Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dh06.r1000.mx.aol.com (Internet Inbound) with ESMTP id 93FAA3800008D; Wed, 10 Aug 2011 12:24:09 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1QrBYv-0003Dg-W3 for rs_out_1@blacksheep.org; Wed, 10 Aug 2011 17:23:21 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1QrBYv-0003DX-2c for rsgb_lf_group@blacksheep.org; Wed, 10 Aug 2011 17:23:21 +0100 Received: from smtp7.freeserve.com ([80.12.242.2] helo=smtp6.freeserve.com) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from <g8fzk@g8fzk.fsnet.co.uk>) id 1QrBYt-0003mp-7R for rsgb_lf_group@blacksheep.org; Wed, 10 Aug 2011 17:23:21 +0100 Received: from me-wanadoo.net (localhost [127.0.0.1]) by mwinf3j07.me.freeserve.com (SMTP Server) with ESMTP id 5A7033000098 for <rsgb_lf_group@blacksheep.org>; Wed, 10 Aug 2011 18:23:13 +0200 (CEST) Received: from me-wanadoo.net (localhost [127.0.0.1]) by mwinf3j07.me.freeserve.com (SMTP Server) with ESMTP id 4D7DC300009D for <rsgb_lf_group@blacksheep.org>; Wed, 10 Aug 2011 18:23:13 +0200 (CEST) Received: from AGB (unknown [2.26.14.137]) by mwinf3j07.me.freeserve.com (SMTP Server) with SMTP id EC9D83000098 for <rsgb_lf_group@blacksheep.org>; Wed, 10 Aug 2011 18:23:12 +0200 (CEST) X-ME-UUID: 20110810162312969.EC9D83000098@mwinf3j07.me.freeserve.com Message-ID: <09706552FC574901BA413DC5295F48F5@AGB> From: "Graham" <g8fzk@g8fzk.fsnet.co.uk> To: <rsgb_lf_group@blacksheep.org> References: <4E418609.6020500@iup.uni-heidelberg.de> <67A6F7BF45BF4A0193A3DCB53000A283@PcMinto> <008401cc56ce$2f1fb2c0$0401a8c0@xphd97xgq27nyf> <12C475F3F4C84B818461753F2E8A60A6@PcMinto> <4E41AECB.90808@iup.uni-heidelberg.de> <8D68749D37B94275855FDBA46A3F6C97@PcMinto> <4E427DFB.50801@iup.uni-heidelberg.de> <0FA38FC9F88F41738D007D00C0B66503@PcMinto> <002e01cc5772$40601a30$0401a8c0@xphd97xgq27nyf> In-Reply-To: <002e01cc5772$40601a30$0401a8c0@xphd97xgq27nyf> Date: Wed, 10 Aug 2011 17:23:12 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 X-Antivirus: avast! (VPS 110810-0, 10/08/2011), Outbound message X-Antivirus-Status: Clean X-Spam-Score: 0.2 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,RCVD_ILLEGAL_IP=0.234 Subject: Re: LF: Re: Re: HB9ASB... Content-Type: multipart/alternative; boundary="----=_NextPart_000_00F7_01CC5782.2E989BA0" 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_MESSAGE, MISSING_OUTLOOK_NAME 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-SCOLL-SCORE: 0:2:495522816:93952408 X-AOL-SCOLL-URL_COUNT: 0 x-aol-sid: 3039ac1d411a4e42b0a9548e 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_00F7_01CC5782.2E989BA0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Im sure one station uses a battery and radio link from the = probe Ae so no feeder ? G. From: mal hamilton=20 Sent: Wednesday, August 10, 2011 4:29 PM To: rsgb_lf_group@blacksheep.org=20 Subject: LF: Re: Re: HB9ASB... This miniwhip/probe seems to be a very complicated antenna and difficult = to explain its properties.=20 I suggest someone takes this antenna out into the middle of a field away = from any noise source and work out how it actualljy performs. because using it in a noisy environment at various heights in different = locations introduces too many variables for accurate evaluation. A random simple piece of wire with a suitable preamp and a counterpoise = would probably work better. Decca used a metal barrell probe and preamp at their RX stations maybe = someone knows how they performed, although their sites were in a rural = quiet environment.=20 The argument at present about this type of antenna needs to be = concentrated on actual performance and not about environmental LOCATION, = move it up or down a bit, use longer feed line, get it above the roof = etc, Earth the outer braid before it enters the shack, use an isolation = transformer.=20 Let us have your observations. de mal/g3kev ----- Original Message -----=20 From: Minto Witteveen=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Wednesday, August 10, 2011 4:01 PM Subject: LF: Re: HB9ASB... Hi Stefan, Some comments: I think the mechanism is that the unwanted signal on the screen causes = a=20 potential difference between gate and source of the first (J)FET. So=20 this causes a current flow in the output stage and so a signal at the = RX=20 input. I fail to see how that could be the main cause=E2=80=A6 because = cutting the power to the miniwhip should then eliminate the QRM, but it = does not! It probably attributes somewhat - only some 10-15 dB, but = that leaves 9+20 dB for another explanation. (i.e. my = balanced-unbalanced hypothesis)=20 It would almost have the same effect (when ignoring the C between = cable=20 and ground along to the choke near the antenna ground) as placing the=20 choke near the antenna ground, both are in series and increase the=20 current reducing impedance, yes... But I have to disagree. A choke (only) at the TX would accomplish = nothing (in fact it may even make it worse). With a choke at the RX end = the coax will =E2=80=93 acting as an antenna - still pick up all kinds = of noise in the house, and this get transported via the outside of the = coax to the miniwhip. Placing the chocke+ground near the miniwhip will = on the other hand attenuate all the noise that is picked up along the = coax. An (additional) choke at the RX end _might_ make things worse at LF = because in that case the noise will not be bled to earth there, with the = result that the overall noise voltage on the outside might be still = higher. Hm, i rather expect a galvanic coupling i.e. stray currenty on the=20 supply cable of the RX. What happens if you run the RX on batteries? = The=20 same dependency? Running the 817 on batteries makes no difference. And galvanic = coupling is unlikely because the QRM completely disappears when I = disconnect the coax in the shack=E2=80=A6. And the coax is not connected = to anything else up to the miniwhip.=20 As for the necessity of a current balun or common mode choke when = going form unbalanced to balanced: picture a classic dipole fed by = coax. (TX) current runs through the center conductor. Kirchofs law = states that the same current must flow in the other direction (on the = inside of the braid). Now at the dipole the current from the center = conductor only has one way to go: into 1 half of the dipole. But the = current on the inside of the braid has two paths: into the second half = of the dipole AND into the outer side of the braid. The actual = distribution is determined by the relative impedances these two other = halves of the dipole have at the specific frequency. Enter the choke, = which effectively blocks the path to the outer side of the braid. The = same mechanism is true for reception. Today it's nice WX here! And in NL? What can I say=E2=80=A6 at least it isn=E2=80=99t raining today. But = unfortunately I have other duties (QRL) Overall an interesting discussion!! I am curious if there are any = other (competing) theories J =20 Regards, Minto pa3bca Hi Minto, Am 10.08.2011 13:10, schrieb Minto Witteveen: > Hi Stefan, (et al) > > Well I beg to differ.. :-) > What I think happens is this: The outside of the coax picks up=20 > electromagnetic radiation like any antenna (including QRM generated = by=20 > fluorescent lamps and Alinco switching power supplies). This signal=20 > travels along the coax to the Miniwhip. (also in the direction of = the=20 > receiver but that is not important here as the signal is on the=20 > outside of the coax). > Upon arrival at the miniwhip this signal on the outside of the coax=20 > has nowhere to go =C2=ADbut to the _inside_ of the outer mantle of = the coax=20 > =E2=80=93 it =E2=80=98rounds the corner=E2=80=99 at the end of the = coax so to speak. I think the mechanism is that the unwanted signal on the screen causes = a=20 potential difference between gate and source of the first (J)FET. So=20 this causes a current flow in the output stage and so a signal at the = RX=20 input. A common mode choke between RX and the antenna ground should form a = low=20 pass filter for unwanted signals coming from the shack. Using a common = mode choke without a local ground should have little effect, except = the=20 coax is some 100m long (between choke and probe) ;-) Ah BTW regarding the discussion "the cable to the E field probe is the = actual antenna": One could just try what happens if one disconnects = the=20 power supply. If the signal is still present then the cable is the=20 antenna, if the signal is gone: The probe must be the antenna. Isn't=20 it?! :-) > So how to avoid the QRM that is picked up by the coax to = =E2=80=98travel back=E2=80=99=20 > via the inside: for the miniwhip it is indeed best (as Roelof=20 > mentioned) to short these signals to earth _outside_ the house,=20 > preferably as close to the miniwhip as possible. Grounding there = would=20 > to the trick, aided by a (large enough) common mode choke between = the=20 > ground point and the house. The QRM that is picked up in the house=20 > would be =E2=80=93 after attenuation by the choke - directed into = the ground=20 > and not up into the pole and the miniwhip. Yes yes, totally agreed. > Whatever happens in the house would then be largely irrelevant. = Adding=20 > a common mode choke close to the rig will do little extra. (it would = > only attenuate QRM getting from the shack=E2=80=99s earth system to = the=20 > outside of the coax). It would almost have the same effect (when ignoring the C between = cable=20 and ground along to the choke near the antenna ground) as placing the=20 choke near the antenna ground, both are in series and increase the=20 current reducing impedance, yes... > Any signals picked up by the vertical coax between the earthing = point=20 > and the whip will add to the received signal, but at low frequencies = > it will not be much. > So far for theory. Now the proof of the pudding: DCF39 is now > = S9+40=20 > dB. My old trusty QRM generator (Alinco SMPS) generates S9+25 at=20 > 135.500. When I switch off the miniwhip (cut the power) DCF39 drops=20 > down to just above the noise floor. As expected. Ah yes, that's what i meant above (should have read your mail = completely=20 before answering ;-) ). This is the proof that Mal cannot be right = when=20 saying "the coax is the actual antenna". > But the Alinco signal only drops down some 15 dB and remains the = only=20 > signal that is audible. This is exactly what I would expect: the QRM = > travels along the outside of the coax to the miniwhip, = =E2=80=98rounds the=20 > corner=E2=80=99 and comes back via the inside of the coax shield. = Further=20 > proof that it indeed takes this route: if I disconnect the coax in = the=20 > shack the Alinco smps signal disappears also (so it is not received=20 > via any other path). Hm, i rather expect a galvanic coupling i.e. stray currenty on the=20 supply cable of the RX. What happens if you run the RX on batteries? = The=20 same dependency? There could be several reasons apply here... > Last year I already bought 3 meters of copper pipe to drive into the = > ground in the backyard. Bet never got around to finish the = job=E2=80=A6 Today it's nice WX here! And in NL? > > The main reason the signal strength is much higher with the elevated = > miniwhip is (I think) caused by the fact that I am surrounded by = other=20 > houses, gardens, trees etc. Not comparable with an open = field=E2=80=A6 Yes. 73, Stefan /DK7FC ------=_NextPart_000_00F7_01CC5782.2E989BA0 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML xmlns:o =3D "urn:schemas-microsoft-com:office:office"><HEAD> <META content=3Dtext/html;charset=3Dutf-8 http-equiv=3DContent-Type> <META name=3DGENERATOR content=3D"MSHTML 8.00.6001.19088"> <STYLE></STYLE> </HEAD> <BODY style=3D"PADDING-LEFT: 10px; PADDING-RIGHT: 10px; PADDING-TOP: = 15px" dir=3Dltr=20 id=3DMailContainerBody leftMargin=3D0 topMargin=3D0 bgColor=3D#ffffff=20 CanvasTabStop=3D"true" name=3D"Compose message area"> <DIV><FONT size=3D2 face=3DArial>Im sure one = station uses=20 a battery and radio link from=20 the probe Ae so no = feeder =20 ?</FONT></DIV> <DIV><FONT size=3D2 face=3DArial></FONT> </DIV> <DIV><FONT size=3D2 face=3DArial>G.</FONT></DIV> <DIV style=3D"FONT: 10pt Tahoma"> <DIV><BR></DIV> <DIV style=3D"BACKGROUND: #f5f5f5"> <DIV style=3D"font-color: black"><B>From:</B> <A = title=3Dg3kevmal@talktalk.net=20 href=3D"mailto:g3kevmal@talktalk.net">mal hamilton</A> </DIV> <DIV><B>Sent:</B> Wednesday, August 10, 2011 4:29 PM</DIV> <DIV><B>To:</B> <A title=3Drsgb_lf_group@blacksheep.org=20 href=3D"mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org= </A>=20 </DIV> <DIV><B>Subject:</B> LF: Re: Re: HB9ASB...</DIV></DIV></DIV> <DIV><BR></DIV> <DIV><FONT face=3DArial>This miniwhip/probe seems to be a very = complicated antenna=20 and difficult to explain its properties. </FONT></DIV> <DIV><FONT face=3DArial>I suggest someone takes this antenna out into = the middle=20 of a field away from any noise source and work out how it actualljy=20 performs.</FONT></DIV> <DIV><FONT face=3DArial>because using it in a noisy environment at = various heights=20 in different locations introduces too many variables for accurate=20 evaluation.</FONT></DIV> <DIV><FONT face=3DArial>A random simple piece of wire with a = suitable preamp=20 and a counterpoise would probably work better.</FONT></DIV> <DIV><FONT face=3DArial>Decca used a metal barrell probe and preamp = at their=20 RX stations maybe someone knows how they performed, although their sites = were in=20 a rural quiet environment. </FONT></DIV> <DIV><FONT face=3DArial>The argument at present about this type of=20 antenna needs to be concentrated on actual performance and not = about=20 environmental LOCATION, move it up or down a bit, use longer feed line, = get it=20 above the roof etc, Earth the outer braid before it enters the = shack, use=20 an isolation transformer. </FONT></DIV> <DIV><FONT face=3DArial>Let us have your observations.</FONT></DIV> <DIV><FONT face=3DArial>de mal/g3kev</FONT></DIV> <DIV> </DIV> <BLOCKQUOTE=20 style=3D"BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; = PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"=20 dir=3Dltr> <DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV> <DIV=20 style=3D"FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: = black"><B>From:</B>=20 <A title=3Dminto.witteveen@gmail.com=20 href=3D"mailto:minto.witteveen@gmail.com">Minto Witteveen</A> </DIV> <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A = title=3Drsgb_lf_group@blacksheep.org=20 = href=3D"mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org= </A>=20 </DIV> <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Wednesday, August 10, = 2011 4:01=20 PM</DIV> <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> LF: Re: = HB9ASB...</DIV> <DIV><BR></DIV> <DIV dir=3Dltr> <DIV style=3D"FONT-FAMILY: 'Arial'; COLOR: #000000; FONT-SIZE: 10pt"> <DIV> <P style=3D"MARGIN: 0in 0in 10pt" class=3DMsoNormal>Hi = Stefan,<o:p></o:p></P> <P style=3D"MARGIN: 0in 0in 10pt" class=3DMsoNormal>Some = comments:<o:p></o:p></P> <P style=3D"MARGIN: 0in 0in 10pt 0.5in" class=3DMsoNormal><I=20 style=3D"mso-bidi-font-style: normal">I think the mechanism is that = the unwanted=20 signal on the screen causes a <BR>potential difference between gate = and source=20 of the first (J)FET. So <BR>this causes a current flow in the output = stage and=20 so a signal at the RX <BR>input.<o:p></o:p></I></P> <P style=3D"MARGIN: 0in 0in 10pt" class=3DMsoNormal>I fail to see how = that could=20 be the main cause=E2=80=A6 because cutting the power to the miniwhip = should then=20 eliminate the QRM, but it does not! It probably attributes somewhat - = <SPAN=20 style=3D"mso-spacerun: yes"> </SPAN>only some 10-15 dB, but that = leaves=20 <SPAN style=3D"mso-spacerun: yes"> </SPAN>9+20 dB for another = explanation.=20 (i.e. my balanced-unbalanced hypothesis) <o:p></o:p></P> <P style=3D"MARGIN: 0in 0in 10pt 0.5in" class=3DMsoNormal><I=20 style=3D"mso-bidi-font-style: normal">It would almost have the same = effect (when=20 ignoring the C between cable <BR>and ground along to the choke near = the=20 antenna ground) as placing the <BR>choke near the antenna ground, both = are in=20 series and increase the <BR>current reducing impedance,=20 yes...<o:p></o:p></I></P> <P style=3D"MARGIN: 0in 0in 10pt" class=3DMsoNormal>But I have to = disagree. A=20 choke (only) at the TX would accomplish nothing (in fact it may even = make it=20 worse). With a choke at the RX end the coax will =E2=80=93 acting as = an antenna -=20 still pick up all kinds of noise in the house, and this get = transported via=20 the outside of the coax to the miniwhip. Placing the chocke+ground = near the=20 miniwhip will on the other hand attenuate all the noise that is picked = up=20 along the coax.<BR>An (additional) choke at the RX end _might_ make = things=20 worse at LF because in that case the noise will not be bled to earth = there,=20 with the result that the overall noise voltage on the outside might be = still=20 higher.<o:p></o:p></P> <P style=3D"MARGIN: 0in 0in 10pt 0.5in" class=3DMsoNormal><I=20 style=3D"mso-bidi-font-style: normal">Hm, i rather expect a galvanic = coupling=20 i.e. stray currenty on the <BR>supply cable of the RX. What happens if = you run=20 the RX on batteries? The <BR>same dependency?<o:p></o:p></I></P> <P style=3D"MARGIN: 0in 0in 10pt" class=3DMsoNormal>Running the 817 on = batteries=20 makes no difference. And galvanic coupling is unlikely because the QRM = completely disappears when I disconnect the coax in the = shack=E2=80=A6. And the coax=20 is not connected to anything else up to the miniwhip. <BR>As for the = necessity=20 of a current balun or common mode choke when going form unbalanced to=20 balanced:<SPAN style=3D"mso-spacerun: yes"> </SPAN>picture a = classic=20 dipole fed by coax. (TX) current runs through the center conductor. = Kirchofs=20 law states that the same current must flow in the other direction (on = the=20 inside of the braid). Now at the dipole the current from the center = conductor=20 only has one way to go: into 1 half of the dipole. But the current on = the=20 inside of the braid has two paths: into the second half of the dipole = AND into=20 the outer side of the braid. The actual distribution is determined by = the=20 relative impedances these two other halves of the dipole have at the = specific=20 frequency. Enter the choke, which effectively blocks the path to the = outer=20 side of the braid. The same mechanism is true for = reception.<o:p></o:p></P> <P style=3D"MARGIN: 0in 0in 10pt 0.5in" class=3DMsoNormal><I=20 style=3D"mso-bidi-font-style: normal">Today it's nice WX here! And in=20 NL?<o:p></o:p></I></P> <P style=3D"MARGIN: 0in 0in 10pt" class=3DMsoNormal>What can I = say=E2=80=A6 at least it=20 isn=E2=80=99t raining today. But unfortunately I have other duties=20 (QRL)<o:p></o:p></P> <P style=3D"MARGIN: 0in 0in 10pt" class=3DMsoNormal>Overall an = interesting=20 discussion!! I am curious if there are any other (competing) theories = <SPAN=20 style=3D"FONT-FAMILY: wingdings; mso-ascii-font-family: calibri; = mso-ascii-theme-font: minor-latin; mso-hansi-font-family: calibri; = mso-hansi-theme-font: minor-latin; mso-char-type: symbol; = mso-symbol-font-family: wingdings"><SPAN=20 style=3D"mso-char-type: symbol; mso-symbol-font-family: = wingdings">J</SPAN></SPAN><o:p></o:p></P> <P style=3D"MARGIN: 0in 0in 10pt" = class=3DMsoNormal><o:p></o:p> </P> <P style=3D"MARGIN: 0in 0in 10pt" class=3DMsoNormal>Regards,<BR>Minto=20 pa3bca<o:p></o:p></P> <P style=3D"MARGIN: 0in 0in 10pt" class=3DMsoNormal>Hi = Minto,<BR><BR>Am 10.08.2011=20 13:10, schrieb Minto Witteveen:<BR>> Hi Stefan, (et = al)<BR>><BR>>=20 Well I beg to differ.. :-)<BR>> What I think happens is this: The = outside=20 of the coax picks up <BR>> electromagnetic radiation like any = antenna=20 (including QRM generated by <BR>> fluorescent lamps and Alinco = switching=20 power supplies). This signal <BR>> travels along the coax to the = Miniwhip.=20 (also in the direction of the <BR>> receiver but that is not = important here=20 as the signal is on the <BR>> outside of the coax).<BR>> Upon = arrival at=20 the miniwhip this signal on the outside of the coax <BR>> has = nowhere to go=20 ­but to the _inside_ of the outer mantle of the coax <BR>> = =E2=80=93 it =E2=80=98rounds=20 the corner=E2=80=99 at the end of the coax so to speak.<BR>I think the = mechanism is=20 that the unwanted signal on the screen causes a <BR>potential = difference=20 between gate and source of the first (J)FET. So <BR>this causes a = current flow=20 in the output stage and so a signal at the RX <BR>input.<BR>A common = mode=20 choke between RX and the antenna ground should form a low <BR>pass = filter for=20 unwanted signals coming from the shack. Using a common <BR>mode choke = without=20 a local ground should have little effect, except the <BR>coax is some = 100m=20 long (between choke and probe) ;-)<BR><BR>Ah BTW regarding the = discussion "the=20 cable to the E field probe is the <BR>actual antenna": One could just = try what=20 happens if one disconnects the <BR>power supply. If the signal is = still=20 present then the cable is the <BR>antenna, if the signal is gone: The = probe=20 must be the antenna. Isn't <BR>it?! :-)<BR><BR><BR>> So how to = avoid the=20 QRM that is picked up by the coax to =E2=80=98travel back=E2=80=99 = <BR>> via the inside:=20 for the miniwhip it is indeed best (as Roelof <BR>> mentioned) to = short=20 these signals to earth _outside_ the house, <BR>> preferably as = close to=20 the miniwhip as possible. Grounding there would <BR>> to the trick, = aided=20 by a (large enough) common mode choke between the <BR>> ground = point and=20 the house. The QRM that is picked up in the house <BR>> would be = =E2=80=93 after=20 attenuation by the choke - directed into the ground <BR>> and not = up into=20 the pole and the miniwhip.<BR><BR>Yes yes, totally agreed.<BR>> = Whatever=20 happens in the house would then be largely irrelevant. Adding <BR>> = a=20 common mode choke close to the rig will do little extra. (it would = <BR>>=20 only attenuate QRM getting from the shack=E2=80=99s earth system to = the <BR>>=20 outside of the coax).<BR>It would almost have the same effect (when = ignoring=20 the C between cable <BR>and ground along to the choke near the antenna = ground)=20 as placing the <BR>choke near the antenna ground, both are in series = and=20 increase the <BR>current reducing impedance, yes...<BR><BR>> Any = signals=20 picked up by the vertical coax between the earthing point <BR>> and = the=20 whip will add to the received signal, but at low frequencies <BR>> = it will=20 not be much.<BR>> So far for theory. Now the proof of the pudding: = DCF39 is=20 now > S9+40 <BR>> dB. My old trusty QRM generator (Alinco SMPS)=20 generates S9+25 at <BR>> 135.500. When I switch off the miniwhip = (cut the=20 power) DCF39 drops <BR>> down to just above the noise floor. As=20 expected.<BR>Ah yes, that's what i meant above (should have read your = mail=20 completely <BR>before answering ;-) ). This is the proof that Mal = cannot be=20 right when <BR>saying "the coax is the actual antenna".<BR>> But = the Alinco=20 signal only drops down some 15 dB and remains the only <BR>> signal = that is=20 audible. This is exactly what I would expect: the QRM <BR>> travels = along=20 the outside of the coax to the miniwhip, =E2=80=98rounds the <BR>> = corner=E2=80=99 and=20 comes back via the inside of the coax shield. Further <BR>> proof = that it=20 indeed takes this route: if I disconnect the coax in the <BR>> = shack the=20 Alinco smps signal disappears also (so it is not received <BR>> via = any=20 other path).<BR>Hm, i rather expect a galvanic coupling i.e. stray = currenty on=20 the <BR>supply cable of the RX. What happens if you run the RX on = batteries?=20 The <BR>same dependency?<BR>There could be several reasons apply=20 here...<BR><BR>> Last year I already bought 3 meters of copper pipe = to=20 drive into the <BR>> ground in the backyard. Bet never got around = to finish=20 the job=E2=80=A6<BR>Today it's nice WX here! And in = NL?<BR>><BR>> The main=20 reason the signal strength is much higher with the elevated <BR>> = miniwhip=20 is (I think) caused by the fact that I am surrounded by other <BR>> = houses,=20 gardens, trees etc. Not comparable with an open = field=E2=80=A6<BR>Yes.<BR><BR>73,=20 Stefan /DK7FC<BR><BR style=3D"mso-special-character: line-break"><BR=20 style=3D"mso-special-character: = line-break"><o:p></o:p></P></DIV></DIV></DIV></BLOCKQUOTE> <br>= <br>= </BODY></HTML> ------=_NextPart_000_00F7_01CC5782.2E989BA0--