Message-ID: <002101caa3f0$4f85fca0$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
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>
Date: Tue, 2 Feb 2010 10:13:04 -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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also,
avoid sharp Right angle bends and Roundabouts, keep straight ahead. If=
 the
bend is too sharp there is a tendency to go straight on and burn a hol=
e in
the fibre cable. Good Coax might be the best bet in the the amateur co=
ntext.
Apart from the broad band advantage of fibre I don't see the necessity=
 and
extra engineering required, interface connections etc for a simple pre=
amp
connection on MF.
 G3KEV

----- Original Message -----
From: "Ken" <ken.h.wright@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Monday, February 01, 2010 5:56 PM
Subject: 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 850n=
m
> 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=
 optical
> wavelength is the data sheet quoting this attenuation figure at? If=
 you
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 th=
e
fibre,
> ideally the LED should be mounted in mating coupler so the so the fi=
bre
may
> be mated up to it, air gaps of fractions of a millimeter will introd=
uce
> 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 (f=
or
> 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 nois=
e,
> probably in combination with a second BF862 in the input stage of th=
e RX.
> The SFH250V has even much better switching times. I have already ord=
ered
> 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 10=
s 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 amplifie=
r
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: 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,
including
> the diode(s)?
>
>
> Chris Trask
> N7ZWY
> WDX3HLB
> Senior Member IEEE
> http://www.home.earthlink.net/~christrask/
>
>
>
>
>
>