I have been experimenting and using loops on the broadcast band back
to 1996 and 1990 on 160 meters. On 160 meters a loop should be .08 to
.10 wavelength max. for bidirectional broadside peaking and sharp
nulling. For outside installations I've never found any appreciable null
skewing difference between shielded amd unshielded loops but a shielded
loop does works better inside.
My unshielded loop has a diameter of three feet with a secondary
winding of 68.5 feet and a primary of 6.5 feet and resonates between
437-1996 kc with a mini 365 pf tuning capacitor. I use RG-8X as a
feedline with a Palomar Engineers preamp.
With a feedpoint impedance of only a few ohms, feedpoint/feedline
matching is generally a waste of time and effort, just let the preamp do
the job. One time I did use a 10 ohm/50 ohm UNUN with no appreciable
observed signal transfer difference. You can use a double or triple
turns primary pickup loop for better inductive signal coupling and
therefore get away with less preamplification. When using a loop inside
no preamp is needed but you do run the risk of null skewing due to house
wiring.
73 And Take Care,
Thomas Giella, KN4LF
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