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#2680 by SeeShells on 23 May, 2016 16:38
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First VNA results from my old TE311 frustum. Not very good, and physical tuning just seemed to make it worse. Physical tuning did nothing to affect the RL peak frequency, though it did have other effects at different frequencies not shown here. It also looks like I have two modes very near one another. I could remove the tuning section and solder on the small end-plate to see if that improves things, but I think it's best to move on to a new frustum.
Dual resonance mode is perhaps not a bad thing since the magnetron is wideband. Before you chuck it, try trimming back the monopole of re-orienting it at different angles. Secondary reflections can be a pain. Don't think its your tuning section, it would have moved an RL peak if it was.
You're good Dave. It makes a lot of sense.
Shell -
#2681 by SeeShells on 23 May, 2016 16:45
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First VNA results from my old TE311 frustum. Not very good, and physical tuning just seemed to make it worse. Physical tuning did nothing to affect the RL peak frequency, though it did have other effects at different frequencies not shown here. It also looks like I have two modes very near one another. I could remove the tuning section and solder on the small end-plate to see if that improves things, but I think it's best to move on to a new frustum.
Dual resonance mode is perhaps not a bad thing since the magnetron is wideband.
Good point. I'm going to run a number of tests on it before another frustum is ready. I need to get those two modes in the 2.445Ghz - 2.45Ghz range. Maybe I can try some dialectric inserts as well.
Is your magnetron coupled without any extra "parts" directly into the frustum? Do you have a spare launcher off an old magnetron end you can use? instead of the monopole? How long is your antenna probe for your VNA?
Shell -
#2682 by Monomorphic on 23 May, 2016 17:07
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First VNA results from my old TE311 frustum. Not very good, and physical tuning just seemed to make it worse. Physical tuning did nothing to affect the RL peak frequency, though it did have other effects at different frequencies not shown here. It also looks like I have two modes very near one another. I could remove the tuning section and solder on the small end-plate to see if that improves things, but I think it's best to move on to a new frustum.
Dual resonance mode is perhaps not a bad thing since the magnetron is wideband.
Good point. I'm going to run a number of tests on it before another frustum is ready. I need to get those two modes in the 2.445Ghz - 2.45Ghz range. Maybe I can try some dialectric inserts as well.
Is your magnetron coupled without any extra "parts" directly into the frustum? Do you have a spare launcher off an old magnetron end you can use? instead of the monopole? How long is your antenna probe for your VNA?
Shell
I use direct insertion of the magnetron like rfmwguy, only on side wall. I do have a spare launcher but need to see a close-up of the one you built to see how you connected the coax. The antenna probe is 3cm, with about two and a half feet of coax.
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#2683 by SeeShells on 23 May, 2016 17:20
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My antenna into the cavity. Directly and into the waveguides.First VNA results from my old TE311 frustum. Not very good, and physical tuning just seemed to make it worse. Physical tuning did nothing to affect the RL peak frequency, though it did have other effects at different frequencies not shown here. It also looks like I have two modes very near one another. I could remove the tuning section and solder on the small end-plate to see if that improves things, but I think it's best to move on to a new frustum.
Dual resonance mode is perhaps not a bad thing since the magnetron is wideband.
Good point. I'm going to run a number of tests on it before another frustum is ready. I need to get those two modes in the 2.445Ghz - 2.45Ghz range. Maybe I can try some dialectric inserts as well.
Is your magnetron coupled without any extra "parts" directly into the frustum? Do you have a spare launcher off an old magnetron end you can use? instead of the monopole? How long is your antenna probe for your VNA?
Shell
I use direct insertion of the magnetron like rfmwguy, only on side wall. I do have a spare launcher but need to see a close-up of the one you built to see how you connected the coax. The antenna probe is 3cm, with about two and a half feet of coax.
Added: ~30cm long and affords a wider BW into the cavity. Feed by coax from a maggie to waveguide to antenna to coax to frustum. Keeps the maggie off the frustum and the heat as well as the magnetic properties and a possable DC componet.
You may want to look at the DC component from your magnetron provided by your power supply, that could effect the frustum and provide a magnetic field on the frustum skewing results.
Shell
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#2684 by keithpickering on 23 May, 2016 19:45
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The Pendulum I would build
Confession: I'm not handy with tools. I couldn't possibly build the device I describe here. But maybe somebody could, or might at least incorporate some of these ideas.
1. The device is built on two platforms which both hang from an axle. The lower platform, below the axle, is for equipment. The upper platform, above the axle, is for an adustable counterweight. Ideally the lower platform should be as close to the axis as possible, which will reduce the mass of the counterweight (since the mass of the entire apparatus should be minimized).
The counterweight allows you to adjust the position of the center-of-gravity of the device. Ideally it should be just slightly below the axle. The closer to the axle it is, the less force is required to move the pendulum.
The major part of the pendulum is a triangular lattice, with the test article at the lower point of the triangle. The triangle should be easily capable of transmitting thrust force from the test article to the equipment platform with no strain deformation. The longer the distance from axle to test article, the greater the leverage the test article has to rotate the pendulum, and the smaller the force that can be measured.
2. AC electrical power is delivered to the rotating platform via three brushes on the axle (positive, neutral, ground). This powers the coolant pump and the RF source, and optionally any controlling or measuring device, such as a Raspberry Pi.
Here I assume that we're using a real, honest-to-god tunable RF source from a ham radio outlet or something similar. In that case, run a standard antenna coax from the transmitter to the antenna inside the test article. If you're using a magnetron I doubt you could get a coax waveguide to to work (but I've been wrong before). In that case, your best bet is probably a copper tube waveguide of appropriate resonant diameter.
3. The big bugaboo in the field so far is the possibility of thermal effects overwhelming any thrust. It is clear from various simulations that most of the energy in the frustum resonates in the narrow end. This implies that the narrow end heats more during operation, which would mean that the air around the narrow end becomes hotter and less dense. Then greater air pressure on the big endplate moves the frustum toward the narrow end, and hey! you've got thrust! (NOT!)
To avoid this issue, I would do two things. First, I would cool the test article with a glycol coolant loop. Cold glycol from the radiator would be routed around the narrow end (first) so that the narrow end cools the most. The loop then winds around the test article to the large end and returns to the pump and radiator, which ride on the equipment platform. Ideally, if you're putting 100W of RF into the test article, you want something close to 100W of heat coming out through the radiator.
Second, I would enclose the test article in a convection box (which is really an anti-convection box). The idea is that if any air currents do occur from heating of the test article, they would be trapped in the box and produce no net thrust. The box can be made of anything, although for best results it should be made air-tight. The box would need three pass-throughs: coolant in, coolant out, and RF in. All three should be as close to the middle of the box as possible.
And if you're making it air-tight anyway, there's certainly no reason you couldn't draw a vacuum in the box too. (That requires two more passthroughs, for valves.) Even a partial vacuum would go a long way to reducing convection effects -- and reducing criticism from Dr. Rodal ;) If you're doing a vacuum convection box, a coolant loop may not really be needed, although the test article would get hot in there. So you may want a heat-sink instead.
4. Measurement of thrust (if any) is done by means of a laser pointer on the ground and a mirror (M1) attatched to the underside of the equipment platform. (Naturally, a first-surface mirror should be used.) The laser is pointed directly upward so that its initial beam (R0) hits M1. As the pendulum rotates through an angle φ, the beam reflected from M1 (which we call the R1 beam) returns to the ground at angle 2φ. At this point, you can either measure the position of R1 and compute the angle; or, alternatively, you can arrange a second mirror (M2) on the ground to intercept R1 and return it back to M1 on the platform. This beam, R2, reflects off M2 at angle 2φ, goes back up to M1, reflects off M1 a second time and returns to the ground at angle 4φ.
5. The torque τ on any pendulum varies according to its mass m, length L from center of gravity to center of rotation, angle of rotation from vertical φ, and gravitational acceleration g. So:
τ = -m g L sin(φ)
Because the test article is firmly attached to the pendulum at distance L' from the center of rotation, it produces a torque τ'.
τ' = T L'
where T is the trust produced by the test article. When the device is turned on, the thrust produced by the test article is leveraged into torque and rotates the pendulum through angle φ until τ + τ' = 0 and the two torques balance. So the thrust produced is
T = m g L sin(φ) / L'
Since m, g, L, and L' are known at the time of construction, it only remains to measure angle φ.
6. The uncertainty of the measurement produced depends on many details of construction, but we can make some ballpark assumptions: start with mass of 10 kg, distance L of .01 m (thanks, counterweight!) and distance L' of 1 meter. Then, assume we're using M2 for double reflection, and that a laser pointer spot can be determined to the nearest 1 mm. Assume the final reflected beam travels 1.5 meters at angle 4φ where it is measured 1 mm from its initial position. Then 4φ = atan(1/1500) = .038 degrees, and φ = .0095 degrees; sin(φ) = 1.67e-4; and the smallest measurable thrust is
T = 10 * 9.8 * .01 * 1.67e-4 / 1 = 163 μN
Although this seems fully adequate, it could be improved by making the apparatus lighter, or by lengthening the lever arm of the test article (L' gets bigger), or by moving the center of gravity closer to the center of rotation (L gets smaller). It might also be improved by throwing the laser a longer distance before measuring (though of course the spot gets fuzzier).
Comments and suggestions are welcome. -
#2685 by Monomorphic on 23 May, 2016 19:53
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My antenna into the cavity. Directly and into the waveguides.
I'm referring to rfmwguy's VNA antenna setup. I believe he said you fabricated it. I tore down an extra identical magnetron I had and am curious how to best connect the coax.
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#2686 by X_RaY on 23 May, 2016 20:08
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https://forum.nasaspaceflight.com/index.php?topic=39004.msg1491956#msg1491956My antenna into the cavity. Directly and into the waveguides.
I'm referring to rfmwguy's VNA antenna setup. I believe he said you fabricated it. I tore down an extra identical magnetron I had and am curious how to best connect the coax.
This was shown by zellerium some times ago...
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#2687 by Monomorphic on 23 May, 2016 20:10
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RL sweep from 1Ghz to 3Ghz. One regular sweep and one with full mechanical tuning. Notice the differences in the traces is mainly at the higher frequency. Slowing the sweep seems to provide more precise results. I'm going to see if I can identify that high Q mode around 1.75Ghz using FEKO.
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#2688 by Monomorphic on 23 May, 2016 20:20
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https://forum.nasaspaceflight.com/index.php?topic=39004.msg1491956#msg1491956My antenna into the cavity. Directly and into the waveguides.
I'm referring to rfmwguy's VNA antenna setup. I believe he said you fabricated it. I tore down an extra identical magnetron I had and am curious how to best connect the coax.
This was shown by zellerium some times ago...
My magnetron is a little different. Will need to do some pretty major dissecting to gain access to the magnetron antenna - which is why I went with a 3cm monopole - it's basically the same thing except thicker and flattened at the end.
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#2689 by X_RaY on 23 May, 2016 20:27
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For me it looks like we are watching into the magnetrons cavity itself. Is it possible that the antenna can be connected when you remove the upper part with the cooler?
https://forum.nasaspaceflight.com/index.php?topic=39004.msg1491956#msg1491956My antenna into the cavity. Directly and into the waveguides.
I'm referring to rfmwguy's VNA antenna setup. I believe he said you fabricated it. I tore down an extra identical magnetron I had and am curious how to best connect the coax.
This was shown by zellerium some times ago...
My magnetron is a little different. Will need to do some pretty major dissecting to gain access to the magnetron antenna - which is why I went with a 3cm monopole - it's basically the same thing except thicker and flattened at the end.
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#2690 by Monomorphic on 23 May, 2016 20:31
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For me it looks like we are watching into the magnetrons cavity. Is it possible that the antenna can be connected when you remove the upper part with the cooler?
Yes, I think so. I can see the antenna when I look into the hole, but it is too far in to get a soldering iron on. This magnetron isn't very easy to disassemble. The rest of the unit is completely soldered shut. I will have to cut through the center of the thickest part - not easy. -
#2691 by JaimeZX on 23 May, 2016 20:58
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@frobnicat Even though a gnat weighs in at 2mg it takes more than 20uN of lift for it to fly. A torsional pendulum with fine enough wire can measure smaller than 20uN, even a DYIers (depending on the thickness, stiffness and length of the wire).
Shells - what is your plan for reducing gnat-thrust-related error in your test rig? I'm concerned that a zap-light would cause unwanted EM interference in the area.
Obviously an "air door" is out of the question.
To control fruit flies in our kitchen we put apple cider vinegar in a jar and cover it with perforated saran wrap; this attracts the flies which then drown in the vinegar. I'm not sure if this will work for gnats, but you would also need to time the placement of the trap; too soon and you would wind up attracting additional traffic to the area, too late and they won't have 'found' the trap.
A CONUNDRUM.
We may need to do a series of trap placement timing runs to determine the best sequence of events.
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#2692 by rq3 on 23 May, 2016 22:47
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First VNA results from my old TE311 frustum. Not very good, and physical tuning just seemed to make it worse. Physical tuning did nothing to the RL peak frequency, though it did have other effects at different frequencies not shown here. It also looks like I have two modes very near one another. I could remove the tuning section and solder on the small end-plate to see if that improves things, but I think it's best to move on to a new frustum.
I believe what you are seeing here is an artifact of the VNA, not a true representation of return loss. The VNA you are using is a digitized zero-IF receiver, and you're probably seeing aliasing from extreme over-drive of the front end of the receiver. -
#2693 by Monomorphic on 23 May, 2016 23:04
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This is pretty cool! I was able to identify the high Q mode at ~1.75Ghz as TM011 using FEKO. This told me my build was off by about 11Mhz. Using that info I identified the next mode as TM11x. And then the next as TE211.
I suspect that if I eliminate the tuning section and solder everything together, I can get within 2.445 - 2.45Ghz, as per simulations, with a much higher Q. This was also predicted by simulations a while back.
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#2694 by SeeShells on 23 May, 2016 23:36
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hmmm. I thought of adding a banana inside of the frustum and installing a grid for the bottom plate. Hey, free gnations.@frobnicat Even though a gnat weighs in at 2mg it takes more than 20uN of lift for it to fly. A torsional pendulum with fine enough wire can measure smaller than 20uN, even a DYIers (depending on the thickness, stiffness and length of the wire).
Shells - what is your plan for reducing gnat-thrust-related error in your test rig? I'm concerned that a zap-light would cause unwanted EM interference in the area.
Obviously an "air door" is out of the question.
To control fruit flies in our kitchen we put apple cider vinegar in a jar and cover it with perforated saran wrap; this attracts the flies which then drown in the vinegar. I'm not sure if this will work for gnats, but you would also need to time the placement of the trap; too soon and you would wind up attracting additional traffic to the area, too late and they won't have 'found' the trap.
A CONUNDRUM.
We may need to do a series of trap placement timing runs to determine the best sequence of events.
Shell
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#2695 by SeeShells on 23 May, 2016 23:42
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For me it looks like we are watching into the magnetrons cavity. Is it possible that the antenna can be connected when you remove the upper part with the cooler?
Yes, I think so. I can see the antenna when I look into the hole, but it is too far in to get a soldering iron on. This magnetron isn't very easy to disassemble. The rest of the unit is completely soldered shut. I will have to cut through the center of the thickest part - not easy.
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#2696 by Star One on 23 May, 2016 23:44
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Any relevance to this thread as this represents some new but also old thinking on the behaviour of particles in this particular case photons.
http://www.wired.com/2016/05/new-support-alternative-quantum-view/ -
#2697 by jmossman on 24 May, 2016 01:02
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This is pretty cool! I was able to identify the high Q mode at ~1.75Ghz as TM011 using FEKO. This told me my build was off by about 11Mhz. Using that info I identified the next mode as TM11x. And then the next as TE211.
Nice correlation.
I suspect that if I eliminate the tuning section and solder everything together, I can get within 2.445 - 2.45Ghz, as per simulations, with a much higher Q. This was also predicted by simulations a while back.
Out of curiousity, does FEKO show a monopole antenna as the best way to excite your target mode? If not, would swapping the monopole for the "preferred antenna" (and orientation) be a different/?better? method of verifying the modes/ReturnLoss/Q available within your cavity using the VNA? -
#2698 by rq3 on 24 May, 2016 01:11
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For me it looks like we are watching into the magnetrons cavity. Is it possible that the antenna can be connected when you remove the upper part with the cooler?
Yes, I think so. I can see the antenna when I look into the hole, but it is too far in to get a soldering iron on. This magnetron isn't very easy to disassemble. The rest of the unit is completely soldered shut. I will have to cut through the center of the thickest part - not easy.
I hope you folks aren't forgetting that a magnetron is, after all, a vacuum tube? Just like an old style cathode ray tube (CRT television picture tube). It's designed to run under hard vacuum, and to run HOT, internally.
Just because it doesn't look like a standard glass "fire bottle" doesn't mean it isn't one! -
#2699 by mwvp on 24 May, 2016 03:29
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Any relevance to this thread as this represents some new but also old thinking on the behaviour of particles in this particular case photons.
http://www.wired.com/2016/05/new-support-alternative-quantum-view/
Very relevant to me; I was/am researching actuation applications of parametric instabilities in electroactive polymer gels before the EM Drive distracted me. I can't get away from similarities. Last couple days I've watched a few video on Casimir, dark energy and inflation and find the dynamic Casimir effect experiment, modulating a microwave cavity with a sqid to produce particles, seems to be parametric instability/Faraday waves. And there are similarities to optical refrigeration and optomechanical excitation, which I believe involve the dynamics at work with the EM Drive.
Anyways, here are some great videos that illustrate the pilot-wave concept, even if they don't elucidate the quantum-vacuum as well. A play list featuring (of course) Yves Couder's classics:
For some reason, I can't get the you-tube playlist with the Couder vids to show up. If you want to see more, search you-tube for "Yves Couder". Its worth the bother.
Another video at a site with lots of eye-candy:
http://gfm.aps.org/meetings/dfd-2015/55f71c7b69702d060d750500
Thinking about the metaphor, the wave-tank is the vacuum. The droplets represent bosons and fermions. But how do you 'splash' the EM vacuum into boson or fermion droplets? Metaphors only go so far.
