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
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
<g3kevmal@talktalk.net>
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
