My version of
the loop is based on the information in this QST
I added several modifications to N7FKI's design. A one-turn pickup winding fed to a BNC connector was included for use with receivers with a low-impedance antenna input. This facility has been little used as the loop is generally used with portable receivers with internal loop antennas by placing the RX on the built-in pad as pictured below. Fahnestock Clips were installed in parallel with the 365 pf tuning capacitor to allow a range of fixed padding capacitors to be inserted to lower the tuning range into the beacon band - see capacitor values in last photo. A switch was installed to insert a 47 pf mica capacitor in series with the 365 pf tuning capacitor to spread-out the tuning at the upper band-end and to assure tuning to 1700 KHz. This was easy to do, but not optimum and removing a turn would have been better.
The sensitivity boost provided by this loop is quite considerable often bringing signals which are barely there up to a fully readable level. I have used it mostly with the Tecsun PL-380 or a Sony 7600-GR. The Tecsun is fairly deaf in the beacon band and the loop makes it usable there.
Overall view of the loop with a Tecsun PL-380 on the pad
Base assembly showing tuning capacitor,range extending switch and clips
Another view of the base assembly showing the tuning capacitor,range extending switch and clips
The low-impedance output connector side of the base assembly
The wing nut on the through bolt squeezes the two base blocks to hold the loop tightly
Base assembly showing the tuning capacitor and hoop tension bold and wing nut
Beacon band capacitors and table of frequencies covered by each capacitor. The 1770 pF is a parallel of 2 smaller caps.
Main Site - The Inland Marine Radio History Archive
Link checked and page code revised 02/25/2021