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[195.171.43.25]) by mx.google.com with ESMTP id s9si1298315wjf.70.2014.03.09.05.52.25 for ; Sun, 09 Mar 2014 05:52:26 -0700 (PDT) Received-SPF: neutral (google.com: 195.171.43.25 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) client-ip=195.171.43.25; Authentication-Results: mx.google.com; spf=neutral (google.com: 195.171.43.25 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) smtp.mail=owner-rsgb_lf_group@blacksheep.org; dkim=pass header.i=@mx.aol.com Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1WMcbL-0003U1-Ax for rs_out_1@blacksheep.org; Sun, 09 Mar 2014 12:13:07 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1WMcbK-0003Ts-AN for rsgb_lf_group@blacksheep.org; Sun, 09 Mar 2014 12:13:06 +0000 Received: from omr-d05.mx.aol.com ([205.188.109.202]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.82) (envelope-from ) id 1WMcbG-00016M-BF for rsgb_lf_group@blacksheep.org; Sun, 09 Mar 2014 12:13:05 +0000 Received: from mtaout-mcc02.mx.aol.com (mtaout-mcc02.mx.aol.com [172.26.253.78]) by omr-d05.mx.aol.com (Outbound Mail Relay) with ESMTP id 28E8B700000A2 for ; Sun, 9 Mar 2014 08:12:59 -0400 (EDT) Received: from White (95-91-237-52-dynip.superkabel.de [95.91.237.52]) by mtaout-mcc02.mx.aol.com (MUA/Third Party Client Interface) with ESMTPA id 51F623800009E for ; Sun, 9 Mar 2014 08:12:58 -0400 (EDT) Message-ID: From: "Markus Vester" To: References: <2662DF5AA7FA416CBB09CDB90BBFF7B1@White> <016101cf39df$4f4c89a0$ede59ce0$@comcast.net>, <01dc01cf3a3f$86997bb0$93cc7310$@comcast.net>, <2FC5CAB271A6437CB35A5B100185CEDA@White> <025101cf3a52$e0925750$a1b705f0$@comcast.net> <7DB9DD5669FC4C648838510DCAC08AFB@White> <531A506E.9040103@abelian.org> <531A5C19.9060209@abelian.org> <02ba01cf3aa3$debaad50$9c3007f0$@comcast.net> <531AF126.2060600@abelian.org> <850A470A5B9F4483BED8B49D4791044A@White>,<531B1D0C.3070208@abelian.org> ,<531B4E01.7000304@abelian.org> <039f01cf3b72$bfa1db80$3ee59280$@comcast.net> <76F90E9771CA44F3981F679241E1A005@White> Date: Sun, 9 Mar 2014 13:12:52 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 12.0.1606 X-MimeOLE: Produced By Microsoft MimeOLE V12.0.1606 x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20121107; t=1394367179; bh=zSfRI8j848sktYtOSpqc1QQ1JHm2Da/BWBlXDK7boyc=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=bB5molFQJFdxoeA39wGAHFumMLNTUf6W76hqaHiDtFNw1XxilrHuXKBPcx0IVkOmg EkiwMAKvdLKIq4NHuOCE0d274zWZ7Lmww4451tn+sAi4sH9V1RR3WgoZ76mU8unoFm zCtbEdqsZDjGTnC/qgjo9ea1QQXzUa/ARwYjQ69s= x-aol-sid: 3039ac1afd4e531c5aca00ad X-AOL-IP: 95.91.237.52 X-Spam-Score: 0.0 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Reviewing Bob's direct mails, he mentioned a body of evidence of improved groundwave propagation at low temperatures and frost, based mostly on mediumwave broadcast experience. That seems to contradict the notion that decreased conductivity would hinder propagation. [...] 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 [205.188.109.202 listed in list.dnswl.org] 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (markusvester[at]aol.com) -0.0 T_RP_MATCHES_RCVD Envelope sender domain matches handover relay domain -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: 47fcd6cd61a909b5d814376ce37acc80 Subject: Re: LF: Daytime 29.499 kHz Content-Type: multipart/alternative; boundary="----=_NextPart_000_0050_01CF3B99.4768CF80" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.6 required=5.0 tests=HTML_40_50,HTML_MESSAGE, MAILTO_TO_SPAM_ADDR,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 Dies ist eine mehrteilige Nachricht im MIME-Format. ------=_NextPart_000_0050_01CF3B99.4768CF80 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Reviewing Bob's direct mails, he mentioned a body of evidence of = improved groundwave propagation at low temperatures and frost, based = mostly on mediumwave broadcast experience. That seems to contradict the = notion that decreased conductivity would hinder propagation. Maybe the clue to this riddle is the contribution of dielectric = permittivity and displacement currents, which increases with frequency. = For each material, there is a crossover frequency above which omega * = epsilon becomes greater than sigma. In that high frequency regime, earth = may be acting more as a lossy dielectric waveguide, refracting the wave = around the curvature. Lower conductivity will then mean lower loss = tangent and less absorption. On the other hand, at VLF frequencies = displacement currents just tend to be neglegible, and we are looking at = a purely conductive (quasi metallic) boundary, where ohmic losses = increase with surface resistance. Still wondering about that horizontal dipole above ice (Siple station): = It may radiate effectively, but mostly upwards! This may be good for = exciting steep magnetospheric whistler modes, but would it also be = useful for long-distance communication? Best 73, Markus (DF6NM) From: Markus Vester=20 Sent: Sunday, March 09, 2014 10:25 AM To: rsgb_lf_group@blacksheep.org=20 Subject: Re: LF: Daytime 29.499 kHz Thanks Jim for the detailed information. Bob and I had discussed the = temperature effects in a private mail exchange, and hadn't quite come o = the same conclusions.=20 My take on the subject was that with lower temperatures groundwave = propagation is more (not less) attenuated. But regarding the near field, = losses and E-field shunting from trees around the antenna decrease with = frost, so radiation efficiency improves significantly. This effect is = probably not covered by the literature, as commercial LF antennas tend = to be installed above a ground screen on a clear field. With = valley-spanning installations (eg. the former Haiku antenna on Oahu), it = was mentioned that forestry beneath the antenna had been removed to = reduce losses. =20 Best 73, Markus (DF6NM) From: hvanesce=20 Sent: Sunday, March 09, 2014 9:36 AM To: rsgb_lf_group@blacksheep.org=20 Subject: RE: LF: Daytime 29.499 kHz Bob, =20 Some information below on the effects of above-freezing and = below-freezing temperatures on various VLF losses, including (a) = ground-wave losses, (b) near-field ground effects losses and (c) skywave = (waveguide) ground effects losses.=20 =20 A short preface: The discussion below is for a VLF system with a vertical transmit = antenna. In a VLF system with a vertical transmit antenna, high surface = conductivity under the antenna and in the near and far fields is = desirable. (1) In a VLF system with a horizontal antenna, low surface conductivity = under the antenna is desired, and high surface conductivity is desired = elsewhere in the near field, and in the far field. (1) This makes Antarctica a great place for VLF QRP: ice under the antenna; = salt water elsewhere (whence the 42 km long dipole at Siple Station: = https://s3.amazonaws.com/Antarctica/AJUS/AJUSvXVIIIn5/AJUSvXVIIIn5p270.pd= f http://nova.stanford.edu/~vlf/Antarctica/Siple/ ) =20 =20 =20 Temperature coefficients of conductivity: As temperature drops, non-frozen soil conductivity (mhos, siemens) = decreases by roughly 1.9% per degree C. (2) As temperature drops below freezing, soil VLF conductivity decreases = rapidly; the rate of change is highly dependent on soil type, but a 2:1 = change per 10 degrees C at 10 kHz (for below-freezing temperatures) is a = reasonable example for some soils. (3) =20 Near field and ground wave losses: As conductivity decreases (i.e. with decreasing temperature), VLF = near-field and ground wave losses increase non-linearly (4) At 30kHz, ground wave amplitude is low at 5000 km (4) At 30kHz, ground-wave loss in non-frozen soil of poor conductivity = (10^-4 mhos/m) might be 20dB greater (20dB more loss) than in non-frozen = soil of fairly good conductivity (10^-2 mhos/m) (4) At 30kHz, ground-wave loss in frozen soil would be very high (4)=20 All of the above might suggest a very low amplitude ground wave at TA = distances in mid-winter (ground wave including direct, ground-reflected, = Norton surface and trapped surface waves) =20 In that case the long-path part of the problem reduces to skywave losses = (skywave ionospheric losses and skywave ground-effects losses): Skywave loss (waveguide loss in this case) due to ground effects is = nominally: =20 d_alpha_gnd =3D [.046 * sqrt(f)] * 1/{h * sqrt(s) * sqrt[1 - = (fc/f)^2]} (in units of dB per 1000 km) (5) =20 where f =3D 29,500 (Hz), fc ~ 2100 (Hz) (day) or 1700 (Hz) (night), h ~ = 70 (kilometers), .0001 < s < .01 [s for sigma (conductivity), in mhos = per meter; range of values from .01 for very good (highly conductive) = soil to .0001 for frozen earth; values below .0001 occur in arctic = regions, but such regions tend to have snow and ice above the soil. A = different formula is used for snow and ice losses at frequencies below 1 = MHz] =20 The formula above may be sufficient for analysis of cold-weather = propagation losses over distances of 5 Mm or more. Besides propagation = losses, there are near-field and antenna-system losses. =20 Near-field and antenna-system losses: VLF near-field and antenna-system losses associated with ground effects, = increase as temperature (and therefore conductivity) decline. The = increase in near-field and antenna-system losses can be between sqrt (s) = and s^1.5, but the nominal value of these losses is hard to determine = analytically for an electrically-short antenna. The calculation for = ice/snow cover for your antenna system may be easier to determine = analytically; if you're interested I'll send a notional formula. If your VLF signal reports do not change appreciably after a snowfall or = an ice storm, that information can be used to help generate a = temperature model of your ground-effects-related near-field and = antenna-system losses, in which case you might have a good starting = point for a whole-system model for all temperatures. Noting what = happens to signal reports after a freeze, after a snowfall and after an = ice-storm can help to nail down the most difficult part of the system = model for a VLF system with an electrically short antenna = (antenna-system losses and near-field losses). In summary: A) VLF near-field and antenna-system losses associated with ground = effects, increase as temperature declines. Noting what happens to = signal reports after a freeze, after a snowfall and after an ice-storm = can help to establish a good model for these. Such a model will be = useful at all temperatures, and very helpful in the optimization of an = electrically-short VLF antenna.=20 B) The formula above for d_alpha_gnd (relative ground-effects losses = incurred by the skywave in the waveguide) gives values from about 2 dB = per megameter to 6 dB per megameter at 29.5 kHz for soil conditions = ranging from fairly good to frozen. This formula is useful by itself for = assessing the difference in far-field path loss at various temperatures. = Total path loss includes other terms that add to and subtract from* = d_alpha_gnd, but those terms are not necessary for assessing changes in = ground-effects-related skywave path losses (in the waveguide) over = temperature.=20 C) Ideally, you would add (A) to (B) to obtain the sum of the = predominant contributors to loss variation over temperature.=20 =20 * terms such as the convergence factor, and reinforcements at = discontinuities, subtract from path loss =20 (1) Biggs, AGARD, 1970 (2) a general approximation; Corwin 2005, Ma 2010 (3) Moore 1992 (4) Watt 3.2 (5) Watt 3.4.33 =20 =20 73, Jim AA5BW =20 =20 From: owner-rsgb_lf_group@blacksheep.org = [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Bob Raide Sent: Saturday, March 8, 2014 10:33 AM To: rsgb_lf_group@blacksheep.org Subject: RE: LF: Daytime 29.499 kHz =20 Paul; It is not only the ground but the air temp has great influence and maybe = much more than the shallow depths of the ground freezing-Bob =20 > Date: Sat, 8 Mar 2014 17:06:09 +0000 > From: vlf0403@abelian.org > To: rsgb_lf_group@blacksheep.org > Subject: Re: LF: Daytime 29.499 kHz >=20 >=20 > Bob wrote: >=20 > > Wonder what effects soil conductivity changes has on the > > propagation at these VLF freqs?? >=20 > I have no information. You would expect ground resistance > to rise, but would that make noticeable difference to > propagation if it is only a freezing of a shallow surface > layer? >=20 > I had to go to a narrower bandwidth to produce phase and > amplitude plots for last night's test >=20 > http://abelian.org/vlf/tmp/29499_140308a.gif >=20 > Signal is down by some 5dB compared with some recent > tests. >=20 > Nothing detected this afternoon. >=20 > Propagation seems normal, noise floor normal. >=20 > Maybe the cold and frozen ground is affecting the tx > efficiency, some lower Q of the loading coil - antenna - > ground loop, or a reduction of effective height. >=20 > Will be interesting to see what happens after the thaw. >=20 > -- > Paul Nicholson > -- >=20 ------=_NextPart_000_0050_01CF3B99.4768CF80 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Reviewing Bob's direct mails, he = mentioned a body=20 of evidence of improved groundwave propagation at low temperatures and=20 frost, based mostly on mediumwave broadcast experience. That = seems to=20 contradict the notion that decreased conductivity would hinder = propagation.
 
Maybe the clue to this riddle is=20 the contribution of dielectric permittivity and displacement = currents,=20 which increases with frequency. For each material, there is a crossover=20 frequency above which omega * epsilon = becomes=20 greater than sigma. In that high frequency regime, earth may be = acting more=20 as a lossy dielectric waveguide, refracting the wave around the = curvature.=20 Lower conductivity will then mean lower loss tangent and less = absorption.=20 On the other hand, at VLF frequencies displacement = currents just tend=20 to be neglegible, and we are looking at a purely conductive (quasi=20 metallic) boundary, where ohmic losses increase with surface=20 resistance.
 
Still wondering about that = horizontal dipole=20 above ice (Siple station): It may radiate effectively, but mostly = upwards! This=20 may be good for exciting steep magnetospheric whistler modes, but = would it=20 also be useful for long-distance communication?
 
Best 73,
Markus (DF6NM)

Sent: Sunday, March 09, 2014 10:25 AM
Subject: Re: LF: Daytime 29.499 kHz

Thanks Jim for the detailed = information.=20 Bob and I had discussed the = temperature effects=20 in a private mail exchange, and hadn't quite come o the same = conclusions.=20
 
My take on the subject was that with = lower=20 temperatures groundwave propagation is more (not less) attenuated.=20 But regarding the near field, losses and E-field shunting from = trees=20 around the antenna decrease with frost, so radiation = efficiency improves=20 significantly. This effect is probably not covered by the literature,=20 as commercial LF antennas tend to be installed above a ground = screen=20 on a clear field. With valley-spanning installations (eg. the = former Haiku=20 antenna on Oahu), it was mentioned that forestry beneath the=20 antenna had been removed to=20 reduce losses.   
 
Best 73,
Markus (DF6NM)

From: hvanesce
Sent: Sunday, March 09, 2014 9:36 AM
Subject: RE: LF: Daytime 29.499 kHz

Bob,

 

Some=20 information below on the effects of above-freezing and below-freezing=20 temperatures on various VLF losses, including (a) ground-wave losses, = (b)=20 near-field ground effects losses and (c) skywave (waveguide) ground = effects=20 losses.

 

A=20 short preface:

The=20 discussion below is for a VLF system with a vertical transmit=20 antenna.

In=20 a VLF system with a vertical transmit antenna, high surface conductivity = under=20 the antenna and in the near and far fields is desirable. =20 (1)

In=20 a VLF system with a horizontal antenna, low surface conductivity under = the=20 antenna is desired, and high surface conductivity is desired elsewhere = in the=20 near field, and in the far field.  (1)

This=20 makes Antarctica a great place for VLF QRP: ice under the antenna; salt = water=20 elsewhere (whence the 42 km long dipole at Siple Station: https://s3.amazonaws.com/Antarctica/AJUS/AJUSvXVIIIn5/AJUSvXVI= IIn5p270.pdf         =20  http://nova.stan= ford.edu/~vlf/Antarctica/Siple/=20 )    

 

 

Temperature=20 coefficients of conductivity:

As=20 temperature drops, non-frozen soil conductivity (mhos, siemens) = decreases by=20 roughly 1.9%  per degree C. (2)

As=20 temperature drops below freezing, soil VLF conductivity decreases = rapidly; the=20 rate of change is highly dependent on soil type, but a 2:1 change per 10 = degrees=20 C at 10 kHz (for below-freezing temperatures) is a reasonable example = for some=20 soils. (3)

 

Near=20 field and ground wave losses:

As=20 conductivity decreases (i.e. with decreasing temperature), VLF = near-field and=20 ground wave losses increase non-linearly (4)

At=20 30kHz, ground wave amplitude is low at 5000 km (4)

At=20 30kHz, ground-wave loss in non-frozen soil of poor conductivity (10^-4 = mhos/m)=20 might be 20dB greater (20dB more loss) than in non-frozen soil of fairly = good=20 conductivity (10^-2 mhos/m)   (4)

At=20 30kHz, ground-wave loss in frozen soil would be very high (4)=20

All=20 of the above might suggest a very low amplitude ground wave at TA = distances in=20 mid-winter (ground wave including direct, ground-reflected, Norton = surface and=20 trapped surface waves)

 

In=20 that case the long-path part of the problem reduces to skywave losses = (skywave=20 ionospheric losses and skywave ground-effects = losses):

Skywave=20 loss (waveguide loss in this case) due to ground effects is=20 nominally:

 

d_alpha_gnd=20 =3D [.046 * sqrt(f)]  *  1/{h * sqrt(s) * sqrt[1 =96=20 (fc/f)^2]}    (in units of dB per 1000 km) =20    (5)

 

where=20 f =3D 29,500 (Hz), fc ~ 2100 (Hz) (day) or 1700 (Hz) (night), h ~ 70 = (kilometers),=20  .0001 < s < .01  [s for sigma (conductivity), in mhos = per=20 meter; range of values from .01 for very good (highly conductive) soil = to .0001=20 for frozen earth; values below .0001 occur in arctic regions, but such = regions=20 tend to have snow and ice above the soil. A different formula is used = for snow=20 and ice losses at frequencies below 1 MHz]

 

The=20 formula above may be sufficient for analysis of cold-weather propagation = losses=20 over distances of 5 Mm or more. Besides propagation losses, there are = near-field=20 and antenna-system losses.

 

Near-field=20 and antenna-system losses:

VLF=20 near-field and antenna-system losses associated with ground effects, = increase as=20 temperature (and therefore conductivity) decline. The increase in = near-field and=20 antenna-system losses can be between sqrt (s) and s^1.5, but the nominal = value=20 of these losses is hard to determine analytically for an = electrically-short=20 antenna. The calculation for ice/snow cover for your antenna system may = be=20 easier to determine analytically; if you=92re interested I=92ll send a = notional=20 formula.

If=20 your VLF signal reports do not change appreciably after a snowfall or an = ice=20 storm, that information can be used to help generate a temperature model = of your=20 ground-effects-related near-field and antenna-system losses, in which = case you=20 might have a good starting point for a whole-system model for all = temperatures.=20  Noting what happens to signal reports after a freeze, after a = snowfall and=20 after an ice-storm can help to nail down the most difficult part of the = system=20 model for a VLF system with an electrically short antenna = (antenna-system losses=20 and near-field losses).

In=20 summary:

A)    =20 VLF=20 near-field and antenna-system losses associated with ground effects, = increase as=20 temperature declines.  Noting what happens to signal reports after = a=20 freeze, after a snowfall and after an ice-storm can help to establish a = good=20 model for these. Such a model will be useful at all temperatures, and = very=20 helpful in the optimization of an electrically-short VLF antenna.=20

B)    =20 The=20 formula above for d_alpha_gnd (relative ground-effects losses incurred = by the=20 skywave in the waveguide) gives values from about 2 dB per megameter to = 6 dB per=20 megameter at 29.5 kHz for soil conditions ranging from fairly good to = frozen.=20 This formula is useful by itself for assessing the difference in = far-field path=20 loss at various temperatures. Total path loss includes other terms that = add to=20 and subtract from* d_alpha_gnd, but those terms are not necessary for = assessing=20 changes in ground-effects-related skywave path losses (in the waveguide) = over=20 temperature.

C)    =20 Ideally,=20 you would add (A) to (B) to obtain the sum of the predominant = contributors to=20 loss variation over temperature.

 

*=20 terms such as the convergence factor, and reinforcements at = discontinuities,=20 subtract from path loss

 

(1)   =20 Biggs,=20 AGARD, 1970

(2)   =20 a=20 general approximation; Corwin 2005, Ma 2010

(3)   =20 Moore=20 1992

(4)   =20 Watt=20 3.2

(5)   =20 Watt=20 3.4.33

 

 

73, =20 Jim AA5BW

 

 

From:=20 owner-rsgb_lf_group@blacksheep.org = [mailto:owner-rsgb_lf_group@blacksheep.org]=20 On Behalf Of Bob Raide
Sent: Saturday, March 8, 2014 = 10:33=20 AM
To: rsgb_lf_group@blacksheep.org
Subject: RE: LF: = Daytime=20 29.499 kHz

 

Paul;
It=20 is not only the ground but the air temp has great influence and maybe = much more=20 than the shallow depths of the ground=20 freezing-Bob
 

> Date:=20 Sat, 8 Mar 2014 17:06:09 +0000
> From: vlf0403@abelian.org
> To: = rsgb_lf_group@blacksheep.org=
>=20 Subject: Re: LF: Daytime 29.499 kHz
>
>
> Bob = wrote:
>=20
> > Wonder what effects soil conductivity changes has on = the
>=20 > propagation at these VLF freqs??
>
> I have no = information.=20 You would expect ground resistance
> to rise, but would that make=20 noticeable difference to
> propagation if it is only a freezing of = a=20 shallow surface
> layer?
>
> I had to go to a = narrower=20 bandwidth to produce phase and
> amplitude plots for last night's=20 test
>
> http://abelian.org/= vlf/tmp/29499_140308a.gif
>=20
> Signal is down by some 5dB compared with some recent
>=20 tests.
>
> Nothing detected this afternoon.
> =
>=20 Propagation seems normal, noise floor normal.
>
> Maybe the = cold=20 and frozen ground is affecting the tx
> efficiency, some lower Q = of the=20 loading coil - antenna -
> ground loop, or a reduction of = effective=20 height.
>
> Will be interesting to see what happens after = the=20 thaw.
>
> --
> Paul Nicholson
> --
>=20

------=_NextPart_000_0050_01CF3B99.4768CF80--