Re: Topband: ADC Overload from MW transmitters

[JC]

<< What do we do with them?>>

We do what we are!  Gentlemen !giving always a good example.

 Even almost 40 year later worth reading W1BB.

W1BB>>
GENTLEMENT BAND!!??? ---Shall stress the importance of keeping this UNIQUE
band "The GENTLEMEN! Band", as its reputation has been for so many years,
just that ?? We're having sum "growing pains" with big influx of New-Comers,
who are not yet thoroughly steeped, (and maybe never will be), in the
tradition of the band, or cognizant of the advantages to themselves, and to
ALL, to keep it so!! SEEMS that each one of us who enjoys these unique
advantages, and the thrill of 160, should want to, individually, help to
keep it this way -- by contributing all the "input" in the direction we are
in - by welcoming, educating, befriending, exhibiting a good example, and
Wining the same support from these new-Comers. Meanwhile being sure of our
own motives, and the example we give is correct and right - to acknowledge
our own mistakes, and not make them twice. As "Gentlemen" of 160, shouldn't
we try to MINIMIZE the bickering between CW/PHONE, and to find ways to
cooperate with each other in eliminating friction and QRM??? By meticulously
RESPECTING the "Gentlemen's Agreement" that 1800-10 would be CW
--1810-25/SSB --1825-30 the "DX Window" 1830-1850/SSB and CW. Seems like
a really Gud set-up, especially for phone., since all other bands do not
have an exclusive phone segment!!! BUT we must remember that NO-ONE has any
"LEGAL" requirement to respect these Fys - this "Gents" partitioning,
because the "status" of the band --- it is really NOT an Amateur Band at
all!!! It is a Govt/Services (USCG/LORAN) band, wherein we Amateurs have the
PRIVILEGE only of operating there, IF we cause no QRM to the Govt Services.
For this reason it cannot be, and is not legally partitioned into PHONE/CW
segments. SO that, our only hope of "order" is in this so called
"Gentlemen's Agreement SOOOooo.! one MUST NOT tell either CW,AM,SSB stns to
"get the Hout of there". In the first place, it is the wrong approach
anyway! Secondly, each one had as much RIGHT to be ANYWHERE he wish' as
anyone else. It is a problem of educating to the advantages and winning
everyone's RESPECT for these frequencies! -- -- My experience over many
years, is that 99% of the 160m men are real good guys, ready & willing to
cooperate, for the good of all, IF they are treated fairly and with RESPECT.
We've run across only a few selfish, cantankerous and sour individuals, who
insist on their "Rights", regardless of how much it hurts the other 99% ---
One must exercise a LOT of restraint, patience, perseverance when this
happens, not to be "Touchy", or over sensitive, with these QRMers,
understanding that outside of the two or three "stinkers", the .problem in
mostly through ignorance carelessness, and not intentional. We have to
CONTINUALLY educate and help them and each other. REGARDING the two or three
"Stinkers", the INTENTIONAL QRMers, with their strings of dots/dashes on Fy,
swishes, modulated noises intentionally calling CQ on DX/Fys, In Window, etc
(See-QST/MAR p9, "Malicious QRM") Even here my experience is that "patience
has its reward". The BEST WAY to handle them is TO PAY NO ATTENTION
WHATSOEVER NOT EVEN MENTION it or them over the air. Me while, not
accomplishing their mission of causing trouble, annoying, or "Stirring Up A
Hornets Nest' they get tired and go away. -- The WORST thing to do is to
TAKE NOTICE of them, talk about them, call them names, retaliate, etc - this
is JUST what they are striving for To make acknowledgement of the trouble
they are causing, only makes a bad matter worse (This applies only to the
INTENTIONAL QRMers) (Others, it is helpful to acknowledge and try to help.)
One of those "Stinkers" on the West Coast has been caught and punished
severely. There'll be others surely, as we perfect means of detection and
"coping". Additionally, "Stinkerism" has its own reward!! Many New-Comers to
160 are heard to say what a difference and pleasure it is to operate on 160,
compared to HF bands. Let's keep it that way!! We can, with patience,
perseverance, tact and understanding. OK?? Comments??
<<

73's
JC
N4IS



_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Rich Chatelain]

Thank you for posting that JC ! I have never read that before and it is very
appropriate.

Rich K7ZV

-Original Message-
From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of JC
Sent: Friday, October 23, 2015 5:58 AM
To: 'topband'
Subject: Re: Topband: ADC Overload from MW transmitters

<< What do we do with them?>>

We do what we are!  Gentlemen !giving always a good example.

 Even almost 40 year later worth reading W1BB.

W1BB>>
GENTLEMENT BAND!!??? ---Shall stress the importance of keeping this UNIQUE
band "The GENTLEMEN! Band", as its reputation has been for so many years,
just that ?? We're having sum "growing pains" with big influx of New-Comers,
who are not yet thoroughly steeped, (and maybe never will be), in the
tradition of the band, or cognizant of the advantages to themselves, and to
ALL, to keep it so!! SEEMS that each one of us who enjoys these unique
advantages, and the thrill of 160, should want to, individually, help to
keep it this way -- by contributing all the "input" in the direction we are
in - by welcoming, educating, befriending, exhibiting a good example, and
Wining the same support from these new-Comers. Meanwhile being sure of our
own motives, and the example we give is correct and right - to acknowledge
our own mistakes, and not make them twice. As "Gentlemen" of 160, shouldn't
we try to MINIMIZE the bickering between CW/PHONE, and to find ways to
cooperate with each other in eliminating friction and QRM??? By meticulously
RESPECTING the "Gentlemen's Agreement" that 1800-10 would be CW
--1810-25/SSB --1825-30 the "DX Window" 1830-1850/SSB and CW. Seems like
a really Gud set-up, especially for phone., since all other bands do not
have an exclusive phone segment!!! BUT we must remember that NO-ONE has any
"LEGAL" requirement to respect these Fys - this "Gents" partitioning,
because the "status" of the band --- it is really NOT an Amateur Band at
all!!! It is a Govt/Services (USCG/LORAN) band, wherein we Amateurs have the
PRIVILEGE only of operating there, IF we cause no QRM to the Govt Services.
For this reason it cannot be, and is not legally partitioned into PHONE/CW
segments. SO that, our only hope of "order" is in this so called
"Gentlemen's Agreement SOOOooo.! one MUST NOT tell either CW,AM,SSB stns to
"get the Hout of there". In the first place, it is the wrong approach
anyway! Secondly, each one had as much RIGHT to be ANYWHERE he wish' as
anyone else. It is a problem of educating to the advantages and winning
everyone's RESPECT for these frequencies! -- -- My experience over many
years, is that 99% of the 160m men are real good guys, ready & willing to
cooperate, for the good of all, IF they are treated fairly and with RESPECT.
We've run across only a few selfish, cantankerous and sour individuals, who
insist on their "Rights", regardless of how much it hurts the other 99% ---
One must exercise a LOT of restraint, patience, perseverance when this
happens, not to be "Touchy", or over sensitive, with these QRMers,
understanding that outside of the two or three "stinkers", the .problem in
mostly through ignorance carelessness, and not intentional. We have to
CONTINUALLY educate and help them and each other. REGARDING the two or three
"Stinkers", the INTENTIONAL QRMers, with their strings of dots/dashes on Fy,
swishes, modulated noises intentionally calling CQ on DX/Fys, In Window, etc
(See-QST/MAR p9, "Malicious QRM") Even here my experience is that "patience
has its reward". The BEST WAY to handle them is TO PAY NO ATTENTION
WHATSOEVER NOT EVEN MENTION it or them over the air. Me while, not
accomplishing their mission of causing trouble, annoying, or "Stirring Up A
Hornets Nest' they get tired and go away. -- The WORST thing to do is to
TAKE NOTICE of them, talk about them, call them names, retaliate, etc - this
is JUST what they are striving for To make acknowledgement of the trouble
they are causing, only makes a bad matter worse (This applies only to the
INTENTIONAL QRMers) (Others, it is helpful to acknowledge and try to help.)
One of those "Stinkers" on the West Coast has been caught and punished
severely. There'll be others surely, as we perfect means of detection and
"coping". Additionally, "Stinkerism" has its own reward!! Many New-Comers to
160 are heard to say what a difference and pleasure it is to operate on 160,
compared to HF bands. Let's keep it that way!! We can, with patience,
perseverance, tact and understanding. OK?? Comments??
<<

73's
JC
N4IS



_
Topband Reflector Archives - http://www.contesting.com/_topband

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Mike Waters]

Great advice indeed.

On Fri, Oct 23, 2015 at 7:57 AM, JC  wrote:

> The BEST WAY to handle them is TO PAY NO ATTENTION WHATSOEVER NOT EVEN
> MENTION it or them ... The WORST thing to do is to TAKE NOTICE of them,
> talk about them, call them names, retaliate, etc.   acknowledgement ...
> only makes a bad matter worse
>

73, Mike
www.w0btu.com
_
Topband Reflector Archives - http://www.contesting.com/_topband

Topband: ADC Overload from MW transmitters

[K1FZ-Bruce]

Thanks for the reminder JC. 
  Remember. 160 meters was not included in most ham gear not so 
long ago. It's a gift we should treasure. 
 

73
Bruce-k1fz
 
BOG antenna notes have been updated at a new address.   
www.qsl.net/k1fz/bogantennanotes.html

 
 

On Fri, 23 Oct 2015 08:57:38 -0400, JC  wrote:

  >

We do what we are! Gentlemen ! giving always a good example. 

Even almost 40 year later worth reading W1BB. 



_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Gary Smith]

Hear Hear!

Gary
KA1J

> I vote you take your contentious attitude somewhere else MIKE DURKIN
> 
> Cecil
> K5DL
> 
> Sent using recycled electrons.
> 
> > On Oct 20, 2015, at 1:07 AM, MIKE DURKIN <patriot...@msn.com> wrote:
> > 
> > Come on Bill ...  did i say you did ?
> >> also-- I did not put forth any opinion about ADC or SDR.
> > 
> > Now, you said that you always read well written info from Tom, I didn't see 
> > that structure ... 
> > Id like to know what SDR was so poor.
> > 
> > SPAM SPAM SPAM SPAM ... (with a guys voice trying to sound like a old 
> > woman) Flying Circus any one?
> > 
> > 
> >> From: bayc...@mediacombb.net
> >> To: patriot...@msn.com; topband@contesting.com
> >> Subject: Re: Topband: ADC Overload from MW transmitters
> >> Date: Tue, 20 Oct 2015 00:52:15 -0500
> >> 
> >> Mike--
> >> It is obvious that you do not know who Tom is.
> >> and-- the word SPAM followed by six exclamation points IS an expletive. 
> >> also-- I did not put forth any opinion about ADC or SDR.
> >> Bill--W4BSG
> >> 
> >> -Original Message- 
> >> From: MIKE DURKIN
> >> Sent: Tuesday, October 20, 2015 12:07 AM
> >> To: topband@contesting.com
> >> Subject: Re: Topband: ADC Overload from MW transmitters
> >> 
> >> If i must 
> >> 
> >> Tom never mentioned what type of SDR would be wiped out by moderate 
> >> signals 
> >> ...
> >> 
> >> That in its self has three problems ...
> >> 
> >> NO filtering? (should this be called -- comparing apples to apples, not 
> >> apples to turds)
> >> poor ADC (real cheap soundcard 8bit)?
> >> insanely bad phase error in the nearby transmitter OR the wonderfull SDR 
> >> that he built.
> >> 
> >> Nearly the entire email was lamented as a setup for a flame war by simply 
> >> omitting details ... that is not the actions of a good engineering radio 
> >> operator ... hence ... SPAM. -- it was a showing off the effort put into 
> >> the 
> >> SDR i guess.
> >> 
> >> And i worry about you Bill  the word "SPAM" being an expletive in your 
> >> vocabulary ...
> >> 
> >> I think of many responses on here to ADC overload as this -- 
> >> 
> >> When dealing with a computer .. the quality of work/info put into it will 
> >> have the same ratio that you will get out of it -- qubed.
> >> 
> >> how many samples per second are true overload  and i mean overload --  
> >> not phase error -- if you don't know the difference you really shouldn't 
> >> put 
> >> forth an opinion as truth.
> >> 
> >> That video that was posted in this discussion(awhile ago) did point out 
> >> the 
> >> difference quite well and understandable by almost anyone .. check it out, 
> >> if not again.
> >> 
> >> Not sure if i should really send this .. but, what the hell.
> >> 
> >> 
> >> 
> >> 
> >>> From: bayc...@mediacombb.net
> >>> To: patriot...@msn.com; topband@contesting.com
> >>> Date: Mon, 19 Oct 2015 17:41:41 -0500
> >>> Subject: Re: Topband: ADC Overload from MW transmitters
> >>> 
> >>> 
> >>> 
> >>> -Original Message- 
> >>> From: MIKE DURKIN
> >>> Sent: Monday, October 19, 2015 10:47 AM
> >>> To: topband@contesting.com
> >>> Subject: Re: Topband: ADC Overload from MW transmitters
> >>> 
> >>> SPAM !!
> >>> 
> >>> Mike--
> >>> Can you explain this opinion?
> >>> In my experience, almost anything Tom takes the trouble to publish is well
> >>> thought-out and worth reading. Your expletive puzzles me.
> >>> Bill--W4BSG
> >>> 
> >>> 
> >>> ---
> >>> This email has been checked for viruses by Avast antivirus software.
> >>> https://www.avast.com/antivirus
> >>> 
> >>> _
> >>> Topband Reflector Archives - http://www.contesting.com/_topband
> >> 
> >> _
> >> Topband Reflector Archives - http://www.contesting.com/_topband 
> >> 
> >> 
> >> ---
> >> This email has been checked for viruses by Avast antivirus software.
> >> https://www.avast.com/antivirus
> > 
> > _
> > Topband Reflector Archives - http://www.contesting.com/_topband
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
> 




---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Doug Renwick]

Ahhh, the social justice warriors (SJW) have arrived.  What do we do with
them?
Doug 

-Original Message-

Hear Hear!

Gary
KA1J

> I vote you take your contentious attitude somewhere else MIKE DURKIN
> 
> Cecil
> K5DL
> 
> Sent using recycled electrons.
> 
> > On Oct 20, 2015, at 1:07 AM, MIKE DURKIN <patriot...@msn.com> wrote:
> > 
> > Come on Bill ...  did i say you did ?
> >> also-- I did not put forth any opinion about ADC or SDR.
> > 
> > Now, you said that you always read well written info from Tom, I didn't
see that structure ... 
> > Id like to know what SDR was so poor.
> > 
> > SPAM SPAM SPAM SPAM ... (with a guys voice trying to sound like a old
woman) Flying Circus any one?
> > 
> > 
> >> From: bayc...@mediacombb.net
> >> To: patriot...@msn.com; topband@contesting.com
> >> Subject: Re: Topband: ADC Overload from MW transmitters
> >> Date: Tue, 20 Oct 2015 00:52:15 -0500
> >> 
> >> Mike--
> >> It is obvious that you do not know who Tom is.
> >> and-- the word SPAM followed by six exclamation points IS an expletive.

> >> also-- I did not put forth any opinion about ADC or SDR.
> >> Bill--W4BSG
> >> 
> >> -Original Message- 
> >> From: MIKE DURKIN
> >> Sent: Tuesday, October 20, 2015 12:07 AM
> >> To: topband@contesting.com
> >> Subject: Re: Topband: ADC Overload from MW transmitters
> >> 
> >> If i must 
> >> 
> >> Tom never mentioned what type of SDR would be wiped out by moderate
signals 
> >> ...
> >> 
> >> That in its self has three problems ...
> >> 
> >> NO filtering? (should this be called -- comparing apples to apples, not

> >> apples to turds)
> >> poor ADC (real cheap soundcard 8bit)?
> >> insanely bad phase error in the nearby transmitter OR the wonderfull
SDR 
> >> that he built.
> >> 
> >> Nearly the entire email was lamented as a setup for a flame war by
simply 
> >> omitting details ... that is not the actions of a good engineering
radio 
> >> operator ... hence ... SPAM. -- it was a showing off the effort put
into the 
> >> SDR i guess.
> >> 
> >> And i worry about you Bill  the word "SPAM" being an expletive in
your 
> >> vocabulary ...
> >> 
> >> I think of many responses on here to ADC overload as this -- 
> >> 
> >> When dealing with a computer .. the quality of work/info put into it
will 
> >> have the same ratio that you will get out of it -- qubed.
> >> 
> >> how many samples per second are true overload  and i mean overload
--  
> >> not phase error -- if you don't know the difference you really
shouldn't put 
> >> forth an opinion as truth.
> >> 
> >> That video that was posted in this discussion(awhile ago) did point out
the 
> >> difference quite well and understandable by almost anyone .. check it
out, 
> >> if not again.
> >> 
> >> Not sure if i should really send this .. but, what the hell.
> >> 
> >> 
> >> 
> >> 
> >>> From: bayc...@mediacombb.net
> >>> To: patriot...@msn.com; topband@contesting.com
> >>> Date: Mon, 19 Oct 2015 17:41:41 -0500
> >>> Subject: Re: Topband: ADC Overload from MW transmitters
> >>> 
> >>> 
> >>> 
> >>> -Original Message- 
> >>> From: MIKE DURKIN
> >>> Sent: Monday, October 19, 2015 10:47 AM
> >>> To: topband@contesting.com
> >>> Subject: Re: Topband: ADC Overload from MW transmitters
> >>> 
> >>> SPAM !!
> >>> 
> >>> Mike--
> >>> Can you explain this opinion?
> >>> In my experience, almost anything Tom takes the trouble to publish is
well
> >>> thought-out and worth reading. Your expletive puzzles me.
> >>> Bill--W4BSG
> >>> 
> >>> 
> >>> ---
> >>> This email has been checked for viruses by Avast antivirus software.
> >>> https://www.avast.com/antivirus
> >>> 
> >>> _
> >>> Topband Reflector Archives - http://www.contesting.com/_topband
> >> 
> >> _
> >> Topband Reflector Archives - http://www.contesting.com/_topband 
> >> 
> >> 
> >> ---
> >> This email has been checked for viruses by Avast antivirus software.
> >> https://www.avast.com/antivirus
> > 
> > _
> > Topband Reflector Archives - http://www.contesting.com/_topband
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
> 




---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_
Topband Reflector Archives - http://www.contesting.com/_topband


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Peter Voelpel]

I guess it was a SDR-1000 or Flex5000

73
Peter

-Original Message-
From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of MIKE
DURKIN
Sent: Dienstag, 20. Oktober 2015 08:08
To: topband@contesting.com
Subject: Re: Topband: ADC Overload from MW transmitters

Come on Bill ...  did i say you did ?
>also-- I did not put forth any opinion about ADC or SDR.

Now, you said that you always read well written info from Tom, I didn't see
that structure ... 
Id like to know what SDR was so poor.

SPAM SPAM SPAM SPAM ... (with a guys voice trying to sound like a old woman)
Flying Circus any one?


> From: bayc...@mediacombb.net
> To: patriot...@msn.com; topband@contesting.com
> Subject: Re: Topband: ADC Overload from MW transmitters
> Date: Tue, 20 Oct 2015 00:52:15 -0500
> 
> Mike--
> It is obvious that you do not know who Tom is.
> and-- the word SPAM followed by six exclamation points IS an expletive. 
> also-- I did not put forth any opinion about ADC or SDR.
> Bill--W4BSG
> 
> -Original Message- 
> From: MIKE DURKIN
> Sent: Tuesday, October 20, 2015 12:07 AM
> To: topband@contesting.com
> Subject: Re: Topband: ADC Overload from MW transmitters
> 
> If i must 
> 
> Tom never mentioned what type of SDR would be wiped out by moderate
signals 
> ...
> 
> That in its self has three problems ...
> 
> NO filtering? (should this be called -- comparing apples to apples, not 
> apples to turds)
> poor ADC (real cheap soundcard 8bit)?
> insanely bad phase error in the nearby transmitter OR the wonderfull SDR 
> that he built.
> 
> Nearly the entire email was lamented as a setup for a flame war by simply 
> omitting details ... that is not the actions of a good engineering radio 
> operator ... hence ... SPAM. -- it was a showing off the effort put into
the 
> SDR i guess.
> 
> And i worry about you Bill  the word "SPAM" being an expletive in your

> vocabulary ...
> 
> I think of many responses on here to ADC overload as this -- 
> 
> When dealing with a computer .. the quality of work/info put into it will 
> have the same ratio that you will get out of it -- qubed.
> 
> how many samples per second are true overload  and i mean overload --

> not phase error -- if you don't know the difference you really shouldn't
put 
> forth an opinion as truth.
> 
> That video that was posted in this discussion(awhile ago) did point out
the 
> difference quite well and understandable by almost anyone .. check it out,

> if not again.
> 
> Not sure if i should really send this .. but, what the hell.
> 
> 
> 
> 
> > From: bayc...@mediacombb.net
> > To: patriot...@msn.com; topband@contesting.com
> > Date: Mon, 19 Oct 2015 17:41:41 -0500
> > Subject: Re: Topband: ADC Overload from MW transmitters
> >
> >
> >
> > -Original Message- 
> > From: MIKE DURKIN
> > Sent: Monday, October 19, 2015 10:47 AM
> > To: topband@contesting.com
> > Subject: Re: Topband: ADC Overload from MW transmitters
> >
> > SPAM !!
> >
> > Mike--
> > Can you explain this opinion?
> > In my experience, almost anything Tom takes the trouble to publish is
well
> > thought-out and worth reading. Your expletive puzzles me.
> > Bill--W4BSG
> >
> >
> > ---
> > This email has been checked for viruses by Avast antivirus software.
> > https://www.avast.com/antivirus
> >
> > _
> > Topband Reflector Archives - http://www.contesting.com/_topband
> 
> _
> Topband Reflector Archives - http://www.contesting.com/_topband 
> 
> 
> ---
> This email has been checked for viruses by Avast antivirus software.
> https://www.avast.com/antivirus
> 
  
_
Topband Reflector Archives - http://www.contesting.com/_topband

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Cecil Acuff]

I vote you take your contentious attitude somewhere else MIKE DURKIN

Cecil
K5DL

Sent using recycled electrons.

> On Oct 20, 2015, at 1:07 AM, MIKE DURKIN <patriot...@msn.com> wrote:
> 
> Come on Bill ...  did i say you did ?
>> also-- I did not put forth any opinion about ADC or SDR.
> 
> Now, you said that you always read well written info from Tom, I didn't see 
> that structure ... 
> Id like to know what SDR was so poor.
> 
> SPAM SPAM SPAM SPAM ... (with a guys voice trying to sound like a old woman) 
> Flying Circus any one?
> 
> 
>> From: bayc...@mediacombb.net
>> To: patriot...@msn.com; topband@contesting.com
>> Subject: Re: Topband: ADC Overload from MW transmitters
>> Date: Tue, 20 Oct 2015 00:52:15 -0500
>> 
>> Mike--
>> It is obvious that you do not know who Tom is.
>> and-- the word SPAM followed by six exclamation points IS an expletive. 
>> also-- I did not put forth any opinion about ADC or SDR.
>> Bill--W4BSG
>> 
>> -Original Message- 
>> From: MIKE DURKIN
>> Sent: Tuesday, October 20, 2015 12:07 AM
>> To: topband@contesting.com
>> Subject: Re: Topband: ADC Overload from MW transmitters
>> 
>> If i must 
>> 
>> Tom never mentioned what type of SDR would be wiped out by moderate signals 
>> ...
>> 
>> That in its self has three problems ...
>> 
>> NO filtering? (should this be called -- comparing apples to apples, not 
>> apples to turds)
>> poor ADC (real cheap soundcard 8bit)?
>> insanely bad phase error in the nearby transmitter OR the wonderfull SDR 
>> that he built.
>> 
>> Nearly the entire email was lamented as a setup for a flame war by simply 
>> omitting details ... that is not the actions of a good engineering radio 
>> operator ... hence ... SPAM. -- it was a showing off the effort put into the 
>> SDR i guess.
>> 
>> And i worry about you Bill  the word "SPAM" being an expletive in your 
>> vocabulary ...
>> 
>> I think of many responses on here to ADC overload as this -- 
>> 
>> When dealing with a computer .. the quality of work/info put into it will 
>> have the same ratio that you will get out of it -- qubed.
>> 
>> how many samples per second are true overload  and i mean overload --  
>> not phase error -- if you don't know the difference you really shouldn't put 
>> forth an opinion as truth.
>> 
>> That video that was posted in this discussion(awhile ago) did point out the 
>> difference quite well and understandable by almost anyone .. check it out, 
>> if not again.
>> 
>> Not sure if i should really send this .. but, what the hell.
>> 
>> 
>> 
>> 
>>> From: bayc...@mediacombb.net
>>> To: patriot...@msn.com; topband@contesting.com
>>> Date: Mon, 19 Oct 2015 17:41:41 -0500
>>> Subject: Re: Topband: ADC Overload from MW transmitters
>>> 
>>> 
>>> 
>>> -Original Message- 
>>> From: MIKE DURKIN
>>> Sent: Monday, October 19, 2015 10:47 AM
>>> To: topband@contesting.com
>>> Subject: Re: Topband: ADC Overload from MW transmitters
>>> 
>>> SPAM !!
>>> 
>>> Mike--
>>> Can you explain this opinion?
>>> In my experience, almost anything Tom takes the trouble to publish is well
>>> thought-out and worth reading. Your expletive puzzles me.
>>> Bill--W4BSG
>>> 
>>> 
>>> ---
>>> This email has been checked for viruses by Avast antivirus software.
>>> https://www.avast.com/antivirus
>>> 
>>> _
>>> Topband Reflector Archives - http://www.contesting.com/_topband
>> 
>> _
>> Topband Reflector Archives - http://www.contesting.com/_topband 
>> 
>> 
>> ---
>> This email has been checked for viruses by Avast antivirus software.
>> https://www.avast.com/antivirus
> 
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Steve Ireland]

Hi Jim

Clearly in a large US city, there is going to be a whole larger degree of 
difficulty than here. 

Perth is still pretty much a small city in world terms, with a population of 
about 2 million. In addition to the ABC transmitters, we have about half a 
dozen other transmitters, but only two of these have signals of any size – 6PR 
(10kW) and 6IX (2kW), with the former of these putting in the largest signal to 
me, with its transmitter/antenna on the banks of the Swan River estuary about 
15km away.

When I used my HPSDR, originally I had no filtering in front of the ADC and had 
some overload problems on 160m from the local BC stations. However, a simple 
Chebyshev HPF got rid of this. Later when I added the Alex bandpass filters, 
which are part of the HPSDR design, there was no longer any need for the HPF.

The main point, as Phil says in his post, is that the amount of protection an 
ADC is going to need will vary widely, depending on factors such as local AM BC 
transmitters and how strong they are. In my case, all I had to do was to use 
the general coverage facility of the SDR to look at the medium wave here, see 
which of the signals were largest and look for a suitable HPF design 
accordingly .

Vy 73

Steve, VK6VZ



> That's typical of medium-size cities in the US for high power broadcasters, 
> but major cities typically have twice as many. Both large and medium-size 
> cities, as well as smaller ones, typically have 6-10 stations in the 5kW 
> range, and more in the 1kW range. Chicago is typical of a large city (like 
> New York, Boston, Los Angeles, San Francisco) -- it has 50kW on 670 kHz, 720 
> kHz, 780 kHz, 890 kHz, and 1,000 kHz. There's also a daytime only station 
> with 50kW on 1160 kHz. Cincinnati is typical of smaller cities like 
> Indianapolis, Detroit, Minneapolis, Cleveland, St Louis, and New Orleans, 
> with 2-3 50kW stations and many smaller ones. Cincinnati 50kW stations are on 
> 700 kHz and 1530 kHz. 

I grew up in a small town in WV, with three 5 kW stations within two miles on 
800 kHz, 930 kHz, and 1470 kHz. 

Bottom line -- there's a lot more broadcasting in the US than in most 
countries. 

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Tom W8JI]

I think the problem here is some people read this as a SDR radios never 
overload, or are superior in every case.


Apparently one person thought they were junk because multiple modest 
strength signals would add up to overload them, and that triggered the 
response that was misinterpreted to mean they never overload under any 
condition or were always superior to roofing filtered systems common in 
standard receivers.


In the case I had here, a *single* transmitter totally wiped the SDR out. 
The overload was nothing like the desense or noise in a traditional 
receiver. It just was totally useless. It was useless at any signal spacing, 
because it had no front end selectivity at all that would reduce levels.


For my application, it was useless. It was far worse than a K3, which a few 
kHz spacing would duplex on most antenna combinations. When the K3 (or 
FT1000MP MKV's)  did overload, the overload was a desense or composite noise 
type sound. It would take out noise floor signals worse, be progressively 
less problem for stronger signals, and never be bothered with any antenna 
combinations with strong signals. When the SDR overloaded, it was just 
totally gone for everything, and wider frequency spacing with the local TX 
made absolutely no difference like it does with a normal receiver. I assume 
this was from overflowing the ADC, but it was a very dramatic sounding 
overload.


That, coupled with the fact it did not have a traditional knob and panel 
system and had some transmitter spurs, made it useless here. But that was 
this setup and this application, where a local 1500 watt transmitter within 
a few thousand feet of the RX antennas was being used while receiving. This 
was a single transmitter multi-op, where one TX signal was allowed on the 
air at a time but two or more operators were making contacts.


I still never find any SDR I listened to, even that one without a 
transmitter running, better than analog detection for my ears on 
"in-the-noise" signals.


73 Tom








- Original Message - 
From: "Steve Ireland" <vk...@arach.net.au>

To: <topband@contesting.com>
Sent: Monday, October 19, 2015 8:07 AM
Subject: Re: Topband: ADC Overload from MW transmitters



Hi Jim

Clearly in a large US city, there is going to be a whole larger degree of 
difficulty than here.


Perth is still pretty much a small city in world terms, with a population 
of about 2 million. In addition to the ABC transmitters, we have about 
half a dozen other transmitters, but only two of these have signals of any 
size – 6PR (10kW) and 6IX (2kW), with the former of these putting in the 
largest signal to me, with its transmitter/antenna on the banks of the 
Swan River estuary about 15km away.


When I used my HPSDR, originally I had no filtering in front of the ADC 
and had some overload problems on 160m from the local BC stations. 
However, a simple Chebyshev HPF got rid of this. Later when I added the 
Alex bandpass filters, which are part of the HPSDR design, there was no 
longer any need for the HPF.


The main point, as Phil says in his post, is that the amount of protection 
an ADC is going to need will vary widely, depending on factors such as 
local AM BC transmitters and how strong they are. In my case, all I had to 
do was to use the general coverage facility of the SDR to look at the 
medium wave here, see which of the signals were largest and look for a 
suitable HPF design accordingly .


Vy 73

Steve, VK6VZ



That's typical of medium-size cities in the US for high power 
broadcasters, but major cities typically have twice as many. Both large 
and medium-size cities, as well as smaller ones, typically have 6-10 
stations in the 5kW range, and more in the 1kW range. Chicago is typical 
of a large city (like New York, Boston, Los Angeles, San Francisco) -- it 
has 50kW on 670 kHz, 720 kHz, 780 kHz, 890 kHz, and 1,000 kHz. There's 
also a daytime only station with 50kW on 1160 kHz. Cincinnati is typical 
of smaller cities like Indianapolis, Detroit, Minneapolis, Cleveland, St 
Louis, and New Orleans, with 2-3 50kW stations and many smaller ones. 
Cincinnati 50kW stations are on 700 kHz and 1530 kHz.


I grew up in a small town in WV, with three 5 kW stations within two miles 
on 800 kHz, 930 kHz, and 1470 kHz.


Bottom line -- there's a lot more broadcasting in the US than in most 
countries.


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_
Topband Reflector Archives - http://www.contesting.com/_topband

-
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2014.0.4830 / Virus Database: 4365/10847 - Release Date: 10/18/15



_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[MIKE DURKIN]

SPAM !!

> From: w...@w8ji.com
> To: topband@contesting.com
> Date: Mon, 19 Oct 2015 10:58:44 -0400
> Subject: Re: Topband: ADC Overload from MW transmitters
> 
> I think the problem here is some people read this as a SDR radios never 
> overload, or are superior in every case.
> 
> Apparently one person thought they were junk because multiple modest 
> strength signals would add up to overload them, and that triggered the 
> response that was misinterpreted to mean they never overload under any 
> condition or were always superior to roofing filtered systems common in 
> standard receivers.
> 
> In the case I had here, a *single* transmitter totally wiped the SDR out. 
> The overload was nothing like the desense or noise in a traditional 
> receiver. It just was totally useless. It was useless at any signal spacing, 
> because it had no front end selectivity at all that would reduce levels.
> 
> For my application, it was useless. It was far worse than a K3, which a few 
> kHz spacing would duplex on most antenna combinations. When the K3 (or 
> FT1000MP MKV's)  did overload, the overload was a desense or composite noise 
> type sound. It would take out noise floor signals worse, be progressively 
> less problem for stronger signals, and never be bothered with any antenna 
> combinations with strong signals. When the SDR overloaded, it was just 
> totally gone for everything, and wider frequency spacing with the local TX 
> made absolutely no difference like it does with a normal receiver. I assume 
> this was from overflowing the ADC, but it was a very dramatic sounding 
> overload.
> 
> That, coupled with the fact it did not have a traditional knob and panel 
> system and had some transmitter spurs, made it useless here. But that was 
> this setup and this application, where a local 1500 watt transmitter within 
> a few thousand feet of the RX antennas was being used while receiving. This 
> was a single transmitter multi-op, where one TX signal was allowed on the 
> air at a time but two or more operators were making contacts.
> 
> I still never find any SDR I listened to, even that one without a 
> transmitter running, better than analog detection for my ears on 
> "in-the-noise" signals.
> 
> 73 Tom
> 
> 
> 
> 
> 
> 
> 
> 
> - Original Message - 
> From: "Steve Ireland" <vk...@arach.net.au>
> To: <topband@contesting.com>
> Sent: Monday, October 19, 2015 8:07 AM
> Subject: Re: Topband: ADC Overload from MW transmitters
> 
> 
> > Hi Jim
> >
> > Clearly in a large US city, there is going to be a whole larger degree of 
> > difficulty than here.
> >
> > Perth is still pretty much a small city in world terms, with a population 
> > of about 2 million. In addition to the ABC transmitters, we have about 
> > half a dozen other transmitters, but only two of these have signals of any 
> > size – 6PR (10kW) and 6IX (2kW), with the former of these putting in the 
> > largest signal to me, with its transmitter/antenna on the banks of the 
> > Swan River estuary about 15km away.
> >
> > When I used my HPSDR, originally I had no filtering in front of the ADC 
> > and had some overload problems on 160m from the local BC stations. 
> > However, a simple Chebyshev HPF got rid of this. Later when I added the 
> > Alex bandpass filters, which are part of the HPSDR design, there was no 
> > longer any need for the HPF.
> >
> > The main point, as Phil says in his post, is that the amount of protection 
> > an ADC is going to need will vary widely, depending on factors such as 
> > local AM BC transmitters and how strong they are. In my case, all I had to 
> > do was to use the general coverage facility of the SDR to look at the 
> > medium wave here, see which of the signals were largest and look for a 
> > suitable HPF design accordingly .
> >
> > Vy 73
> >
> > Steve, VK6VZ
> >
> >
> >
> >> That's typical of medium-size cities in the US for high power 
> >> broadcasters, but major cities typically have twice as many. Both large 
> >> and medium-size cities, as well as smaller ones, typically have 6-10 
> >> stations in the 5kW range, and more in the 1kW range. Chicago is typical 
> >> of a large city (like New York, Boston, Los Angeles, San Francisco) -- it 
> >> has 50kW on 670 kHz, 720 kHz, 780 kHz, 890 kHz, and 1,000 kHz. There's 
> >> also a daytime only station with 50kW on 1160 kHz. Cincinnati is typical 
> >> of smaller cities like Indianapolis, Detroit, Minneapolis, Cleveland, St 
> >> Louis, and New Orleans, with 2-3 50kW stations and

Re: Topband: ADC Overload from MW transmitters

[bruce whitney via Topband]

This has been an interesting discussion.
I heard a rumor that a very prominent and successfully competent multi-multi 
contester in IL was going to an all SDR multiple computer control set-up. Which 
would seem to be problematic in light of this discussion? 
Anyone else hear this?
Bruce W8RA


On Mon, 10/19/15, Tom W8JI <w...@w8ji.com> wrote:

 Subject: Re: Topband: ADC Overload from MW transmitters
 To: topband@contesting.com
 Date: Monday, October 19, 2015, 10:58 AM
 
 I think the problem here is some
 people read this as a SDR radios never 
 overload, or are superior in every case.
 
 Apparently one person thought they were junk because
 multiple modest 
 strength signals would add up to overload them, and that
 triggered the 
 response that was misinterpreted to mean they never overload
 under any 
 condition or were always superior to roofing filtered
 systems common in 
 standard receivers.
 
 In the case I had here, a *single* transmitter totally wiped
 the SDR out. 
 The overload was nothing like the desense or noise in a
 traditional 
 receiver. It just was totally useless. It was useless at any
 signal spacing, 
 because it had no front end selectivity at all that would
 reduce levels.
 
 For my application, it was useless. It was far worse than a
 K3, which a few 
 kHz spacing would duplex on most antenna combinations. When
 the K3 (or 
 FT1000MP MKV's)  did overload, the overload was a
 desense or composite noise 
 type sound. It would take out noise floor signals worse, be
 progressively 
 less problem for stronger signals, and never be bothered
 with any antenna 
 combinations with strong signals. When the SDR overloaded,
 it was just 
 totally gone for everything, and wider frequency spacing
 with the local TX 
 made absolutely no difference like it does with a normal
 receiver. I assume 
 this was from overflowing the ADC, but it was a very
 dramatic sounding 
 overload.
 
 That, coupled with the fact it did not have a traditional
 knob and panel 
 system and had some transmitter spurs, made it useless here.
 But that was 
 this setup and this application, where a local 1500 watt
 transmitter within 
 a few thousand feet of the RX antennas was being used while
 receiving. This 
 was a single transmitter multi-op, where one TX signal was
 allowed on the 
 air at a time but two or more operators were making
 contacts.
 
 I still never find any SDR I listened to, even that one
 without a 
 transmitter running, better than analog detection for my
 ears on 
 "in-the-noise" signals.
 
 73 Tom
 
 
 
 
 
 
 
 
 - Original Message - 
 From: "Steve Ireland" <vk...@arach.net.au>
 To: <topband@contesting.com>
 Sent: Monday, October 19, 2015 8:07 AM
 Subject: Re: Topband: ADC Overload from MW transmitters
 
 
 > Hi Jim
 >
 > Clearly in a large US city, there is going to be a
 whole larger degree of 
 > difficulty than here.
 >
 > Perth is still pretty much a small city in world terms,
 with a population 
 > of about 2 million. In addition to the ABC
 transmitters, we have about 
 > half a dozen other transmitters, but only two of these
 have signals of any 
 > size – 6PR (10kW) and 6IX (2kW), with the former of
 these putting in the 
 > largest signal to me, with its transmitter/antenna on
 the banks of the 
 > Swan River estuary about 15km away.
 >
 > When I used my HPSDR, originally I had no filtering in
 front of the ADC 
 > and had some overload problems on 160m from the local
 BC stations. 
 > However, a simple Chebyshev HPF got rid of this. Later
 when I added the 
 > Alex bandpass filters, which are part of the HPSDR
 design, there was no 
 > longer any need for the HPF.
 >
 > The main point, as Phil says in his post, is that the
 amount of protection 
 > an ADC is going to need will vary widely, depending on
 factors such as 
 > local AM BC transmitters and how strong they are. In my
 case, all I had to 
 > do was to use the general coverage facility of the SDR
 to look at the 
 > medium wave here, see which of the signals were largest
 and look for a 
 > suitable HPF design accordingly .
 >
 > Vy 73
 >
 > Steve, VK6VZ
 >
 >
 >
 >> That's typical of medium-size cities in the US for
 high power 
 >> broadcasters, but major cities typically have twice
 as many. Both large 
 >> and medium-size cities, as well as smaller ones,
 typically have 6-10 
 >> stations in the 5kW range, and more in the 1kW
 range. Chicago is typical 
 >> of a large city (like New York, Boston, Los
 Angeles, San Francisco) -- it 
 >> has 50kW on 670 kHz, 720 kHz, 780 kHz, 890 kHz, and
 1,000 kHz. There's 
 >> also a daytime only station with 50kW on 1160 kHz.
 Cincinnati is typical 
 >> of smaller cities like Indianapolis, Detroit,
 Minneapolis, Cleveland, St 
 >> Louis, and New Orleans, wit

Re: Topband: ADC Overload from MW transmitters

[Tom W8JI]

I'm still of the opinion --right or wrong-- that there will *always* be
hams using analog technology that will be able to out-hear anyone using an
SDR (even DDS) to copy very weak CW signals at the low end of 160. *But I
have an open mind.* I think it was Barry N1EU that disagreed with me on
that (I think he has an Anan DDS SDR). But we need people like him that
drive us to investigate SDR further. :-)


I think it depends on the individual. If an individual has the mental 
ability to "process" noise out of the signal, external filtering and "noise 
reduction" won't mean nearly as much. Some people I've operated with are 
better than I am, some the same, and many others just cannot hear the 
signals unless they are crystal clear.


I'm poor at SSB, but good at tone.

My first experience with this was when a group of people came over to pick 
me up to go to the Cincinnati hamfest. I was working VK's on 160 (using a 
modified SX101) through heavy noise, copying the callsigns fairly easy, but 
no one else could even tell there were signals.


Another case was at Dayton, when MFJ was demonstrating a DSP. I could hear 
the signals the same with or without the DSP, and people walking up were 
marveling. Others walking up couldn't hear the difference.


When a human is part of the decoding system, results will vary.

A similar thing is true for results at different stations, when we talk 
about overload. One size does not fit all applications. I see now where the 
one station's comments about a bunch of modest signals overloading an SDR 
kicked off the "popular folklore" rebuttal, but 1500 watt transmitters into 
antennas less than 2 wavelengths from an RX antenna are not the same as 
something far out of band one or more miles away.


We have to read carefully, and not mix cases.   :)

73 Tom 


_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Mike Waters]

I'm still of the opinion --right or wrong-- that there will *always* be
hams using analog technology that will be able to out-hear anyone using an
SDR (even DDS) to copy very weak CW signals at the low end of 160. *But I
have an open mind.* I think it was Barry N1EU that disagreed with me on
that (I think he has an Anan DDS SDR). But we need people like him that
drive us to investigate SDR further. :-)

Regardless of whether analog or DSP eventually proves superior for digging
the very weakest of CW signals out of the noise, today's SDR technology
still has a place in the serious Topbander's shack. Its auto-notch and
advanced noise blanking features can reduce operator fatigue. Rather than
constantly tuning up and down the band searching, an SDR display
simultaneously displays most of the signals from (for example) 1800 to
1835. And CW Skimmer even takes it beyond that, even displaying all but the
weakest callsigns in the waterfall.

SDR technology is rapidly advancing. I've been trying to learn some of the
concepts of the unbelievably complex mathematics behind DSP software, even
though I don't understand most of it, don't know calculus, or (yet) how FFT
(Fast Fourier Transform) algorithms work their magic. What I've learned so
far almost makes me want to take some online advanced math courses at the
Khan Academy. (Not that it will help me copy anything. :-)

Perhaps what we need is a video of some real-world digital vs. analog
comparisons.

73, Mike
www.w0btu.com

On Mon, Oct 19, 2015 at 9:58 AM, Tom W8JI  wrote:

> I still never find any SDR I listened to, even that one without a
> transmitter running, better than analog detection for my ears on
> "in-the-noise" signals.
>
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Bill Aycock]

-Original Message- 
From: MIKE DURKIN

Sent: Monday, October 19, 2015 10:47 AM
To: topband@contesting.com
Subject: Re: Topband: ADC Overload from MW transmitters

SPAM !!

Mike--
Can you explain this opinion?
In my experience, almost anything Tom takes the trouble to publish is well 
thought-out and worth reading. Your expletive puzzles me.
Bill--W4BSG 



---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[John Bohnovic]

On 10/19/2015 11:59 AM, bruce whitney via Topband wrote:

This has been an interesting discussion.
I heard a rumor that a very prominent and successfully competent multi-multi 
contester in IL was going to an all SDR multiple computer control set-up. Which 
would seem to be problematic in light of this discussion?
Anyone else hear this?
Bruce W8RA

Hi Bruce,

A local told me that a contest station in 9 land was going to replace 
all of his K3(s) with Flex transceivers  and I can't remember the model 
number of the Flex radios he is going to convert too.


73..de John/K4WJ
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[shristov]

Rudy Bakalov via Topband  wrote:

> This is not true - higher sample rates are just as effective in 
> reducing overload as higher bit resolution.
...
> The higher sample rates reduces the probability of multiple signals 
> happening at the same time and overloading the ADC.


A higher sample rate alone
will not change the probability of overloading the ADC.
The percentage of meaningless samples will stay the same,
and consequences of overloading will not change.

A higher sample rate will help only if:
  a) it results in a higher equivalent bit resolution, and
  b) the input full-scale range is increased so to keep the equivalent LSB 
value at the previous level.


73,

Sinisa YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[MIKE DURKIN]

If i must 

Tom never mentioned what type of SDR would be wiped out by moderate signals ... 

That in its self has three problems ... 

NO filtering? (should this be called -- comparing apples to apples, not apples 
to turds)
poor ADC (real cheap soundcard 8bit)?
insanely bad phase error in the nearby transmitter OR the wonderfull SDR that 
he built.

Nearly the entire email was lamented as a setup for a flame war by simply 
omitting details ... that is not the actions of a good engineering radio 
operator ... hence ... SPAM. -- it was a showing off the effort put into the 
SDR i guess.

And i worry about you Bill  the word "SPAM" being an expletive in your 
vocabulary ... 

I think of many responses on here to ADC overload as this -- 

When dealing with a computer .. the quality of work/info put into it will have 
the same ratio that you will get out of it -- qubed.

how many samples per second are true overload  and i mean overload -- not 
phase error -- if you don't know the difference you really shouldn't put forth 
an opinion as truth.

That video that was posted in this discussion(awhile ago) did point out the 
difference quite well and understandable by almost anyone .. check it out, if 
not again.

Not sure if i should really send this .. but, what the hell.




> From: bayc...@mediacombb.net
> To: patriot...@msn.com; topband@contesting.com
> Date: Mon, 19 Oct 2015 17:41:41 -0500
> Subject: Re: Topband: ADC Overload from MW transmitters
> 
> 
> 
> -Original Message- 
> From: MIKE DURKIN
> Sent: Monday, October 19, 2015 10:47 AM
> To: topband@contesting.com
> Subject: Re: Topband: ADC Overload from MW transmitters
> 
> SPAM !!
> 
> Mike--
> Can you explain this opinion?
> In my experience, almost anything Tom takes the trouble to publish is well 
> thought-out and worth reading. Your expletive puzzles me.
> Bill--W4BSG 
> 
> 
> ---
> This email has been checked for viruses by Avast antivirus software.
> https://www.avast.com/antivirus
> 
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
  
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Jim Brown]

On Mon,10/19/2015 10:07 PM, MIKE DURKIN wrote:

Tom never mentioned what type of SDR would be wiped out by moderate signals ...


Tom cited an SDR wiped out by a VERY STRONG IN-BAND local signal.

73, Jim
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Bill Aycock]

Mike--
It is obvious that you do not know who Tom is.
and-- the word SPAM followed by six exclamation points IS an expletive. 
also-- I did not put forth any opinion about ADC or SDR.

Bill--W4BSG

-Original Message- 
From: MIKE DURKIN

Sent: Tuesday, October 20, 2015 12:07 AM
To: topband@contesting.com
Subject: Re: Topband: ADC Overload from MW transmitters

If i must 

Tom never mentioned what type of SDR would be wiped out by moderate signals 
...


That in its self has three problems ...

NO filtering? (should this be called -- comparing apples to apples, not 
apples to turds)

poor ADC (real cheap soundcard 8bit)?
insanely bad phase error in the nearby transmitter OR the wonderfull SDR 
that he built.


Nearly the entire email was lamented as a setup for a flame war by simply 
omitting details ... that is not the actions of a good engineering radio 
operator ... hence ... SPAM. -- it was a showing off the effort put into the 
SDR i guess.


And i worry about you Bill  the word "SPAM" being an expletive in your 
vocabulary ...


I think of many responses on here to ADC overload as this -- 

When dealing with a computer .. the quality of work/info put into it will 
have the same ratio that you will get out of it -- qubed.


how many samples per second are true overload  and i mean overload --  
not phase error -- if you don't know the difference you really shouldn't put 
forth an opinion as truth.


That video that was posted in this discussion(awhile ago) did point out the 
difference quite well and understandable by almost anyone .. check it out, 
if not again.


Not sure if i should really send this .. but, what the hell.





From: bayc...@mediacombb.net
To: patriot...@msn.com; topband@contesting.com
Date: Mon, 19 Oct 2015 17:41:41 -0500
Subject: Re: Topband: ADC Overload from MW transmitters



-Original Message- 
From: MIKE DURKIN

Sent: Monday, October 19, 2015 10:47 AM
To: topband@contesting.com
Subject: Re: Topband: ADC Overload from MW transmitters

SPAM !!

Mike--
Can you explain this opinion?
In my experience, almost anything Tom takes the trouble to publish is well
thought-out and worth reading. Your expletive puzzles me.
Bill--W4BSG


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_
Topband Reflector Archives - http://www.contesting.com/_topband


_
Topband Reflector Archives - http://www.contesting.com/_topband 



---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Tom W8JI]

If there is one transmitter per band and no duplex, I think it would work 
fine. (If you can get old timers to use knobless radios.) External filters 
would easily correct any problems.


The issue is duplex on one band at high local signal levels, where an 
external filter would be much too complicated.



- Original Message - 
From: "bruce whitney" <zuce...@yahoo.com>

To: <topband@contesting.com>; "Tom W8JI" <w...@w8ji.com>
Sent: Monday, October 19, 2015 11:59 AM
Subject: Re: Topband: ADC Overload from MW transmitters


This has been an interesting discussion.
I heard a rumor that a very prominent and successfully competent multi-multi 
contester in IL was going to an all SDR multiple computer control set-up. 
Which would seem to be problematic in light of this discussion?

Anyone else hear this?
Bruce W8RA


On Mon, 10/19/15, Tom W8JI <w...@w8ji.com> wrote:

Subject: Re: Topband: ADC Overload from MW transmitters
To: topband@contesting.com
Date: Monday, October 19, 2015, 10:58 AM

I think the problem here is some
people read this as a SDR radios never
overload, or are superior in every case.

Apparently one person thought they were junk because
multiple modest
strength signals would add up to overload them, and that
triggered the
response that was misinterpreted to mean they never overload
under any
condition or were always superior to roofing filtered
systems common in
standard receivers.

In the case I had here, a *single* transmitter totally wiped
the SDR out.
The overload was nothing like the desense or noise in a
traditional
receiver. It just was totally useless. It was useless at any
signal spacing,
because it had no front end selectivity at all that would
reduce levels.

For my application, it was useless. It was far worse than a
K3, which a few
kHz spacing would duplex on most antenna combinations. When
the K3 (or
FT1000MP MKV's) did overload, the overload was a
desense or composite noise
type sound. It would take out noise floor signals worse, be
progressively
less problem for stronger signals, and never be bothered
with any antenna
combinations with strong signals. When the SDR overloaded,
it was just
totally gone for everything, and wider frequency spacing
with the local TX
made absolutely no difference like it does with a normal
receiver. I assume
this was from overflowing the ADC, but it was a very
dramatic sounding
overload.

That, coupled with the fact it did not have a traditional
knob and panel
system and had some transmitter spurs, made it useless here.
But that was
this setup and this application, where a local 1500 watt
transmitter within
a few thousand feet of the RX antennas was being used while
receiving. This
was a single transmitter multi-op, where one TX signal was
allowed on the
air at a time but two or more operators were making
contacts.

I still never find any SDR I listened to, even that one
without a
transmitter running, better than analog detection for my
ears on
"in-the-noise" signals.

73 Tom








- Original Message - 
From: "Steve Ireland" <vk...@arach.net.au>

To: <topband@contesting.com>
Sent: Monday, October 19, 2015 8:07 AM
Subject: Re: Topband: ADC Overload from MW transmitters


> Hi Jim
>
> Clearly in a large US city, there is going to be a
whole larger degree of
> difficulty than here.
>
> Perth is still pretty much a small city in world terms,
with a population
> of about 2 million. In addition to the ABC
transmitters, we have about
> half a dozen other transmitters, but only two of these
have signals of any
> size – 6PR (10kW) and 6IX (2kW), with the former of
these putting in the
> largest signal to me, with its transmitter/antenna on
the banks of the
> Swan River estuary about 15km away.
>
> When I used my HPSDR, originally I had no filtering in
front of the ADC
> and had some overload problems on 160m from the local
BC stations.
> However, a simple Chebyshev HPF got rid of this. Later
when I added the
> Alex bandpass filters, which are part of the HPSDR
design, there was no
> longer any need for the HPF.
>
> The main point, as Phil says in his post, is that the
amount of protection
> an ADC is going to need will vary widely, depending on
factors such as
> local AM BC transmitters and how strong they are. In my
case, all I had to
> do was to use the general coverage facility of the SDR
to look at the
> medium wave here, see which of the signals were largest
and look for a
> suitable HPF design accordingly .
>
> Vy 73
>
> Steve, VK6VZ
>
>
>
>> That's typical of medium-size cities in the US for
high power
>> broadcasters, but major cities typically have twice
as many. Both large
>> and medium-size cities, as well as smaller ones,
typically have 6-10
>> stations in the 5kW range, and more in the 1kW
range.

Re: Topband: ADC Overload from MW transmitters

[Jim Brown]

Does that mean "don't bother me with facts, I've made up my mind?"

Tom presented his experience. He's a damn good engineer, so we should 
pay attention to it.


Much earlier in this thread, I observed that most serious contesting 
stations using more than one transmitter will have bandpass filters in 
the RX path, which will, for all practical purposes, eliminate overload 
from signals that are far out of band, but they won't eliminate overload 
from IN-band signals. Two examples of this are 1) two transmitters on 
the same band, as is commonly done by serious competitors in 160M 
contests and by multi-ops in DX contests; and nearly in-band broadcast 
signals, as on 40M and 20M.


Yes, a few contesters are beginning to use the higher quality SDRs (they 
currently own and use Flex 6700s). One group, near me, is working on a 
multi-multi site on a mountain peak in the 3,000 ft range, which they 
plan to operate by remote control. There are serious engineers in the 
group and I suspect they're spending serious bucks on the station, so 
there's no doubt that it will include serious bandpass filtering. :)


I suspect that remote control and the ability to see a bandscope over a 
robust remote link has something to do with their choice of radios.


73, Jim K9YC

On Mon,10/19/2015 8:47 AM, MIKE DURKIN wrote:

SPAM !!


_
Topband Reflector Archives - http://www.contesting.com/_topband

Topband: ADC overload from MW transmitters

[Steve Ireland]

G’day

For those topbanders, who have medium wave stations nearby and are thinking 
about trying a DDC/DUC SDR, you may find the comments below from Phil 
VK6APH/VK6PH (in answer to a query on the Apache Labs reflector a few years 
ago) of interest.

Phil lives line of sight from the Australian Broadcasting Transmitter 
installation in the northern suburbs of Perth. There are three AM transmitters 
there which run 24 hours a day, seven days a week:  
6PB at 10 kW on 585 kHz; 6RN at 20 kW on 810 kHz; and 6WF at 50 kW on 720 kHz, 
so this is a very demanding situation for the various DDC/DUC transceivers, 
including the HPSDR, that Phil uses/designs. 

HPSDR users on topband include Greg ZL3IX and Luke VK3HJ.

--
“Unlike conventional superhets the presence of strong in-band and
out-of-band signals is not necessarily a concern as long as these do not
instantaneously add and overload the ADC.

In fact signals below this level actually improve the overall performance
by adding "dither" to the ADC input.

However, as pointed out by others, once ADC overload has occurred then it
can't be undone with post processing.

The presence of very high signals in the MW broadcast band can be an issue
for some users. In general a HPF will provide enough attenuation to
prevent these signals overloading the ADC.

However, there are still a few issues. When developing the Alex filters
for HPSDR I found that at signal levels of > 0dBm even 2" diameter toroids
would produce measurable IMD products. In which case air wound inductors
would be necessary. The size of these would prevent them being included
in the same enclose as the rest of the radio. Placing these in a separate
enclosure also prevents clocks etc from the radio being picked up.

The issue of MW broadcast overload may not be such an issue when operating
on the HF bands. This depends on the performance of the HF antenna well
away from its intended operating frequency. In my case, I live in
line-of-site from a MW broadcast station. Unless I use a wide band active
loop antenna, or operate on 160m, then I don't require any filtering
before the attenuator/preamp/ADC.

The signals adjacent to the 40m band in Europe have incredible signal
strengths. Depending on the band noise floor an attenuator many be all
that is needed to prevent these signals from causing ADC overload and
still provide an acceptable S/N for the wanted signals. If not, then a high
Q preselector is required.

My experience with supporting hundreds of HPSDR users is that there is no
universal solution. Each users faces a different set of circumstances.

It would appear that the natural frequency response of the *majority* of 
users antennas (plus ATU if used) allows operation on the HF Bands without
the need to use an attenuator or other filters.

Designing a front end that will be overload proof in all circumstances
would be not be cost effective. In which case providing flexible support
for the selection of external filters is the best approach and the one
that HPSDR and Apache have taken.

All of the software that supports HPSDR and Apache products provides an
indication of ADC overload. The KISS Konsole and cuSDR PC software also
displays the entire spectrum from 0-55 MHz so the user can see exactly
what frequency band(s) is responsible for any overload.

73 Phil...VK6APH

--
Enjoyed the recent discussion about ADC overload with DDC/DUC SDRs, in 
particular the number of contributors and the increasing degree of knowledge 
about ADC overload that now exists. 

Vy 73

Steve, VK6VZ

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC overload from MW transmitters

[Jim Brown]

On Sun,10/18/2015 8:59 PM, Steve Ireland wrote:

Phil lives line of sight from the Australian Broadcasting Transmitter 
installation in the northern suburbs of Perth. There are three AM transmitters 
there which run 24 hours a day, seven days a week:
6PB at 10 kW on 585 kHz; 6RN at 20 kW on 810 kHz; and 6WF at 50 kW on 720 kHz,


That's typical of medium-size cities in the US for high power 
broadcasters, but major cities typically have twice as many. Both large 
and medium-size cities, as well as smaller ones, typically have 6-10 
stations in the 5kW range, and more in the 1kW range. Chicago is typical 
of a large city (like New York, Boston, Los Angeles, San Francisco) -- 
it has 50kW on 670 kHz, 720 kHz, 780 kHz, 890 kHz, and 1,000 kHz. 
There's also a daytime only station with 50kW on 1160 kHz. Cincinnati is 
typical of smaller cities like Indianapolis, Detroit, Minneapolis, 
Cleveland, St Louis, and New Orleans, with 2-3 50kW stations and many 
smaller ones. Cincinnati 50kW stations are on 700 kHz and 1530 kHz.


I grew up in a small town in WV, with three 5 kW stations within two 
miles on 800 kHz, 930 kHz, and 1470 kHz.


Bottom line -- there's a lot more broadcasting in the US than in most 
countries.


73, Jim K9YC


_
Topband Reflector Archives - http://www.contesting.com/_topband

Topband: ADC Overload

[Stoskopf]

I always marveled with my TT Orion 1, before I died, on SSB when a very
strong signal was on frequency that often a weak one would stand out in
the noise suppressed band.  Never found out if this was from the DSP or
earlier analog string. N0UU

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Tim Shoppa]

I have used Orions and agree, the NR (not noise blanker) is remarkably
effective for marginal, below the noise level, signals on SSB. This was
definitely DSP techniques.

Other more modern DSP rigs (e.g. K3, Eagle) do not have that exact feature
in their DSP. I'm not saying that K3 and Eagle DSP are bad - just that they
don't work the same magic that the Orion DSP NR does in that particular
situation.

Tim N3QE

On Wed, Oct 14, 2015 at 12:34 PM,  wrote:

> I always marveled with my TT Orion 1, before I died, on SSB when a very
> strong signal was on frequency that often a weak one would stand out in
> the noise suppressed band.  Never found out if this was from the DSP or
> earlier analog string. N0UU
>
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
>
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Barry N1EU]

It might be a matter of terminology, but the technique actually involves
RAISING the AGC Threshold so that gain compression only kicks in on the
strongest signals and there's a linear gain curve for everything below that
level.  From s1 to s9 is a delta of ~48dB, so a full implementation of
K3NA's advice (with HIGH headphone isolation) would involve a threshold set
above s9.

73, Barry N1EU

On Tue, Oct 13, 2015 at 8:18 PM, W5JR Mike  wrote:

> That's exactly how I set mine up. Lower the AGC-T to where the band noise
> and weak/moderately weak signals aren't hitting the threshold. So maybe
> S4-5+ signals do hit the threshold. I'm able to still hear the "at noise
> floor" signals without pain in the ears from strong signals. They're loud,
> but manageable.
>
> tnx
> Mike / W5JR
> Alpharetta GA
>
> > On Oct 13, 2015, at 6:25 PM, Stephen Hicks, N5AC 
> wrote:
> >
> >> On Tue, Oct 13, 2015 at 3:56 PM, Barry N1EU 
> wrote:
> >>
> >> But my main
> >> point here is that a high end xcvr vendor should hopefully not hamstring
> >> the receiver AGC with a lower dynamic range and prevent such techniques.
> >>
> >> Thanks for listening & 73,
> >> Barry N1EU
> >
> > ​You can certainly adjust the levels to whatever suits you -- I threw
> 40dB
> > out as a typical number.  For more dynamic range, you can lower the AGC
> > threshold.  You can, of course, turn it off and have the full dynamic
> > range, but I don't know of anyone that would find this comfortable.​
> >
> > ​73,
> > Steve​
> >
> >
> > Stephen Hicks, N5AC
> > VP Engineering
> > FlexRadio Systems™
> > 4616 W Howard Ln Ste 1-150
> > Austin, TX 78728
> > Phone: 512-535-4713 x205
> > Email: st...@flexradio.com
> > Web: www.flexradio.com
> > Click Here for PGP Public Key
> > 
> >
> >
> >
> > *Tune In Excitement™*
> > PowerSDR™ is a trademark of FlexRadio Systems
> > _
> > Topband Reflector Archives - http://www.contesting.com/_topband
>
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Ward Silver]

Perhaps an alternative analogy would be helpful here...

Each of the many signals can be imagined as its own phasor. One end of 
the phasor is anchored on the origin (0 V) and the other is spinning 
around the origin at the frequency of the signal with a length equal to 
its amplitude.  Since the ADC responds to instantaneous voltage, what 
matters is the vector sum of all those many phasors.  A large number of 
the phasors must align perfectly to add up to extreme voltages that 
overload the ADC.  As you might imagine, this happens very, very rarely 
under most circumstances. Even when it does happen, it only happens for 
a fleeting instant because of the semi-random phase and frequency 
relationships between the phasors.  Thus, Jim's bell curve in which the 
extreme voltage probability is very low.


One caution about circumstances: if there are truly large signals 
present (such as at a multi-multi station or near an AM or SW broadcast 
station) many fewer phasors must align to create the overload voltage 
and so the overload happens more frequently. Still, the alignment is 
quite brief and after the raw sample set is decimated, overloads lasting 
for just a few samples or less don't have a lot of effect.


73, Ward N0AX

On 10/14/2015 11:00 AM, topband-requ...@contesting.com wrote:

My example considered an SDR transceiver that received two signals, each with 
instantaneous RF voltage that varied from +3V to -3V, and for simplicity I 
assumed each signal could have only seven values spanning this range. I didn't 
make it clear that these are independent signals on different frequencies. Thus 
every time the ADC in an SDR samples the voltage sum of the two signals at its 
input, it will get a different result. For example, with one sample the SDR may 
see a voltage of +1V, which comes from +2V from one signal and -1V from the 
other signal. A later sample might produce a voltage of -2V, which could come 
from +1V from one signal and -3V from the other. In other words, with each 
sample, the SDR will measure a different voltage, because the signals have 
different frequencies and are not in phase with each other.

Suppose now that we let the SDR sample the voltage a million times, one after 
another. Then the Central Limit Theorem tells us how those million measurements 
will be distributed, in other words how many times the SDR will measure 6V, 5V, 
4V...0...-4V,-5V,and -6V.  What the CLT tells us is that the distribution of 
these measurements generally follow a bell-shaped curve, with the peak at 0V. 
This means that most of the time, the SDR will measure approximately 0V at its 
input. Only infrequently will it measure the large +6V and -6V voltages, 
because those large voltages are at the extreme edges of the bell-shaped 
distribution.


_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[W5JR Mike]

Yes, *raise* the trigger threshold. 

tnx
Mike / W5JR
Alpharetta GA

> On Oct 14, 2015, at 5:44 AM, Barry N1EU  wrote:
> 
> It might be a matter of terminology, but the technique actually involves
> RAISING the AGC Threshold so that gain compression only kicks in on the
> strongest signals and there's a linear gain curve for everything below that
> level.  From s1 to s9 is a delta of ~48dB, so a full implementation of
> K3NA's advice (with HIGH headphone isolation) would involve a threshold set
> above s9.
> 
> 73, Barry N1EU
> 
>> On Tue, Oct 13, 2015 at 8:18 PM, W5JR Mike  wrote:
>> 
>> That's exactly how I set mine up. Lower the AGC-T to where the band noise
>> and weak/moderately weak signals aren't hitting the threshold. So maybe
>> S4-5+ signals do hit the threshold. I'm able to still hear the "at noise
>> floor" signals without pain in the ears from strong signals. They're loud,
>> but manageable.
>> 
>> tnx
>> Mike / W5JR
>> Alpharetta GA
>> 
 On Oct 13, 2015, at 6:25 PM, Stephen Hicks, N5AC 
>>> wrote:
>>> 
 On Tue, Oct 13, 2015 at 3:56 PM, Barry N1EU 
>> wrote:
 
 But my main
 point here is that a high end xcvr vendor should hopefully not hamstring
 the receiver AGC with a lower dynamic range and prevent such techniques.
 
 Thanks for listening & 73,
 Barry N1EU
>>> 
>>> ​You can certainly adjust the levels to whatever suits you -- I threw
>> 40dB
>>> out as a typical number.  For more dynamic range, you can lower the AGC
>>> threshold.  You can, of course, turn it off and have the full dynamic
>>> range, but I don't know of anyone that would find this comfortable.​
>>> 
>>> ​73,
>>> Steve​
>>> 
>>> 
>>> Stephen Hicks, N5AC
>>> VP Engineering
>>> FlexRadio Systems™
>>> 4616 W Howard Ln Ste 1-150
>>> Austin, TX 78728
>>> Phone: 512-535-4713 x205
>>> Email: st...@flexradio.com
>>> Web: www.flexradio.com
>>> Click Here for PGP Public Key
>>> 
>>> 
>>> 
>>> 
>>> *Tune In Excitement™*
>>> PowerSDR™ is a trademark of FlexRadio Systems
>>> _
>>> Topband Reflector Archives - http://www.contesting.com/_topband
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Barry N1EU]

Thanks Mike for explaining the context!  I've done extensive weak signal
listening with an Apache Labs ANAN-100D (DDC SDR running OpenHPSDR
software/firmware) compared with a slew of highly regarded analog and
hybrid (dsp i.f.) receivers and if anything, the SDR betters them
slightly.  My subjective impression is also that the DDC SDR sounds
slightly "cleaner" with slightly less "grundge".

And a response to one of Mark's comments - the filter shaping in the DDC
SDR is not normally brickwall shaped.  The shape is configurable by
selecting dsp buffer size and there's a trade-off between receive latency
and filter slope - see http://anan-100d.wikidot.com/100d-buffer for
passband plots - my dsp filter slopes are on par with xtal filter slopes.

73, Barry N1EU

On Tue, Oct 13, 2015 at 1:35 AM, Mike Waters  wrote:

> Hi Barry,
>
> Thanks for your input. Yes, I believe we included direct sampling digital
> receivers (SDR) versus superhet receivers.
>
> The post I made here today is not complete; rather that re-post
> everything, I included a link to the early August discussion, which
> explained in detail what I meant. This is what I asked:
>
> "I'd like to know whether it's ever been established that some very
> talented
> hams can out-hear the best SDRs and/or DSP available. Can a skilled
> ear-brain combo (such as some highly-skilled and talented 160 meter
> contesters) beat state-of-the art digital signal processing when it comes
> to copying the very weakest of signals buried in the noise?
>
> "I always thought Linrad was the best DSP software, though I never got it
> working right here (older sound card issues in Xubuntu).
>
> "I asked the following question at
>
> http://www.eham.net/ehamforum/smf/index.php?topic=104388.msg861047#msg861047
> : "Are there any people who can hear weak signals with a good analog
> receiver, who --if they could instantly switch their antenna and headphones
> from the analog RX over to the best SDR made today-- simply couldn't hear
> any better with today's best SDRs and/or DSP software?"
>
> "There's been a few opinions, but how about multiple valid tests?"
>
> There were a number of replies, both on the Linrad and the Topband
> reflectors. Sounds like you don't agree with most. What direct-sampling
> receiver did you mean?
>
> 73, Mike
> www.w0btu.com
>
> On Mon, Oct 12, 2015 at 6:53 PM, Barry N1EU  wrote:
>
>> On Mon, Oct 12, 2015 at 10:28 PM, Mike Waters  wrote:
>>
>> > But as a recent thread here* established, there is *NO* SDR that can
>> > perform as
>> > well as a good ear-brain combo for copying the very weakest of signals
>> > buried in the noise. Maybe someday, but the future has not arrived yet.
>> :-)
>> >
>> >
>> The statement is a bit ambiguous.  I don't know what you mean by "SDR" in
>> the statement above.  If you're talking about dsp noise reduction versus
>> no
>> noise reduction, I agree.  But if you're talking about direct sampling
>> digital receivers (SDR) versus superhet receivers, I categorically
>> disagree.
>>
>> 73, Barry N1EU
>>
>
>
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Stephen Hicks, N5AC]

​I though your original post was excellent, Jim, and right on the money.​

On Tue, Oct 13, 2015 at 1:29 PM, Jim Garland <4cx2...@miamioh.edu> wrote:

> Having said that, here's the fly in the ointment. There are several
> assumptions buried in the Central Limit Theorem, so its validity isn't as
> universal as I was suggesting. One assumption is that all these signals
> have to have about the same amplitude. If one signal is vastly stronger
> than the others, as Tom W8JI finds in his contest station, then that will
> dominate the input of the SDR and you won't get this cancellation effect.
>

I showed
​a simulation of ​
this last weekend at DCC -- when the other signal drops to ~10dB below the
first, on first glance the data seen by the ADC looks a lot like just the
one, stronger signal.  This video can be seen here:

https://www.youtube.com/watch?v=CgYtpyNp7hg

Forward in to minute #9 for the start of the discussion or minute #13 to
see the simulation​.

A single strong signal that reaches the overload point of the receiver will
have serious detrimental effects.  These signals will be in the S9+70-80dB
range.  Two signals at this level will also have a serious detrimental
effect requiring them to be 6dB lower than a single signal that would cause
issues.  The answer here is generally to filter signals like this.
Receiver preselectors in the front of the radio are designed to knock
signals like this down 20-30dB.  I think it should be rare to have a
co-located signal that would be in the S9+90dB range that would not be
helped by a preselector.  But, when you have multiple operators on the same
band, you lose the benefit of a preselector and have to rely, instead, on
station design, stubs, etc. to increase antenna isolation.  W2VJN's book is
an excellent reference on dealing with interference locally.


> Similarly, if you have a really strong AM broadcast station near your QTH,
> then that could still overload the ADC in your SDR transceiver. Keep in
> mind that the Central Limit Theorem is a complex mathematical statement
> whose validity is only as good as the validity of its underlying
> assumptions. To me, the CLT provides a ballpark guess as to how an SDR will
> perform, but it shouldn't be taken too literally. The real world has a
> habit of not conforming to mathematical theorems!
>

​Agreed.  AM broadcast can be a especially difficult to deal with because
of the amplitudes involved.  A HPF below 160m is a good solution.  Our
radios all have this, but the filter is removed if you tune below 1.8MHz
(because your intention appears to be to look at the broadcast band rather
than reject it)​.  I don't believe a broadcast filter is generally used in
a superhet because they require bandpass filters and the bandpass filters
necessarily filter the broadcast band too.


>
> As I've thought more about this issue, I think a key advantage of an SDR
> actually comes, not just from the cancellation effect, but from the fact
> that an SDR has no front-end RF amplifier or subsequent IF amplifiers.
>

​The presence of a front-end amplifier does vary by design -- some designs
have an amplifier in front of the data converter.  The typical NF of a data
converter in this frequency range is 20-30dB, but this can be affected by a
transformer on the front of the ADC or an amplifier.  Because the NF
requirement for many HF bands is below that of the converter, many designs
can run without the amplifier which can have benefits as amplifiers can
introduce issues such as distortion and loss of dynamic range.  We use the
AD9467 and generally run without an amplifier, but the amplifier is
required on the higher bands.  Other common designs use the LTC2208/9
family and the recommendation on that ADC is to use an amplifier and so
they typically have one.​

Not having mixers and amplifiers further down the chain (IF) is a clear win
for direct sampling SDRs.


> Basically the HF spectrum goes directly into the SDR's analog-to-digital
> converter. I believe (hope someone can verify this) that modern, fast ADCs
> can handle a volt or more at their inputs without overloading, which gives
> them a tremendous advantage over superhet radios which use high gain RF and
> IF amplfiers.
>

​This is all correct.  The part we use has 2-2.5V peak-to-peak max input
(selectable).  The LTC2209 operates in either 1.5V or 2.25V peak-to-peak
modes.​


> Signals in the millivolt range that fall outside the IF passband in
> conventional superhets won't capture the receiver's AGC and can therefore
> overload or dessense the front end. That won't be a problem with SDR radios
> that can handle a volt or more without overloading their ADC.
>

​Correct.  There is no RF AGC in a typical "good" direct sampling design.
The only AGC that exists is to map the total dynamic range (in excess of
100dB) into the available "comfortable" dynamic range of your ear (the ear
has a total dynamic range of something around 130dB, but for comfortable
listening we assume 

Re: Topband: ADC Overload

[Jim Garland]

Hi Jim and the group,
I apologize for creating confusion in my earlier post about the Central Limit 
Theorem. Let me try to clarify a few points that I glossed over. My example 
considered an SDR transceiver that received two signals, each with 
instantaneous RF voltage that varied from +3V to -3V, and for simplicity I 
assumed each signal could have only seven values spanning this range. I didn't 
make it clear that these are independent signals on different frequencies. Thus 
every time the ADC in an SDR samples the voltage sum of the two signals at its 
input, it will get a different result. For example, with one sample the SDR may 
see a voltage of +1V, which comes from +2V from one signal and -1V from the 
other signal. A later sample might produce a voltage of -2V, which could come 
from +1V from one signal and -3V from the other. In other words, with each 
sample, the SDR will measure a different voltage, because the signals have 
different frequencies and are not in phase with each other. 

Suppose now that we let the SDR sample the voltage a million times, one after 
another. Then the Central Limit Theorem tells us how those million measurements 
will be distributed, in other words how many times the SDR will measure 6V, 5V, 
4V...0...-4V,-5V,and -6V.  What the CLT tells us is that the distribution of 
these measurements generally follow a bell-shaped curve, with the peak at 0V. 
This means that most of the time, the SDR will measure approximately 0V at its 
input. Only infrequently will it measure the large +6V and -6V voltages, 
because those large voltages are at the extreme edges of the bell-shaped 
distribution. If the SDR overloads at, say, +/-6V, then it will only overload 
when the sample measures that extreme voltage, which is not very often. Note 
that this doesn't have anything to do with the AGC action of the radio.

Now, here's where I treated things too glibly in my earlier post. I asserted 
that with more independent signals, as one might find on the entire crowded HF 
spectrum, the distribution of the instantaneous RF voltage from the entire 
spectrum tends to peak sharply at zero volts, which means paradoxically that 
the more signals the radio hears, the more immune to overload it becomes. (The 
explanation of the paradox is that all these signals tend to cancel each other. 
For every positive voltage from one signal there is a negative voltage from 
some other signal.)

Having said that, here's the fly in the ointment. There are several assumptions 
buried in the Central Limit Theorem, so its validity isn't as universal as I 
was suggesting. One assumption is that all these signals have to have about the 
same amplitude. If one signal is vastly stronger than the others, as Tom W8JI 
finds in his contest station, then that will dominate the input of the SDR and 
you won't get this cancellation effect. Similarly, if you have a really strong 
AM broadcast station near your QTH, then that could still overload the ADC in 
your SDR transceiver. Keep in mind that the Central Limit Theorem is a complex 
mathematical statement whose validity is only as good as the validity of its 
underlying assumptions. To me, the CLT provides a ballpark guess as to how an 
SDR will perform, but it shouldn't be taken too literally. The real world has a 
habit of not conforming to mathematical theorems! 

As I've thought more about this issue, I think a key advantage of an SDR 
actually comes, not just from the cancellation effect, but from the fact that 
an SDR has no front-end RF amplifier or subsequent IF amplifiers. Basically the 
HF spectrum goes directly into the SDR's analog-to-digital converter. I believe 
(hope someone can verify this) that modern, fast ADCs can handle a volt or more 
at their inputs without overloading, which gives them a tremendous advantage 
over superhet radios which use high gain RF and IF amplfiers. Signals in the 
millivolt range that fall outside the IF passband in conventional superhets 
won't capture the receiver's AGC and can therefore overload or dessense the 
front end. That won't be a problem with SDR radios that can handle a volt or 
more without overloading their ADC. 
73,
Jim W8ZR


> -Original Message-
> From: James Wolf [mailto:jbw...@comcast.net]
> Sent: Monday, October 12, 2015 9:45 PM
> To: 'Jim Garland'
> Cc: topband@contesting.com
> Subject: RE: Topband: ADC Overload
> 
> Jim,
> 
> I sense a flaw in the CLT argument, which is likely a lack of understanding 
> on my part.
> What you are describing sounds more like AGC action.  In-other-words, moving 
> the
> minimum detector level up the bell curve such that we have now lost any 
> capability of
> listening down into a hole between strong stations and copying the weak 
> station (which is
> really what we are talking about).  That scenario now sounds like a corner 
> case.
> Other wise, what happened to the two +3V stations that a

Re: Topband: ADC Overload

[Barry N1EU]

On Tue, Oct 13, 2015 at 8:26 PM, Stephen Hicks, N5AC 
wrote:

>
> The only AGC that exists is to map the total dynamic range (in excess of
> 100dB) into the available "comfortable" dynamic range of your ear (the ear
> has a total dynamic range of something around 130dB, but for comfortable
> listening we assume something in the order of 40dB.  It is not comfortable
> to strain to hear a weak signal at the bottom volume level only to have a
> strong signal blow your earphones off).​


This is a slight skew in topic but wanted to make a quick comment on the
dynamic range figure Steve.  I hope the Flex 6K AGC provides
configurability for the user to exceed 40dB audio dynamic range if desired.

Back in 2006, there was much interest in understanding why some receivers
seemed to homogenize multiple signals in a calling pileup (use case: you're
calling CQ in a contest or on a dxpedition and many are responding on
frequency).  K3NA in particular published article(s) promoting a technique
to use highly isolating headphones to drastically lower the audio noise
floor, together with high dynamic range receiver audio to provide the
greatest perceived amplitude difference between weaker and stronger calling
stations.  The idea was to have the band noise/weakest signals close to the
hearing threshold and the strongest signals right below the ear's
attenuation reflex level.  I believe the resulting dynamic range that was
targeted was approximately 60dB.  Several contesters implemented K3NA's
technique with good results and improved pileup readability.  But my main
point here is that a high end xcvr vendor should hopefully not hamstring
the receiver AGC with a lower dynamic range and prevent such techniques.

Thanks for listening & 73,
Barry N1EU
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[W5JR Mike]

That's exactly how I set mine up. Lower the AGC-T to where the band noise and 
weak/moderately weak signals aren't hitting the threshold. So maybe S4-5+ 
signals do hit the threshold. I'm able to still hear the "at noise floor" 
signals without pain in the ears from strong signals. They're loud, but 
manageable. 

tnx
Mike / W5JR
Alpharetta GA

> On Oct 13, 2015, at 6:25 PM, Stephen Hicks, N5AC  wrote:
> 
>> On Tue, Oct 13, 2015 at 3:56 PM, Barry N1EU  wrote:
>> 
>> But my main
>> point here is that a high end xcvr vendor should hopefully not hamstring
>> the receiver AGC with a lower dynamic range and prevent such techniques.
>> 
>> Thanks for listening & 73,
>> Barry N1EU
> 
> ​You can certainly adjust the levels to whatever suits you -- I threw 40dB
> out as a typical number.  For more dynamic range, you can lower the AGC
> threshold.  You can, of course, turn it off and have the full dynamic
> range, but I don't know of anyone that would find this comfortable.​
> 
> ​73,
> Steve​
> 
> 
> Stephen Hicks, N5AC
> VP Engineering
> FlexRadio Systems™
> 4616 W Howard Ln Ste 1-150
> Austin, TX 78728
> Phone: 512-535-4713 x205
> Email: st...@flexradio.com
> Web: www.flexradio.com
> Click Here for PGP Public Key
> 
> 
> 
> 
> *Tune In Excitement™*
> PowerSDR™ is a trademark of FlexRadio Systems
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Stephen Hicks, N5AC]

On Tue, Oct 13, 2015 at 3:56 PM, Barry N1EU  wrote:

> But my main
> point here is that a high end xcvr vendor should hopefully not hamstring
> the receiver AGC with a lower dynamic range and prevent such techniques.
>
> Thanks for listening & 73,
> Barry N1EU
>

​You can certainly adjust the levels to whatever suits you -- I threw 40dB
out as a typical number.  For more dynamic range, you can lower the AGC
threshold.  You can, of course, turn it off and have the full dynamic
range, but I don't know of anyone that would find this comfortable.​

​73,
Steve​


Stephen Hicks, N5AC
VP Engineering
FlexRadio Systems™
4616 W Howard Ln Ste 1-150
Austin, TX 78728
Phone: 512-535-4713 x205
Email: st...@flexradio.com
Web: www.flexradio.com
Click Here for PGP Public Key




*Tune In Excitement™*
PowerSDR™ is a trademark of FlexRadio Systems
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Paul Christensen]

>"The favorable SDR averaging doesn't apply when the RF voltage at the receiver 
>input is dominated by one huge signal, and if that signal exceeds the 
>capability of the ADC in the radio, overload can definitely occur. So, 
>although I believe that nearly all manufacturers will soon migrate to superior 
>SDR technology, the "big gun" multi-multi contesters may want to hang onto 
>their old Yaesu/ Icom/Kenwood transceivers (or else use bandpass filters on 
>the inputs of their SDR rigs)!
73, Jim W8ZR"

Nice explanation of CLT in this context, Jim.   So, as you and Tom point out, 
1, 2 or 3 extremely strong stations falling within the wideband SDR input can, 
and does cause severe OL effects in our SDR receivers.  

Then what if we *deliberately* inject hundreds, if not thousands of discrete RF 
carriers into our SDR receivers from say...an internal RF carrier or noise 
generator, mixed with the desired RF signal to mitigate OL caused by a few 
strong carriers?  It would be interesting to see the math and note what, if any 
reasonable limits apply, even if the amount of OL protection is small but there 
nonetheless.  If this is a viable form of OL mitigation, then by now, someone 
must have already addressed this, possibly in an academic or IEEE paper?

Paul, W9AC

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Jim Garland]

, 
there are no more amplifiers to overload! 

As you can probably tell, I'm pretty solidly in the SDR camp. I use a Flex 6300 
(though for contesting I've only used the radio in single-operator contests.) I 
can do A-B comparisons in my station between my Flex 6300, Elecraft K3, and 
Yaesu FTDX5000, and just in terms of raw performance (setting aside the display 
advantages of the Flex) I prefer the Flex 6300 to the other rigs, especially on 
160m. I've never experienced overload problems of any sort. 

However, recall I said that "in most cases" SDR radios are superior to 
conventional superhets. In thinking about Tom W8JI's experience in his 
multi-multi contest environment, I think I can reconcile his SDR overload 
problems with my contrasting favorable experience in my station. In a 
multi-multi contest, the voltage at the input of nearby receivers will be 
dominated by a small number of very strong signals from the nearby QRO 
transmitters, often by only one signal. The favorable SDR averaging doesn't 
apply when the RF voltage at the receiver input is dominated by one huge 
signal, and if that signal exceeds the capability of the ADC in the radio, 
overload can definitely occur. So, although I believe that nearly all 
manufacturers will soon migrate to superior SDR technology, the "big gun" 
multi-multi contesters may want to hang onto their old Yaesu/ Icom/Kenwood 
transceivers (or else use bandpass filters on the inputs of their SDR rigs)!
73,
Jim W8ZR

> -Original Message-
> From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Stephen 
> Hicks,
> N5AC
> Sent: Sunday, October 11, 2015 9:24 AM
> To: topband@contesting.com
> Subject: Topband: ADC Overload
> 
> Rick,
> 
> I hope it's not an issue for me to post here directly.  I am posting here
> because I believe that amateur radio has a huge educational component and
> ultimately incorrect information services no one.  I got started when I was
> 12 and really knew very little about the hobby.  My journey, like most
> hams, has been a long, exciting educational process.  Still, there are so
> many that know so much more than I do.  I am constantly amazed at the
> breadth and depth of the hobby and the people in it.  My points below are
> to clarify what I have observed, calculated and believe to be true and are
> presented in the interest of mutual education:
> 
> On Sun, Oct 11, 2015 at 6:17 AM, wrote:
> 
> >
> > I have no experience with Flex Radio equipment, (it might be great stuff
> > for
> > all I know), so I will confine my comments to the theory discussed in the
> > "ADC overload myths debunked"
> > paper.  A lot of what I read didn't make a lot of sense to me, or seemed
> > irrelevant.
> >
> > To begin with, I'm not sure as to the exact nature of the "myth".
> 
> 
> Recently, a post was made to a reflector that definitively stated that
> direct sampling receivers simply did not function -- that they would
> overload with a minimal number of signals and/or signals of relatively
> small magnitude.
> 
> 
> > Initally,
> > the myth is supposed to be that hams think average power of an ensemble of
> > uncorrelated signals is the sum of the power of the components.  This is
> > not
> > a myth, it is true.  Then it is suggested that hams believe peak voltages
> > add up, as in a 6 dB increase for two signals.  Supposedly, hams don't
> > realize that the high peaks only occur rarely.  I'm not aware of any ham
> > lore exhibiting this misunderstanding.
> 
> 
> > The discussion of crest factor obscures the fact that average power still
> > adds.  100 signals at S9 still has a power of 20 dB over S9, on the
> > average.
> > Once in a while it looks like 40 dB over S9.  The rest of the time, the
> > combined power of all the signals still tests the dynamic range of the
> > receiver.  It's not like a bunch of S9 signals is no worse than a single
> > S9 signal.
> >
> 
> The misunderstanding centers around a belief that an ADC reacts negatively
> to a large average power.  There are two primary beliefs rolled into this
> one: (1) That by taking the sum of any number of known signals in the power
> domain we can reach a total, that when compared with the overload point of
> the ADC, will definitively predict an overload of the ADC, and (2) That the
> overload of an ADC  is a singular and complete event -- when it occurs the
> ADC no longer functions.
> 
> Addressing each of these individually and getting more specific, the first
> (1) belief is that if we have an ADC that overloads at +10dBm, that I can
> take 100 -10dBm signals and completely overload the ADC to a point of
> non-functioning.  This really seems like 

Re: Topband: ADC Overload

[Richard (Rick) Karlquist]

Then what if we *deliberately* inject hundreds, if not thousands of discrete RF 
carriers into our SDR receivers from say...an internal RF carrier or noise 
generator, mixed with the desired RF signal to mitigate OL caused by a few 
strong carriers?  It would be interesting to see the math and note what, if any 
reasonable limits apply, even if the amount of OL protection is small but there 
nonetheless.  If this is a viable form of OL mitigation, then by now, someone 
must have already addressed this, possibly in an academic or IEEE paper?

Paul, W9AC



That roughly describes the FM broadcast band near San Bruno
Mountain, south of San Francisco, which is chock full of
FM transmitter sites.  It is an extremely difficult RF
environment.  The picket fence spectrum definitely is
not beneficial.  Instead, the stations mix with each other
in the receiver front end and fill in any clear channels
with garbage.  I did some consulting for a company that
made FM-SCA receivers and developed an 8 stage voltage tuned
preselector for their receiver that worked as well as
the six stage air variable preselector in my circa 1978
Technic's tuner that sold for $450 at that time.  I also
tried a WJ mixer with 1/2 watt LO drive as the front end
of a superhet, but without a preselector.  There was
no comparison; the non preselected high power mixer
was nowhere near as good as the preselected receivers.
Of course, an ordinary car radio driven near the
mountain is far worse than than any of the above.

At the Maker Faire a couple of years ago, they had
a start up company that was exhibiting an FM receiver
that digitized the entire FM band.  I'd like to see
what that would have done around San Bruno Mountain.

Rick N6RK
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[JC]

Hi Guys

It's well know the ability to copy weak signal near strong carriers. I run a
QS1R using HDSDR all the time shearing the same RX antenna with my IC7800.
In the last 10 years only once I worked a new country on 160 listening on
the SDR that I was not able to copy using the IC7800. David summer was
operating "simplex" from 4U1ITU once on 160m. and the pile up with US and
European station was very  "peculiar" on 1820.00. Everybody on the same
frequency. Yes the SDR is a better receiver but for practical reasons not
the more efficient radio to operate. 

Just have a driver problem with windows and you will find yourself hours
trying to find why the IP address does not match the SDR anymore or other
silly software things that takes hours to fix. 

I was not surprised to know from a good friend that some big contest
stations run DOS PC's!!

Here where the ADC overload gets complicated, when the ADC overload the
noise floor goes up for several seconds(or minutes), plus the pops. On low
bands all receiver antennas has different gain as you move up in frequency.
Like a Flag or beverage gain on 160m is low but the same antenna has  20 db
more gain on 10 MHz. Using the most common high pass filter to reduce AM BC
band bellow 1.8MHz infront a 20 db gain preamp, does not attenuate signals
from broadcast bands near 5 MHz, 7 MHz, 9 Mhz, 11 MHz, etc.  Endeed the
signal can be 40 dBm stronger than it should be in a vertical without
preamp. If the preamp is not tuned or have a band  pass filter after it ,the
problem of overload become a huge one, and you don't even know where the
overload  is coming from. AM BC reduces power during the night but
propagation brings strong signal from HF broadcast at night, specially near
SR and SS. It is not all the same during the day time or during the night.

If you check the top contest results you can find a good reason why the top
stations are using only few Radios models.

Regards
JC
N4IS 





_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Barry N1EU]

On Mon, Oct 12, 2015 at 10:28 PM, Mike Waters  wrote:

> But as a recent thread here* established, there is *NO* SDR that can
> perform as
> well as a good ear-brain combo for copying the very weakest of signals
> buried in the noise. Maybe someday, but the future has not arrived yet. :-)
>
>
The statement is a bit ambiguous.  I don't know what you mean by "SDR" in
the statement above.  If you're talking about dsp noise reduction versus no
noise reduction, I agree.  But if you're talking about direct sampling
digital receivers (SDR) versus superhet receivers, I categorically disagree.

73, Barry N1EU
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Mike Waters]

Hi Barry,

Thanks for your input. Yes, I believe we included direct sampling digital
receivers (SDR) versus superhet receivers.

The post I made here today is not complete; rather that re-post everything,
I included a link to the early August discussion, which explained in detail
what I meant. This is what I asked:

"I'd like to know whether it's ever been established that some very talented
hams can out-hear the best SDRs and/or DSP available. Can a skilled
ear-brain combo (such as some highly-skilled and talented 160 meter
contesters) beat state-of-the art digital signal processing when it comes
to copying the very weakest of signals buried in the noise?

"I always thought Linrad was the best DSP software, though I never got it
working right here (older sound card issues in Xubuntu).

"I asked the following question at
http://www.eham.net/ehamforum/smf/index.php?topic=104388.msg861047#msg861047
: "Are there any people who can hear weak signals with a good analog
receiver, who --if they could instantly switch their antenna and headphones
from the analog RX over to the best SDR made today-- simply couldn't hear
any better with today's best SDRs and/or DSP software?"

"There's been a few opinions, but how about multiple valid tests?"

There were a number of replies, both on the Linrad and the Topband
reflectors. Sounds like you don't agree with most. What direct-sampling
receiver did you mean?

73, Mike
www.w0btu.com

On Mon, Oct 12, 2015 at 6:53 PM, Barry N1EU  wrote:

> On Mon, Oct 12, 2015 at 10:28 PM, Mike Waters  wrote:
>
> > But as a recent thread here* established, there is *NO* SDR that can
> > perform as
> > well as a good ear-brain combo for copying the very weakest of signals
> > buried in the noise. Maybe someday, but the future has not arrived yet.
> :-)
> >
> >
> The statement is a bit ambiguous.  I don't know what you mean by "SDR" in
> the statement above.  If you're talking about dsp noise reduction versus no
> noise reduction, I agree.  But if you're talking about direct sampling
> digital receivers (SDR) versus superhet receivers, I categorically
> disagree.
>
> 73, Barry N1EU
>
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[Mike Waters]

An SDR is better for several things, yes. One advantage is that
near-perfect extremely narrow filters can (and do) exist in software. But
as a recent thread here* established, there is *NO* SDR that can perform as
well as a good ear-brain combo for copying the very weakest of signals
buried in the noise. Maybe someday, but the future has not arrived yet. :-)

*I posted a question here and the Linrad reflector on August 4, and
received many informative replies. Many can be viewed at
lists.contesting.com/_topband/2015-08/msg8.html

73, Mike
www.w0btu.com

On Mon, Oct 12, 2015 at 4:15 PM, JC  wrote:

>
> It's well know the ability to copy weak signal near strong carriers.
> ...Yes the SDR is a better receiver but...
>
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload

[James Wolf]

Jim,

I sense a flaw in the CLT argument, which is likely a lack of understanding on 
my part.  What you are describing sounds more like AGC action.  In-other-words, 
moving the minimum detector level up the bell curve such that we have now lost 
any capability of listening down into a hole between strong stations and 
copying the weak station (which is really what we are talking about).  That 
scenario now sounds like a corner case. 
Other wise, what happened to the two +3V stations that add up to +6V.   Do they 
still show up on the bell curve, and if they no longer add up to +6V, why not?

Thanks for the insight,

Jim - KR9U

-Original Message-
From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Jim Garland
Sent: Monday, October 12, 2015 2:35 PM
To: st...@flexradio.com; topband@contesting.com
Cc: 'K1JD John'; 'Phillip Townsend Lontz'
Subject: Re: Topband: ADC Overload

Interesting comments, Steve, and to me quite on the mark. (In an ealier life, I 
was a physics prof, though I've forgotten most of what I once knew).

Re the comment by another list member that "there are various distractions such 
as the Central Limit Theorem...that don't add much to the discussion":  On the 
contrary, I believe the CLT is actually crucial to this discussion. Here's my 
attempt at an intuitive explanation of the CLT using a _very_ simplified 
example. I hope this contributes to this interesting discussion.

Suppose we have an SDR radio that hears two identical signals, and that the ADC 
in the receiver overloads when the instantaneous antenna voltage at the 
receiver input is greater than +/- 5V. Now let's assume that each of our 
identical signals has a maximum instantaneous RF voltage of +/- 3V, so that the 
receiver will overload when both signals add up to give either +6V or -6V. The 
question that the Central Limit Theorem addresses is how frequently this 
overload condition will occur. Here's how it works.

We'll keep things simple by assuming each of our two signals can take on only 
seven values of voltage: +3V, +2V,+1V, 0V, -1V, -2V, and -3V. (In reality of 
course, for a CW signal, the signals are sine waves varying continuously from 
+3V to -3V.) Every time the SDR samples these signals, it sees the 
instantaneous sum of their voltages. Since each signal has seven possible 
values, the sum of the voltages can have 7x7=49 possible values, which range 
from +6V down to -6V. 

If you make a list of all possible combinations of these two signals, you'll 
find that of the 49 possibilities, 0V comes up seven times, 1V comes up six 
times, 2V comes up 5 times and so forth, until you get to 6V (when the maximum 
value of signal adds up exactly). The reason 0V comes up seven times is because 
there are seven ways to get 0 by adding the voltages from the two signals, 
i.e., 0V plus 0V, +1V plus -1V, -1V plus +1V, +2V plus -2V, -2V plus +2V, +3V 
plus -3V, and -3V plus +3V. By contrast, there is only one way to get +6V, 
which is +3V plus +3V, and similarly for --6V.

Now if the ADC in the receiver overloads at any voltage greater than  +/- 5V, 
as we have assumed, then it will overload only two times in every 49 samples, 
once when the voltage is +6V and once when the voltage is -6V. If you draw a 
graph of all the possible combinations of voltages, plotting the numbers of 
times each combination of voltages comes up, you'll see that the graph 
resembles a bell-shaped curve, (called a "normal" distribution) peaked at zero. 
The maximum values of +6V and -6V are at the tail ends of the distribution.

So in this simplified example, our SDR radio will overload 2 out of every 49 
samples, or about four percent of the time. That's not terrible, but not 
wonderful either. It means that we'd hear a pop in our receiver about four 
percent of the time. But suppose we let our two signals take on a continuous 
range of values between +3V and -3V. instead of only seven possible values. 
Unforunately, things don't get much better. The data points on our bell-shaped 
curve would smooth out, but we'd still overload roughly four percent of the 
time. The general shape of the curve doesn't change.

But...here's the interesting thing. Suppose instead of only two signals, we 
have thousands of signals appearing at our antenna terminals, and we'll 
continue to assume each of our thousands of signals varies from +/- 3V. Now 
when we add up the voltages of each of these signals, we find something 
remarkable. The sums of the voltages of all these signals is still a 
bell-shaped curve peaked at zero volts and extending from +6V down to -6V, but 
with one significant change. The bell-shaped curve narrows in, becoming very 
sharply peaked at 0V. The extremes of the curve, which would overload our 
receiver, almost never happens. This peaking of the curve is what the Central 
Limit Theorem tells us, and basically it is the reason SDR radios are in most 
cases nearly immune from overload. The more s

Topband: ADC Overload

[Stephen Hicks, N5AC]

Rick,

I hope it's not an issue for me to post here directly.  I am posting here
because I believe that amateur radio has a huge educational component and
ultimately incorrect information services no one.  I got started when I was
12 and really knew very little about the hobby.  My journey, like most
hams, has been a long, exciting educational process.  Still, there are so
many that know so much more than I do.  I am constantly amazed at the
breadth and depth of the hobby and the people in it.  My points below are
to clarify what I have observed, calculated and believe to be true and are
presented in the interest of mutual education:

On Sun, Oct 11, 2015 at 6:17 AM, wrote:

>
> I have no experience with Flex Radio equipment, (it might be great stuff
> for
> all I know), so I will confine my comments to the theory discussed in the
> "ADC overload myths debunked"
> paper.  A lot of what I read didn't make a lot of sense to me, or seemed
> irrelevant.
>
> To begin with, I'm not sure as to the exact nature of the "myth".


Recently, a post was made to a reflector that definitively stated that
direct sampling receivers simply did not function -- that they would
overload with a minimal number of signals and/or signals of relatively
small magnitude.


> Initally,
> the myth is supposed to be that hams think average power of an ensemble of
> uncorrelated signals is the sum of the power of the components.  This is
> not
> a myth, it is true.  Then it is suggested that hams believe peak voltages
> add up, as in a 6 dB increase for two signals.  Supposedly, hams don't
> realize that the high peaks only occur rarely.  I'm not aware of any ham
> lore exhibiting this misunderstanding.


> The discussion of crest factor obscures the fact that average power still
> adds.  100 signals at S9 still has a power of 20 dB over S9, on the
> average.
> Once in a while it looks like 40 dB over S9.  The rest of the time, the
> combined power of all the signals still tests the dynamic range of the
> receiver.  It's not like a bunch of S9 signals is no worse than a single
> S9 signal.
>

The misunderstanding centers around a belief that an ADC reacts negatively
to a large average power.  There are two primary beliefs rolled into this
one: (1) That by taking the sum of any number of known signals in the power
domain we can reach a total, that when compared with the overload point of
the ADC, will definitively predict an overload of the ADC, and (2) That the
overload of an ADC  is a singular and complete event -- when it occurs the
ADC no longer functions.

Addressing each of these individually and getting more specific, the first
(1) belief is that if we have an ADC that overloads at +10dBm, that I can
take 100 -10dBm signals and completely overload the ADC to a point of
non-functioning.  This really seems like common sense to most.  We all
fully expect to be able to take 100 disparate signal generators, feed them
through a lossless combiner, read a power meter and see +10dBm and then
stick that in the ADC and overload it.  But this is not how it works.

To understand what actually happens, we have to look at how a discrete
sampled system works.  The ADCs we use are oversampled and run at somewhere
between 100-300MHz.  Each sample period, the ADC essentially takes a
voltage reading on the antenna and records this value, transmitting it to
to the computing element in an SDR.  The instantaneous voltage of any
RF signal varies with the sine wave that defines the RF carrier so it
varies from the bias point of the ADC to the bias plus the voltage
amplitude of the signal, back through the bias point, down to the the bias
minus the amplitude of the signal and back to the bias point each cycle of
the RF signal.  It is a sine wave of given voltage amplitude centered
around the bias point of the ADC.

If I add a second signal of equal amplitude, the second signal will add to
the first and I will get an instantaneous voltage that is the sum of the
two signals. But the voltage is not simply 2x the voltage of the first --
this is only the case if the two signals are on exactly the same frequency,
phase and amplitude.  What actually happens is a beat-note between the two
signals who's envelope oscillates in time at the frequency of the beat note
(difference in frequency of the two signals).  Periodically, the peaks of
the two signals will be exactly aligned and we will get a doubling of the
voltage.  For two signals this happens fairly frequently.  Similar to the
two signals adding, they will also subtract to result in a voltage
magnitude (absolute value) lower than either of the two signals would have
by themselves.  For example, one signal might be at +1V while the other is
at -0.66V.  The resulting voltage measured in the converter, due to linear
superposition, is +0.33V.

Assuming for a moment that the two signals are large compared to the
overload of the ADC, say they are at +7dBm compared to the +10dBm overload
of the converter, they will 

Re: Topband: ADC Overload

[Mike Waters]

I hope it's not, too. :-)

SDR fascinates me, and I intend to experiment with the technology on 160
meters starting with a Softrock Xtall Lite 9.0 and the matching switchable
BPF.

73, Mike
www.w0btu.com

On Sun, Oct 11, 2015 at 10:23 AM, Stephen Hicks, N5AC 
wrote:

>
> I hope it's not an issue for me to post here directly. ...
_
Topband Reflector Archives - http://www.contesting.com/_topband