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#2720
by
TheTraveller
on 25 May, 2016 08:22
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#2721
by
mikegem
on 25 May, 2016 12:41
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X-ray or whom-ever might know,
what happens between the filament and the anode in the diagram above. Is it an arc or is it more ordered than that, some sort of plasma. I ask because it seems logical that it should transmit all the output power of the maggie. I understand that the frequency is generated by the epicycles that the electrons move in (corralled by the magnetic field between the permanent magnets) until they are grounded, the difficulty I am having is understanding how all this can happen without loss of the vacuum or melting of the filament.
No arc, no plasma, just electron flow from filament to anode, modified by the imposed magnetic field. See:
http://www.radartutorial.eu/08.transmitters/Magnetron.en.html for a brief explanation of normal magnetron operation. Arcs & plasmas can happen, but only as failure modes.
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#2722
by
Monomorphic
on 25 May, 2016 12:53
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No arc, no plasma, just electron flow from filament to anode, modified by the imposed magnetic field. See:
This is a good image showing the probe surrounded by an insulator. It's very hard to get to that probe to attach the coax (for VNA) without having to cut through fairly thick solid copper and steel.
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#2723
by
Monomorphic
on 25 May, 2016 14:33
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HDPE rod arrived. Plus my spectrum analyser arrives on Friday. Here are a few images showing how that is going to work, as well as the VNA antenna - while I had the emdrive opened up.
I need to find the plastic connectors NASA used for their HDPE inserts. Hopefully that's something easily available at lowes.
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#2724
by
D_Dom
on 25 May, 2016 16:04
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Attending Space Tech conference in Pasadena today. Many space qualified electronics vendors exhibiting here. If anybody wants me to find HE for flight worthy experiments I can ask around. Working off my phone, will check back in here occasionally, PM me.
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#2725
by
Monomorphic
on 25 May, 2016 17:22
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TUNING WORKS!
The HDPE insert was the key. Tuning the frustum is now as simple as tuning a church organ. I'm now in that magnetron sweet spot of 2.445Ghz - 2.45Ghz, when before I was at 2.457Ghz. It looks like I have the ability to tune over nearly 20Mhz.
EDIT: tuning is closer to 12Mhz, not 20Mhz.
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#2726
by
Eusa
on 25 May, 2016 18:37
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TUNING WORKS!
The HDPE insert was the key. Tuning the frustum is now as simple as tuning a church organ. I'm now in that magnetron sweet spot of 2.445Ghz - 2.45Ghz, when before I was at 2.457Ghz. It looks like I have the ability to tune over nearly 20Mhz.
If only your frustum had spherical ends...
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#2727
by
Monomorphic
on 25 May, 2016 21:14
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TUNING WORKS!
The HDPE insert was the key. Tuning the frustum is now as simple as tuning a church organ. I'm now in that magnetron sweet spot of 2.445Ghz - 2.45Ghz, when before I was at 2.457Ghz. It looks like I have the ability to tune over nearly 20Mhz.
Good job, Jamie!. This wider RL BW will allow the mag to focus right where it needs to be. The other side of the coin is the Q is much lower, since the 3dB points on the RL curve are ~20+ MHz. To narrow this up, all you need to do is reduce the length of the insert and retune center. There's probably a magic balance between Q and proper mag operation. That's the fun kind of stuff I enjoy working to resolve.
I'm showing Δf at -3dB as 3.2Mhz. With center frequency at 2.448Ghz that gives me a Q factor of 765. That's better than Tajmar and Cal Polytech and about 1/2 Yang.
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#2728
by
Monomorphic
on 25 May, 2016 21:24
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TUNING WORKS!
The HDPE insert was the key. Tuning the frustum is now as simple as tuning a church organ. I'm now in that magnetron sweet spot of 2.445Ghz - 2.45Ghz, when before I was at 2.457Ghz. It looks like I have the ability to tune over nearly 20Mhz.
Good job, Jamie!. This wider RL BW will allow the mag to focus right where it needs to be. The other side of the coin is the Q is much lower, since the 3dB points on the RL curve are ~20+ MHz. To narrow this up, all you need to do is reduce the length of the insert and retune center. There's probably a magic balance between Q and proper mag operation. That's the fun kind of stuff I enjoy working to resolve.
I'm showing Δf at -3dB as 3.2Mhz. With center frequency at 2.448Ghz that gives me a Q factor of 765. That's better than Tajmar and Cal Polytech and about 1/2 Yang.
Are you measuring 3dB from notch depth or insertion?
This is how I did it.
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#2729
by
Monomorphic
on 25 May, 2016 21:33
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OK, this is off RL peak and I was referring to 3dB below insertion. This is why I wrote in my test report that we need to standardize. Either way is fine, Yang and EW were reporting on a couple of different methods at one time.
Forgive me for not knowing, but what's the difference between insertion and peak? 20Mhz is huge and off the chart shown here. There's only 5Mhz between 2.445Ghz and 2.45Ghz.
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#2730
by
CuriousDreamer
on 25 May, 2016 22:46
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...
U.S. lawmaker orders NASA to plan for trip to Alpha Centauri by 100th anniversary of moon landing
...
This is pretty exciting, but at the same time could be a bad thing... I am excited for the emphasis on interstellar tech research and development... But if NASA doesn't get the funding they need and fails to show progress when the deadline approaches it could be used as an excuse to remove even more funding from NASA.
Just a thought on the dark side.
~Dreamer
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#2731
by
Elmar Moelzer
on 25 May, 2016 23:32
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Lawmakers should stay out of science. They have demonstrated over and over again, that they have no clue whatsoever.
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#2732
by
1
on 25 May, 2016 23:47
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A year? Hell, NASA can do this in a minute.
"All concepts are currently unfeasible without sufficient funding to accompany the committee's generous amounts of 'encouragement'.
Love,
NASA"
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#2733
by
A_M_Swallow
on 26 May, 2016 00:07
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***Big News from DC 5/23/16***
U.S. lawmaker orders NASA to plan for trip to Alpha Centauri by 100th anniversary of moon landing
http://www.sciencemag.org/news/2016/05/us-lawmaker-orders-nasa-plan-trip-alpha-centauri-100th-anniversary-moon-landing
"Interstellar propulsion research. —
Current NASA propulsion investments include advancements in chemical, solar electric, and nuclear thermal propulsion. However, even in their ultimate theoretically achievable implementations, none of these could approach cruise velocities of one-tenth the speed of light (0.1c), nor could any other fission-based approach (including nuclear electric or pulsed fission). The Committee encourages NASA to study and develop propulsion concepts that could enable an interstellar scientific probe with the capability of achieving a cruise velocity of 0.1c. These efforts shall be centered on enabling such a mission to Alpha Centauri, which can be launched by the one-hundredth anniversary, 2069, of the Apollo 11 moon landing. Propulsion concepts may include, but are not limited to fusion-based implementations (including antimatter-catalyzed fusion and the Bussard interstellar ramjet); matter-antimatter annihilation reactions; multiple forms of beamed energy approaches; and immense ‘sails’ that intercept solar photons or the solar wind. At the present time, none of these are beyond technology readiness level (TRL) 1 or 2. The NASA Innovative Advanced Concepts (NIAC) program is currently funding concept studies of directed energy propulsion for wafer-sized spacecraft that in principle could achieve velocities exceeding 0.1c and an electric sail that intercepts solar wind protons. Over the past few years NIAC has also funded mission-level concept studies of two fusion based propulsion concepts. Therefore, within one year of enactment of this Act, NASA shall submit an interstellar propulsion technology assessment report with a draft conceptual roadmap, which may include an overview of potential advance propulsion concepts for such an interstellar mission, including technical challenges, technology readiness level assessments, risks, and potential near term milestones and funding requirements."
{snip}
Note: Bold is my notation - Dave
Alpha Centauri may be the nearest star but it may not be the most interesting destination.
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#2734
by
zellerium
on 26 May, 2016 00:54
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OK, this is off RL peak and I was referring to 3dB below insertion. This is why I wrote in my test report that we need to standardize. Either way is fine, Yang and EW were reporting on a couple of different methods at one time.
Forgive me for not knowing, but what's the difference between insertion and peak? 20Mhz is huge and off the chart shown here. There's only 5Mhz between 2.445Ghz and 2.45Ghz.
We measured our quality at -3 dB below 0 dB, not 3 dB above the minimum reflection.
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#2735
by
Elmar Moelzer
on 26 May, 2016 00:56
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Alpha Centauri may be the nearest star but it may not be the most interesting destination.
Wouldn't that be Proxima Centauri?
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#2736
by
Elmar Moelzer
on 26 May, 2016 01:46
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These are government oversight committees and just doing their job. This rep is pro space and perhaps is listening to constituants who want bigger things than what's been delivered in the past few decades.
I have nothing against doing bigger things. My problem is specifically with lawmakers thinking that they are smarter than the people at NASA (which they never are).
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#2737
by
zen-in
on 26 May, 2016 02:56
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Alpha Centauri may be the nearest star but it may not be the most interesting destination.
Wouldn't that be Proxima Centauri?
Yes, and if NASA waits for 30,000 years Alpha Centauri will be closest and only 3.2 LY away from Earth
https://en.wikipedia.org/wiki/Proxima_Centauri
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#2738
by
Stormbringer
on 26 May, 2016 03:06
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Alpha Centauri may be the nearest star but it may not be the most interesting destination.
Wouldn't that be Proxima Centauri?
If they did it right they could probably go to all three stars in the AP system. once you get across that 4.3 light year gulf somehow you could almost literally pee on the other two stars in that system from there. the only near term way to do Alpha Centauri is probably by laser sail. In that case you should be able to zap hundreds of probes in that direction for little added cost because you could mass produce them and lob one every few miliseconds. These probes would be so small there is no way to cost overrun on the probes themselves or the electric bill once the laser facility, aiming tech, communication tech and its power supply are paid for.
EDIT: The lasers will be on anyway for as long as it takes to get the first probe up to the target velocity. meanwhile probes launched a short time afterwards would be accelerated in the time it took to accelerate the first probe plus what ever the interval between feeding probes into the power laser beam per number of probes sent.
Because the probes would be so small they would almost have to be manufactured via some process analogous to printing IC chips. The upshot is once the design for the first probe is finalized there is not much cost difference between one probe and thousands. the designs are loaded in to a CAM machine and produced in any number needed with dozens or hundreds being minted at the same time.
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#2739
by
FattyLumpkin
on 26 May, 2016 04:09
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