GPS Antenna Feed Line Decision
Attila wrote:
The supplies for LNAs are usually quite benign given two constraints:
* * *
- Low frequency (0Hz to bandwidth of signal) noise is low
But 1) is a bit harder as it also includes 1/f noise, temperature,
(upstream) supply and load effects.
The LT3042 is better in this regard than anything short of a heroic
effort with discrete components, IF you use a larger-than-normal bypass
capacitor on the SET pin. With Cset = 22uF, the noise density is
<20nV/sqrtHz down to 10Hz. 220uF is somewhat better, but not by a whole
decade because of the 1/f noise of the error/output amplifier.
The down side of a large Cset is that the power supply takes longer to
reach its final voltage. A 5v supply reaches 90% voltage in about 25
seconds, and 99% in about 40 seconds. A 10v supply takes twice as long,
and a 15v supply, three times. The LT3042 does have a "fast start"
mode, which can reduce these times considerably (to ~0.5sec, ~1sec, and
~1.5sec, respectively) -- but still longer than usual for a regulated
supply. For applications like continuously-on LNA power, there should
be no problem with any of these times.
The LT3042 is a bit of a pain to use, with its buried ground/heatsink
tab, but it is very good, and is the lowest noise fully integrated
regulator available, AFAIK.
Best regards,
Charles
I work with a broadcast station.
We just had a HD FM radio transmitter upgrade done.
In the upgrade package from GatesAir was a GPS antenna with a F fitting.
The provided feedline was RG-223 with a TNC on one end and a SMA on the
other.
Also provided was a TNC to F adapter.
The new exciter has a GPS receiver installed to provide 1 PPS to the
exciter.
There was also another piece of equipment that required 1 PPS and they
provided an antenna and no feedline with that one.
Either piece would output 1 PPS, so the second antenna was not needed.
So you wonder what the "professionals" had in mind with the adapters.
Low bidder for the antenna??
73
Glenn
WB4UIV
On 9/3/2017 10:09 AM, Wes wrote:
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
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--
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
On 9/3/17 3:41 PM, Charles Steinmetz wrote:
Attila wrote:
The supplies for LNAs are usually quite benign given two constraints:
* * *
- Low frequency (0Hz to bandwidth of signal) noise is low
But 1) is a bit harder as it also includes 1/f noise, temperature,
(upstream) supply and load effects.
The LT3042 is better in this regard than anything short of a heroic
effort with discrete components, IF you use a larger-than-normal bypass
capacitor on the SET pin. With Cset = 22uF, the noise density is
<20nV/sqrtHz down to 10Hz. 220uF is somewhat better, but not by a whole
decade because of the 1/f noise of the error/output amplifier.
The down side of a large Cset is that the power supply takes longer to
reach its final voltage. A 5v supply reaches 90% voltage in about 25
seconds, and 99% in about 40 seconds. A 10v supply takes twice as long,
and a 15v supply, three times. The LT3042 does have a "fast start"
mode, which can reduce these times considerably (to ~0.5sec, ~1sec, and
~1.5sec, respectively) -- but still longer than usual for a regulated
supply. For applications like continuously-on LNA power, there should
be no problem with any of these times.
The LT3042 is a bit of a pain to use, with its buried ground/heatsink
tab, but it is very good, and is the lowest noise fully integrated
regulator available, AFAIK.
I love that part - the PSRR is awesome up to MHz. So many of those
linear regulators are great at kHz, but not so hot up higher.
You want quiet, the 3042 is your friend.
On 09/02/2017 02:57 PM, Clay Autery 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...
I have a modest 26dB antenna on a six feet pole of plastic piping, the piping is
strapped to my deck post. The antenna is probably ten feet high added to my deck.
I use a 40' RG6 that my Comcast chap overestimated, and he said, "Just use it as you need."
I measured the theoretical 1.4 SWR with as pretty much dead on. So long as my GPS boxes
agree with consumer time, as measured by the cheap "atomic" clocks from super cheap vendors,
I am happy with the set up. I have no need of phase and jitter, so long as they average out.
I just had to buy some "F" connectors and use adapters to convert to the GPS 50 ohm inputs.
Works like a charm. And good enough for me.
Best wishes,
Ian, G4ICV, AB2GR
Hi
If you are running into a TBolt, it’s got an F connector and 75 ohm cable
spec’d already …. The 50 ohm / 75 ohm thing didn’t seem to bother
Trimble. They certainly looked at it before going that way ….
Bob
On Sep 4, 2017, at 12:31 AM, Ian Stirling is@opus131.com wrote:
On 09/02/2017 02:57 PM, Clay Autery 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...
I have a modest 26dB antenna on a six feet pole of plastic piping, the piping is
strapped to my deck post. The antenna is probably ten feet high added to my deck.
I use a 40' RG6 that my Comcast chap overestimated, and he said, "Just use it as you need."
I measured the theoretical 1.4 SWR with as pretty much dead on. So long as my GPS boxes
agree with consumer time, as measured by the cheap "atomic" clocks from super cheap vendors,
I am happy with the set up. I have no need of phase and jitter, so long as they average out.
I just had to buy some "F" connectors and use adapters to convert to the GPS 50 ohm inputs.
Works like a charm. And good enough for me.
Best wishes,
Ian, G4ICV, AB2GR
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Not being as nutty as many on this list I only skimmed the papers you provided.
Interesting and I will stand corrected regarding the use of 75 ohm cable in 50
ohm systems in critical situations. In situations like my own, I'm not going to
fuss about it.
I realize this is NIST, the 1384 paper was probably peer-reviewed, and I
shouldn't question, nevertheless fools rush in.
In the block diagram of Figure 3 and the accompanying text, is described
installing attenuators to increase return loss (RL) to what is claimed to be 40
dB. Forty dB RL is in the realm of precision calibration standards.
(https://www.maurymw.com/Precision/Precision_Fixed_Terminations.php) and it's
not trivial to measure on a single device. Here we have a cascaded of two
attenuators, two bias tees and a length of cable.
If these are COTS attenuators, their own return loss is unlikely to be 40 dB.
In fact grabbing an old HP catalog off my bookshelf (I'm dating myself) I see a
typical type N attenuator specified as 1.2 VSWR (~21 dB RL). I went on a quick
"shopping" trip looking for an L-band, type N bias tee. I'll spare you the
links, but typically they are also rated at 1.2 VSWR.
Perhaps NIST, with an unlimited supply of tax money, splurged and manufactured
bias tees with >40 dB RL. Maybe they did the same with the attenuators. We'll
never know because they didn't provide an equipment list or a measurement
procedure. They said nothing about the cable either, other than they started
with RG-58 and replaced it with "better" cable.
A few words about cable, since that is what this discussion is all about.
Cable, regardless of type and manufacturer, has its own RL, also known in that
business as Structural Return Loss (SRL) See:
https://www.belden.com/docs/upload/hdcarltp.pdf and
http://www.keysight.com/upload/cmc_upload/All/E206COMPTEST_METHOD.pdf.
At least the authors admit, "Thus far we have seen little difference in the data."
Wes
On 9/3/2017 3:02 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
On 9/4/17 1:18 PM, Wes wrote:
If these are COTS attenuators, their own return loss is unlikely to be
40 dB. In fact grabbing an old HP catalog off my bookshelf (I'm dating
myself) I see a typical type N attenuator specified as 1.2 VSWR (~21 dB
RL). I went on a quick "shopping" trip looking for an L-band, type N
bias tee. I'll spare you the links, but typically they are also rated
at 1.2 VSWR.
Be careful, that's the "catalog spec" which means "what we can
inexpensively measure"..
It's like SMA connectors, which are specified at 1.05:1 or 1.1:1 and
<0.3dB loss.
https://www.amphenolrf.com/connectors/sma.html
In reality, they are a LOT better, it's just that measuring that in a
production environment is tough.
I'd not want to set up a manufacturing test set that measured loss with
an uncertainty of 0.01 dB.
I'll point folks to:
Jesch's paper in 1976
http://ieeexplore.ieee.org/document/6312234/
and then Maury
https://www.maurymw.com/pdf/datasheets/5A-021.pdf
Someone at Maury did a paper which I can't find right now where they
measured a bunch of SMA connectors over hundreds if not thousands of
mate/demate cycles.
RF cafe has a nice summary
http://www.rfcafe.com/references/articles/Joe-Cahak/rf-connectors-cables-joe-cahak-6-2014.htm
Perhaps NIST, with an unlimited supply of tax money, splurged and
manufactured bias tees with >40 dB RL. Maybe they did the same with the
attenuators. We'll never know because they didn't provide an equipment
list or a measurement procedure. They said nothing about the cable
either, other than they started with RG-58 and replaced it with "better"
cable.
But you could probably send an email to the author and ask. NIST, like
JPL, is one of those places where people work forever. Tom Otoshi, who
wrote a report on N connectors in 1963 cited by Maury, above, still
works at JPL (I think.. I confess I haven't seen him recently, he might
have retired, but he was certainly around in the last 10 years), and
given the span of years, that N connector work was probably when he was
a just out of school engineer.
A few words about cable, since that is what this discussion is all
about. Cable, regardless of type and manufacturer, has its own RL, also
known in that business as Structural Return Loss (SRL) See:
https://www.belden.com/docs/upload/hdcarltp.pdf and
http://www.keysight.com/upload/cmc_upload/All/E206COMPTEST_METHOD.pdf.
At least the authors admit, "Thus far we have seen little difference in
the data."
Wes
On 9/3/2017 3:02 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
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Hi
A lot depends on just which outfit you buy your attenuators from. There
certainly are outfits out there that supply you just over 20 db RL when
the spec is 20. They also don’t charge very much for their attenuators ….
Bob
On Sep 4, 2017, at 4:53 PM, jimlux jimlux@earthlink.net wrote:
On 9/4/17 1:18 PM, Wes wrote:
If these are COTS attenuators, their own return loss is unlikely to be
40 dB. In fact grabbing an old HP catalog off my bookshelf (I'm dating
myself) I see a typical type N attenuator specified as 1.2 VSWR (~21 dB
RL). I went on a quick "shopping" trip looking for an L-band, type N
bias tee. I'll spare you the links, but typically they are also rated
at 1.2 VSWR.
Be careful, that's the "catalog spec" which means "what we can inexpensively measure"..
It's like SMA connectors, which are specified at 1.05:1 or 1.1:1 and <0.3dB loss.
https://www.amphenolrf.com/connectors/sma.html
In reality, they are a LOT better, it's just that measuring that in a production environment is tough.
I'd not want to set up a manufacturing test set that measured loss with an uncertainty of 0.01 dB.
I'll point folks to:
Jesch's paper in 1976
http://ieeexplore.ieee.org/document/6312234/
and then Maury
https://www.maurymw.com/pdf/datasheets/5A-021.pdf
Someone at Maury did a paper which I can't find right now where they measured a bunch of SMA connectors over hundreds if not thousands of mate/demate cycles.
RF cafe has a nice summary
http://www.rfcafe.com/references/articles/Joe-Cahak/rf-connectors-cables-joe-cahak-6-2014.htm
Perhaps NIST, with an unlimited supply of tax money, splurged and
manufactured bias tees with >40 dB RL. Maybe they did the same with the
attenuators. We'll never know because they didn't provide an equipment
list or a measurement procedure. They said nothing about the cable
either, other than they started with RG-58 and replaced it with "better"
cable.
But you could probably send an email to the author and ask. NIST, like JPL, is one of those places where people work forever. Tom Otoshi, who wrote a report on N connectors in 1963 cited by Maury, above, still works at JPL (I think.. I confess I haven't seen him recently, he might have retired, but he was certainly around in the last 10 years), and given the span of years, that N connector work was probably when he was a just out of school engineer.
A few words about cable, since that is what this discussion is all
about. Cable, regardless of type and manufacturer, has its own RL, also
known in that business as Structural Return Loss (SRL) See:
https://www.belden.com/docs/upload/hdcarltp.pdf and
http://www.keysight.com/upload/cmc_upload/All/E206COMPTEST_METHOD.pdf.
At least the authors admit, "Thus far we have seen little difference in
the data."
Wes
On 9/3/2017 3:02 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
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I'm dating myself again but when I was employed at Hughes Aircraft we had an HP
salesman dedicated to servicing just us. So most everything came direct from
them or Wiltron. I liked traveling to HP events with him. Hughes had a miserly
expense reporting process. His was, "I count the money in my wallet before I
leave. I count it again when I get back. The difference is my expense."
Wes
. On 9/4/2017 2:26 PM, Bob kb8tq wrote:
Hi
A lot depends on just which outfit you buy your attenuators from. There
certainly are outfits out there that supply you just over 20 db RL when
the spec is 20. They also don’t charge very much for their attenuators ….
Bob