Message-ID: <4CF4F3CD.8070107@iup.uni-heidelberg.de>
Date: Tue, 30 Nov 2010 13:53:33 +0100
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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References: <4CED6CC1.6070302@iup.uni-heidelberg.de> <4CED70E9.8080603@iup.uni-heidelberg.de> <167558.43607.qm@web111907.mail.gq1.yahoo.com>
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Subject: Re: LF: new VLF antenna at DK7FC
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Hi Daniele,

Am 30.11.2010 07:40, schrieb Daniele Tincani:
> Hello Stefan,
> I'm about to complete the construction of an E-probe based on your=20
> design (the original one, with both BF862 on the same board). The=20
> resulting PCB size is not that small as I preferred not to shrink it,=20
> for example all passive components are normal through-hole parts,=20
> mounted horizontally, etc. (only the 6 x 1N4148 at the output are=20
> mounted vertically). Now I have to decide about a suitable box, length=
=20
> of probe, type of connectors/cables, etc.. What do you suggest, based=20
> on your experience?
You can choose what you want. Either just use bonding tape and some=20
aluminium foil (connected to ground) or a normal metallic housing. Even=20
no shielding is OK. I have managed to solder the whole circuit on a 3cm=20
x 4cm PCB and it can be done even more compact by using no PCB but just=20
soldering the parts together and fix them by some tape. Then it can be=20
put into a PVC tube or so.
> For example, is a metal box mandatory (or highly recommended)? Is the=20
> length of probe critical (e.g. not longer than x, not shorter than y)?
On 137 kHz i found that 30...35 cm of a 2mm diameter copper wire is=20
optimal. This is what i am using on VLF as well but maybe more is=20
suitable as well. It depends on your location! So, if you have a strong=20
LF BCD stn near your QTH it might be useful to limit the signal on the=20
gate, not to overdrive the JFET. A longer probe will give a stronger=20
signal but perhaps no better SNR! The longer the probe, the higher the=20
probability for IM! Just try the 35 cm cm length. It works here and on=20
the 4X1RF grabber as you can see :-) Or use a longer probe and cut it in=
=20
some steps to see a difference. This is of course a litte tricky without=
=20
having a test signal out of some distance.

The wind forecast for saturday is promising! If this is confirmed on=20
Thursday, i will announce my 9th experiment this weekend. Maybe you can=20
check all 3 antennas then ;-)

73 and good luck!

Stefan/DK7FC

PS: If the results are then still bad, it is probably not caused by the=20
antenna design but due to the location or EMC issues. So then you have=20
one worry less ;-)
> Any suggestion is welcome.
> Best regards
> Daniele
>
> ------------------------------------------------------------------------
> *From:* Stefan Sch=E4fer <Stefan.Schaefer@iup.uni-heidelberg.de>
> *To:* rsgb_lf_group@blacksheep.org
> *Sent:* Wed, November 24, 2010 9:09:13 PM
> *Subject:* Re: LF: new VLF antenna at DK7FC
>
> ...and the tiny twisted pair cable can be wound several times through=20
> a high mu ferroxube core!
>
> Attached a photo of the new antenna, in about 30m above GND at the=20
> university of Heidelberg
>
> 73, Stefan
>

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Hi Daniele,<br>
<br>
Am 30.11.2010 07:40, schrieb Daniele Tincani:
<blockquote cite="mid:167558.43607.qm@web111907.mail.gq1.yahoo.com"   type="cite">
  <style type="text/css"><!-- DIV {margin:0px;} --></style>
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div>Hello Stefan,</div>
  <div>&nbsp;</div>
  <div>I'm about to complete the construction of an E-probe based on
your design (the original one, with both BF862 on the same board). The
resulting PCB size is not that small as I preferred not to shrink it,
for example&nbsp;all&nbsp;passive components are normal through-hole parts,
mounted horizontally, etc. (only the 6 x 1N4148 at the output are
mounted vertically). Now I have to decide about a suitable box, length
of probe, type of connectors/cables, etc.. What do you suggest, based
on your experience?</div>
  </div>
</blockquote>
You can choose what you want. Either just use bonding tape and some
aluminium foil (connected to ground) or a normal metallic housing. Even
no shielding is OK. I have managed to solder the whole circuit on a 3cm
x 4cm PCB and it can be done even more compact by using no PCB but just
soldering the parts together and fix them by some tape. Then it can be
put into a PVC tube or so.<br>
<blockquote cite="mid:167558.43607.qm@web111907.mail.gq1.yahoo.com"   type="cite">
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div> For example, is a metal box mandatory (or highly recommended)?
Is the length of probe critical (e.g. not longer than x, not shorter
than y)?</div>
  </div>
</blockquote>
On 137 kHz i found that 30...35 cm of a 2mm diameter copper wire is
optimal. This is what i am using on VLF as well but maybe more is
suitable as well. It depends on your location! So, if you have a strong
LF BCD stn near your QTH it might be useful to limit the signal on the
gate, not to overdrive the JFET. A longer probe will give a stronger
signal but perhaps no better SNR! The longer the probe, the higher the
probability for IM! Just try the 35 cm cm length. It works here and on
the 4X1RF grabber as you can see :-) Or use a longer probe and cut it
in some steps to see a difference. This is of course a litte tricky
without having a test signal out of some distance.<br>
<br>
The wind forecast for saturday is promising! If this is confirmed on
Thursday, i will announce my 9th experiment this weekend. Maybe you can
check all 3 antennas then ;-)<br>
<br>
73 and good luck!<br>
<br>
Stefan/DK7FC<br>
<br>
PS: If the results are then still bad, it is probably not caused by the
antenna design but due to the location or EMC issues. So then you have
one worry less ;-)<br>
<blockquote cite="mid:167558.43607.qm@web111907.mail.gq1.yahoo.com"   type="cite">
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div> Any suggestion is welcome.</div>
  <div>&nbsp;</div>
  <div>Best regards</div>
  <div>Daniele</div>
  <div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;"><br>
  <div style="font-family: arial,helvetica,sans-serif; font-size: 13px;"><font   face="Tahoma" size="2">
  <hr size="1"><b><span style="font-weight: bold;">From:</span></b>
Stefan Sch&auml;fer <a class="moz-txt-link-rfc2396E" href="mailto:Stefan.Schaefer@iup.uni-heidelberg.de">&lt;Stefan.Schaefer@iup.uni-heidelberg.de&gt;</a><br>
  <b><span style="font-weight: bold;">To:</span></b>
<a class="moz-txt-link-abbreviated" href="mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org</a><br>
  <b><span style="font-weight: bold;">Sent:</span></b> Wed, November
24, 2010 9:09:13 PM<br>
  <b><span style="font-weight: bold;">Subject:</span></b> Re: LF: new
VLF antenna at DK7FC<br>
  </font><br>
...and the tiny twisted pair cable can be wound several times through a
high mu ferroxube core!<br>
  <br>
Attached a photo of the new antenna, in about 30m above GND at the
university of Heidelberg<br>
  <br>
73, Stefan<br>
  </div>
  </div>
  </div>
  <br>
</blockquote>
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