Discussion:
Thunderbolt - trouble locking with some types of antennas
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jimlux
2017-08-02 13:04:57 UTC
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BTW, I saw that the JPL receiver at ISS got upgraded to support Galileo.
Cool stuff.
well, not exactly upgraded - the hardware didn't change - being bolted
to the exterior of ISS inside a box inside a box - it was a software
change - which is what Software Defined Radios are all about.

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Brooke Clarke
2017-07-31 21:17:54 UTC
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Hi Jerry:

The Trimble is the oldest mass produced GPS receiver I know of and because the early receivers used high gain antennas
it seems that Trimble kept that idea for the newer designs. They like about 41 dB gain between the antenna and the input
to the receiver.
http://www.prc68.com/I/Trimpack.shtml#Ant
Newer designs probably place that gain in the front end rather than at the antenna. But having around 20 dB of gain at
the antenna gretly decreases the effect of feed line loss on noise figure.
--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

-------- Original Message --------
Due to access problems, I run my Thunderbolt with a Symmetricom 58532A
antenna placed indoor near a window facing South… can’t get much worse but
most of the time it will be locked onto 3 or 4 satellites. I recently
bought a www.leobodnar.com <http://www.leobodnar.com> GPSDO for my SDR ham
radio setup. I was very surprised to find that this minimalist GPSDO using
a small patch antenna with internal LNA placed near my window had satellite
& PPL lock within a few seconds. It requires 3-4 satellite locks for its
PPL. However, when I attached the patch antenna to my Thunderbolt –
satellite signal strength were zero or minus for all satellites. The specs
for the patch antenna are listed below.
I would appreciate any advice understanding this behavior.
Jerry NY2KW
Center Frequency 1575.42MHz±3 MHz
V.S.W.R 1.5:1
Band Width ±5 MHz
Impendence 50 ohm
Peak Gain >3dBic Based on 7×7cm ground plane
Gain Coverage >-4dBic at –90°<0<+90°(over 75% Volume)
Polarization RHCP
LNA/Filter
LNA Gain (Without cable) 28+/-3dB
Noise Figure 1.5dB Typ.
Filter Out Band Attenuation (f° =1575.42MHz)
7dB Min f0+/-20MHZ
20dB Min f0+/-50MHZ
30dB Min f0+/-100MHZ
V.S.W.R <2.0
DC Voltage 2.7V/3.0V/3.3V/5.0V/3.0V to 5.0V/other
DC Current 5mA /11mA/15mA Max
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Didier Juges
2017-08-01 18:13:10 UTC
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" having around 20 dB of gain at the antenna greatly decreases the effect
of feed line loss on noise figure."

And that would be consistent with usage for a timing receiver which is
expected to have a well exposed antenna and a significant line length, as
opposed to navigation receivers where the antenna is expected to have a
short feed line.
Post by Brooke Clarke
The Trimble is the oldest mass produced GPS receiver I know of and because
the early receivers used high gain antennas it seems that Trimble kept that
idea for the newer designs. They like about 41 dB gain between the antenna
and the input to the receiver.
http://www.prc68.com/I/Trimpack.shtml#Ant
Newer designs probably place that gain in the front end rather than at the
antenna. But having around 20 dB of gain at the antenna gretly decreases
the effect of feed line loss on noise figure.
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
-------- Original Message --------
Due to access problems, I run my Thunderbolt with a Symmetricom 58532A
antenna placed indoor near a window facing South… can’t get much worse but
most of the time it will be locked onto 3 or 4 satellites. I recently
bought a www.leobodnar.com <http://www.leobodnar.com> GPSDO for my SDR ham
radio setup. I was very surprised to find that this minimalist GPSDO using
a small patch antenna with internal LNA placed near my window had satellite
& PPL lock within a few seconds. It requires 3-4 satellite locks for its
PPL. However, when I attached the patch antenna to my Thunderbolt –
satellite signal strength were zero or minus for all satellites. The specs
for the patch antenna are listed below.
I would appreciate any advice understanding this behavior.
Jerry NY2KW
Center Frequency 1575.42MHz±3 MHz
V.S.W.R 1.5:1
Band Width ±5 MHz
Impendence 50 ohm
Peak Gain >3dBic Based on 7×7cm ground plane
Gain Coverage >-4dBic at –90°<0<+90°(over 75% Volume)
Polarization RHCP
LNA/Filter
LNA Gain (Without cable) 28+/-3dB
Noise Figure 1.5dB Typ.
Filter Out Band Attenuation (f° =1575.42MHz)
7dB Min f0+/-20MHZ
20dB Min f0+/-50MHZ
30dB Min f0+/-100MHZ
V.S.W.R <2.0
DC Voltage 2.7V/3.0V/3.3V/5.0V/3.0V to 5.0V/other
DC Current 5mA /11mA/15mA Max
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Arnold Tibus
2017-07-31 19:07:07 UTC
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Hello Jerry,
I think the problem is not at the antenna, I consider the 58532A to be a
lot better than these smal patch antennas.
But the point is that modern receivers have a significant better sensivity!
In my opinion, indoor position of any kind of antenna is not a good
solution if you want to get
low jitter results. Indoor antennas do get mostly indirect reception via
reflections oft the
SAT-signals, so even the position indicated is not really precise.
When possible, any antenna should be positioned to get a free view to
the sky 360 deg
and at least about 20 deg in elevation.
My antenna is mounted on the top of the roof outside at the highest
point with abt.
10m coax cable down to my good old thunderbolt providing best reception
possible.

I wish you good luck for your further investigations,

73
Arnold, DK2WT
Due to access problems, I run my Thunderbolt with a Symmetricom 58532A
antenna placed indoor near a window facing South… can’t get much worse but
most of the time it will be locked onto 3 or 4 satellites. I recently
bought a www.leobodnar.com <http://www.leobodnar.com> GPSDO for my SDR ham
radio setup. I was very surprised to find that this minimalist GPSDO using
a small patch antenna with internal LNA placed near my window had satellite
& PPL lock within a few seconds. It requires 3-4 satellite locks for its
PPL. However, when I attached the patch antenna to my Thunderbolt –
satellite signal strength were zero or minus for all satellites. The specs
for the patch antenna are listed below.
I would appreciate any advice understanding this behavior.
Jerry NY2KW
Center Frequency 1575.42MHz±3 MHz
V.S.W.R 1.5:1
Band Width ±5 MHz
Impendence 50 ohm
Peak Gain >3dBic Based on 7×7cm ground plane
Gain Coverage >-4dBic at –90°<0<+90°(over 75% Volume)
Polarization RHCP
LNA/Filter
LNA Gain (Without cable) 28+/-3dB
Noise Figure 1.5dB Typ.
Filter Out Band Attenuation (f° =1575.42MHz)
7dB Min f0+/-20MHZ
20dB Min f0+/-50MHZ
30dB Min f0+/-100MHZ
V.S.W.R <2.0
DC Voltage 2.7V/3.0V/3.3V/5.0V/3.0V to 5.0V/other
DC Current 5mA /11mA/15mA Max
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Magnus Danielson
2017-08-02 15:08:10 UTC
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Hi Jim,
Post by jimlux
BTW, I saw that the JPL receiver at ISS got upgraded to support Galileo.
Cool stuff.
well, not exactly upgraded - the hardware didn't change - being bolted
to the exterior of ISS inside a box inside a box - it was a software
change - which is what Software Defined Radios are all about.
Yeah, I know, it got a software upgrade. :)

Recall when I handed you some clues on how to measure the noise of the
input of that receiver. Some time-nuttery truely goes to space. :)

Cheers,
Magnus
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jimlux
2017-08-01 18:31:43 UTC
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"The newer the receiver, the more horsepower in the silicon. In the case of
GPS, that
gives you more correlators to do DSP. The sensitivity improvement is a
direct result
of that. If you take a look at the guts of a TBolt, they date to the late
1990’s. That’s
a long time in silicon years …."
It seems that more correlators would speed up the time to first fix, not
necessarily the sensitivity, particularly I do not see how it would
directly affect the capability to stay locked when signal strength
fluctuates?
On the other hand, more correlators may help when there is multipath and a
whole bunch of extraneous signals are fed into the receiver, so maybe the
apparent lack of sensitivity is really the inability to see the signal from
the chaff, not necessarily sensitivity in terms of noise figure.
There's also "more sophisticated correlators" and "more sophisticated
tracking loops" that are enabled by more computational horsepower. The
days of "independent" PN tracking loops for each signal are probably
long gone, and there's clever "aiding" of the loops by estimating the
on-the-fly variations.



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