Return-Path: Received: from mtain-dc02.r1000.mx.aol.com (mtain-dc02.r1000.mx.aol.com [172.29.64.130]) by air-dc07.mail.aol.com (v129.4) with ESMTP id MAILINDC073-86534c0bc0172ed; Sun, 06 Jun 2010 11:34:47 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-dc02.r1000.mx.aol.com (Internet Inbound) with ESMTP id 364DE380000F0; Sun, 6 Jun 2010 11:34:46 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OLHrB-0007BD-G4 for rs_out_1@blacksheep.org; Sun, 06 Jun 2010 16:33:49 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OLHrA-0007B4-QE for rsgb_lf_group@blacksheep.org; Sun, 06 Jun 2010 16:33:48 +0100 Received: from mail.gmx.net ([213.165.64.20]) by relay1.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1OLHr8-00045W-JP for rsgb_lf_group@blacksheep.org; Sun, 06 Jun 2010 16:33:48 +0100 Received: (qmail invoked by alias); 06 Jun 2010 15:33:39 -0000 Received: from p5DC43188.dip.t-dialin.net (EHLO Clemens04) [93.196.49.136] by mail.gmx.net (mp013) with SMTP; 06 Jun 2010 17:33:39 +0200 X-Authenticated: #17214767 X-Provags-ID: V01U2FsdGVkX184Yl5aDrw4Nu49hpaiSLhWyzkPe2GdZZVgaV0eqQ c8lVEsH0MIp5T4 Message-ID: <015f01cb058d$a3500890$0201a8c0@Clemens04> From: "Clemens Paul" To: References: <004801cb04d6$e9740b80$0401a8c0@xphd97xgq27nyf> <004301cb0544$56965980$0201a8c0@Clemens04> Date: Sun, 6 Jun 2010 17:33:33 +0200 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3664 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3664 X-Y-GMX-Trusted: 0 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: Re: Re: VLF 9 kcs: preamp and antenna noise Content-Type: multipart/alternative; boundary="----=_NextPart_000_015B_01CB059E.6320D9A0" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=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 x-aol-global-disposition: G x-aol-sid: 3039ac1d40824c0bc0166f67 X-AOL-IP: 193.82.116.20 ------=_NextPart_000_015B_01CB059E.6320D9A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Markus,Jim, the point of Jim was (i believe) to take a dummy with approximately th= e same impedance of the antenna (at the rx input) to have a more exact reference for co= mparison of rx or preamp noise versus antenna noise. My point which maybe I did not express clearly enough was that three= different passive loads caused the same noise at perseus with a NF of around 28dB. So any of these extremely different loads can be used as a dummy refer= ence against antenna noise_at_this_RX_noise_figure with the same result. Building an extra special dummy would be of no practical use for this= NF of 28dB. As Jim points out in his second email: >But unless the noise figure of the preamp/receiver is quite low, this= effect >will often be masked by internal noise in practice. My antennas are a 88m longwire and a PA0RDT miniwhip. When switched to the rx input both give a huge rise in noise with stat= ic crackling,no buzz, so I'm sure to have a real good SNR here with alphas up to 20dB over= noise at ~12kHz. As Markus says the noise at VLF is around 140dB kTo, so one could 'aff= ord' an antenna loss of 102dB to have a 10dB SNR margin with a NF of 28dB. That's an antenna efficiency of 0,00000001585. Do tiny (in wavelength) antennas have even lower efficiency (including mismatch losses)? 73 Clemens DL4RAJ ----- Original Message -----=20 From: Markus Vester To: rsgb_lf_group@blacksheep.org Sent: Sunday, June 06, 2010 9:38 AM Subject: LF: Re: VLF 9 kcs: preamp and antenna noise Clemens, I believe what Jim was suggesting is a comparison of preamp noise ou= tput with the antenna=20 connected versus a passive load, rather than between different passive= load impedances. The=20 intention is to demonstrate that the receiver noise contribution is ne= glegible against external=20 noise, which is on the order of +140 dB kTo minus antenna losses. Thus= a very good preamp noise=20 figure is beneficial only with very short nonresonant antennas, or tin= y loops. The challenge for a VLF frontend would mainly lie in decoupling the= antenna as much as=20 possible from local interference sources. One difficulty is that meani= ngful comparisons can only=20 be done at times of low external noise. Currently there seems to a sho= rt window with low QRN=20 during most mornings, but this is probably the worst season of the yea= r. Best 73, Markus (DF6NM) From: Clemens Paul Sent: Sunday, June 06, 2010 8:48 AM To: rsgb_lf_group@blacksheep.org Subject: LF: Re: Re: 9 kcs Jim, >Since the RX or preamp noise level can be > strongly dependent on the source impedance, I can not confirm this with my RX,a Perseus SDR. When I switch on 9kHz or any other qrg between 50 Ohm, open and shor= t, I always get the same reading within a tenth of dB,e.g -118,4dBm RMS= at a BW of 732Hz (arbitrarily chosen) The reading also stays constant between the three sourcees when I do the same test with preamp ot attenuator on. Maybe your observation is true for RX/preamp inputs with considerable reactance in the input impedance. 73 Clemens DL4RAJ ----- Original Message -----=20 From: "James Moritz" To: Sent: Sunday, June 06, 2010 12:29 AM Subject: LF: Re: 9 kcs ... > A better test of receiver performance at 9kHz is to compare the no= ise level > with and without the antenna. Since the RX or preamp noise level= can be > strongly dependent on the source impedance, it is best to replace= the actual > antenna with a "dummy antenna" with similar impedance when making= this > comparison. For example, for my loop antenna, I have a change-over= switch > that connects the preamp input to a small choke with about the sam= e > inductance and resistance as the actual antenna. This enables quic= k > comparisons to be made between noise levels at different times and > locations, and is also a good check on the local QRM level. Obviou= sly, you > want the antenna noise level to be at least several dB greater tha= n that > with the dummy antenna, which is usually easily achieved. > > The general band signal and noise levels are being regularly monit= ored at > several locations - you can see the info at http://abelian.org/.= But you > already know that... > > Cheers, Jim Moritz > 73 de M0BMU > --------------------------------------------------------------------= ------------ Eingehende eMail ist virenfrei. Von AVG =FCberpr=FCft - www.avg.de Version: 9.0.829 / Virendatenbank: 271.1.1/2919 - Ausgabedatum: 06/0= 5/10 08:25:00 ----------------------------------------------------------------------= -------- Eingehende eMail ist virenfrei. Von AVG =FCberpr=FCft - www.avg.de Version: 9.0.829 / Virendatenbank: 271.1.1/2920 - Ausgabedatum: 06/0= 5/10 20:25:00 ------=_NextPart_000_015B_01CB059E.6320D9A0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Markus,Jim,
 
the point of Jim was (i bel= ieve) to take=20 a dummy with approximately the same impedance
of the antenna (at the rx input) to= have a more=20 exact reference for comparison
of rx or preamp noise versus antenna= =20 noise.
My point which maybe I did not expres= s clearly=20 enough was that three different passive loads
caused the same noise at perseus with= a NF of=20 around 28dB.
So any of these extremely different= loads can be=20 used as a dummy reference against antenna
noise_at_this_RX_noise_figure with th= e same=20 result.
Building an extra special dummy would= be of no=20 practical use for this NF of 28dB. 
As Jim points out in his second= =20 email:
>But unless the noise figure of the preamp/receiver is quite= low, this=20 effect
>will often be masked by internal noise in practice.
My antennas are a 88m longwire and a PA0RDT miniwhip.
When switched to the rx input both give a huge rise in noise with= static=20 crackling,no buzz,
so I'm sure to have a real good SNR here with alphas up= to 20dB=20 over noise at ~12kHz.
As Markus says the noise at VLF is around 140dB kTo, so one could= 'afford'=20 an antenna
loss of 102dB to have a 10dB SNR margin with a NF of 28dB.
That's an antenna efficiency of 0,00000001585.
Do tiny (in wavelength) antennas have even=20 lower efficiency (including
mismatch losses)?
 
73
Clemens
DL4RAJ
 
 
----- Original Message -----
Sent: Sunday, June 06, 2010= 9:38 AM
Subject: LF: Re: VLF 9 kcs:= preamp and=20 antenna noise

Clemens,
 
I believe what Jim was suggesting&n= bsp;is a=20 comparison of preamp noise output with the antenna connect= ed versus=20 a passive load, rather than between different passive load impedance= s. The=20 intention is to demonstrate that the receiver noise contribution is= neglegible=20 against external noise, which is = on the order=20 of +140 dB kTo minus antenna losses. Thus a very good prea= mp noise=20 figure is beneficial only with very short nonresonant= antennas,=20 or tiny loops.
 
The challenge for a VLF f= rontend would=20 mainly lie in decoupling the antenna as much as possible from= local=20 interference sources. One difficulty is that meaningful co= mparisons=20 can only be done at times of low external noise. Currently= there=20 seems to a short window with low QRN during most mornings,= but this=20 is probably the worst season of the year.
 
Best 73,
Markus (DF6NM)

Sent: Sunday, June 06, 2010 8:48 AM
Subject: LF: Re: Re: 9 kcs
=
Jim,

>Since the RX or preamp noise level can be
&g= t;=20 strongly dependent on the source impedance,

I can not confirm= this with=20 my RX,a Perseus SDR.
When I switch on 9kHz or any other qrg betwe= en 50 Ohm,=20 open and short,
I always get the same reading within a tenth of= dB,e.g=20 -118,4dBm RMS at a BW of
732Hz (arbitrarily chosen)
The readin= g also=20 stays constant between the three sourcees
when I do the same test= with=20 preamp ot attenuator on.
Maybe your observation is true for RX/pr= eamp=20 inputs with
considerable reactance in the input=20 impedance.

73
Clemens
DL4RAJ

----- Original Mess= age -----=20
From: "James Moritz" <james.moritz@btopenworld.com>
To:=20 <rsgb_lf_grou= p@blacksheep.org>
Sent:=20 Sunday, June 06, 2010 12:29 AM
Subject: LF: Re: 9 kcs
...
> A better test of receiver performance at 9kHz is to compar= e the=20 noise level
> with and without the antenna. Since the RX or pr= eamp noise=20 level can be
> strongly dependent on the source impedance, it= is best to=20 replace the actual
> antenna with a "dummy antenna" with simil= ar=20 impedance when making this
> comparison. For example, for my= loop=20 antenna, I have a change-over switch
> that connects the pream= p input to=20 a small choke with about the same
> inductance and resistance= as the=20 actual antenna. This enables quick
> comparisons to be made be= tween=20 noise levels at different times and
> locations, and is also= a good=20 check on the local QRM level. Obviously, you
> want the antenn= a noise=20 level to be at least several dB greater than that
> with the= dummy=20 antenna, which is usually easily achieved.
>
> The gener= al band=20 signal and noise levels are being regularly monitored at
> sev= eral=20 locations - you can see the info at http://abelian.org/. But you
> already=20 know that...
>
> Cheers, Jim Moritz
> 73 de=20 M0BMU
>


-------------------------------------------= -------------------------------------



Eingehende=20 eMail ist virenfrei.
Von AVG =FCberpr=FCft - www.avg.de
Version: 9.0.829 / Virendatenbank:=20 271.1.1/2919 - Ausgabedatum: 06/05/10 08:25:00


Eingehende eMail ist virenfrei.
Von AVG =FCberpr=FCft= - www.avg.de=20
Version: 9.0.829 / Virendatenbank: 271.1.1/2920 - Ausgabedatum:= 06/05/10=20 20:25:00
------=_NextPart_000_015B_01CB059E.6320D9A0--