A transformer is N O T a balun, it's a transformer!? If everything is balanced at the DM? "output" of a transformer, yes, they can function as a balun.? However, if there is any imbalance on the DM end, especially with any complex portion of the impedance, the balun function falls apart quickly.? Again, consult the following:
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In regards to the usefulness of a common mode choke (CMC), have a read of the attachment - real data.? All my bifilar CMCs measure in excess of 2k¦¸ to CM energy and less than 0.4 dB loss to DM energy through 21 MHz.? They function well as a balun.? You might view them as a transmission line transformer, but that is not how they function or are designed.? As such, they come in between 72 and 94 ohms on the T-240-31 cores and exhibit a velocity constant of very close to 0.56.?
On Sat, Apr 2, 2022 at 8:12 PM Starsekr via <Starsekr=[email protected]> wrote:
Dave, I'll disagree with your terminology.? A common mode choke is a resistance to common mode current on the coax (the outside of the coax shield), not a balun (balanced to unbalanced) transformer.? They do different things and pretty much cannot be efficiently combined in one toroid.? If you look at the enginnering notes on the Palomar Enginnering website they state the impedance of a full wave loop is about 100 ohms and needs a 2:1 balun transformer.? ?Smaller loops, down to the 0.1 wave length have much smaller input impedances, down to 1 or 2 ohms, and are often coupled with? 1:5 ratio feeder loops,? Usually balanced loads don't reflect much common mode energy back into the coax if a wideband balun is used to feed the load, but a common mode choke never hurt anybody.
