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. 

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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" 

To: 
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.


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-
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



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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" 
> To: 
> 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 - 

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  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" 
 To: 
 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 

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 


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Re: Topband: [Bulk] Re: ADC Overload from MW transmitters

[Grant Saviers]

Not having any particular axe to grind, I'll pile on a bit with some 
comments.


1.  The superhet/SDR vs direct sampling radio manufacturer and 
technology competition is and will continue to be very good for the ham 
community.


2.  The early days of CD audio yielded, "I can't stand the sound" for 
which there were sound engineering reasons. Today with 24bit 196KHz 
sampling and playback, I think it is impossible to discern that analog 
signals via LP vinyl are technically superior.  However, that won't sway 
a number of folks who "like the sound of analog". Sounding "different" 
will always appeal to some segment Direct Sampling vs superhet/IF DSP vs 
pure superhet.  btw I suspect that the inherent amplitude/phase 
distortions at the audio level of different amateur radio filtering 
techniques affects intelligibility more than is commonly recognized.


3. Unfortunately, the ham radio market isn't currently large enough for 
a major Si firm to design for our needs.  The requirements are driven by 
the cell base station market and perhaps a bit of military needs.  So 
sample rates are going up beyond the current 300 MSPS rather than more 
bits of resolution which would solve the overload concerns.  However, as 
the technology of fast + wide A to D's disperses, there may be a 
boutique firm that takes up the challenge as has happened in the audio 
market where the best A/D's are not made by Analog Devices, TI, or 
Linear Tech.


4. It seems that the overload issue is now confined by consensus to 
duplex operations on the same band since high pass and bandpass filters 
and stubs take care of most BCB/MW/multi multi overload situations.  I 
agree that overload otherwise is a minor concern.


5. As always there will be a range of good and not as good 
implementations of technologies.  Also, the terminology of "SDR" is a 
mess since it is applied to several generations - 1. outboard audio DSP, 
2. integrated audio DSP, 3. integrated IF DSP, and 4. direct RF 
sampling.  Many posts seem to me to confuse generations 3 and 4 and 
perhaps different capability radios.


6. Moore's Law continues and more MIPS and FPGA gates will become 
cheaper and better.  It seems to me that the direct sampling technology 
offers a number of opportunities for better signal processing than IF 
SDR's.  Maybe not, time will tell.  FLEX has a teaser with "wide band 
noise reduction" in their latest 6000 release.  What is that?


7. One thing unlikely in affordable superhets in the opportunity to 
decode many signals on many bands simultaneously.  The contest rule 
writers have/are going to have increasing difficulty with what that 
capability means to contesting.  e.g. a 5 band skimmer for SSB? (since 
my Samsung S5 has nearly perfect speech recognition in a noisy car, is 
that too far out?).


8. The content (syntax and semantics) of contest and DX messages are 
mostly proscribed, so our brains ability to discern (or make a good 
guess) of content in very poor signal to noise and QRM/QRN situations is 
pretty impressive and varies hugely among operators. (rant: why do 
DXpedition callers insist on telling me their state or they are QRP or 
are running 50w to a dipole in the basement?)


9. This thread has been quite interesting and informative.

73,
Grant KZ1W
ex TX5D, TX7G, E51MKW


On 10/19/2015 13:06 PM, Tom W8JI wrote:

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 

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.
>
_
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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 



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Re: Topband: [Bulk] Re: ADC Overload from MW transmitters

[Rudy Bakalov via Topband]

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.  In addition, the higher rate allows for capturing smaller increments in 
signals and as the delta becomes smaller you need fewer bits.

Rudy N2WQ

Sent using a tiny keyboard.  Please excuse brevity, typos, or inappropriate 
autocorrect.


> On Oct 20, 2015, at 7:07 AM, Grant Saviers  wrote:
> 
>  So sample rates are going up beyond the current 300 MSPS rather than more 
> bits of resolution which would solve the overload concerns.
_
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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
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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
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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
> 
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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
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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


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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" 

To: ; "Tom W8JI" 
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  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" 

To: 
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 

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 !!


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