top of my head, a linear
supply that charges a battery or batteries that provide the top voltage
or voltages in multiple ranges which are then regulated/filtered to
provide dead flat DC at the desired levels.
I am not an engineer or an expert of any kind. I'll have to go learn
all this. <grin>
The supplies for LNAs are usually quite benign given two constraints:
- Low frequency (0Hz to bandwidth of signal) noise is low
- High frequency noise within the signal range is low.
It is usually quite easy to achieve 2) by using some L-C filter.
But 1) is a bit harder as it also includes 1/f noise, temperature,
(upstream) supply and load effects.
Attila Kinali
--
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering. -- The Doctor
For precision timing measurements, I would think that there would be
concern about the double reflections of a badly mismatched low loss
transmission line (such as using 75 ohm line in a 50 ohm environment).
The re-reflected signal will act similar to multipath (as a delayed
aggressor) on all satellite signals equally. The impedance mismatch
delayed reflection aggressor could aggravate timing errors due to
changes in temperature or stress in the cable. Whether this is important
for you depends on how time-nutty you want to get.
See these papers:
Effects of Antenna Cables on GPS Timing Receivers:
http://tf.boulder.nist.gov/general/pdf/1384.pdf
Absolute Calibration of a Geodetic Time Transfer System:
http://xenon.colorado.edu/paperIrevise2.pdf
Bill Byrom N5BB
On 09/03/2017 06:02 PM, Bill Byrom wrote:
For precision timing measurements, I would think that there would be
concern about the double reflections of a badly mismatched low loss
transmission line (such as using 75 ohm line in a 50 ohm environment).
The re-reflected signal will act similar to multipath (as a delayed
aggressor) on all satellite signals equally. The impedance mismatch
delayed reflection aggressor could aggravate timing errors due to
changes in temperature or stress in the cable. Whether this is important
for you depends on how time-nutty you want to get.
See these papers:
Effects of Antenna Cables on GPS Timing Receivers:
http://tf.boulder.nist.gov/general/pdf/1384.pdf
Absolute Calibration of a Geodetic Time Transfer System:
http://xenon.colorado.edu/paperIrevise2.pdf
Bill Byrom N5BB
Thank you Bill, very interesting.
Wes, that waveguide is looking better all the time.
It will be difficult to control the temperature of it though.