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Tracking Notch Filter (TNF)

Ken - VE5KCKen - VE5KC Member
edited June 23 in New Ideas
When I first saw there were Tracking Notch Filters, I thought this is great, just what I needed. I tried TNF but it didn't do what I was expecting... At first I thought it was not working.

It comes down to a difference in interpreting the meaning of tracking.

On 80 meters I have a carrier that moves around part of the band, it is not always in the same frequency range and sometime it is not there (or not bothering me). It is very annoying and I was hopping that the TNF would be the answer and would track the the moving carrier. I have had no luck finding were it comes from and it affects all radios I've used at this QTH. The big difference, with my Flex I can see what is happening.

Would it be possible to have TNFs that could actually follow a moving carrier to keep it notched out when in comes into the bandpass of the signal you are listening to?

73..  Ken - VE5KC


  • Alan - KA4BAlan - KA4B Member ✭✭
    edited September 2018
    Ken, within the slice the Auto Notch Filter would do that for you, wouldn't it?
  • Ken - VE5KCKen - VE5KC Member
    edited April 2015
    It's not doing it for me.

    I'm still very new, only had my 6500 for a bit over a week.

  • Wayne VK4ACNWayne VK4ACN Member
    edited April 2015
    I didnt think my Tnf was working either when I got my 6500, till I realised how to turn it  on.  The lower left TNF button, turns it on.  Works a treat now.
    Try that

  • Ken - NM9PKen - NM9P Member ✭✭
    edited June 23
    Tracking Notch Filter "tracks" the same place in the frequency spectrum, regardless of the position of the panadapter or the slice. Most notch filters (i.e. All the others) are locked to the audio spectrum of the receive bandwidth. Or they are automatic filters that will lock to a frequency within the receiver bandwidth. On the Flex, we have two options... We can set the tracking filters, which are permanent, but adjustable notches in the RF spectrum. Or we can use the ANF (Automatic Notch Filter) which will automatically notch a single interfering tone within the receiver bandwidth. This will lock to the tone and adjust itself, within certain parameters, as it drifts or is wavered by a QRMer. Currently the ANF works, but needs attention, which it will get in release V.1.5. At present, it tends to add more audio distortion than many will tolerate. If you carefully adjust AGC-T and the ANF slider, you can find a sweet spot where it is sometimes tolerable, but learning to quickly adjust a TNF by dragging it around the passband give a much better notch with little distortion at all.
  • Dale KB5VEDale KB5VE Member ✭✭
    edited June 23
    Good post Ken. The tnf is a great feature especially in a urban area where you have so many constant noise interference sources. You can build a tnf and allow it to stay there u tile you turn it off. I realize the Dsp noise functions are not up to par and I have complete confidence it will be addressed. But I personally have no need for the NR or even the ANF most of the time. I live in a urban subdivision with all the little sweeping noises and the occasional raspy surge and of course plain ole atmospheric noise. I use the fantastic AGC threshold adjustment and occasially the NB (which works great on the noise it is designed for). I wonder if some out there are expecting something which is not really necessary. I have a friend who wants his hf rig to sound like FM , he uses rf gain, NR and some times the squelch to totally quiten his reciever. Hey that ok it's his choice as it is all our choices to run as we want, but then a weak station will come in and we will talk to the station and my friend will have to turn off all the items he has turned on just to be able to hear him. As a 11 year old kid in 1958 I remember sitting in my bedroom with head set on listening to the white noise on my SW reciever waiting for that station to come on the air. All in all I really feel most of these I handed Dsp recieve features are good but the old addiage you do not get anything for nothing, so as you turn on all these features somewhere you will pay a price. That's just my opinion.
  • Ken - NM9PKen - NM9P Member ✭✭
    edited December 2016
    Like you, I have found that the utility of these features depends upon my operating purpose.

    For example, most of the time I didn't need the ANF, but when rag chewing on 80 and the "QRM Club" starts up because they want the frequency my group is on, instead of waiting another 20-30 minutes until we are done (We only use the frequency from 8 - 10 p.m. and usually are done by 9:30 p.m) and start sweeping carriers, etc, it would be nice to have the automatic notch filter take over so we can continue the contact.  

    Currently, it adds too much audio distortion to be satisfactory to me, but most of the time I can adjust a TNF and get by, so I am content to wait for V.1.5, which promises to be awesome.

    NB can be adjusted carefully and be usable "enough" at present, but as winter progresses, I am getting more powerline interference from "arcs and sparks" especially on 17-6 Meters.  The NB is moderately effective, but not as good as the NB on my 1500 or my modified Kenwood TS-850 (Which was useless until I modified it)   This, too, will be receiving the "Science Project" treatment in V.1.5 and I am confident that we will see things never done on amateur level receivers before. (governments and military can afford a "no price is too high" approach to noise reduction.)

    But there are some who seem to expect miracles from DSP that will never happen.  NB can eliminate or reduce impulse noise, but there is a cost to dynamic range and splatter; ANF and TNF can eliminate offending steady or slowly moving carriers, but you cannot eliminate a carrier frequency and maintain perfect fidelity in the desired signal. NR can reduce hiss, but you will sacrifice high frequency response.  it is all a trade-off.

    And I am not aware of anything that will easily make weak signals pop out of general wideband hiss and hash that is all across the spectrum.

    There have been some articles written (probably 20-30 years ago) about vocal squelch, i.e. a circuit that senses the more rapidly changing base frequencies of human speech and will keep the squelch closed until it detects a human speech pattern.  This was done by analog timing and filtering circuits back then, but could be implemented "easily" with software DSP (giving a big wink to the programmers!)  This would be a very interesting tool on a noisy rag chew band, or when monitoring 6 meters for an opening.  A programmable slow sweep on 6 meters with a vocal squelch that worked well would be a big hit for me!  It would be immune to static crashes, and atmospheric whistlers, etc.

    I could think of many other things that could be done, theoretically, with the DSP engine in this rig, given the proper amount of time and programming resources.  

    But there are also a lot of other things that may never be practical.  

    They should probably be the subject of another post so as not to hijack this thread.
    It would be interesting to pursue this on another thread...

    Ken - NM9P

  • Ken - VE5KCKen - VE5KC Member
    edited May 2017
    Today I had some time to check this out further and the varying carrier cooperated by being there for the test.

    I think I have things figured out.. Some comments say the filter has to be turned on.. What I find is I have two options.. Yellow filter line, a manually inserted TNF and a Green filter line a fixed, remembered TNF. In no case does/will the filter track (follow) the moving carrier.

    So, would it be possible to have another option to make a TNF actually track the offending carrier?


  • Alan - KA4BAlan - KA4B Member ✭✭
    edited February 2015
    Ken, the Auto Notch Filter will track the carrier for you.
  • Ken - VE5KCKen - VE5KC Member
    edited April 2015
    The TNF will stay locked to a fixed frequency carrier, when you are changing the position of the slice. It will not lock to a carrier that is moving around the band.

    If I am wrong about this, then what am I doing wrong and how do I make it work?
  • Jay NationJay Nation Member
    edited August 2016
    I stopped listening to noise when I got my SDR-1000, there was really no need to listen to it anymore. sliding the the filter edges around and backing off the AGC-T and adjusting the slice volume seems to work for me I don't use the NR in SmartSDR and luckily don't need the NB. Out here in rural nowhere the loudest noise I have to deal with in the shack outside the signals in the passband, is weather, a few cows, and the open collectors on a neighbors dualie. NR won't fix any of those. Something for SmartSDR v3.0 maybe? 
    Clouds,Cows,and Mind Control?

    73, Jay - NO5J
  • Alan - KA4BAlan - KA4B Member ✭✭
    edited February 2015
    TNF will not follow the carrier.  ANF will.
  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    ANF works on an audio (not RF) tone within the RX passband.  If it moves, it will attempt to reacquire the tone and notch it.  If it is moving too quickly, the DSP will not have time to converge on the offending signal.
  • R2AGGR2AGG Member
    edited December 2016
    Could someone from the users to talk about the "TNF"? I could not use it. Here the video. 

  • Ed.GEd.G FlexRadio Employee ✭✭
    edited December 2016
    You need to enable the TNFs by clicking on the TNF bottom/icon on the bottom left of the SmartSDR screen. The TNFs are bright yellow when they enabled and grey when disabled.
  • R2AGGR2AGG Member
    edited December 2016
    Great. It works great!

    Best 73!
  • Mike KasrichMike Kasrich Member
    edited December 2015
    I'm more interested in how to remove the line from the screen. I was just fooling around, seeing what each feature did on the 6300 I have. I hit TNF and now can get rid of the line. I figured you could toogle it on and off but that is not the case.
  • W7NGAW7NGA Member ✭✭
    edited January 2018
    Mike, right-click on the line.
  • KF4HRKF4HR Member ✭✭
    edited February 2017
    Mike, you can also park your cursor on the yellow filter line, press and hold your left mouse button, slide your mouse up and down to widen or narrow the filter, then right click to select how deep you want the filter to be.
  • Walt - KZ1FWalt - KZ1F Member
    edited November 2016
    It took me a kind of long time to realize what you just said, that sliding the mouse pointer either up or down would widen or narrow the fliter. Be very careful though. You can narrow the filter to the point finding it to delete it is difficult. Also, to your original question, both Dan and Butch are correct but I found, especially initially, it difficult to position the mouse over it UNTIL YOU GET THE CROSS HAIRS, depress button 1 while it is still showing the cross hairs. It's second nature now but initially it was more difficult than it should maybe have been.
  • KF4HRKF4HR Member ✭✭
    edited December 2016
    Walt brings up a good point.  I found by switching from a mouse to a trackball it made it easier to get the cursor properly centered on the yellow line (and obtain the 4-arrow cross hair), especially when the filter line is at its most narrow. 

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