[Elecraft] how did I calculate the loss?

[Charles Greene]

Change "differential mode current" to "common mode current" below 
concerning saturation.

At 07:13 AM 12/17/2003, Charles Greene wrote:
>John,
>
>I sorta backed into the design.  I first made a balun; the final design 
>was a little different.  I tried it on my W3EDP antenna at 100 watts.  The 
>W3EDP antenna is known to have high impedances on some bands, and the SWR 
>measurement was higher than 5:1 on some bands, but the balun did not 
>become hot as it would have if it had any but minor losses.  So I figured 
>out how to measure the efficiency by placing the balun in a thermos and 
>measuring the temperature rise during a timed operation.   I measured the 
>efficiency to 1% accuracy.  Subsequent improvements in technique improved 
>the accuracy to 0.1%.  I tried the 4:1 balun on my G5RV where it worked 
>fine at 100 watts, but replaced it with a 1:1 balun as that was a better match.
>
>The balun offered as a kit by Elecraft is a better design than the Low 
>Power Balun which is flat only through 35 MHz.  It is flat enough to be 
>useful on 6 meters.  It is unique, and I highly recommend it.  I lately 
>have learned how to design a 4:1 balun using a single core, and I built 
>one in a tiny plastic box weighing slightly over one oz. in a 135' OCF 
>(Windom) that gets hoisted to the top, with a RG58 feed line.  It works 
>fine with a K2/100 and antenna tuner on most bands.  When I get around to 
>it, I will put this design on N0SS's web site
>
>A balun usually does not decrease the losses in a system.  It enables you 
>to use low loss twin lead then transform it to unbalanced near the antenna 
>tuner and eliminate lossy coax.  The twin lead will carry RF without 
>excessive loss and radiation when the SWR is high on the feed line without 
>radiation; the coax will not.
>
>Some one mentioned that the fact that a current was balanced or not on a 
>twin lead or open wire feed line was dependent on the antenna and not the 
>source.  If balanced, there should be no radiation.  Hooking a twin lead 
>to a KX1, one side to ground does not change this, therefore there should 
>be minimum radiation from a 300 ohm ladder line, one side connected to 
>ground and one side to the business end of a KX1 antenna tuner (or any 
>other antenna tuner).  To expand this a bit, this holds true for an end 
>fed zepp, whether or not the 300 ohm ladder line is elevated or just 
>laying on the ground, as in a portable installation.  This gives some 
>possibilities for antennas for the KX1 involving getting a wire into the 
>shack without losses and radiation as it departs from the part up in the air.
>
>Concerning saturation.  I have a whole mess of baluns I have been able to 
>saturate in certain situations, even at powers on the order of 15 
>watts.  The situations involve high differential mode current on a 
>coax.  It has never happened on feeding an open wire feed line, or on an 
>dipole or OCF antenna.  When saturated, they lose effectiveness, and the 
>wire and core get hot.  Unless heated to over 135 deg C, the ferrite 
>material will recover after the RF current is removed.  More likely, the 
>balun will fail due to over voltage.  The magnetic wire varnish insulation 
>is good for about 500 volts peak, and the insulation on the ferrite 
>material the same, so this should give you some idea of the safe operating 
>impedance and power.   Be mindful that there is always the possibility of 
>a nick in the insulation during construction.  Larger baluns capable of 
>more power use glass tape and teflon insulated wires.
>
>I realize this line has deviated from the original subject (sorry Eric), 
>but some suggested feeding the 8030 with open wire line and a balun, and 
>one thing lead to another.

73, Chas,  W1CG
K2 462b, 3571