[HCDX] Rowley, MA Antenna Shoot-Out, Part 2

[MarkWA1ION@xxxxxxx]

Rowley, MA Antenna Shoot-Out, Part 2

Beverage-on-Ground testing continued before sunset on 16 JUN at the salt-marsh site (Nelson Island) on the eastern end of Stackyard Road in Rowley, MA.

Where I left off last time was proving that the active whip phased against the 152 m (500 ft.) wire running to the east outperformed other combinations that included 152 m east wire versus 76 m (250 ft.) west wire, 152 m east wire versus 76 m east wire, and whip versus 76 m east wire.

This time, the tide was lower and the difference between terminating and not terminating the 152 m wire was not all that much.  Even in the best circumstances, I only get about 6-8 dB of front-to-back improvement over this BOG's inherently-good forward directivity.  This time around, tests were generally conducted with the 152 m east wire unterminated.  The point of the latest tests was to see if phasing the 152 m wire versus a 99 m (325 ft.) wire also running east could give results that would outperform the previous winner (whip-versus-wire).  Neil Kazaross had suggested this test.  Something that did surprise me was that, even though both wires were pointed in the same direction and spaced about 1.5 m apart, they did give different receptions on some frequencies.  The shorter 99 m wire actually had better rejection off the sides.  Before skip started, with the 99 m wire Providence, RI groundwave stations on 630 and 920 were knocked down well below the strengths of competing Canadian Maritimers CFCY and CJCH.  One could mistake this for the 99 m wire having better pick-up to the east and northeast, but that was disproved by the better pre-sunset reception of Morocco-1044 and several other Trans-Atlantics on the 152 m wire.  With the sun still bright at 7:50 p.m. local, the 152 m wire had 1044 at a clean-copy S9 whereas the 99 m wire had a weaker (about S5) and noisier/sloppier signal.

A series of phasing test cases were performed to rate:
(a) 152 m wire versus 99 m wire, 
(b) 152 m wire versus whip, and 
(c) 99 m wire versus whip.  

Channels such as WAMG-890 / Algeria-890.98, WCAP-980 / Algeria-981, WCMX-1000 / Spain-999, and WQEW-1560 / France-1557 (to mention a few) were very illustrative.

Once again it was the 152 m wire versus whip that gave the best results, with a tie for second place going to the 152 m wire versus 99 m wire and the 99 m wire versus whip combinations.

The key distinguishing characteristic here is suppression of short-skip pick-up relative to lower angle incoming signals.  Since the 99 m wire is decidedly inferior in this regard to either the whip or the 152 m wire, it causes poorer null stability when used.  Stations such as WCMX-1000, at about 75 km distance, have primarily a groundwave component on the 152 m wire and on the whip.  Around sunset when a shorter wire such as 99 m this time (and 76 m previously) is used, it gets a good deal of short-skip "in-fill" as well as the groundwave.  When such a wire is used as part of a phased pair, nulls aren't as deep or as stable.  You get a lot of selective fading where the carrier is nulled more than the sidebands, leaving "crunchy" audio.  Two antennas that, of their own accord, substantially reject high-angle skip give much cleaner nulls when phased: it is more often that the entire "pest" signal - sidebands and carrier - is reduced to greater depth for a greater amount of time.  This is exactly what you'd expect and the latest tests at Rowley prove it.  It is also why loop-versus-whip isn't quite as good as two spaced whips, whip-versus-(low angle getting) wire, or two spaced phased Beverages.  Eliminating the high angle pick-up first is imperative for high-quality nulling.

Now let's see what Neil's (or anyone else's) idea is for my next test.

Mark Connelly, WA1ION - Billerica, MA, USA

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