Hello Chris, 
 
I am not a communication engineer (but a power electronic engineer ;-) ), so 
rather an amateur in this field. So my answer is kept simple ;-)
 
In the datasheet of this cable i just found that attenuation is less than 
150dB/km, so abt 3dB for my 20m cable. I have tried a cable of 2m (for indoor 
tests) and changed the cable to 20m. The difference (e.g. of DCF39 in the Argo 
monitor) is less than one S unit.
 
In the moment i use a SFH350V (photo transistor)as the receiver. But recently i 
read in the web that a photodiode has (significant) less noise. So i want to 
try a SFH250V in a next step to reduce the overall noise, probably in 
combination with a second BF862 in the input stage of the RX. The SFH250V has 
even much better switching times. I have already ordered some of those. I will 
try this and send the circuit here...
 
The cable i use has a PE shielding which is not suitable to exist 10s of years 
in the summer sun. But the distributor told me, it will be no problem for some 
years. And since LF is a living project, this is enough for me.
 
The losses of the cable must be compensated by a gain of an amplifier within 
the system. This gain is not reached without a noise (e.g. by a OPA) but this 
noise can be much smaller than the noise that you fed into a sensitive RX 
antenna, i expect. But the main aspect is, that one doesn't have to worry any 
more if it could be possible that a noise is fed from the PC/RX/house to the 
preamp by the cable.
 
73s, Stefan/DK7FC
 
 

________________________________

Von: [email protected] im Auftrag von Chris Trask
Gesendet: So 31.01.2010 14:57
An: [email protected]; [email protected]
Betreff: Re: LF: 2nd try of sending the pic of my loop preamp with the BF862



>
> Some OMs informed me, that the picture of the loop preamp is
> in a strange design. That may be come, since i (have to) use
> outlook exchange (?)
>
> Now i try to do it again. Those who asked for the picture,
> please give my a short confirmation if the picture is in the
> correct format now.
>
> I do some modifications to the RX in the moment and will send
> the new and perhaps better circuit soon. But the setup is
> already working vy fine!
>

     That is a very interesting approach to minimizing induced noise on the RX 
cable.  What are the loss characteristics of the optical link, including the 
diode(s)?


Chris Trask
N7ZWY
WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/

<<winmail.dat>>