Re: Bit OT: Why nulls improve with tilting?

Russ Edmunds <wb2bjh@...>

Reason 1: Most MW transmitting towers sned the signals with both vertical and horizontal components. Some have added hardware to greatly reduce the skywave component, while others have not. Therefore, the tilt is sometimes required to eliminate some of the skywave.
Reason 2: Building on one above, the tilt feature is useful in nulling your locals because there is almost always some localized skywave component present.
Reason 3: MW signals at distance are reflected in the ionosphere and sent back to earth. This introduces a vertical aspect to the received signal. Therefore a tilt feature could be used in some cases to 'stablize' a wek DX signal.
I see no reason why most loop antennas having the tilt feature could not be used for peaking, althouhgh the more prevalent use is in nulling.

Russ Edmunds
Blue Bell, PA ( 360' ASL )
[15 mi NNW of Philadelphia]
40:08:45N; 75:16:04W, Grid FN20id

FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'
AM: Modified Sony ICF 2010 barefoot

--- On Wed, 11/3/10, huelbe_garcia@... wrote:

From: huelbe_garcia@...
Subject: [ultralightdx] Bit OT: Why nulls improve with tilting?
To: ultralightdx@...
Date: Wednesday, November 3, 2010, 10:32 PM

Hello all!

Stephen posted a few hours ago a note on something I always wondered the reason: tilting the antenna does improve nulls of groundwaves. I can't think on an good explanation why this happens :) 

As all MF stations use vertical irradiators, I think no tilting would be needed to null the station completely, specially when tuning groundwaves.

But this is not the case. Most of the time, the local stations need some tilt to null it out. Only when I hear not-so-local stations (say some 20mi/30km away), tilting is not needed anymore.

Would you guys guide me why we need tilting on groudwave MF?

Thanks a lot!


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