Re: Topband: Commond mode choke for Beverage

[Filipe Lopes]

Thanks for this testing suggestiong Eddie, it will sure be a good way to
check if it works or not.

73's Filipe Lopes
CT1ILT - CR6K
F4VPX - TM3M

2015-10-12 20:14 GMT+02:00 Eduardo Araujo :

> >> With these ferrites I ask the same question, should I put the choke
> close
> >> to the 9:1 Balun or near the switching box and how many turns? some bevs
> >> have the feed point at +- 60m away from the switching box.
>
> My two cents..It was interesting during the installation of the last
> beverage, we have only #31 core, so we placed it at the receiver side.
> Disconnecting the coax at the bev feed point and shorting the coax there,
> many AM broadcast stations could be heard and some of them strong,
> indicating that even though one choke was at the receiver side the coax was
> acting like an antenna. The coax was just lying on the ground and is 40/50
> mts long.
> When we got more cores and placed one choke at that place close to the
> short, repeating the test before and after most broadcast vanished and only
> one could be heard very week.
> '73 Eddie, LU2DKT
>
>
>
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Commond mode choke for Beverage

[Filipe Lopes]

Thanks JC,

I am reading it right now, very interesting indeed.

73's Filipe Lopes
CT1ILT - CR6K
F4VPX - TM3M

2015-10-12 22:27 GMT+02:00 JC :

> Hi Felipe
>
>
>
> It works like a voltage divider where the impedance to ground should be
> lower as possible to give you more attenuation  like 1k/500ohms versus 1K/5
> ohms divider. You should use the choke near a good ground before entering
> the station. If you switch box have a good ground it’s a good place to
> install  it.
>
> More turns better, but it is limited by the diameter of the coaxial cable,
> like RG58/RG142 allows 12 to14 turns. RG213  only 8 turns.
>
>
>
> Jim K9YC and a fantastic documentation about chokes. Please read this
> document
>
>
>
> http://audiosystemsgroup.com/RFI-Ham.pdf
>
>
>
> You will be a specialist after reading this guide.
>
>
>
> Regards
>
> JC
>
> N4IS
>
>
>
> *From:* Filipe Lopes [mailto:ct1...@gmail.com]
> *Sent:* Monday, October 12, 2015 9:52 AM
> *To:* JC 
> *Cc:* topBand 
> *Subject:* Re: Topband: Commond mode choke for Beverage
>
>
>
> Hello JC,
>
>
>
> Thanks for your answer.
>
>
>
> I just ordered a few 2631803802 and 5943003801 from mouser.
>
>
>
> With these ferrites I ask the same question, should I put the choke close
> to the 9:1 Balun or near the switching box and how many turns? some bevs
> have the feed point at +- 60m away from the switching box.
>
>
>
>
> 73's Filipe Lopes
>
> CT1ILT - CR6K
>
> F4VPX - TM3M
>
>
>
> 2015-10-12 15:40 GMT+02:00 JC :
>
> Hi Filipe
>
> Zero , you should use material #31  or #77 , The core you have is not good
> for low bands.
>
> JC
> N4IS
>
> -Original Message-
> From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Filipe
> Lopes
> Sent: Monday, October 12, 2015 8:46 AM
> To: topBand 
> Subject: Topband: Commond mode choke for Beverage
>
> Hi guys,
>
> I am about to add a common mode choke to isolate the antenna from its
> feedline to each of my beverages and I only have FT240-61 ferrites. My
> question is how many turns should I do on the ferrite using RG58 (all my
> bevs are fed with RG58). Also should I put the choke near the 9:1 balun or
> near my bev switching box?
>
> Thanks in advance.
>
> 73's Filipe Lopes
> CT1ILT - CR6K
> F4VPX - TM3M
>
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
>
>
>
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Commond mode choke for Beverage

[Filipe Lopes]

Thanks for this grounding tip too Jim.


73's Filipe Lopes
CT1ILT - CR6K
F4VPX - TM3M

2015-10-13 4:03 GMT+02:00 Jim Brown :

> On Mon,10/12/2015 1:27 PM, JC wrote:
>
>> It works like a voltage divider where the impedance to ground should be
>> lower as possible to give you more attenuation  like 1k/500ohms versus 1K/5
>> ohms divider.
>>
>
> Yes.
>
> But to expand on this -- often the interference is coupled into a gain
> stage or RX by a Pin One Problem. ALWAYS make the first connection of any
> cable shield to the shielding enclosure of EVERY active device. Follow this
> rule regardless of the function of the cable -- input, output, control
> line, RF or audio.
>
> It's also good practice to bring RX antennas into the shack via the same
> grounding panel used for TX antennas. And that panel must be tied to local
> ground rods, those rods bonded to all other grounds, to the shack desk, etc.
>
> 73, Jim K9YC
>
> _
> 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 add up to +6V.   Do 
> they still
> show up on the bell curve, and if 

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

Topband: High Pass Filter

[Jay Terleski]

Rick,

No one has had a problem and we have many good reviews from users.

The units do not overload at +7 dbm or more from what we have tested. That
is usually good enough.

I have a 50 kW AM 6 miles away from me works fine.

But if they should then we would refund fully any filter that failed to
perform to the customers satisfaction.

Jay, WX0B


Jay Terleski
President
Array Solutions
214 954 7140
_
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