Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-df05.r1000.mx.aol.com (Internet Inbound) with ESMTP id 33B8B380001EA; Wed, 10 Aug 2011 11:03:12 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1QrAIA-0002bg-M0 for rs_out_1@blacksheep.org; Wed, 10 Aug 2011 16:01:58 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1QrAI9-0002bX-Qe for rsgb_lf_group@blacksheep.org; Wed, 10 Aug 2011 16:01:57 +0100 Received: from mail-ew0-f43.google.com ([209.85.215.43]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1QrAI6-0002B9-U0 for rsgb_lf_group@blacksheep.org; Wed, 10 Aug 2011 16:01:57 +0100 Received: by ewy20 with SMTP id 20so832014ewy.16 for ; Wed, 10 Aug 2011 08:01:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=message-id:from:to:references:in-reply-to:subject:date:mime-version :content-type:x-priority:x-msmail-priority:importance:x-mailer :x-mimeole; bh=qZDXGC2z9GYeZeOfCzxNqr1B6a9zpjZGBZmxz9ILUcM=; b=oaX6EI8jdSTmyvQ0wv4Pq49Ra8lVmLv38f0TKKBetpl9m2+EDcePE9LXTMEm+bG0so 1SFhrnsJZrZsbQ2npitxgkQiv1+36St0JNd2bWzRWtC4DR2su83I4MTdmNPqecT4NOc0 jrCHEHxBpRuJTcjDVWQ3L655ObJ4kkDJCGbdI= Received: by 10.14.4.214 with SMTP id 62mr2556155eej.129.1312988508968; Wed, 10 Aug 2011 08:01:48 -0700 (PDT) Received: from PcMinto (h50208.upc-h.chello.nl [62.194.50.208]) by mx.google.com with ESMTPS id n51sm483839eef.17.2011.08.10.08.01.46 (version=SSLv3 cipher=OTHER); Wed, 10 Aug 2011 08:01:46 -0700 (PDT) Message-ID: <0FA38FC9F88F41738D007D00C0B66503@PcMinto> From: Minto Witteveen To: 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> In-Reply-To: <4E427DFB.50801@iup.uni-heidelberg.de> Date: Wed, 10 Aug 2011 17:01:38 +0200 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 15.4.3538.513 X-MimeOLE: Produced By Microsoft MimeOLE V15.4.3538.513 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: Re: HB9ASB... Content-Type: multipart/alternative; boundary="----=_NextPart_000_017B_01CC577F.2B83C1E0" 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: 0:2:472499488:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d271.2 ; domain : gmail.com DKIM : fail x-aol-sid: 3039ac1d40d94e429db05a20 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_017B_01CC577F.2B83C1E0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Stefan, Some comments: I think the mechanism is that the unwanted signal on the screen causes a = 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 = 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 = 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 = > 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 = 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 = 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=20 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=20 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 = > 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 = > a common mode choke close to the rig will do little extra. (it would=20 > 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=20 > 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 = 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=20 > 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 = > 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 = same dependency? There could be several reasons apply here... > Last year I already bought 3 meters of copper pipe to drive into the=20 > 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=20 > miniwhip is (I think) caused by the fact that I am surrounded by other = > houses, gardens, trees etc. Not comparable with an open field=E2=80=A6 Yes. 73, Stefan /DK7FC ------=_NextPart_000_017B_01CC577F.2B83C1E0 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

Hi = Stefan,

Some = comments:

I think the mechanism is that the = unwanted=20 signal on the screen causes a
potential difference between gate and = source=20 of the first (J)FET. So
this causes a current flow in the output = stage and=20 so a signal at the RX
input.

I fail to see how = that could be=20 the main cause=E2=80=A6 because cutting the power to the miniwhip should = then eliminate=20 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=20 balanced-unbalanced hypothesis)

It would almost have the same = effect (when=20 ignoring the C between cable
and ground along to the choke near the = antenna=20 ground) as placing the
choke near the antenna ground, both are in = series and=20 increase the
current reducing impedance, yes...

But I have to = disagree. A choke=20 (only) at the TX would accomplish nothing (in fact it may even make it = worse).=20 With a choke at the RX end the coax will =E2=80=93 acting as an antenna = - still pick up=20 all kinds of noise in the house, and this get transported via the = outside of the=20 coax to the miniwhip. Placing the chocke+ground near the miniwhip will = on the=20 other hand attenuate all the noise that is picked up along the = coax.
An=20 (additional) choke at the RX end _might_ make things worse at LF because = in that=20 case the noise will not be bled to earth there, with the result that the = overall=20 noise voltage on the outside might be still higher.

Hm, i rather expect a galvanic = coupling i.e.=20 stray currenty on the
supply cable of the RX. What happens if you = run the RX=20 on batteries? The
same dependency?

Running the 817 on = batteries=20 makes no difference. And galvanic coupling is unlikely because the QRM=20 completely disappears when I disconnect the coax in the shack=E2=80=A6. = And the coax is=20 not connected to anything else up to the miniwhip.
As for the = necessity of a=20 current balun or common mode choke when going form unbalanced to = balanced:  picture a classic dipole fed = by coax.=20 (TX) current runs through the center conductor. Kirchofs law states that = the=20 same current must flow in the other direction (on the inside of the = braid). Now=20 at the dipole the current from the center conductor only has one way to = go: into=20 1 half of the dipole. But the current on the inside of the braid has two = paths:=20 into the second half of the dipole AND into the outer side of the braid. = The=20 actual distribution is determined by the relative impedances these two = other=20 halves of the dipole have at the specific frequency. Enter the choke, = which=20 effectively blocks the path to the outer side of the braid. The same = mechanism=20 is true for reception.

Today it's nice WX here! And in=20 NL?

What can I = say=E2=80=A6 at least it=20 isn=E2=80=99t raining today. But unfortunately I have other duties = (QRL)

Overall an = interesting=20 discussion!! I am curious if there are any other (competing) theories = J

 

Regards,
Minto=20 pa3bca

Hi Minto,

Am = 10.08.2011=20 13:10, schrieb Minto Witteveen:
> Hi Stefan, (et = al)
>
> Well=20 I beg to differ.. :-)
> What I think happens is this: The outside = of the=20 coax picks up
> electromagnetic radiation like any antenna = (including QRM=20 generated by
> fluorescent lamps and Alinco switching power = supplies).=20 This signal
> travels along the coax to the Miniwhip. (also in = the=20 direction of the
> receiver but that is not important here as the = signal=20 is on the
> outside of the coax).
> Upon arrival at the = miniwhip=20 this signal on the outside of the coax
> has nowhere to go = ­but to=20 the _inside_ of the outer mantle of the coax
> =E2=80=93 it = =E2=80=98rounds the corner=E2=80=99=20 at the end of the coax so to speak.
I think the mechanism is that the = unwanted signal on the screen causes a
potential difference between = gate and=20 source of the first (J)FET. So
this causes a current flow in the = output=20 stage and so a signal at the RX
input.
A common mode choke = between RX and=20 the antenna ground should form a low
pass filter for unwanted = signals coming=20 from the shack. Using a common
mode choke without a local ground = should have=20 little effect, except the
coax is some 100m long (between choke and = probe)=20 ;-)

Ah BTW regarding the discussion "the cable to the E field = probe is=20 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 =
it?! :-)


> So how to avoid the QRM that is picked up = by the=20 coax to =E2=80=98travel back=E2=80=99
> via the inside: for the = miniwhip it is indeed=20 best (as Roelof
> mentioned) to short these signals to earth = _outside_=20 the house,
> preferably as close to the miniwhip as possible. = Grounding=20 there would
> to the trick, aided by a (large enough) common mode = choke=20 between the
> ground point and the house. The QRM that is picked = up in=20 the house
> would be =E2=80=93 after attenuation by the choke - = directed into the=20 ground
> and not up into the pole and the miniwhip.

Yes = yes,=20 totally agreed.
> Whatever happens in the house would then be = largely=20 irrelevant. Adding
> a common mode choke close to the rig will do = little=20 extra. (it would
> only attenuate QRM getting from the = shack=E2=80=99s earth=20 system to the
> outside of the coax).
It would almost have the = same=20 effect (when ignoring the C between cable
and ground along to the = choke near=20 the antenna ground) as placing the
choke near the antenna ground, = both are=20 in series and increase the
current reducing impedance, = yes...

>=20 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=20 will not be much.
> So far for theory. Now the proof of the = pudding: DCF39=20 is now > S9+40
> dB. My old trusty QRM generator (Alinco SMPS) = generates S9+25 at
> 135.500. When I switch off the miniwhip (cut = the=20 power) DCF39 drops
> down to just above the noise floor. As=20 expected.
Ah yes, that's what i meant above (should have read your = mail=20 completely
before answering ;-) ). This is the proof that Mal cannot = be=20 right when
saying "the coax is the actual antenna".
> But the = Alinco=20 signal only drops down some 15 dB and remains the only
> signal = that is=20 audible. This is exactly what I would expect: the QRM
> travels = along the=20 outside of the coax to the miniwhip, =E2=80=98rounds the
> = corner=E2=80=99 and comes back=20 via the inside of the coax shield. Further
> proof that it indeed = takes=20 this route: if I disconnect the coax in the
> shack the Alinco = smps=20 signal disappears also (so it is not received
> via any other=20 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...

>=20 Last year I already bought 3 meters of copper pipe to drive into the =
>=20 ground in the backyard. Bet never got around to finish the = job=E2=80=A6
Today it's=20 nice WX here! And in NL?
>
> The main reason the signal = strength is=20 much higher with the elevated
> miniwhip is (I think) caused by = the fact=20 that I am surrounded by other
> houses, gardens, trees etc. Not=20 comparable with an open field=E2=80=A6
Yes.

73, Stefan = /DK7FC

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