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Message-ID: <0A1CC2C5367040E284D30F87A4967547@lindavideo>
From: "Ken" <ken.h.wright@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <12077821.1264946261487.JavaMail.root@wamui-cynical.atl.sa.earthlink.net> <38A51B74B884D74083D7950AD0DD85E82A1ACF@File-Server-HST.hst.e-technik.tu-darmstadt.de> <4C25D51A6FE646D5B8D9D37C87EA6BBC@lindavideo> <38A51B74B884D74083D7950AD0DD85E82A1AD4@File-Server-HST.hst.e-technik.tu-darmstadt.de>
Date: Wed, 3 Feb 2010 09:51:31 -0000
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Subject: Re: LF: 2nd try of sending the pic of my loop preamp with the BF862
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Hi Stefan.
Thanks for the reply, if you know anyone in the telecoms industry try=
 and=20
obtain some off cuts of fibre, either 50/125 multimode, or 8/125 singl=
e=20
mode, the first figure is the core diameter, the second the outer clad=
ding=20
diameter all in microns, better still if you can persuade them to put=
 a=20
connector on the ends, I expect optical connectors have changed somewh=
at=20
since I retired, also as Mal said dont use to tight bends or the fibre=
 may=20
fracture with time. Anything is possible, I did some experiments coupl=
ing a=20
fibre into an ordinary flashlight for use as fibre identification, and=
 it=20
worked very well. Keep up the good work, when you have a good system=
 maybe=20
you will write a paper on it for us all, that is what our great hobby=
 is all=20
about.

73
Ken

M0KHW


----- Original Message -----=20
From: "Stefan Sch=E4fer" <schaefer@hst.tu-darmstadt.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, February 02, 2010 11:50 PM
Subject: AW: LF: 2nd try of sending the pic of my loop preamp with the=
 BF862


Hey Ken,

Tnx for your statement. Well, i am not an expert in optic links and th=
e=20
parts i choose are probably not the best, that are available for this=
=20
application.

Theese parts were available for me and they are suitable in principle,=
=20
although the attenuation may be some dB less. Today i measured the gai=
n of a=20
single BF862 in a preamp application for LF and i calculated a voltage=
 gain=20
of 26dB. Well, in that case it is not so important for me if the cable=
 has=20
3dB loss or 0,03dB loss. The main aspect is, that the local noise is=
=20
decoupled. Because if it is not decoupled, the SNR can quickly decreas=
e by=20
more than 20dB, as i saw. And 3dB losses are not 3dB less SNR.

Perhaps the transmission system can be improved by using special parts=
. But=20
are they available for everyone (private, not commercial customers) an=
d are=20
they in a range below 5EUR? Perhaps you can tell me/us a more suitable=
 type=20
of cable that is perhaps even cheeper?
The parts i use in the moment have no special mounting. The fiber opti=
c=20
cable is just cut with a gripper and stuck plugged in the housing of=
 the=20
LED, thats all. And it can be done many times, thats important...

So, do you have an idea of better parts that are cheep and available,=
 with=20
variable length of the cable, so not preassembled? :-)

73, Stefan/DK7FC

________________________________

Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von Ken
Gesendet: Mo 01.02.2010 18:56
An: rsgb_lf_group@blacksheep.org
Betreff: Re: LF: 2nd try of sending the pic of my loop preamp with the=
 BF862



Hi Stefan.
150dB/km, is a very high loss for modern fibre, even thhe early 850nm
multimode fibre was only 1 or 2dB /km and modern single mode fibre at=
 1300nm
or 1550nm the attenuation is substantially  less than 1dB/km. What opt=
ical
wavelength is the data sheet quoting this attenuation figure at? If yo=
u are
using a red LED into a single mode fibre then the attenuation will be=
 high,
the launch power will also depend on how the  LED is coupled into the=
 fibre,
ideally the LED should be mounted in mating coupler so the so the fibr=
e may
be mated up to it, air gaps of fractions of a millimeter will introduc=
e
attenuation. The same applies when you mount your receive photodiode.=
 In the
1980's and 90,s I spent many years both specifying and commissioning=
 optical
line sysyems in the UK. I hope this info will be of use to you.

73s.
Ken
M0KHW



----- Original Message -----
From: "Stefan Sch=E4fer" <schaefer@hst.tu-darmstadt.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, January 31, 2010 10:43 PM
Subject: AW: LF: 2nd try of sending the pic of my loop preamp with the=
 BF862


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 DC=
F39 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 no=
ise.
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 order=
ed
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 pr=
oblem
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 sens=
itive
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/ho=
use to
the preamp by the cable.

73s, Stefan/DK7FC



________________________________

Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von Chris Trask
Gesendet: So 31.01.2010 14:57
An: rsgb_lf_group@blacksheep.org; rsgb_lf_group@blacksheep.org
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, incl=
uding
the diode(s)?


Chris Trask
N7ZWY
WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/