Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-me06.r1000.mx.aol.com (Internet Inbound) with ESMTP id 9B6F738000095; Wed, 11 Jul 2012 17:45:33 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Sp4JL-0002g3-0f for rs_out_1@blacksheep.org; Wed, 11 Jul 2012 22:19:03 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Sp4JK-0002fu-1q for rsgb_lf_group@blacksheep.org; Wed, 11 Jul 2012 22:19:02 +0100 Received: from smtpout3.wanadoo.co.uk ([80.12.242.59] helo=smtpout.wanadoo.co.uk) by relay1.thorcom.net with esmtp (Exim 4.77) (envelope-from ) id 1Sp4JH-0005aw-8W for rsgb_lf_group@blacksheep.org; Wed, 11 Jul 2012 22:19:00 +0100 Received: from AGB ([2.26.14.231]) by mwinf5d42 with ME id Z9Ju1j00G4z6akJ039Jvky; Wed, 11 Jul 2012 23:18:55 +0200 Message-ID: From: "Graham" To: References: , <4FFC3518.1030405@xs4all.nl>, <4FFD5313.6103.333D978@mike.dennison.ntlworld.com> <8CF2DB3D98F0811-2624-787AF@webmail-m156.sysops.aol.com> In-Reply-To: <8CF2DB3D98F0811-2624-787AF@webmail-m156.sysops.aol.com> Date: Wed, 11 Jul 2012 22:18:54 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 X-Spam-Score: 0.0 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Yes its a difficult area to work in , Op is scanning a 200 hz audio band , with the possibility of some 60 simultaneous decodes ... Pulse lengthening , could be defined as increasing the noise energy in the pass band , as the decaying ringing exists 'after' the expected falling edge of the pulse and is therefore a 'new' energy source ? assumedly the 'new' power is supplied by the driver amplifier [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [80.12.242.59 listed in list.dnswl.org] 0.0 HTML_MESSAGE BODY: HTML included in message X-Scan-Signature: ce481d129b1a7277ee248e941d6e5100 Subject: Re: LF: OPERA Question Content-Type: multipart/alternative; boundary="----=_NextPart_000_00D4_01CD5FB3.28863080" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.2 required=5.0 tests=CASHCASHCASH, HTML_FONTCOLOR_UNKNOWN,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-SCOLL-SCORE: 0:2:482924960:93952408 X-AOL-SCOLL-URL_COUNT: 0 x-aol-sid: 3039ac1d608e4ffdf3fd2d1e X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none This is a multi-part message in MIME format. ------=_NextPart_000_00D4_01CD5FB3.28863080 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Yes its a difficult area to work in , Op is scanning a 200 hz audio band , with the possibility of some = 60 simultaneous decodes ...=20 Pulse lengthening , could be defined as increasing the noise = energy in the pass band , as the decaying ringing exists 'after' = the expected falling edge of the pulse and is therefore a 'new' = energy source ? assumedly the 'new' power is supplied by the = driver amplifier=20 I think the bottom line is , that anything that can change the = signal parameters , before being presented to the computational = engine is to be avoided , narrow filters may also induce higher = phase changes / Hz than wider ones , which would degrade the = matching process , the whole DSP side of things seems to be = bottomless pit of questions , the deeper you dig , the more = abstract things get ...=20 On a practical side , testing with differing filters would give = a indication as to what the implications are on performance ...=20 73 -G. From: Markus Vester=20 Sent: Wednesday, July 11, 2012 8:38 PM To: rsgb_lf_group@blacksheep.org=20 Subject: Re: LF: OPERA Question Hi Graham, Mike, given the ratio of occupied signal bandwidth (a few Hz) to filter = bandwidth in question (a few 100 Hz), I don't believe there will be any = significant impact of analog filters on signal shape. Neither on = background noise, directly. However in the presence of impulsive noise, eg lightning statics, the = effectiveness of a noiseblanker will be severely degraded if the = duration of the pulses is prolonged by narrow filters with long = ringdown. The sharper the better - especially at VLF where spherics are = dominated by the short cracks from return strokes. However strong = carriers should be excluded from the passband before noiseblanker = action, as otherwise they will be contaminated by sidebands from the = cutouts. Best 73, MArkus (DF6NM)=20 -----Urspr=C3=BCngliche Mitteilung-----=20 Von: Graham An: rsgb_lf_group Cc: james.moritz Verschickt: Mi, 11 Jul 2012 4:15 pm Betreff: Re: LF: OPERA Question ''At first glance it appears crazy'' Mike, Welcome to the crazy world of JR ! The basic explanation is the narrow filters increase the noise = power=20 in a limited bandwidth , ringing due to the Q , similar to CW , = narrow=20 filters tend to round the CW signal The DSP engine is better equipped to differentiate between carrier = and=20 noise and has a much greater dynamic range , so optimum results = are=20 obtained , when the signal is presented to the interface, as close = to to=20 the original as possible , the DSP filter profiles are tailored to = the=20 mode/speed in use This can be noticed with the new generation of SDR support = software ,=20 where audio/voice recovery can be superior to conventional hardware=20 based systems With hardware filtering , there are transit (group) delays which can = alter the amplitude / time , either from on/off keying or with = FSK,=20 this can be observed when sending wide band FSK , although the = audio=20 level remains constant and 'phase continuous' , its possible some = times=20 to see a 'am modulation' envelope on the carrier ... $$$$ can=20 solve this problem , but for most Ham kit its something that=20 'happens' Physical constraints , if there is a very large carrier in the = pass=20 band and this is pushing the hardware into non-linearity / A/D to = over range , giving quantising errors, then , yes filtering would = help , but its more likely its the analogue path that's causing=20 intermod products .....reducing the rf/if gain will provide the = solution I think that's about the picture , if Jim's about , im sure he = will=20 fill in the gaps 73 -G.. -------------------------------------------------- From: "Mike Dennison" Sent: Wednesday, July 11, 2012 10:18 AM To: ; Subject: Re: LF: OPERA Question >> Narrow IF filters are not desirable and reduce the >> performance of the demodulator , better simply use SSB filter >> GL ..73 -G.. > > Graham, > > Why is that the case? What does the considerable extra bandwidth > achieve? Is the SSB bandwidth optimal, or would it be even better > with 10kHz bandwidth, or 100kHz?. Why is 3kHz better than perhaps > 1kHz or 2kHz? > > At first glance it appears crazy to let in all sorts of adjacent > channel QRM (the bandwidth is more than ten times the size of the > entire Opera window) when using a mode that occupies a fraction of > 1Hz. > > Is it simply that the 1.7kHz Tx tone is high enough for the SSB > filter to kill its harmonics, and on receive it is difficult to get a > 1.7kHz tone out of a CW filter, even with passband shifting. > > Am I missing something? > > 73 de Mike, G3XDV > g3xdv.blogspot.co.uk > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > >=20 ------=_NextPart_000_00D4_01CD5FB3.28863080 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable
Yes its a  difficult  area  to  work  in = ,
 
Op is  scanning  a  200 hz  audio  band , = with=20 the  possibility of  some  60  simultaneous  = decodes=20 ...
 
Pulse lengthening , could  be  defined  as  = increasing=20 the  noise  energy in the  pass  band , as the  = decaying  ringing  exists 'after' the  expected=20 falling   edge of the  pulse and  is  therefore = a=20 'new'  energy source ?  assumedly   the 'new'   = power  is  supplied by the  driver amplifier
 
I think the  bottom line  is , that  anything =20 that  can  change the  signal  parameters , before=20 being  presented  to the  computational   = engine =20 is to  be  avoided , narrow  filters  may  = also =20 induce  higher  phase  changes  / Hz  = than  wider=20 ones , which  would  degrade  the  matching process = ,=20  the  whole   DSP  side of  things  = seems=20 to  be  bottomless pit  of  questions  , the=20 deeper  you  dig , the  more  abstract  = things =20 get ...
 
On a  practical  side ,  testing  with =20 differing  filters  would  give  a  indication = as=20 to  what  the  implications  are  on = performance =20 ...
 
73 -G.
 

Sent: Wednesday, July 11, 2012 8:38 PM
To: rsgb_lf_group@blacksheep.org= =20
Subject: Re: LF: OPERA Question

Hi Graham, Mike,
 
given the ratio of occupied signal bandwidth (a few Hz) to filter = bandwidth=20 in question (a few 100 Hz), I don't believe there will be any=20 significant impact of analog filters on signal shape. Neither on = background=20 noise, directly.
 
However in the presence of impulsive noise, eg lightning = statics, the=20 effectiveness of a noiseblanker will be severely degraded if the = duration=20 of the pulses is prolonged by narrow filters with = long ringdown. The=20 sharper the better - especially at VLF where spherics are = dominated by the short cracks from return strokes. However = strong=20 carriers should be excluded from the passband before noiseblanker = action,=20 as otherwise they will be contaminated by sidebands from the = cutouts.
 
Best 73,
MArkus (DF6NM) 


-----Urspr=C3=BCngliche=20 Mitteilung-----
Von: Graham <g8fzk@g8fzk.fsnet.co.uk>
An:=20 rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Cc: james.moritz=20 <james.moritz@btopenworld.com>
Verschickt: Mi, 11 Jul 2012 4:15 = pm
Betreff: Re: LF: OPERA Question

''At first glance it appears crazy''

Mike,

Welcome to the crazy world of  JR  !

The  basic  explanation is the  narrow filters  increase the  noise =
power=20
in a limited   bandwidth , ringing  due to the  Q , similar to  CW , =
narrow=20
filters tend to  round  the  CW signal

The DSP  engine  is  better equipped to  differentiate between  carrier =
and=20
noise and  has a  much  greater  dynamic  range , so  optimum results  =
are=20
obtained , when the  signal is  presented  to the  interface, as close =
to to=20
the  original as  possible , the  DSP filter profiles are  tailored to =
the=20
mode/speed in use

This can be  noticed  with the  new  generation of   SDR  support =
software ,=20
where  audio/voice recovery  can be  superior to conventional hardware=20
based systems

With hardware filtering , there  are  transit  (group) delays which  can =

alter the  amplitude / time  , either  from  on/off  keying  or  with =
FSK,=20
this can  be  observed when  sending  wide  band  FSK , although  the  =
audio=20
level  remains  constant and  'phase continuous'  , its possible  some =
times=20
to  see a  'am modulation'  envelope  on the  carrier    ... $$$$   can=20
solve this  problem , but  for  most  Ham  kit its  something  that=20
'happens'

Physical  constraints , if  there  is  a  very large  carrier in the  =
pass=20
band  and  this  is pushing  the  hardware into  non-linearity / A/D  to =

over  range  , giving   quantising  errors, then  , yes  filtering would =

help , but  its more  likely  its the  analogue  path  that's  causing=20
intermod products .....reducing  the  rf/if gain will  provide the  =
solution

I think that's  about the  picture , if  Jim's  about , im sure  he  =
will=20
fill in the  gaps

73 -G..




--------------------------------------------------
From: "Mike Dennison" <mike.dennison@ntlworld.com=
>
Sent: Wednesday, July 11, 2012 10:18 AM
To: <rsgb_lf_group@blacksheep.org=
>; <rsgb_lf_group@yahoogroups=
.co.uk>
Subject: Re: LF:  OPERA  Question

>> Narrow   IF filters  are  not  desirable  and   reduce the
>> performance of the  demodulator  , better  simply  use  SSB  =
filter
>> GL ..73 -G..
>
> Graham,
>
> Why is that the case? What does the considerable extra bandwidth
> achieve? Is the SSB bandwidth optimal, or would it be even better
> with 10kHz bandwidth, or 100kHz?. Why is 3kHz better than perhaps
> 1kHz or 2kHz?
>
> At first glance it appears crazy to let in all sorts of adjacent
> channel QRM (the bandwidth is more than ten times the size of the
> entire Opera window) when using a mode that occupies a fraction of
> 1Hz.
>
> Is it simply that the 1.7kHz Tx tone is high enough for the SSB
> filter to kill its harmonics, and on receive it is difficult to get =
a
> 1.7kHz tone out of a CW filter, even with passband shifting.
>
> Am I missing something?
>
> 73 de Mike, G3XDV
> g3xdv.blogspot.co.uk
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
>
>=20
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