DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws;
  s=s1024; d=btinternet.com;
  h=Message-ID:X-YMail-OSG:Received:X-Mailer:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding;
  b=3Z6p8e+V8G87tc8RVgArH2NtsGKQtMmtq8VhdNa0GIYU2NgQ3zLNntnHWWrSMTCXMe1+qr/Eth85yRew7Fcdj7yYkYLjpl9/Hi9WvNAPL/VQKM1jjfR9Z+/PQmr3ROiHMOds1Jjgwgjjtt3ZTzIoFEQ0JdtwstxrITYZj1fzdJc=;
Message-ID: <572685.58103.qm@web86501.mail.ird.yahoo.com>
Date: Wed, 16 Dec 2009 20:37:56 +0000 (GMT)
From: ALAN MELIA <alan.melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
In-Reply-To: <38A51B74B884D74083D7950AD0DD85E828ACB3@File-Server-HST.hst.e-technik.tu-darmstadt.de>
MIME-Version: 1.0
DomainKey-Status: good (testing) 
Subject: Re: LF: Noise cancelling by using optic transmission of RX signals
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


Hi Stephan, well if you are running an optic cable why not run power as we=
ll. It should be relatively easy to keep the pick out of the power rail.=
 If you are worreied about pick up on the power rails use a rechargable ba=
ttery and just use the power feed when you are not receiving for rechargin=
g the battery.

Coax is not always the answer, and the old fashioned method of balanced pa=
irs is often more effective, If you use a centre-tapped transformer at eac=
h end you can even feed the power down the "phanton circuit". My old affil=
iation to a telephone company is showing :-))

Alan G3NYK

--- On Wed, 16/12/09, Stefan Sch=C3=A4fer <schaefer@hst.tu-darmstadt.de>=
 wrote:

> From: Stefan Sch=C3=A4fer <schaefer@hst.tu-darmstadt.de>
> Subject: LF: Noise cancelling by using optic transmission of RX signals
> To: rsgb_lf_group@blacksheep.org
> Date: Wednesday, 16 December, 2009, 16:51
>=20
>=20
>=20
> =20
>=20
>=20
> =20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
> =20
>=20
>=20
>=20
> Dear Lowfers,
>=20
>=20
> I
> want to
> start a new subject (for me it's
> new)...
>=20
> The
> last weeks
> I still had RX problems, either with the tx antenna or with
> the short E-flied RX
> antenna.
>=20
> I
> found out
> that the noise was/is generated by my notebook which made
> RXing difficult, even
> in regions without any else local QRM (what could almost
> bring me to shut down
> the PC and just do nice and easy CW QSOs without anything
> else! (but most
> traffic is in QRSS...)).
>=20
> Then
> I have
> done mni tests with many many ferrite cores (that I found
> in an older emc lab
> in our institute), e.g. 20x FT50-77 plus 20x FT50-43 plus
> 20x FT50-61 and e few
> others. I placed them all in series, partly in the near of
> the preamp and/or in
> the near of the RX. Sure, there was a significant reduction
> of noise but lastly
> the noise remains.=20
>=20
> Accidentally,
> during a test with my VFO connected to the same 12V supply
> of my preamp, I observed
> a strong line in the argo monitor EVEN without an antenna
> (short wire)
> connected to the VFO and when turned the amplitude to zero!
> That meant for me, the
> VFO and its supply is not suppressed enough and so some RF
> comes to the preamp
> by the coax and supply line! (the preamp is supplied by a
> battery). I thought, I
> can use this (normally unwanted) coupling path to test the
> blocking capability
> of the ferrite cores and so I tried it with all variations
> and later with an
> additional BIG ferrite core and many turns of RG174. As I
> meant, surely there
> is a significant noise reduction but the line in argo was
> still well visible!
>=20
> What
> I have
> done then (since 4 days) is using a coupling link by an
> optic transmission of
> the 137kHz signal between the preamp and my RX using a SFH750V
> as the TX Diode and a SFH350
> as the RX and abt 20m of a fiber optic cable (yes, there
> are surely more suited
> components but these were available in the moment). These
> are also used as
> optic links into high end audio systems and therefore easy
> to get...
>=20
> Now,
> when
> placing the preamp on the same place then during the tests
> before and just
> changing the coax by the fiber optic cable, the line by the
> VFO was completely
> gone!! Just with an antenna connected to the VFO and high
> amplitude (and thus e
> real near-field =E2=80=9Cconnection=E2=80=9D) it came back. The
> overall noise level
> decreased to its absolute minimum during all the tests.
>=20
>=20
> Before
> I used
> this optic cable the only signal that could be received
> (out of the city with
> much much qrm) was DCF39 and DLF and so on. Now, DCF39 came
> out with much
> better SNR and I saw the first LF Stn at all, it was Ossi /
> OE5ODL transmitting
> his 5s in the evening (tnx! very nice SNR in QRSS3
> mode).
>=20
> My
> conclusion
> is, that the qrm is always brought to the very sensitive
> E-field antenna by the
> coax, even when doing many usual suppression methods cause
> there always remains
> a residual coupling impedance between both sides of the
> cable. Furthermore a
> long coax cable, say 20m away from the shack carries some
> qrm to the near of
> the rx antenna so the effective distance to the shack is
> always reduced.
>=20
> One
> small disadvantage
> of this method is the need for a battery supply. My TX
> diode needs abt 20mA and
> is now working since 3 days with a 7AH Lead Acid battery.
> In the future I plan
> to use a stereo optic cable. Then, one could switch the
> preamp on and off by
> the seconds line doing it the opposite way. So, smaller
> batteries could be
> used, which is necessary when mounting the preamp to a
> shaky fiber mast if one
> does not want to change the batteries each few hours
> ;-)
>=20
> Signal
> distortion seems to be no problem, as I can confirm until
> now.
>=20
> Now,
> my K2 has
> an optical LF input! ;-)
>=20
> Perhaps
> this
> will give some ideas to the local qrm bothered stns who
> tried everything with
> ferrite cores, isolating transformers and so on without a
> satisfying result.
>=20
> NOTE: I do not know if anyone has tried
> this before and has
> written a publication about that. My goal is not
> to be the hero in inventions, to become popular and
> especially not to compete with
> anyone (like it seems
> to be usual in career/job to be the one who gets the pay
> rise) but just to
> share my ideas to those who are interested to try something
> new (?). I do not
> say that my solution is the best at all and so on! But, if
> it will help only
> one Lowfer getting new ideas and improving his station, and
> if this improvement
> results in more activity on the band, then it would have
> helped all of us!
>=20
> =20
>=20
> =20
>=20
> 73s
> es 55 de
> Stefan / DK7FC
>=20
>=20
>=20
> =20
>=20
>=20
>=20