Originally Posted by WB2UAQ
For tuner applications, using a 4:1 Guanella and switching the chokes in parallel when you need 1:1 just seems daft to me. Using the same two cores you can build a 4:1 voltage balun followed by a 1:1 current balun, which will maintain better current balance over a wide load range; when you don't need the 4:1 impedance transformation simple switch out the 4:1 voltage balun. Switching two 4:1 Guanella chokes in parallel to achieve a 1:1 current balun throws away half your hard-fought CM performance.
G'day all. Some results: I've been evaluating my various home made baluns in ATU 'Tuned line' applications with interesting results. I've tested 1:1 and 4:1 voltage and current baluns and a 4:1 'hybrid' balun. At least for tuned line ATU applications, the 4:1 voltage and the 4:1 'hybrid' balun fared best and could happily 'tune' any band without any complaint and with apparent minimal loss.
The 1:1 current balun worked satisfactorily on several bands but stubbornly refused to allow a low SWR (through a T match tuner) on several bands. My 4:1 current baluns wound on two separate ferrite cores appear to work about as well as the other 4:1 baluns, but the slightly 'simpler' (in construction) 4:1 hybrid balun is fine in all respects and wins out overall. As expected, the 4:1 'hybrid' balun seems to deliver superior current balance. Regards, Felix vk4fuq.
Last edited by VK4FUQ; 06-14-2012 at 11:40 AM.
I agree. 1:1 current baluns work well as an isolator within a narrow impedance range, but outside of that range the losses increase. They are wound for a specific impedance determined by wire diameter and spacing.
The dual balun I put in my tuner is used in the 4:1 mode on all bands except one where the line impedance was measured close to 60 ohms. On the other bands, the impedances were 200 ohms or more where the 4:1 Guanella shines.
I tested all the balun combinations on all the bands before settling with the Guanella 4:1 with the lowest overall losses. The 4:1 Guanella also made my cheaply built t-match tuner happier with all settings in the middle of their ranges.
My preference would be a link coupled balanced tuner instead of a high pass T-match with a balun, but we don't have much of a choice anymore other than home built.