Return-Path: Received: from rly-mb01.mx.aol.com (rly-mb01.mail.aol.com [172.21.131.154]) by air-mb03.mail.aol.com (v126.13) with ESMTP id MAILINMB034-cea4b168f9030; Wed, 02 Dec 2009 11:02:45 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mb01.mx.aol.com (v125.7) with ESMTP id MAILRELAYINMB016-cea4b168f9030; Wed, 02 Dec 2009 11:02:26 -0500 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NFrdr-0004lV-Vn for rs_out_1@blacksheep.org; Wed, 02 Dec 2009 16:01:23 +0000 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NFrdr-0004lM-40 for rsgb_lf_group@blacksheep.org; Wed, 02 Dec 2009 16:01:23 +0000 Received: from lnx500.hrz.tu-darmstadt.de ([130.83.156.225]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1NFrdp-0005ow-2F for rsgb_lf_group@blacksheep.org; Wed, 02 Dec 2009 16:01:23 +0000 Received: from FILE-SERVER-HST.hst.e-technik.tu-darmstadt.de (File-Server-HST.hst.e-technik.tu-darmstadt.de [130.83.212.129]) by lnx500.hrz.tu-darmstadt.de (8.14.2/8.14.2/HRZ/PMX) with SMTP id nB2G1Iqe006018 for ; Wed, 2 Dec 2009 17:01:19 +0100 (envelope-from schaefer@hst.tu-darmstadt.de) Received: from [127.0.0.1] (helo=File-Server-HST.hst.e-technik.tu-darmstadt.de) by FILE-SERVER-HST.hst.e-technik.tu-darmstadt.de with AVK MailGateway; for ; Wed, 02 Dec 2009 17:01:19 +0100 Content-class: urn:content-classes:message MIME-Version: 1.0 X-MimeOLE: Produced By Microsoft Exchange V6.5 Date: Wed, 2 Dec 2009 17:01:19 +0100 Message-ID: <38A51B74B884D74083D7950AD0DD85E828AAF4@File-Server-HST.hst.e-technik.tu-darmstadt.de> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: LF: Results of optimising an active antenna Thread-Index: AcpylfL6ykJKYUwPSv68FbViQSZ8HgAmscnwAA033wA= From: =?iso-8859-1?Q?Stefan_Sch=E4fer?= To: X-AVK-Virus-Check: AVB 19.601;02.12.2009 X-PMX-TU: seen v0.99a by 5.5.8.383112, Antispam-Engine: 2.7.2.376379, Antispam-Data: 2009.12.2.155420 X-PMX-SPAMCHECK: outgoing mail X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01CA7368.AE5DFDFD" Subject: LF: Results of optimising an active antenna X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.6 required=5.0 tests=HTML_40_50, HTML_FONTCOLOR_UNKNOWN,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-Mailer: Unknown (No Version) ------_=_NextPart_001_01CA7368.AE5DFDFD Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Mike, Bernd, LF,=20 Thank you very much for your transmission yesterday in the evening! I coul= d do very useful tests and improve my little rx-antenna significantly. I'm not sure if anyone who uses a short E-field active antenna as a rx ant= enna knows about the dependence of wire length and the height above ground= so I want to give a report of the results of my tests yesterday in the da= rk. Perhaps some others could improve their antenna by these explanations.= .. (First I tried to sent the pictures into the mail but the mail size became= more than 100kB and so the mail wasn't reflected, as it seems. So I do mo= dify the mail cancelling the Pictures. I put them on my page at qrz.com an= d those who are interested in the results of my improvements can find them= there (at the lower end of the site)...) For the first test I tried the active antenna with a wire of 1,4m. The low= er end of the wire was abt 2m above gnd (observed signal of G3XDV)(Argo wi= thout AGC and RX with fast AGC). There was almost nothing to see. Then, I= reduced the wire length to 80cm while the hight above gnd keeping constan= t. Results were much better as can be seen.=20 Next: 40cm wire length: even much better!=20 Next: 30cm: signal gets lower but qrm also. SNR slightly better.=20 Next: 25cm is the best, as I think.=20 Next: 20cm Signal becomes worse. So, the optimum seems to be at around 25.= ..30cm!=20 Next: 20cm in a height of 4m: Signal comes up but noise also. No significa= nt increase of SNR The signals of Ossi/OE5ODL were audible in all the tests and vy gd to cpi.= But the signal was too strong to see any differences between the S/N rati= os (a Picture is also available). =20 My Conclusion: It seems that a short receiving antenna can bee seen as a= capacitive divider out of the capacity between far field and antenna and= the capacity between antenna and ground. If the wire length is to much,= the input stage becomes nonlinear/goes into saturation. If the height abo= ve ground is increased the signal comes up, but not the signal/noise ratio= (surely there will be a benefit if such an antenna is placed in a region= with heavy local qrm. Then, the height should be increased and the wire= length can be decreased). So, one cannot say "the more the better" talkin= g about the wire length! It's exciting, we can receive our "QRP"-Signals (compared to HF) over a di= stance of 100s or 1000s of km with a wire that is 1/10000 Lambda! In compa= rison, in the 80m band that would be an antenna of 8mm (!) ;-) With this improvement I get new hope for receiving anything out of the cit= y, where my home QTH is... I hope this report isn't nerving because of the long text (and pictures)= and size. I try to stay always below 100kB. Perhaps some RXs can be impro= ved or Lowfers gets motivated to try such an antenna... 73, Stefan/DK7FC PS: Mike, what's your locator? I want to check the distance and take a vie= w to your QTH (on http://f6fvy.free.fr/qthLocator/fullScreen.php everyone= can type the searched QTH-Locator and watch the QTH of the received stn).= So one can see the distance and the wave travelling path and if the stn= in directly at the beach or in the mountains and so on. Vy fine! PPS: I forward this message to Bernd, the constructor of the preamp. I thi= nk he doesn't know that the antenna gets even better when reducing the wir= e length! (tnx Bernd!)=20 =20 =20 ------_=_NextPart_001_01CA7368.AE5DFDFD Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Hi Mike, Bernd, LF,

Thank you very much for your transmission yesterday in the evening! I could do very useful tests and improve my little rx-antenna significantly.=

I'm not sure if anyone who uses a short E-field active antenna as a rx antenna kno= ws about the dependence of wire length and the height above ground so I want= to give a report of the results of my tests yesterday in the dark. Perhaps so= me others could improve their antenna by these explanations…

(First I= tried to sent the pictures into the mail but the mail size became more than 100kB and so the mail wasn’t reflected, as it seems. So I do modify the mail cancelling the Pictures.= I put them on my page at qrz.com and those who are interested in the results of= my improvements can find them there (at the lower end of the site)…)

For the first test I tried the active antenna with a wire of 1,4m. The lower end= of the wire was abt 2m above gnd (observed signal of G3XDV)(Argo without AGC and= RX with fast AGC). There was almost nothing to see. Then, I reduced the wire length to 80cm while the hight above gnd keeping constant. Results were mu= ch better as can be seen.

Next: 40cm wire length: even much better!

Next: 30cm: signal gets lower but qrm also. SNR slightly better.

Next: 25cm is the best, as I think.

Next: 20cm Signal becomes worse. So, the optimum seems to be at around 25…30cm!

Next: 20cm in a height of 4m: Signal comes up but noise also. No significant increase= of SNR

The signals of Ossi/OE5ODL were audible in all the tests and vy gd to cpi. But the sig= nal was too strong to see any differences between the S/N ratios (a Picture is= also available).

 

My Conclusion: It seems that a short receiving antenna can bee seen as a capacitive divider out of the capacity between far field and antenna and= the capacity between antenna and ground. If the wire length is to much, the in= put stage becomes nonlinear/goes into saturation. If the height above ground= is increased the signal comes up, but not the signal/noise ratio(surely there will be a be= nefit if such an antenna is placed in a region with heavy local qrm. Then, the height sh= ould be increased and the wire length can be decreased). So, one cannot say “the more the betterR= 21; talking about the wire length!

It’s exciting, we can receive our “QRP”-Signals (compared to HF) ov= er a distance of 100s or 1000s of km with a wire that is 1/10000 Lambda! In comparison, in the 80m band= that would be an antenna of 8mm (!) ;-)

With this improvement I get new hope for receiving anything out of the city, where= my home QTH is…

I hope this report isn’t nerving because of the long text (and pictures) and size. I try to stay always be= low 100kB. Perhaps some RXs can be improved or Lowfers gets motivated to try such an antenna…

73, Stefan/DK7FC

PS: Mike, what's your locator? I want to check the distance and take a view to your= QTH (on http://f6fvy.free.fr/qthLocator/fullSc= reen.php everyone can type the searched QTH-Locator and watch the QTH of the receiv= ed stn). So one can see the distance and the wave travelling path and if the= stn in directly at the beach or in the mountains and so on. Vy fine!

PPS: I forward this message to Bernd, the constructor of the preamp. I think he doesn’t know that the antenna gets even better when reducing the wir= e length! (tnx Bernd!)

 

 

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