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# Tag Info

41

Metal in a microwave is really not a big problem. The walls of every microwave ever made are metal, the window contains metal mesh, mine has a metal shelf and a metal base for the turntable. The general guideline of "do not put metal objects into a microwave" does make sense - metal in the oven has to have a certain shape, size, alloy, distance from other ...

21

The metal walls of the microwave oven reflect the microwave radiation. A metal object in the middle of the microwave field can do several things. It could reflect the radiation like the walls do. That's bad if there is nothing else in the oven to eventually absorb the radiation. All that microwave power ultimately has to end up somewhere. It's better ...

19

So you want to transport that 2.5 GHz (or even 5 GHz ?) Wifi signal over TV COAX cable ? Indeed to the non-RF people you'd just think that would work. And it does BUT there will be almost no signal coming through that cable. The Wifi signal will be attenuated so much in that COAX cable that it will defeat the whole purpose of having an antenna on the roof. ...

16

Simple thought or practical experiment: If he's right then the heating time to bring water to boiling point is independent of the quantity of water. One cup will take as long as two. If you're right two cups of water will take twice as long to boil.

14

Neither a mitred nor curved bend is as 'good' as the equivalent length of straight track. There are two main aspects to goodness, S11 and S21. S11. Other things being equal, width and thickness of trace, dielectric performance, the curved bend can be designed to have good S11 to a higher frequency than the mitred. That's because the mitre is effectively a ...

13

The R&S instruments are equipped with female test port adapters. Edit: archived pdf You can replace the N type with a more suitable type for higher frequencies.

13

Wah! WAH! Ok, you're putting yourself and your friend in deadly danger. First of all, your 29\$ device is not a substitute for proper RF qualification. It simply isn't. You might be able to find a concentrated leak in the expected frequency range with that, but all you said is that you tweaked around with the magnetron, probably replaced it, and might have ...

11

A Magnetron is a "vacuum tube". One limit on vacuum tube lifetime is cathode emissivity - the ability to provide electrons for the 'tube' to 'modulate'. Decay mechanisms can be complex but a first approximation relates to the availability of materials which liberate electrons and the action of trace gases on the cathode surface. [The material is usually ...

9

First of all is it possible to create 10 GHz wave on a PCB? Any clue on how to do something like, regarding the circuitry? If by "creating" you mean propagating and/or radiating, the answer is yes. However, you need to use specific board substrates like Rogers 4000 series, with low losses and controlled dielectric constant up to that frequency. Your ...

9

1.3GHz rectangular pulses.... is this actually digital data? If it is and the clock frequency is 1.3GHz then the actual frequency of the signal is 650MHz and I would recommend the frequency of concern to be 3rd harmonic which is 1950MHz. At this kind of frequency I would just make sure that you account for the effect of the soldermask in your impedance ...

9

Some magnetrons use beryllium oxide as the "ceramic" looking insulators inside of the ring magnets on both the "Stem" and the "Antenna" ends. Reference the image below, the beryllium oxide parts are the pink items in the middle. They are totally inert if undisturbed. Not all magnetrons use that for the insulators, but it's virtually impossible to tell if ...

8

When they say "don't put metal objects in a microwave" what they really mean is "don't put the food in a metal container." Obviously the container will reflect the microwaves and the food won't cook. Now here's the problem. If the energy is not going into the food, it has to go somewhere. In general you should not operate a microwave without food in it, and ...

8

I got one possible reason from this article: "Each magnetron’s cathode has a special coating to enhance performance. Over time this material is consumed during normal operation." Although that article deals with magnetrons for radar, I think it still applies as the principle of operation is the same. It is also mentioned that RF power reflected back into ...

8

Magnetrons are cheap, reliable, pretty efficient (65% or so- and they tolerate high temperatures so heat sinking is easy) and made with mature technology. They are also reasonably tolerant of VSWR issues (if the user does not put a proper load in the oven, for example). They don't really allow the frequency to change much without expensive mechanical tuning ...

7

My apologies for the long answer but this is a complicated bit of technology and needs an appreciation of the physics behind it. To understand the operation of a reflex klystron I think you need to start with a basic understanding of a tuned circuit made up from a capacitor (C) and inductor (L). Normally we use separate components in devices such as radio ...

7

It isn't the metal mesh leaking so much as the joint around the door. Rather than employing a continuous metal-to-metal contact around the edge of the door to seal it when closed, most microwave ovens use a quarter-wave "trap" — basically a shaped "groove" of the correct dimensions that surrounds the door opening (usually hidden behind a dielectric ...

7

I'm not going to go through this with equations, because that requires roughly a full chapter of a textbook. I'll just give a rough outline. When electromagnetic waves travel through a material, they exert an oscillating force on the charged particles within that material. The charges move in response to this force, causing the material to be polarized. The ...

7

The Patch-Plane Antenna The antenna in question is is called a patch-plane (or plane-patch) antenna -- a patch antenna with a reference plane behind it. You can see it here (the four lighter green squares near the corners). According to the datasheet, the directivity looks like this: From behind its detection capability is about 63 times weaker assuming ...

7

No. There's no physical difference between digital signals and analog signals on the air. Both are converted to analog voltages. The only things about the electrical system that attaches to the antenna that matter for an antenna are center frequency bandwidth impedance Selling an antenna "for digital transmissions" is like selling a car to "transport ...

7

I am less than a year in a high frequency PCB design. So below is not my answer but advises from three different sources. Source 1. A friend of mine with a microwave experience longer than my age Option 1: make an opening over the top of the trace, coat it with immersion gold. My note: I know ENIG is not a best choice for ultra high speed signals, so ...

7

From the article you've linked (p.70): [...] the efficiency of the power amplifier can be limited by the transistor output capacitance [...] $C_{ds}$, [...] if this capacitance is not absorbed into multiharmonic load network without compromising the ability to properly terminate the second and third harmonic components. So, first hint: you have ...

7

To avoid the possible number of obstacles between the phones and the cell tower. And height position point is often in sight (or almost) from many ground-level points. Obstacles cause reflections, scattering and absorption effects that compromise the S/N ratio.

6

ROM (MaskROM) Nope. Well, yes, but only for what it was already used for. Mask ROM means that the programming is directly part of the silicon and cannot be changed.

6

You must use coaxial cable of the proper impedance. The most common impedance for coax cable is 50 ohms or 75 ohms. If the cable you want to use matches the impedance of the interface AND the antenna, then go for it. But if you use cable of the wrong impedance you will get significant attenuation of the signal to the point where it may not work at all. In ...

6

A $TE_{10}$ mode has one lobe in the E-field strength pattern in the x direction (the longer transverse direction) and 0 lobes in the y direction. A $TE_{11}$ mode has one lobe in the E-field strength pattern in the x direction and 1 lobe in the y direction. A $TE_{21}$ mode has two lobes in the E-field strength pattern in the x direction and 1 lobe ...

6

Sure. Place a $\frac\lambda2$ dipole in your microwave oven and see how the kV's spark over the feed point. You could of course harvest that power. It's an EM field – what did you expect? So, the proof of concept being trivial, making a device that makes this safe and reliable to use is pretty much impossible – the microwave oven is designed to produce a ...

6

Two Reasons: Pout and S11. N connectors have a large surface contact area for >1A power levels or >10dB and large diameter means better "potential return loss over a wide GHz range is possible with machining tolerances of 0.1% affecting this. However SMA is more common for low power apps but quality varies with undocumented suppliers. (greatly and not ...

6

A bowl of water is the standard load for testing microwave ovens. Use a microwave-safe material for the bowl. Simple plastics like polyethylene or polypropylene are OK, not melamine which will overheat. Glass is OK, as are most plain ceramics, but some decorative ceramic glazes can overheat. It's not so much that the absorption of microwave energy by the ...

6

24 GHz and 60 GHz are significantly more expensive to deal with – whilst your average FR4 PCB is totally sufficient in material $\epsilon$ uniformity and $\tan\delta$, it won't do > 20 GHz. Reliable connectors become very expensive. Also, you either get much more loss per distance, or you use the reduced wavelength to build an antenna with larger ...

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