[RFI] Transformers for RX Antennas

[Jim Brown]

On 10/28/2018 1:25 PM, JW via RFI wrote:
> Even a K9AY loop (half sized) placed in the front yard away from utilities required an extra 1:1 transformer in-line with the coax to knock down the house-made noise such that external signals could be picked up. The 9:1 xfmr used at the feedpoint was insufficient to keep 'noise' out of that antenna.

For years, we've been shooting ourselves in the foot by building 
transformers for RX antennas with the windings laying on top of each 
other. The result is very high capacitance between windings, which 
couples common mode noise. Simply by separating the windings, that 
capacitance gets very small and breaks the common mode circuit. I wind 
primary and secondary on opposite sides of a toroid core. With the right 
core for the frequency range, the loss in the transformer is too small 
to matter for RX (a dB or so).

There's a new applications note on transformers and chokes for RX 
antennas on my website. k9yc.com/publish.htm

73, Jim K9YC