Return-Path: Received: from mtain-mj04.r1000.mx.aol.com (mtain-mj04.r1000.mail.aol.com [172.21.164.88]) by air-df02.mail.aol.com (v129.4) with ESMTP id MAILINDF024-5ee94bfcfd6d35f; Wed, 26 May 2010 06:52:29 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-mj04.r1000.mx.aol.com (Internet Inbound) with ESMTP id 7BF1438000049; Wed, 26 May 2010 06:52:27 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OHECn-0005t7-MN for rs_out_1@blacksheep.org; Wed, 26 May 2010 11:51:21 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OHECn-0005sy-13 for rsgb_lf_group@blacksheep.org; Wed, 26 May 2010 11:51:21 +0100 Received: from mail-fx0-f43.google.com ([209.85.161.43]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1OHECk-0005Ea-9b for rsgb_lf_group@blacksheep.org; Wed, 26 May 2010 11:51:20 +0100 Received: by fxm13 with SMTP id 13so3941467fxm.16 for ; Wed, 26 May 2010 03:51:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type; bh=HOGqjmGojKtbHsL/5nN33X6UpW888JWJA5ft5gehDjc=; b=dtJ9Xjmdwe0nYtRUJESLbBYjSPNDmV9If1nYmhylOtpn4D6qF+wSlMMIKNUKqRY0jQ RIN7ujCfDlAn0pcN+K8WoQOq53W4bVIWwv77bC97XP0Qd/ebomJsqbNRBpeShAhdSjUn WZeWG1ZUGGTAWD+XaVDOg0O18Tl5kxDT+jLWs= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=gnm596N/sdgpX9tJw76ySLKavwuRnZ5mMm56Sh15ozkDVyvn5kYp2LnnNrRYb2zWns mqYx86t5kgUzjzjctE2dWf7yrUBBx4PAvd8RCTUu31ioMP53cwiTeTuODr16IXuhkgT9 0919ngnTrb2ITLv7wZ4cnip9Ziw0zTx/6i5hM= MIME-Version: 1.0 Received: by 10.204.32.9 with SMTP id a9mr2796402bkd.44.1274871071990; Wed, 26 May 2010 03:51:11 -0700 (PDT) Received: by 10.204.58.204 with HTTP; Wed, 26 May 2010 03:51:11 -0700 (PDT) In-Reply-To: References: <38A51B74B884D74083D7950AD0DD85E82A1C00@File-Server-HST.hst.e-technik.tu-darmstadt.de> Date: Wed, 26 May 2010 11:51:11 +0100 Message-ID: From: Roger Lapthorn To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: AW: 8.97kHz - Near field and radiated signals? Content-Type: multipart/alternative; boundary=00032555653261645d04877d0dae X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.8 required=5.0 tests=HTML_30_40,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 x-aol-global-disposition: G X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d299.1 ; domain : gmail.com DKIM : pass x-aol-sid: 3039400c89a84bfcfd6b6d30 X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --00032555653261645d04877d0dae Content-Type: text/plain; charset=ISO-8859-1 Thanks to all for the explanations. I'm glad others get confused too!! 73s Roger G3XBM On 26 May 2010 10:54, Rik Strobbe wrote: > Chris, Roger, > > there seems to be a lot of confusion. > I just looked it up in some old tekstbooks, but they are very brief on this > matter. > A quick "google" wasn't of much help either. > A clue maybe in one of the tekstboooks that made a difference between the > far field, the radiating near field and the reactive near field (defined as > "very close to the antenna"). > In the radiating near field signal attenuation is given as 40dB/decade (for > the H-field), in the reactive near field as 60dB/decade. > > I guess that the best way to find out is to try it. If G6ALB has a computer > you can just hook up your portabe RX to the PC (connect the RX to the > soundcard input instead of the earpiece), if possibe with the RX outdoors. > > If we take the worst case (56 dB): > Assuming that the bandwith for CW copy with the simple RX is 100Hz and and > you have good CW copy (let's say at least 10dB S/N) you will need an extra > 46dB , what means reducing bandwith to 0.0025Hz (= QRSS400, or over > 6min/dot). So a good point to start with is a 10 min or 15 min on/off cycle > (and a xtal controlled TX). > > 73, Rik ON7YD - OR7T > > ------------------------------ > *Van:* owner-rsgb_lf_group@blacksheep.org [ > owner-rsgb_lf_group@blacksheep.org] namens Rik Strobbe [ > Rik.Strobbe@fys.kuleuven.be] > *Verzonden:* woensdag 26 mei 2010 11:01 > > *Aan:* rsgb_lf_group@blacksheep.org > *Onderwerp:* RE: LF: AW: 8.97kHz - Near field and radiated signals? > > Roger, > > sorry, I made a mistake. > in the near field the H field drops 40dB/decade and the E-field drops > 60dB/decade. > Assuming the ground antenna acts as a loop (= H-field) the signal drop > between 0.4km and 3km will be 35dB. > The defintion of near field is vague, depending on the source it goes from > 0.1 wavelength to 1 wavelength. > But at 1kHz even 0.1 lambda is 30km, so you are defenitely in the near > field. > > 73, Rik ON7YD - OR7T > > ------------------------------ > *Van:* owner-rsgb_lf_group@blacksheep.org [ > owner-rsgb_lf_group@blacksheep.org] namens Roger Lapthorn [ > rogerlapthorn@gmail.com] > *Verzonden:* woensdag 26 mei 2010 10:43 > *Aan:* rsgb_lf_group@blacksheep.org > *Onderwerp:* Re: LF: AW: 8.97kHz - Near field and radiated signals? > > Rick (et al), > > I am confused by the near field attenuation rates quoted. Some quote *18dB > for doubling distance* which would mean an additional path loss of 56dB > going from 0.4km to 3km. This makes a lot of difference to what may or may > not be possible. > > Which is the correct figure? Help! > > 73s > Roger G3XBM > > > On 26 May 2010 09:31, Rik Strobbe wrote: > >> Roger, >> >> >> >> the near fiels signal drops with the 3rd power of the distance. >> >> So 3km versus 0.4km = 422 times weaker = -26dB >> >> Going from regular CW to QRSS30 will give you a 24dB benefit, so there is >> a fair chance to be copied at 3km in this mode. Of course the signal needs >> to be very frequency stable, it has to be better than an free running >> oscillator. >> >> Moving up in frequency would also help. >> >> And if you can lay your hands on an old stereo amp it would provide an >> extra 10dB TX power. >> >> >> >> Even if your goal is regular CW over a 3km path, starting with QRSS will >> most likely give a visible signal at 3km and allow you to watch any >> progress. >> >> >> >> 73, Rik ON7YD - OR7T >> >> >> >>> - The best DX targets are quite modest: I would like to exceed 1km >>> >>> initially with the TX power I currently have (around 4W). If I could >>> reach >>> G6ALB in the next village 3kms away I would be delighted. If I got any >>> further I would be both amazed and VERY happy! >>> >> > > > -- > http://g3xbm-qrp.blogspot.com/ > http://www.g3xbm.co.uk > http://www.youtube.com/user/g3xbm > G3XBM GQRP 1678 ISWL G11088 > -- http://g3xbm-qrp.blogspot.com/ http://www.g3xbm.co.uk http://www.youtube.com/user/g3xbm G3XBM GQRP 1678 ISWL G11088 --00032555653261645d04877d0dae Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Thanks to all for the explanations.
I'm glad others get confused= too!!

73s
Roger G3XBM

On 26= May 2010 10:54, Rik Strobbe <Rik.Strobbe@fys.kuleuven.be> wrote:<= br>
Chris, Roger,
=A0
there seems to be a lot of confusion= .
I just looked it up in=A0some old te= kstbooks, but=A0they are=A0very brief on this matter.
A quick "google" wasn'= t of much help either.
A clue maybe in one of the tekstbooo= ks that made a difference between the far field, the radiating near field= and the reactive near field (defined as "very close to the antenna&q= uot;).
In the radiating near field signal= attenuation is given as 40dB/decade (for the H-field), in the reactive ne= ar field as 60dB/decade.
=A0
I guess that the best way to find ou= t is=A0to try it. If G6ALB has a computer you can just hook up your portab= e RX to the PC (connect the RX to the soundcard input instead of the earpi= ece), if possibe with the RX outdoors.
=A0
If we take the worst case (56 dB):=
Assuming=A0=A0that the bandwith for= CW copy with the simple RX is 100Hz and and you have good CW copy (let= 9;s say at least 10dB S/N)=A0you will need an extra 46dB=A0, what means re= ducing bandwith to 0.0025Hz (=3D QRSS400, or over 6min/dot). So a good point to start with is a 10 min or 15 min on/off cycle (and a= xtal controlled TX).
=A0
73, Rik=A0 ON7YD - OR7T<= /font>
=A0
Van: owner-rsgb_lf= _group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Ri= k Strobbe [Rik.Strobbe@fys.kuleuven.be]
Verzonden: woensdag 26 mei 2010 11:01

Aan: rsgb_lf_group@blacksheep.org
Onderwerp: RE: LF: AW: 8.97kHz - Near field and radiated sign= als?

Roger,
=A0
sorry, I made a mistake.
in the near field the H field drops= 40dB/decade and the E-field drops 60dB/decade.
Assuming the ground antenna acts as= a loop (=3D H-field) the signal drop between 0.4km and 3km will be 35dB.<= /font>
The defintion of near field is vague= , depending on the source it goes from 0.1 wavelength to 1 wavelength.
But at 1kHz even 0.1 lambda is 30km,= so you are defenitely in the near field.
=A0
73, Rik=A0 ON7YD - OR7T
=A0
Van: owner-rsgb_lf= _group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Ro= ger Lapthorn [rogerlapthorn@gmail.com]
Verzonden: woensdag 26 mei 2010 10:43
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: LF: AW: 8.97kHz - Near field and radiated signals?
Rick (et al),

I am confused by the near field attenuation rates quoted. Some quote 18= dB for doubling distance which would mean an additional path loss of= 56dB going from 0.4km to 3km. This makes a lot of difference to what may= or may not be possible.

Which is the correct figure? Help!

73s
Roger G3XBM


On 26 May 2010 09:31, Rik Strobbe <= Rik.Strobbe@fys.kuleuven.be> wrote:

Roger,

=A0

the near fiels signal drops with the= 3rd power of the distance.

So 3km versus 0.4km =3D 422 times weak= er =3D -26dB

Going from regular CW to QRSS30 will= give you a 24dB benefit, so there is a fair chance to be copied at 3km in= this mode. Of course the signal needs to be very frequency stable, it has= to be better than an free running oscillator.

Moving up in frequency would also help= .

And if you can lay your hands on an ol= d stereo amp it would provide an extra 10dB TX power.

=A0

Even if your goal is regular CW over= =A0a 3km path, starting with QRSS will most likely give a visible signal= at 3km and allow you to watch any progress.

=A0

73, Rik=A0 ON7YD - OR7T

=A0

=A0- The best DX targets are quite modest: I would like to exceed 1km=


=A0initially with the TX power I currently have (around 4W). If I could re= ach
=A0G6ALB in the next village 3kms away I would be delighted. If I got any<= br> =A0further I would be both amazed and VERY happy!



--
http://g3xbm-= qrp.blogspot.com/
http://www.g3xbm.co.u= k
http://www= .youtube.com/user/g3xbm
G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088



--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088
--00032555653261645d04877d0dae--