[IRCA] Super loop day 3

["Andy Ikin" <andrew.ikin@xxxxxxxxxxxxxxx>]

Hello Folks,

First I would like to take this opportunity to thank John and Kevin for testing out the K9AY and Super Loop arrays at Grayland. 

The original development of the K9AY array goes back at least 5 years, when I was experimenting with an early design of the Broadband Phasing unit. Whilst I could Broadband phase pairs of active loops or active dipoles, the K9AY would only work in one direction. Hence, the project was put on hold. So I continued with the broadband loop array primarily because this can be used in an urban environment where dominant local E-Field noise may cause arrays of active whips, Flags and K9AYs to limited by local noise. However, about a year ago I had another go at  trying to get the K9AY array to work. I managed to find out why it didn't work before by replacing the antenna with active dipoles and plotting the Phase and Amplitude  for several null adjustments, and then repeating the test using Broadband loops. The net result was that the perimeter wire fence was disturbing the H Field. Hence, this was screwing up the pattern of one of the K9AYs ( the K9AY requires the correct E and H !
 Field balance to obtain its directivity ).  Once I had moved the K9AY array about 20m away from the fence it worked flawlessly with 40m antenna spacing. I even got it to work down to 250kHz with only 20m spacing. So all was well I thought until a second array was installed in Yorkshire. The first pair of  the K9AYs worked okay. But the second pair ( East West ) just wouldn't provide any real F/B. After many e-mail exchanges with the user the problem was fixed when metal support pole was insulated from the ground. Soon afterwards I shipped out a K9AY array for John to test. 

John has already reported that the absence of finding a good ground connexion degrades the F/B. In an effort to mitigate this feature, I redesigned to the K9AY Head to increase the output loading from 450 to 800 Ohms and reduce the matching transformer primary to secondary capacitance to just a few pF. This I thought may allow for the use of radials in lieu of a decent ground connexion. Well it just didn't work for me or John. At this stage John was on the point of giving up on testing the array until he arrives back in Oklahoma. Then I suggested that the new K9AY Head could be configured as active Flag or KAZ antenna amplifer. John, suggested an array of two super loops; the rest is history. So the way forward looks like either the Flag or KAZ array using the new FLAG100 modules as these are directly compatible with the Wellbrook "variable cross-fire" loop antenna controller. 

Back to the array design: The use of a 20dB gain amplifier in each K9AY head may at first sight seem "over the top". This was found to be necessary to make sure that the output at the deepest null or highest F/B would always be greater than any signal pick-up on the feeder. Also the amplification is required to maintain an adequate Antenna Factor at the low end of the band. 

The key feature of a 2 element of the  K9AY array is the "variable cross-fire" or variable delayline controller. This ensures the correct phasing across the band, with ability of the user adjust the phase and amplitude to give the best overall F/B. Also individual signals to the back of the array can be  phase and amplitude tweaked to increase the null without screwing up the overall F/B. Furthermore, small phase and amplitude errors don't screw-up the pattern.  

Finally a word of warning, Flag and K9AY arrays are not tolerant to nearby objects, such as metal structures, power and phone lines. Hence, I would recommend at least 40m clear space around any of these antennas.

Kind regards

Andrew

Wellbrook Communications
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