K9AY Low Band Receive Antenna

Noise is a major problem on the low bands.  Special receive only antennas are often  used to cut down on noise from other directions to help pull out weak DX signals. One very popular receive antenna is the Beverage, which is essentially a very long wire usually about 6'-8' above the ground. Although very effective, Beverages are often 500' to 1000' long, so are not practical for hams with small lots.  

Gary Breed, K9AY, developed a receive loop system that takes up very little space.  The array consists of two diamond shaped wire loops at right angles.  Each loop is fed through an impedance transformer against ground. The other end of the loop is grounded through a resistor in the 500-800 ohm range.  A switch box at the base allows selecting one of the loops and which ends have the feed point and termination resistor. This gives directivity in four directions with instant switching.  I used self sealing RG-6 coax back to the shack.  This type of coax is inexpensive and low loss.

The mast is made of PVC tubing and is about 25' long. The bottom section is made from two 10' sections of 2" diameter PVC. A length of 2" X 2" wood with the edges beveled down was inserted at the splice point to add strength. A PVC reducer is used to connect the final 5' which is made from 1 1/2" PVC. A 5' iron pipe was driven into the ground and the PVC pipe slips over it.  

In November 2009  I rebuilt the switching box at the base of the antenna.  I substituted a NEMA plastic box for the die cast aluminum box I had been using. The impedance transformer used to be a tapped coil type.  Based on suggestions in the literature, I replaced it with a transformer with a separate primary and secondary. That made a noticeable noise reduction improvement. Finally, I put in the ability to adjust the termination resistance.  Initial results indicate it does little in the desired direction, but it adjusts the angle of the back side null.  I can often improve null off the back by 15 dB or more.

My 350' beverages in their best directions are almost always better than the K9AY array. The advantage of the K9AY is that it covers directions I don't have a Beverage, and it only takes up an area about 25' X 25'.

  

K9AY array at W9XT.  This can be switched in 4 directions: NE, SE, SW & NW.

This is the updated switch box at the base of the antenna.   The board on the bottom of the case contains the impedance transformer and relays to switch directions.  The board on the side of the case has a number of resistors that are switched in and out to vary the termination.  This has little effect in the desired direction, but can improve the null off the back by 15dB or more.

© 2009 - 2018 Gary C. Sutcliffe

  

  

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