apf gain control needed. 0-10db adjustable would be great.

Carl K5HK

Icom just came out with v2.00 firmware for the IC7600.  One added feature besides the waterfall was the addition of a gain control for the APF 0-6db user adjustable.   On the IC7600 setting the gain at 6db really brings signals out of the noise floor similar to pre v1.2 SmartSDR.  Since SmartSDR on the Flex 6500 early version change around 1.2 the apf gain is almost non-existent / noticable when APF is initiated.  The earlier version had a nice gain peak that really brought weak cw signals out of the noise floor.  Please strongly consider adding a gain control for APF of 0-10db to help optimize weak signal reception.  

Al_NN4ZZ

Hi Carl,
Interesting that Icom has that now.   My Yaesu FTDX900 also has a control for the gain.     

Agree with your assessment and here is a link to what you are asking for on the Flex---  it has 23 votes so far.  More votes can't hurt.....

https://community.flexradio.com/flexradio/topics/ssdr_v1_2_apf_could_use_more_gain_it_seems_diminish...

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

Steve N4LQ

Interesting that new firmware release for the IC-7600 added a gain increase to their APF. It's probably partly psychological since one could just turn up the volume but somehow it helps. 

Carl K5HK

Steve,  No it is more than psychological.....I can copy better than just turning up the volume because it peaks the signal out of the noise.  Volume/AF alone brings up noise with the tone peak alas.   SmartSDR did a nice job on that briefly before v1.2 but they changed the way it and other functions were implimented at v1.2 and lost that gain peak on APF.   I don't know whether they could just go back to old way of implementing APF and solve the problem or whether a gain control would even help in a APf function but it sure works good on the IC7600.

W5UN_Dave

I agree with this completely. The APF was a great addition (thanks for listening Gerald). My K3 APF severely out performs the 6700 APF. I know the Flex boys can beat this! I still go back to my K3 when doing very weak signal digging on 160 meters, or on any band for that matter.

km9r.mike

# 25

Carl K5HK

Dave,

Don't see anything from Gerald in this thread.  Did you contact him via email or phone and please give more detail as to what he said about how they are addressing the APF problems.  Thanks/73, Carl/K5HK

Steve-N5AC

There is currently a gain control for APF and it ranges from 3-12dB of gain -- BUT the output of the APF goes to the AGC to prevent overload and level the output.  The net effect is that it lowers the noise around the APF giving you better SNR without raising the volume at the same time.  To us, this seems to make sense.  However if you want to APF to also raise the volume, it's not going to do what you want -- you would have to increase the APF and raise the volume to achieve that.  I would be interested on comments based on this information and your experience with APF.

Steve N4LQ

Steve

What I do here is feed the audio into an external audio filter (Autek QF-1A). This makes CW stand above the noise plus it makes the sidetone blend beautifully with the received signal for cleaner QSK. I also use a speaker which is near resonant at 600 hz. 

Also this eliminates the need to "ride" the AGC-T as if it were a 1940's receiver. The external filter cleans up the mushy overload. Hey...If AGC-T is "AGC Threshold" then how come it still works with AGC turned off? Or is it really a threshold control?

I can't think of one radio that filters everything like this but it seems far superior to anything I've tried. 

BTW: All audio filters introduce their own noise. I tried many of the SCAF design but all were too noisy. So far this old Autek wins.

Steve N4LQ

Al_NN4ZZ

Steve,
I agree with Carl, Paul, Ken and others that before V1.2 the CW signals popped above the noise more.  Turning up the volume does not have the same effect.  Something changed.  

My understanding from some previous posts is the current control affects the Q or shape/narrowness of the peaking.   Other radios offer this capability to make it very narrow down to about 5 hz.   Maybe more control over this would be helpful also. From the manual:




The suggestion to expose the gain control was to let us tailor it to our preference like many of the others implementations of APF.   But if you are saying the existing slider is the gain (not bandwidth), maybe we just need a wider range of gain control.  

https://community.flexradio.com/flexradio/topics/ssdr_v1_2_apf_could_use_more_gain_it_seems_diminish...



Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

Tim - W4TME

If AGC-T is "AGC Threshold" then how come it still works with AGC turned off? Or is it really a threshold control?

A little light reading of the SmartSDR Software User's Guide answers this question:

When AGC is set to OFF, this means that a fixed amount of gain determined by the AGC-T setting will be applied to both fast and slow signals regardless of their level.  The more you adjust the AGC-T to the right, the more gain is applied and the louder the signal and noise will be.  The benefits of increasing SNR with AGC will be lost in this mode.  The other down side of turning AGC off is that the operator must to pay attention to the 'RF Gain' manually to avoid distortion due to overload by strong signals.  

Steve N4LQ

RE: "The other down side of turning AGC off is that the operator must to pay attention to the 'RF Gain' manually to avoid distortion due to overload by strong signals. "

The same downside applies when the AGC is ON. To me it seems like that unlabeled slider control is actually an RF gain control no matter if AGC is off or on. I think that explains why the so called AGC-T works either way and that's because AGC-T isn't actually AGC-T. One can have AGC turned on and still be BLASTED by strong signals but maybe worse.

W5UN_Dave

Steve, N5AC, with all due respect, the way to know if the Flex APF is working well is to hook up your K3 and practice for a while doing VERY weak signal reception, then use the K3 APF to familiarize yourself of how a very good APF works. Do this under very weak signal conditions with diversity enabled. You will be amazed how much better the K3 APF is at peaking up those signals which weren't even readable before applying  and tuning the K3 APF.

Right now, the K3 APF is my standard.

W5UN_Dave

I used an Autek QF-1A analog peaking filter for years during the early part (back in the 1980's and 90's) of my 2 meter CW EME work. I could not have made more than half as many contacts without it.

That being said, there is no reason that a peaking filter just as good or better than the QF1A could not be built into the SDR radio. The secret is to permit  the APF to have a little ringing at it's deepest setting, which tends to cause the signal to "jump out" of the background noise. (one time that ringing actually helps). The other thing is to permit the user some means of easily controlling audio pitch (best done with a knob in one hz increments).

Carl K5HK

Steve,

Thanks for you response.  On further testing I notice that when I adjust the single APF slider on 100hz cw bandwidth I can hear a distinct peak on weak signals when apf set 80-90%.  I think it would still be useful to have seperate gain control for APF however although operating results are much improved now that I have set apf to 80-90 percent verses lower setttings.  I assume gain is increased with Q by that control.  

What would be the bandwidth/gain range correlated to 80-90% apf setting when CW bandwidth at 100hz?  I appreciate the clarification and hope my input helpful to others.  It actually brings weak signals out of the background now like pre 1.2v did.

73, Carl K5HK

Al_NN4ZZ

Hi Carl,
I also keep the current slider set to about 90.   I don't see a lot of variation as I move it up and down but it does seem better closer to the high end.  I leave APF on since I don't see any negative effects and it does work, but I would like to see it work better.  
IMHO It's not quite as good as some other radios.   But I think with more user control over the gain and Q (or bandwidth) it could be the best.

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

Walt - KZ1F

Note to all: Don't click it twice, it will erase your vote. So watch the counter when you 'like' it as it might drop if you've already 'liked' it in the past.

Steve N4LQ

Someone explain how increasing the slice volume is different than increasing APF volume.

Al_NN4ZZ

Hi Steve,
Here is my attempt to explain what I hear as the difference.  Others may be able to provide a better explanation. 

Increase in Slice Volume -- both the signal and noise volume are increased in the same proportion

Increase in APF Volume - the signal (CW tone frequency) volume is increased and the noise (audio frequencies not in the narrow bandwidth) are decreased.  The difference between the two levels is greater.  The CW signal seems to pop up out of the noise. 

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com 

Steve N4LQ

I guess I'm trying to relate this to an analog system which may not be relevant but normally "filters" don't amplify. the amplification comes after the filter. So you're right back to increasing slice gain again. In fact, analog filters attenuate. Whatever the filter passes, including noise, is going to be amplified.
This is why I wonder if some of this isn't just imagined. 

Al_NN4ZZ

From above.....

Steve - N5AC, VP Engineering

There is currently a gain control for APF and it ranges from 3-12dB of gain

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

Steve N4LQ

But is it really adjusting the gain of the filter or of the amplifier? Given the difference between a filter and an amplifier I suspect the latter. 

Ken - NM9P

The only way I have ever experienced being blasted by strong signals with AGC ON was if I had AGC turned WAY too far to the left (reducing sensitivity on all but the strongest signals) and turned the slice volume too high in order to compensate. Then when a signal was finally strong enough to get over the threshold, it played at the "normal" boosted volume., which was then blasting. Overdoing it on the AGC-T, very far below the knee or sweet spot, requires excessive audio gain settings.

Steve N4LQ

Yea but a $4500 rig shouldn't have a "sweet spot" or at least it should find it itself. IMHO

Jay Nation

My understanding, and I'm probably wrong, is that the APF function is less a filter and more an equalizer. It boosts or cuts the audio frequency thats been selected. My guess is its similar to a TNF filter as in it only acts on a narrow slice of the AF passband, and within that slice it finds the signal applys whatever gain is set on the gain slider and cuts the gain of everything else in that narrow slice. in other words it filters out everything but the signal and enhances the signal itself. Its a very selective graphic equalizer. It finds the peak signal inside the narrow slice, centers on the peak, trys to follow it and only apply the boost to the peak and cuts everything but the peak.
Sort of a reverse ANF. 
I repeat. My understanding is a guess.

Jay - NO5J    

Steve N4LQ

There was a time when I understood my radios but these are strictly appliances. 

Jay Nation

Right. But it's a software defined appliance. It's only doing what it's programmed to do. When it's not working as intended, it might need a better program. You will know it's time to sell, when those better versions stop, They don't have to stop. Figuring out how to emulate an appliance in software is hard and slow. Getting it exactly correct is only going to happen once. If that happens, why even consider selling the perfect appliance, that it's finally become? That might be profitable, others will want a perfect appliance too. A real sellers market, you set the price, and the buyer won't even complain about the shipping cost. Sometimes, I wish I was software defined, and that I could code myself a better life. But I'm stuck with reality.
 
The weird is 10 over S9, I think.
Jay - NO5J        

Walt - KZ1F

@Jay - reality is what you make it. To do otherwise is to exist in someone else's reality. We are all our own self fullfilling prophecy.

Carl K5HK

My feeling too Al and why I have kept reposing this question several times since v1.2 made APF worse.   I am sure Flex will continue to refine it but if we don't keep pointing it out with respect to other rigs apf functions why would they worry.

Carl K5HK

Dave,

Yes I could do the same thing.  The reason I keep revisiting this here is that SmartSDR is perfectly capable of doing it all in the rig and anything I had is a ton of external stuff to tweak and all the attended wires, plugs and cables asking for RFI problem.   One of the big reason I choose flex is because they are really trying to do all this in software.  I just feel they have in the past and can do better on this issue.

Steve-N5AC

Let me take another stab at this and see if it helps.  In a digital world, signals are time sampled. The samples exist in a number space that is either floating point or fixed point.  Regardless of the floating/fixed question, there are a fixed number of bits that represent the signal.  In a fixed point system, this is the number of bits in the number, like 16, 24, etc.  In a floating point system, most engineers use the IEEE-754 standard because it is implemented in most modern processors.  In floating point, there is amazing total dynamic range, but lower instantaneous dynamic range.  For example, with a single precision floating point number, we can represent 10^-126 in one sample and 10^127 in the next sample, for a total dynamic range of over 2,500dB.  But in radios, the signals occur at the same time so it is all about the bits in the mantissa (part that holds the numbers and not the exponent).  In a single precision IEEE-754 float there are 23-bits of mantissa. If we figure on about 3dB per bit, this is only 69-72dB of dynamic range.

So why does this matter talking about APF?  When we are placing a signal inside that number space, we shoot for the best SNR which means "price is right rules" -- get as close to the largest number you can, but don't go over the largest number that can be represented in the number space.  Why?  The signal would clip; clipping causes distortion; distortion is bad.  So we have to guess for a normal volume, how much louder might signals get temporarily so we are sure we have the headroom to accommodate them when this happens.  Then we build the system around that nominal level.

Now, we add APF or some other filter.  As has been pointed out, arguably the best way to make filters work in a system is to make them unity gain in the passband.  This way, you can insert or remove filters and the overall volume of the system doesn't change.  But we have an issue in that operators tend not to always recognize the benefit in increased SNR (what you really want) and instead seem to want the volume to increase when filters that are billed as helping you hear a signal are engaged.  So we gave the APF some gain.  If we do not put AGC after APF, then you could raise the level of the APF with its gain past the number space limits and into distortion.  Then we would hear "when I turn APF all the way up it sounds distorted."  

Also there are calls for higher-Q in APF, but the Q is already reasonably large.  We would argue that having some noise in the background is useful as a reference to make adjustments and copy the CW.  If you engage a 50Hz bandpass filter and crank the APF all the way up, I would argue that you're not doing yourself any favors -- you are limiting all sound to a 50Hz region which will make any noise in that region sound exactly like the tone you are listening for.  APF on top of this further exacerbates the problem by limiting the tone to a very narrow region of frequencies.  Any noise that makes it to the AGC will, by definition, only reside in this narrow frequency band and will sound exactly like random CW on the frequency you are listening for.

Sometimes when we hear customer feedback it makes complete sense, we realize how we could do something different, we implement it and everyone is happy.  In this case, it feels to me like there is a gap between perception of operation (how the system feels to you when you operate it -- does it do what you want and expect), how the system actually works and everyone's understanding of what to do next (including ours).  You guys know we're happy to make changes that will result in better operation for most folks.  This is what we're all about.  But if we add more gain to APF, it's going to get squashed in the AGC, as it should.  If you don't like this answer, you need to turn down your AGC and turn up your volume -- you will have lower SNR overall, but APF will make the volume get louder when you turn it on.  If we place APF after AGC, you will be able to overload the digital range of the system or we eliminate the gain in APF and then we're back to "it doesn't seem to do anything."