Return-Path: Received: from mtain-mc06.r1000.mx.aol.com (mtain-mc06.r1000.mx.aol.com [172.29.96.78]) by air-mb06.mail.aol.com (v129.4) with ESMTP id MAILINMB061-a6fc4ced793e331; Wed, 24 Nov 2010 15:44:46 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-mc06.r1000.mx.aol.com (Internet Inbound) with ESMTP id 4BBCA38000108; Wed, 24 Nov 2010 15:44:43 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PLMBr-0001Eu-CF for rs_out_1@blacksheep.org; Wed, 24 Nov 2010 20:43:43 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PLMBq-0001El-Py for rsgb_lf_group@blacksheep.org; Wed, 24 Nov 2010 20:43:42 +0000 Received: from mail-gw0-f43.google.com ([74.125.83.43]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PLMBn-0007s2-7L for rsgb_lf_group@blacksheep.org; Wed, 24 Nov 2010 20:43:42 +0000 Received: by gwb17 with SMTP id 17so103665gwb.16 for ; Wed, 24 Nov 2010 12:43:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type; bh=Xo8OdCdcVYLPUbd00EM3xQ0t3oKrCATJhZpzt5yUAYI=; b=WtsDJ/5kCtQ8X4ne30cjV377PVF/o4/2nnmLhsHdjpxcSr4KA96IQjVwxUyg2+EsJS nbdvB7s+Iox8yZNm4I03mhR5QqIDZXktm8dAI4UW+Kav2AAC4qa584z92VYXZKglfq1Z hsRs7TdGOI+/n6wfIaGECZM/FNuXWZWRkU7B4= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=VRztenFa/tBANMsikioYaG2NOrLWlkdgQhR53ELHyIwKo1XDch5PvX0pcSGsLEESIa g9Cu9F3T14qw9xG1IqmBoga4welUGYo8auqHmB6hkF9yAIxzfFwavbixOrQPCSC4ZHbK 9apnBTdFdUZ41gtTgM521sjJ+uTxSwzh34WS0= MIME-Version: 1.0 Received: by 10.204.119.15 with SMTP id x15mr9295603bkq.22.1290631409394; Wed, 24 Nov 2010 12:43:29 -0800 (PST) Received: by 10.204.48.215 with HTTP; Wed, 24 Nov 2010 12:43:29 -0800 (PST) In-Reply-To: <4CED6CC1.6070302@iup.uni-heidelberg.de> References: <4CED6CC1.6070302@iup.uni-heidelberg.de> Date: Wed, 24 Nov 2010 20:43:29 +0000 Message-ID: From: Roger Lapthorn To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: new VLF antenna at DK7FC Content-Type: multipart/alternative; boundary=00504502cebeb165370495d28afe X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d267.2 ; domain : gmail.com DKIM : pass x-aol-sid: 3039ac1d604e4ced793b36fb X-AOL-IP: 195.171.43.25 X-Mailer: Unknown (No Version) --00504502cebeb165370495d28afe Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi Stefan, I am unclear about the connection back to the shack. Are you using three wires (in the CAT5 cable) then to feed power, ground and signal back to th= e shack from the FET? No isolation transformers etc? Do you use this also on 136kHz and 500kHz with different filters? 73s Roger G3XBM 2010/11/24 Stefan Sch=E4fer > Dear VLF, > > Full of euphorism i want to tell you about my new VLF RX antenna. > You know my active antenna for VLF which is in use at my grabber: > http://www.iup.uni-heidelberg.de/schaefer_vlf/8,97kHz%20active%20E%20fie= ld%20antenna%20by%20DK7FC.jpg > > I have had the idea to separate the E field active antenna into a front= end > and the rest of the circuit can be left in the shack! > The front end consists out of the first JFET, the 1MOhm and 10 MOhm > resistor, the electrode(wire) and the C=3D20 nF. The diodes can be left= away. > The rest of the circuit is now placed inside the shack. > > This has the following advantages: > -The gain and or filters can be adjusted and optimised in the shack! > -There is no need for a (separate) power supply on the top of the antenn= a > -No need for a (metallic) box on the top of the antenna > -the electronic parts can be shrinked together with the wire(s) by shrin= k > tubes (waterproof) > -No need for a coupling-decoupling network at the antenna for the power > supply > - If the use of batteries is an advantage, they can easily be > replaced/charged/measured in the shack! > - A single twisted pair cable (e.g. 1/4 of a CAT5 cable) can be used > -When a tiny fishing rod is used to keep the active antenna apart from= the > house, the distance can be increased due to optimised lightweight > :-) > > I just have used a single twisted pair cable out of a CAT5 cable (now > unshielded) at almost 30m length between the front end and the amp stage= in > the shack. This allows me to get more distance to the tram line which ca= uses > strong QRM on VLF on my grabber antenna. Now, this new antenna is on the > other side of the house. > > See the difference between the 2 wideband captures: Old system, bottom > capture of > http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html = and > the new system, bottom of > http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html > > So, at least on VLF this is a great chance to reduce the local noise. Ma= ybe > some others can do the same since a very small twisted pair cable is alm= ost > invisible and cheep (i've used a 10m cable and soldered the pairs in > series). No matter what the maximum distance might be but i can imagine= 100m > will be not the problem! I will check to do the same on LF. Since the le= ngth > is still << Lambda i do not expect much trouble. > > 73, Stefan/DK7FC > > --=20 http://g3xbm-qrp.blogspot.com/ http://www.g3xbm.co.uk http://www.youtube.com/user/g3xbm G3XBM GQRP 1678 ISWL G11088 --00504502cebeb165370495d28afe Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi Stefan,

I am unclear about the connection back to the shack. Are= you using three wires (in the CAT5 cable) then to feed power, ground and= signal back to the shack from the FET? No isolation transformers etc?
=
Do you use this also on 136kHz and 500kHz with different filters?

7= 3s
Roger G3XBM

2010/11/24 Stefan Sch= =E4fer <Stefan.Schaefer@iup.uni-heidelberg.de>
Dear VLF,

Full of euphorism i want to tell you about my new VLF RX antenna.
You know my active antenna for VLF which is in use at my grabber: http://www.iup.uni-heid= elberg.de/schaefer_vlf/8,97kHz%20active%20E%20field%20antenna%20by%20DK7FC= .jpg

I have had the idea to separate the E field active antenna into a front en= d and the rest of the circuit can be left in the shack!
The front end consists out of the first JFET, the 1MOhm and 10 MOhm resist= or, the electrode(wire) and the C=3D20 nF. The diodes can be left away. Th= e rest of the circuit is now placed inside the shack.

This has the following advantages:
-The gain and or filters can be adjusted and optimised in the shack!
-There is no need for a (separate) power supply on the top of the antenna<= br> -No need for a (metallic) box on the top of the antenna
-the electronic parts can be shrinked together with the wire(s) by shrink= tubes (waterproof)
-No need for a coupling-decoupling network at the antenna for the power su= pply
- If the use of batteries is an advantage, they can easily be replaced/cha= rged/measured in the shack!
- A single twisted pair cable (e.g. 1/4 of a CAT5 cable) can be used
-When a tiny fishing rod is used to keep the active antenna apart from the= house, the distance can be increased due to optimised lightweight
:-)

I just have used a single twisted pair cable out of a CAT5 cable (now unsh= ielded) at almost 30m length between the front end and the amp stage in th= e shack. This allows me to get more distance to the tram line which causes= strong QRM on VLF on my grabber antenna. Now, this new antenna is on the= other side of the house.

See the difference between the 2 wideband captures: Old system, bottom cap= ture of http://www.iup.uni-heidelberg.de/schaefer= _vlf/DK7FC_VLF_Grabber.html =A0 and the new system, bottom of http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF= _Grabber2.html

So, at least on VLF this is a great chance to reduce the local noise. Mayb= e some others can do the same since a very small twisted pair cable is alm= ost invisible and cheep (i've used a 10m cable and soldered the pairs= in series). No matter what the maximum distance might be but i can imagin= e 100m will be not the problem! I will check to do the same on LF. Since= the length is still << Lambda i do not expect much trouble.

73, Stefan/DK7FC




--
http://g3xbm-qrp.blogspot.com/<= br>http://www.g3xbm.c= o.uk
http://www= .youtube.com/user/g3xbm
G3XBM=A0=A0 GQRP 1678=A0=A0=A0 ISWL G11088<= br> --00504502cebeb165370495d28afe--