You are taking about Military and 007 Bond pocket Zappers, I am talking
about Commercial LF/MF/HF installations including Coastal stations.
g3kev
----- Original Message -----
From: "Andy Talbot" <[email protected]>
To: <[email protected]>
Sent: Tuesday, January 03, 2012 2:22 PM
Subject: Re: LF: Antennas
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 <[email protected]> wrote:
> This is NOT the case at my QTH. The signal over noise is excellent because
I
> live in a QUIET location 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 environment with lots of noise then
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 and coastal receiving radio stations could use
> Ferrite sticks, micro probes they would not go to the vast expense of
> installing large wire arrays.
> Out in Rural 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 in the immediate
> vicinity nor as far as I can see looking for miles across the countryside
> to cause 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 Schäfer
> To: [email protected]
> Sent: Tuesday, January 03, 2012 12:51 PM
> Subject: Re: LF: Antennas
>
> Hi Rik,
>
> Am 03.01.2012 13:38, schrieb Rik Strobbe:
>
> Depends on how "gain" is defined. Larges antennas pick up more
> signal, but also more noise.
> It is the signal to noise ratio that is important, and this
> is no better than with smaller antennas.
> With a large antenna a signal will be S9 and noise at S7. With a small
> antenna the same signal will be S3 with noise at S1. In both cases SNR 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
worse,
> 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 ON7YD - OR7T
>
> ________________________________
> Van: [email protected]
[[email protected]]
> namens mal hamilton [[email protected]]
> Verzonden: dinsdag 3 januari 2012 11:57
> Aan: [email protected]
> Onderwerp: Re: LF: Antennas
>
> Like you say with the larger antennas Attenuation is needed there is so
much
> more gain over the smaller variety.
> My antennas both on LF es MF have attenuation control to reduce the gain,
a
> good position to be in I suppose.
> g3kev
>
>
> ----- Original Message -----
> From: Rik Strobbe
> To: [email protected]
> Sent: Tuesday, January 03, 2012 10:48 AM
> Subject: RE: LF: Antennas
>
> Hello Doug,
>
> over the past decade I have tested small loop antennas, a miniwhip
(PA0RDT)
> and a "big" transmitting antenna for receiving purposes and found that
each
> of them has its own advantages, as well on 137kHz as on 500kHz.
>
> Loop antenna
> Advantages:
> - very frequency selective, can be useful to attenuate broadcast
> - 8-shaped pattern can be useful to null out QRM sources
> - if large enough you don't need a pre-amp
> - you can move the loop around your property to find the best (now noise)
> location
> Disadvantages:
> - not omnidirectional, so you might need to rotate the loop
> - single band antenna
>
> Miniwhip:
> Advantages:
> - broadband, can be used from (V)LF to HF
> - omnidirectional
> - you can move the loop around your property to find the best (now noise)
> location
> Disadvantages:
> - pre-amp (built in), so you need to feed it with a DC voltage. This has
> to be done with some care as it can introduce QRM.
> - broadband so your RX needs to be able to handle the all
> signals. Can be solved by a BPF in front of the RX.
>
> "Big" TX antenna (Marconi):
> Advantes:
> - readily available if you also TX on 137/500kHz
> - no TX/RX antenna switching if you also TX on 137/500kHz
> - no pre-amp needed (in contradiction, often you will need an attenuator).
> - some frequency selectivity, but not as good as a loop
> Disadvantages:
> - big, often not worth the effort if you only want to RX
> - cannot be moved around to minimize QRM
>
> Conclusion:
> If you have a TX antenna and the local QRM is not too bad you can use it
> as RX antenna, so no need for an additional RX antenna. If you use a loop
RX
> antenna it should be at sufficient distance from your TX
> antenna, otherwise it will pick up all the QRM from the TX antenna.
> I did not notice that effect with the miniwhip.
> If you want to RX only a loop or miniwhip seems the best (most economical)
> option.
> I compared the miniwhip and my TX antenna on many occasions
> and could not notice a significant difference (as RX antenna).
> During the winter 2010-2011 Canadian and
> US beacons were copied regulary with good (audible) signals on 500kHz.
>
> 73, Rik ON7YD - OR7T
> ________________________________
> Van: [email protected]
[[email protected]]
> namens Douglas D. Williams [[email protected]]
> Verzonden: maandag 2 januari 2012 22:53
> Aan: [email protected]
> Onderwerp: Re: LF: Antennas
>
> Mal, you lost me on this one. Are you suggesting I (or we.....here in
North
> America) erect large verticals, inv L systems, Rhombics, and V beams in
> order to receive EU LF signals?
>
>
> I thought I was doing pretty well with my micro RX antenna!
>
>
> Doug KB4OEr
>
>
>
>
> On Mon, Jan 2, 2012 at 6:28 PM, mal hamilton <[email protected]>
wrote:
>>
>> LF es MF
>> Reports from across the pond and other DX locations as far as Tenneesee
>> and Kansas using micro probe antennas
>> are great for QRSS speeds but not suitable for audio reception.
>> Take 160 metres for example where it is normal
>> to work world wide on cw but antennas in use are large verticals, inv L
>> systems, Rhombics and V beams, therefore to have any chance
>> of receiving signals at audio level on LF or MF large antennas of
>> the calibre used on 160 metres are necessary.
>> As well as TX at this QTH I also use large arrays for RX
>> and often hear signals from NA that would not be audible with small
loops,
>> micro probes or ferrite sticks
>> Recently on 500 I was able to copy a W stn 579 but a DL stn copied only
on
>> screen, when I asked what strength the signal was I got no
>> reply!!!!!!!!!!!!! using a micro probe antenna.
>> If a proper large antenna system is not used on LF es MF then there
>> is virtually NIL chance of an audio report from across the pond for EU
stns
>> es vice versa
>> Back some years ago I had audio reports from the Boston area but
>> the antennas were proper wire arrays as used on 160 metres
>> Small hand held antennas are fine for High
>> Power BC strength signals but not for low power amateur signals to be
heard
>> No commercial LF/MF station would even consider an antenna of the micro
>> variety.
>> When I was in the business some years ago on LF/MF Rhombics
>> and V-Beams were the norm
>> de mal/g3kev
>>
>>
>>
>>
>
>
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