Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1797917 times)

Offline SeeShells

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@rfmwguy or any that care to answer.

Everyone (almost) believes that the highest Q will produce the largest results, that's not quite true, that means there is evidence (Chinese tests) that a slight off tuned resonance or sweeping through a resonance mode can produce higher thrust values.

I'm asking because it will help develop my thinking on the next step of MW control and testing. I'm grasping here for thoughts and ideas of why that might be true.

Shell

EDIT: readability

Have we run a Meep simulation of the input signal being an oscillating signal from one frequency to another and back down again? I'm not even sure Meep can do that.

Perhaps, creating something like a square wave pattern would be ideal instead of sinusoidal.
A Magnetron naturally pulses and sprays all sorts of byproducts around 2.45 GHz. If I were to take another step, it would be to reduce power and spurious to see if the "junk" helps or hurts the cause.
I've thought of something like this...
http://www.ecnmag.com/articles/2011/05/ac-dc-power-supply-considerations-home-appliances

Offline SeeShells

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@rfmwguy or any that care to answer.

Everyone (almost) believes that the highest Q will produce the largest results, that's not quite true, that means there is evidence (Chinese tests) that a slight off tuned resonance or sweeping through a resonance mode can produce higher thrust values.

I'm asking because it will help develop my thinking on the next step of MW control and testing. I'm grasping here for thoughts and ideas of why that might be true.

Shell

EDIT: readability
FWIW, High Q and pure signals are where I've always tried to be, but this thing is different somehow. Before putting time/money at signal purity, CW and highest Q possible, I'm just trying to test a basic concept. There is a good chance that I'll stop there if I have null results and pass the hat to someone else. First, we take baby steps with whatever we have, then tweak it...mainly to test other's claims. So my advice is take a swing at it without over-engineering/over-thinking it. The smallest amount of positive results can lead to modifications, such as top-hat tuning, reduced power/cleaner signal, etc.
You're right but I'm thinking after this very basic run. I sometimes feel that I'm pounding a nail with a large rock this first test, when I need a small hammer.

Shell - have you made any progress in getting a VNA from local hams?   I think a VNA may be a very useful piece of test gear, particular as the EMDrive locks in to freq/modulation and/or changes mode; particular if the data can be captured at a high enough data rate.    Just FYI, here are a couple of links to a (more or less) affordable 2 port VNA.

http://miniradiosolutions.com/   -the mini VNA tiny will go to 3Ghz

http://www.hamradio.com/detail.cfm?pid=H0-013596  HRO has them for about $575.   

**Context Switch**
"Mote in God's Eye" - one of the books I re-read every few years.   Maybe the best science fiction ever - perhaps excluding Heinlein.  I still want to be Sir Kevin Renner when I grow up.

Herman-W5HLP
My old business partner was K8MBV and one major geek.

No luck on the VNA (still looking) and I wish I had the extra to buy it and a few other things but I'll make due.

Shell

Offline rfmwguy

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A Magnetron naturally pulses and sprays all sorts of byproducts around 2.45 GHz. If I were to take another step, it would be to reduce power and spurious to see if the "junk" helps or hurts the cause.

What is your guesstimate for the date of your first test ?
Still the end of July, but I'm getting the donor microwave today, then the new copper screen later in the week.

Offline WarpTech

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Your equation for Pout is wrong.

Pout = d/dt(0.5 m v2) = m v a + 0.5 v2 dm/dt

When you leave out dm/dt, it results in your over-unity paradox. In order to have acceleration, dm/dt cannot be zero. The kinetic energy gained can never exceed the change in mass, dm * c2.
Todd

While I understand the physics I would like to offer an example that seems to violate this.   An electrodynamic tether uses solar electrical power to energize a long cable that is normal to the geomagnetic field.   DC power flows through the tether and then back through space with the help of charged particles. 


I'm not sure what you mean by that...

Quote
The Lorentz force on the tether, F = B X I * L causes the tether to accelerate....


If it is accelerating, it is either gaining mass or losing mass, therefore dm/dt =/= 0. There is no "other" way to accelerate anything. The force equation must be balanced by an equal and opposite force.

Quote
...Considering the geomagnetic field to be constant for sake of argument and also if the current is constant, the acceleration of the tether will be constant.   

The geomagnetic field strength does vary around the Earth but we will ignore that.   The geomagnetic field strength also doesn't change when the observer is moving.    And of course dM/dt = 0.    How is this apparent paradox resolved?

Both of these assumptions are incorrect and will probably lead to the paradox. The Geomagnetic field, like any other magnetic field, will vary depending on the inertial reference frame. In the case of an accelerating "non-inertial" reference frame, there is no argument to make these assumptions anymore. You must consider the relative motion between the source and the tether. A changing magnetic flux will generate an EMF that will oppose the current and the changing flux. The current "I" will not be constant.
Todd

Offline deltaMass

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I see that Shawyer's "latest paper"  8)  contains a specification of 2/3 N/W. This corresponds to a breakeven velocity of 3 m/s, mechanically an easily attainable value. Can we therefore expect Shawyer to branch out into the power generation field in the near future?
Just a little follow-up here to answer a question that some may be asking: "What is a reasonable value of Newtons/Watt such that overunity could be achieved with a rotary device in a terrestrial lab?"

It's a mechanical limitation. An aggressive spec. is something like 1,000 gee with a 1 metre radius arm. That's about 1,000 rpm and a tangential velocity of about 100 m/s. That in turn calls for a minimum k-value of
0.02 N/W.
Keep that figure in mind.
@kdhilliard has been kind enough to point out to me that the correct figure here should be 0.01 N/W, because the power breakeven velocity is what's important from a practical point of view. To recap:
Energy breakeven velocity = 2/k
Power breakeven velocity = 1/k

The power breakeven proof is not difficult:
Pout = d/dt(0.5 m v2) = m v a = Pin when v := vp
So vp = Pin / (m a) = Pin / F = Pin / (k Pin) = 1/k
QED

Your equation for Pout is wrong.

Pout = d/dt(0.5 m v2) = m v a + 0.5 v2 dm/dt

When you leave out dm/dt, it results in your over-unity paradox. In order to have acceleration, dm/dt cannot be zero. The kinetic energy gained can never exceed the change in mass, dm * c2.
Todd
Ahem. You do realise that the system under discussion here might be a little EmDrive mounted at the periphery of a wheel?  Is the implication that maybe the spokes get fatter or thinner to produce the dm/dt?  8)

When you write "In order to have acceleration, dm/dt cannot be zero" I feel like I'm Bob In Wonderland. I cannot believe that you can write that with a straight face. Look, in the nicest possible way, I think that's complete nonsense.

Here's something for your "dm/dt" to chew on. The discrepancy between Ein and Eout grows with time. Take my toy model parameters and calculate the dm/dt value you predict.

There's a rather nice irony here.
In the Woodward universe, one cannot have propellantless propulsion without dm/dt, and this leads to over-unity.
In the Todd Desiato universe, dm/dt is demanded from a propellantless drive in order to avoid over-unity.

Let me come at this a different way. The over-unity condition occurs when considering only the input and output energy budgets. No differentiation. How will you shoehorn your dm/dt into that?
Here's a reminder of how that goes:

k := F/Pin in Newton/Watt
v = a t = (F/m) t
Ein = Pin t
Eout = 0.5 m v2

From the first 2 equations we get
t = (m v) / (k Pin)

At breakeven, Ein = Eout  and v := v0
or
2 Pin m v0 / (k Pin) = mv02
so
v0 = 2/k

Show me please where dm/dt figures in there

ETA Note that 'm' cancels in that final equation, so that v0 is independent of m, as shown. Isn't that a problem when trying to shoehorn in a dm/dt term?

ETA2 Don't make the mistake of thinking that relativistic corrections make enough of a difference to matter here, when we're talking about velocities of around 100 m/s. Is that what you're in fact doing?
« Last Edit: 07/08/2015 09:09 PM by deltaMass »

Offline SeeShells

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For rfvp in response to Post #3648

The generic DIY-er can easily and cheaply make or have made a frustum projected to resonate at 2.45 GHz.  Can he/she design and build the circuitry necessary to phase lock it to an external reference or injection lock it to the frustum?  Or mechanically lock the frustum to the magnetron?  When hooked to the frustum, which of the many resonant frequencies does it lock to?  How does the DIY-er know?  If no thrust is detected with the first mode, how does he test the other resonant modes?  If the magnetron is injection locked to the frustum how does the experimenter tune the magnetron outside the bandwidth of the thruster to determine if the thrust is related to resonance or an artifact of the test apparatus?
----

***I'm trying to secure the equipment needed to do just that. I wish I still had my business as I had fun toys like Spec Analysers and O-Scopes and Power Supplies and and and. Miss it.
Controlling a 1000 w magnetron is not that hard, there are ways to make it a full wave 100% duty cycle and control the bandwidth and power out and even frequency lock it to the frustum cavity. What is the fly in the ointment is that thrusts have been measured with the magnetron unaltered and stuck onto the Frustum. I built a lot of flexibility into this first design and tried to stabilize the testing rig for repeatability. Simply it's hitting it with a rock first to see if it hollers, then get a set of micrometers to fine tune. To me it's like putting a firecracker into a can to see it fly when you should just tap it on the side, but it's data that needs to be gotten and I've said it before we need data. Not as much as CERN thank God.

-----
Put a tuning slug on the frustum.  How does that affect the Q and mode(s) of resonance?  How does the DIY-er know?   When tuning, what is the feedback to the person doing the tuning, so that he knows what is going on? 

*** You insert a simple loop probe the cavity, monitor the frequencies. Simple stuff.

-----
Don’t get me wrong; I am VERY supportive of DIY-ers who have the initiative to try to ‘make it happen’; I am just pessimistic as to their chances of success using a free-running magnetron and not as sanguine as you about the triviality of ‘just tune the frustum and allow the magnetron to injection lock to it ‘ solutions to the known problems.  I am aware that magnetrons HAVE been used, reportedly with success.  I am also aware that one reason that the reported success of the magnetrons is greeted with so much skepticism is that with a magnetron it is difficult to know your test environment with precision.  The good news is that if the magnetron is hooked to the frustum and unambiguous thrust appears and disappears in concert with the magnetron being turned on and off, victory can be declared, and we can turn the data over to the theorists to figure out why.  Of course the theorists would probably like to know such details as which mode was being excited, the exact frequency that was responsible for the thrust, the Q at that mode, the power being injected within the bandwidth of the frustum and so on, but that could probably be determined post hoc.  The bad news would occur if thrust DIDN’T occur.  Especially if the frustum had a relatively high Q.  Would the principle be falsified?  Operating in the wrong mode?  Spectral output of the magnetron places little or no energy into the bandwidth of the frustum?  What next?
-------

****See my first comment on a raw magnetron radiation spewing malstrom into the cavity. If we really knew what was the best configuration and the theory was solid we wouldn't need to start off with a worse case. And it may be this is the key.

It needs to be tested in this configuration... data we need more data. What happens if we control the frequency, power and the lock to give the best Q and poof it doesn't work? I built a lot of flexibility into this first frustum to start the step by step detailed analysis of power, frequencies, harmonics, different physical cavity lengths, antenna placements, dipole to helical to modified helical generating 1/4 wave backfires, waveguide insertion, dual slaved magnetrons into a wave guide locked to the cavity resonance, different end plate configurations small and large.

I'm doing this test not to have fun as much as we need data, we need to know detailed step by step piece by piece analysis. Also and i posted this here before and it may be corny but i don't care.
Because I choose to dream.
 
I believe we are at a cusp of our growth on this ball of mud and if we don't evolve from this tiny seed called earth we may perish and never know the glorious heights that await us, or the true challenges of a universe that has no bounds. Yes, I dream, for humanity.
-------

As for SeeShells and the other builders:  I don’t know where you are geographically or what access you have to microwave stuff in your ‘day job’, but if you are in the Northern VA/DC/Suburban MD area I MAY be able to get you access to such desirable widgets as a vector network analyzer, precision sig gens (including vector signal generators that in addition to the standard am/fm/cw allow you to generate signals with an arbitrary output spectrum), power meters, spectrum analyzers, and power amplifiers in the 100+ watt range.   I am retired, but there is some possibility, considering the implications of real microwave thrusters, that my old employer would give me access, on a not to interfere basis, to any or all of the above.  I haven’t asked.  Yet.

****Sorry you're on the other side of the country from me, (Colorado) but thanks so much.


Offline frobnicat

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...

Your equation for Pout is wrong.

Pout = d/dt(0.5 m v2) = m v a + 0.5 v2 dm/dt

When you leave out dm/dt, it results in your over-unity paradox. In order to have acceleration, dm/dt cannot be zero. The kinetic energy gained can never exceed the change in mass, dm * c2.
Todd

While I understand the physics I would like to offer an example that seems to violate this.   An electrodynamic tether uses solar electrical power to energize a long cable that is normal to the geomagnetic field.   DC power flows through the tether and then back through space with the help of charged particles.  The Lorentz force on the tether, F = B X I * L causes the tether to accelerate.   Considering the geomagnetic field to be constant for sake of argument and also if the current is constant, the acceleration of the tether will be constant.   The geomagnetic field strength does vary around the Earth but we will ignore that.   The geomagnetic field strength also doesn't change when the observer is moving.    And of course dM/dt = 0.    How is this apparent paradox resolved?

Specifically when pushing on an external DC field, a relative velocity (of device wrt source of field) will naturally impact on "efficiency" (i.e. thrust/power). On your example, F constant, B constant, I constant, but P=U*I and U depends on the relative velocity as per the counter electromotive force. The faster the device, the higher the tension U to overcome this counter electromotive force (while maintaining a stationary I). So higher velocity => higher U => higher P : at constant thrust it requires more power the faster device goes. Same can be said for a car on a road, or a plane in air. In all those cases, the momentum is exchanged between a device and a massive medium that defines a natural rest frame.

What is the natural massive medium that defines a natural rest frame for a device in deep space ? Quantum vacuum is theoretically and experimentally (so far) invariant, it defines no natural rest frame. Saying that we can push on vacuum like a propeller push on water or like a tire pull on road or like an electrodynamic tether thrusts on geomagnetic field is a bad analogy (energy wise). If it is possible to push on quantum vacuum, the analogy, for the medium, would be more like an infinity of conveyor belts crisscrossing in space at all possible relative velocities, and our "car" jumps from belt to belt, always choosing a belt at close velocity. Obviously, most of the kinetic energy gained by such "rest frame jumping" is given by the belts (which, as Rodal put it, implies a mutable vacuum), not by the mechanism that drives the jumping.

Given the fundamental inertial frame invariance of quantum vacuum, making it a "medium" completely different from others (asphalt, water, air, geomagnetic field, gravity field from a massive body...) this "crisscrossing conveyor belts" analogy seems less misleading. It is coherent with what I grock (not much) of White's QV conjecture : I have seen nowhere that the virtual particles were "harvested" (start of interaction of virtual particle with device's fields) at a relative velocity that would change as the device gained velocity (relative to a start of journey). Unlike air with a propeller for instance, where the particles (air molecules) are clearly harvested at greater relative velocities against the thrust vector as a plane gained more velocity (relative to start).

Oh, I see the EMF argument is made already by WarpTech.

Sidenote : I'm not endorsing the view of a mutable vacuum, nor that of "gravinertial transistors" à la Woodward, just saying that both seem to implicitly use a kind of crisscrossing conveyor belt model of space, and have "free energy" as a natural consequence. Edit : also see Stochastic electrodynamics for a similar line of thinking (not endorsing either).
« Last Edit: 07/08/2015 08:26 PM by frobnicat »

Offline BL

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In response to SeeShells' Post #3877

“It needs to be tested in this configuration... data we need more data. What happens if we control the frequency, power and the lock to give the best Q and poof it doesn't work? I built a lot of flexibility into this first frustum to start the step by step detailed analysis of power, frequencies, harmonics, different physical cavity lengths, antenna placements, dipole to helical to modified helical generating 1/4 wave backfires, waveguide insertion, dual slaved magnetrons into a wave guide locked to the cavity resonance, different end plate configurations small and large.”

Sounds like a real, genuine engineer who knows what they are doing.  Need a lab tech?

Only semi-serious.  Got home issues that would prevent me from leaving Northern VA  for an extended period.  If those could be resolved would be willing to follow directions and help any way I could.  FWIW:  I would be willing to work cheap.  I. e. free.

If my situation change before your testing is complete I'll let you know.

Offline WarpTech

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Show me please where dm/dt figures in there
...

Ein = Pin * t = c2 * integral(dm/dt)*dt
Eout = 0.5 * (m + integral(dm/dt)*dt) * v2

break even occurs when v = c, Ein = Eout

(1/m(t))*integral(dm/dt)*dt = (1/2)(v/c)^2 * 1/(1 - (1/2)(v/c)^2) = 1 at v = c.



Todd

« Last Edit: 07/08/2015 09:28 PM by WarpTech »

Offline frobnicat

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In other words, until a high Q frustum is tested with a stable, high power source whose frequency, power, and even output spectrum can be controlled at will, with wide enough frequency coverage to allow excitation at ALL resonant modes, it will not be possible, except for blind squirrel luck, to either confirm OR reject the existence of the generic EmDrive principle. 
...

Sound arguments, fair conclusion. But you seem to imply in your posts that the risk is more in false negatives (a working principle and experimenters failing to record thrust from it) rather than false positives (a bogus principle and experimenters failing to report null results, down to a certain sensitivity). So far we don't have much negatives (true or false). We will see with the numerous builder runs to come if it is changing... but as a sceptic my fear is in the difficulty of not getting any signal from pumping watts or kilowatts in a system built on the cheap for maximum sensitivity and with eagerness to see something, assuming there is no real propellantless effect and only spurious couplings with surroundings.

Offline SeeShells

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In response to SeeShells' Post #3877

“It needs to be tested in this configuration... data we need more data. What happens if we control the frequency, power and the lock to give the best Q and poof it doesn't work? I built a lot of flexibility into this first frustum to start the step by step detailed analysis of power, frequencies, harmonics, different physical cavity lengths, antenna placements, dipole to helical to modified helical generating 1/4 wave backfires, waveguide insertion, dual slaved magnetrons into a wave guide locked to the cavity resonance, different end plate configurations small and large.”

Sounds like a real, genuine engineer who knows what they are doing.  Need a lab tech?

Only semi-serious.  Got home issues that would prevent me from leaving Northern VA  for an extended period.  If those could be resolved would be willing to follow directions and help any way I could.  FWIW:  I would be willing to work cheap.  I. e. free.

If my situation change before your testing is complete I'll let you know.

That makes me feel very good and before this thing is over who knows where it will lead. Thank you for your offer.


Shell

PS: Good luck on your home situation.

Offline ElizabethGreene

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A Magnetron naturally pulses and sprays all sorts of byproducts around 2.45 GHz. If I were to take another step, it would be to reduce power and spurious to see if the "junk" helps or hurts the cause.

This is correct.  Magnetrons throw dirty RF.

Building a Microwave Filter requires the same skills as building an EmDrive resonator.  Is it worth filtering the magnetron output to get the output where you want it?

You can clean up the magnetron output for cheaper than moving to solid state.

In increasing order of cost/complexity:
-Swap out your power supply for something more stable
-Actively cool the magnetron
-Filter and impedance match the output
-Use a microcontroller to dynamically tune the magnetron.

Tuning is the wrong word here.  It's moving the peak of the magnetron output around by changing the magnetic field.  Wrap some turns of wire around the magnet coils, measure the post-filter field strength with a micro-controller, and reduce or increase the current to the magnet bias coils with a feedback loop.

This last bit is essentially what MasinaElectrica is doing, just with the micro-controller and filter feedback intelligence instead of manually moving the peak.

I've looked for digestible resources on constructing traveling wave amplifiers to make solid state oscillators a realistic possibility.  I have, to date, failed.

Offline flux_capacitor

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In other words, until a high Q frustum is tested with a stable, high power source whose frequency, power, and even output spectrum can be controlled at will, with wide enough frequency coverage to allow excitation at ALL resonant modes, it will not be possible, except for blind squirrel luck, to either confirm OR reject the existence of the generic EmDrive principle.
A Magnetron naturally pulses and sprays all sorts of byproducts around 2.45 GHz. If I were to take another step, it would be to reduce power and spurious to see if the "junk" helps or hurts the cause.

Ok then, why no DIYer plan to use a klystron?
Until now, we have two microwave power sources for planned experiments:

* magnetrons from microwave ovens, which are high-power (700-2000W) but also "dirty" (frequency-drifting wide-band spectrum)
* solid-state WiFi amps, which are a cleaner source but very low power (0.1-20W)

Klystrons are low or high power (depends of the model, from milliwatts to tens of kilowatts) and produce a very clean, highly stable and narrow-band output frequency. So for very high-Q cavities, notably with spherical end plates, why nobody thinks about using a klystron?
Some high-power klystrons are on sale on eBay, mainly from Varian. IMHO they should be considered as an alternative to the noisier magnetrons, for high-Q cavities with spherical end plates. What do you think?

EDIT: see this 3.5kW C-band (6GHz) Varian klystron for example.
« Last Edit: 07/08/2015 09:57 PM by flux_capacitor »

Offline ElizabethGreene

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Ok then, why no DIYer plan to use a klystron?

Having watched ebay for these, I have the following observations.
-Most are old, and the seller knows nothing about them.  I,e. operating frequency.
-I've been unable to find an old varian catalog to decode the part numbers.
-The high power units can be very expensive.

On the last point, the last one I bookmarked was a 2.5KW C band unit.  It sold for $1/watt.

Offline flux_capacitor

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-I've been unable to find an old varian catalog to decode the part numbers.
Just found this: http://www.cpii.com/docs/related/37/VA936-VKC7936%20C-Band.pdf

Question: What is exactly the "instantaneous 40 MHz bandwidth at –1dB points"?
« Last Edit: 07/08/2015 10:17 PM by flux_capacitor »

Offline deltaMass

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...

Show me please where dm/dt figures in there
...

Ein = Pin * t = c2 * integral(dm/dt)*dt
Eout = 0.5 * (m + integral(dm/dt)*dt) * v2

break even occurs when v = c, Ein = Eout

(1/m(t))*integral(dm/dt)*dt = (1/2)(v/c)^2 * 1/(1 - (1/2)(v/c)^2) = 1 at v = c.



Todd
Sorry, but I don't understand the final line of algebra. Please expand.

Offline rfmwguy

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-I've been unable to find an old varian catalog to decode the part numbers.
Just found this: http://www.cpii.com/docs/related/37/VA936-VKC7936%20C-Band.pdf

Question: What is exactly the "instantaneous 40 MHz bandwidth at –1dB points"?
Believe this refers to 1db bandwidth of signal, meaning signal is broadband, 40 mhz wide unmodulated. What is missing here is spurious and harmonic specs. look for a spurious spec...

Offline mwvp

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For rfvp in response to Post #3648
...
The generic DIY-er can easily and cheaply make or have made a frustum projected to resonate at 2.45 GHz.

Who's sanguine now? Not I on that point. I don't do metal fab well. Tried to interest some mechanically-inclined local hackers here around Chicago a month back, none seemed enthused.

Can he/she design and build the circuitry necessary to phase lock it to an external reference or injection lock it to the frustum?  Or mechanically lock the frustum to the magnetron?  When hooked to the frustum, which of the many resonant frequencies does it lock to?  How does the DIY-er know?  If no thrust is detected with the first mode, how does he test the other resonant modes?  If the magnetron is injection locked to the frustum how does the experimenter tune the magnetron out side the bandwidth of the thruster to determine if the thrust is related to resonance or an artifact of the test apparatus?

Like everything, one learns by reading, research, forums, trial and error, or has experience. I guess I take a lot for granted, having worked on mil and commercial radio systems in my career and having read a lot of ham-lit. As well as built a lot of home-brew gadgets.

Specifically, AFAIK particular modes are excited by hitting the right frequency and injecting either an E or H field with the appropriate method at the appropriate point, matching impedance. A mode diagram was posted here a while back. Then trial and error.

Servos can tune screws, insert dielectrics, piezo elements can warp thin metal plate.

To figure out the mode, one could insert steamed CoCl soaked paper, or let thermal paper blacken where the field is highest. Better would be to insert several tiny E or H probes going to mixers to determine the intensity and phase at interesting points.

I understand a magnetron can be tuned by the supply voltage, which needs to be stabilized without the ripple present in cheap oven supplies.

I was thinking pulsing the magnetron and measuring the vibration would be an interesting test, even if not conclusive and keep average power low, and the cavity from heating and detuning.

Put a tuning slug on the frustum.  How does that affect the Q and mode(s) of resonance?  How does the DIY-er know?   When tuning, what is the feedback to the person doing the tuning, so that he knows what is going on?

I suspect a tuning slug will adversely affect performance. They're little screws, not giant bolts though. I gather you know from looking at waveguides, gunplexers, TV tunners, radar detector, radios with cavity filters I've stripped, et. And books and trade journal articles, which I have somewhere that discuss why and how to use 2 screws for waveguide tuning. I forget.

For feedback a small field probe is apparently used by Nasa and Shawyer. I was thinking if a couple points are tapped, an FM discriminator (see Wikipedia) could be made that would servo mechanically tuning the frustrum, provided the loop-bandwidth was low-pass filtered to eliminate the (IMHO good) Sagnac-doppler shifts responsible for forces and motion from the bad thermal detuning.

Of course, the way to find out if that's right or effective to to test it.

I have a vague memory of fixing dozens of HF servo-driven antenna tuners decades ago, after air force techs mangled them. Some of the stuff I worked on I can still remember well enough to roughly draw a schematic of, like a UHF ultrasonic TDR pulser. But not those tuners.

I am just pessimistic as to their chances of success using a free-running magnetron and not as sanguine as you about the triviality of ‘just tune the frustum and allow the magnetron to injection lock to it ‘ solutions to the known problems.

I'm not sanguine at all. If I was, perhaps I'd be working on one and not chatting about it. However, if offered a choice between:

1. Use a cheap low-power ss amp and attempt to measure uN forces
2. Use an expensive and fragile high-power ss amp and measure low mN to high uN forces
3. Use a cheap, robust magnetron and measure mN forces

I would pick 3. YMMV.

The bad news would occur if thrust DIDN’T occur.  Especially if the frustum had a relatively high Q.  Would the principle be falsified?  Operating in the wrong mode?  Spectral output of the magnetron places little or no energy into the bandwidth of the frustum?  What next?

To falsify Shawyer, I suppose you need to replicate closely what he did and how he did it, same with NWPU or Nasa. I think one could tell by network analysis and sniffing spots in the resonator whether the right mode and energy is present.

(I’d use an external circulator just for fun though.). 

Yes, very nice to have. I hear they are non-trivial to design and build.

a TWTA/solid state amp driven by a precision sig gen—where you KNOW what is going on--sound much more attractive to ME.  YMMV.

Uh, yea. I wish I had a million dollars worth of test equipment and plumbing around, as I've had in the past. I got a frequency counter, grid-dip meters, diode detectors & stuff in my junk box. Oh, and perhaps I could use my wifi dongle as a spectrum analyzer, with some software.

As for SeeShells and the other builders:  I don’t know where you are geographically or what access you have to microwave stuff in your ‘day job’, but if you are in the Northern VA/DC/Suburban MD area I MAY be able to get you access to such desirable widgets as a vector network analyzer, precision sig gens (including vector signal generators that in addition to the standard am/fm/cw allow you to generate signals with an arbitrary output spectrum), power meters, spectrum analyzers, and power amplifiers in the 100+ watt range.   I am retired, but there is some possibility, considering the implications of real microwave thrusters, that my old employer would give me access, on a not to interfere basis, to any or all of the above.  I haven’t asked.  Yet.

Ah, must be nice. Too bad I'm around Chicago  :'(

Offline rfmwguy

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A Magnetron naturally pulses and sprays all sorts of byproducts around 2.45 GHz. If I were to take another step, it would be to reduce power and spurious to see if the "junk" helps or hurts the cause.

This is correct.  Magnetrons throw dirty RF.

Building a Microwave Filter requires the same skills as building an EmDrive resonator.  Is it worth filtering the magnetron output to get the output where you want it?

You can clean up the magnetron output for cheaper than moving to solid state.

In increasing order of cost/complexity:
-Swap out your power supply for something more stable
-Actively cool the magnetron
-Filter and impedance match the output
-Use a microcontroller to dynamically tune the magnetron.

Tuning is the wrong word here.  It's moving the peak of the magnetron output around by changing the magnetic field.  Wrap some turns of wire around the magnet coils, measure the post-filter field strength with a micro-controller, and reduce or increase the current to the magnet bias coils with a feedback loop.

This last bit is essentially what MasinaElectrica is doing, just with the micro-controller and filter feedback intelligence instead of manually moving the peak.

I've looked for digestible resources on constructing traveling wave amplifiers to make solid state oscillators a realistic possibility.  I have, to date, failed.
I am going with dirty power first. There are many combline bp filters, but at this stage, maybe its the chaos of em that makes it tick...too early to say for sure imho.

Offline flux_capacitor

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-I've been unable to find an old varian catalog to decode the part numbers.
Just found this: http://www.cpii.com/docs/related/37/VA936-VKC7936%20C-Band.pdf

Question: What is exactly the "instantaneous 40 MHz bandwidth at –1dB points"?
Believe this refers to 1db bandwidth of signal, meaning signal is broadband, 40 mhz wide unmodulated. What is missing here is spurious and harmonic specs. look for a spurious spec...

Ok. Should this "40 MHz instantaneous bandwidth" be a problem, other CPI klystrons are more compact and have a narrower instantaneous bandwidth, like those from their Communications & Medical Products Division:
- VKS2200 Series (bandwidth 8-9 MHz / power 1000-2500 W / S-band freq. 1.700-2.660 GHz / classic version)
- VKS2509 Series (bandwidth 8-9 MHz / power 2000-2500 W / S-band freq. 1.700-2.230 GHz / Multi Stage Depressed Collector, more efficient version)

Those S-band klystrons seem ideal for EmDrive research: compact form factor, very narrow band, high power (kilowatts) and operating frequency similar to 2.45GHz oven magnetrons, so cavities built for them are about the same size.

CPI also makes higher power (10 to 500 kW) S-band CW klystrons in their Microwave Power Products Division. A bit high for DIYers…
They also make pulsed versions. So far I'm not aware of any EmDrive test using a pulsed MW source instead of CW. I saw that for big high-end klystrons, output power even scales up to megawatts!

I am going with dirty power first. There are many combline bp filters, but at this stage, maybe its the chaos of em that makes it tick...too early to say for sure imho.
Sure. Paul March talked about that possibility. But Shawyer also said the dirty magnetrons are good for flat end plates, but high-Q cavities with spherical end plates require a cleaner source of microwaves.
« Last Edit: 07/08/2015 11:33 PM by flux_capacitor »

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