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Feb 20, 2012

The MFJ-1786 Magnetic Loop Antenna

Well, I bit the bullet today and placed my order with MFJ for an MFJ-1786 magnetic loop antenna. I have been looking at these for years, and have always been fascinated by mag loops. Mag loops are very efficient and are much smaller than full size (resonant) loops. They have the reputation of being immune to noise affecting the electric field ("static") generated in the near field, meaning all that QRM given off by consumer electronics and power lines. They are extremely narrow in bandwidth, which is why this one comes with a dedicated tuning device. Interesting write-up on magnetic loops here.

The MFJ-1786 works anywhere between 10 and 30 MHz. That covers the 30 meter band up to the 10 meter band.  They also sell the MFJ-1788 which goes down to 40 meters, but I have read that it can have trouble tuning up down there so I am playing it safe and sticking to the higher bands.

I have never used a loop before and am very excited to get one on the air. I have heard hams use them, and invariably, they are coming in the strongest of all in the group.

MFJ-1786 Magnetic Loop Antenna
MFJ Magnetic Loop Antenna
You can read the reviews on the MFJ-1786 on eHam reviews here.

This 36 inch diameter loop antenna lets you operate 10 through 30 MHz continuously -- including the WARC bands. It may be mounted for vertical or horizontal polarization!

Does both DX and local contacts when mounted vertically. Get both low angle radiation for excellent DX and high angle radiation for local, close-in contacts. Handles 150 Watts. Fast/Slow tune buttons and built-in two range Cross-Needle SWR/Wattmeter lets you quickly tune to your exact frequency.

All welded construction, no mechanical joints, welded butterfly capacitor with no rotating contacts, large 1.050 inch diameter round radiator gives you highest possible efficiency. Each plate in the tuning capacitor is welded for low loss and polished to prevent high voltage arcing, welded to the radiator, has nylon bearing, anti-backlash mechanism, limit switches, continuous no-step DC motor -- gives smooth precision tuning. Heavy duty thick ABS plastic housing has ultraviolet inhibitor protection.

Here is the radiation pattern of a horizontally-mounted Super Hi-Q Loop Antenna.

The radiation pattern of a small loop antenna is essentially omni-directional with the exception of two very narrow nulls in the axis of the loop. If you visualize the loop as a "wheel", the nulls are in the same directions that the "wheel's axle" would run.

Signals will be attenuated more than 10 dB if they arrive within 15 degrees of the axis of the loop.
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