The current balun can be readily demonstrated to provide equal and opposite currents to highly unbalanced loads. A simple test is to connect a balun to a load consisting of a 50 ohm resistor connected to a common or ground place and similarly a 100 ohm resistor. Measurement of the r-f voltage across the resistors will show that equal currents are being forced through each as the voltage across the 100 ohm resistor will be twice that of the 50 ohm resistor.
Roy Lewallen W7EL and Walt Maxwell W2DU have both discussed this test and Roy described a test fixture for demonstration. I have built the fixture and carried out the test with a simple W2DU bead balun and found almost perfect balance with equal currents being delivered to unequal load resistances. Simple 1:1 current or choke baluns such as the bead baluns are relatively insensitive to load impedance. I use them to transition from ladderline feeding multiband balanced antenna loads to coax to enter the shack to the tuners. The load seen by the baluns varies widely with band as would be expected. The Elecraft 4:1 balun is unique in its design and is able to provide an approximate 4:1 transformation over a wide range of frequencies and load impedances. Thus there is little need to restrict its connection to the input of a tuning unit. Teacher wasn't wrong, Geoffrey - it has just been a long time! 73, George W5YR (58 years a ham the end of this month) Fairview, TX [EMAIL PROTECTED] http://www.w5yr.com ----- Original Message ----- From: "Geoffrey Mackenzie-Kennedy" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: "Elecraft Discussion List" <[email protected]> Sent: Friday, August 06, 2004 10:47 AM Subject: [Elecraft] Performance of baluns. Hello all, Have noticed over the recent years that current baluns are used in places where the load/source Z is not purely resistive (OK will allow a little reactance) , example - an incoming transmission line that looks like R +j (quite a lot) goes to a balun then the to an ATU then to the TX. I was brought up to understand that in such a case, outgoing transmitter power would NOT result in equal and 180 degrees out of phase currents on the transmision line wires. i.e. the antenna would see an "unbalanced source" I was always told to put the balun between the Tx and the ATU, and to make sure that the ATU presented the balun with a R +/- j0 load , or simply put was "tuned up". (Loved those swinging links). I appreciate that there are a lot of "but ifs", but was Teacher right in the fundamentals? If so, it might go some way to explain why some antennas that are looking for a balanced feed are misbehaved. 73 Geoff GM4ESD _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
