[Lf] LF what to expect.]

[Andre' Kesteloot]

James Moritz wrote:

> Dear Mike & LF Group,
>
> When atmospheric noise is low, the background noise in UK and
> the rest of Europe normally seems to be Loran sidebands - ie. the
> rythmic chattering sound that has been likened to 'galloping
> horses'. If you can't hear this, and there is no QRN or QRM, then
> either you have a deaf receiver, or there is some local noise
> source raising the noise floor. If you can hear it - well, that's all you
> can hope for! At night, I find the QRN almost always swamps the
> Loran sidebands. Being able to hear the Loran sidebands seems
> to be a good indicator of adequate sensitivity - LF is nothing if not
> noisy!
>
> At my QTH (Hertfordshire, SE England), the signal from DCF39 is
> close to 1mV/m - much stronger than even the local amateur LF
> stations. Translating this into s-meter terms, it would be about S9
> plus 20 to 40dB, but of course the actual readings will depend a lot
> on antenna, preamp gain, RX sensitivity at LF and so on. It would
> be some dB's less in GW, so Mike's s-meter reading sounds about
> right. A reasonable expectation for the noise floor on a quiet
> morning (no QRN) at my QTH might be 60dB down on DCF39,
> perhaps S2 - S4 on Mike's s-meter. The majority of DX amateur
> signals are not far above the noise, if not below it.
>
> Loop antennas may or may not improve the noise situation,
> depending on circumstances - but one thing you must watch out for
> is that if your LF loop is anywhere near a resonant LF transmitting
> antenna, signals and noise will certainly couple from the TX ant to
> the loop. This can make a drastic difference at times. Try shorting
> or open-circuiting the loading coil on the TX ant, and seeing if there
> is any difference. Also, although loops can sometimes give good
> noise rejection, they can also be very good at picking up noise
> from nearby sources, such as mains or telephone wiring, TV's and
> monitors, etc, etc. Experimenting with the loop position is
> worthwhile - a few metres can make all the difference.
>
> Keep up the good work Mike, nice to hear more sigs coming from
> Wales.
>
> Cheers, Jim Moritz
> 73 de M0BMU