Comment summary #8
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Comment 71 ... 80
| date | article | author | comment |
| 04 mei 2019 12:17:45 | Extreme low voltage oscillator | Jindra | I would argue that putting two BF245A in parallel does not increase gain. Contrary to what you suggest, their transconductance (measured in mA/V) must be average of individual gm of each of the two JFETs. On the other hand, BF245A has very low drain current at Vgs = 0V (according to data sheet, between 0.5 and 2.2 mA). By putting two BF245A in parallel you increase the current and that probably enables the oscillations to start. In other words, the initial resistance between Vin and the coil is lower. You could probably achieve the same by using a single BF245B or BF245C. However, using two JFETs in parallel will allow for higher maximum drain current and power loss. I think it is a good idea. Maybe I would try 2x BF245B in parallel and look if the output improves. |
| 22 apr 2019 12:12:59 | Measuring capacitance and ESR | Freddy | Yes, it is certainly possible to determen the distance of the plates by measuring the capacitance. But be aware that the capacitance is very small: at a distance of 0.1 mm the capacitance is only 8.85 pF! 100 Hz or even 10 kHz is too low to do it reliable. Even at 1 MHz the reactance is 18 kΩ, but feasible. |
| 21 apr 2019 01:46:35 | Measuring capacitance and ESR | Daniel | I'd like to measure the distance of two narrow metallic plates with size around 1cm^2 and 1cm^2 at a frequency of at least 100Hz, preferably rather around 1-10 kHz. I think measuring the capacity is the best way to measure the distance. (I have a good microscope to measure the precise distance, but is is very slow. However, it is suitable to calibrate a fast method.) Which of these method do you suggest to measure the capacity? Or none of them? |
| 19 feb 2019 16:20:21 | Magnetic permeability | Freddy | First you say you're changing the core material, now you say the material is (and stays?) air?. And why would you measure the permability of air? Are you using the circuits and calculations given in this article? |
| 19 feb 2019 15:26:43 | Magnetic permeability | Costa | I'm measuring voltage, the core is air, the inductance of coil is 90uH with air in the core, should i build a coil with higher inductance? |
| 15 feb 2019 00:20:07 | Magnetic permeability | Freddy | What are the measured values: current and voltage? Has the core an air gap? |
| 14 feb 2019 15:17:51 | Magnetic permeability | Costa | Hi, thank you for this excelent article. i built this circuit with a resistor ( 10-100 ohms ) and a inductor, with a frequency of 100hz to 500 khz. I changed the core material but the voltage of a inductor didn't vary for any frequency. what can i do? |
| 11 feb 2019 15:47:40 | Additive synthese waveform generator | Bing | Version 71.0.3578.98 (Official Build) (64-bit) This is the chrome version I have. It's a work laptop. I don't think I can update it. :-( It's working now. :-) |
| 11 feb 2019 15:40:27 | Additive synthese waveform generator | Bing | Freddy, This worked on chrome last Sunday, but now it is not working again. Could you please check if the new code is removed by accident. My school issued laptop only has chrome and explorer. Thank you, Bing |
| 10 feb 2019 21:46:48 | Additive synthese waveform generator | Freddy | The latest code is still there. What Chrome version are you using. I have version 72.0.3626.96 (Official build) (64-bits). Did you refresh the page as suggested? |