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Date: Tue, 3 Jan 2012 14:22:41 +0000
Message-ID: <CAA8k23T=VWKT+BegKwEQ74mKVooeV4RBG0ZVScRQT1n=bmMtbg@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Antennas
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What commercial receiving station is listening to frequencies below
2MHz regularly?.   And of course thay have large arrays; they need
beam steering, real seripus gain and a capability to generate nulls on
jammers.

Although, having said that, all modern HF DF / Intercept kit now makes
use of phased arrays of multiple small air loops (< 1m square).  Which
gives better results and is instantly reconfigureable, capaple of
adaptive and blind null steering, and can even separate two or more
signals on the same frequency.

And yes, I have worked on these modern of HF Intercept and DF
facilities and know their capabilities.  Mostly military, rather than
commercial though,   and the arrays were rarely bigger than 100m
linear dimensions and no higher than head height.  Take a look at the
Baldock setup.   I think its in the public domain, somewhere.

Andy
www.g4jnt.com


On 3 January 2012 14:03, mal hamilton <g3kevmal@talktalk.net> wrote:
> This is NOT the case at my QTH. The signal over noise is excellent becaus=
e I
> live in a QUIET location=A0 S9 signal with virtually no NOISE
> from the large antenna.
> Why do commercial receiving stations use large antenna farms out in the
> countryside ?? They do not use ferrite sticks or micro probes
> If you have always lived in an Urban=A0environment with lots of noise the=
n you
> do not understand what I am talking about.
> Go out into the countryside, put up a large antenna array and compare it
> against pocket size antennas, then you will be in a position to comment.
> If International commercial=A0and coastal receiving radio stations could =
use
> Ferrite sticks, micro probes they would not go to the=A0vast expense of
> installing large wire arrays.
> Out in=A0Rural areas large antennas equals big gain and very little noise
> whereas in Urban areas what ever sort of antenna you use there is likely =
to
> be a noise problem.
> One other point at my QTH there are no overhead wires=A0in the immediate
> vicinity nor as far as I can see looking for miles across the countryside
> to=A0cause noise pollution.
> A large antenna at your qth might capture more noise than signal, hardly =
the
> place to live for a LF experimenter!!
> g3kev
>
>
>
>
> ----- Original Message -----
> From: Stefan Sch=E4fer
> To: rsgb_lf_group@blacksheep.org
> Sent: Tuesday, January 03, 2012 12:51 PM
> Subject: Re: LF: Antennas
>
> Hi Rik,
>
> Am 03.01.2012 13:38, schrieb Rik Strobbe:
>
> Depends=A0on=A0how "gain" is defined.=A0Larges=A0antennas=A0pick up more
> signal,=A0but=A0also more noise.
> It=A0is the=A0signal to=A0noise ratio=A0that is important, and=A0this
> is=A0no=A0better=A0than=A0with smaller antennas.
> With=A0a=A0large antenna a=A0signal=A0will=A0be=A0S9 and=A0noise at S7.=
=A0With a=A0small
> antenna the=A0same=A0signal=A0will=A0be=A0S3=A0with=A0noise at S1. In=A0b=
oth cases=A0SNR is
> the same.
>
>
> This is exactly the thing that he never will understand. Often discussed =
and
> somehow logical, anyway. This is why he says that a small antenna is wors=
e,
> since he runs a RX that needs a high signal input level. Thus a small
> antenna, e.g. a ferrite antenna without a suitable preamp, gives poor
> results....
>
> 73, Stefan
>
>
>
>
>
> 73, Rik=A0=A0ON7YD - OR7T
>
> ________________________________
> Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.o=
rg]
> namens mal hamilton [g3kevmal@talktalk.net]
> Verzonden: dinsdag 3 januari 2012 11:57
> Aan: rsgb_lf_group@blacksheep.org
> Onderwerp: Re: LF: Antennas
>
> Like you say with the larger antennas Attenuation is needed there is so m=
uch
> more gain over the smaller variety.
> My antennas both=A0on LF es MF have=A0attenuation control =A0to reduce th=
e gain, a
> good position to be in I suppose.
> g3kev
>
>
> ----- Original Message -----
> From: Rik Strobbe
> To: rsgb_lf_group@blacksheep.org
> Sent: Tuesday, January 03, 2012 10:48 AM
> Subject: RE: LF: Antennas
>
> Hello=A0Doug,
>
> over the past decade I have=A0tested=A0small loop antennas, a=A0miniwhip =
(PA0RDT)
> and a "big"=A0transmitting antenna=A0for=A0receiving=A0purposes and=A0fou=
nd=A0that=A0each
> of=A0them has=A0its=A0own advantages,=A0as=A0well=A0on=A0137kHz as=A0on 5=
00kHz.
>
> Loop antenna
> Advantages:
> -=A0very=A0frequency selective,=A0can=A0be=A0useful to=A0attenuate=A0broa=
dcast
> -=A08-shaped=A0pattern=A0can=A0be=A0useful to=A0null out=A0QRM sources
> -=A0if=A0large=A0enough=A0you=A0don't=A0need a pre-amp
> -=A0you=A0can move the loop=A0around=A0your=A0property to=A0find the best=
 (now noise)
> location
> Disadvantages:
> -=A0not omnidirectional,=A0so=A0you=A0might=A0need to=A0rotate the loop
> - single band antenna
>
> Miniwhip:
> Advantages:
> - broadband,=A0can=A0be=A0used=A0from (V)LF to HF
> - omnidirectional
> -=A0you=A0can move the loop=A0around=A0your=A0property to=A0find the best=
 (now noise)
> location
> Disadvantages:
> -=A0pre-amp (built in),=A0so=A0you=A0need to=A0feed=A0it=A0with a=A0DC vo=
ltage.=A0This has
> to=A0be=A0done=A0with=A0some care as=A0it=A0can=A0introduce QRM.
> -=A0broadband=A0so=A0your=A0RX=A0needs to=A0be=A0able to=A0handle the all
> signals.=A0Can=A0be=A0solved=A0by a=A0BPF in front of the RX.
>
> "Big"=A0TX antenna (Marconi):
> Advantes:
> -=A0readily=A0available=A0if=A0you=A0also=A0TX=A0on 137/500kHz
> -=A0no TX/RX antenna=A0switching=A0if=A0you=A0also=A0TX=A0on 137/500kHz
> -=A0no=A0pre-amp=A0needed (in contradiction,=A0often=A0you=A0will=A0need=
=A0an attenuator).
> -=A0some=A0frequency selectivity,=A0but=A0not as=A0good as a loop
> Disadvantages:
> - big,=A0often=A0not=A0worth the=A0effort=A0if=A0you=A0only want to RX
> -=A0cannot=A0be=A0moved=A0around to=A0minimize QRM
>
> Conclusion:
> If=A0you have a=A0TX antenna and the=A0local=A0QRM is=A0not=A0too bad=A0y=
ou=A0can=A0use=A0it
> as=A0RX antenna,=A0so=A0no=A0need=A0for=A0an=A0additional=A0RX antenna.=
=A0If=A0you=A0use a loop=A0RX
> antenna=A0it=A0should=A0be at=A0sufficient=A0distance=A0from=A0your=A0TX
> antenna,=A0otherwise=A0it=A0will=A0pick up all the=A0QRM=A0from the=A0TX =
antenna.
> I=A0did=A0not=A0notice=A0that effect=A0with the miniwhip.
> If=A0you want to=A0RX=A0only a loop=A0or=A0miniwhip=A0seems=A0the best (m=
ost economical)
> option.
> I=A0compared the=A0miniwhip and=A0my=A0TX antenna=A0on=A0many occasions
> and=A0could=A0not=A0notice a significant=A0difference (as=A0RX antenna).
> During=A0the winter 2010-2011 Canadian and
> US=A0beacons=A0were=A0copied=A0regulary=A0with=A0good (audible)=A0signals=
=A0on 500kHz.
>
> 73, Rik=A0=A0ON7YD=A0- OR7T
> ________________________________
> Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.o=
rg]
> namens Douglas D. Williams [kb4oer@gmail.com]
> Verzonden: maandag 2 januari 2012 22:53
> Aan: rsgb_lf_group@blacksheep.org
> Onderwerp: Re: LF: Antennas
>
> Mal,=A0you lost me=A0on=A0this one. Are=A0you=A0suggesting I (or we.....h=
ere in=A0North
> America)=A0erect=A0large verticals,=A0inv L systems, Rhombics, and V=A0be=
ams in
> order to=A0receive EU=A0LF signals?
>
>
> I=A0thought I was=A0doing=A0pretty=A0well=A0with=A0my micro=A0RX antenna!
>
>
> Doug=A0KB4OEr
>
>
>
>
> On=A0Mon, Jan 2, 2012 at 6:28 PM, mal=A0hamilton <g3kevmal@talktalk.net> =
wrote:
>>
>> LF=A0es MF
>> Reports=A0from=A0across the pond and=A0other=A0DX=A0locations as=A0far a=
s=A0Tenneesee
>> and Kansas=A0using micro=A0probe=A0antennas
>> are=A0great=A0for=A0QRSS=A0speeds=A0but=A0not=A0suitable=A0for audio rec=
eption.
>> Take=A0160=A0metres=A0for=A0example=A0where=A0it is=A0normal
>> to=A0work=A0world=A0wide=A0on=A0cw=A0but=A0antennas in=A0use are=A0large=
 verticals,=A0inv L
>> systems,=A0Rhombics and V beams,=A0therefore to have=A0any=A0chance
>> of=A0receiving=A0signals at audio level=A0on=A0LF=A0or=A0MF=A0large=A0an=
tennas of
>> the=A0calibre=A0used=A0on 160=A0metres are necessary.
>> As=A0well as=A0TX at=A0this=A0QTH I=A0also=A0use=A0large=A0arrays=A0for=
=A0RX
>> and=A0often=A0hear=A0signals=A0from NA=A0that=A0would=A0not=A0be=A0audib=
le=A0with=A0small loops,
>> micro probes=A0or=A0ferrite sticks
>> Recently=A0on 500 I was=A0able to=A0copy a W=A0stn 579=A0but a DL=A0stn=
=A0copied=A0only=A0on
>> screen,=A0when I=A0asked=A0what=A0strength the=A0signal was I=A0got=A0no
>> reply!!!!!!!!!!!!!=A0using a micro=A0probe antenna.
>> If=A0a proper=A0large antenna system is=A0not=A0used=A0on=A0LF es=A0MF=
=A0then=A0there
>> is=A0virtually=A0NIL=A0chance of=A0an audio report=A0from=A0across the p=
ond=A0for EU=A0stns
>> es=A0vice versa
>> Back=A0some=A0years=A0ago I had audio reports=A0from the Boston=A0area=
=A0but
>> the=A0antennas=A0were proper=A0wire=A0arrays as=A0used=A0on 160 metres
>> Small=A0hand held=A0antennas are fine=A0for=A0High
>> Power=A0=A0BC=A0strength=A0signals=A0but=A0not=A0for low power amateur=
=A0signals to=A0be heard
>> No commercial LF/MF station=A0would even=A0consider=A0an antenna of the =
micro
>> variety.
>> When=A0I was in the business=A0some=A0years=A0ago=A0on LF/MF=A0Rhombics
>> and=A0V-Beams=A0were the norm
>> de mal/g3kev
>>
>>
>>
>>
>
>