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To All from PA0SE

On LF I use a simple audio signal clipper that brings all signals in the headphones to the same level. It may not improve readibility but makes listening much less tiring by limiting all sorts of crashes and other impulsive noises.

I have the clipper always in use and would not do without anymore.

The clipper consists of two germanium diodes type OA85 connected anti-parallel over the output of the receiver. To be effective both the voltage and the impedance at the point were the diodes are connected must be sufficiently high. I use passive audio bandpass filters between receiver and headphones and the diodes are connected over the first tuned circuit of the filters where impedance and voltage are high enough. (Do not put the clipper behind the filter.)

When you use low resistance headphones the system will not work. Perhaps you can find a suitable point for the diodes in the audio section of the receiver: for instance the voltage over the volume control may be high enough for the purpose.

If you find in your junkbox a pair of old valve-type audio output transformers (for example with a ratio of 5000 to 8 ohms or thereabouts) you could connect the high impedance windings together and put the diodes there as well. The low impedance windings are connected to the receiver output and the headphones respectively.

I also tried anti-parallel diodes in series with the receiver output as advocated by Jan Smeets, ON4ASZ/EA3DPD ("Technical Topics", RadCom, March 1998) hoping they would improve readability of weak signals in noise. The idea was that the output level of the receiver would be adjusted so that signal + noise would just overcome the threshold voltage of the diodes and the noise alone not. But it did not work. Understandable in retrospect, considering the wide amplitude variations of noise.

73, Dick, PA0SE

JO22GD

V.d. Marckstraat 5

2352 RA Leiderdorp

The Netherlands

Tel. +31 71 589 27 34

E-mail: d.w.rollema@freeler.nl (new address, but this may change soon again as the new provider Freeler makes a mess of it)