Return-Path: Received: from mtain-mg05.r1000.mx.aol.com (mtain-mg05.r1000.mx.aol.com [172.29.96.205]) by air-da03.mail.aol.com (v129.4) with ESMTP id MAILINDA032-86134c0b50ea34f; Sun, 06 Jun 2010 03:40:26 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-mg05.r1000.mx.aol.com (Internet Inbound) with ESMTP id 00C4B3800035B; Sun, 6 Jun 2010 03:40:24 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OLARl-0000RE-9M for rs_out_1@blacksheep.org; Sun, 06 Jun 2010 08:39:05 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OLARk-0000R5-Kc for rsgb_lf_group@blacksheep.org; Sun, 06 Jun 2010 08:39:04 +0100 Received: from imr-ma01.mx.aol.com ([64.12.206.39]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1OLARi-0001vi-56 for rsgb_lf_group@blacksheep.org; Sun, 06 Jun 2010 08:39:04 +0100 Received: from mtaout-da04.r1000.mx.aol.com (mtaout-da04.r1000.mx.aol.com [172.29.51.132]) by imr-ma01.mx.aol.com (8.14.1/8.14.1) with ESMTP id o567csma015126 for ; Sun, 6 Jun 2010 03:38:54 -0400 Received: from White (g229166082.adsl.alicedsl.de [92.229.166.82]) by mtaout-da04.r1000.mx.aol.com (MUA/Third Party Client Interface) with ESMTPA id 88234E0000A4 for ; Sun, 6 Jun 2010 03:38:51 -0400 (EDT) Message-ID: From: "Markus Vester" To: References: <004801cb04d6$e9740b80$0401a8c0@xphd97xgq27nyf> <004301cb0544$56965980$0201a8c0@Clemens04> Date: Sun, 6 Jun 2010 09:38:47 +0200 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-Spam-Score: 1.3 (+) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,RCVD_IN_BL_SPAMCOP_NET=1.332 Subject: LF: Re: VLF 9 kcs: preamp and antenna noise Content-Type: multipart/alternative; boundary="----=_NextPart_000_0010_01CB055C.0FFDEA20" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.6 required=5.0 tests=HTML_20_30,HTML_MESSAGE, 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 x-aol-global-disposition: G x-aol-sid: 3039ac1d60cd4c0b50e85397 X-AOL-IP: 193.82.116.20 ------=_NextPart_000_0010_01CB055C.0FFDEA20 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Clemens, I believe what Jim was suggesting is a comparison of preamp noise outp= ut with the antenna connected versus a passive load, rather than betwe= en different passive load impedances. The intention is to demonstrate= that the receiver noise contribution is neglegible against external= noise, which is on the order of +140 dB kTo minus antenna losses. Thu= s a very good preamp noise figure is beneficial only with very short= nonresonant antennas, or tiny loops. The challenge for a VLF frontend would mainly lie in decoupling the an= tenna as much as possible from local interference sources. One difficu= lty is that meaningful comparisons can only be done at times of low ex= ternal noise. Currently there seems to a short window with low QRN dur= ing most mornings, but this is probably the worst season of the year. Best 73, Markus (DF6NM) From: Clemens Paul=20 Sent: Sunday, June 06, 2010 8:48 AM To: rsgb_lf_group@blacksheep.org=20 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 short, 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 nois= e 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 th= e actual > antenna with a "dummy antenna" with similar impedance when making th= is > 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 same > inductance and resistance as the actual antenna. This enables quick > comparisons to be made between noise levels at different times and > locations, and is also a good check on the local QRM level. Obviousl= y, you > want the antenna noise level to be at least several dB greater than= that > with the dummy antenna, which is usually easily achieved. > > The general band signal and noise levels are being regularly monitor= ed 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: 06/05/= 10 08:25:00 ------=_NextPart_000_0010_01CB055C.0FFDEA20 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Clemens,
 
I believe what Jim was suggesting&nbs= p;is a=20 comparison of preamp noise output with the antenna connected= versus a=20 passive load, rather than between different passive load impedances.= The=20 intention is to demonstrate that the receiver noise contribution is ne= glegible=20 against external noise, which is on= the order of=20 +140 dB kTo minus antenna losses. Thus a very good preamp no= ise figure=20 is beneficial only with very short nonresonant antennas= ,=20 or tiny loops.
 
The challenge for a VLF fro= ntend would=20 mainly lie in decoupling the antenna as much as possible from loc= al=20 interference sources. One difficulty is that meaningful comp= arisons=20 can only be done at times of low external noise. Currently= there seems=20 to a short window with low QRN during most mornings, but thi= s is=20 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
>= strongly=20 dependent on the source impedance,

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

73
Clemens
DL4RAJ
-----=20 Original Message -----
From: "James Moritz" <james.moritz@btopenworld.com>To:=20 <rsgb_lf_group@bl= acksheep.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 compare= the noise=20 level
> with and without the antenna. Since the RX or preamp noi= se level=20 can be
> strongly dependent on the source impedance, it is best= to replace=20 the actual
> antenna with a "dummy antenna" with similar impedan= ce when=20 making this
> comparison. For example, for my loop antenna, I ha= ve a=20 change-over switch
> that connects the preamp input to a small= choke with=20 about the same
> inductance and resistance as the actual antenna= . This=20 enables quick
> comparisons to be made between noise levels at= different=20 times and
> locations, and is also a good check on the local QRM= level.=20 Obviously, you
> want the antenna noise level to be at least sev= eral dB=20 greater than that
> with the dummy antenna, which is usually eas= ily=20 achieved.
>
> The general band signal and noise levels are= being=20 regularly monitored at
> several locations - you can see the inf= o at http://abelian.org/. But yo= u
> already know=20 that...
>
> Cheers, Jim Moritz
> 73 de=20 M0BMU
>


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



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