[Fwd: LF: Receiving]

[Andre' Kesteloot]

Rik Strobbe wrote:

> At 15:44 14/04/99 +0200, DJ1ZB wrote:
> >If a receiver needs some input attenuation at LF on large aerials, as
> reported
> >by ON7YD on his TS440, for instance, the better way should be to realize
> this
> >"attenuation" by the loss of a simple coil filter using one to four resonant
> >circuits. But such an arrangement would need less resistive attenuation to
> stop
> >the overload of the receiver, therefore even some additional
> preamplification
> >(and selectivity) might be possible, with resonant circuits carefully
> arranged
> >ahead and behind amplification so that in an empty band the S-meter hangs
> >around "S1". Then it should even be possible to receive the commercial LF
> >stations with an indication of S9+30dB if the receiver has sufficient AGC
> >range.
> Resonant circuits have the advantage to attenuate out-of-the-band signals
> selective. But to my experience it can have 2 'hooks' :
> 1. Attenuation of close to the band signals (eg. DBF39 / DCF39) is minimal
> 2. When using unsuitable ferrites these filtere can even create
> intermodulation-signals themselves
> I did some experiments with bandpass filters but at the end a simple
> attenuator did the best job (with me) and has the advantage that the
> attenuation can easily be adjusted to optimum ratio between the wanted
> signal and IM-products.
> I managed to built a 3-stage 136kHz filter with about 700Hz bandwidth
> (-3dB), but when I connected it to the big antenna it produced a lot of noise.
> But I am sure that with the proper ferite materials and filter component
> dimensions a usefull filter can be constructed.
> It would be great if those who already constructed good filter would let
> the others benefit from their experience.
>
> 73, Rik
>
> Rik Strobbe  ON7YD
> rik.strobbe@fys.kuleuven.ac.be
> Villadreef 14  B-3128 Baal  BELGIUM   (JO20IX)