OK, so now we are agreed on the very small number that would have to be measured to tell the difference between 65Km and 65.1 Km, can you calculate the change (drop) in transmitter power output that would be required to make the receiver at 65Km think it was at 65.1Km?
Is it possible for a transmitter to maintain the stability of its power output to bette than this, and by how much better does it need to be to make such a source of error insignificant?
What does this imply in terms of the stability of the voltage supplies to the transmitter?
It might be worth pointing out that an error of only 1% in the measurement of transmitted power would produce an error of 2km in distance estimation at 100km. This 1% corresponds to a 0.04dB measurement accuracy, which is round about the limit of modern RF Power measurement accuracy.
Absolute power accuracy may not be essential but decreasing the error by a factor of ten (this corresponds to 0.004dB and I don’t think you can buy a meter that will go anywhere near this accuracy) would still give an error of 200m. Still, producing a transmitter with this level of power stability would require a power supply with voltage fluctuations of better than 0.005%. Not quite sure what sort of high power supply could achieve that stability. “Expensive but achievable”? What evidence is there of this?
The radiation pattern of transmitting and receiving arrays would also need to be known to within a similar accuracy. The pattern could not be calculated but would need to be measured under all possible local conditions of weather, temperature and humidity. Depending upon what frequency the system operated on, the radiation pattern could be affected significantly (when you’re talking in terms of tiny fractions of a dB) by rain on a nearby flat roof, a passing truck or a sudden, local cloudburst.
Furthermore, an antenna at ground level and its feeder system would be subject to actual physical disturbance by wind (and even by vibrations from passing traffic). This will affect its pointing angle and the match it presents to the transmitter – hence the actual level of transmitted power. Again, a variation in reflection coefficient from 0.1 to 0.09 would represent a change in transmitted power in the order of 0.05dB. Who could rely on better than that? Can this be irrelevant and / or eliminated?
If spread spectrum is used, then the bandwidth of the system would introduce matching variations over the band. Can we be sure that the system characterisation could eliminate such variations reliably?
Many of these factors could, of course, be averaged out (ultra ultra low bandwidth measurement, effectively) but just how long would you want to wait for the measurement result to emerge? And then, how are you going to characterise the receiving equipment, in every possible location it may arrive at, to the same degree of accuracy?
Any Engineer or Physicist would know that there is a limit to how much money and time you can throw at any measurement problem. Even CERN acknowledge that there are limits to what can be achieved in Geneva.
At the outset the question was about atmospheric propagation and I understood the transmitter and receiver to be terrestrial.
Somewhere along the line discussion of space vehicles crept in.
For terrestrial propagation there is a big difference in propagation characteristics over land and sea.
So where, in gneneral terms, are the TX and Rx located?
A back of a fag packet calculation tells you that, if there is 0.04dB error (that is about 1%), the resulting error in distance measurement, at 100km, of 2km.
which is round about the limit of modern RF Power measurement accuracy.
Analytic calculations tend to be more straightforward than numerical ones; it is very easy to check it but it seems right to me.
You don't spell it out but your figures seem to imply that a power measurement error of 0.013dB wold give an error of 0.1 km in 65km (yes?). Is that so very different from my simple result?
Why does 10W of uncertainty in 1kW of RF power upset you? Power, as with many quantities has measurement error proportional to its value.
Your description of errors as being "transient" assumes that you are measuring over at least a year, if you want to attempt to cancel seasonal fluctuations. Is that really the serious intention?
A GPS satellite receiver will give you 10m accuracy about a minute after switch on. Who can supply all this data for analysis at the "processing stage"? You can't monitor all these variables - and the actual accuracy of monitoring is again limited.
If you have no evidence of actual figures and cannot justify your claims of possible improvement in all the areas so far mentioned then the system cannot work.
To improve simple SNR by a factor of 3dB, you need to analyse,in broad terms, for twice as long. Powers of two will rapidly build up and give you a ridiculous required time for your analysis.
A transmitter needs to be matched to its load. This is very difficult to achieve over a wide bandwidth. The result is always a 'frequency response' with undulations in the order of 1dB for most applications. This is adequate for most applications (digital and analogue). I'm not sure where a breed of transmitter/ matching network / feeder / matching network / antenna will come from for which the frequency response is much better than that. Don't tell me - it's been accounted for or it's a trivial problem. It is a relevant factor.
A transmitter at an altitude of 20km would be on a plane or balloon. They both move about a lot. How would the variations be measured in order to eliminate them? GPS, perhaps. Why not cut out the middle man and just use GPS?
200m - 300m underground?! What's all that about. If you mean under water then your available frequency bands are a bit limited. Submarines can use just a few tens of kHz whilst submerged.
Also, you don't say where the receiver will be. There would be even more problems in characterising the conditions at the receiver - which will be changing, presumable, as it moves about, over ground of varying conductivity, air of varying temperature, past obstacles that will cause multipath propagation / reflections / diffraction. Are these all going to be "accounted for"?
Yes - DATA is what you need and, to get enough data to average out all the effects mentioned and others requires a long time and a lot of monitoring points to gather. Even if you could process it all instantly, you still have to wait for it to build up. As has been said many times, it boils down to bandwidth / time. What time do you think you would need in order to reduce inherent variations, some of them of 'several' dB to a total of what would have to be in the order of 0.001dB?
One grouse you have had is the lack of numbers in the objections. Well, now you have some but you still say that any problem can be overcome.
You still haven't told the forum whether you have any practical Engineering (or Physics) experience which can qualify you to decide on the relevance of the many practical implications. Are you, in fact, any more than a software developer? Some of my best friends (and family) are software developers but they would not make wild assertions on engineering matters.)
... limit of modern RF Power measurement accuracy...?
Do I understand your scheme to be that you are continually measuring the Tx power and somehow communicating this to the receiver, which your statement seems to imply?
And by Tx power I mean the actual radiated power, not the input power to the Tx system.
It really is a huge software simulation we're discussion, in which "resources" can be increased by adding a couple of zeros to the end of the value of a variable.
We can filter out long term fluctuations with a filter having microsecond impulse response and measure all the parameters we could think of with the same speed.
It sounds fun but it has wasted quite a lot of my time as I thought it was a serious, physical, application we were discussing. No wonder you were shy about declaring your qualifications situation.
So as not to and on an ad hominem, I might ask what this statement is supposed to mean:
"Given the patterns, echos can be disregarded for trilateration purposes, but could be used to fill in gaps due to noise. So, they may prove more useful than a hindrance at the processing stage."
afik, multipath propagation has never been a positive aid to any form of radio transmission system. Unless you include Radar, of course, and even there, clutter is a damned nuisance.
But, in a simulation / game anything is possible.
It reflects very poorly on the project, which is totally unsubstantiated without some backup of referenced facts or track record. Do you think you could actually sell it to anyone without either of those two?
What more do you need than trilateration of a spread spectrum signal in the sub-1000Hz range?
Two questions:
1. What are the potential sources of loss?
2. What is the expected accuracy?
Stop making up your own questions.