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#3420
by
X_RaY
on 01 Jun, 2018 14:55
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Jamie I do have a concern about your use of a circular coupler in the middle of the small end plate.
Exciting a cavity needs to generate travelling waves that move in opposite directions. This is normally achieved by using a sidewall coupler where the big end lobe E field strength is the highest. That point is 1/4 guide wave from the big end. As such when the coupler is excited, some of the energy propogates toward the big end being 1/4 guide wave away, gets a 180 deg flip and comes back to the coupler in phase with the exciting freq.
I have very little doubt that TE013 is being excited with the circular antenna at the small end because simulations show that it is TE013. Also, when adjusting the screws on the small end, the RL trace moves up and down - which generally means the cavity is resonating, not the system. The microwaves reflect off the small end and destructively interfere with the waves reflecting off the big end. This also requires moving the antenna up and down along the Z axis to find the best spot.
Jamie, may it be possible that your antenna placement in the middle of the small end works well with your own cavity (i.e. it indeed triggers a resonant TE013 mode) but not with some other aspect ratios like the cavity design just presented by TT (as you didn't find any TE013 mode with this cavity in a 2.4–2.5GHz sweep simulation for the antenna located at small end axis)?
The Eigen-frequencies of a cavity resonator is given from its dimensions. When a coupler is placed into the cavity its presence can push the resonant frequency a bit, depending on its shape. This effect does not change the Eigen-frequency spectrum much. Different kind of couplers are able to excite a Eigenresonance. Depending on the vectors field generated by the antenna the coupling factor changes. The Loop antenna used by Jamie is of course a good choice to excite TE01p modes, but if there is no Eigen-frequency solution of this kind within the bandwidth there is nothing to excite.
For the given dimensions TE012(~2 GHz) and TE013(~2.3 GHz) are much lower in frequency, TE014(~2.65GHz) is above the discussed band between 2.4 GHz and 2.5 GHz
The small end is only 13MHz above cutoff. Know from experience that neither Feko nor COMSOL properly handle cutoff in a tapered cavity where the small end is very close to cutoff. You may doubt that but it is the case.
When the cavity is built, will share the VNA scan showing there is resonance where it was predicted. Do hope that example will end the unquestionability of the resonance results from Feko and COMSOL when dealing with small ends that are just above cutoff.
There will be a few more unexpected design and build reveals as the build and test process moves forward. You see I have been here before and know the pathway.
It Is Time For The EmDrive To Come Out Of The Dark.
It is more likely that your calculation program cannot handle the CutOff condition. The FEA software solves the maxwell equations and was developed to calculate such problems correctly.
We already had this discussion some time ago.
I look forward to the results of your experiments.
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#3421
by
TheTraveller
on 01 Jun, 2018 15:09
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.........
It is more likely that your calculation program cannot handle the CutOff condition. The FEA software solves the maxwell equations and was developed to calculate such problems correctly.
We already had this discussion some time ago.
I look forward to the results of your experiments.
You expressed your opinion, which based on a lack of EmDrive experience is understandable. However you will learn that opinion is not reflected in experimental data.
Roger also once thought COMSOL told the truth, but found from experimental data that it did not. Which is why he developed another method to calc resonance in cavities with the small end close to cutoff. A method I copied.
It Is Time For The EmDrive To Come Out Of The Dark.
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#3422
by
meberbs
on 01 Jun, 2018 15:28
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.........
It is more likely that your calculation program cannot handle the CutOff condition. The FEA software solves the maxwell equations and was developed to calculate such problems correctly.
We already had this discussion some time ago.
I look forward to the results of your experiments.
You expressed your opinion, which based on a lack of EmDrive experience is understandable. However you will learn that opinion is not reflected in experimental data.
Roger also once thought COMSOL told the truth, but found from experimental data that it did not. Which is why he developed another method to calc resonance in cavities with the small end close to cutoff. A method I copied.
It Is Time For The EmDrive To Come Out Of The Dark.
You need to learn the difference between opinion and fact.
It is a fact that FEA programs have correctly calculated modes for every cavity tested in these threads (to within model fidelity to the actual build). Shawyer's methods are limited and the ones that have problems dealing with "cutoff" conditions, as well as generally being limited to only certain modes. Despite being asked repeatedly, you have never provided a cavity shape that experimentally resonates significantly differently than the FEA programs predict. Forgetting everything about propellantless thrust, such a finding would be revolutionary on its own.
You keep dispensing advice about RF systems, claiming things based on "experiment" when you have never even claimed to have done the experiments that would be required to support your assertions. When you disagree with people who obviously have RF backgrounds, while claiming that people who are running experiments need an RF engineer to tell them that they are doing it wrong, it is insulting. You clearly have no actual background yourself.
Please stop making unsupported and false assertions, and come back if you ever actually run an experiment to support your claims.
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#3423
by
bad_astra
on 01 Jun, 2018 15:45
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You expressed your opinion, which based on a lack of EmDrive experience is understandable. However you will learn that opinion is not reflected in experimental data.
It Is Time For The EmDrive To Come Out Of The Dark.
Care to show your experimental data?
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#3424
by
TheTraveller
on 01 Jun, 2018 15:59
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You expressed your opinion, which based on a lack of EmDrive experience is understandable. However you will learn that opinion is not reflected in experimental data.
It Is Time For The EmDrive To Come Out Of The Dark.
Care to show your experimental data?
Need to build this KISS thruster 1st. This time there will be plenty of build photos & videos as the project develops.
Going out tomorrow to buy most of the hardware. Build activity will start next week.
100W Rf amp is on order. Should be able to buy everything else needed from local suppliers. Do have a few bits & pieces from previous efforts.
Early day tomorrow chasing bits & pieces. Past my bed time. Nite, nite.
It Is Time For The EmDrive To Come Out Of The Dark
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#3425
by
meberbs
on 01 Jun, 2018 16:01
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Please stop making unsupported and false assertions, and come back if you ever actually run an experiment to support your claims.
Your opinion is your opinion.
And the facts I stated are facts. Tautologies are useless.
Never having built an EmDrive nor conducted experimental work with one does limit your experience base to form correct knowledge. So it is understandable you and others have issues.
Pot, Kettle, Black. You have not provided any evidence that you have ever built an emDrive either. What you claim to have built (without evidence) involved end plates not even being firmly attached, and was one of the most simplistic, poorly controlled force measurement setups done by anyone.
It Is Time For The EmDrive To Come Out Of The Dark
Actions are much greater than words. Every time you say things like this while still having provided no data, you are just reinforcing your hypocrisy. You have been claiming you would have something to show "soon" or "in a few months" for years. You don't get to say "soon" to excuse that statement.
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#3426
by
RonM
on 01 Jun, 2018 16:06
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It Is Time For The EmDrive To Come Out Of The Dark
You've been posting about your EM drive builds since 2015. Yes, it's time for you to show something. Pictures and videos of your test rig, data from tests, etc.
You expressed your opinion, which based on a lack of EmDrive experience is understandable. However you will learn that opinion is not reflected in experimental data.
It Is Time For The EmDrive To Come Out Of The Dark.
Care to show your experimental data?
Need to build this KISS thruster 1st. This time there will be plenty of build photos & videos as the project develops.
Going out tomorrow to buy most of the hardware. Build activity will start next week.
100W Rf amp is on order. Should be able to buy everything else needed from local suppliers. Do have a few bits & pieces from previous efforts.
Early day tomorrow chasing bits & pieces. Past my bed time. Nite, nite.
It Is Time For The EmDrive To Come Out Of The Dark
Really? You've been saying this for years and you still haven't built one.
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#3427
by
Monomorphic
on 01 Jun, 2018 16:54
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The coupler needs to be 1/4 guide wavelength from the big end plate and not 1/4 excitation wavelength from the big end plate. As the guide wavelength alters as the cavity diameter alters, it is not a straight forward measurement. Which is why the coupler Rf connector needs to be designed into a sliding arrangement that can be moved toward and away from the big end to optimise coupler efficiency and lowest VSWR without needing nor using an external 3 pot tuner.
Plus you may need to bend the antenna a bit and move it in and out a bit to get an even better position and coupler efficiency.
Here is a sweep using the 1/4 wavelength stub. I will try the half-loop next.
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#3428
by
X_RaY
on 01 Jun, 2018 20:09
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...
BTW I'll offer to visit Tajmar with a complete KISS thruster & test rig system and work with him & his team to repeat the rotary test rig demo in his lab.
I would be happy to see the result of your development at TU-Dresden for some tests. I also hope that the team there follows this conversation to notice your offer and accept.
cheers
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#3429
by
Monomorphic
on 01 Jun, 2018 21:26
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Here is a sweep using the 1/4 wavelength stub. I will try the half-loop next.
The half-loop showed the exact same modes as the 1/4 wavelength stub, only the half-loop antenna was more under-coupled (even though it was the same length as the stub). I'm not going to bother with pasting images of the E-fields or surface currents - they are the same as in the above image.
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#3430
by
Monomorphic
on 01 Jun, 2018 21:43
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X_Ray, would we call this mode at 2.456Ghz TE313?
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#3431
by
TheTraveller
on 01 Jun, 2018 22:46
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X_Ray, would we call this mode at 2.456Ghz TE313?
Jamie,
Thanks for doing this. It is TE013 at 2.453GHz as predicted by my spreadsheet as attached. Your resonance is shown at 2.455GHz or 2MHz higher than my value. Seems we agree.
Haven't used this spreadsheet for some time now. Will do some work on it as it will be released as part of the KISS thruster design & build package.
Note the very lengthened 1/2 guide wave lobe at the small end of your simulation. Exactually as predicted with a small end very close to cutoff, being 16MHz above cutoff. That may be a bit tight, so the small end dia may increase a bit to give future builders a bit of build tolerance to work with.
The wavy side wall eddy currents are caused by the coupler not being exactually at 1/4 guide wave from the big end. Which is why in the KISS thruster build, the coupler will be able to be moved closer or further away from the big end to achieve ideal coupler excitation vs travelling wave phase matching.
BTW in TE313 mode the small end is heavily cutoff with a cutoff freq of 2.672GHz. So any excitation needs to be above the cutoff freq.
It Is Time For The EmDrive To Come Out Of The Shadows
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#3432
by
WarpTech
on 01 Jun, 2018 23:15
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TheTraveller, you said you were looking for a bucket with proper dimension. It might be easier to 3-D print one or turn one from a wood log section.
I bought a copper ice bucket that has the right shape, but just a warning that these buckets are NOT spun. They are hand pounded or welded. Neither of the two I bought were symmetrical, very oblong in fact and not good for resonance. Jamie's method would work better.
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#3433
by
TheTraveller
on 01 Jun, 2018 23:29
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TheTraveller, you said you were looking for a bucket with proper dimension. It might be easier to 3-D print one or turn one from a wood log section.
I bought a copper ice bucket that has the right shape, but just a warning that these buckets are NOT spun. They are hand pounded or welded. Neither of the two I bought were symmetrical, very oblong in fact and not good for resonance. Jamie's method would work better.
Fair comment.
The form I'm going out today to buy is molded plastic, so I expect it to be very round. Do have 6 round hoop rings of various diameters that I will use to ensure it is round and to hold the 0.55mm Cu against the form while the butt joint is secured. The hoop rings will stay on the frustum to ensure it stays round and to give it additional strength / rigidity.
This is my 1st frustum fabrication using an internal form. Do expect the job will be made MUCH simpler and quicker using the internal form.
Using the hoop rings is a trick I learned from Dave, RfMwGuy. As attached.
BTW the frustum copper sheet will be highly polished BEFORE cutting it and wrapping it around the form. It is NOT easy to highly polish the inside of a built frustum. So please take note as highly polishing a flat sheet of Cu is fairly easy.
Will wrap the form with Cling Wrap to ensure the form does not scratch the highly polished Cu sheet.
It Is Time For The EmDrive To Come Out Of The Shadows
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#3434
by
Carl G
on 02 Jun, 2018 01:23
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Some notes. Only post in English on here. This is not a Chinese site. TheTraveller is historically copy and paste, rinse and repeat in his comments. Ignore him unless he provides some actual content like the rare occasion as above.
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#3435
by
TheTraveller
on 02 Jun, 2018 03:54
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Got most of what I need. Missing are 2 sheets of 101 Cu 0.55mm x 450mm x 900mm as the sheet metal supplier's guillotine was being serviced. Plus the 100W Rf amp, Li Ion 18650 Lit Ion batteries and a few connectors plus coax.
The black box is a USB freq gen that missed the trip with all my other gear to my partners lab/workshop in the EU.
However you should get the idea how this will come together and be a KISS thruster and KISS rotary test rig.
BTW the internal frustum form I bought is 300mm Bd x 180mm Sd x 280mm high. Will now make the necessary adjustments to the build frustum.
It Is Time For The EmDrive To Come Out Of The Shadows
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#3436
by
TheTraveller
on 02 Jun, 2018 04:49
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Updated overview.
It Is Time For The EmDrive To Come Out Of The Shadows
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#3437
by
Jim Davis
on 02 Jun, 2018 04:55
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However you should get the idea how this will come together and be a KISS thruster and KISS rotary test rig.
Just out of curiosity, why couldn't this have been done last year or the year before? What came together recently to allow this to be done this year?
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#3438
by
TheTraveller
on 02 Jun, 2018 05:07
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However you should get the idea how this will come together and be a KISS thruster and KISS rotary test rig.
Just out of curiosity, why couldn't this have been done last year or the year before? What came together recently to allow this to be done this year?
I engaged in a commercial contract with a mid size EU based aerospace company to develop a TRL 9 EmDrive thruster. That unit will soon be tested in space and commercial release is scheduled late 2019. More details AFTER the release.
I have always wanted to get back to building the KISS thruster and now my partners have given me the Green light. Well provisional Green light as I have a lot of restrictions on what I can show and tell about. My KISS plans are passed by them before I post them here and elsewhere.
Actually the delay was a good thing as I have a lot more experience to throw into building the thruster, the Rf system, how to tune the coupler, explaining how it works, etc.
It Is Time For The EmDrive To Come Out Of The Shadows
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#3439
by
TheTraveller
on 02 Jun, 2018 05:58
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Based on the form, the KISS thruster dimensions and predicted data are:
Bd: 300mm
Sd: 180mm
Len: 280mm
Mode: TE013
Freq: 2.282GHz
Cutoff: 2.031GHz
CufOff headroom: 251MHz
Qu: 48.6K
Force at 100W forward: 20.5mN
Specific Force: 0.205N/kWrf
Freq is outside the ISM S Band, so need to work on the dimension sets that the form can deliver. Can increase freq by reducing length but doing that increases the small end diameter, which causes the Df to drop, which drops the generated force.
Need to find the best compromise.
It Is Time For The EmDrive To Come Out Of The Shadows