Tag Archives: satellite
GPS and SatNav. Removing Misconceptions
The Global Positioning System (GPS), originally designed for military use, has, as it has developed, revolutionised the art or skill of getting from one place to another among the general user population. Its development in coverage and reliability along with other technologies has enabled reasonably cheap SatNav systems for general usage, in our vehicles, mobile phones and other applications. Because of its reliability and growing popularity I believe SatNav is becoming widely accepted but without due consideration as to what it is really about. Many misconceptions have grown, some maybe not important, but in some cases having no awareness or the wrong ideas of what you have got or how it works could lead to problems of various severity.
The technology is fantastic but it is not without fault, just like any other technology it can go wrong. So let us remove these misconceptions and try to understand just where it can go wrong and how serious it may be.
First let us look at what SatNav is. We do know but do not really consider it in full. Now this is merely a loose use of words but many say they have GPS in their car. Well, yes they do, but they also have a full SatNav. This involves some method of obtaining position from orbiting satellites, some form of electronic map to put this position on, some software to navigate from here to there, and you may have engine sensor inputs to provide an inertial navigation back up when satellite signals are lost. Thats essentially your SatNav system.
It is just a circumstance that the positioning system is mostly GPS. This is just one Global Navigation Satellite System (GNSS). Others are developed or in development. GPS is just the most commonly used. If you have car SatNav, this, with the inertial back up, if you have it, is what you are using. GPS is also included in mobile phones.
This next makes me somewhat laugh. I have heard some claim they can get SatNav on their mobile phone in the cupboard under the stairs. I am deeply curious of what advanced technology achieves this. The signal from GPS satellites is line of sight. An obstruction will block any satellite it is in the way of. A broom cupboard will block the lot of them. Now the mobile can also be located by the cell network. Although not as accurate, defaulting to the cell network when GPS is lost is handy. But, I do not think this can be classed as SatNav. No satellites are being used. Thats the, er, advanced technology out of the way with.
So far it is wordage and a bit of a lack in awareness. The end result is that by some method you can get a position. If you happen to be off road and lose GPS it may be important to realise you have lost some accuracy. GPS could be 10m or better. The cell being 50m at best in urban areas, no great problem, but worse in rural areas, maybe a problem.
Another one. There are many who say with pride that they know how GPS works. Triangulation. I believe they fall for this because its a legacy from before GPS where control networks were surveyed in by measuring angles. A GPS receiver, specifically the antenna, which may or may not be attached to the box, is positioned by trilateration, using ranges. This was harder to achieve with accuracy in those older days.
Also, satellite pseudoranges are not measured directly, hence along with inaccuracies the term pseudo. They are determined from time differences and light speed, more correctly, the speed of electromagnetic waves as the GPS signal is in the radio or microwave bands, depending on who you listen to. The nearly 300 million m/sec assumed in range calculations is only valid in a total vacuum. Some of the GPS inaccuracies are due to varying light speed. Nanosecond accuracy is required. A thousandth of a second error (1millisec) equates to 200 miles or 300km. Not many realise the importance of such small times.
Now accuracy has been mentioned, this leads to my favourite but that is another story that can be found in GPS and SatNav. Pinpoint Accuracy Explained by the same author.
GPS and SatNav. Removing Misconceptions
The Global Positioning System (GPS), originally designed for military use, has, as it has developed, revolutionised the art or skill of getting from one place to another among the general user population. Its development in coverage and reliability along with other technologies has enabled reasonably cheap SatNav systems for general usage, in our vehicles, mobile phones and other applications. Because of its reliability and growing popularity I believe SatNav is becoming widely accepted but without due consideration as to what it is really about. Many misconceptions have grown, some maybe not important, but in some cases having no awareness or the wrong ideas of what you have got or how it works could lead to problems of various severity.
The technology is fantastic but it is not without fault, just like any other technology it can go wrong. So let us remove these misconceptions and try to understand just where it can go wrong and how serious it may be.
First let us look at what SatNav is. We do know but do not really consider it in full. Now this is merely a loose use of words but many say they have GPS in their car. Well, yes they do, but they also have a full SatNav. This involves some method of obtaining position from orbiting satellites, some form of electronic map to put this position on, some software to navigate from here to there, and you may have engine sensor inputs to provide an inertial navigation back up when satellite signals are lost. Thats essentially your SatNav system.
It is just a circumstance that the positioning system is mostly GPS. This is just one Global Navigation Satellite System (GNSS). Others are developed or in development. GPS is just the most commonly used. If you have car SatNav, this, with the inertial back up, if you have it, is what you are using. GPS is also included in mobile phones.
This next makes me somewhat laugh. I have heard some claim they can get SatNav on their mobile phone in the cupboard under the stairs. I am deeply curious of what advanced technology achieves this. The signal from GPS satellites is line of sight. An obstruction will block any satellite it is in the way of. A broom cupboard will block the lot of them. Now the mobile can also be located by the cell network. Although not as accurate, defaulting to the cell network when GPS is lost is handy. But, I do not think this can be classed as SatNav. No satellites are being used. Thats the, er, advanced technology out of the way with.
So far it is wordage and a bit of a lack in awareness. The end result is that by some method you can get a position. If you happen to be off road and lose GPS it may be important to realise you have lost some accuracy. GPS could be 10m or better. The cell being 50m at best in urban areas, no great problem, but worse in rural areas, maybe a problem.
Another one. There are many who say with pride that they know how GPS works. Triangulation. I believe they fall for this because its a legacy from before GPS where control networks were surveyed in by measuring angles. A GPS receiver, specifically the antenna, which may or may not be attached to the box, is positioned by trilateration, using ranges. This was harder to achieve with accuracy in those older days.
Also, satellite pseudoranges are not measured directly, hence along with inaccuracies the term pseudo. They are determined from time differences and light speed, more correctly, the speed of electromagnetic waves as the GPS signal is in the radio or microwave bands, depending on who you listen to. The nearly 300 million m/sec assumed in range calculations is only valid in a total vacuum. Some of the GPS inaccuracies are due to varying light speed. Nanosecond accuracy is required. A thousandth of a second error (1millisec) equates to 200 miles or 300km. Not many realise the importance of such small times.
Now accuracy has been mentioned, this leads to my favourite but that is another story that can be found in GPS and SatNav. Pinpoint Accuracy Explained by the same author.
RF Generators With regard to Prototype production
Electronic devices used for creating signals with transmission frequencies are done with the assistance of radio frequency generators, also known as RF generators. The way in which AM radios were created is originally the reason for the term “radio frequency.” Signal frequencies produced when we talk, also known by the term “audio frequencies,” tend to not go very far. Range was expanded by placing the audio frequencies of voice or music on top of a radio wave, which could be transmitted many miles. A radio frequency of 100 kilohertz can be accomplished by AM transmitters.
RF, or radio frequency, even when not equipment that is a radio, still indicates the transmission frequency. RF frequencies may be found in everyday items such as cell phones, which measure at is estimated at 900 megahertz, and the standard GPS is approximately 1.5 gigahertz. RF generators are needed in order to convert the audio frequency for each of these transmission mediums.
Signal is multiplied further up to the transmission frequency, which generates a low frequency of 44 kilohertz for broadcasting a digital signal from a satellite. By combining digital and transmission signals together, which were generated by the RF generator, you’re producing a modulated signal, which is then transmitted to the satellite. Any satellite home receiver works going the other way using this same concept. Signal generators will boost the broadcast received and convert it to a 44 kilohertz baseband frequency.
Requiring a substantial amount of power to reach the satellite, the RF generator can be utilized in broadcasting work. This equates to a generator that is large, costly, and requires a lot of power. Conversely, your satellite receiver uses a much lower-power generator, which is in turn, more affordable and smaller. In fact, for any system, whether it be satellite radio, cell phones, or FM radio, there are always a lot more receivers manufactured than transmitters. This generally requires that receiver manufacturers design their components fully to the the board level. Using modular components costs too much for these units which must be priced at their absolute least expensive to be able to compete in the market.
Fabrication of archetype units, which have the identical form and functionality as the end product, are produced by competing businesses often. Having the potential for being really expensive and taking up a lot of time, even a slight modification is highly challenging with this type of tactic. And changes are always required, regardless if the prototypes are very similar to earlier manufactured products. A better method is to start with a prototype unit constructed with off-the-shelf components. For example, if you are planning to try it, you’ll find it much easier to buy an all-purpose generator versus spending time developing your own RF generator.
This needs to be accomplished at the same time as the in-house generator layout, or it can be done as an initial measure in order to eliminate serious flaws associated with earlier designs. This will enable you to try out different alternative design paths right away. Instead of having the first look take two years, a prototype unit can be put together for managers and investors in only ninety days.