Return-Path: Received: (qmail 6586 invoked from network); 5 Feb 2001 17:07:44 -0000 Received: from unknown (HELO warrior-inbound.servers.plus.net) (212.159.14.227) by extortion.plus.net with SMTP; 5 Feb 2001 17:07:44 -0000 Received: (qmail 14276 invoked from network); 5 Feb 2001 17:10:35 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by warrior with SMTP; 5 Feb 2001 17:10:35 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.16 #1) id 14Poze-0007YF-00 for rsgb_lf_group-outgoing@blacksheep.org; Mon, 05 Feb 2001 16:59:58 +0000 Received: from mail2.globocabo.com.br ([200.231.181.97] helo=ntweb.globocabo.com.br) by post.thorcom.com with esmtp (Exim 3.16 #1) id 14Pozb-0007Y8-00 for rsgb_lf_group@blacksheep.org; Mon, 05 Feb 2001 16:59:56 +0000 Received: from spovdesi1625 (SPOVD-ESI-1625 [5.8.14.13]) by ntweb.globocabo.com.br with SMTP (Microsoft Exchange Internet Mail Service Version 5.5.2653.13) id D9WD9ZC9; Mon, 5 Feb 2001 14:55:42 -0300 Message-ID: <015b01c08f9c$bfb2a540$0d0e0805@globocabo.com.br> From: "PY3CRX PY2PLL" To: "LF Group" References: <5501.200102051521@gemini> Subject: LF: Re: PLL / Loop antennas Date: Mon, 5 Feb 2001 15:54:51 -0200 MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="------------070204020707080409000201" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4133.2400 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: This is a multi-part message in MIME format. --------------070204020707080409000201 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: 8bit

Hi James et all ...

James=> In the LF range, and loop inductances of the order of 10s of uH, 0.1 ohm will be significant.

The copper octagon inductance I'm using to test (4.8m perimeter) is 3.48 uhy, so not so low. The HF resistance (skin effects) are something like 0,018 ohm at 260KHz.

This values, generated by Rejloop1 and Antenna Optimizer - both softwares gave basically the same results - was used on a third calculation tool (RF1.1 from Academic Tech - Au).

The C values that Rej1 states, when applied to Antenna Optimizer, made loop shows 0,0XX ohm +/-j 0,00XX.

Using this values on RF 1.1 I tried to model this loop this simplified way (software accepts xformer inductances/DC resistance):

Then trimming turn ratio, the calculated Z aproaches 50 ohm. I know it's a simple aproximation, there's more losses but ... The good part: I built a 50 ohm resistive swr bridge and using the signal generator I could confirm the predicted SWRs on 120, 260, 400 and 600 KHz (27 ... 68 ohm j +/- 0).

James => Bearing in mind multiple switches will probably be needed, this can be a real problem. We found relays were really the only option for remote switching, and even then you have to be careful - reed relays had losses around 0.1 - 0.5 ohms, much higher than their DC resistance. The best bet are relays intended for UHF antenna changeover duty.

It's a receive only design for now. But I'll re-run calculations adding common relays/capacitor losses to see what expect.

My other objective is cross measured FS versus predicted software values.

Thanks on the sugestions James.

73
Marcus
PY3CRX/PY2PLL
S. B. do Campo - GG66rf
http://py.qsl.br
Active from "DC" to 24GHz

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