|[AMRadio] AM Audio|
bbruhns at erols.com
Sat Aug 20 11:59:30 EDT 2005
Cool! Here is a crude Ascii-art diagram. Heh heh,
yeah, it's supposed to be a triangle. The base of the
triangle is the input voltage, the left side is the
voltage across the resistor, and the right side is the
voltage across the inductor.
This is the situation when the resistance equals the
inductor impedance. The angle between the V(R) and
V(L) is 90 degrees, and you would calculate the voltage
compared to V(in) as V(L) = V(R) = V(in) * sin(45 deg)
= V(in) * 0.7071 because the angle of V(R) and V(L)
compared to V(in) is 45 degrees.
/ 90 \
V(R) / \ V(L)
Bacon, WA3WDR (modern artist!)
----- Original Message -----
From: "Geoff" <w5omr at satx.rr.com>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Saturday, August 20, 2005 11:23 AM
Subject: Re: [AMRadio] AM Audio
> Bob Bruhns wrote:
> > <>Yes, that will work. But remember, you want
> > equal voltages across the resistor and the
> > Surprisingly, this will not be 50% of the applied
> > voltage, but it will be about 71% of the applied
> > voltage. This adds up to about 1.414 times the
> > applied voltage! You should confirm this by
> > measuring both voltages directly.
> > This happens because the impedance of the
> > inductor is reactive, and the current is equal, so
> > the phases ofthe voltages differ by 90 degrees.
> > This phase shift causes a partial cancellation when
> > the voltages are added, so 71 + 71 = 100 instead
>> of 142. It's interesting to observe.
> Actually, Bacon, John's entire message was thus...
> you two agree. and I present it here, so that others
> may learn from this experience, as well.
> If all you need is a measurement of inductance, the
easiest thing is to series up a variable resistor with
the choke and apply a low voltage from a filament XFMR
(6 - 20 volts). Adjust the resistor so that the
voltage measured across the choke is equal to the
voltage across the resistor. If for instance a 10 volt
source is used, you will measure about 7 volts across
the resistor as well as across the choke.
> You are probably asking why it is not 5 Volts across
each and the answer to that is because of the phase
difference of 45 degrees when XL = R. The sine of 45
degrees is .707 and .707 X 10 Volts is about 7 volts.
But the main thing is what ever the voltage is, by
equalizing the voltage across the resistor and choke
results in the creation of a resistance that is equal
to XL of the choke at 60 CPS.
> Measure the resistance of the variable resistor after
equalizing the voltage
> drops and you have the XL of the choke at 60 cps.
> L = XL / 2 * pi * F
> L = XL / 6.28 * 60
> L = XL / 376.8
> Divide the resistance by 376.8 and you have the
> Thanks for the response. From all the active posters
> I admire and respect the intellect for the
> and talents mostly of WA3WDR, K4KYV, WA3VJB,
> KD5OEI and of course, WA5BXO, and not necessarily
> in that order.
> 73 = Best Regards,
> AMRadio mailing list
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