Bit OT: Why nulls improve with tilting?


huelbe_garcia@fastimap.com <huelbe_garcia@...>
 

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.


Rik
 

I have wondered the same thing. The only thing I could think of, is that by tilting a loop antenna, you are narrowing the beam. The figure 8 pattern is as viewed from above in 2 dimensions, but it is actually a cone in each direction and by tilting, you are using a narrower section of the cone. That is just my guess. I hope some one who really knows will chime in and tell us. - FARMERIK

--- In ultralightdx@..., "huelbe_garcia@..." <huelbe_garcia@...> wrote:

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.


Kevin Schanilec
 

I'll try and give it a shot. The antenna pattern is shaped like a donut, like the picture at:
http://www.fmx.dk/projects/wing_cam/119-1935_IMG.JPG

In this picture, imagine the ferrite loopstick sticking horizontally through the donut, with nulls at either end. The null zone is actually conical, meaning that you have to point the null properly in all three directions, including azimuth (elevation).

Now imagine a local pest that is coming in at, say, 45 degrees above the horizon. If you left your loopstick perfectly level, as in the picture above, signals coming from 45 degrees up will still be heard quite nicely. However, if you point it upward 45 degrees, the maximum null will also be 45 degrees up, matching the elevation of the pest's signal, and therefore the null is achieved.

For signals from far away, the angle of arrival is perhaps a few degrees at most above the horizon, and nulls are generally achieved with the loopstick essentially level, since the null of the loopstick is pointing more or less at the horizon

Hope this helps - Kevin S
Bainbridge Island, WA

--- In ultralightdx@..., "farmerik" <farmerik@...> wrote:

I have wondered the same thing. The only thing I could think of, is that by tilting a loop antenna, you are narrowing the beam. The figure 8 pattern is as viewed from above in 2 dimensions, but it is actually a cone in each direction and by tilting, you are using a narrower section of the cone. That is just my guess. I hope some one who really knows will chime in and tell us. - FARMERIK

--- In ultralightdx@..., "huelbe_garcia@" <huelbe_garcia@> wrote:

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.


Gary Kinsman
 

Hi Kevin,

I've long wondered about this. Thanks for the explanation.

So, if I'm understanding you correctly, the tilting of the Quantum Loop antennas can be used for nulling, but not for peaking, since they tilt only in the long dimension of the ferrite loop element.

Regards,
Gary

--- In ultralightdx@..., "dhsatyadhana" <dhsatyadhana@...> wrote:

I'll try and give it a shot. The antenna pattern is shaped like a donut, like the picture at:
http://www.fmx.dk/projects/wing_cam/119-1935_IMG.JPG

In this picture, imagine the ferrite loopstick sticking horizontally through the donut, with nulls at either end. The null zone is actually conical, meaning that you have to point the null properly in all three directions, including azimuth (elevation).

Now imagine a local pest that is coming in at, say, 45 degrees above the horizon. If you left your loopstick perfectly level, as in the picture above, signals coming from 45 degrees up will still be heard quite nicely. However, if you point it upward 45 degrees, the maximum null will also be 45 degrees up, matching the elevation of the pest's signal, and therefore the null is achieved.

For signals from far away, the angle of arrival is perhaps a few degrees at most above the horizon, and nulls are generally achieved with the loopstick essentially level, since the null of the loopstick is pointing more or less at the horizon

Hope this helps - Kevin S
Bainbridge Island, WA


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!

Huelbe.


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.
>


Kevin Schanilec
 

Hey Gary:

The "peak" is only a dB or three greater than the signal 20-30 degrees away from the bearing of the peak, so you really won't see much difference. So yeah, you get a peak of sorts, but your ear would probably never hear it, since the receiver's AGC would likely smooth out any differences.

However, the null is many dB less than the response just a degree or two away from the null bearing, so the null is substantially more profound than the peak.


Kevin

--- In ultralightdx@..., "gkinsman1" <gkinsman@...> wrote:

Hi Kevin,

I've long wondered about this. Thanks for the explanation.

So, if I'm understanding you correctly, the tilting of the Quantum Loop antennas can be used for nulling, but not for peaking, since they tilt only in the long dimension of the ferrite loop element.

Regards,
Gary

--- In ultralightdx@..., "dhsatyadhana" <dhsatyadhana@> wrote:

I'll try and give it a shot. The antenna pattern is shaped like a donut, like the picture at:
http://www.fmx.dk/projects/wing_cam/119-1935_IMG.JPG

In this picture, imagine the ferrite loopstick sticking horizontally through the donut, with nulls at either end. The null zone is actually conical, meaning that you have to point the null properly in all three directions, including azimuth (elevation).

Now imagine a local pest that is coming in at, say, 45 degrees above the horizon. If you left your loopstick perfectly level, as in the picture above, signals coming from 45 degrees up will still be heard quite nicely. However, if you point it upward 45 degrees, the maximum null will also be 45 degrees up, matching the elevation of the pest's signal, and therefore the null is achieved.

For signals from far away, the angle of arrival is perhaps a few degrees at most above the horizon, and nulls are generally achieved with the loopstick essentially level, since the null of the loopstick is pointing more or less at the horizon

Hope this helps - Kevin S
Bainbridge Island, WA


huelbe_garcia@fastimap.com <huelbe_garcia@...>
 

Hi Kevin, Farmerik!

Thanks for the inputs!

But your comments left me thinking: if the radiation comes at 45 degrees, isn't it a sky wave? For me, it's much more confortable :) to imagine ground waves coming at 0 degrees (following the surface) all times.

Antenas and transmission lines sometime refer their physical size in wavelenghts (l) or degrees of l. Something I'm wondering (but might be insane hihi) is the tilt angle is related to the distance between TX and RX; the angle is the sub-multiple of l of this distance.

Something like:
TX f = 600KHz
l = 500 meters
d TX-RX in meters 1062.5 meters
d TX-TX in l = 2.125
d TX-RX in degrees = 720 degrees + 45 degrees
tilt angle to null = 45 degrees

Just wondering :)

Huelbe.

On 11/4/2010 2:06 AM, dhsatyadhana wrote:
I'll try and give it a shot.  The antenna pattern is shaped like a donut, like the picture at:
http://www.fmx.dk/projects/wing_cam/119-1935_IMG.JPG

In this picture, imagine the ferrite loopstick sticking horizontally through the donut, with nulls at either end.  The null zone is actually conical, meaning that you have to point the null properly in all three directions, including azimuth (elevation).

Now imagine a local pest that is coming in at, say, 45 degrees above the horizon.  If you left your loopstick perfectly level, as in the picture above, signals coming from 45 degrees up will still be heard quite nicely.  However, if you point it upward 45 degrees, the maximum null will also be 45 degrees up, matching the elevation of the pest's signal, and therefore the null is achieved.

For signals from far away, the angle of arrival is perhaps a few degrees at most above the horizon, and nulls are generally achieved with the loopstick essentially level, since the null of the loopstick is pointing more or less at the horizon

Hope this helps - Kevin S
Bainbridge Island, WA



--- In ultralightdx@..., "farmerik"  wrote:
I have wondered the same thing. The only thing I could think of, is that by tilting a loop antenna, you are narrowing the beam. The figure 8 pattern is as viewed from above in 2 dimensions, but it is actually a cone in each direction and by tilting, you are using a narrower section of the cone. That is just my guess. I hope some one who really knows will chime in and tell us. - FARMERIK

--- In ultralightdx@..., "huelbe_garcia@"  wrote:
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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Russ Edmunds <wb2bjh@...>
 

You can't think of a signal coming in as one single element ( say at your 45 degrees ). Most MW signals are multipath, including locals. When you hear fading, that is ofetn indicative of multiple paths interacting. Thus a received signal can have multiple components.

Skywave signals ( which includes nighttime reception of anything beyond semi-locals ) are reflected back to earth, and so there could be several different elements arriving at any given receiver due to multiple paths from transmitter to ionosphere being reflected but also to multiple reflection points as well. Thus while the various signal elements will all have arrival angles within a fairly small range of angles, they won't all be identical either.

Some signals ( usually either lower powered semi-locals or higher powered stations just beyond semi-local range, but also some much more distant signals ) may arrive with elements more than a few degrees apart, in which case you might get multiple nulls.

But where we're talking about a small-to-medium loop antenna ( including the internal ferrite in a ULR ), in most cases, the small differences in arrival angles won't be noticeable.

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 Thu, 11/4/10, huelbe_garcia@... wrote:

From: huelbe_garcia@...
Subject: Re: [ultralightdx] Re: Bit OT: Why nulls improve with tilting?
To: ultralightdx@...
Cc: "dhsatyadhana"
Date: Thursday, November 4, 2010, 11:08 PM

 

Hi Kevin, Farmerik!

Thanks for the inputs!

But your comments left me thinking: if the radiation comes at 45 degrees, isn't it a sky wave? For me, it's much more confortable :) to imagine ground waves coming at 0 degrees (following the surface) all times.

Antenas and transmission lines sometime refer their physical size in wavelenghts (l) or degrees of l. Something I'm wondering (but might be insane hihi) is the tilt angle is related to the distance between TX and RX; the angle is the sub-multiple of l of this distance.

Something like:
TX f = 600KHz
l = 500 meters
d TX-RX in meters 1062.5 meters
d TX-TX in l = 2.125
d TX-RX in degrees = 720 degrees + 45 degrees
tilt angle to null = 45 degrees

Just wondering :)

Huelbe.

On 11/4/2010 2:06 AM, dhsatyadhana wrote:

I'll try and give it a shot.  The antenna pattern is shaped like a donut, like the picture at:
http://www.fmx.dk/projects/wing_cam/119-1935_IMG.JPG

In this picture, imagine the ferrite loopstick sticking horizontally through the donut, with nulls at either end. The null zone is actually conical, meaning that you have to point the null properly in all three directions, including azimuth (elevation).

Now imagine a local pest that is coming in at, say, 45 degrees above the horizon. If you left your loopstick perfectly level, as in the picture above, signals coming from 45 degrees up will still be heard quite nicely. However, if you point it upward 45 degrees, the maximum null will also be 45 degrees up, matching the elevation of the pest's signal, and therefore the null is achieved.

For signals from far away, the angle of arrival is perhaps a few degrees at most above the horizon, and nulls are generally achieved with the loopstick essentially level, since the null of the loopstick is pointing more or less at the horizon

Hope this helps - Kevin S
Bainbridge Island, WA



--- In ultralightdx@..., "farmerik" wrote:
I have wondered the same thing. The only thing I could think of, is that by tilting a loop antenna, you are narrowing the beam. The figure 8 pattern is as viewed from above in 2 dimensions, but it is actually a cone in each direction and by tilting, you are using a narrower section of the cone. That is just my guess. I hope some one who really knows will chime in and tell us. - FARMERIK

--- In ultralightdx@..., "huelbe_garcia@" wrote:
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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