Re: [IRCA] Wellbrook versus Beverage comparisons

[Chuck Hutton <charlesh3@xxxxxxx>]

 	<4AF81524.9050409@xxxxxxxxxxx>
 

 <19740415002512.4B7781E1ABAC5A50@xxxxxxxxxxxxxxxxxxxxxxxx>
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0


The "averaging" is a form of "diversity reception". People have taken measu=
rements and found that fading is not identical (time-wise) when antennas ar=
e separated as little as 1/10 of a wavelength and almost non-identical as s=
eparation reaches 1/4 wavelength. This is a big reason why a long=2C long a=
ntenna like the Beverage seems to deliver more usable signals.
=20
As for aperture and sampling=2C size is not such a great way to evaluate th=
ings. A horizontal travelling wave antenna like the Beverage is a very inef=
ficient sampler. While exact figures depend on ground and height above grou=
nd=2C a decent rule of thumb is that it extracts about 10% of the signal co=
mpared to a vertical.
=20
=20
Chuck

----------------------------------------
> Date: Mon=2C 9 Nov 2009 16:53:32 +0000
> To: irca@xxxxxxxxxxxxxxxx
> From: nhp@xxxxxxxx
> Subject: Re: [IRCA] Wellbrook versus Beverage comparisons
>
> At 13:12 11/9/2009=2C you wrote:
>>Nick Hall-Patch wrote:
>>
>>>I don't really know the technical reasons
>>>for this=2C but it makes sense that a big antenna will deliver a more
>>>robust signal than a smaller one will.
>>
>>It's all about the aperture of the antenna.
>>
>>Even though the larger antenna has a less-tight F/B or forward lobe=2C th=
e fact that it is physically larger means that it is coupled into a greater=
 area of space. So it has a larger aperture.
>>
>>Because of this=2C i.e. it's coupling into a larger physical area=2C it c=
an average out the effects of ionospheric refraction of the signal=2C fadin=
g=2C etc. over a larger area. This often is perceived as a better signal=2C=
 or a steadier signal.
>>
>>Hope that made sense.
>
> Thanks for replying on this Rick. The explanation does ring a few bells (=
my antenna theory is pretty rusty=2C and I never considered it to be great)=
.
>
> I guess I'm not surprised that a 450m Beverage antenna does a better job =
of sampling a wavefront than a phased small antenna system of 40m spacing=
=2C as one is a wavelength or more at MW frequencies=2C while the other is =
a smallish fraction a of a wavelength.
>
> But I'm a tad surprised that a 7m x 15m corner fed loop gives noticeably =
better reception than a 5m x10m Flag even if it's also a "splashier" signal=
=2C as both are a very small fraction of a wavelength. Perhaps your explana=
tion gives way to mine (that when there is so little signal available for d=
emodulation=2C that a small increase makes a significant improvement in the=
 output signal's readability) with these small antennas=2C and that my comp=
arison of the Grayland antennas and mine was not apt?
>
> Thanks again for getting the brain cells working a bit.
>
> best wishes=2C
>
> Nick
>
>
>
> *****************************
> Nick Hall-Patch
> Victoria=2C BC
> Canada
>
> _______________________________________________
> 		 	   		  =
_______________________________________________
IRCA mailing list
IRCA@xxxxxxxxxxxxxxxx
http://montreal.kotalampi.com/mailman/listinfo/irca

Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers

For more information: http://www.ircaonline.org

To Post a message: irca@xxxxxxxxxxxxxxxx