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RF Current meters

Steven Greenfield AE7HD #432 The advantage of the chip resistor would be frequency range and true RMS readings. ? I hope not! RMS power is a useless parameter . You can compute it analytically, but it is pretty meaningless. The mean power is what is relevant, as that causes the same heating as DC would.? I'm a bit confused. He said RMS, not RMS power. Isn't "RMS power" a meaningless term? Voltage and current can be RMS, and the end result is precisely what you say, the same heating (work) as DC would do. The discussion was about RF current, so I assumed "RMS" meant "RMS current", in this context. Steve Greenfield AE7HD
Chuck Moore All Messages By This Member #435 The page posted by BH1BPG may be of interest. Limited frequency range but useful for many. https://sites.google.com/site/linuxdigitallab/rf-homebrew-instrument/thermistor-rf-power-meter
John Griessen All Messages By This Member #436 On 9/2/22 07:34, SCMenasian wrote: I'd like to suggest another option. I have some Platinum RTD temperature sensors bought for another project. They are very stable and accurate as temperature sensors and relatively cheap. They are also very small - small enough to be used as an RF load in a BNC or SMA fixture, with bandwidth extending, possibly, to the low GHz region. Mine have leads; but they are available in surface mount packages. 100 Ohms is the most commonly supplied resistance; so 2 in parallel could make a nice 50 Ohm load.? A third sensor could serve as a reference in a bridge circuit. Alteratively, one might preheat to a known temperature with DC and measure the DC power drop required to achieve the same temperature with RF applied. Other readout options also exist, including lock-in if the RF power can be modulated. That sounds good. How would you do the RF load connection to coax to not have reflections? What is the "mount package" like? Solves the connection to coax problem?
SCMenasian All Messages By This Member #437 I think the basic RF connection would be very simple. I often make fairly well matched 50 ohm loads by connecting 2 100 ohm chip resistors from a BNC center pin to ground connections (radial and spaced 180 degrees on either side). The interesting part depends upon how one plans the readout and the thermal design [both should be allowed to heat up significantly (for sensitivity) and equally (for accuracy)]. The readout will probably require a capacitor and, possibly, and inducttor for RF/DC isolation in proximity to the RTD sensors.
Dr. David Kirkby, Kirkby Microwave Ltd Member Profile All Messages By This Member #439 On Fri, 2 Sept 2022 at 14:23, Tom, wb6b <wb6b@...> wrote: On Fri, Sep 2, 2022 at 05:29 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote: I hope not! RMS power is a useless parameter . You can compute it analytically, but it is pretty meaningless. The mean power is what is relevant, as that causes the same heating as DC would.? I think the measured amperage would be RMS, by virtue of measuring the temperature of the resistor. Guided by the title of thread, was only referring to current.? Yes, that was my mis-understanding of what was written. Sorry.? Interesting calculator for temperature to peak wavelength. I've had some trying out some common temperature values. The sample curves in the description are nice for getting a feel for how far the hot body spectrum would extend into the near infrared.? ? Yes. I should probably plot that on a log scale to get a better idea of how little/radiation is at 900 nm. ? The more I think about it, the more I think it is not going to work too well without heating the nichrome wire more than I really want to. Anyway, I should find out in a few days. I will probably play around with it towards the latter part of next week. Tom, wb6b
Dr. David Kirkby, Kirkby Microwave Ltd Member Profile All Messages By This Member #440 On Fri, 2 Sept 2022 at 03:08, Tom, wb6b <wb6b@...> wrote: Following this thread with interest. Interesting about the indirect temperature measurement ideas. Here is a link from a quick search. I'm sure there are other, maybe better, choices with a little more searching. There are far infrared sensors with digital interfaces (I2C), too. The wavelengths used for non-contact temperature measurement seem to be around the?8 ?m to 14 ?m range. Tom, wb6b Farnell had some of those therompiles. I bought one of these It cost about 5x what the IR LED did, but is much cheaper than the bolometer which Neil, G4DBN mentioned. But I may well buy one of them. But I can mess around with the IR LED and thermopile for little outlay. Dave
John KN5L All Messages By This Member #457 Hi David, On 9/2/22 7:29 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote: I am personally interested in doing this in a low impedance circuit. That probably means having a transformer with a single turn on the secondary. A bit of nichrome wire as the secondary would be convenient if it could be the current sense too. Using an Injection Transformer, as in HP4342 Q Meter, uses known Power or voltage applied to a Constant Voltage Injection System. An example Injection Transformer Fixture shown in: Section "Injection Transformer Q Measurement" Using an Oscilloscope for voltage measurement. As mentioned before, Oscilloscopes do not make highly accurate voltage meters. A simSmith model is included in web page, a way to measuring the measurement. Note applied Q, 200 in the case, does not match measured Q, 196.7. Required is a 10 Mohm voltmeter. As used in HP 4342A. Though an Injection Transformer fixture, with oscilloscope, could be valuable for evaluating differences between inductors. As described in HP 4342A documentation, there are internal errors which are accounted for. 4342A calibration procedure includes many calibration adjustments. John KN5L
Steve Hendrix All Messages By This Member #785 开云体育 I love this kind of "kitchen table science" and teaching it to youngsters. Would there be any possibility of getting her science fair report? Steve Hendrix On 2022-09-01 09:35 AM, Jeff Green wrote: toggle quoted message Show quoted text I? meant to add this to my post. I realize it sounds impossible to do at home but our daughter won a regional science fair by making a transistor in the high school art room. Was it a good transistor?? Define good. It was much better then the first 2N device, The 2N23.? Consider Japan used young women to hand assemble transistors for their first transistor radios. I wrote a report for an economics class explaining how thinking outside the box allowed Japan to get a jump start on the US/West for transistors. I had a nice book by a British EE that showed all the steps.? If you are determined enough, you can make a lot more stuff "on the kitchen table" then you'd believe.
Adrian Godwin All Messages By This Member #786 You might find Jeri Ellsworth's work interesting : toggle quoted message Show quoted text On Mon, Sep 26, 2022 at 1:01 PM Steve Hendrix <SteveHx@...> wrote: I love this kind of "kitchen table science" and teaching it to youngsters. Would there be any possibility of getting her science fair report? Steve Hendrix On 2022-09-01 09:35 AM, Jeff Green wrote: I? meant to add this to my post. I realize it sounds impossible to do at home but our daughter won a regional science fair by making a transistor in the high school art room. Was it a good transistor?? Define good. It was much better then the first 2N device, The 2N23.? Consider Japan used young women to hand assemble transistors for their first transistor radios. I wrote a report for an economics class explaining how thinking outside the box allowed Japan to get a jump start on the US/West for transistors. I had a nice book by a British EE that showed all the steps.? If you are determined enough, you can make a lot more stuff "on the kitchen table" then you'd believe.

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