The K9AY

A recent conversation with N1LN caused me to dig out the schematic  for my slightly customized K9AY, built back in pre-blog 2006.  In general it has been a great antenna, and it has earned its permanent place in the antenna farm.

In its current location, it is not as good as it was in its original ‘test of concept’ location.  Practicality won out over performance.  The antenna now occupies a space in the rear corner of the yard.  That permanent location places it in close proximity to a chain link fence on two sides, and a storage shed is nestled into its NW quadrant. Significantly less than ideal location.

This location reduces the effectiveness of the F/B ratio, but the lower noise level makes the antenna a better choice for RX on both 160 and 80 in most cases.  When conditions on 160 and 80 are QRN free, the transmit antennas are sometimes better on RX. Sometimes.

On the days where noise is an issue, the K9AY is almost always a better choice, especially if there is also QRM which can be nulled off the rear of the K9AY.  I built the antenna as described by K9AY, with the additional mod to provide control voltages on a cable separate from the coax.  I was also forced to use the SPDT relays I had on hand at the time of construction.  The transformer used was constructed on an FT-125-K core, with 8 turns on the low [coax] side and 27 turns on the high[antenna] side. The antenna ground floats, i.e., it is NOT tied directly to the coax ground at the feedpoint.

The KazShack customized schematic that resulted from the mods….PDF format only.

The external relay controls were built into a small ‘Lock and Lock’ food container.  The lock-n-lock box has proven to be a great choice for an el-cheapo waterproof enclosure.  The gasketed lid locks firmly onto the box – not a single leak after five years.  The control cables and terminals were placed on the ground facing side, and the box was mounted on a small piece of scrap aluminum angle that happened to be handy at the time of construction.  The whole thing was given a random brown and green overcoat of paint for a bit of camo and UV protection.  So far so good, and the plastic appears to have remained supple in its partly sunny location.  Several radials were added at the base, attached to the antenna ground only.

The chain link fence reduces the F/B ratio, but in certain instances the level of offending QRM/QRN can still sometimes be dropped by several S units.  It performed much better in the free and clear test location, but that was just not practical.

Less often discussed in ham circles, the K9AY is an OUTSTANDING AM broadcast band SWL antenna.  I have been able to catch every nighttime LSU game as broadcast by WWL 870 in New Orleans.  That is not always possible on any of the transmit antennas.

The antenna doesn’t compare to a 2 wave length beverage, but it sure beats the crap out of listening on the transmit antennas in high noise conditions.  A pennant, flag, or EWE might be slightly better, but all are less practical given the space available.  Overall, I’m very happy with the performance of the K9AY rx antenna.

Engineer the possible.