Return-Path: Received: from mtain-md05.r1000.mx.aol.com (mtain-md05.r1000.mx.aol.com [172.29.96.89]) by air-dc10.mail.aol.com (v129.4) with ESMTP id MAILINDC101-86064c0bc982161; Sun, 06 Jun 2010 12:14:58 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-md05.r1000.mx.aol.com (Internet Inbound) with ESMTP id 14A4F380000EC; Sun, 6 Jun 2010 12:14:56 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OLIUF-0003cj-B5 for rs_out_1@blacksheep.org; Sun, 06 Jun 2010 17:14:11 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OLIUE-0003cS-4a for rsgb_lf_group@blacksheep.org; Sun, 06 Jun 2010 17:14:10 +0100 Received: from out1.ip04ir2.opaltelecom.net ([62.24.128.240]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1OLIUB-0004L1-B0 for rsgb_lf_group@blacksheep.org; Sun, 06 Jun 2010 17:14:10 +0100 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AjwFAJ9mC0xcEYOI/2dsb2JhbACBQ40/gwGMRnG9TIUXBA X-IronPort-AV: E=Sophos;i="4.53,373,1272841200"; d="scan'208,217";a="293754109" Received: from unknown (HELO xphd97xgq27nyf) ([92.17.131.136]) by out1.ip04ir2.opaltelecom.net with SMTP; 06 Jun 2010 17:13:44 +0100 Message-ID: <001901cb0593$3c44e2f0$0401a8c0@xphd97xgq27nyf> From: "mal hamilton" To: References: <004801cb04d6$e9740b80$0401a8c0@xphd97xgq27nyf> <004301cb0544$56965980$0201a8c0@Clemens04> ,<015f01cb058d$a3500890$0201a8c0@Clemens04> Date: Sun, 6 Jun 2010 17:13:43 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: Re: RE: Re: Re: VLF 9 kcs: preamp and antenna noise Content-Type: multipart/alternative; boundary="----=_NextPart_000_0016_01CB059B.9DAEA7D0" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.9 required=5.0 tests=HTML_30_40,HTML_FONTCOLOR_BLUE, 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: 3039ac1d60594c0bc9806dda X-AOL-IP: 193.82.116.20 ------=_NextPart_000_0016_01CB059B.9DAEA7D0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Now we are getting somewhere regarding discussion about vlf reception,= sensitivity and NF etc.=20 g3kev ----- Original Message -----=20 From: Rik Strobbe=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Sunday, June 06, 2010 4:49 PM Subject: LF: RE: Re: Re: VLF 9 kcs: preamp and antenna noise Clemens, As Markus says the noise at VLF is around 140dB kTo, so one could 'a= fford' 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 (includi= ng mismatch losses)? although 100dB seems very large it is possible te get a lower antenn= e efficiency, in particular with small antennas at LF. But there is an very simple test to find out if you have to worry ab= out the RX noise figure: if you connect the antenna and there is a sig= nificant increase in noise level (let's say > 10dB) then you do not ha= ve to worry. 73, Rik ON7YD - OR7T ----------------------------------------------------------------------= -------- Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksh= eep.org] namens Clemens Paul [cpaul@gmx.net] Verzonden: zondag 6 juni 2010 17:33 Aan: rsgb_lf_group@blacksheep.org Onderwerp: LF: Re: Re: VLF 9 kcs: preamp and antenna noise Markus,Jim, the point of Jim was (i believe) to take a dummy with approximately= the same impedance of the antenna (at the rx input) to have a more exact reference for= comparison 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 ref= erence against antenna noise_at_this_RX_noise_figure with the same result. Building an extra special dummy would be of no practical use for thi= s NF of 28dB.=20 As Jim points out in his second email: >But unless the noise figure of the preamp/receiver is quite low, th= is 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 st= atic 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 'a= fford' 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 (includi= ng mismatch losses)? 73 Clemens DL4RAJ ----- Original Message -----=20 From: Markus Vester=20 To: rsgb_lf_group@blacksheep.org=20 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= output with the antenna connected versus a passive load, rather than= between different passive load impedances. The intention is to demons= trate that the receiver noise contribution is neglegible against exter= nal noise, which is on the order of +140 dB kTo minus antenna losses.= Thus a very good preamp noise figure is beneficial only with very sho= rt nonresonant antennas, or tiny loops. The challenge for a VLF frontend would mainly lie in decoupling th= e antenna as much as possible from local interference sources. One dif= ficulty is that meaningful comparisons can only be done at times of lo= w external noise. Currently there seems to a short window with low QRN= during most mornings, but this is probably the worst season of the ye= ar. 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 sh= ort, 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= noise 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 replac= e the actual > antenna with a "dummy antenna" with similar impedance when makin= g this > comparison. For example, for my loop antenna, I have a change-ov= er switch > that connects the preamp input to a small choke with about the= same > inductance and resistance as the actual antenna. This enables qu= ick > comparisons to be made between noise levels at different times= and > locations, and is also a good check on the local QRM level. Obvi= ously, 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 mon= itored 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 ----------------------------------------------------------------------= ------ 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 20:25:00=20 ------=_NextPart_000_0016_01CB059B.9DAEA7D0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Now we are getting somewhere regardin= g discussion=20 about vlf reception, sensitivity and NF etc.
g3kev
 
----- Original Message -----
From:=20 Rik Strobbe
Sent: Sunday, June 06, 2010= 4:49 PM
Subject: LF: RE: Re: Re: VLF= 9 kcs:=20 preamp and antenna noise

Clemens,
 
As Markus says the noise at VLF is ar= ound 140dB=20 kTo, so one could 'afford' an antenna
loss of 102dB to have a 10dB SNR marg= in with a NF=20 of 28dB.
That's an antenna efficiency of= =20 0,00000001585.
Do tiny (in wavelength)=20 antennas have even lower efficiency=20 (including
mismatch losses)?
&= nbsp;
although 100dB seems= very large it=20 is possible te get a lower antenne efficiency, in particular with sm= all=20 antennas at LF.
But there= is an very=20 simple test to find out if you have to worry about the RX noise figu= re: if you=20 connect the antenna and there is a significant increase in noise lev= el (let's=20 say > 10dB) then you do not have to worry.
&n= bsp;
73, Rik&n= bsp; ON7YD -=20 OR7T
Van:=20 owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.o= rg] namens=20 Clemens Paul [cpaul@gmx.net]
Verzonden: zondag 6 juni 2010= =20 17:33
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: LF: Re:=20 Re: VLF 9 kcs: preamp and antenna noise

Markus,Jim,
 
the point of Jim was (i= believe) to=20 take 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 antenn= a=20 noise.
My point which maybe I did not expr= ess clearly=20 enough was that three different passive loads
caused the same noise at perseus wi= th 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= the same=20 result.
Building an extra special dummy wou= ld be of no=20 practical use for this NF of 28dB. 
As Jim points out in his secon= d=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 wi= th 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 cou= ld=20 'afford' 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=20 AM
Subject: LF: Re: VLF 9 kcs:= preamp and=20 antenna noise

Clemens,
 
I believe what Jim was suggesting=  is a=20 comparison of preamp noise output with the antenna conne= cted=20 versus a passive load, rather than between different passive load= =20 impedances. The intention is to demonstrate that the receiver nois= e=20 contribution is neglegible against external noise, which is on the order of +140 dB kTo minus= antenna=20 losses. Thus a very good preamp noise figure is ben= eficial=20 only with very short nonresonant antennas, or tiny= =20 loops.
 
The challenge for a VLF = ;frontend=20 would mainly lie in decoupling the antenna as much as possibl= e from=20 local interference sources. One difficulty is that meani= ngful=20 comparisons can only be done at times of low external=20 noise. Currently there seems to a short window with= low QRN=20 during most mornings, but this is probably the worst season of the= =20 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
= >=20 strongly dependent on the source impedance,

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

73
Clemens
DL4RAJ

----- Original Me= ssage=20 -----
From: "James Moritz" <james.moritz@btopenworld.com>
To:=20 <rsgb_lf_= group@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 comp= are the=20 noise level
> with and without the antenna. Since the RX or= preamp=20 noise level can be
> strongly dependent on the source impeda= nce, it is=20 best to replace the actual
> antenna with a "dummy antenna"= with=20 similar impedance when making this
> comparison. For example= , for my=20 loop antenna, I have a change-over switch
> that connects th= e preamp=20 input to a small choke with about the same
> inductance and= resistance=20 as the actual antenna. This enables quick
> comparisons to= be made=20 between noise levels at different times and
> locations, and= is also a=20 good check on the local QRM level. Obviously, you
> want the= antenna=20 noise level to be at least several dB greater than that
> wi= th the=20 dummy antenna, which is usually easily achieved.
>
>= The general=20 band signal and noise levels are being regularly monitored at
&= gt;=20 several locations - you can see the info at http://abelian.org/. But you
&g= t; already know=20 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=FCf= t - www.avg.de=20
Version: 9.0.829 / Virendatenbank: 271.1.1/2920 - Ausgabedatum= : 06/05/10=20 20:25:00
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