[AMRadio] Re: Choke calculations

Mike Dorworth, K4XM k4xm at arczip.com
Sun Aug 21 18:39:32 EDT 2005

 This was covered in QST for February 1963. page 16-17
The methode discussed uses a center tapped transformer and a full wave
rectifier. The choke is placed in series with the resistor and the voltages
are adjusted to be the same. The calculations are always at 120 Hz. It is
not necessary for the voltages to be equal if a small amount of error is OK.
The formula is XsubL equals Voltage across Reactor times the Resistance
divided by the Resistor value.  For 240 ma he uses 1250 ohm at 72 watts
resistor and about 300 volts from a replacement xformer. Heavy overloads for
a short time will not hurt the transformer. We have been here before. 73
Mike K4XM

----- Original Message -----
From: "Patrick Jankowiak" <recycler at swbell.net>
To: <amradio at mailman.qth.net>
Sent: Sunday, August 21, 2005 6:12 PM
Subject: [AMRadio] Re: Choke calculations

> Now THAT is the key to happiness!
> Since we might wish to also measure the inductance of a choke with some
> amount of DC current flowing through it, does anyone have an idea how to
> this?
> In an example of a 10H choke, which would have 3768 ohms impedance, how
> would I pass 0.5 amp through it's 80 ohms of DC resistance without messing
> up the impedance measurement method?
> To me the obstacle looks like the issue of the power supply feeding the
> choke having a very low impedance compare to the measurement value to be
> made. Add to this the desire for a range of 0.1 to 100H and it's a real
> issue, at least from a calibration standpoint.
> I am certain some one on this list has done this before. It has to have
> been done in the choke factories of olden times!
> Patrick

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