Return-Path: Received: from rly-mg06.mx.aol.com (rly-mg06.mail.aol.com [172.20.83.112]) by air-mg08.mail.aol.com (v121.4) with ESMTP id MAILINMG082-a1b476fdb25d4; Mon, 24 Dec 2007 11:16:03 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mg06.mx.aol.com (v121.4) with ESMTP id MAILRELAYINMG065-a1b476fdb25d4; Mon, 24 Dec 2007 11:15:36 -0500 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1J6pwm-0005hK-Se for rs_out_1@blacksheep.org; Mon, 24 Dec 2007 16:14:32 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1J6pwm-0005hB-Dg for rsgb_lf_group@blacksheep.org; Mon, 24 Dec 2007 16:14:32 +0000 Received: from smtp-vbr11.xs4all.nl ([194.109.24.31]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1J6pwg-0007if-AP for rsgb_lf_group@blacksheep.org; Mon, 24 Dec 2007 16:14:32 +0000 Received: from PCRoelof (ndb.demon.nl [82.161.81.65]) by smtp-vbr11.xs4all.nl (8.13.8/8.13.8) with SMTP id lBOGDwNX078205 for ; Mon, 24 Dec 2007 17:14:03 +0100 (CET) (envelope-from roelof@ndb.demon.nl) Message-ID: <001a01c84647$e542c600$2101a8c0@PCRoelof> From: "Roelof Bakker" To: References: Date: Mon, 24 Dec 2007 16:13:12 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 X-Virus-Scanned: by XS4ALL Virus Scanner X-Karma: 0: X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: Re: E-field probes. Content-Type: multipart/alternative; boundary="----=_NextPart_000_0017_01C84647.E1FD5F00" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.8 required=5.0 tests=HTML_30_40,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-IP: 193.82.116.20 X-AOL-SCOLL-AUTHENTICATION: listenair ; SPF_helo : n X-AOL-SCOLL-AUTHENTICATION: listenair ; SPF_822_from : n ------=_NextPart_000_0017_01C84647.E1FD5F00 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hello David, The pa0rdt-Mini-Whip was designed as a low noise reception antenna at LF, be= cause at my location a loop antenna appeared to pick up to much noise. This type of antenna does work very well at low frequencies, in fact it exce= ls at VLF. On the other end of the spectrum, reception drops off above 20 MHz, though I= have received signals up to 50 MHz. The frequency response of the buffer amplifier is flat to at least 100 MHz,=20= so this is not the cause of degraded performance versus frequency. Hajo, DJ1ZB, has done some computer analyses, but his work does not confirm=20= a decrease in performance up to 100 MHz. The capacitance of the probe and the input capacitance of the FET form a vol= tage devider for rf. Theoretical this should also give a flat frequency response; which does not=20= happen in practice. This might be due to straight circuit capacitances. A mini-whip with leaded parts has a PCB antenna measuring 30 x 40 mm. Using SMD parts 22 x 26 mm of copper clad PCB is neccessary for the same sig= nal levels. This is approximately 50% less. One solution could be to increase the capacitance of the probe and decrease=20= the gate resistor of the FET. Doing so the gate capacitance has less impact on the frequency response as i= t is swamped by the gate resistor. To be honest, I have not done much work in this area yet, as my main interes= t is reception at LF. I have tried some circuits with a very low input capacitance, which yielded=20= an even smaller probe. Which was not much use in practice. A combination of a very low input capacitance and a low gate resistor could=20= do the trick. Best regards, Roelof Bakker, pa0rdt =20 --=20 Mijn Postvak In wordt beschermd door SPAMfighter. 578 spam-mails zijn er tot op heden geblokkeerd. Download de gratis SPAMfighter via deze link: http://www.spamfighter.com/lnl ------=_NextPart_000_0017_01C84647.E1FD5F00 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hello David,
 
The pa0rdt-Mini-Whip was designed as a low=20= noise=20 reception antenna at LF, because at my location a loop antenna appeared= to=20 pick up to much noise.
This type of antenna does work very well at= low=20 frequencies, in fact it excels at VLF.
On the other end of the spectrum, rece= ption=20 drops off above 20 MHz, though I have received signals up to 50=20 MHz.
The frequency response of the buffer amplif= ier is=20 flat to at least 100 MHz, so this is not the cause of degraded performance=20 versus frequency.
 
Hajo, DJ1ZB, has done some computer an= alyses,=20 but his work does not confirm a decrease in performance up to 100=20 MHz.
 
The capacitance of the probe and the input=20 capacitance of the FET form a voltage devider for rf.
Theoretical this should also give a flat fr= equency=20 response; which does not happen in practice.
This might be due to straight circuit=20 capacitances.
A mini-whip with leaded parts has a PCB ant= enna=20 measuring 30 x 40 mm.
Using SMD parts 22 x 26 mm of copper c= lad PCB=20 is neccessary for the same signal levels.
This is approximately 50% less.
 
One solution could be to increase the=20 capacitance of the probe and decrease the gate resistor of the FET.
Doing so the gate capacitance has less impa= ct on=20 the frequency response as it is swamped by the gate resistor.
 
To be honest, I have not done much work in=20= this=20 area yet, as my main interest is reception at LF.
I have tried some circuits with a very low=20= input=20 capacitance, which yielded an even smaller probe.
Which was not much use in=20 practice.
 
A combination of a very low input capacitan= ce and a=20 low gate resistor could do the trick.
 
Best regards,
Roelof Bakker, pa0rdt
 
 
 

Mijn Postvak In wordt beschermd door SPAMfighter
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