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Type: Posts; User: chuckey

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  1. Replies
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    Closed: Re: LDR used as an amplifier

    This circuit looks as though its from the 1930s, when amplifying was difficult and expensive, can't see the point now.
    Frank
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    Closed: Re: TDA7294 problem low sound

    Choice of two problems:- 1 there is a wiring fault, 2 bad layout or decoupling causing high frequency oscillations. So if you have a scope put it on the output see if you can see any wave form with...
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    Closed: Re: Transformers for circuit designs

    I go with Warpspeed's solution for a one off.
    Frank
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    996

    Closed: re: Series inductors in filter

    If you can align them end to end with the turns in the same direction then you will get additional mutual inductance, This is not weird, its free inductance!
    Frank
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    Closed: Re: How to test this crystal oscillator?

    You can calculate the frequency stability, but its meaning less as the rest of the circuit will be less stable then the crystal. Unless you actually build your clock or have a rubidium controlled...
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    Closed: Re: Power supply build query

    Correct battery := http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.X+black%26decker+hpb18+battery.TRS0&_nkw=+black%26decker+hpb18+battery&_sacat=0
    £13 ~16$
    ...
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    Closed: Re: Controlling voltage spikes for dc fan

    I have found that the small DC fans with their internal IC drivers require a very low impedance source for them to work. From this I would guess that at the end of commutation, the driver IC will...
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    Closed: Re: I need your help in one SMPS problem

    Seconds? Eh, not a catastrophic voltage over load then? Some sneak leakage/discharge path? does anything get warm/ hot?
    Frank
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    Closed: Re: Frequency converter oscillator question

    Its late at night but have you not done a (8 -3.6) followed by another -3.6, which I think is close to (8-7.2?). So why not 8 - 2 X 3.6?

    Oscillator frequency is ever so importent with respect to...
  10. Closed: Re: What is meant by cavity backed antennas,what is the need for it .

    A cavity is just a tuned circuit. Its main advantage is that you you a very wide choice of frequency responses and impedances to play with. It should be made from copper or some other low resistance...
  11. Closed: Re: What is best antenna for these RF remote modules

    First off all deepest apologies to OP, range varies as aerial size. Despite trying to loggon for days to correct my stupid typo, Browser + site + Google Chrome have stopped me. Removing Chrome has...
  12. Closed: Re: Practical current source with standard power supply

    A current source has an internal impedance much higher then the external load . Opposite to a convention voltage source. So a 1mA current generator might have an output impedance of 1M ohm to drive a...
  13. Closed: Re: What is best antenna for these RF remote modules

    Having fiddled about with these sort of things for years, the basic expression is range varies as the reciprocal of size. The smallest I might have seen would be 100mm long time 3mm diam coil- range...
  14. Closed: Re: Why two types of input impedance in laboratory instruments?

    The high impedance is so the instrument can be bridged across high impedance tuned circuits.
    Frank
  15. Closed: Re: Help in understanding PNP Transistor as a switch.

    With 3.3V from your micro on the base the emitter can only be 3.3+- .8 or so, i.e. 2.5 or 4.1V or you will destroy the transistor.
    If you want your emitter to switch , say +12V/0V then the first...
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    Closed: Re: Breaking Capacity Rating of MCB

    No its the prospective capacity to deliver current from your network i.e. loop impedance.
    Frank
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    Closed: Re: Getting 65A off a PCB to another PCB

    "
    The trick with the bolt is that it has to be elastic and stretch sufficiently to hold the joint in compression, even when your fibreglass compresses slightly over time.
    "
    NO!, N0!, NO!
    ...
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    Closed: Re: Breaking Capacity Rating of MCB

    Yes its all to do with the fault current. If your MCB is fed from a 1MW transformer 5m away the fault current would be a lot higher then if it is 200m away in a factory sub-circuit.
    Frank
  19. Closed: Re: Compare two high performance preamplifiers for HF

    I am old and its late at night so I did not get to grips with the norton amp article. How ever I wa involved with 20 dB HF LN amps in the 1980s, that were basically class B 2N3866 running at 50mA...
  20. Closed: Re: Project for interested novice that will give him most taste of electronics?

    How about a square wave signal injector and a signal tracer?
    Frank
  21. Closed: Re: Does higher Q factor leads to higher resonance frequency which means higher bandw

    Q
    physically measure of power loss in cavity no, its a "goodness" factor of the tuned circuit. On its own, it can only indicate the minimum bandwidth (b/w = Fres/Q).
    Higher Q means good...
  22. Closed: Re: PIR .5Hz noise seen in 2nd stage output amplifier

    PIR detectors detect infra red or " heat waves" :- https://en.wikipedia.org/wiki/Passive_infrared_sensor Their action is capacitively coupled so any heat draft will cause an output. Stop breathing,...
  23. Closed: Re: Antenna Basic Parameters

    Aerials can have any impedance, from a couple of ohms to thousands of ohms and may have some reactance as well. The impedance has to be matched to that of the aerial terminal of the receiver or...
  24. Closed: Re: Does higher Q factor leads to higher resonance frequency which means higher bandw

    I think that you have to be careful with the difference between Qu (unloaded) and Ql (loaded). Qu means the components are high quality, Ql should be as low as consistent with bandwidth. As Ql...
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    Closed: Re: Capacitive and Inductive Impedance

    Using the j operator simplifies the mathematics when analysing circuits with Rs, Cs and Ls. It labels components so they are known to have currents and voltages at 90 degrees to each other and the +...
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