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

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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
>
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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
>
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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.


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Topband: Pre-Stew

[Tim Shoppa]

Ahem... Pre-Stew is in THREE days!

Tim N3QE



On Wednesday, October 14, 2015, Tree  wrote:

> Good day all - thought I would share some more experience I have had with
> loading a tower with a SteppIR on top of it.
>
> As I reported last season - I used a loaded tower at NE7D with a DB-18E on
> it to work the K1N DX pedition.
>
> Recently - I acquired a MonsterIR and after talking to ZL3IX, I decided to
> connect the two elements at each end of the boom to the boom.  This is
> pretty easy to do - contact me off list if you want more data.
>
> I am happy to report this all seems to be working with no issues to the
> normal operation of the beam.  The tower is 77 feet tall and works very
> well with "only" 20 radials on the ground.  I will be increasing it to
> about 40 soon.
>
> I also asked SteppIR if they had ever had any customer complain about
> problems associated with loading a tower with one of their antennas on top
> - and they have not.  Of course - it might just mean the ZL3IX, NE7D and I
> are the only ones who have tried.  :-)
>
> I find that the frequency setting for the Monster affects things on 160
> meters as expected.  I can move the low SWR point up and down the band
> some.  My nominal setting for 1825 kHz is around 9 MHz.  My gamma is about
> 45 feet high - spaced two feet from the tower.  I don't know my exact gamma
> capacitance - but it equates to about 10 feet of RG8 coax used as a
> capacitor.
>
> See you on the band!!  I also put up a Hi-Z 4 square for RXing.
>
> Oh - and the PreStew is coming up in about 10 days!!!
>
> Tree N6TR/7
> Hillsboro, OR
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
>
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Topband: Loading tower with SteppIR on top

[Tree]

Good day all - thought I would share some more experience I have had with
loading a tower with a SteppIR on top of it.

As I reported last season - I used a loaded tower at NE7D with a DB-18E on
it to work the K1N DX pedition.

Recently - I acquired a MonsterIR and after talking to ZL3IX, I decided to
connect the two elements at each end of the boom to the boom.  This is
pretty easy to do - contact me off list if you want more data.

I am happy to report this all seems to be working with no issues to the
normal operation of the beam.  The tower is 77 feet tall and works very
well with "only" 20 radials on the ground.  I will be increasing it to
about 40 soon.

I also asked SteppIR if they had ever had any customer complain about
problems associated with loading a tower with one of their antennas on top
- and they have not.  Of course - it might just mean the ZL3IX, NE7D and I
are the only ones who have tried.  :-)

I find that the frequency setting for the Monster affects things on 160
meters as expected.  I can move the low SWR point up and down the band
some.  My nominal setting for 1825 kHz is around 9 MHz.  My gamma is about
45 feet high - spaced two feet from the tower.  I don't know my exact gamma
capacitance - but it equates to about 10 feet of RG8 coax used as a
capacitor.

See you on the band!!  I also put up a Hi-Z 4 square for RXing.

Oh - and the PreStew is coming up in about 10 days!!!

Tree N6TR/7
Hillsboro, OR
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Topband: 2015 Summer Stew Results Posted

[Tree]

The results for the Topband Summer Stew are now available

http://www.kkn.net/stew/2015_SummerStew.txt

The PreStew is coming up this weekend.  Full rules are available here:

http://www.kkn.net/stew/

Hope to hear you on 160 meters this weekend.

73 Tree N6TR
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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
_
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Re: Topband: Pre-Stew

[Tree]

Oh my!!!  You would think I would know that.

The PreStew is in THREE DAYS everyone!

Full rules here: http://www.kkn.net/stew/

I will try to get the Summer Stew scores posted before it starts.

Tree

On Wed, Oct 14, 2015 at 3:50 PM, Tim Shoppa  wrote:

> Ahem... Pre-Stew is in THREE days!
>
> Tim N3QE
>
>
>
> On Wednesday, October 14, 2015, Tree  wrote:
>
> > Good day all - thought I would share some more experience I have had with
> > loading a tower with a SteppIR on top of it.
> >
> > As I reported last season - I used a loaded tower at NE7D with a DB-18E
> on
> > it to work the K1N DX pedition.
> >
> > Recently - I acquired a MonsterIR and after talking to ZL3IX, I decided
> to
> > connect the two elements at each end of the boom to the boom.  This is
> > pretty easy to do - contact me off list if you want more data.
> >
> > I am happy to report this all seems to be working with no issues to the
> > normal operation of the beam.  The tower is 77 feet tall and works very
> > well with "only" 20 radials on the ground.  I will be increasing it to
> > about 40 soon.
> >
> > I also asked SteppIR if they had ever had any customer complain about
> > problems associated with loading a tower with one of their antennas on
> top
> > - and they have not.  Of course - it might just mean the ZL3IX, NE7D and
> I
> > are the only ones who have tried.  :-)
> >
> > I find that the frequency setting for the Monster affects things on 160
> > meters as expected.  I can move the low SWR point up and down the band
> > some.  My nominal setting for 1825 kHz is around 9 MHz.  My gamma is
> about
> > 45 feet high - spaced two feet from the tower.  I don't know my exact
> gamma
> > capacitance - but it equates to about 10 feet of RG8 coax used as a
> > capacitor.
> >
> > See you on the band!!  I also put up a Hi-Z 4 square for RXing.
> >
> > Oh - and the PreStew is coming up in about 10 days!!!
> >
> > Tree N6TR/7
> > Hillsboro, OR
> > _
> > Topband Reflector Archives - http://www.contesting.com/_topband
> >
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
>
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