Dear Jan-Martin, LF Group,
At 12:03 12/11/2002 +0000, you wrote:
Signal strength last night for DCF39 was 80-150µV (-75...-80dBU)
At your distance, the field strength of DCF39 should be roughly +60 dBuV/m
- so if under quiet band conditions the band noise is around 0dBuV/m in a
bandwidth of a few hundred Hz, the receiver will have to have a noise level
below about -135 or -140dBu to achieve optimum sensitivity. So you might
need a preamp!
Not sure if it is still a point to ground the center of the tuned loop.
I have used several loops here for LF reception, and have never found any
advantage in grounding the loop centre tap, allthough in theory it ought to
improve rejection of E-field signals. That might just be because of the
nature of the QRM at my location, though. I have to say I am skeptical
about the idea of E-field rejection being an important benefit in reducing
noise pick up at LF. In fact, I find a small, screened, LF loop to be quite
a good mains cable detector. The big advantage of a small loop RX antenna
over TX type antennas is that is easy to move the loop around until you
find a position where the noise level is low - but you can do the same
thing with a whip antenna. The other benefit of the loop is the directional
nulls, of course.
Cheers, Jim Moritz
73 de M0BMU
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