Dear group, 

In the picture in this mail i show the circuit of the simpelst way to transform 
the optic signal back to an alternating voltage that can be connected to the RX 
imput. It is the version with a phototransistor. This way is working and a good 
start point for further (individual) experiments, e.g. if noise really 
decreases significantly...

The potentiometer should be adjusted to a miximum signal on the s-meter, 
depending to the input impedance of the cable (cable + RX). It can be replaced 
later by a fixed resistor. The 100k resistor can be replaced by an inductance 
and adjusted to maximum strenght and so on. First, the circuit should be 
supplied by a battery and later by the power supply of the RX. So it can be 
seen if there comes an additional noise by the supply. I have integrated this 
little circuit in my K2, to minimise the effort of cables and housings. A 
simple switch can be used to change the input (optic / coax). So one can 
compare both transmission paths...

Due to the snow the post has problems to reach my house and so i still do not 
have the SFH250V (photodiode). But soon i will try it this way and will see if 
noise even can be even decreased...

 

73 es gl ;-)

Stefan/DK7FC

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