DSP - ANF Performance Specification

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The community has many discussions about the SSDR DSP functions and many of these are qualitative posts saying that ANF, for instance, needs to be fixed. How about tightening focus?

So, lets take ANF. For me it seems to work okay and not having anything to compare I’m satisfied. But then I’m mostly on CW. Nevertheless, what exactly is the spec for the ANF? We have a sense of what it is supposed to do, but within what limits? Its a software subsystem tightly integrated into SSDR so Flex must have some specs to test their design. That spec they must hold close to not reveal intent and there isn’t much detail in paragraph 15.4 of the users guide nor specific performance specs.

That said, you can’t fix that which you cannot measure. We all know this.

Here’s an attempt at a provisional ANF performance spec, ultimately, in some fashion a “users’” desired specification:


  1. Modes of operation: SSB, AM

  2. Attenuation of interfering audio tone: 30 – 50dB

  3. Effect on desired signal in passband: ? %THD?

  4. Number of simultaneous tones notched in the passband: 5

  5. Passband effectiveness: 1.8 to 5 khz

  6. Number of slices using ANL: 1 to 8

  7. Attack time: less than 100 msec

  8. Effect on slice noise floor: none seen on spectrum

  9. Effect on slice IMD: none (how to measure)

  10. ?


Then, measure SSDR with with our “users’” specification? These are sort of in order, my order, of importance. Users might consider more or less spec items. Users might consider different required values.  Quantitative results might be a challenge.

All of the above is my idea of what to measure, I’m certain it can be improved.

By looking closely at the ANF’s desired spec a technical discussion can be had that may in fact be useful to Flex engineering. There are no hardware limitations as far as I know.

My thought is to move away from Flex flogging and into the tech specifics that we hams can debate. Field performance of the ANF (also for any comparable rig) can be measured using user accepted provisional specs as a grading rubric. Getting to this point is not easy in a public forum, but, perhaps it needs to be done to move forward.


Similar quantitative specs and answers for NB. NR and WNB could be considered.

So, for ANF, what exactly is it that we want?



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N5LB - Lionel B

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Posted 4 weeks ago

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Photo of Chris Tate  - N6WM

Chris Tate - N6WM, Elmer

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Lionel--

First-- IMO, Spot on.  Keeping issues on point, specific and with supporting information either about the way it acts differently then desired, or specifically how it is not perceived as working correctly and how to duplicate the issue is the best way to get the visibility of the team.  It speeds re-creation of the issue both in alpha testing and in the programming lab, and is our best chance to get certain issues corrected.  Keeping on point while being respectful is simply the right way to do it and a win win for everyone in the flex community. 
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Jim Gilliam

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I think he misses the boat completely. The problem with the ANF is when someone talks the notch depth decidedly reduces. The ANF should respond to a notch exactly like the TNF. The TNF works superbly.


Jim, K6QE
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Chris Tate - N6WM, Elmer

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Jim. What he is saying is there is a perceived issue with ANF, and the best way to help identify the issue specifically is to lay out in technical detail, what specifically is perceived not working, show instructions on how to duplicate the issue, and finally what the desired behavior would be, and leave it at that, without any criticism.  My comment was on the presentation strategy, not the specific issue.  

 
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Bill -VA3WTB

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Chris, I understand what you just said and I understand the thread, But bare with me a bit please.

If I understand things that Gerald said in the past, is that Flex is doing the DSP funtions very none conventional. They were developing something no one else was doing, as an example, wide band DSP coding. I would imagine Flex is keeping their work guarded?

So then, how can we be sientific and staying within the focus here without really understanding just how Flex is even aproaching this?
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Geoff - AB6BT

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I don't believe we need to know the algorithms or topology used internally. Just consider it a black box function. Define what you want it to do and leave the engineering of how to accomplish that function up to Flex. 
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Chris Tate - N6WM, Elmer

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I couldn't have said it better myself.
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Bill -VA3WTB

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Sorry I must have misunderstood you Chris
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James Whiteway

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Chris, one sure way to test the ANF is to listen to some of the roundtables on 75 and 40 meters on Friday and Saturday nights! Plenty of jamming tuner uppers to test against. And lots of kilowatts too!
:-)
Seriously, the issue can be reproduced tuning an amp into a dummy load with one radio on the same frequency as a qso in progress on another radio hooked to an external antenna.
Or even using a signal generator in place of the second radio and amp(and dummy load)
That will reproduce the blowby that happens with a strong carrier tuning on top of a qso.
No setting I have tried to date with the ANF will stop the offending signal from popping thru the top of a conversation one is trying to monitor. The closest thing to helping is dropping the AGC-T all the way to zero. But, even then blowby can happen.
The Icom 7300 and several other radios I have or had, handle the situation with ease. That's what frustrates me. A $5,000.00 radio cannot do as well as a $850 radio on such a situation as this. I would have thought it would be just the opposite, but it's not.
Other than that and a few other issues, the 6600M is a great radio. But, it's a shame this issue has continued from v1.x til v3.x. My sincere hope is the basics are fixed in all three versions of SSDR. Had I not traded up to the 6600M, I would, in all likelihood, would have still been on v1.x till multi client(aka MultiFlex) came along.
James
WD5GWY
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Robert Lonn

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Keep in mind Flex cant talk about this WBN and other features of their radios!! , it is a Secret. Flex is working with the newly created Space Force.. The Wide Band filter is actually designed to eliminate noise generated from the Inter Steller Warp Drive engines created from Alien Space Craft..This must be true, since I heard this on "Coast To Coast" late night AM radio!!! LOL

Robert
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N5LB - Lionel B

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Notch depth decreasing with desired signal variation (increasing-the same in both directions?) seems undesirable, depending on magnitude.  That said, the effect may not be brought to zero, like the TNF, and if that be the case, perhaps some acceptable limit needs to be established.  This particular issue I think has been reported in the past.

Is it possible to determine at what, in passband signal strength does the effect become apparent? Is it influenced by bandwidth?  What is the variation? What other features, NR, NB, WNB are in use? Do they have any effect on ANF performance?  One would expect not and therefore could be dropped out of the ANF discussion, if the answer is "no." If yes, well, oh boy.....engineering would probably want to disentangle. 

It seems a "notch depth variation with signal strength" is an expectation that could reasonably be included in specifying ANF performance.  Or, as posted, perhaps the intended limit is zero, as is the case with TNF's.  I suggest the effect is also related to, or identifiable with, receive signal distortion or degradation that I seem to recall reading in the community. 

There isn't much field data to capture the effect nor to agree upon limits, except to desire "zero.". Some field data is going to be needed, a significant challenge.

ANF, I think can, as someone mentioned, be considered a black box, in general.

I would be interested in technical details of the ANF performance disappointments.  Is notch depth variation as a function of signal strength the central issue? The only issue?

So,  reported ANF performance issues, at this moment:

1. Notch depth varies with signal strength.   (Performance Spec would be how much variation is acceptable and under what conditions). Someone implied that how engineerring achieves the spec is not relevant. I agree.

2.  ??

What else is wanted for ANF performance?
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Mark K1LSB

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Lionel,

My main problem with the performance of the Flex ANF is not that it's not 100% effective in all cases, but rather that it so severely degrades the quality of the audio any time it's activated.

The TNF function displays the same objectionable behavior. It's very aggravating any time I need to use either feature -- I'm torn between deciding whether to grit my teeth and put up with the degraded audio or just shrug and put up with the squeal of the birdie. 
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Burch - K4QXX

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Interesting. I have the same issues as you with the ANF but the TNF function works well for me. 
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Lawrence Gray

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I agree with the need for a specification, but this is work that FlexRadio should be doing.  They should benchmark Noise Reduction, Noise Blanking, and Notch Filtering features in other ham transceivers.

It is actually kind of easy to do.  For example, I purchased ANAN radios specifically to check what other hams told me regarding the superiority of ANAN's recovered audio.  The ANAN NR and NR2 features basically eliminate noise without having a noticeable effect on the audio.  The NB and SNB features remove various  periodic noise without having a noticeable effect on the audio.  The ANF feature removes carriers, period--no effect on the audio and carriers are completely removed.   Any honest comparison of the recovered audio, in real operating conditions, of a Flex to that of an ANAN quickly reveals the superiority of ANAN's DSP functionality.

In the company I operated, we regularly benchmarked ourselves against our competitors--this is a key method for product improvement.  My suggestion is that FlexRadio honestly benchmark themselves against the competition and use that information to develop the specifications for improved DSP functionality.

When FlexRadio introduced the "knob" versions of the 6400 and 6600, Flex entered the mainstream transceiver market.  Hams in the "knob" radio market space are used to noise mitigation features that work well and expect a transceiver in the FlexRadio price range to have these features.

The relatively poor noise mitigation features of the Flex 6000 series have been repeatedly discussed at length over several years without any substantial improvement.   I don't don't think it is unreasonable to ask FlexRadio to address these issues.

Larry, W1IZZ
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Mark K1LSB

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Makes me wonder how people like Simon Brown does it all. He's truly a one-man show -- he does all of the programming / debugging / implementing of all of the code himself (and he's a prolific coder). His software supports well over a dozen hardware manufacturers' products. He regularly interfaces (even cuts up) with his users on the groups.io page, and somehow still manages to find time to take off for gardening and DXpeditions. He usually states, weeks or months ahead of time, what new features will be in his next release, and he has always maintained a "release early, release often" policy. If someone in his user group posts up about a new bug they've discovered, you'll often see Simon requesting, "Post some screenshots so I can see what's happening". Often, just a few hours later he'll post up in the same thread, "I've found the problem, it's fixed in the next release".

And good gawd, his software user interface is simply beautiful. I used his software for several years before buying my Flex 6300, and the difference between the visual presentation of his software vs SSDR is like night and day. Sometimes I fire up my old SDRPlay receiver just so I can once again immerse myself in the rich user experience of Simon's SDR Console. It's almost like coming home again. Anyone who's used his SDRC v3 knows exactly what I'm talking about. The user experience just tosses everything (and everyone) else into the weeds.

And his software is free. All he asks for is some donation if you can.

Unfortunately he doesn't support the Flex 6000 series, perhaps because no one's ever requested it. Hey, maybe I should inquire into it..
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Neal Pollack, N6YFM

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Maybe FRS should hire Simon and point him at the steaming pile of DSP
code :-)
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Bill -VA3WTB

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Simon does a great job.
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Mark K1LSB

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I'll upvote that post!
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Dan KG0AQ

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"I can wait for a fix." -- Dan KG0AQ

Mark,

I became a flexer a long time ago. It began with the SDR-1000 and now my 6400. I have seen updates everyday...back in the SDR-1000 days when it was open source. It was more of a hobby company back then. 

Fast forward to 2019 and they have become a "real" company. Like any real company they follow the money. For Flex now that was V3 and multi whatever. That's fine by me. I'm not interested in V3 functions but they are a FOR profit company...it is their call. They listen to all customers but generally ones that they will profit from.

As I stated in the first EHam 6400 review, you have to be a patient person with Flex Radio and their software. If not go buy one of the other big three and be happy instantly and it will never change...besides firmware upgrades.

Our society has become a want it now, fast food, drive through mentality society. Once more, it's only a hobby. My advice is to chill and ANF will get fixed.

Somehow I have 312 countries confirmed with a bad ANF. No big deal breaker.

BTW  I love the WNB and TNF. They work well for what they were designed to do.

73 Dan KG0AQ
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Dan KG0AQ

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"So, for ANF, what exactly is it that we want?"

I want it to work as good or better than my 20 year old Icom 706 MKIIG. I don't think that is too much to ask. Almost any knob and button radio made in the last 20 years has a better ANF than my 2018 Flex 6400.

 Go to 40, 80 or 160 SSB any night and turn it on. Tell me what you think? You can't miss it failing miserably with +S9 signals..

Flex doesn't need specific engineering input. They know it's broke and should know how to fix or they wouldn't be good software based electrical engineers.. It's not like a bug that just happened. Every hardware DSP chip made in last 20 years works decent.  Sad, but fixable...someday. I can wait.
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Robert Lonn

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So I was on 20 meters about an hour ago.. While listening to this W2 in New York here in California,, a strong carrier popped up within the 2.3 KHz Bandpass, looked to be about 1.1 KHz away, someone tuning up his TX.. I hit the ANF and , boom, it was gone while the W2 was still readable.. I think that tells me everything is working fine!!! The W2 was a S5, the tune up was a S-9,,  Robert
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Craig Williams

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I agree but I was flamed in the community for my comments.
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Neal Pollack, N6YFM

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Hopefully you are no longer smoldering...   :-)
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Dan KG0AQ

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On weak signals and low noise floors the ANF works...ok. Go above S9 with a SSB signal and it falls apart.  Try listening to 40-160M tonight and post your thoughts.  73
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N5LB - Lionel B

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Dan, I'll try it on 75 this evening. Robert's experience above indicates it works when the intended signal is much lower than the carrier, as you also point out.  So is it reasonable to say that at some point, unknown, the ratio, signal to carrier, "breaks" the ANF; I think it is but at what point and if we reversed the ratio, does it still fail?

I have good signal generator and if I can find a combiner around here it will be an interesting experiment.  Maybe someone else in the community can try this.  I suspect Flex has but maybe in the lab and not in the adverse conditions we routinely encounter; not much value in replicating a lab test.

Has anyone ever used the ANF on multiple carriers? Does it work? Is it supposed to work?  
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N5LB - Lionel B

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testing ANF on 75 a bust here, way too much atmos.  But on 40m, with S6 atoms noise, and lightning crashes:

AGC on slow througout.

ex:1 signal, LSB 7233, S9, carrier 7230 S9. BW 3.3Khz. ANF seems to have no effect at any setting.
ex: 2 tuned to 7230.950 LSB BW 2.4 kHz, many overlapping SSB. carrier at S9 on 7230, ANF setting has an effect but very small and carrier still audible. 
ex: 3 tuning around 7230 to 7233 BW at 2.4, location of the offending carrier has an effect on the ANF performance. As the carrier is closer to the the tuned frequency the ANF performance is better but still does not knock out the carrier.
ex: 4 moved to 7300 SW station, BW 2.4khz, LSB, carrier at +20db over, tuned to 7301, so 1 Khz tone, ANF knocks the heterodyne completely out with some variation on modulation peaks.  Variation is minor. 
ex: 5 moved to 7315 SW station with carrier at +30 to +40 QSB, tuned to 7316 and ANF eliminates the heterodyne- AT ANY SETTING.   Once again, modulation peaks cause ANF performance to vary, but again, minor. 
ex: 6 on 7270.7 an S6 carrier, slightly above background noise, at 7269.7, ANF had no effect at any setting. BW 2.4Khz.

It's just data and a few scenarios.  But I would say that ANF performance is a function of the intended signal, and it's modulation peaks, AND the background atmos noise.  

Can anyone replicate and/or add to the data?

As a one off, I tried the ANF on CW signals, LSB mode two or three signals in the passband.  The ANF takes out one but not all and notch effect varies with keying, that is there is a time to attack the heterodyne and time to release. No real measurement here, but the release time seems shorter than the attack time.   ANF can take out one heterdyne only based on this informal test.

I feel this is a minor step in characterizing the ANF in real world scenarios and the results, though far from definitive, do seem to substantiate the comments posted by others in the thread.


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Chris Tate - N6WM, Elmer

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So based on what I am hearing here, it sounds like it works in certain conditions worse or not at all in high noise floor conditions, and usually on only 1 heterodyne, with improvement of success the closer into the tx qrg you get.  thats a sentence I can wrap my head around and a good message to the dev team.
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Bill -VA3WTB

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Chris, why I said what I said yesterday is because it is interesting how Flex is doing this.

In PSDR for the ANF there are settings we can custom. Taps, Gain, Delay, leak.

I wonder if they are making the same changes in the SSDR code mush as the same way in PSDR?

Or is there much more involved.
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N5LB - Lionel B

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I decided on a more analytic approach so I brought up Spectrum Lab - DAX to SL. 

Interesting data.

NB. NR, WNB off, AGC slow, AGCT set at approx knee.

Radio China just came up on 7285 so tuned to 7286 LSB and RC carrier showing about -70 dBm and I have a 1,000 hz heterodyne.

Using Spectrum Lab and ANF OFF the 1,000hz showed about -26 dB.
ANF On at 50% -45 dB
ANF On at 100% -57 dB. 

All of these are +/- due to QSB.

But interestingly, the Radio China modulation did not seem to have a major "audible" effect.  That is there was very little change that resulted in me hearing the tone.  On SL I could see the amplitude of the 1000Hz tone moving up and down with modulation, as expected, but the attenuation from the ANF stayed about the same.

I did a similar run using WWV at 10Mhz and offset by 1000 hz and even with the various voice announcements and time ticks and tones I was still seeing 35 - 40 dB notch on the 1000 hz tone.  It never was audible.

This seems to contradict what I found last night, but conditions are different at 2000z versus 0100z with a lot more noise,, signals, and QSB. 

I'm going to try Spectrum Labs on the later evening 40m conditions and try to get some meaningful data.

So, yes, the ANF works, and it is really pretty darn good with nulls in some cases of 40 dB.  But it seems affected by numerous factors, and using a haphazard search for test cases leaves a lot to be desired in identifying those factors.  My guess, the very high level of noise. QRM in the passband is too much data for the ANF to process.  That said, I have zero knowledge of how they handle the ANF process; so maybe I'm way off. 

The ANF zeroes in, apparently, on the strongest heterodyne and perhaps with multiple heterodynes (40m at 0100z + for example) at near the same amplitude it loses the ability to process the data.

I guess information can be good with a proper dose of skepticism. 

If anyone else wants to try Spectrum Lab, it's free, and the input can easily be selected from DAX. It has a bit of a learning curve - it's sort of a Swiss army knife of audio analysis.

It would be very interesting to have more data from users reporting significantly poor ANF performance to see if their scenario can be replicated.

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Craig Williams

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Finally an actual measurement. What a relief.
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Neal Pollack, N6YFM

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Does Spectrum lab run OK on Windows 10?   Is this the site;
https://www.qsl.net/dl4yhf/spectra1.html

Is there a tutorial or getting started document somewhere for interfacing the
Spectrum Lab program to Flex DAX audio stream?

Cheers,

Neal
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N5LB - Lionel B

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Works fine on W10x64.  It has help files and a manual.  Interface to DAX is straightforward.  On SL Audio I/O one of the choices will be Flex DAX 1 or 2. 
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Neal Pollack, N6YFM

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Thanks!
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Gary Schulz

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Is ANF supposed to work on AM or not?  My issues are far from subtle; The actual button is not clickable when on AM for me...  Also WNB just causes the spectrum to jump up and down and it acts like the AGC just starts pumping/oscillating.  Debating the relative performance of the DSP NR type functions is basically a moot point because non of the functions seem to perform well at all, at least on my 6700...My Elecraft KX3 seems to do a better job in many circumstances though I know it is not done in SW.
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Burch - K4QXX

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I have issues with the ANF but the WNB works great for me.  If you are getting pumping with the WNB, you have the level to high.  On some bands I can run the WNB at 90% or more and on other bands I can't run it more than about 70%.  Some days I have S9 noise on 20 meters and the WNB takes it down to S5.  If you run the WNB to high you can get all sorts of artifacts and pumping on the panadapter.
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Joe N3HEE

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Have you identified the actual noise source that your WNB works with ?  I have not seen any improvement at all with WNB turned on.  I suspect it only works on a very limited number of noise types ?
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Burch - K4QXX

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My issue is with powerline noise.  I have a buzz sound on most HF bands.  It gets really bad when it's dry outside.  Once the summer rains come and clean off the lines here in Florida, my noise gets better.  Before flex added the WNB, some days I couldn't use my flex and had to use another radio.  The WNB has done wonders to my situation.  That said, the two NBs on my old Flex 5000 worked better than the WNB on the 6000.  But the WNB was a huge improvement for my type of noise.
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K5ROX

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Flex ANF is 90% unusable.  ANF on every other radio I have works great, I have many.

If my memory serves me well flex Power SDR had a decent ANF.......
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Bill -VA3WTB

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I still use PSDR and I still can't get DSP to work that great. I can say though, I have noise here at times were the WNB drops the noise by 30db, it saves the day at times. And without a hint of distortion.

The ANF sure needs more work. but I still would not buy another radio to get a better ANF.
(Edited)
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Mark K1LSB

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The WNB does seem to work well on some types of noise. I have no complaint about WNB.
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Gary Schulz

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Strange. My WNB only causes my entire spectrum to jump up and down (like AGC pumping) and yes it happens at all different signal levels and gain/threshold settings. Completely useless on my 6700 and ANF is not selectable on AM where I need it most. Odd that some see benefit with these functions while many see only audio distortion (I see that with NB)... The other radios I have actually work reasonably well with noise reduction modes so not sure how this could be too location dependent.
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Robert Lonn

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Last night I spent about 2 hours on my 6600M.. 20,40 and 80 plus several Marine radio frequencies and SWL stations..I figure I could test out the ANF if a hetrodine was to appear..,, I ran into a situation 3 times where I felt it was a good test to turn on the ANF, and see what happens.. My expectations was very low after reading all these threads.. I dont use the ANF that often, I am more focused on the NR function.. Well, in all 3 cases the ANF completely eliminated the hetrodine, I mean 100% gone with zero impact to the quality of the audio.. So for me my testing left me 100% satisfied! I did not switch to SmartSDR to see if running remote would change anything? I would expect the results to be the same.. Still on version 2.xxxxxx.. I have had very good results from the NR, WBN and NB functions, just depends on what the noise source is.. With a ICOM IC-R8600 sitting next to the Flex, but better yet, a JRC NRD-545 that also has a Auto Tracking notch filter, i will try to make some comparison.. I know the NRD-545 notch has been very impressive in the past.. Not sure why so many folks are not having decent results from the ANF?? 

Robert




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Craig Williams

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Yup, I knew I could not be the only one.
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James Whiteway

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Just an FYI for those of us hoping that the upcoming v2.50 maintenance release would contain improvements to the ANF, the short answer is no.
According to Tim Ellison on the FRS Facebook page, when I posed the question to him, if the ANF issues would receive some needed attention, his response was:
"James Whiteway If it wasn't in 3.0.19 and the upcoming maintenance release for 3.0.19, then the answer is no. If we decide to do a 2.6, it might, but that is just speculation on my part. There is no talk at this time about doing a 2.6
"
I find his answer disappointing, but at least it is a clear, and honest, answer. It gives me an idea as to what, if any, options, I might look for to address this problem for myself.
I can either upgrade to v3.0.10 and hope someday, this issue, along with others, finally receive the attention they need. Or, I can look towards other manufacturers of SDR radios that already have a basic features working to their full potential. ( along with some other, useful to me features)
Time will tell.
James
WD5GWY

Oh, Bill. It appears.you were spot on, with your statement regarding the .v2.50 update. If I came across as
a bit harsh in my response to you, please accept my sincere apologies