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
