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From: "Dave G3WCB" <ganymede444@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Date: Wed, 16 Dec 2009 21:26:33 -0000
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Subject: LF: RE: Noise cancelling by using optic transmission of RX signals
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Hello, Stefan.

This is very interesting. I have a MiniWhip on a pole some distance from the
house, and it seems that most of the interference (ADSL hash) seems to be
re-radiated by the coax outer and picked up by the antenna.

A relatively short optical link of one or two metres may still reduce the
pick-up, as it would break the "copper" connection to the antenna.

Alternatively, it might be possible to transvert the amplified LF signal up
to a vhf frequency and then set up a remote RX some distance away.

You could switch the power on and off by using a pressure switch from a
discarded washing machine connected to the shack by a lenght of 6mm plastic
tubing. Apply slight positive pressure to turn on the antenna circuitry!

73, Dave G3WCB IO91RM nr Windsor, S.E. England.
  -----Original Message-----
  From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of Stefan Schäfer
  Sent: 16 December 2009 16:51
  To: rsgb_lf_group@blacksheep.org
  Subject: LF: Noise cancelling by using optic transmission of RX signals


  Dear Lowfers,

  I want to start a new subject (for me it's new)...

  The last weeks I still had RX problems, either with the tx antenna or with
the short E-flied RX antenna.

  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...)).

  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.

  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!

  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...

  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 “connection”) it came back. The
overall noise level decreased to its absolute minimum during all the tests.

  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).

  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.

  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 ;-)

  Signal distortion seems to be no problem, as I can confirm until now.

  Now, my K2 has an optical LF input! ;-)

  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.

  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!





  73s es 55 de Stefan / DK7FC

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<DIV><SPAN class=3D619331321-16122009><FONT face=3DArial color=3D#0000=
ff size=3D2>Hello,=20
Stefan.</FONT></SPAN></DIV>
<DIV><SPAN class=3D619331321-16122009><FONT face=3DArial color=3D#0000=
ff   size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D619331321-16122009><FONT face=3DArial color=3D#0000=
ff size=3D2>This=20
is very interesting. I have a MiniWhip on a pole some distance from th=
e house,=20
and it seems that most of the interference (ADSL hash) seems to be re-=
radiated=20
by the coax outer and picked up by the antenna.</FONT></SPAN></DIV>
<DIV><SPAN class=3D619331321-16122009><FONT face=3DArial color=3D#0000=
ff   size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D619331321-16122009><FONT face=3DArial color=3D#0000=
ff size=3D2>A=20
relatively short optical link of one or two metres may still reduce th=
e pick-up,=20
as it would break the "copper" connection to the antenna.</FONT></SPAN=
></DIV>
<DIV><SPAN class=3D619331321-16122009><FONT face=3DArial color=3D#0000=
ff   size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D619331321-16122009><FONT face=3DArial color=3D#0000=
ff   size=3D2>Alternatively, it might be possible to transvert the amp=
lified LF signal=20
up to a vhf frequency and then set up a remote RX some distance=20
away.</FONT></SPAN></DIV>
<DIV><SPAN class=3D619331321-16122009></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D619331321-16122009><FONT face=3DArial color=3D#0000=
ff size=3D2>You=20
could switch the power on and off by using a pressure switch from a di=
scarded=20
washing machine connected to the shack by a lenght of 6mm&nbsp;plastic=
 tubing.=20
Apply slight positive pressure to turn on the antenna=20
circuitry!</FONT></SPAN></DIV>
<DIV><SPAN class=3D619331321-16122009></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D619331321-16122009><FONT face=3DArial color=3D#0000=
ff size=3D2>73,=20
Dave G3WCB IO91RM nr Windsor, S.E.&nbsp;England.</FONT>&nbsp;</SPAN></=
DIV>
<BLOCKQUOTE dir=3Dltr style=3D"MARGIN-RIGHT: 0px">
  <DIV class=3DOutlookMessageHeader dir=3Dltr align=3Dleft><FONT face=
=3DTahoma     size=3D2>-----Original Message-----<BR><B>From:</B>=20
  owner-rsgb_lf_group@blacksheep.org=20
  [mailto:owner-rsgb_lf_group@blacksheep.org]<B>On Behalf Of </B>Stefa=
n=20
  Sch=E4fer<BR><B>Sent:</B> 16 December 2009 16:51<BR><B>To:</B>=20
  rsgb_lf_group@blacksheep.org<BR><B>Subject:</B> LF: Noise cancelling=
 by using=20
  optic transmission of RX signals<BR><BR></FONT></DIV>
  <DIV class=3DSection1>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" size=3D2><SPAN la=
ng=3DEN-GB     style=3D"FONT-SIZE: 10pt; LINE-HEIGHT: 150%">Dear Lowfe=
rs, </SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">I want to=20
  start a new subject (for me it's new)...</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">The last=20
  weeks I still had RX problems, either with the tx antenna or with th=
e short=20
  E-flied RX antenna.</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">I found=20
  out that the noise was/is generated by my notebook which made RXing=
 difficult,=20
  even in regions without any else local QRM (what could almost bring=
 me to shut=20
  down the PC and just do nice and easy CW QSOs without anything else!=
 (but most=20
  traffic is in QRSS...)).</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">Then I=20
  have done mni tests with many many ferrite cores (that I found in an=
 older emc=20
  lab in our institute), e.g. 20x FT50-77 plus 20x FT50-43 plus 20x FT=
50-61 and=20
  e few others. I placed them all in series, partly in the near of the=
 preamp=20
  and/or in the near of the RX. Sure, there was a significant reductio=
n of noise=20
  but lastly the noise remains. </SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB     style=3D"FONT-SIZE: 10pt; COLOR: blac=
k; LINE-HEIGHT: 150%">Accidentally, during=20
  a test with my VFO connected to the same 12V supply of my preamp, I=
 observed a=20
  strong line in the argo monitor EVEN without an antenna (short wire)=
 connected=20
  to the VFO and when turned the amplitude to zero! That meant for me,=
 the VFO=20
  and its supply is not suppressed enough and so some RF comes to the=
 preamp by=20
  the coax and supply line! (the preamp is supplied by a battery). I=
 thought, I=20
  can use this (normally unwanted) coupling path to test the blocking=
 capability=20
  of the ferrite cores and so I tried it with all variations and later=
 with an=20
  additional BIG ferrite core and many turns of RG174. As I meant, sur=
ely there=20
  is a significant noise reduction but the line in argo was still well=
=20
  visible!</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">What I=20
  have done then (since 4 days) is using a coupling link by an optic=
=20
  transmission of the 137kHz signal between the preamp and my RX using=
 a <A     href=3D"http://www.datasheetcatalog.org/datasheets/105/48656=
4_DS.pdf">SFH750V</A>=20
  as the TX Diode and a <A     href=3D"http://www.datasheetcatalog.org=
/datasheets/90/486530_DS.pdf">SFH350</A>=20
  as the RX and abt 20m of a fiber optic cable (yes, there are surely=
 more=20
  suited components but these were available in the moment). These are=
 also used=20
  as optic links into high end audio systems and therefore easy to=20
  get...</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">Now, when=20
  placing the preamp on the same place then during the tests before an=
d just=20
  changing the coax by the fiber optic cable, the line by the VFO was=
 completely=20
  gone!! Just with an antenna connected to the VFO and high amplitude=
 (and thus=20
  e real near-field =93connection=94) it came back. The overall noise=
 level=20
  decreased to its absolute minimum during all the tests. </SPAN></FON=
T></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">Before I=20
  used this optic cable the only signal that could be received (out of=
 the city=20
  with much much qrm) was DCF39 and DLF and so on. Now, DCF39 came out=
 with much=20
  better SNR and I saw the first LF Stn at all, it was Ossi / OE5ODL=
=20
  transmitting his 5s in the evening (tnx! very nice SNR in QRSS3=20
  mode).</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">My=20
  conclusion is, that the qrm is always brought to the very sensitive=
 E-field=20
  antenna by the coax, even when doing many usual suppression methods=
 cause=20
  there always remains a residual coupling impedance between both side=
s of the=20
  cable. Furthermore a long coax cable, say 20m away from the shack ca=
rries some=20
  qrm to the near of the rx antenna so the effective distance to the=
 shack is=20
  always reduced.</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">One small=20
  disadvantage of this method is the need for a battery supply. My TX=
 diode=20
  needs abt 20mA and is now working since 3 days with a 7AH Lead Acid=
 battery.=20
  In the future I plan to use a stereo optic cable. Then, one could sw=
itch the=20
  preamp on and off by the seconds line doing it the opposite way. So,=
 smaller=20
  batteries could be used, which is necessary when mounting the preamp=
 to a=20
  shaky fiber mast if one does not want to change the batteries each=
 few hours=20
  ;-)</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">Signal=20
  distortion seems to be no problem, as I can confirm until=20
  now.</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">Now, my=20
  </SPAN></FONT><FONT color=3Dblack><SPAN lang=3DEN-GB     style=3D"CO=
LOR: black">K2</SPAN></FONT><FONT color=3Dblack><SPAN lang=3DEN-GB  =
   style=3D"COLOR: black"> has an optical LF input! ;-)</SPAN></FONT><=
/P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">Perhaps=20
  this will give some ideas to the local qrm bothered stns who tried=
 everything=20
  with ferrite cores, isolating transformers and so on without a satis=
fying=20
  result.</SPAN></FONT></P>
  <P class=3DMsoPlainText><B><U><FONT face=3D"Courier New" color=3Dbla=
ck size=3D2><SPAN     lang=3DEN-GB     style=3D"FONT-WEIGHT: bold; FON=
T-SIZE: 10pt; COLOR: black; LINE-HEIGHT: 150%">NOTE:</SPAN></FONT></U>=
</B><FONT     color=3Dblack><SPAN lang=3DEN-GB style=3D"COLOR: black">=
 I do not know if anyone has=20
  tried this before and has written a publication about that. My goal=
 is=20
  <B><SPAN style=3D"FONT-WEIGHT: bold">not</SPAN></B> to be the hero=
 in=20
  inventions, to become popular and especially <B><SPAN     style=3D"F=
ONT-WEIGHT: bold">not</SPAN></B> to compete with anyone (like it seems=
=20
  to be usual in career/job to be the one who gets the pay rise) but=
 just to=20
  share my ideas to those who are interested to try something new (?).=
 I do not=20
  say that my solution is the best at all and so on! But, if it will=
 help only=20
  one Lowfer getting new ideas and improving his station, and if this=
=20
  improvement results in more activity on the band, then it would have=
 helped=20
  all of us!</SPAN></FONT></P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB     style=3D"FONT-SIZE: 10pt; COLOR: blac=
k; LINE-HEIGHT: 150%"></SPAN></FONT>&nbsp;</P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB     style=3D"FONT-SIZE: 10pt; COLOR: blac=
k; LINE-HEIGHT: 150%"></SPAN></FONT>&nbsp;</P>
  <P class=3DMsoPlainText><FONT face=3D"Courier New" color=3Dblack siz=
e=3D2><SPAN     lang=3DEN-GB style=3D"FONT-SIZE: 10pt; COLOR: black;=
 LINE-HEIGHT: 150%">73s es 55=20
  de Stefan / DK7FC</SPAN></FONT></P></DIV></BLOCKQUOTE></BODY></HTML>

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