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 w6MF3BQB027439 for ; Sun, 22 Jul 2018 17:03:14 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1fhFml-0008SW-Co for rs_out_1@blacksheep.org; Sun, 22 Jul 2018 15:56:35 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1fhFks-0008SF-1r for rsgb_lf_group@blacksheep.org; Sun, 22 Jul 2018 15:54:38 +0100 Received: from mail-wm0-x22f.google.com ([2a00:1450:400c:c09::22f]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.91_59-0488984) (envelope-from ) id 1fhFkl-0003es-9p for rsgb_lf_group@blacksheep.org; Sun, 22 Jul 2018 15:54:32 +0100 Received: by mail-wm0-x22f.google.com with SMTP id c14-v6so13555909wmb.4 for ; Sun, 22 Jul 2018 07:54:31 -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=from:mime-version:subject:date:references:to:in-reply-to:message-id; bh=Y88zDKYLi9aG4HdL/VWcQq2oktsKBau92QUL0CDd/Ns=; b=dWQhivGXF/7oIri/SpMxmVujfvGD90KVbytt3/qSLwSKDADIi/dugC0iBsvISqn6Sg 4gSKwmnNnwgEMYrkmbrOOGs9Utb42qPDUXjsspYroi5mi9biW7BE5OLgWwYdSe5YF/Gh LKTbXv4LaeM1xm921DlE+WrahQsRSXcqHh6RPIi/W/UkWZWB6DFA6wd/Hit06dlgVvO2 u8030E0BHqoyDYoif6SY2XrAysmJ7TMzAeVKruvBtkFRVbasPe8OaQBYnQ28QlvaF8Ut XTHtPBiH344fwhVhqj7x+junlLE5k6s7lhT+CaTv9t8YyNwqMiXcy7DdM+l+qLJyhsO4 pV9g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:mime-version:subject:date:references:to :in-reply-to:message-id; bh=Y88zDKYLi9aG4HdL/VWcQq2oktsKBau92QUL0CDd/Ns=; b=JDtzI7xCXwMuqwkkSNTypsR/vaAdjnRiDsvCfG5560sAxAf0gTefJo4k0cbKB2zPxA NJHAAi1mbjj3RynnCJxxSWXX35vC2rTRQ8bN2zqfVS/FNCV9lkY3x6CjmdJq90gpsSlr a2VlQa9G+KZqwqf0gKEgAKyrFfhpqSj5J82Q4VzpPqu/z/nBc9PKBau8uGY5qWOEV/RL PICM4vMtapFuD3Om9bFFnAjvHtYhKCF9awMcgHJ0QQ57CjBdAyW0ShtJYPxbyIi0eEYG 4LeOvzwZqFQlP7nB+/bykTipeDN1SOlglSQ8fMOQaMrIzDXz/4L6mjf5nnxwTzyR/Kyd 18jQ== X-Gm-Message-State: AOUpUlFIVeu8v3PDQxgedN4lX58K4VmyocFVZJFCccxY8HDJsgKF++Gj XP7QND7qWHboQ7wEWtrEi47CxhXF X-Google-Smtp-Source: AAOMgpdyCLDmAvJ6JKaNEjJoelYBX80TcmDwKkTZq8wUuFtrtG1ZnxnDp2Yx3CXXZd9EiV5DOAJBcA== X-Received: by 2002:a1c:1802:: with SMTP id 2-v6mr5364487wmy.81.1532271270118; Sun, 22 Jul 2018 07:54:30 -0700 (PDT) Received: from [127.0.0.1] ([82.98.23.94]) by smtp.gmail.com with ESMTPSA id a11-v6sm7849188wrr.81.2018.07.22.07.54.28 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 22 Jul 2018 07:54:29 -0700 (PDT) From: John Rabson Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) Date: Sun, 22 Jul 2018 16:54:27 +0200 References: <164c230a3b7-c97-798@webjasstg-vaa58.srv.aolmail.net> To: rsgb_lf_group@blacksheep.org In-Reply-To: <164c230a3b7-c97-798@webjasstg-vaa58.srv.aolmail.net> Message-Id: <4B15F2D2-90AB-40F5-B1AD-671DD0BEB12A@gmail.com> X-Mailer: Apple Mail (2.3445.9.1) X-Spam-Score: 0.3 (/) 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: In the cave radio field, we have tried a number of such configurations underground and also in out-of-service rail tunnels. Discussion of the results can be found in several issues of the Cave Radio & Electronics Group Journal. Go to http://bcra.org.uk/pub/cregj/covers.html and search for ferrite transmitting antennas. Back copies of the Journal are available for download – a subscription available for a modest fee. [...] Content analysis details: (0.3 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [2a00:1450:400c:c09:0:0:0:22f listed in] [list.dnswl.org] 0.2 FREEMAIL_ENVFROM_END_DIGIT Envelope-from freemail username ends in digit (john.rabson07[at]gmail.com) 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (john.rabson07[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: eb65b97b00a71049be1fa526941c7b31 Content-Type: multipart/alternative; boundary="Apple-Mail=_90108D93-D4D6-48B4-9B34-964D6F7D5E56" Subject: Re: LF: Transmitting with a small ferrite antenna X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.3 required=5.0 tests=FROM_ENDS_IN_NUMS,HTML_20_30, 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 --Apple-Mail=_90108D93-D4D6-48B4-9B34-964D6F7D5E56 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 In the cave radio field, we have tried a number of such configurations = underground and also in out-of-service rail tunnels. Discussion of the results can be found in several issues of the Cave = Radio & Electronics Group Journal. Go to = http://bcra.org.uk/pub/cregj/covers.html = and search for ferrite = transmitting antennas. Back copies of the Journal are available for = download =E2=80=93 a subscription available for a modest fee. The electrical properties required of such an antenna depend on = frequency and bandwidth. For cave radio speech systems, a common centre = frequency is 88.5 kHz (87 kHz USB) with a bandwidth of about 3 kHz and a = maximum transmitter output power of the order of 4 W. These systems = normally work in the in the induction regime, the ERP is not significant = and may be of the order of uW.=20 Data systems have also been investigated on this and other low = frequencies. In general these require significantly less bandwidth. =20 For a theoretical analysis of such antennas see David Gibson=E2=80=99s = doctoral thesis (Leeds 2003?). Some years ago, I was sent a ferrite-rod based antenna for analysis. It = was intended for use with the =10=10=10=10=10Molefone. Unfortunately it = arrived shortly before I emigrated and the device disappeared somewhere = among my household effects (420 cardboard boxes to start with). It has = recently come to light and I hope to examine it in detail later in the = year. 73 John F5VLF G3PAI > On 22 Jul 2018, at 15:32, Markus Vester wrote: >=20 > This morning I attempted to transmit from a small ferrite antenna. It = consists of a number of 9 mm diameter ferrite rods, with 7 bundled in = parallel. The bundles were stacked with overlap to ~ 35 cm total length, = and n=3D47 turns of litz wire were wound around the middle. Total = ferrite cross section is a=3D4.45 cm^2 and volume V=3D156 cm^3, weighing = 0.77 kg (including the coil). The coil was resonated and matched by = several 1 nF high-Q ceramic capacitors. >=20 > Under small signal conditions (-17 dBm), the electric parameters at = 137.5 kHz were > L =3D 0.50 mH, R =3D 0.62 ohm, Q =3D 690. > Applying about half a watt significantly increased inductance and = losses, and the tuning became sharply hysteretic ("jumpy"). For fine = tuning, a small rod was placed at a variable distance beside the = antenna. > Then I connected my PA and drove about 25 Watts into the antenna. = Losses and inductance increased further: > I =3D 1.3 A, U =3D 867 V (rms), L =3D 0.77 mH, R =3D 14.8 ohmn, Q =3D = 45, > with the Q-factor now so low that tuning jumps disappeared again. The = central part under the coil became quite hot, so a tiny fan was added = which held the steady-state temperature at ~55 =C2=B0C. >=20 > =46rom the induced voltage we can calculate the flux density in the = middle of the rod as > B =3D U / n / a / omega =3D 48 mT (rms), > decreasing approximately linearly toward the ends (similar to a small = electric dipole). The average Bav=3D24 mT then results in a dipole = moment of > iA =3D V Bav / =C2=B50 =3D 156 cm^3 * 24 mT / =C2=B50 =3D 3.0 Am^2 > which results in a radiated power > EMRP =3D 62.34 kohm * iA^2 / lambda^4 =3D 25 nW. > Thus the efficiency of this transmit antenna is only 1 ppb ! >=20 > Anyway I attempted to detect the tiny signal on the DL0AO LF grabber, = 48 km from here:=20 > https://lf.u01.de > Transmitting on 137.780 kHz (6:29 to 8:22 UT) indeed produced a = detectable trace in the QRSS-60 window (below the Slonim Loran line on = 137781.25 Hz). Then I attempted to send a 4-character EbNaut = transmission on 137.510 KHz, which was successfully decoded with some = margin. >=20 > Now if that's not QRP... anyway fascinating, considering that the = small ferrite antenna might be carried in a handbag, buried in the = ground or taken to a cave. >=20 > Best 73, > Markus (DF6NM) >=20 > = --Apple-Mail=_90108D93-D4D6-48B4-9B34-964D6F7D5E56 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
In the cave radio field, we have tried a = number of such configurations underground and also in out-of-service rail tunnels.

Discussion of the results can be found = in several issues of the Cave Radio & Electronics Group Journal. Go = to http://bcra.org.uk/pub/cregj/covers.html and search for = ferrite transmitting antennas. Back copies of the Journal are available = for download =E2=80=93 a subscription available for a modest = fee.

The = electrical properties required of such an antenna depend on frequency = and bandwidth. For cave radio speech systems, a common centre frequency = is 88.5 kHz (87 kHz USB) with a bandwidth of about 3 kHz and a maximum = transmitter output power of the order of 4 W. These systems normally = work in the in the induction regime, the ERP is not significant and may = be of the order of uW. 

Data systems have also been = investigated on this and other low frequencies. In general these require = significantly less bandwidth.  

For a theoretical analysis of such = antennas see David Gibson=E2=80=99s doctoral thesis (Leeds = 2003?).

Some = years ago, I was sent a ferrite-rod based antenna for analysis. It was = intended for use with the =10=10=10=10=10Molefone. Unfortunately it = arrived shortly before I emigrated and the device disappeared somewhere = among my household effects (420 cardboard boxes to start with). It has = recently come to light and I hope to examine it in detail later in the = year.

73 John F5VLF G3PAI

On = 22 Jul 2018, at 15:32, Markus Vester <markusvester@aol.com> wrote:

This morning I attempted to = transmit from a small ferrite antenna. It consists of a number of 9 mm = diameter ferrite rods, with 7 bundled in parallel. The bundles were = stacked with overlap to ~ 35 cm total length, and n=3D47 turns of litz = wire were wound around the middle. Total ferrite cross section is a=3D4.45= cm^2 and volume V=3D156 cm^3, weighing 0.77 kg (including the coil). = The coil was resonated and matched by several 1 nF high-Q ceramic = capacitors.

Under small = signal conditions (-17 dBm), the electric parameters at 137.5 kHz = were
 L =3D 0.50 mH, R =3D 0.62 ohm, Q =3D 690.
Applying about half a watt = significantly increased inductance and losses, and the tuning became = sharply hysteretic ("jumpy"). For fine tuning, a small rod was placed at = a variable distance beside the antenna.
Then I = connected my PA and drove about 25 Watts into the antenna. Losses and = inductance increased further:
 I =3D 1.3 A, U =3D 867 = V (rms), L =3D 0.77 mH, R =3D 14.8 ohmn, Q =3D 45,
with = the Q-factor now so low that tuning jumps disappeared again. The central = part under the coil became quite hot, so a tiny fan was added which held = the steady-state temperature at ~55 =C2=B0C.

=46rom the induced voltage we can calculate = the flux density in the middle of the rod as
 B = =3D U / n / a / omega =3D 48 mT (rms),
decreasing = approximately linearly toward the ends (similar to a small electric = dipole). The average Bav=3D24 mT then results in a dipole moment = of
 iA =3D V Bav / =C2=B50 =3D 156 cm^3 * 24 mT / =C2=B5= 0 =3D 3.0 Am^2
which results in a radiated power
 EMRP =3D 62.34 kohm * iA^2 / lambda^4 =3D 25 nW.
Thus the efficiency of this transmit antenna is only 1 ppb = !

Anyway I attempted to detect = the tiny signal on the DL0AO LF grabber, 48 km from here:
https://lf.u01.de
Transmitting on 137.780 = kHz (6:29 to 8:22 UT) indeed produced a detectable trace in the QRSS-60 = window (below the Slonim Loran line on 137781.25 Hz). Then I attempted = to send a 4-character EbNaut transmission on 137.510 KHz, which was = successfully decoded with some margin.

Now if that's not QRP... anyway fascinating, considering that = the small ferrite antenna might be carried in a handbag, buried in the = ground or taken to a cave.

Best = 73,
Markus (DF6NM)

=
<Ferrite_TX_Antenna.jpg= ><dl0ao_qrss60_180722_08= 20_small.jpg><dl0ao_07220844_result.= png>

= --Apple-Mail=_90108D93-D4D6-48B4-9B34-964D6F7D5E56--