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I was having trouble with my WNB on 20 Meters, ....

Ken - NM9PKen - NM9P Member ✭✭
I was getting a lot of pumping of the WNB on 20 meters and figured that there must be some strong station with very sharp transitions (distortion) on the signal.  Guess what I found?  Radio Havana at 15.370 MHz running 60 KHz wide and very distorted.

Here is a link to my recording.  With such distortion and sharp edges (or crossover, or whatever others call it) it is no wonder that the WNB was catching impulses and pumping.

https://youtu.be/0XHk8Q9WDSk

This is a ridiculous signal....
But it made me wonder.  Is there a way to define the WNB so that it samples a more limited bandwidth of signals in order to do its work so that I can exclude such nasty out of band signals from the WNB's calculations?

Ken - NM9P

Completed · Last Updated

Answers

  • G8ZPXG8ZPX Member
    edited July 2018
    Ken,

    I have also seen this on the upper end of 40m band around 7.160 - 7.200. In Europe we often see some very strong international broadcast stations above 7.2. This renders the WNB almost unusable on 40m, and to an extent 80m SSB DX segment as well. So yes please, a more definable "passband" for the WNB should be very very effective.

    Also, I feel that as it could be configured to just process say the current panadapor visible range then we might actually see more dynamic noise reduction because it can be better focused on the noise we are currently experiencing, not the much wider bandwidth we don't really care about.

    Looking forward to the WNB focus slider...

    73 de Steve G1XOW
  • K1UO - LarryK1UO - Larry Member ✭✭
    edited December 2017

    This is a "me too" moment... 


    Great idea to allow adjustment to the Band range of interest somehow.

  • DH2IDDH2ID Member ✭✭
    edited December 2016
    @Ken, @ Steve I like the idea of a WNB focus slider or bandwidth sliders showing
    the focus and bandwitdth numbers. That should not be difficult to implement.
    73, Alex - DH2ID
  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited June 23
    The answer is no, there is not a control that will allow you to define the WNB bandwidth.  Making the panadapter bandwidth smaller will effectively reduce the bandwidth WNB uses, but I do not think you can get it narrow enough.  You can try it and see if that makes a difference.

    In addition, I have added these comments into a program change request (technical a feature request) as item #3807 in our bug tracker
  • G8ZPXG8ZPX Member
    edited July 2016
    Hi Tim,

    Are you saying that the WNB bandwidth already follows the pan bandwidth then?

    If so, then that doesn't tally with the findings of Ken and myself. When you go hunting for what is causing the pumping effect you typically find the source is some 150-300 kHz HF of the currently displayed max pan freq (i.e. off screen).

    So some kind of width control would certainly allow more experimentation in the field and may result in some good feedback in to the product. I accept that one thing you cannot simulate or test in the lab is the myriad of QRM sources around the world, and thus how the QRM affects individual stations in different ways.

    73 de Steve G!XOW
    
  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    The amount of bandwidth used by WNB is determined by the width of the panadapter, not the exact bandwidth of the panadapter.  There is a minimum amount of bandwidth that is required to collect enough data in order to accurately run the wide band blanking algorithm and remove the offending signals from the spectrum display.
  • Ted_Spiegel_NX6CTed_Spiegel_NX6C Member ✭✭
    edited December 2016
    Tim,
       This is very helpful.  did I miss this fact in the documents?
    Ted
    NX6C
  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    I am not certain we described that particular behavior.  It really only becomes relevant if the panadapter is really wide (as in MHz)
  • Steve G1XOWSteve G1XOW Member
    edited September 2016
    Tim

    Next time I see it on 40m I will make a video for you.

    Normally I have an on-screen pan of about 100kHz. Typically the QRM source is around 150-300 kHz HF of what I am looking at (in the 41m am broadcast band).

    The last one I remember was a far-east station, radio china or similar. It was about s9+20 and pretty wide on my half-wave vertical. Using the WNB was thus impossible on 7.160MHz.

    I will try a tacking filter on it next time and see it that helps. Not sure if the WNB sampling is pre or post TNF? 

  • Ken - NM9PKen - NM9P Member ✭✭
    edited December 2016
    Hey, that's an idea I hadn't considered before! 

    Would a wide TNF filter take this station out of consideration for the WNB?  I have never even tested to see how wide a TNF can go.

    My guess is that the WNB takes its samples from the ADC before the tap that drives the notching or demodulation routines.  But it would be an interesting, but probably very complicated, set of calculations to have "exclusion zones" from the WNB......
  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    The WNB processing is before TNF.
  • HCampbell  WB4IVFHCampbell WB4IVF Member ✭✭
    edited June 23

     Ken, thanks a heap for tracking down the cause of the pumping.  I’ve noticed similar behavior many times but never took the time to investigate further.  If WNB can be improved in such cases by giving the user the option of narrowing the range that WNB searches (maybe even down to the slice receiver range?) then I’m all for it.  Great idea! 



  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    The problem is the bandwidth sampled has to be wide enough to gather an appropriate amount of data to properly correlate the noise and effectively remove it from the spectrum.  We have optimized that in the current implementation and make the bandwidth smaller will make WNB less effective.
  • Ken - NM9PKen - NM9P Member ✭✭
    edited December 2016
    That makes sense, Tim.  More information means better analysis of correlation.

    It stimulates another thought, though.  (My mind drifting off again into half-informed, off the wall SDR theory......)

    Knowing that you need a certain bandwidth to analyse in order to assure good performance, would it be possible to have some control as to from WHERE that bandwidth is sampled?  For example....if my antenna response is not even and some of the samples are being gathered from "dead" sections of the antennas receive response, could the "sample band" be shifted a little to take advantage of a more representative sample of the actual noise being received by the station?  

    OR, if there is a nasty signal like the Radio Havana signal I posted, could the sample bandwidth be shifted AWAY from that end of the panadapter to include more of the bandwidth on the lower end and less on the high side so that the offending signal and its sharp peaks is not included into the sample to distort the algorithm?

    Think of this sort of like a giant "IF Shift" knob on my old Icom rig that didn't change the actual bandwith of the filter, but shifted the location of the filter bandwidth up or down to emphasize either the higher end or the lower end of a signal.   If the sample is, for example, 500 KHz wide with a 200 KHz wide panadapter, instead of having an extra 150 KHz evenly spaced on each side of the panadapter, it could be shifted to sample 50 on one side and 250 on the other, or vice verse, (or 0 and 300) as needed to give a more effective sample to the WNB.  

    Just my brain going into overdrive, thinking up more possibilities....(I probably need to visit Austin and sit down with the software engineers over a couple of Red Bull's and get this stuff out of my system.)  (;>p)

    Ken - NM9P
  • Steve G1XOWSteve G1XOW Member
    edited June 23
    In an attempt to provide some valuable feedback regarding the WNB problem to Flex software coders, I've just made a short video to demonstrate the problem. It appears to be confined to the bands that also have a big AM broadcast segment at one end of the ham band (especially, 20, 40 and 80m in my case). It looks like the WNB is sampling at least 2-3MHz wide which will always mean that some non-ham band sigs will get included. This seems excessively wide sampling to correlate against just a few kHz that we are actually interested in. Could SSDR limit WNBs sample scope to the ham band limits, or have some definable slider upper/lower limits?  This may result in WNB being less effective when set for narrower sampling, but better that than it being entirely usable for some.

    Personally I don't find much need for WNB at my quiet country location but others may need this facility to work without the overload pumping action when AM broadcasters are around.

    https://youtu.be/r9Sq9ftBv-M

    73 de Steve G1XOW

  • Gerald-K5SDRGerald-K5SDR FlexRadio Employee ✭✭
    edited December 2016
    Hi Steve,

    Thanks for the video because it helps me to make a few observations as follows:
    1. I see that you are operating a FLEX-6300, which does not have ham band preselectors as do the 6500 and 6700.  Analog preselectors will reduce the effect of out of band signals.
    2. Based on what I see and hear on the video there is no correlate impulse noise on the band where you would benefit from using WNB.
    3. Your setting of the WNB slider appears to be too high based on the conditions.  Drop the slider until the pumping just goes away.  We provide a wide range on the slider to allow you to adapt to varied conditions.  The more aggressive the setting the more likely other signals can interfere.
    4. WNB operates in the time domain much like you would see on an oscilloscope trace to identify the noise pulses.  This requires a wide bandwidth by definition.
    5. NB may be more suitable in some cases because it operates over a 24 kHz bandwidth.
    Hope that helps.
    Gerald
  • Steve-N5ACSteve-N5AC Community Manager admin
    edited December 2016
    Also, I've not spent a lot of time looking over everything but my first thought was that NM9P had the preamp on in the first video.  This could have led to an overload condition depending on signal levels.  I would try turning the preamp off and even possibly into attenuation as a diagnostic to see if this is a factor.
  • W9OYW9OY Alpha Team Member ✭✭
    edited September 2016
    Radio Havana is basically radio Miami.  I other words in Indiana you're not all that far.  I live 400 miles from Radio Havana and on 6 mhz it is consistently the loudest signal I ever encounter including a 10kw AMer 2.5 miles away and a 50kw AMer 10 miles away.  Havana's array is aimed directly at my QTH.  I use Havana as my test case for preamps etc.  That being said its still >35 dBm below where my Flex runs out of headroom.  They used to run a Czech TESLA transmitter but new ones are now installed.  

    73  W9OY
  • Ken - NM9PKen - NM9P Member ✭✭
    edited December 2016
    Steve, I have never had any overload problems before. This signal was about S9+40 to 50. Although I don't remember turning off the preamp, I did shift antennas. The vertical was about 20 dB down, and the signal was still very wide and distorted. Even with NO antenna, it was the worst sounding, widest, AM signal I have ever heard, except for one CBer who was splattering about 1.5 MHz each side of center! I wish I had a recording of that one! Anyway, the Radio Havana had extremely sharp modulation products and the distortion was of a type I don't think I have ever heard before. It was just strange. If I hear it again, I will compare preamp and attenuators settings.
  • Steve G1XOWSteve G1XOW Member
    edited May 16
    Gerald,

    As I said in my post, personally I don't need WNB so it's not an issue for me. The few experiments I did proved it was pointless as it was impossible to make the massive AM broadcast signals low enough relative to the signal we are interested in. Being up to 10 times louder than the miniscule DX in the noise I am trying to receive.

    There is no facility for "spot-attenuation", and a sig 10 times louder that is just out of the 20m band cannot be reduced by filters to any large degree without badly affecting performance of the desired in-band signal too. I use the well respected Heros Filter (external to the F6k) which makes no difference with such close-in sigs.

    I also tried adjusting the slider downward (it was set at about 40 in the video to ensure the demonstration). Once the slider drops below about 20 there is no benefit anyway. Also, I have notice the same pumping affect at the top end of 40m (7.170) even with the slider set at 0 and WNB turned on.

    I feel there is a fundamental design flaw in the math/sampling scheme. The massive AM broadcast signals being sampled versus the tiny desired signals will never lead to happy math (weighted averaging) and thus the blanking will be ineffective when any big sigs are present. I suspect the same would be true in any big contest such as WPX SSB too.

    To work really well, some tweaking is required (or the ability to notch-out the AM broadcast bands QRM prior to averaging), Otherwise its function will only be useful in a small number of cases (those without big AM BC QRM), and hence why some claim WNB is a gift from god, yet others think the opposite.

    In a nutshell, it needs more work based around real-life environmental situations to be a really useful facility.

    73 de Steve G1XOW
  • edited September 2016
    Got Two Tracking Filter Boards from SV1AFN plus his preamp board via Ebay for my ICOM IC-7300 HF thru 6 meters Rig to cut out out of band Rx interference

    Using an Arduino Switch Band Decoder IP Switch Unit from RemoteQTH.com 

    This 9-Band switchable filter ( uses 2-in series BPF filters with a mid-section preamp ) from SV1AFN " HF Bands Preselector Boards" with a DX Engineering RTR1A
    switch box or radio's with only one Antenna port & no way to add preamps/filtrs.

    It may be possible to use this Band Switching Tracking Filter reading Band Data 
    from DDUtil to feed the RemoteQTH.com Switch Band Decoder 

    This might be the Answer for a Flex6300 (No-Preselct Filters) but may be way 
    overkill for a Flex6500/Flex6700 that already has internal preselect filter built-in.

    Will see if I can adapt this to my Flex6500 just as a test to see what happens.

    Like I said - way overkill for a Flex6500/Flex6700  

    Any comments welcome 

    73 Mike WB6DJI
  • Ken - NM9PKen - NM9P Member ✭✭
    edited December 2016
    Are those receive-only filters?  If so, on the 6500/6700 they would work nicely in the RXA/Loop or RXB/Loop and would never be in line with the transmitter.

    In any case, for me this is not a regular, continuing situation and I posted it mostly because the signal from Radio Havana was so extraordinarily wide and distorted.  I have seen extremely sharp modulation kick a noise blanker before, but never this badly, and not this badly with WNB.  

    I still do not think it is overload in my case, and I have NEVER seen any signals as strong as the ones that Steve - G1XOW posted, even with two 1200 Watt stations less than a mile away from my station.  I have been amazed at how crunch-proof this rig has been,

    But the event brought up the interesting thought of what I will call "band shifting" the WNB sampling band, for lack of other technical terminology.  

    It has been an interesting and enlightening discussion of the whole WNB subroutine.
  • edited September 2016
    These are receive only BPF Filters
  • Steve G1XOWSteve G1XOW Member
    edited September 2016
    On my front-end I already have the Heros pre-selector. https://www.herostechnology.co.uk/pages/SCR_Preselector.html

    However, as the QRM source is only about 7-800kHz away, any passive analogue filtering will not be sharp enough when so close to the passband. You'd need a kind of tracking notch filter prior to the WNB sampling to do any good. I.e. **** our / notch the QRM from the sampling scope.
  • K9SOK9SO Member ✭✭
    edited January 2019
    FYI, nice band openings with huge pileups on 40m this morning gave me a chance to investigate a bit further. Definite problem with WNB selected but also see the noise pumping with the NB function activated. Nowhere near as bad, but quite noticeable. Able to copy strong stations in the noise with the narrow band NB on 5-10KHz away ... dissappears when turned off. 

    Not really a problem for me now that I know to shut them off. Thanks again for the hints. Much appreciated. 

    73,
    Fred

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