Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dk01.r1000.mx.aol.com (Internet Inbound) with ESMTP id C3CAF3800009B; Tue, 29 Jan 2013 06:30:25 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1U09NV-0006vj-1d for rs_out_1@blacksheep.org; Tue, 29 Jan 2013 11:29:25 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1U09NU-0006vX-C1 for rsgb_lf_group@blacksheep.org; Tue, 29 Jan 2013 11:29:24 +0000 Received: from out1.ip03ir2.opaltelecom.net ([62.24.128.239]) by relay1.thorcom.net with esmtp (Exim 4.77) (envelope-from ) id 1U09NR-0007TZ-RR for rsgb_lf_group@blacksheep.org; Tue, 29 Jan 2013 11:29:23 +0000 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AlgJAKyxB1FcHn0j/2dsb2JhbABEgkipMpFeBH8Xc4IZBQEBDQEBAyAhCAIsAQEIAgEDEQQBAQoXIgEEGAIGDAoODwQBCQECAgEBAQsEh14DEwifQpEUhkQDiV+MFIEfg1YDiCyFUoY9iyGBaoUSgnc X-IronPort-AV: E=Sophos;i="4.84,559,1355097600"; d="scan'208,217";a="412677447" Received: from host-92-30-125-35.as13285.net (HELO xphd97xgq27nyf) ([92.30.125.35]) by out1.ip03ir2.opaltelecom.net with SMTP; 29 Jan 2013 11:28:59 +0000 Message-ID: <002701cdfe13$d44d1e70$0401a8c0@xphd97xgq27nyf> From: "mal hamilton" To: "rsgb" Date: Tue, 29 Jan 2013 11:28:57 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 X-Spam-Score: 2.9 (++) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: ----- Original Message ----- From: mal hamilton To: mal hamilton Sent: Tuesday, January 29, 2013 11:22 AM Subject: Re: [rsgb_lf_group] Impedance transformation on 136 kHz - advice needed PS Robert An audio amp is not the best method and inefficient even at 137 Khz. A better approach is a purpose built amplifier with a couple of FETS class D or E. There is plenty of info available about building such amplifiers [...] Content analysis details: (2.9 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 SPF_PASS SPF: sender matches SPF record 0.0 HTML_MESSAGE BODY: HTML included in message 2.9 AXB_XMAILER_MIMEOLE_OL_024C2 AXB_XMAILER_MIMEOLE_OL_024C2 0.0 FAKE_REPLY_C FAKE_REPLY_C X-Scan-Signature: 3fa31248af9b7a1d533bfdae0dc25a10 Subject: LF: Re: [rsgb_lf_group] Impedance transformation on 136 kHz - advice needed Content-Type: multipart/alternative; boundary="----=_NextPart_000_0024_01CDFE13.D41B11F0" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.1 required=5.0 tests=HTML_60_70,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-sid: 3039ac1db4055107b2d14be5 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none This is a multi-part message in MIME format. ------=_NextPart_000_0024_01CDFE13.D41B11F0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable ----- Original Message -----=20 From: mal hamilton=20 To: mal hamilton=20 Sent: Tuesday, January 29, 2013 11:22 AM Subject: Re: [rsgb_lf_group] Impedance transformation on 136 kHz - = advice needed PS Robert An audio amp is not the best method and inefficient even at 137 Khz. A better approach is a purpose built amplifier with a couple of FETS = class D or E. There is plenty of info available about building such = amplifiers ----- Original Message -----=20 From: mal hamilton=20 To: rsgb_lf_group@yahoogroups.co.uk=20 Sent: Tuesday, January 29, 2013 11:19 AM Subject: Re: [rsgb_lf_group] Impedance transformation on 136 kHz - = advice needed Robert Use a capacitor of around 10 uF in series with the amp output then a = 4 to 50 ohm transformer. Old tv LOPT are suitable or material similar to 3C9 material. Prim turns around 8 and Sec 28 turns. This is a rough guide to get = started de mal/g3kev ----- Original Message -----=20 From: robert_la4ana=20 To: rsgb_lf_group@yahoogroups.co.uk=20 Sent: Tuesday, January 29, 2013 9:51 AM Subject: [rsgb_lf_group] Impedance transformation on 136 kHz - = advice needed =20 Hi Group, As I am planning to use an audio amplifier as a PA on 136 kHz, I = need to transform the amplifier output (100 Watt at 4-8 Ohm) to 50 Ohm to = match it to the coax cable to the antenna, possibly with a 50 Ohm = low-pass filter in between. Not much information is available on the = Internet about such a specific configuration. I am fond of capacitor = impedance transformation, which I use with success for matching and tuning = my loop antenna on 475 kHz. Could I employ the same concept to step up = impedance from 4 Ohm to 50 Ohm at the output of my audio amplifier? I have also looked into using ferrite toroids as transformers but = the sheer amount of information on this subject, often incomplete and contradictory, is confusing me. It looks like many are using = "3C90" as a core material, but this type of core seems difficult to acquire - = at least for me here in Norway. I understand that "type 77" material = could also be used and this one is easier to get by. If I would opt for = an FT140-77 core, would this be suitable as a transformer toroid for = 100 Watt on 136 kHz or would I need a bigger one? And how many primary = and secondary turns would such a tranformer need to step up from 4-8 = Ohm to 50 Ohm? I would be very grateful for some input on this subject before I = start ordering (the wrong) components. 73 de Robert, LA4ANA __._,_.___ Reply to sender | Reply to group | Reply via web post | Start a = new topic=20 Messages in this topic (1)=20 Recent Activity: a.. New Members 3 a.. New Photos 4=20 Visit Your Group=20 Switch to: Text-Only, Daily Digest . Unsubscribe . Terms of Use. =20 __,_._,___ ------=_NextPart_000_0024_01CDFE13.D41B11F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
----- Original Message -----
From:=20 mal=20 hamilton
Sent: Tuesday, January 29, 2013 = 11:22=20 AM
Subject: Re: [rsgb_lf_group] = Impedance=20 transformation on 136 kHz - advice needed

PS
 
Robert
An audio amp is not the best method and = inefficient even=20 at 137 Khz.
A better approach is a purpose built = amplifier=20 with a couple of FETS class D or E. There is plenty of info available = about=20 building such amplifiers
 
 
----- Original Message -----
From:=20 mal=20 hamilton
To: rsgb_lf_group@yahoogroups= .co.uk=20
Sent: Tuesday, January 29, = 2013 11:19=20 AM
Subject: Re: [rsgb_lf_group] = Impedance=20 transformation on 136 kHz - advice needed

Robert
Use a capacitor of around 10 uF in series = with the amp=20 output then a 4 to 50 ohm transformer.
Old tv  LOPT are suitable or = material=20 similar to 3C9 material.
Prim turns around 8 and Sec 28 turns. = This is a=20 rough guide to get started
 
de mal/g3kev
 
----- Original Message ----- =
From:=20 robert_la4ana
To: rsgb_lf_group@yahoogroups= .co.uk=20
Sent: Tuesday, January 29, = 2013 9:51=20 AM
Subject: [rsgb_lf_group] = Impedance=20 transformation on 136 kHz - advice needed

  =


Hi Group,

As I am planning to use an audio amplifier = as a PA=20 on 136 kHz, I need to
transform the amplifier output (100 Watt = at 4-8=20 Ohm) to 50 Ohm to match
it to the coax cable to the antenna, = possibly=20 with a 50 Ohm low-pass
filter in between. Not much information = is=20 available on the Internet
about such a specific configuration. = I am=20 fond of capacitor impedance
transformation, which I use with = success=20 for matching and tuning my loop
antenna on 475 kHz. Could I = employ the=20 same concept to step up impedance
from 4 Ohm to 50 Ohm at the = output of=20 my audio amplifier?

I have also looked into using ferrite = toroids=20 as transformers but the
sheer amount of information on this = subject,=20 often incomplete and
contradictory, is confusing me. It looks = like many=20 are using "3C90" as a
core material, but this type of core = seems=20 difficult to acquire - at
least for me here in Norway. I = understand=20 that "type 77" material could
also be used and this one is = easier to=20 get by. If I would opt for an
FT140-77 core, would this be = suitable as=20 a transformer toroid for 100
Watt on 136 kHz or would I need a = bigger=20 one? And how many primary and
secondary turns would such a = tranformer=20 need to step up from 4-8 Ohm to
50 Ohm?

I would be very = grateful=20 for some input on this subject before I start
ordering (the = wrong)=20 components.

73 de = Robert,

LA4ANA

=
__._,_.___
Reply=20 to sender | Reply=20 to group | Reply=20 via web post | Start=20 a new topic
Messages=20 in this topic (1) =
Recent=20 Activity:=20 New=20 Members 3=20 New=20 Photos 4=20
Visit=20 Your Group
=20
Switch to: Text-Only,=20 Daily=20 Digest =95 Unsubscribe=20 =95 Terms of=20 Use
.

__,_._,___
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