Return-Path: Received: from mtain-db07.r1000.mx.aol.com (mtain-db07.r1000.mx.aol.com [172.29.64.91]) by air-ma08.mail.aol.com (v129.4) with ESMTP id MAILINMA084-b5334c0bc515290; Sun, 06 Jun 2010 11:56:05 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-db07.r1000.mx.aol.com (Internet Inbound) with ESMTP id 2E8AE380000B2; Sun, 6 Jun 2010 11:56:03 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OLIBe-0005LS-Ib for rs_out_1@blacksheep.org; Sun, 06 Jun 2010 16:54:58 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OLIBd-0005LJ-Qd for rsgb_lf_group@blacksheep.org; Sun, 06 Jun 2010 16:54:57 +0100 Received: from cavuit01.kulnet.kuleuven.be ([134.58.240.43]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1OLIBb-0004BU-MC for rsgb_lf_group@blacksheep.org; Sun, 06 Jun 2010 16:54:57 +0100 Received: from smtps01.kuleuven.be (smtpshost01.kulnet.kuleuven.be [134.58.240.74]) by cavuit01.kulnet.kuleuven.be (Postfix) with ESMTP id BAAB27B802A for ; Sun, 6 Jun 2010 17:54:47 +0200 (CEST) Received: from ICTS-S-HUB-N3.luna.kuleuven.be (icts-s-hub-n3.luna.kuleuven.be [10.112.9.13]) by smtps01.kuleuven.be (Postfix) with ESMTP id B14A431E703 for ; Sun, 6 Jun 2010 17:54:47 +0200 (CEST) Received: from ICTS-S-EXC2-CA.luna.kuleuven.be ([10.112.11.13]) by ICTS-S-HUB-N3.luna.kuleuven.be ([10.112.9.13]) with mapi; Sun, 6 Jun 2010 17:54:47 +0200 X-Kuleuven: This mail passed the K.U.Leuven mailcluster From: Rik Strobbe To: "rsgb_lf_group@blacksheep.org" Date: Sun, 6 Jun 2010 17:49:56 +0200 Thread-Topic: Re: Re: VLF 9 kcs: preamp and antenna noise Thread-Index: AcsFjh4x1jOSzCGsSHeEXzqVcbq2RgAAcr7k Message-ID: References: <004801cb04d6$e9740b80$0401a8c0@xphd97xgq27nyf> <004301cb0544$56965980$0201a8c0@Clemens04> ,<015f01cb058d$a3500890$0201a8c0@Clemens04> In-Reply-To: <015f01cb058d$a3500890$0201a8c0@Clemens04> Accept-Language: nl-NL, nl-BE Content-Language: nl-BE X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: nl-NL, nl-BE MIME-Version: 1.0 X-KULeuven-Information: Katholieke Universiteit Leuven X-KULeuven-Scanned: Found to be clean X-KULeuven-Envelope-From: rik.strobbe@fys.kuleuven.be X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: RE: Re: Re: VLF 9 kcs: preamp and antenna noise Content-Type: multipart/alternative; boundary="_000_BF4A524700075746A6467658DFC7102C5107CB1259ICTSSEXC2CAlu_" 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,TO_ADDRESS_EQ_REAL 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: 3039ac1d405b4c0bc51300dc X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --_000_BF4A524700075746A6467658DFC7102C5107CB1259ICTSSEXC2CAlu_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Clemens, As Markus says the noise at VLF is around 140dB kTo, so one could '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 lower efficiency (including mismatch losses)? although 100dB seems very large it is possible te get a lower antenne effi= ciency, in particular with small antennas at LF. But there is an very simple test to find out if you have to worry about th= e RX noise figure: if you connect the antenna and there is a significant= increase in noise level (let's say > 10dB) then you do not have to worry. 73, Rik ON7YD - OR7T ________________________________ Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or= g] 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 sa= me impedance of the antenna (at the rx input) to have a more exact reference for compar= ison of rx or preamp noise versus antenna noise. My point which maybe I did not express clearly enough was that three diffe= rent 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 reference= 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 eff= ect >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= 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 '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 lower efficiency (including mismatch losses)? 73 Clemens DL4RAJ ----- Original Message ----- 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 output= with the antenna connected versus a passive load, rather than between dif= ferent 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. Thus a very good pre= amp 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 antenn= a as much as possible from local interference sources. One difficulty is= that meaningful comparisons can only be done at times of low external noi= se. Currently there seems to a short window with low QRN during most morni= ngs, but this is probably the worst season of the year. 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 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 ----- 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 le= vel > 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 ac= tual > antenna with a "dummy antenna" with similar impedance when making this > comparison. For example, for my loop antenna, I have a change-over switc= h > 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. Obviously,= 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 monitored= 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 Version: 9.0.829 / Virendatenbank: 271.1.1/2920 - Ausgabedatum: 06/05/10= 20:25:00 --_000_BF4A524700075746A6467658DFC7102C5107CB1259ICTSSEXC2CAlu_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Clemens,
 
As Markus says the noise at VLF is around= 140dB kTo, so one could 'afford' an antenna
loss of 102dB to have a 10dB SNR margin= with a NF of 28dB.
That's an antenna efficiency of 0,00= 000001585.
Do tiny (in wavelength) antennas&nbs= p;have even lower efficiency (including
mismatch losses)?
 
although 100dB seems ver= y large it is possible te get a lower antenne efficiency, in particular wi= th small antennas at LF.
But there= is an very simple test to find out if you have to worry about the RX nois= e figure: if you connect the antenna and there is a significant increase= in noise level (let's say > 10dB) then you do not have to worry.
&nbs= p;
73, Rik&nbs= p; ON7YD - OR7T
Van: owner-rsgb_= lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Clemen= s 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 bel= ieve) 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 expres= s 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 reference against antenna
noise_at_this_RX_noise_figure with th= e 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 sta= tic 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 'af= ford' 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 -----
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&nbs= p;is a comparison of preamp noise output with the antenna connec= ted versus a passive load, rather than between different passive load impe= dances. 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 ante= nna losses. Thus a very good preamp noise figure is benefic= ial only with very short nonresonant antennas, or tiny loop= s.
 
The challenge for a VLF fro= ntend would mainly lie in decoupling the antenna as much as possible= from local interference sources. One difficulty is that meaning= ful comparisons can only be done at times of low external noise. = ;Currently there seems to a short window with low QRN during most mornings= , but this 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
> 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 -----
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blac= ksheep.org>
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 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 sw= itch
> 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. Obviously= , 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 monitore= d at
> several locations - you can see the info at http://abelian.org/. But you
> already know that...
>
> Cheers, Jim Moritz
> 73 de M0BMU
>


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