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Flex 6000 Receiver Tuning - How the AGC-T works

RX Receiver tuning by Tim W4TME – Do you know how the AGC-T works?

Video Transcript

This video’s full transcript has been provided below for your convenience.

Hi, my name is Tim Ellison. I’m W4TME, and I’m going to talk to you today about Optimizing Reception for the Flex 6000. Affectionately called, Can You Hear Me Now? How is reception optimized for the Flex 6000? In general, what we’re going to be doing is we’re going to be using a set of techniques and features that come with the Flex 6000 series radios to optimize the Signal to Noise Ratio.

You’re going to hear me talk a lot about SNR and Signal to Noise Ratio, and for those who are unfamiliar with the term, it essentially means that we are trying to improve the mixture of signal and noise so that there’s more signal than noise. Just think of it as being outside in a very windy, windy day and if you’re whispering, it’s hard to hear, but if you’re screaming, then you’ll be able to be heard more easily. And that’s essentially an example of having more signal against the noise background.

There are multiple features provided with the Flex 6000 hardware and software to improve the signal-to-noise ratio, and I’m going to discuss all of those. The higher the signal-to-noise ratio, the easier it is to hear weak signals at or near the noise floor. And this is very important for people doing weak signal digital modes and CW, Dxing, trying to find those signals right there at the noise floor.

For phone type operation, it is important, but it’s not quite as important because you do have to hit a certain threshold with voice so that you can make it out over the noise. And one of the key things that I want to walk away with on this slide is that when you’re using these techniques, a lot of times less is more. I’ve seen a lot of situations where people have tried to improve their signal-to-noise ratio, and they’ve got all the features turned on. And that really is detrimental to optimizing your signal-to-noise because they’re specialized tools for different noise and you shouldn’t be using tools that you don’t have to. That’s the takeaway.

Let’s talk about the different types of areas that we’re going to discuss. One is going to be the Flex 6000, the hardware itself. The 6000 is direct sampling SDR provides for a low noise, distortion free reception and high RMDR, our Reciprocal Mixing Dynamic Range Receiver. You can’t hear weak signals if you have a bad receiver, and the Flex 6000 is one of the absolute best that’s out there, based on the SDR design.

In the radios, we do have an RF Preamp, and we use a low noise figure Preamp for improving system sensitivity and lowering the RF signal-to-noise Ratio. And this is an important step that often gets overlooked by people when they’re setting up their radios and we’ll talk about that.

The AGC, this is like the silver bullet of noise mitigation and for optimizing signals-to-noise Ratio. The AGC in SmartSDR is an incredibly powerful feature, it’s got great capabilities, and if it’s used correctly, will make the difference between not hearing weak signals and hearing weak signals. And we will spend quite a bit of time talking about the AGC. There are noise mitigation features in the software. We do have a noise reduction, a noise blanker, a wideband noise blanker, and we’ll talk about the different kinds of noise that those type of noise mitigation features address and when and when not to use them.

And then we do have some signal enhancement capabilities too, with certain radios you can do diversity reception. We do have an equalizer that it can be used on receive. And this is a very important feature in the radio. And for CW people, we have an automatic peeking filter and we’ll talk a little bit about that too.

“The Flex 6000 are great for listening and wearing headphones for long periods of time, without worry about stress or listening fatigues.”

Let’s talk about the hardware. Direct sampling SDR provides for a low noise distortion, free reception and high RMDR reciprocal mixing dynamic range receiver. Direct sampling with wideband ADC, we are able to achieve a very low minimum detectable signal or MDs. And having a receiver that has really good MDs characteristics is very important.

Along with certain analog devices, such as mixers, are non-linear. Meaning that when you put a signal through them, you are going to get noise and inject it into the signal. And we’ve done a very, very concerted effort to engineer our radios, where there are no non-line your devices in the RF signal path. There is no IMD that’s imparted into the signal. And what this results in is a IMD free received signal. The receiver is in very, very quiet, you don’t have the IMD.

Where IMD can cause some problems is with listening fatigue. You can’t actually hear it, but your brain hears it. And your brain is constantly trying to compensate for the distortion that it’s hearing. And that’s what brings on listening to fatigue. The Flex 6000 are great for listening and wearing headphones for long periods of time, without worry about stress or listening fatigues. The Flex 6000 utilizes decimation to improve the effective bit depth of the ADC, which increases the reciprocal mixing dynamic range and provides for improved signal-to-noise ratio and for performance. The greater your dynamic range of the receiver, the better signal-to-noise performance you can get out of that radio.

And last but not least, preselectors. We have preselectors in most of the models of our radios that attenuate strong out band signals for better RF isolation. Overly strong signals can somewhat desensitize the radio. And this is most common in a multi contest station where you’ve got multiple radios that are close by to one another that are all operating at high power. Preselectors can be very beneficial there. We start out with really good hardware features making the receiver one of the top receivers. And it only gets better from here.

Understanding how the RF Preamp works

The one thing I would do want to talk about is understanding the RF Preamp. The RF Preamp in the radio is a little bit misunderstood by people. They expect that if you crank the Preamp up, that you should see the noise and the signal increase in volume. And that’s not actually the way that it works. What we do is we utilize low noise figure RF Preamps, and it’s to minimize additional noise in the received path, not just to amplify signal and noise. RF Preamps do not actually change the signal level at the antenna connector, but what they can do is to improve the signal-to-noise ratio of incoming signals.

And you can visually see this on our radios by watching the noise floor on the pan adapter drop. And this is true in all cases except for one situation. And that where the antenna is, what we call, noise limited. Which means that you have such a high noise level at your location, at the spirit type noise, adding pre-amplification will not provide you any kind of benefit.

One of the things that we look at is that if you enable the Preamp, you want to see the noise floor start to go down. If the noise floor drops, as you increase Preamp gain, then you’re going to start exposing signals that are below the noise floor, which are not in the atmospheric noise floor. And this is what I talked about, about where your radio is not noise limited. And when you do that, that improves the signal-to-noise ratio, because you’re actually dropping the level of the noise while the level of signal stays higher.

Essentially what you’re doing is that if signal and noise are here and you drop noise down, the signal over here is going to be higher and you’re going to be able to hear it. If the noise floor does not drop, when you add Preamp gain, then you are noise limited. And it’s essentially what you’re doing is, in the example where you’ve got noise and signal, when you do that, you’re actually bringing the noise level up, signal level always stays the same. You’re going to be hearing more noise and you’re going to bury that signal. And as you bury the signal and what you’re doing there is you’re lowering the signal-to-noise ratio.

[10:00]

There is one caveat and this generally is not a detriment, but as you add Preamp gain, you’re actually subtracting from the dynamic range of the radio.

For example, if you add 10 dB of Pre amplification, you’re actually going to take 10 dB away of dynamic range. For people who are looking for weak signals and trying to get that out, you really don’t care about that upper level dynamic range where you lost 10 D. Where you care about that is that if you are on a band that’s got incredibly strong signals and incredibly weak signals. In that case, you may see some detriment. But in general, because we have such high dynamic range receivers, you’re talking about, in my example, 10 dB, you’re talking about the difference between 105 or 110 dB of dynamic range going down to 95 or 100 dB of dynamic range. And you can look on Sherwood’s page and see that any radio that’s got greater than 95 dB of dynamic range is a very, very good receiver.

How does the AGC work in SmartSDR

Let’s talk about the AGC because the AGC is one of the more powerful features in the radio. And it’s a little bit misunderstood. A lot of people like to say, “Oh, well, the AGC and setting the threshold is just like changing the RF gain in a traditional radio.” And that’s not actually true. The behavior seems kind of the same. And so some people equate that, but it actually really isn’t. What the AGC does is that it changes the gain or the volume of the recovered signal so that you can maintain a suitable listing level.

And what that means is that if you’re listening to two signals in the band and one is incredibly, incredibly strong, and the other one is weak, with the AGC set, you can actually reduce the volume of the strong signal where that will make it a little bit more comfortable or easier to listen to. And won’t over wash out the weak signals. The AGC threshold is the main control for the AGC algorithm. And it sets the maximum gain or the maximum volume applied under any circumstance.

And I’m going to show a graph of this in just a few minutes, it’ll help clarify this. But since the noise floor in the radio is relatively constant on any given band, at any given time, the AGC should be adjusted using the AGC threshold so that the AGC never applies gain or volume to the band noise, but only applies volume to signals, which are above the band noise. In doing so, the AGC can reduce the ambient level of noise that you hear and help signals pop out of the noise. And this is absolutely true. I’ve had people that have called me when they finally were able to get the AGC working right, they said it was just amazing how the signals would just come out of the noise floor.

One of the cool things about our radio is that each slice receiver has its own independent AGC settings. You can be working multiple bands that have different noise characteristics on the bands and each receiver you can fine tune and adjust for that.

Let’s talk a little bit more about some of the details inside the AGC. The AGC in SmartSDR is a dual track system. Meaning that it can track both slow and fast increases in signal strength and make an appropriate gain correction decisions based on the presence of each. And not all noise or all signals that the AGC is listening to are the same. You can be listening to rag chew or sideband in the summer and you’ll have lightning crashes. The lightning crash is a very fast, pulse type noise that hits the receiver. And our AGC is able to track those type of noises as versus a strong sideband signal coming on the radio and can correct and make gain changes based on the slow and the fast increases in signal strength.

This makes the AGC a lot more smoother and works better over a vast variety of band conditions. There is a speed or an aggressiveness setting in the AGC. You’ll see it’s set for fast, medium, or slow. And this determines how quickly or slowly the AGC recovers after attenuating a strong signal. Fast is obvious. It will recover and change or reduce that gain change down quickly. And then there’s a medium and a slow. And there are advantages for using fast, medium, and slow. And we’ll talk about that in a little bit.

There is a setting of AGC off, and when the AGC is off the dual track algorithm, AGC algorithm, is not in play. It is not working at all. All you’re doing with the AGC off is that you’re adding a fixed amount of gain to the signal volume, no matter whether it’s noise or signals, weak signal or strong signal, it’s all going to be amplified the same. And in general, you never really want to operate the radio with the AGC off. There can be situations where you want to do that. And one of those would be that if you’re using a digital mode application that has its own internal AGC capabilities, then you may want to turn it off so that you don’t have two AGCs trying to compete against one another.

Noise mitigation features

What is RF noise or EMI?

Let’s talk about some of the noise mitigation features. What is RF noise or electromagnetic interference or EMI? RF noise or EMI is a complex wave form, which is a pattern, whose source can be either manmade or natural, and is generated by changing of currents or voltages. That’s the technical term of it. RF noise can have a periodic or a well correlated wave form, a signature, or it can have a random wave form. Some examples of periodic or correlated noise is ignition noise, where you hear a pop, pop, pop, pop, pop, pop, pop, that’s happening at a certain frequency. That is an example of periodic noise. Or you can hear noise that sounds more like bacon frying or sizzle, and that is a more random type noise or what they call white noise.

And those two type of noise have completely different wave form signatures. The different noise mitigation features in the radio are designed to address these different types of noise patterns. If you’ve got a periodic noise, you want to use a noise mitigation feature that’s going to take care of periodic noise. Whereas if you have a high bit of random noise, then you’ll want to use the noise reduction feature, which is actually designed to address more random noise.

One of the key points that, I’ll say this several times throughout the presentation, and hopefully the point will make it home, is that if you use the wrong noise mitigation feature for the type of noise that you’re experiencing, it can be significantly detrimental to your optimal reception. If you turn a noise blanker on that’s expecting to hear this periodic noise, and it doesn’t have that periodic noise, it’s going to try to apply the algorithm to signal and that’s where things start getting worse. You just want to be very careful about that. And we’ll talk a little bit about that too, in the future.

“Once you’ve gotten the Preamp set and the AGC set, that’s going to take care of about 80, 85 to 100% of your noise issues or optimizing reception.”

The noise mitigation features that are in the radio. The first one I want to talk about is noise reduction. The noise reduction feature is designed to address random noise patterns, often referred to as white noise. The noise reduction adaptive filter increases the correlation between the signal input and the signal output, with the assumption that noise is uncorrelated and should be canceled out. That’s essentially how the noise reduction algorithm works. We have a wideband noise blanker, which we call WNB for short. And it is an exclusive feature of the Flex 6000 and can be used to address fast rise time pulse-type noise. That is very broad banded in nature. And this type of noise can be periodic noise from power line hash and car ignitions.

The wideband noise reduction operates at the SCU level rather than at the Slice level. It’s applied to the entire pan adapter. And one of the neat things about the wideband noise reduction is that we’re actually subtracting the noise from the pan adapter itself.

[20:00]

When wideband noise reduction is working effectively, you can actually see the noise decrease in the pan adapter, you see the noise floor drop. And I’ve actually seen situations where wideband noise, the wideband noise blanker was able to affect a 20 to 30 dB decrease in band noise. And if you’re talking the difference between minus 90 dBm and negative 120 dBm for your noise floor, that’s a significant amount of difference, getting rid of a lot of noise.

We also have a regular noise blinker or a NB, and it’s designed to mitigate large impulses type noise and periodic noise. And it differs from the wideband noise blanker in that the normal noise blanker works at the Slice level. The Slice is actually processing 24 kilohertz of bandwidth. And the noise blanker is working on that 20 kilohertz with a bandwidth of the slices its processing. And it addresses periodic noise, just like the wideband noise blanker does, but it will take care of certain periodic type noises that the wideband noise blanker can’t take out.

The good thing is that you can actually use any of these noise mitigation features in concert with one another. If you’ve got a mixture of periodic noise and pulse noise, using the noise blanker and the noise reduction together may provide you some additional benefits.

SmartSDR signal enhancement features

There are also some enhancement features that are within SmartSDR that can be used. And one of those is utilizing the equalizer. I know some of our hands out there suffer from hearing loss, certain frequencies, what we call frequency-specific sensorineural hearing loss, and you can actually use the receive EQ to help increase frequencies, where you may have some hearing loss in those areas. Utilizing the EQ on receive can can help. And this can be used for CW and for phone Mo modes.

There is an automatic peaking filter or APF. This filter is available when operating CW and it’s a peaking filter. And what it does is that at the frequency of your side tone, which is where you’re zero beading in the signal that you’re listening to, we have a peaking filter that actually increases the gain and puts what would be the inverse of a notch filter, there onto that signal to help bring that signal out of the noise.

The other feature that’s in the radio that we have is stereo diversity reception. Now this feature is only capable in dual SCU radio. It’s only available in the Flex 6700 or the Flex 6000 / 6000M series radios that are dual SCUs. And how this feature works is that you have two independent receivers with two independent antennas, and you’re receiving the same signal on both receivers at the same time, and you’re mixing their audio together. You mix the audio together, but you pan it out so that one receiver is in one ear, one receiver is in the other ear. And what that helps with is primarily with selective fading. If one antenna receiver combination is hearing the signal a little bit better than the other antenna receiver combination, then your brain will be able to listen to both of those and will pick the ear where it’s got the predominantly better signal-to-noise ratio. And that’s one way that you can use diversity reception for increasing SNR.

How to achieve optimal reception

Improving SNR in 4 steps

How do we do all this? I’ve talked about the different features and capabilities in the software. Let’s get down to the nitty gritty and talk about actually how we do this. And it’s a very simple process. There’s essentially four steps that you get go through. And while this might seem kind of complicated and everything, once you do this four or five, six times, it becomes incredibly second nature, and it doesn’t take very long to do it all. At the beginning, it will take you a little bit of time to get your radio set up, but once you see the benefits of it and you do it long enough, you’re going to gain, what we call, muscle memory. Where you’ll be able to set the AGC rather quickly.

Step one in the radio is that we want to make sure that the receiver, the hardware is optimized for signal-to-noise ratio first. And we do that by setting the RF Preamp for the current band conditions in the antenna system. You may have high gain antennas or low gain antennas, which will require different types of RF Preamp type settings. And also the bands, if you’re up on 10 meters or six meters where band noise is fairly low, versus down at 80 or 160 meters, where band noise can be incredibly high, you’re going to have two sets of very different Preamp settings for those type of band conditions.

The second step. And this is actually the most important step in the process is select the AGC aggressiveness and properly set the AGC threshold, or the AGCT. And I put a little thing in here that this is the most important step and it truly is. Once you’ve gotten the Preamp set and the AGC set, that’s going to take care of about 80, 85 to 100% of your noise issues or optimizing reception.

It’s at this point that you’re going to want to try using some of the noise mitigation techniques, the noise blanker, the noise reduction, the wideband noise blanker, and see if that helps improve your signal-to-noise ratio. There are certain times where you can try these things and they’re not going to work. And that’s okay. It means that the type of noise that you’re hearing is not the type of noise that these features necessarily will improve. Now. I will like to say that there is no magic bullet here where you’re going to set this, and then all of a sudden all the band noise goes away and all you’re going to hear is full quieting, single side band on 20 meters. It’s just not going to work like that.

The demodulation modes, there’s always noise there. You’re going to hear that unless you’re operating digital voice or a different kind of demodulation mode. We just want to get that expectation out of the way.

The last thing you want to do, once you set the first three steps up, is to see if any of the signal enhancement is needed by using the EQ or on CW, the APF, or if you’ve got the correct setup for diversity, use diversity reception. Now that we’ve gone through the four steps, let’s go through each one of them individually and talk about them in a little bit more detail.

Step 1 Adjusting the RF Preamp

Adjusting the Preamp. Selecting the Preamp is not a set and forgive at step, changing band conditions especially at the lower RF frequencies will require readjustment of the radio. In general, no Preamp amplification is normally needed on most of the HF bands due to environmental and atmospheric noise being the predominant type of noise at your QTHs versus the internal radio noise. And you’ll go through the process of setting the RF Preamp, there’s a procedure we’re going to talk about here just a second. But just in general to know that as your operating higher in frequency, that’s really where the RF Preamp really is going to show you the most benefit.

Some rules of thumb here with the RF Preamp. If you increase the RF Preamp gain and the noise floor in your pan adapter visibly drops down, then you have improved the signal-to-noise ratio and the ability to pull weak signals out of the noise. If you add 10 dB of attenuation to your noise floor, and the signal does not rise, then that means that your noise figure is well below the atmospheric noise. By adding 10 dB of attenuation, you’ve actually added an additional 10 dB of dynamic range. Now where the attenuation can be a benefit is again, on those low bands, 160, 80 meters, when there’s a high noise level. Sometimes attenuating that noise out will give you better dynamic range and will optimize the signal-to-noise ratio for reception on those bands.

[30:00]

This is the steps to adjust the Preamp. You’re going to use your Slice S-Meter, and you’re going to change it into dBm mode because you’re going to want to a meter that’s got a little bit more accuracy. Not accuracy, excuse me. A little bit more precision so that you can see the differences in the changes that you’re going to be making. The first thing you want to do is disable all the noise mitigation, turn off the noise blanker, the wideband noise blanker, the noise reduction, APF turn all of that off. You don’t want that affecting the RF Preamp behavior here. Tune to a portion of band where there are no signals, so that you’re only hearing the noise form. Disconnect the antenna. You can either do that physically by changing your antenna switch to disconnect it. Or you can just change the receive antenna on the Slice to a antenna port that does not have an antenna connected to it.

With the antenna disconnected, you’re going to want to read off the S-Meter and get your dBm reading. Then you’re going to go back and you’re going to switch your antenna back on, and you’re going to notice that there’s going to be a change in the signal strength. The signal strength going to go up because you’re adding an antenna that’s bringing signal in. What you ideally want to see is the difference between no antenna connected and your antenna connected with no signals on the band is about an eight to 10 dB increase in signal. And basically, you’re going to be looking at your S-Meter for that. If you add 10 dB of gain, and you see that signal drop eight or… Excuse me. You see the signal increase eight to 10 dB when you add the antenna on, you’ve hit the number. If you’re not quite there yet, you can keep adding gain until you see the difference between the antenna disconnected and the antenna connected, where you see that eight to 10 dB differential.

There’s a lot of times where at zero dB, you’re going to make the change and you’re going to see it immediately. And that basically indicates that you’re fairly noise limited, and you don’t need any of the RF Preamp. When we get down to it, if the signal level at the antenna connector, it goes up significantly by more than 10 dB, you have too much gain, you need to reduce your RF Preamp gain. If the signal goes up by much less than eight dB, then you need more gain. Like I said, you just play around with the gain settings on the RF gain until you hit that eight to 10 dB difference between the antenna being connected and disconnected.

Step 2 Adjusting the AGC

Setting AGC speed

Once you’ve set that, the RF Preamp, in general if you’re sitting down for the evening and you don’t hear a lot of changes in the band conditions, it doesn’t get noisy or quieter, then you can pretty well leave the Preamp alone. But if you do notice that band conditions are changing, you may want to just jump back and rerun that process again, real quickly. Just to make sure that your Preamp stays optimized for the band conditions.

Now that we’ve got the Preamp done, we’re going to talk about the AGC. And I put this in red so that it would stand out and properly adjusting the AGC is the most important step, and it’s the most powerful noise mitigation feature that is in the radio.

And primarily most people, when they’re receiving the noise they’re hearing, it’s atmospheric noise. It’s band noise. Occasionally, you’ll be overwhelmed with manmade noise, but primarily most of it is atmospheric. And setting the AGC threshold correctly will help mitigate that type of atmospheric noise. The first thing you want to do is you want to set the AGC speed or aggressiveness mode, which is fast, medium, or slow. And how you set this really depends on a couple of things. If you’re listening to a loud voice or rag chew or things like this, you may want to use AGC slow so that it will resist increasing the game between syllables. And keeps more of an even kind of keel volume with what’s going on. The AGC slow is also preferred for high signal-to-noise ratio conditions on quiet bands.

I primarily, when I’m operating, I’m usually switching between medium and slow, most of the time. Occasionally I’ll use fast. Fast and medium provide a faster level of recovery for situations where you want the system to follow more closely, to follow more closely the dominant signal in the passband. And this is preferred in more noisier conditions. If you have a higher band noise in general, you might want to use the medium or the high AGC setting. That’s a pretty quick thing, you just set that based on the overall operating conditions you’re experiencing at that time.

Setting AGC threshold

Now we get to a setting the threshold. And setting the AGC threshold, it’s very, very, very, very, very important. And this is where all the magic happens, really. And it’s a pretty simple procedure for doing this.

Again, we’re going to want to take the receiver, we’re going to tune to an area where there’re no signals, where all you’re hearing is just the band noise. Tune to that quiet spot where you can only hear the noise floor. Then starting with the ACC threshold value, somewhere about the midpoint and 50 is not a bad point to start, you want to start to adjust the AGC-T slider slowly to the left or to lower values, for lower gain. And you want to make the adjustments slowly and wait a bit, excuse me. And then listen for the volume change. What you’re going to do is you’re going to start decreasing the AGC threshold go down and down and down and down and down, until you start to hear the noise not being amplified, the noise is going to get quieter.

And what you’re listening for is basically about a 50% reduction or a 3 dB noise decrease in noise volume and you just hear that through your ear until you’re at a point where you’re hearing about half the amount of noise volume that you heard before. When you get to that point, that’s pretty close to the AGC knee. And that’s the point that you want to be at. Once you find the threshold where the band noise starts to decrease, this is called the sweet spot. And depending on the AGC conditions, that number can be anywhere between 35, 45. Once you get below about 25, you may have to add some actual volume to your radio to compensate for the decrease and band noise.

I’ll give you a perfect example. At my QTH on six meters, I’ve got a really, really low noise floor with my Preamp set correctly my noise floors somewhere in the neighborhood negative 140 dBm, and it’s very quiet. My AGC setting sits somewhere between 18 and 19 at that level. You can have very low AGC threshold settings and to compensate for the lower volume, I just turned up the volume on the radio.

Once you found that sweet spot, then you just basically tune the receiver back to where there’s signals present and that’s it. In general, if the noise floor is not changing very often, then once you set the AGCT, it’s fine. Now, when you change bands, you’re going to want to readjust the AGC threshold, or if band conditions change rapidly you’ll want to reset the AGC threshold. But in general, once you set it you can operate for a couple of hours without having to worry too much about changing it.

AGC-T incorrect

I want to do a graphical description of what we’re doing here. And in this graph here, you’re going to see this dotted line that’s down here in the middle of the noise floor. That is the bottom or the base of where the AGC operates. And any signal level above that dotted line, the AGC is going to amplify that signal. And anything a below the solid yellow line, that’s the maximum AGC setting. And anything above that is not going to be amplified. And as you see in this graph, this is set incorrectly because we’ve got the minimum setting way down in this noise. From the dotted line up to the bottom of the noise floor, that area right there, the AGC is amplifying that band noise.

[40:00]

You’re hearing more noise than you should, or you need to be hearing for optimal signal-to-noise ratio. Now, when you adjust that AGC threshold so that you start hearing that decrease in the noise, what you’re doing is you’re actually rising that yellow dotted line up. It’s a little bit harder to see here, because right now that yellow dotted line is right at the noise floor level. You can see that in this red shaded area over here on the left, is that the area that the AGC is amplifying the volume of signals, it’s not amplifying the volume of noise, but it is amplifying the volume of the signals that are in that AGC gain range. Or in that what we call the AGC window.

AGC-T correct

And that’s a visual representation of what you’re doing. You’re actually adjusting the AGC threshold so that you are not amplifying band noise. It’s actually pretty straightforward and simple.

Step 3 Using noise mitigation features

We’ve set the Preamp, we’ve set our AGC threshold. At this point we’re probably 90% there on optimizing our signal-to-noise ratio for the receiver. And this is where we start using noise mitigation features. And essentially this is a try it, if it makes things better, use it, if it doesn’t, don’t use it. And if you have noise that sounds like sizzle or bacon frying, then try turning the noise reduction on. And once you enable the noise reduction, the noise reduction does have a threshold setting that applies the different gains to it. Once you’ve enabled the noise reduction, start moving the threshold slider up into higher values. And if it decreases your noise without adversely affecting your signal, then use it. If not, then turn noise reduction off because you don’t have the right type of noise that noise reduction is going to work on.

The same thing basically goes with Pulse noise. Which is mitigated by the noise blanker or wideband noise reduction. Turn the noise blanker on, adjust the threshold up, if it gets rid of the noise without degrading the received signal, that’s perfect. Then utilize the noise blanker, if not, turn it off. Wideband noise reduction is a little bit different in the fact that there’s actually a visual indicator to let you know that wideband noise reduction is working. if you turn wideband noise reduction on, you’ll see WNB show up in the top right hand corner of the pan adapter. And it’ll either be illuminated boldly, or it’ll be illuminated dimly.

And if WNB shows up dimly, that means that the software is not finding a noise that matches where the wideband noise reduction can actually act on it. You may also see WNB flash. It’ll flash back and forth, where it’s on and off and on and off. In these cases you’ll want to adjust the gain or the threshold setting of wideband noise reduction to see if you can get to a point where a gain setting that’s going to be on where the WNB algorithm is going to be working primarily all the time. If you can’t get it to that point, or it flashes on and off, or stays off, turn wideband noise reduction off, because it can significantly degrade the signal-to-noise ratio of a good signal when the algorithm is trying to work on noise that it just can’t find.

One other point that I wanted to make is that if you do use these noise reduction features and stuff, is that if you change bands or you shut the radio down and you start it up the next day, you’ll want to remember to turn this stuff off, because if you leave it on inadvertently, then you may be degrading your signal-to-noise ratio without actually knowing it.

One of the things that I have noticed after using the radios for close to 15 years now, is that very rarely do I have the type of noise where I need to use the noise reduction or the noise blanker, or the wideband noise blanker. I do have some situations around Christmas where Christmas lights bother me and I do need some of these features there. But in general, the combination of setting the RF Preamp and setting the AGC threshold really does exactly what I need to do to optimize signal-to-noise ratios.

Step 4 Using signal enhancement features

The last step you want to do after you’ve gone through all the noise mitigation features is to see if any of the signal enhancement features can work for you. Like I said if you have selective hearing loss at particular frequencies, say it’s at 1000 hertz, you can use the RX equalizer, go into the 1000 hertz EQ and bump the gain up 4, 5, 6, 8 dB to overcome that. And that should help add back some audio content that your ear is attenuating and can help you hear some of these weak signals better.

I talked about the automatic peaking filter a little bit before that’s used with only with CW. You can try turning on the APF, setting the gain settings and see if you like the way that that peaking filter sounds to your ear. Some people like it, some people don’t. The people who like it, love it, and people who don’t they just say, “Well, it doesn’t do anything for them.” Unfortunately there are no silver bullets where everything works for everybody, but we do have that particular feature in for CW.

Stereo diversity. If you’ve got a Flex 6700 or a Flex 6600 and you’ve got two antennas that are diverse in wavelength, which means that the antennas are separated by an odd multiple of quarter wavelength distance apart from one another. And if you can change the polarity of the two antennas, where one is vertical polarized, the other one’s horizontally polarized. If you can have diverse antenna systems like this, diversity reception can do wonders. Particularly with selective fading. I’ve used it a lot when I’ve been doing broadcast band Dxing down in the AM broadcast band, where there’s a lot of selective fading going on there. And by using horizontally and vertically polarized antennas, it does make listening to weak AM broadcast stations a lot easier.

The features really easy to use in the software. You enable the diversity feature. It automatically creates a brand new slice for you. So you have what’s called a parent slice and a child slice. Each one of these two slices are synchronous. It makes one synchronous receiver, which means when you change the frequency of one, it’s going to change the frequency of the other. Each slice is connected to a separate antenna. And the audio from each one of those slices is panned to the left and right. The optimal way of using diversity reception is with a pair of headphones, where you can listen to the left and right. And what ends up happening is that your brain is listening to both receivers at the same time and will automatically prefer the ear that it is hearing the signal the best out of. And your brain is actually doing the digital signal processing to pick out the receiver which has got the best reception characteristics.

And that basically sums up the talk that I had here. Sorry, that I was rambling and going on quick. We had a lot of material to cover and everything. But I did want to put a slide up here, there’re some links, we have some good articles in our help desk. We also have our documentation, our SmartSDR software user guide just explains all of these features in much greater detail than I have gone over on how to use them. I highly recommend going up and reading up on these as you use these. And also utilize our help desk articles. Those are great places for finding out information.

And I hope you’ve enjoyed this talk. And that concludes my time for right now. And I believe that what we’ve got left here is a Q&A session. I’ll be hanging around for a little while and will be able to answer your questions online. I hope you’ve enjoyed the talk, hope you’re enjoying the virtual Hand Fest and have a great day. Thank you very much.

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