Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by klubnl.pl (8.14.4/8.14.4/Debian-8+deb8u2) with ESMTP id w6HCQoqe007638 for ; Tue, 17 Jul 2018 14:26:51 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ffOys-0001lT-TT for rs_out_1@blacksheep.org; Tue, 17 Jul 2018 13:21:26 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ffOyr-0001lK-UQ for rsgb_lf_group@blacksheep.org; Tue, 17 Jul 2018 13:21:25 +0100 Received: from mail-ed1-x529.google.com ([2a00:1450:4864:20::529]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.91_59-0488984) (envelope-from ) id 1ffOyo-0000Zn-EC for rsgb_lf_group@blacksheep.org; Tue, 17 Jul 2018 13:21:24 +0100 Received: by mail-ed1-x529.google.com with SMTP id s16-v6so1022658edq.12 for ; Tue, 17 Jul 2018 05:21:22 -0700 (PDT) X-DKIM-Result: Domain=gmail.com Result=Good and Known Domain DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to; bh=xWGVQTNVOz6DLu+3dd5R+TxrG/RRGdT78CR/2jWo9ls=; b=vLIXyrRxY1jAH1vLLfKmOyDOFWgEy6aSboo+yInGgkCPxJHhSO0TkbnGR57srbyZEy xeNLpNX3vR8L/KSk9bJEMBIBtgylsCI5XHnus33M5fbFt1Z36A6kj+/og1Ar6uQEZGzx Lxspmw8qxH7a0VEzBX4WEHGuwTT6N5baZ6Z/rY3snY+NqHCOB5VOQHpXCW2R0KP+7XaL T7any6GdPcOAKqLbhjo0jPUCh4Zrg75chnrbdyO+LmRnVKBiEiJmiGKivEtmL2JSMMmn qWwp+XGy+0GrXNDW7zbWNKYAeX8rqLDQFI64wPKdO5mYHmvaqFxcTNdFrazkQvKsvBaN 00kg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to; bh=xWGVQTNVOz6DLu+3dd5R+TxrG/RRGdT78CR/2jWo9ls=; b=eNDm3KbZ7WgJPhC0KuqGa+lR5+mad632HqEoXo6lU5oYs6gLFTka/6djScW8Xso9Hv zifdZXPfn706m//jP9j/qqo3e8F4V4PYNpQeB0n+JaoQKAstAHUfKfY7VDFjHxGBCbyP 7f9cJwCI11N1zEoEFwXFer0CO3nekgrHLH/WBqhw8hPNctdhSFX/AbkWUiTIzQLixueD bKbaGv3qEUO3iOSlqBs0A5tCjBy34hlGJHl+P1N6wPQUHXlfigI2zdhdRP0svI7YvFuo Xh8EkQYKECaQo1N+AcbIZYodkN6R16Tm6Q02TiyKu0cMdYvPeo/sIL8CyAbZgOnsozow VMHA== X-Gm-Message-State: AOUpUlF5bdz0a3oDBLsXuGf+MhBx6uymq1L201+qBGAx3qxEs70mJIW6 ZG666jsvdNrUmM6HxwjKjIMFEapUOVYZTFXDOmc= X-Google-Smtp-Source: AAOMgpfjSNUyXsWsJMA3nCMG5Na+F8dnkwVNzAjdGV4JpTuncBFrEByX7TjE9Ce5b6lB8bCCx4Rj+CCVVJXyETHQbHQ= X-Received: by 2002:a50:adaa:: with SMTP id a39-v6mr2276403edd.194.1531830081492; Tue, 17 Jul 2018 05:21:21 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a50:9626:0:0:0:0:0 with HTTP; Tue, 17 Jul 2018 05:21:21 -0700 (PDT) In-Reply-To: References: <806f6cb0-fac1-64cc-95b6-0c2c5277f8d8@n1bug.com> <5B4C78A7.1010208@posteo.de> <19bdcc7f-1f73-8660-420a-0858bd24beaf@n1bug.com> <5B4C88EF.1090800@posteo.de> From: Andy Talbot Date: Tue, 17 Jul 2018 13:21:21 +0100 Message-ID: To: LineOne X-Spam-Score: 0.0 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see @@CONTACT_ADDRESS@@ for details. Content preview: What's wrong is the mismatch between antenna and feed. Assuming 50R receiver load, your combination of transformers is presenting the antenna with a 20k load. Assuming 8pF per metre your antenna has 72pF, or a reactance of 16k at 137kHz which is commensurate with the load, so about 3dB loss there. The radiation resistance is something like 0.004 ohms in series with that 16k reactive. So all you are seeing is the voltage corresponding to 9m up ( 9 * E in volts per metre) applied across the 20k Rload then, reduced by 3dB due to the reactance. [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [2a00:1450:4864:20:0:0:0:529 listed in] [list.dnswl.org] 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (andy.g4jnt[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid X-Scan-Signature: b14bcaca65d4b584f77d02a84d381cb4 Subject: Re: LF: TX > RX isolation test Content-Type: multipart/alternative; boundary="000000000000dd1883057130fbf8" 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 --000000000000dd1883057130fbf8 Content-Type: text/plain; charset="UTF-8" What's wrong is the mismatch between antenna and feed. Assuming 50R receiver load, your combination of transformers is presenting the antenna with a 20k load. Assuming 8pF per metre your antenna has 72pF, or a reactance of 16k at 137kHz which is commensurate with the load, so about 3dB loss there. The radiation resistance is something like 0.004 ohms in series with that 16k reactive. So all you are seeing is the voltage corresponding to 9m up ( 9 * E in volts per metre) applied across the 20k Rload then, reduced by 3dB due to the reactance. So a lot of loss before your preamp. All active E-probes give an input resistance of at least 1M, often 10M, sometimes even more and usually dominated by input C, of a pF or 2 perhaps. As the probes are shorter than your 9m, they have less series C so the amplifier input R needs to be correspondingly smaller to allow this to be insignificant. It's a different take on an LF receiving antenna, but whatever happens you need a low noise preamp. Conventional E-probes do it in a J-FET, you in a matched amplifier that doesn't look particulary low noise Andy www.g4jnt.com On 17 July 2018 at 12:14, N1BUG wrote: > Hi Stefan, > > On 07/16/2018 08:00 AM, DK7FC wrote: > > What type of preamp are you using (schematic?). For a comparison with > > and without antenna, you need to replace the antenna wire with a > > capacitor of the same C (assume 5...6 pF/m antenna wire, i.e. use 56 pF > > to replace a 10m vertical) connected to the preamp. If this shows as > > e.g. -120 dBfs it should show -105 dBfs with the antennna connected. > > I am not certain we are talking about the same antenna > configuration. This antenna is not an E probe, at least not in the > sense that I understand it. It's a 9m tall whip with 100:1 impedance > transformer at the base. The high Z primary winding connects to > antenna and ground. The low Z secondary goes to 60m of twisted pair > to the shack. At the shack there is a 2:1 transformer feeding a 50 > ohm in/out preamp. This is the preamp I use: > > http://w1vd.com/LFMFHFpreamplifier.pdf > > I can not quite put into words what bothers me about my system but I > get a feeling something is wrong. I think I need to go back to the > beginning and try to understand noise floor / MDS at every stage of > the system... receiver without preamp, with preamp, etc. I am not > sure exactly how to proceed with this evaluation. > > Paul N1BUG > > --000000000000dd1883057130fbf8 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
What's wrong is the mismatch between antenna and feed.= =C2=A0 Assuming 50R receiver load, your combination of transformers is pres= enting the antenna with a 20k load.
Assuming 8pF per metre your antenna= has 72pF, or a reactance of=C2=A0 16k at 137kHz which is commensurate with= the load, so about 3dB loss there.
The radiation resistance is s= omething like 0.004 ohms in series with that 16k reactive. So all you are s= eeing is the voltage corresponding to 9m up ( 9 *=C2=A0 E=C2=A0 in volts pe= r metre)=C2=A0 =C2=A0 applied across the 20k Rload then, reduced by 3dB due= to the reactance.

So a lot of loss before your pr= eamp.=C2=A0 =C2=A0All active E-probes give an input resistance of at least = 1M, often 10M, sometimes even more and usually dominated by input C, of a p= F or 2 perhaps.=C2=A0 As the probes are shorter than your 9m, they have les= s series C so the amplifier input R needs to be correspondingly smaller to = allow this to be insignificant.=C2=A0=C2=A0

It'= ;s a different take on an LF receiving antenna, but whatever happens you ne= ed a low noise preamp.=C2=A0 =C2=A0 Conventional E-probes do it in a J-FET,= you in a matched amplifier that doesn't look particulary low noise


On 17 July 2018 at 12:14, N1BUG <paul@n1bug.co= m> wrote:
Hi Stefan,

On 07/16/2018 08:00 AM, DK7FC wrote:
> What type of preamp are you using (schematic?). For a comparison with =
> and without antenna, you need to replace the antenna wire with a
> capacitor of the same C (assume 5...6 pF/m antenna wire, i.e. use 56 p= F
> to replace a 10m vertical) connected to the preamp. If this shows as <= br> > e.g. -120 dBfs it should show -105 dBfs with the antennna connected.
I am not certain we are talking about the same antenna
configuration. This antenna is not an E probe, at least not in the
sense that I understand it. It's a 9m tall whip with 100:1 impedance transformer at the base. The high Z primary winding connects to
antenna and ground. The low Z secondary goes to 60m of twisted pair
to the shack. At the shack there is a 2:1 transformer feeding a 50
ohm in/out preamp. This is the preamp I use:

http://w1vd.com/LFMFHFpreamplifier.pdf

I can not quite put into words what bothers me about my system but I
get a feeling something is wrong. I think I need to go back to the
beginning and try to understand noise floor / MDS at every stage of
the system... receiver without preamp, with preamp, etc. I am not
sure exactly how to proceed with this evaluation.

Paul N1BUG


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