Return-Path: Received: from rly-dg03.mx.aol.com (rly-dg03.mail.aol.com [172.19.151.87]) by air-dg07.mail.aol.com (v123.3) with ESMTP id MAILINDG073-5b749b0187217a; Thu, 05 Mar 2009 13:22:53 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-dg03.mx.aol.com (v123.3) with ESMTP id MAILRELAYINDG038-5b749b0187217a; Thu, 05 Mar 2009 13:22:45 -0500 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1LfID8-0007fU-Br for rs_out_1@blacksheep.org; Thu, 05 Mar 2009 18:22:22 +0000 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1LfID7-0007fL-LF for rsgb_lf_group@blacksheep.org; Thu, 05 Mar 2009 18:22:21 +0000 Received: from vms173003pub.verizon.net ([206.46.173.3]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1LfID6-00035D-92 for rsgb_lf_group@blacksheep.org; Thu, 05 Mar 2009 18:22:21 +0000 Received: from DR2 ([71.184.212.10]) by vms173003.mailsrvcs.net (Sun Java(tm) System Messaging Server 6.3-7.04 (built Sep 26 2008; 32bit)) with ESMTPA id <0KG100F2JPOUJJZF@vms173003.mailsrvcs.net> for rsgb_lf_group@blacksheep.org; Thu, 05 Mar 2009 12:22:06 -0600 (CST) Message-id: From: "dave.riley3" To: Cc: "600MRG" References: <000a01c99a91$a54a1180$1402a8c0@e7010> <7.0.1.0.1.20090305091934.0181aca8@magma.ca> Date: Thu, 05 Mar 2009 13:22:05 -0500 MIME-version: 1.0 X-Priority: 3 X-MSMail-priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Spam-Score: 3.4 (+++) X-Spam-Report: autolearn=disabled,FORGED_MUA_OUTLOOK=3.36,HTML_MESSAGE=0.001 Subject: Re: LF: Deep copy... Content-type: multipart/alternative; boundary="----=_NextPart_000_000F_01C99D95.60BBD420" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: ** X-Spam-Status: No, hits=2.1 required=5.0 tests=FORGED_MUA_OUTLOOK,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-IP: 193.82.116.20 ------=_NextPart_000_000F_01C99D95.60BBD420 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Thanks to ALL who responded with quick and cogent findings... It has seemed for a time that with the receiver AGC and NBs OFF that I gener= ally can see a deeper signal, depending on conditions... The final audio filter assures that the program does not have to deal with n= oise outside of the passband of interest... TNX Here is today's gnawing question... What is the expected ambient noise say=20= @ 600M one should expect?? Rural, City, Country, remote battery operated, etc. combinations... Especial= ly well away from AC neutral wires... Today I ran the input to the SDR-IQ into a 50 ohm load and set a long integr= ate ( 64+ ) and saw approx -134 dbm of baseband noise with NO signals... I then connected to the outside antenna with no external pre-amp or any non=20= linear device and saw -117 dbm of noise across 10 khz. with a few weak and f= loating predictable BB noises.. At night it is sure to be up to near -100 dbm depending on conditions and no= ises present... What do YOU get for a noise difference between a terminated antenna input an= d your regular receive antenna?? I'm about to place several e-probes about this place in order to mix and mat= ch phase and amplitudes in order to see what net gain can be made to the SNR= with the hope that the most offending noises will not be in the path of a d= esired signal... TNX and ain't this fun??? Dave @ WD2XSH/17 =20 ----- Original Message -----=20 From: Bill de Carle=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Thursday, March 05, 2009 9:58 AM Subject: Re: LF: Deep copy... At 09:25 PM 3/4/2009, you wrote: I seem to get best results while trying to pull signals out of the noise= when the AGC of the receiver is OFF as well as the Noise Blanker and Noise=20= reduction features being OFF... =20 Do you concur?? =20 Also setting a good audio filter to the passband of interest seems to by= pass some heavy static hits as well... I've noticed that when doing HF frequency measurement tests (working to th= e nearest milliHertz) - turning off the AGC under high static conditions see= ms to improve the accuracy of the measurement, at least with the software I=20= use. One plausible explanation is that AGC action necessarily introduces am= plitude modulation (on all signals in the passband). When I process the AGC= 'd signal with what amounts to a very narrow DSP filter the added amplitude=20= modulation shows up as apparent sidebands close-in on the signal I'm trying=20= to measure. If the power in those sidebands is comparable to that of the si= gnal whose frequency I'm looking for, the FFT algorithm (which assumes the r= eal signal has the largest amplitude) gets confused and comes up with an est= imated frequency somewhere between the correct value and that of a nearby si= deband. The effect is small however because the AGC pumping action doesn't=20= occur very fast so the added sidebands are seen to be only some milliHertz a= way from the signal. The sidebands occur on both sides of the "real" signal= , so one might expect them to cancel out but in practice they don't because=20= the amount of error depends on where the "real" signal falls with respect to= the fixed frequency bins of the FFT. It should be possible to model the AG= C action of a particular receiver and compensate for it in the software. No= doubt the phenomenon becomes less significant with smaller FFT's or shorter= integration times. Changing the AGC setting between SLOW-FAST-OFF might he= lp under some conditions. With QRSS-60 signaling rates it can take a long t= ime to find out which setting is optimum, especially when band conditions ar= e changing or the QSB period is close to a bit time, hi! VE2IQ ------=_NextPart_000_000F_01C99D95.60BBD420 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Thanks to ALL who responded with quick and cogen= t=20 findings...
 
It has seemed for a time that with the receiver=20= AGC=20 and NBs OFF that I generally can see a deeper signal, depending on=20 conditions...
 
The final audio filter assures that the program=20= does=20 not have to deal with noise outside of the passband of=20 interest...
 
TNX
 
 
Here is today's gnawing question...  What i= s the=20 expected ambient noise say @ 600M one should expect??
Rural, City, Country, remote battery operated, e= tc.=20 combinations... Especially well away from AC neutral=20 wires...
 
Today I ran the input to the=20 SDR-IQ <= FONT size=3D2>into a 50 ohm load and set a long integrate ( 64+ )  an= d saw approx=20 -134 dbm of baseband noise with NO signals...
 
I then connected to the outside antenna with no=20 external pre-amp or any non linear device and saw -117 dbm of noise across 1= 0=20 khz. with a few weak and floating predictable BB noises..
 
At night it is sure to be up to near -100 dbm=20 depending on conditions and noises present...
 
What do YOU get for a noise difference between a= =20 terminated antenna input and your regular receive=20 antenna??
 
I'm about to place several e-probes about this p= lace=20 in order to mix and match phase and amplitudes in order to see what net gain= can=20 be made to the SNR with the hope that the most offending noises will not be=20= in=20 the path of a desired signal...
 
TNX and ain't this fun???
 
Dave @ WD2XSH/17
 
 
 
 
 
 
 
 
----- Original Message -----
Bill de Carle=
Sent: Thursday, March 05, 2009 9:58= =20 AM
Subject: Re: LF: Deep copy...

At 09:25 PM 3/4/2009, you wrote:
I seem=20= to get=20 best results while trying to pull signals out of the noise when the AGC=20= of=20 the receiver is OFF as well as the Noise Blanker and Noise reduction=20 features being OFF...
 
Do you=20 concur??
 
Also setting a good a= udio=20 filter to the passband of interest seems to bypass some heavy static hit= s as=20 well...

I've noticed that when doing HF frequ= ency=20 measurement tests (working to the nearest milliHertz) - turning off the AG= C=20 under high static conditions seems to improve the accuracy of the measurem= ent,=20 at least with the software I use.  One plausible explanation is that=20= AGC=20 action necessarily introduces amplitude modulation (on all signals in the=20 passband).  When I process the AGC'd signal with what amounts to a ve= ry=20 narrow DSP filter the added amplitude modulation shows up as apparent=20 sidebands close-in on the signal I'm trying to measure.  If the power= in=20 those sidebands is comparable to that of the signal whose frequency I'm=20 looking for, the FFT algorithm (which assumes the real signal has the larg= est=20 amplitude) gets confused and comes up with an estimated frequency somewher= e=20 between the correct value and that of a nearby sideband.  The effect=20= is=20 small however because the AGC pumping action doesn't occur very fast so th= e=20 added sidebands are seen to be only some milliHertz away from the=20 signal.  The sidebands occur on both sides of the "real" signal, so o= ne=20 might expect them to cancel out but in practice they don't because the amo= unt=20 of error depends on where the "real" signal falls with respect to the fixe= d=20 frequency bins of the FFT.  It should be possible to model the AGC ac= tion=20 of a particular receiver and compensate for it in the software.  No d= oubt=20 the phenomenon becomes less significant with smaller FFT's or shorter=20 integration times.  Changing the AGC setting between SLOW-FAST-OFF mi= ght=20 help under some conditions.  With QRSS-60 signaling rates it can take= a=20 long time to find out which setting is optimum, especially when band=20 conditions are changing or the QSB period is close to a bit time,=20 hi!

VE2IQ
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