Author Topic: EM Drive Developments - related to space flight applications - Thread 4  (Read 934508 times)

Offline TheTraveller

but in all cases, they are doing it wrong and should be using 2 ports to measure cavity resonance. We have yet to see anyone do it this way.
Todd

So Dr. Ray Kwok is also wrong?
« Last Edit: 08/07/2015 08:03 pm by TheTraveller »
It Is Time For The EmDrive To Come Out Of The Shadows

Offline Rodal

  • Senior Member
  • *****
  • Posts: 5911
  • USA
  • Liked: 6123
  • Likes Given: 5494
The testiness of this current discussion aside, I am genuinely interested in the reason why there is a difference between these two Q value viewpoints.

As far as I can gather, @TT is saying, "How they did it". @rfmwguy is saying "How it should've been done." and @tleach is saying "This is how it seems to fit McCulloch's formula."

Which BTW, McCulloch doesn't define how to measure Q. He simply redefines it as the number of bounces (reflections), in the time it takes the photon to decay to zero. So that's not even the same definition of the Q that is being kicked around here. @tleach was trying to bridge that gap.

What I conclude is, the experimenters may or may not be measuring it consistently using the same methodology, but in all cases, they are doing it wrong and should be using 2 ports to measure cavity resonance. We have yet to see anyone do it this way.
Todd

Thank you for summarizing the case, clarifying the problem and providing a conclusion.  Well done. 

Offline X_RaY

  • Full Member
  • ****
  • Posts: 834
  • Germany
  • Liked: 1108
  • Likes Given: 2384
The testiness of this current discussion aside, I am genuinely interested in the reason why there is a difference between these two Q value viewpoints.

In the EMDrive world measuring unloaded Q via S11 return loss at the 3bd down bandwidth is how it is measured.

So say Shawyer, Prof Yang, Eagleworks and Prof Tajmar.

I have to agree at this point, BUT for that you MUST know the coupling factor between your generator-antenna-cavity, only for the coupling factor K=1 the full 3dB BW is usable. 

 
PDF: copy and past for translation somewhere ;)
« Last Edit: 08/07/2015 08:28 pm by X_RaY »

Offline rfmwguy

  • EmDrive Builder (retired)
  • Senior Member
  • *****
  • Posts: 2166
  • Liked: 2684
  • Likes Given: 1124
The testiness of this current discussion aside, I am genuinely interested in the reason why there is a difference between these two Q value viewpoints.

As far as I can gather, @TT is saying, "How they did it". @rfmwguy is saying "How it should've been done." and @tleach is saying "This is how it seems to fit McCulloch's formula."

Which BTW, McCulloch doesn't define how to measure Q. He simply redefines it as the number of bounces (reflections), in the time it takes the photon to decay to zero. So that's not even the same definition of the Q that is being kicked around here. @tleach was trying to bridge that gap.

What I conclude is, the experimenters may or may not be measuring it consistently using the same methodology, but in all cases, they are doing it wrong and should be using 2 ports to measure cavity resonance. We have yet to see anyone do it this way.
Todd
It would be oh-so-simple to resolve this. Send a closed, resonant cavity to NIST, the British Standards Institute (BSI) or other reputable body with ONLY 1 PORT and have them measure Q. After they ask where the other port is, they would ask, why would you want to measure a closed cavity system with only one port? IOW, an open system, like an antenna, only needs a single port. A resonant cavity needs 2 to properly measure Q.

I'll stand by this (un)controversial position regardless of the previous experimenters. Quite frankly, I'm surprised at their apparent lack of RF familiarity. This is not a slam, it is a known fact that RF engineering is taught less, practiced less and is receeding into the background of companies and institutions. Reason? Computer science boom and the "plug and play & throw away" mentality of electronics in general.

Open system = 1 port
Closed system (frustum) = 2 port

Case closed. Its the last I will post on this matter at NSF.

Offline X_RaY

  • Full Member
  • ****
  • Posts: 834
  • Germany
  • Liked: 1108
  • Likes Given: 2384
The testiness of this current discussion aside, I am genuinely interested in the reason why there is a difference between these two Q value viewpoints.

As far as I can gather, @TT is saying, "How they did it". @rfmwguy is saying "How it should've been done." and @tleach is saying "This is how it seems to fit McCulloch's formula."

Which BTW, McCulloch doesn't define how to measure Q. He simply redefines it as the number of bounces (reflections), in the time it takes the photon to decay to zero. So that's not even the same definition of the Q that is being kicked around here. @tleach was trying to bridge that gap.

What I conclude is, the experimenters may or may not be measuring it consistently using the same methodology, but in all cases, they are doing it wrong and should be using 2 ports to measure cavity resonance. We have yet to see anyone do it this way.
Todd
It would be oh-so-simple to resolve this. Send a closed, resonant cavity to NIST, the British Standards Institute (BSI) or other reputable body with ONLY 1 PORT and have them measure Q. After they ask where the other port is, they would ask, why would you want to measure a closed cavity system with only one port? IOW, an open system, like an antenna, only needs a single port. A resonant cavity needs 2 to properly measure Q.

I'll stand by this (un)controversial position regardless of the previous experimenters. Quite frankly, I'm surprised at their apparent lack of RF familiarity. This is not a slam, it is a known fact that RF engineering is taught less, practiced less and is receeding into the background of companies and institutions. Reason? Computer science boom and the "plug and play & throw away" mentality of electronics in general.

Open system = 1 port
Closed system (frustum) = 2 port

Case closed. Its the last I will post on this matter at NSF.
???
It may be much more easy to measure with a calibrated(!) 2 port system...
But one can derive the S-parameter based on a 1 port measurement!
In doubt use a circulator and a load..
« Last Edit: 08/07/2015 09:54 pm by X_RaY »

Offline flux_capacitor

  • Full Member
  • ****
  • Posts: 666
  • France
  • Liked: 806
  • Likes Given: 1059
I think the reason why all the EmDrive experimenters to date (Shawyer, Yang, Brady/White, Tajmar) measured the unloaded Q (or Qu) as the S11 1 port return loss (resonant frequency at maximum return loss dB -3dB off this peak return loss dB value) is not because they would not know or don't want to use the more official S22 2-port method, but because the Qu they get from the S11 1-port method is a suitable value that can be plugged readily into their equations to calculate and predict theoretical thrust. Obviously the S22 2-port method does not provide a value for Q usable to calculate thrust, at least according to their equations.
« Last Edit: 08/07/2015 08:42 pm by flux_capacitor »

Offline X_RaY

  • Full Member
  • ****
  • Posts: 834
  • Germany
  • Liked: 1108
  • Likes Given: 2384
I think the reason why all the EmDrive experimenters to date (Shawyer, Yang, Brady/White, Tajmar) measured the unloaded Q (or Qu) as the S11 1 port return loss (resonant frequency at maximum return loss dB -3dB off this peak return loss dB value) is not because they would not know or don't want to use the more official S22 2-port method, but because the Qu they get from the S11 1-port method is just a suitable value that can be plugged readily into their equations to calculate and predict theoretical thrust. Obviously the S22 2-port value does not provide a value usable to calculate thrust, at least according to their equations.
transmission measurement is S12 or S21

Offline flux_capacitor

  • Full Member
  • ****
  • Posts: 666
  • France
  • Liked: 806
  • Likes Given: 1059
I think the reason why all the EmDrive experimenters to date (Shawyer, Yang, Brady/White, Tajmar) measured the unloaded Q (or Qu) as the S11 1 port return loss (resonant frequency at maximum return loss dB -3dB off this peak return loss dB value) is not because they would not know or don't want to use the more official S22 2-port method, but because the Qu they get from the S11 1-port method is just a suitable value that can be plugged readily into their equations to calculate and predict theoretical thrust. Obviously the S22 2-port value does not provide a value usable to calculate thrust, at least according to their equations.
transmission measurement is S12 or S21

Ok thanks but you know what I meant ;)

Offline WarpTech

  • Full Member
  • ****
  • Posts: 1380
  • Do it!
  • Vista, CA
  • Liked: 1431
  • Likes Given: 1904
but in all cases, they are doing it wrong and should be using 2 ports to measure cavity resonance. We have yet to see anyone do it this way.
Todd

So Dr. Ray Kwok is also wrong?

I see nothing incorrect about what Dr. Kwok said. He said "Resonators". An antenna is a resonator and so is a cavity. One is an open system, the other is a closed system. The preferred methods are different at a "National Standards" level, according to @rfmwguy. While I agree 100% that the experimenters to date have consistently used the S11 method, that does not mean it is the "standard" way to do it. You are arguing that "In the EM Drive world" this is how it's done. Perhaps this is true, but is no less true that this is NOT the "standard" way to do it.

Stop arguing about it and accept that fact please. You're driving everyone bonkers with your obstinance and defense of obvious incongruences. I do not follow others. I make mistakes, try to understand learn from them and forge my own path and from what I've seen, that is how most of us here operate.
Todd
« Last Edit: 08/07/2015 08:53 pm by WarpTech »

Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2380
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 3111
  • Likes Given: 2672
I'll provide as much clear clean precise data as I can from my tests. That is my goal. There is no bad Data.

What theorists and non-theorists do with it by massaging it, reformulating it, how they plug it into those theories is beyond my control, but the Data rules here in this level of the EMDrive's development.

Back to //lurking//

Shell

Offline Flyby

  • Full Member
  • ***
  • Posts: 387
  • Belgium
  • Liked: 451
  • Likes Given: 48
Just a question regarding the Q measurement :
Even if we know that the Q's are/were measured in the wrong way, wouldn't it be wise to continue with the faulty system, in order to make all those test comparative?

If measurement standards are changed now to the correct method, all the data we have up till now becomes inaccurate or no longer useable, no?
One can question the validity of the previous information bits that have been gathered, but this sure will not help... throw it all overboard then? ???

Offline X_RaY

  • Full Member
  • ****
  • Posts: 834
  • Germany
  • Liked: 1108
  • Likes Given: 2384
Just a question regarding the Q measurement :
Even if we know that the Q's are/were measured in the wrong way, wouldn't it be wise to continue with the faulty system, in order to make all those test comparative?

If measurement standards are changed now to the correct method, all the data we have up till now becomes inaccurate or no longer useable, no?
One can question the validity of the previous information bits that have been gathered, but this sure will not help... throw it all overboard then? ???
Does everyone knows about the inner impedance of a oven magnetron?
If it is still ~50 Ohm there is no problem, the antenna coupling is as good in as out. 2 port measurement is equal to second port out at 50 Ohm...
In the 2 port case you have 2 times 50 Ohm(simple case) of out coupling means
1/50+1/50=25 Ohm
 Thats the difference, nothing else (with respect to the coupling factor of each single antenna).
1/Q_eff=1/Q_int+1/Q_ext
If Q_ext(ernal) is known, whats the problem to derive Q_int(ernal) based on the measurement data  ???
S-parameter (of a calibrated system) at each antenna(impedance) is all you need to derive the unloaded Q.  It does'nt matter if 1 or 2 antennas will be used.
« Last Edit: 08/08/2015 06:58 am by X_RaY »

Offline Ricvil

  • Full Member
  • *
  • Posts: 146
  • Liked: 98
  • Likes Given: 60
All this discussion about Q is relevant if the expression of the force on total system ( cavity +microwave source) is correct.
Any closed cavity can suffer of a  non null net force produced by a electromagnetic field inside it acting on its HOLE INTERNAL SURFACE, but the source of the EM field is under force too, and MUST be accounted too.
No expression until now, shows the force calculated on entire surface, or take the source of the EM fields into account simultaneously.

Offline deltaMass

  • Full Member
  • ****
  • Posts: 955
  • A Brit in California
  • Liked: 671
  • Likes Given: 275
Q = f / deltaF
where deltaF is the frequency spread between lower and upper -3 dB points.
I think the differences discussed stem from how that -3 dB is measured, no?

Offline rfcavity

  • Member
  • Posts: 37
  • Liked: 46
  • Likes Given: 0
Q = f / deltaF
where deltaF is the frequency spread between lower and upper -3 dB points.
I think the differences discussed stem from how that -3 dB is measured, no?

If this is true then Q should not be used for any kind of thrust estimation or calculation. This kind of Q-factor is a human construct to facilitate easy discussion about simplified performance of RF/microwave things, with some sort of consensus of how to measure it reached 60 years ago (more or less, as demonstrated by this thread). It is essentially distilling the whole spectrum measurement into 3 points. It's very difficult to believe that this would produce better thrust estimation than utilizing the full integrated frequency spectrum of stored energy within the cavity.

In short, Q in this case is just an aspect of a design that should be used to make high level engineering decisions about multiple designs. It should not be used as a direct input to try and find quantitative values of physical phenomena.

Offline X_RaY

  • Full Member
  • ****
  • Posts: 834
  • Germany
  • Liked: 1108
  • Likes Given: 2384
Q = f / deltaF
where deltaF is the frequency spread between lower and upper -3 dB points.
I think the differences discussed stem from how that -3 dB is measured, no?
For a 1 port measurement may be.
http://forum.nasaspaceflight.com/index.php?topic=38203.msg1414228#msg1414228

Offline tleach

  • Member
  • Posts: 78
  • Berthoud, CO
  • Liked: 75
  • Likes Given: 105

@rfmwguy

"Thermal tests done including 5 minute run at 30% power, which is what I'll use for fulcrum test."  So you're actually putting in 30% of 900W which would be approximately 270W.

And then there's the conversion of electrical energy into microwave energy. If we assume that wikepedia is correct, a 900W microwave oven magnetron should run with approximately 64% efficiency. 

https://en.wikipedia.org/wiki/Microwave_oven#Heating_efficiency

That means you're magnetron is only putting 172.8W of energy into your frustum.  I'm officially revising my force prediction (based on my v3 spreadsheet and a projected S12 Q factor of 7000) down 43.41 mN. 

Sorry :-)
« Last Edit: 08/08/2015 04:10 pm by Chris Bergin »
T. Thor Leach

Offline frobnicat

  • Full Member
  • ****
  • Posts: 518
  • Liked: 500
  • Likes Given: 151
Not coming from the RF world, I wonder why this whole discussion about Q can't settle on Q=2*π*energy_stored/energy_dissipated_per_cycle as a standard. Out of curiosity, isn't it possible to switch off a RF source fast enough (a few cycles) and get this Q value by observing only the time constant of the decay of amplitude with a minimally invasive probe ?

BTW, not wanting to sound insistent but there is no answer to my questions about the relation of Q and "losses per round trip" (in the context of a linear resonant set up). If I am making a mistake by thinking "number of bounces" when hearing Q, then I'm not the only one : Think of it like the number of times a photon bounces inside a mirrored cavity. A clarification might be useful.

Offline WarpTech

  • Full Member
  • ****
  • Posts: 1380
  • Do it!
  • Vista, CA
  • Liked: 1431
  • Likes Given: 1904
Not coming from the RF world, I wonder why this whole discussion about Q can't settle on Q=2*π*energy_stored/energy_dissipated_per_cycle as a standard. Out of curiosity, isn't it possible to switch off a RF source fast enough (a few cycles) and get this Q value by observing only the time constant of the decay of amplitude with a minimally invasive probe ?

BTW, not wanting to sound insistent but there is no answer to my questions about the relation of Q and "losses per round trip" (in the context of a linear resonant set up). If I am making a mistake by thinking "number of bounces" when hearing Q, then I'm not the only one : Think of it like the number of times a photon bounces inside a mirrored cavity. A clarification might be useful.

My conjecture on this would be that, a small cone angle will cause more bounces and a higher Q. However, my feeling is that as the wave propagates from the small end to the big end, it is reflecting off the side walls. Each reflection off the side walls imparts a tiny bit of momentum to the frustum. So the more bounces off the side walls (not the end plates) will produce more thrust. This means that a slower group velocity, bouncing over a longer period of time, would give higher thrust. This leads to the idea that the frustum should be shaped more like a trombone with a long throat. But... none of the theories so far support this idea, but none have tried either.
Todd

Offline Rodal

  • Senior Member
  • *****
  • Posts: 5911
  • USA
  • Liked: 6123
  • Likes Given: 5494
Not coming from the RF world, I wonder why this whole discussion about Q can't settle on Q=2*π*energy_stored/energy_dissipated_per_cycle as a standard. Out of curiosity, isn't it possible to switch off a RF source fast enough (a few cycles) and get this Q value by observing only the time constant of the decay of amplitude with a minimally invasive probe ?

BTW, not wanting to sound insistent but there is no answer to my questions about the relation of Q and "losses per round trip" (in the context of a linear resonant set up). If I am making a mistake by thinking "number of bounces" when hearing Q, then I'm not the only one : Think of it like the number of times a photon bounces inside a mirrored cavity. A clarification might be useful.

My conjecture on this would be that, a small cone angle will cause more bounces and a higher Q. However, my feeling is that as the wave propagates from the small end to the big end, it is reflecting off the side walls. Each reflection off the side walls imparts a tiny bit of momentum to the frustum. So the more bounces off the side walls (not the end plates) will produce more thrust. This means that a slower group velocity, bouncing over a longer period of time, would give higher thrust. This leads to the idea that the frustum should be shaped more like a trombone with a long throat. But... none of the theories so far support this idea, but none have tried either.
Todd
Todd, but the axial force component due to the side walls equals Sin[theta]*SideWallForce, where theta is the cone half-angle.  For theta = 0 ( a cylinder) the axial component due to the SideWallForce is Sin[0]*SideWallForce=0, it is zero no matter how large is the SideWallForce.  For small theta, the SideWallForce axial component is very low.  So, even if one grants you that the SideWallForce may be larger for small cone angle, the axial component is small.  Comments?
« Last Edit: 08/08/2015 12:02 am by Rodal »

Tags: