Initial Measurements of the Magnetic Loop Antenna

Here is a plot of the Magnetic Loop Antenna tuned to 14.228 MHz in the 20m band.

loop20m Custom

SWR was 1.10 and the antenna was at resonance with a bandwidth of 40 kHz as predicted.Note that these measurements were taken indoors while mounted on a camera tripod just over three feed high.

This is all a good sign but there is also some issues that I will need to resolve.

First up is the tuning sensitivity. I have ordered a 6:1 reduction drive gear to help this issue. I just cannot fine tune adjust the capacitor to a specific frequency without a reduction mechanism. Next is the sensitivity to my hand being close to the capacitor while tuning. Ultimately I will solve this with a motorized tuner. For now I will just extend the tuning knob with a dowel stick.

Now for the bigger issue. I had originally designed this antenna for use with 20m through 10m limited largely by the range of capacitor I had available. i had settled on buying a piece of coax 9 feet long giving me a diameter of about 2.8 feet. I ended up buying a 10 foot length by mistake so the diameter is actually about 40 inches. While this should improve loop efficiency slightly it has messed up my plans on the high bands. Running a sweep at the extremes of the capacitor range give me a useable range of between 8Mhz and 20Mhz. The low end does not worry me much as I can add a cap in parallel to the variable cap to get the tuning in range. The bigger problem is with the high bands. Plus, I am not sure why they are not in tuning range as my capacitor goes down to 9pF which the design models show is OK.

Stay tuned (no pun intended) as this is a work in process…


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