GNSS TimeReceiver - Revision history

Cmpxchg at 18:08, 19 April 2020

2020-04-19T18:08:43Z

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	== What is a GNSS / GPS re-radiator or -repeater ? ==		== What is a GNSS / GPS re-radiator or -repeater ? ==
	An Indoor GNSS re-radiator uses an indoor, in-room antenna, to transmit a low-power GNSS signal that is a copy of a GNSS signal picked up on the roof.		An Indoor GNSS re-radiator uses an indoor, in-room antenna, to transmit a low-power GNSS signal that is a copy of a GNSS signal picked up on the roof.
	The signal is intended only for devices present in the room. ~~In addition to this, it~~ can be used to directly feed a GNSS, GPS or Galileo Time Receiver placed indoors.		The signal is intended only for devices present in the room.

			== What is a GNSS Time Receiver ? ==
			The receive antenna and cabling of a repeater-system can also be used to directly feed a GNSS, GPS or Galileo Time Receiver placed indoors.
	For such coax-cabled receiver, no re-radiating antenna is needed, but a similar installation is needed to get an accurate copy of the GNSS signal indoors.<br>		For such coax-cabled receiver, no re-radiating antenna is needed, but a similar installation is needed to get an accurate copy of the GNSS signal indoors.<br>
	<br>		<br>

Cmpxchg: /* What is a GNSS / GPS re-radiator ? */

2020-04-19T18:07:16Z

What is a GNSS / GPS re-radiator ?

← Older revision		Revision as of 18:07, 19 April 2020
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	}}		}}

	== What is a GNSS / GPS re-radiator ? ==		== What is a GNSS / GPS re-radiator or -repeater ? ==
	An Indoor GNSS re-radiator uses an indoor, in-room antenna, to transmit a low-power GNSS signal that is a copy of a GNSS signal picked up on the roof.		An Indoor GNSS re-radiator uses an indoor, in-room antenna, to transmit a low-power GNSS signal that is a copy of a GNSS signal picked up on the roof.
	The signal is intended only for devices present in the room. In addition to this, it can be used to directly feed a GNSS, GPS or Galileo Time Receiver placed indoors.		The signal is intended only for devices present in the room. In addition to this, it can be used to directly feed a GNSS, GPS or Galileo Time Receiver placed indoors.

Cmpxchg: Cmpxchg moved page GNSS ReRadiator to GNSS TimeReceiver: Better fitting project goal

2020-04-19T18:06:16Z

Cmpxchg moved page GNSS ReRadiator to GNSS TimeReceiver: Better fitting project goal

← Older revision	Revision as of 18:06, 19 April 2020
(No difference)

Cmpxchg: /* How is an 'active antenna' powered ? */

2020-04-12T21:37:58Z

How is an 'active antenna' powered ?

← Older revision		Revision as of 21:37, 12 April 2020
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	<br>		<br>
	This is similar to how Satellite receiver LNB's are powered. An inductor will provide a DC signal of 3.3 to 5 volts to the		This is similar to how Satellite receiver LNB's are powered. An inductor will provide a DC signal of 3.3 to 5 volts to the
	center conductor of the coaxial cable. A series capacitor ~~is placed after the bias to allow the RF signal to be fed~~ to a receiver's gain stage or filter.<br>		center conductor of the coaxial cable. The inductor passes DC, but will block RF. The RF can pass via a series capacitor, to a receiver's gain stage or filter.<br>
	To be inserted: Schematic of DC bias<br>		To be inserted: Schematic of DC bias<br>
	<br>		<br>
	GPS patch antenna's with a magnetic base are cheap and almost always have one or two gain stages and filters built-in<br>		GPS patch antenna's with a magnetic base are cheap and almost always have one or two gain stages and filters built-in<br>
	<br>		<br>

	== GPS and Galileo space segment, orbits and signals ==		== GPS and Galileo space segment, orbits and signals ==
	GPS satellites orbit the earth in a little less than 12 hours, the aim is half a sidereal day. Galileo satellites use a higher orbit and orbit in around 10 hours.		GPS satellites orbit the earth in a little less than 12 hours, the aim is half a sidereal day. Galileo satellites use a higher orbit and orbit in around 10 hours.

Cmpxchg: /* Why is an 'active antenna' needed ? */

2020-04-12T21:36:25Z

Why is an 'active antenna' needed ?

← Older revision		Revision as of 21:36, 12 April 2020
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	== Why is an 'active antenna' needed ? ==		== Why is an 'active antenna' needed ? ==
	The 'noise figure' of the first amplification stage is the most important, since that noise will dominate the noise-figure of the complete chain. [https://en.wikipedia.org/wiki/Friis_formulas_for_noise Friis formula for noise]. The first amplification stage will always be right behind the antenna itself, before any cable or other element with non-perfect impedance matching and attenuation.<br>		The 'noise figure' of the first amplification stage is the most important, since that noise will dominate the noise-figure of the complete chain. See [https://en.wikipedia.org/wiki/Friis_formulas_for_noise Wikipedia, Friis formula for noise]. The first amplification stage will always be right behind the antenna itself, before any cable or other element with non-perfect impedance matching and attenuation.<br>
	The only thing in front of the first gain stage, or in between two stages, is a filter to supress out-of-band signals. For this, often SAW filters are used, Surface Acoustic Wave filters. These tiny electro-mechanical devices provide enough attenuation outside the designed frequency, while providing ample insertion loss in the pass-band. They are mechanically stable and provide reproducible results.<br>		The only thing in front of the first gain stage, or in between two stages, is a filter to supress out-of-band signals. For this, often SAW filters are used, Surface Acoustic Wave filters. These tiny electro-mechanical devices provide enough attenuation outside the designed frequency, while providing ample insertion loss in the pass-band. They are mechanically stable and provide reproducible results.<br>
	<br>		<br>

Cmpxchg: /* How strong are ReRadiated GNSS signals? */

2020-04-12T21:32:51Z

How strong are ReRadiated GNSS signals?

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	Wifi outputs a factor 1000 more power for the weakest link of about 1 megabits per second, and often a factor million more to have a reasonable speed op 54 mbps.		Wifi outputs a factor 1000 more power for the weakest link of about 1 megabits per second, and often a factor million more to have a reasonable speed op 54 mbps.
	Wifi also uses a different frequency, one intended to be used for cheap and leaky microwave ovens, 2400-2480 MHz.		Wifi also uses a different frequency, one intended to be used for cheap and leaky microwave ovens, 2400-2480 MHz.
	The bandwidth (occupied frequency range) is about 11 MHz, for GPS it is around 2 to 3 MHz worth at 1575.42 MHz centerfrequency.		The bandwidth (occupied frequency range) is about 22 MHz, for GPS it is around 2 to 3 MHz worth at 1575.42 MHz centerfrequency.
	<br>		<br>
	The GPS satellites output each ca 27 watts towards earth on the L1 frequency (1575.42 MHz, ca 2 MHz wide). The temperature of the antenna is very low. After this the signal		The GPS satellites output each ca 27 watts towards earth on the L1 frequency (1575.42 MHz, ca 2 MHz wide). The temperature of the antenna is very low. After this the signal

Cmpxchg: /* How strong are ReRadiated GNSS signals? */

2020-04-12T20:22:28Z

How strong are ReRadiated GNSS signals?

← Older revision		Revision as of 20:22, 12 April 2020
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	Yet, one does not have to cool one's antenna to a few kelvin, like some radio astronomers do to get their radio-pictures of galactic objects.<br>		Yet, one does not have to cool one's antenna to a few kelvin, like some radio astronomers do to get their radio-pictures of galactic objects.<br>
	<br>		<br>
	By comparison, mobile telephones can produce peaks of 2 watts, or 33 dBm, 161.5 dB ~~more~~, or a voltage factor of almost 200 million.		By comparison, mobile telephones can produce peaks of 2 watts, or 33 dBm. Compared to -128.5, this is a difference of 161.5 dB, a voltage factor of almost 200 million.
	At first sight, it is almost a miracle that it ~~does all work out~~. There are a lot of tricks used to make it work. ~~The most powerful feature~~ of GNSS is the efficiency.		<br>
	With 24 satellites each producing 27 watts of RF power, a total of 864 watts, everyone on earth can determine their own position down to a few meters,		At first sight, it is almost a miracle that the weak GPS signal does make it through.
	and even do that without having to reveal their location or identify oneself.<br>		There are a lot of tricks used to make it work, and makes a nice example for both science and signal processing.
			<br>
			Another nice aspect of GNSS systems, is the efficiency at which it operates.
			With 24 satellites each producing 27 watts of RF power, a total of just 864 watts, less than a vacuum cleaner, everyone on earth can determine their own position down to a few meters, and even do that without having to reveal their location or identify oneself.<br>
	If one compares that with many-watt's-each mobile service base stations, spread over all urban area's in the world, it is the most efficient globally deployed radio service ever invented. Another remarkable fact is that is an open service, available to all, operated by the US Air Force.<br>		If one compares that with many-watt's-each mobile service base stations, spread over all urban area's in the world, it is the most efficient globally deployed radio service ever invented. Another remarkable fact is that is an open service, available to all, operated by the US Air Force.<br>
	Compared to domestic wifi accesspoints and wifi devices, it is also impressive. WiFi receivers minimum level is about -98 dBm, about 30 dB less sensitive as GPS.		Compared to domestic wifi accesspoints and wifi devices, it is also impressive. WiFi receivers minimum level is about -98 dBm, about 30 dB less sensitive as GPS.

Cmpxchg: /* How strong are ReRadiated GNSS signals? */

2020-04-12T20:18:40Z

How strong are ReRadiated GNSS signals?

← Older revision		Revision as of 20:18, 12 April 2020
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	If the power level is kept close to the specified -128 dBm outdoor level (GPS), it will not escape the room.<br>		If the power level is kept close to the specified -128 dBm outdoor level (GPS), it will not escape the room.<br>
	<br>		<br>
	GPS is specified at -128 dBm receive level on earth, WiFi receivers minimum level is about -98 dBm, about 30 dB ~~difference, which is~~ a factor of 1000 in power.		GPS is specified in the publicly available Interface Control Document, ICD GPS-200D (or later), at -158.5 dBW or -128.5 dBm receive level on earth, with a 3 dBi isotropic receive antenna, basically an antenna that only picks up signals above it, and not below it, and thus doubles the 'gain' compared to an globe-shaped idealized omnidirectional antenna.<br>
	Wifi uses 2400-2480 MHz ~~and ca~~ 11 MHz ~~wide~~, GPS is 1575.42 MHz ~~and 2 MHz wide. This is a very low level, it is below the thermal noise level for that bandwidth,~~		The power is equivalent to about 100 attoWatts, 0.1 nanoWatt, or 0.0001 microWatt, or 0.0000001 milliWatt. It is so small that one has to know the signal so that it can
	~~and is impossible to see on a spectrum analyser~~. ~~Nevertheless it can be detected, by correlation.<br>~~		be recovered by correlation. The thermal noise level for that bandwidth is many dB's above this, the signal is invisible on a spectrum analyser.
			Yet, one does not have to cool one's antenna to a few kelvin, like some radio astronomers do to get their radio-pictures of galactic objects.<br>
			<br>
			By comparison, mobile telephones can produce peaks of 2 watts, or 33 dBm, 161.5 dB more, or a voltage factor of almost 200 million.
			At first sight, it is almost a miracle that it does all work out. There are a lot of tricks used to make it work. The most powerful feature of GNSS is the efficiency.
			With 24 satellites each producing 27 watts of RF power, a total of 864 watts, everyone on earth can determine their own position down to a few meters,
			and even do that without having to reveal their location or identify oneself.<br>
			If one compares that with many-watt's-each mobile service base stations, spread over all urban area's in the world, it is the most efficient globally deployed radio service ever invented. Another remarkable fact is that is an open service, available to all, operated by the US Air Force.<br>
			Compared to domestic wifi accesspoints and wifi devices, it is also impressive. WiFi receivers minimum level is about -98 dBm, about 30 dB less sensitive as GPS.
			Wifi outputs a factor 1000 more power for the weakest link of about 1 megabits per second, and often a factor million more to have a reasonable speed op 54 mbps.
			Wifi also uses a different frequency, one intended to be used for cheap and leaky microwave ovens, 2400-2480 MHz.
			The bandwidth (occupied frequency range) is about 11 MHz, for GPS it is around 2 to 3 MHz worth at 1575.42 MHz centerfrequency.
	<br>		<br>
	The GPS satellites output each ca 27 watts towards earth on the L1 frequency (1575.42 MHz, ca 2 MHz wide). The temperature of the antenna is very low. After this the signal		The GPS satellites output each ca 27 watts towards earth on the L1 frequency (1575.42 MHz, ca 2 MHz wide). The temperature of the antenna is very low. After this the signal
	travels ca 22000 km, and arrives at a GPS receiver antenna in ~~ca 70~~ milliseconds. These L1 are the only signals that a re-transmitter should transmit.<br>		travels ca 22000 km, and arrives at a GPS receiver antenna in about 77 milliseconds. These L1 are the only signals that a re-transmitter should transmit.<br>

	<br>		<br>
	There is a significant amount of gain needed, many tens of decibels, and this has to be gain with a very low noise-figure, i.e, as few random, uncorrelated noise added by the signal chain.		There is a significant amount of gain needed, many tens of decibels, and this has to be gain with a very low noise-figure, i.e, as few random, uncorrelated noise added by the signal chain.
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	Such noise reduces the chance that a zero-crossing resulting into a digital bit going to the correlator, will not be detected, and correlation or carrier-to-noise ratio will decrease, or tracking of the satelite will be (temporarly) lost.<br>		Such noise reduces the chance that a zero-crossing resulting into a digital bit going to the correlator, will not be detected, and correlation or carrier-to-noise ratio will decrease, or tracking of the satelite will be (temporarly) lost.<br>
	<br>		<br>

	== Why is an 'active antenna' needed ? ==		== Why is an 'active antenna' needed ? ==
	The 'noise figure' of the first amplification stage is the most important, since that noise will dominate the noise-figure of the complete chain. [https://en.wikipedia.org/wiki/Friis_formulas_for_noise Friis formula for noise]. The first amplification stage will always be right behind the antenna itself, before any cable or other element with non-perfect impedance matching and attenuation.<br>		The 'noise figure' of the first amplification stage is the most important, since that noise will dominate the noise-figure of the complete chain. [https://en.wikipedia.org/wiki/Friis_formulas_for_noise Friis formula for noise]. The first amplification stage will always be right behind the antenna itself, before any cable or other element with non-perfect impedance matching and attenuation.<br>

Cmpxchg: /* GPS and Galileo space segment, orbits and signals */

2020-04-12T19:04:25Z

GPS and Galileo space segment, orbits and signals

← Older revision		Revision as of 19:04, 12 April 2020
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	GPS satellites orbit the earth in a little less than 12 hours, the aim is half a sidereal day. Galileo satellites use a higher orbit and orbit in around 10 hours.		GPS satellites orbit the earth in a little less than 12 hours, the aim is half a sidereal day. Galileo satellites use a higher orbit and orbit in around 10 hours.
	Towards the poles one will find more GPS satellites near the equator. Glonass has better coverage of the poles, but a lower chance of direct-overhead satellites near the equator,		Towards the poles one will find more GPS satellites near the equator. Glonass has better coverage of the poles, but a lower chance of direct-overhead satellites near the equator,
	All GPS satellites transmit on several L-band frequencies, but the L1 signal on ~~1574~~.42 MHz is used by 99% of all receivers.<br>		All GPS satellites transmit on several L-band frequencies, but the L1 signal on 1575.42 MHz is used by 99% of all receivers.<br>
	<br>		<br>
	<big>GPS and Galileo signal: CDMA in BSPK and BOC form</big><br>		<big>GPS and Galileo signal: CDMA in BSPK and BOC form</big><br>
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	or the 250 bps Galileo signal<br>		or the 250 bps Galileo signal<br>
	<br>		<br>

	== How is Galileo different from GPS? ==		== How is Galileo different from GPS? ==
	The european Galileo satellite constellation is using a similar concept as GPS, Russia's Glonass and China's Beidou. GPS and Glonass were the first signals, Galileo and Beidou came later.<br>		The european Galileo satellite constellation is using a similar concept as GPS, Russia's Glonass and China's Beidou. GPS and Glonass were the first signals, Galileo and Beidou came later.<br>

Cmpxchg: /* Why is an 'active antenna' needed ? */

2020-04-12T19:03:41Z

Why is an 'active antenna' needed ?

← Older revision		Revision as of 19:03, 12 April 2020
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	== Why is an 'active antenna' needed ? ==		== Why is an 'active antenna' needed ? ==
	The 'noise figure' of the first amplification stage is the most important, since that noise will dominate the noise-figure of the complete chain. [https://en.wikipedia.org/wiki/Friis_formulas_for_noise Friis formula for noise]. The first amplification stage will always be right behind the antenna itself, before any cable or other element with non-perfect impedance matching and attenuation.<br>		The 'noise figure' of the first amplification stage is the most important, since that noise will dominate the noise-figure of the complete chain. [https://en.wikipedia.org/wiki/Friis_formulas_for_noise Friis formula for noise]. The first amplification stage will always be right behind the antenna itself, before any cable or other element with non-perfect impedance matching and attenuation.<br>
	The only thing in front of the first gain stage, or in between two stages, is a filter to supress out-of-band signals. For this, often SAW filters are used, Surface Acoustic Wave filters. These tiny electro-mechanical devices provide enough attenuation outside the designed frequency, while providing ~~amble~~ insertion loss in the pass-band. They are mechanically stable and provide reproducible results.<br>		The only thing in front of the first gain stage, or in between two stages, is a filter to supress out-of-band signals. For this, often SAW filters are used, Surface Acoustic Wave filters. These tiny electro-mechanical devices provide enough attenuation outside the designed frequency, while providing ample insertion loss in the pass-band. They are mechanically stable and provide reproducible results.<br>
	<br>		<br>

	== How is an 'active antenna' powered ? ==		== How is an 'active antenna' powered ? ==
	An 'active antenna' will not radiate signals back via the antenna to the environment. 'Active' means it will amplify the signal before transmitting it down a cable to the receiver.		An 'active antenna' will not radiate signals back via the antenna to the environment. 'Active' means it will amplify the signal before transmitting it down a cable to the receiver.