[IRCA] Switch from unterminated to terminated DKAZ caught on wav file!

[Bill Whitacre <bw@xxxxxxx>]

Itâs not often you actually have a recorded history of setting up an antenna.  I recently had the accidental good fortune to do just that while making antenna adjustments on the final day of a visit to the Grayland Motel, near [oddly enough] Grayland, WA.

The more I listen to the Perseus wav file the more struck I am by how well this antenna works.

Without getting wordy and showing how little I know about antenna theory and radio wave propagation, let me just describe what the file is.  Itâs a Perseus wav file of the whole MW band, 30 seconds long, about 450MB in size.  It runs from about 15 seconds before 1500utc to about 15 seconds after â the âswitchâ from unterminated to terminated occurs at clock reading 1500:55 UTC.  Short reason why is that I âfake outâ the clock on the CPU to start Mestor TOH recordings at :58 instead of the default :59.

The antenna is a 160â DKAZ âaimedâ at about 290 deg. with #20 wire terminated with a Vactrol set to about 900 Ohms but variable with a pot in the âshackâ [Room 15 at the Grayland Motel].

The pattern of an unterminated DKAZ looks like a fat peanut along the axis of the antenna - bi-directional with some attenuation off the sides.  A properly terminated DKAZ looks like a cardioid thatâs flat in the back.

With the antenna âpointingâ at 290 deg. off-the-back is about 110 deg.

Nulls of 30 dB or better on easy-to-null groundwave, straight off-the-back stuff indicate a âhealthyâ DKAZ.  During skywave conditions things get a little more dicey as the signals are coming in at a variety of arrival angles.  At 1500utc in February there is still plenty of skywave - from all directions - coming into Grayland.

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Hereâs a few ânot to missâ items to check out if you download the wav file:

780 - KKOH, Reno [155 deg from Grayland], -54 dB unterm. -> -74 dB term. [20 dB null]

750 - KXTG, Portland [140 deg], -41 dB unterm. -> -67 dB term. [26 dB]

730 - KNFL, Boise [117 deg], -47 dB unterm. -> GONE - totally dominated by "Vancouverâs traffic station!"

Did I mention the DKAZ is wide-band?  I use the 160â version to get better low-band performance, shorter overall lengths work pretty well too though with some reduction in low-band performance.

To illustrate â

1700 - XEPE Tecate, Mexico [156 deg], -57 dB unterm. -> GONE - het from 1701 low-power Aussie

570 - KVI Seattle [61 deg], -51 dB unterm. -> -75 term. [24 dB], note big het from Japan on 567

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If youâre interested in hearing what this sounds/looks like, you can grab the file this way:

- go to http://america.fortw.com:8000
- click on Anonymous login
- look for and click on the 2nd file down from the top
- a window will pop up, click on Download File

Enjoy!

P.S. - I believe you can download and use Perseus software to play wav files without owning a Perseus receiver.  There may also be other software out there these days that will play Perseus files.

Bill Whitacre
Alexandria, VA
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