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
