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#600 by X_RaY on 16 Aug, 2015 20:34
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I see what your doing TT but I'd wonder about ground loops with the antenna just floating out there. How do you plan to adjust for that? Are you grounding your frustum?No. please look at the NASA loop picture. One end of the wire is in contact to the GND and that is the way it will work as a loop.
The 2 ends of the loop in the picture have the same electrical potential!
My crude ascii drawing has failed to deliver. Bad TT bad.
The coax is to stop the feed from the side wall to the loop from radiating. One side of the loop antenna is attached to the coax hot centre feed line and the other side of the loop antenna to the coax shield.
So the same as the NASA picture, just bigger in diameter and with the short section of 2 parallel wires replaced with coax.
If I get the loop diameter and distance from the big end right, should do an excellent job at exciting TE013 mode.
The chassis of the magnetron is one of the two potential (aka GND)
The other switch between +Volts and -Volts against GND.
EDIT:
For the magnetron may be only half of that cycle
+Volts against GND---> nothing---> again +Volts against GND--->...
not sure jet at this point, have to restudy
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#601 by SeeShells on 16 Aug, 2015 20:43
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AKA GND isn't always ground.
I see what your doing TT but I'd wonder about ground loops with the antenna just floating out there. How do you plan to adjust for that? Are you grounding your frustum?No. please look at the NASA loop picture. One end of the wire is in contact to the GND and that is the way it will work as a loop.
The 2 ends of the loop in the picture have the same electrical potential!
My crude ascii drawing has failed to deliver. Bad TT bad.
The coax is to stop the feed from the side wall to the loop from radiating. One side of the loop antenna is attached to the coax hot centre feed line and the other side of the loop antenna to the coax shield.
So the same as the NASA picture, just bigger in diameter and with the short section of 2 parallel wires replaced with coax.
If I get the loop diameter and distance from the big end right, should do an excellent job at exciting TE013 mode.
The chassis of the magnetron is one of the two potential (aka GND)
The other switch between +Volts and -Volts against GND.
https://en.wikipedia.org/wiki/Ground_loop_(electricity)
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#602 by X_RaY on 16 Aug, 2015 20:49
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Right
AKA GND isn't always ground.
I see what your doing TT but I'd wonder about ground loops with the antenna just floating out there. How do you plan to adjust for that? Are you grounding your frustum?No. please look at the NASA loop picture. One end of the wire is in contact to the GND and that is the way it will work as a loop.
The 2 ends of the loop in the picture have the same electrical potential!
My crude ascii drawing has failed to deliver. Bad TT bad.
The coax is to stop the feed from the side wall to the loop from radiating. One side of the loop antenna is attached to the coax hot centre feed line and the other side of the loop antenna to the coax shield.
So the same as the NASA picture, just bigger in diameter and with the short section of 2 parallel wires replaced with coax.
If I get the loop diameter and distance from the big end right, should do an excellent job at exciting TE013 mode.
The chassis of the magnetron is one of the two potential (aka GND)
The other switch between +Volts and -Volts against GND.
https://en.wikipedia.org/wiki/Ground_loop_(electricity) The Voltage difference predicts the current flow.
Technical(per convention) the current flow goes from the + to the - (that's historical issues and cause only a difference of the sign within calculations).
Physically the electrons travel from - to the + potential.
https://translate.google.de/translate?sl=de&tl=en&js=y&prev=_t&hl=de&ie=UTF-8&u=http%3A%2F%2Fwww.frustfrei-lernen.de%2Felektrotechnik%2Fstromrichtung-technisch-physikalisch.html&edit-text=&act=url -
#603 by SeeShells on 16 Aug, 2015 21:00
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And that difference in potentials will and can change in a oscillatory system and cause the ground plane to oscillate with the conductive harmonic path lengths between the grounds.
Right
AKA GND isn't always ground.
I see what your doing TT but I'd wonder about ground loops with the antenna just floating out there. How do you plan to adjust for that? Are you grounding your frustum?No. please look at the NASA loop picture. One end of the wire is in contact to the GND and that is the way it will work as a loop.
The 2 ends of the loop in the picture have the same electrical potential!
My crude ascii drawing has failed to deliver. Bad TT bad.
The coax is to stop the feed from the side wall to the loop from radiating. One side of the loop antenna is attached to the coax hot centre feed line and the other side of the loop antenna to the coax shield.
So the same as the NASA picture, just bigger in diameter and with the short section of 2 parallel wires replaced with coax.
If I get the loop diameter and distance from the big end right, should do an excellent job at exciting TE013 mode.
The chassis of the magnetron is one of the two potential (aka GND)
The other switch between +Volts and -Volts against GND.
https://en.wikipedia.org/wiki/Ground_loop_(electricity) The Voltage difference predicts the current flow -
#604 by ThinkerX on 16 Aug, 2015 21:10
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Quote
Since the wavelength change according to the location where it is measured (free wavelength, guide wavelength, wavelength at the big end, wavelength at the small end, wavelength at the antenna location…) which one must be taken into account to properly design the length (diameter?) of the loop antenna at this "max half-wavelength"?
Multiple antenna's? Use only the one you happen to need at that particular moment. -
#605 by flux_capacitor on 16 Aug, 2015 21:18
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Quote
Since the wavelength change according to the location where it is measured (free wavelength, guide wavelength, wavelength at the big end, wavelength at the small end, wavelength at the antenna location…) which one must be taken into account to properly design the length (diameter?) of the loop antenna at this "max half-wavelength"?
Multiple antenna's? Use only the one you happen to need at that particular moment.
No, I wanted to mean: there are different wavelength values inside the cavity, so which value of the wavelength should be taken, to calculate the length of the loop antenna near the big base? -
#606 by Rodal on 16 Aug, 2015 21:19
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...
So what is then the difference between the contents of this folder
That's for the 64 cycle run. It matches the image, "ezz30-t04.png" and anyway, the 64 cycle run is the only one for which I have generated the z-30 slice data so far.
new-csvs
with the contents of this folder
64-cycle-run ...
Both of them are in the 64 cycle Shell 2D loop ant folder
Are they in fact different? They shouldn't be. 64-cycle run csv's were made prior to changing the magnitude range of the .png files, and the new-csvs data was made in the process of making the .pngs with the new magnitude ranges. I don't have any efficient way to check whether or not they are in fact the same so I uploaded them in case you wanted to check. If they are in fact different then there is something going on with the h5totxt program that I don't understand.
The reason why I had asked for the "location 30" runs to be done for a 32 cycle instead of a 64 cycle is in order to find out whether the 10,000 fold increase in stresses and force is mainly due to the doubling of the running time or whether it is mainly due to the TE012 mode instead of a TM mode as in previous runs.
In order to find out the main reason for this 10,000 fold increase in stress and force we still need the same information to be run for a 32 cycle run to compare with the 64 cycle run. -
#607 by aero on 16 Aug, 2015 21:22
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...
So what is then the difference between the contents of this folder
That's for the 64 cycle run. It matches the image, "ezz30-t04.png" and anyway, the 64 cycle run is the only one for which I have generated the z-30 slice data so far.
new-csvs
with the contents of this folder
64-cycle-run ...
Both of them are in the 64 cycle Shell 2D loop ant folder
Are they in fact different? They shouldn't be. 64-cycle run csv's were made prior to changing the magnitude range of the .png files, and the new-csvs data was made in the process of making the .pngs with the new magnitude ranges. I don't have any efficient way to check whether or not they are in fact the same so I uploaded them in case you wanted to check. If they are in fact different then there is something going on with the h5totxt program that I don't understand.
The reason why I had asked for the "location 30" runs to be done for a 32 cycle instead of a 64 cycle is in order to find out whether the 10,000 fold increase in stresses and force is mainly due to the doubling of the running time or whether it is mainly due to the TE012 mode instead of a TM mode as in previous runs.
In order to find out the main reason for this 10,000 fold increase in stress and force we still need the same information to be run for a 32 cycle run to compare with the 64 cycle run.
Ok - I'll see what i can do. It'll be later today or tomorrow early. -
#608 by Rodal on 16 Aug, 2015 23:14
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And that difference in potentials will and can change in a oscillatory system and cause the ground plane to oscillate with the conductive harmonic path lengths between the grounds.
Right
AKA GND isn't always ground.
I see what your doing TT but I'd wonder about ground loops with the antenna just floating out there. How do you plan to adjust for that? Are you grounding your frustum?No. please look at the NASA loop picture. One end of the wire is in contact to the GND and that is the way it will work as a loop.
The 2 ends of the loop in the picture have the same electrical potential!
My crude ascii drawing has failed to deliver. Bad TT bad.
The coax is to stop the feed from the side wall to the loop from radiating. One side of the loop antenna is attached to the coax hot centre feed line and the other side of the loop antenna to the coax shield.
So the same as the NASA picture, just bigger in diameter and with the short section of 2 parallel wires replaced with coax.
If I get the loop diameter and distance from the big end right, should do an excellent job at exciting TE013 mode.
The chassis of the magnetron is one of the two potential (aka GND)
The other switch between +Volts and -Volts against GND.
https://en.wikipedia.org/wiki/Ground_loop_(electricity) The Voltage difference predicts the current flow
Many of the things being discussed (how to best excite TE01 modes, and discourage other modes) are discussed in
the excellent book by Balanis:
Advanced Engineering Electromagnetics 2nd Edition
by Constantine A. Balanis (Author)
Hardcover: 1040 pages
Publisher: Wiley; 2 edition (January 24, 2012)
Language: English
ISBN-10: 0470589485
ISBN-13: 978-0470589489
<<Although the TE0n modes are very attractive from the attenuation point of view, there are a number of problems associated with their excitation and retention. One of the problems is that the TE01 mode, which is the first of the TE0n modes, is not the dominant mode. Therefore, in order for this mode to be above its cut-off frequency and propagate in the waveguide, a number of other modes (such as the TE11, TM01, TE21 and TM11) with lower cutoff frequencies can also exist. Additional modes can also be present if the operating frequency is chosen well above the cutoff frequency of the TE01 mode in order to provide a margin of safety from being too close to its cutoff frequency.
To support the TE01 mode, the waveguide must be oversized and it can support a number of other modes. One of the problems faced with such a guide is how to excite the desired TE01 mode with sufficient purity and suppress the others. Another problem is how to prevent coupling of the TE01 mode and undesired modes that can exist since the guide is oversized. The presence of the undesired modes causes not only higher losses but dispersion and attenuation distortion to the signal since each exhibits different phase velocities and attenuation. Irregularities in the inner geometry, surface, and direction (such as bends, nonuniform cross-sections, etc.) of the waveguide are the main contributors to the coupling to the undesired modes. However, for the guide to be of any practical use, it must be able to sustain and propagate the desired TE01 and other TE0n modes efficiently over bends of reasonable curvature. One technique that has been implemented to achieve this is to use mode conversion before entering the corner and another conversion when exiting to convert back to the desired TE0n mode(s).
Another method that has been used to discriminate against undesired modes and avoid coupling to them is to introduce filters inside the guide that cause negligible attenuation to the desired TE0n mode(s). The basic principle of these filters is to introduce cuts that are perpendicular to the current paths of the undesired modes and parallel to the current direction of the desired mode(s). Since the current path of the undesired modes is along the axis (z direction) of the guide and the path of the desired TE0n modes is along the circumference (phi direction) , a helical wound wire placed on the inside surface of the guide can serve as a filter that discourages any mode that requires an axial component of current flow but propagates the desired TE0n modes.
Another filter that can be used to suppress undesired modes is to introduce within the guide very thin baffles of lossy material that will act as attenuating sheets. The surfaces of the baffles are placed in the radial direction of the guide so that they are parallel to the Er and Ez components of the undesired modes (which will be damped) and normal to the Ephi component of the TE0n modes that will remain unaffected. Typically, two baffles are used and are placed in a crossed pattern over the cross section of the guide.>>
(Bold added for emphasis)
pp.498-500
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#609 by SeeShells on 16 Aug, 2015 23:53
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http://forum.nasaspaceflight.com/index.php?topic=38203.msg1416759#msg1416759
Got me thinking the quartz rod through the center could support some mode filters if needed.
Nice read Doc.
Shell -
#610 by TheTraveller on 17 Aug, 2015 00:20
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I see what your doing TT but I'd wonder about ground loops with the antenna just floating out there. How do you plan to adjust for that? Are you grounding your frustum?No. please look at the NASA loop picture. One end of the wire is in contact to the GND and that is the way it will work as a loop.
The 2 ends of the loop in the picture have the same electrical potential!
My crude ascii drawing has failed to deliver. Bad TT bad.
The coax is to stop the feed from the side wall to the loop from radiating. One side of the loop antenna is attached to the coax hot centre feed line and the other side of the loop antenna to the coax shield.
So the same as the NASA picture, just bigger in diameter and with the short section of 2 parallel wires replaced with coax.
If I get the loop diameter and distance from the big end right, should do an excellent job at exciting TE013 mode.
On the top of my rotary table but under all the equipment will be a thin copper layer that will serve as my reference ground plane. Everything will be grounded to this high frequency ground reference plane.
Additionally all external wiring will be shielded and will use a 2 turn ferrite (shielded cable will circle through the ferrite donut twice) to filter out high freq noise on the shield grounds.
Of course all power leads will have high frequency decoupling capacitors and ferrite filters.
Anybody who has ever designed and debugged a high frequency pcb knows the value of a solid copper ground plane.
So yes ground loops can be a problem but not if using a large area solid copper ground plane with additional high frequency decoupling capacitors and ferrite donuts. -
#611 by SeeShells on 17 Aug, 2015 00:37
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I see what your doing TT but I'd wonder about ground loops with the antenna just floating out there. How do you plan to adjust for that? Are you grounding your frustum?No. please look at the NASA loop picture. One end of the wire is in contact to the GND and that is the way it will work as a loop.
The 2 ends of the loop in the picture have the same electrical potential!
My crude ascii drawing has failed to deliver. Bad TT bad.
The coax is to stop the feed from the side wall to the loop from radiating. One side of the loop antenna is attached to the coax hot centre feed line and the other side of the loop antenna to the coax shield.
So the same as the NASA picture, just bigger in diameter and with the short section of 2 parallel wires replaced with coax.
If I get the loop diameter and distance from the big end right, should do an excellent job at exciting TE013 mode.
On the top of my rotary table but under all the equipment will be a thin copper layer that will serve as my reference ground plane. Everything will be grounded to this high frequency ground reference plane.
Additionally all external wiring will be shielded and will use a 2 turn ferrite (shielded cable will circle through the ferrite donut twice) to filter out high freq noise on the shield grounds.
Of course all power leads will have high frequency decoupling capacitors and ferrite filters.
Anybody who has ever designed and debugged a high frequency pcb knows the value of a solid copper ground plane.
So yes ground loops can be a problem but not if using a large area solid copper ground plane with additional high frequency decoupling capacitors and ferrite donuts.
It sure can help TT. Also make sure you have what we called a Star ground where all grounds terminated on the same point. -
#612 by SeeShells on 17 Aug, 2015 00:43
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Quote
Since the wavelength change according to the location where it is measured (free wavelength, guide wavelength, wavelength at the big end, wavelength at the small end, wavelength at the antenna location…) which one must be taken into account to properly design the length (diameter?) of the loop antenna at this "max half-wavelength"?
Multiple antenna's? Use only the one you happen to need at that particular moment.
Slowly getting there... slowly. -
#613 by TheTraveller on 17 Aug, 2015 01:04
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http://forum.nasaspaceflight.com/index.php?topic=38203.msg1416759#msg1416759
Got me thinking the quartz rod through the center could support some mode filters if needed.
Nice read Doc.
Shell
What is your estimated max averaged frustum surface temperature when pumping your 800 watts of Rf into the frustum?
From that temperature, how much will your copper end plate diameters grow and how much longer will your copper frustum grow?
You can dramatically increase the surface emissivity by around 5x to 10x by painting the outside surface with a high carbon black paint. This higher thermal emissivity will very significantly reduce your frustum temperature rise and significantly reduce any thermal expansion.
As copper expands 0.0166mm per deg K per m, increasing the surface emissivity 5x could really work wonders for limiting thermal expansion.
On another subject, I see you are thinking about feeding the magnetron Rf into your frustum via a waveguide and not direct inject it. My concern with the waveguide is the frustum will then have an input bandwidth that may not wide enough to accept most of the magnetron output bandwidth. Surley you don't want a Q of 50 like Tajmar used? How do you intend to deal with using a waveguide feed, limited input bandwidth and getting all your magnetron energy inside your frustum? -
#614 by Rodal on 17 Aug, 2015 02:17
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http://forum.nasaspaceflight.com/index.php?topic=38203.msg1416759#msg1416759
Got me thinking the quartz rod through the center could support some mode filters if needed.
Nice read Doc.
Shell
...you are thinking about feeding the magnetron Rf into your frustum via a waveguide and not direct inject it. My concern with the waveguide is the frustum will then have an input bandwidth that may not wide enough to accept most of the magnetron output bandwidth. Surley you don't want a Q of 50 like Tajmar used? How do you intend to deal with using a waveguide feed, limited input bandwidth and getting all your magnetron energy inside your frustum?
True. But comparing different characteristics of transmission lines one has to trade off:
Characteristic Coaxial Waveguide Winner
Unloaded Q Medium High Waveguide
Power Capability Medium High Waveguide
Bandwidth Large Small Coaxial
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#615 by SeeShells on 17 Aug, 2015 03:57
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http://forum.nasaspaceflight.com/index.php?topic=38203.msg1416759#msg1416759
Got me thinking the quartz rod through the center could support some mode filters if needed.
Nice read Doc.
Shell
What is your estimated max averaged frustum surface temperature when pumping your 800 watts of Rf into the frustum?
From that temperature, how much will your copper end plate diameters grow and how much longer will your copper frustum grow?
You can dramatically increase the surface emissivity by around 5x to 10x by painting the outside surface with a high carbon black paint. This higher thermal emissivity will very significantly reduce your frustum temperature rise and significantly reduce any thermal expansion.
As copper expands 0.0166mm per deg K per m, increasing the surface emissivity 5x could really work wonders for limiting thermal expansion.
On another subject, I see you are thinking about feeding the magnetron Rf into your frustum via a waveguide and not direct inject it. My concern with the waveguide is the frustum will then have an input bandwidth that may not wide enough to accept most of the magnetron output bandwidth. Surley you don't want a Q of 50 like Tajmar used? How do you intend to deal with using a waveguide feed, limited input bandwidth and getting all your magnetron energy inside your frustum?
The end plates will grow very little or warp like copper as they are 10mm thick ceramic gold electroplated. With a TEC of 7.2x10^-6/C (40-400C)
http://global.kyocera.com/prdct/fc/list/tokusei/bouchou/index.html
The copper side walls exceeding the top temperature expected
dl = L0 α (t1 - t0)
for 20C start
140C tops
diff in growth Y axis = .0005m
or 0.0197" inches
The connecting quartz rod locking the two plates through the centerline is a fused quartz rod. Transparent to microwaves but with a TEC or Fractional expansion per degree 0.59 C x10^-6 or about .00001m or 100um from 20-140C. The small plate is locked to the large plate and will slide in the frustum extension at the top negating the TEC of the copper side walls.
Two things on the dual waveguide inputs. One: the inputs will be a mirror of each other. Two: I plan before using the magnetron to modify the power supply to narrow the bandwidth and reduce power and go to 100% duty cycle @2.45GHz
http://www.google.com/patents/US3760291
I've tried to look at the issues in the thermal expansions of materials of the Drive and negate the ones I could and design out (ceramic plates) the ones I could. I hope to have a good design.
Hope that helps explain the build and you know the black might be a good idea. Thanks for the inputs!
Shell
speeelings
Added
I did the calculations for the quartz rod a little differently for a temperature spread of 20-140 C TEC and came up with 0.0006m or 60um -
#616 by zen-in on 17 Aug, 2015 05:12
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...
On the top of my rotary table but under all the equipment will be a thin copper layer that will serve as my reference ground plane. Everything will be grounded to this high frequency ground reference plane.
...
Anybody who has ever designed and debugged a high frequency pcb knows the value of a solid copper ground plane.
So yes ground loops can be a problem but not if using a large area solid copper ground plane with additional high frequency decoupling capacitors and ferrite donuts.
At 2.4 GHz ferrite donuts are not needed. Instead an air core inductor inline with each power lead that is not at ground potential is all that is needed. Filter caps on either side of the inductor are used to prevent voltage sag from current transients. They are a high impedance path to RF. But since the inductor only needs to be a few nH. caps are not needed.
The fustrum is your ground plane. No thin copper sheet is needed. Any conductors going to this ersatz ground plane will be many wavelengths long. So it is impossible to make this copper sheet a ground at RF.
The biggest problem with driving a fustrum from a coax feed is matching the loop inside the cavity. It is virtually impossible to make the loop exactly the right length so it will almost never be a 50 Ohms resistive load at the frequency used. It will always be capacitive because of the adjacent cavity walls. So a large part of the RF sent into the cavity will just get reflected back on the shield. Ferrites are only useful up to VHF frequencies so putting ferrite donuts on the coax will have no effect. Maybe coiling the coax will help but a lot of RF will still get radiated because of the mismatch. Matching networks can be used but in that case the return wave is just dissipated in the matching network. -
#617 by deltaMass on 17 Aug, 2015 07:34
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The biggest problem with a frustum is gettin frust that other people fink is real.
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#618 by TheTraveller on 17 Aug, 2015 07:55
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...
On the top of my rotary table but under all the equipment will be a thin copper layer that will serve as my reference ground plane. Everything will be grounded to this high frequency ground reference plane.
...
Anybody who has ever designed and debugged a high frequency pcb knows the value of a solid copper ground plane.
So yes ground loops can be a problem but not if using a large area solid copper ground plane with additional high frequency decoupling capacitors and ferrite donuts.
At 2.4 GHz ferrite donuts are not needed. Instead an air core inductor inline with each power lead that is not at ground potential is all that is needed. Filter caps on either side of the inductor are used to prevent voltage sag from current transients. They are a high impedance path to RF. But since the inductor only needs to be a few nH. caps are not needed.
The fustrum is your ground plane. No thin copper sheet is needed. Any conductors going to this ersatz ground plane will be many wavelengths long. So it is impossible to make this copper sheet a ground at RF.
The biggest problem with driving a fustrum from a coax feed is matching the loop inside the cavity. It is virtually impossible to make the loop exactly the right length so it will almost never be a 50 Ohms resistive load at the frequency used. It will always be capacitive because of the adjacent cavity walls. So a large part of the RF sent into the cavity will just get reflected back on the shield. Ferrites are only useful up to VHF frequencies so putting ferrite donuts on the coax will have no effect. Maybe coiling the coax will help but a lot of RF will still get radiated because of the mismatch. Matching networks can be used but in that case the return wave is just dissipated in the matching network.
Thanks for your input.
The copper sheet is the bottom of the Faraday Cage for both the frustum and the Rf amp as well as their earth reference.
My main noise concern is what will be coming out of the DC power leads for the Rf amp and using the supply wires back to the Lithium Ion 500Wh battery packs as antenna.
I do understand the antenna design needs to be done properly. Plan to try many ideas to get the best coupling to the resonant Rf energy inside the frustum. -
#619 by TheTraveller on 17 Aug, 2015 07:57
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The biggest problem with a frustum is gettin frust that other people think is real.
You don't accept this is real?
https://drive.google.com/folderview?id=0B7kgKijo-p0ifnFrZ2V1UmZEY25FXzNrX0hjNXJmQXR5YzRnaVBqcTdMZUhxcjVkMUUtaXc&usp=sharing
