Re: Bit OT: Why nulls improve with tilting?


pianoplayer88key
 

I've recorded a few clips demonstrating how much of an effect tilt nulling can have, at least for my strongest local on my PL-380.

1170-KCBQ, facing transmitter, outside - would be 77/25 on the G8 that I no longer have
There's no rotate-null recording now, but I was getting 55/25 earlier this afternoon (local sunset has already happened, bringing KCBQ down to ~60/25 when facing them, so I can't record it now).
1170-KCBQ, facing transmitter, in a car  - 61/25
1170-KCBQ, rotate-null, in a car - 43/25 (but maybe could have been rotate-nulled a little better)
And, finally...
1170-KCBQ, tilt-null outside.  RSSI/SNR often dropped to 15/00, although this was extremely difficult to achieve and maintain, as will be evidenced throughout the clips.

It does seem, though, that there comes a point where even tilt-nulling can't tame a pest.  This past weekend I had a few radios at my grandma's house in San Gabriel, CA (1/3 mile from 23kW 1300-KAZN and 50kW 1430-KMRB) and there was no way I could even get the background noise to come up.  The two Asian-language pests (that would make it even more difficult to identify any TPs on 1296, 1305 or especially 1431 although I didn't even try this time) were reading anywhere from 83/25 to 91/25 on the G8 when facing them, and I don't think I was ever able to get below 70dBu or so.

So would tilt-nulling a a local megapest at night (mine would be 760-KFMB running 77/25 to 81/25 on the G8) make it much easier to hear co-channel stations under it, or would it run the risk of at least partially nulling those too?  I think I've heard a Mexican station under the local on 760 at night while tilt-nulling KFMB, and have confirmed it was actually an XE due to hearing the Mexican National Anthem (if I hear it a few more times I'll probably be able to sing/play it without the sheet music, and being within groundwave reception range of at least maybe a couple dozen or so XE stations (including one ~65/25 (G8) in the daytime, 690-XEWW, 32mi, 189°) I'm sure gives me more opportunities to learn Spanish), but I never heard any official ID.


--- In ultralightdx@..., Russ Edmunds wrote:
>
> 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
> wb2bjh@...
> FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'
> AM: Modified Sony ICF 2010 barefoot
>
> --- On Wed, 11/3/10, huelbe_garcia@... huelbe_garcia@... wrote:
>
>
> From: huelbe_garcia@... 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!
>
> Huelbe.
>

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