This photo shows the interior of the tuning box. The RG-59/U 75 ohm coaxial cable outer shield is connected with the feedline through the metal box. There is a break in the coax outer jacket at the top of the loop of about 1" (25mm). The inner conductor is joined in series with a 560pF silver mica capacitor. The loop is tuned via a variable capacitor across the 560pF. The connection to the feed line inner, is taken from one side of the capacitor. With a bit of further experimentation, the inner conductor could be capacitively coupled to reduce the loading effect on the tank circuit and possible increase the matching. I was able to obtain a vswr of around 1.6:1 on 1.850MHz with a spread of about +/- 9kHz to 2:1 points. It certainly knocked out the intermods produced by broadcast stations and allowed me to hear cleanly and allowed the use of a pre-amplifier, which I wasn't able to, before. Further testing and adjusting may yield further improvements.
The tuning box installed
The tuning box is installed and ready. BNC plugs and sockets help make the job easy.
