Return-Path: Received: from mtain-md10.r1000.mx.aol.com (mtain-md10.r1000.mx.aol.com [172.29.96.94]) by air-dd04.mail.aol.com (v129.4) with ESMTP id MAILINDD043-865a4c2131193c7; Tue, 22 Jun 2010 17:54:33 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-md10.r1000.mx.aol.com (Internet Inbound) with ESMTP id B03AC380000C5; Tue, 22 Jun 2010 17:54:31 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ORBOw-0001kH-HI for rs_out_1@blacksheep.org; Tue, 22 Jun 2010 22:53:02 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ORBOv-0001k8-Lp for rsgb_lf_group@blacksheep.org; Tue, 22 Jun 2010 22:53:01 +0100 Received: from out1.ip09ir2.opaltelecom.net ([62.24.128.245]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1ORBOt-0004C2-Sj for rsgb_lf_group@blacksheep.org; Tue, 22 Jun 2010 22:53:01 +0100 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ai8FAF/NIExcEYb9/2dsb2JhbACPOAOPZ3HCWIIRgwoE X-IronPort-AV: E=Sophos;i="4.53,462,1272841200"; d="scan'208,217";a="439289006" Received: from unknown (HELO your91hoehfy9g) ([92.17.134.253]) by out1.ip09ir2.opaltelecom.net with SMTP; 22 Jun 2010 22:52:52 +0100 Message-ID: <000b01cb1255$43fa2c20$0301a8c0@your91hoehfy9g> From: "mal hamilton" To: References: <000c01cb11dc$2b310020$0401a8c0@xphd97xgq27nyf><3A2133327AFB454CAC336E25F96F4352@TonyLaptop><00f301cb1204$27dc76c0$0217aac0@desktop><5CB3170C92154284B48334F50A8DDD89@IBM7FFA209F07C><6AEC4DD1A0F04696AB42F2158C87F963@TonyLaptop> Date: Tue, 22 Jun 2010 22:52:52 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Re: 137 Revival Content-Type: multipart/alternative; boundary="----=_NextPart_000_0008_01CB125D.A5510540" 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-sid: 3039ac1d605e4c21311766fd X-AOL-IP: 193.82.116.20 ------=_NextPart_000_0008_01CB125D.A5510540 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Avoid this modified Electric Chair, guaranteed premature expiry. Jim= has instead offered some good advice. g3kev ----- Original Message -----=20 From: Andy Talbot=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Tuesday, June 22, 2010 9:02 PM Subject: Re: LF: Re: 137 Revival see http://www.g4jnt.com/137tx.pdf for another big one. Andy www.g4jnt.com On 22 June 2010 20:04, James Moritz = wrote: Dear Tony, LF Group, What you need for a 136kHz transmitter depends a lot on the antenn= a it is to be used with, and what you want to do with it. Antenna efficiency is usually low on 136k - a small fraction of a= percent is the norm - and very variable. If you have access to 100 fo= ot high antenna masts, then you will be able to achieve the 1W ERP lim= it with probably less than 100W of TX power. But if you are restricted= to "back garden" sized antennas, you will probably need a kilowatt or= more to reach this radiated power level. If you are restricted to low= er powers and small antennas, your ERP will be well below 1W, although= contacts over quite decent distances can be had with tens of milliwat= ts ERP. Much lower powers are viable at relatively short ranges within= ground-wave propagation distances. But due to the low numbers of acti= ve stations on the band, this severely limits the number of contacts= that will be possible, so 136k is not really a band for QRP transmitt= ers, unless you have a huge antenna available. For CW operation, transmitter design can be pretty simple - a reas= onably stable frequency source, a class D PA stage, and some way of ke= ying it on and off. For extreme-narrow-band QRSS use, improved frequen= cy stability is needed. Usually this means some sort of synthesiser,= although simpler means, such as ceramic resonator based VFOs, are qui= te viable unless extreme stability is required. If you are interested= in data or other "visual" modes, it gets a bit more complex, requirin= g either a home brew modulator operating at 136k, or a transverter to= shift the frequency of an existing rig. Also, amplitude modulation of= the signal is needed for some modes, which requires either a linear= PA, or techniques such as "EER". Go to G3YXM's pages at http://www.wireless.org.uk/, and look at th= e "Circuits", "Features", and "Build a TX" pages for some ideas. The= RSGB books "LF today", and recent editions of the "Radio Communicatio= n Handbook" contain several transmitter designs. I have written up a= 200W multi-mode transverter design using the EER technique at http://= uk500khz.googlegroups.com/web/EER_Transverter_v3.pdf . There are some= designs for 500kHz transmitters also at http://groups.google.com/grou= p/uk500khz on the "files" page, which could be easily adapted to 136kH= z with appropriate component changes. Google-ing for "136kHz transmitt= er" will get you quite a few results. Shoving a lot of power into an antenna that is really too small fo= r the job is never going to be very reliable or foolproof ... but it= is sometimes quite exciting ;-). The class D designs have become popu= lar because they use simple circuits and cheap, readily available, swi= tching MOSFETs to achieve a large output power, but one should be awar= e that most class D circuits will try to deliver very high output curr= ents into low impedance loads, which can lead to damage when the anten= na is mis-tuned, as it inevitably sometimes is. With electrically smal= l elements and large loading coils, antennas are unavoidably high Q wi= th critical tuning which is easily disturbed. Current limiting of the= DC supply or RF output is very desireable. Class D designs are very= efficient and cool-running during normal operation, but can dissipate= a lot of power when badly mis-matched, so conservative design is need= ed for reliability. Good luck on 136kHz, hope to see you on the band this winter! Cheers, Jim Moritz 73 de M0BMU From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_g= roup@blacksheep.org] On Behalf Of Tony Baldwin Sent: 22 June 2010 11:49 To: rsgb_lf_group@blacksheep.org Subject: LF: Re: 137 Revival I fully intend to be QRV on 137 by the winter. On that note, can anyone recommend a reliable foolproof transmit= ter that uses easily available components ? Tony, EI8JK. ------=_NextPart_000_0008_01CB125D.A5510540 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Avoid this modified Electric Chair,= guaranteed=20 premature expiry.  Jim has instead offered some good=20 advice.
g3kev
 
----- Original Message -----
From:=20 Andy Talbot
Sent: Tuesday, June 22, 2010= 9:02=20 PM
Subject: Re: LF: Re: 137 Revi= val

see   = http://www.g4jnt.com/137tx.pdf   =20 for another big one.
 
On 22 June 2010 20:04, James Moritz <james.moritz@btopenworld.com>=20 wrote:
Dear=20 Tony, LF Group,

What you need for a 136kHz transmitter depe= nds a lot=20 on the antenna it is to be used with, and what you want to do with= =20 it.

Antenna efficiency is usually low on 136k - a small fra= ction of a=20 percent is the norm - and very variable. If you have access to 100= foot high=20 antenna masts, then you will be able to achieve the 1W ERP limit= with=20 probably less than 100W of TX power. But if you are restricted to= "back=20 garden" sized antennas, you will probably need a kilowatt or more= to reach=20 this radiated power level. If you are restricted to lower powers= and small=20 antennas, your ERP will be well below 1W, although contacts over= quite=20 decent distances can be had with tens of milliwatts ERP. Much lowe= r powers=20 are viable at relatively short ranges within ground-wave propagati= on=20 distances. But due to the low numbers of active stations on the ba= nd, this=20 severely limits the number of contacts that will be possible, so= 136k is not=20 really a band for QRP transmitters, unless you have a huge antenna= =20 available.

For CW operation, transmitter design can be pret= ty simple=20 - a reasonably stable frequency source, a class D PA stage, and so= me way of=20 keying it on and off. For extreme-narrow-band QRSS use, improved= frequency=20 stability is needed. Usually this means some sort of synthesiser,= although=20 simpler means, such as ceramic resonator based VFOs, are quite via= ble unless=20 extreme stability is required. If you are interested in data or ot= her=20 "visual" modes, it gets a bit more complex, requiring either a hom= e brew=20 modulator operating at 136k, or a transverter to shift the frequen= cy of an=20 existing rig. Also, amplitude modulation of the signal is needed= for some=20 modes, which requires either a linear PA, or techniques such as=20 "EER".

Go to G3YXM's pages at http://www.wireless.org.uk/, and= look at the "Circuits",=20 "Features", and "Build a TX" pages for some ideas. The RSGB books= "LF=20 today", and recent editions of the "Radio Communication Handbook"= contain=20 several transmitter designs. I have written up a 200W multi-mode= transverter=20 design using the EER technique at ht= tp://uk500khz.googlegroups.com/web/EER_Transverter_v3.pdf=20 . There are some designs for 500kHz transmitters also at http://groups.google.com/group/uk500khz on the "files"=20 page, which could be easily adapted to 136kHz with appropriate com= ponent=20 changes. Google-ing for "136kHz transmitter" will get you quite a= few=20 results.

Shoving a lot of power into an antenna that is rea= lly too=20 small for the job is never going to be very reliable or foolproof= ... but it=20 is sometimes quite exciting ;-). The class D designs have become= popular=20 because they use simple circuits and cheap, readily available, swi= tching=20 MOSFETs to achieve a large output power, but one should be aware= that most=20 class D circuits will try to deliver very high output currents int= o low=20 impedance loads, which can lead to damage when the antenna is mis-= tuned, as=20 it inevitably sometimes is. With electrically small elements and= large=20 loading coils, antennas are unavoidably high Q with critical tunin= g which is=20 easily disturbed. Current limiting of the DC supply or RF output= is very=20 desireable. Class D designs are very efficient and cool-running du= ring=20 normal operation, but can dissipate a lot of power when badly mis-= matched,=20 so conservative design is needed for reliability.

Good luck= on=20 136kHz, hope to see you on the band this winter!

Cheers, Ji= m=20 Moritz
73 de M0BMU



  From: owne= r-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_g= roup@blacksheep.org] On Behalf Of Tony=20 Baldwin
  Sent: 22 June 2010 11:49
  To: r= sgb_lf_group@blacksheep.org
  Subject: LF: Re:=20 137 Revival



  I fully intend to be QRV on 137= by the=20 winter.

  On that note, can anyone recommend a reliabl= e=20 foolproof transmitter that uses easily available components=20 ?



  Tony,=20 EI8JK.





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