Has anyone with a signal generator measured the CW filter shape factors by measuring the -6/-60 dB points. It may be a little tough to do with the 10 hz frequency step and the S-meter not being calibrated in decibel level, but has anyone attempted this. I'm only asking because, after years and years of using 1.4:1 shape factor crystal filters, I'm not hearing what I expect to hear from "brick wall" digital filters. By using the term "brick wall" filters, I am assuming that this definition implies a much better approximation to the 1:1 shape factor of a "perfect" filter than is possible with analog filters. This is why I would like to know if anyone has measured this using the 6500 narrow CW filters.
Posted 5 years ago
Charles,
FYI, if you use DDUtil and a FlexControl knob to control the slice frequency you can set the frequency step down to 1HZ. See attached snapshot.
By the way, the filters work better than any I've used so I'll be interested to see what you find out.
Regards, Al / NN4ZZ
FYI, if you use DDUtil and a FlexControl knob to control the slice frequency you can set the frequency step down to 1HZ. See attached snapshot.
By the way, the filters work better than any I've used so I'll be interested to see what you find out.
Regards, Al / NN4ZZ
George Molnar, KF2T, Elmer
Hi Charles,
I agree with your assessment. I think they lost a little on the filters in this beta. They did seem sharper in the original release version, although I have not done any precision measuring. 1.1 should hit in the next couple of weeks; it will be interesting to see how it works out.
I agree with your assessment. I think they lost a little on the filters in this beta. They did seem sharper in the original release version, although I have not done any precision measuring. 1.1 should hit in the next couple of weeks; it will be interesting to see how it works out.
I'll always been critical of analog filter shape factors after spending lots of money on poor shape factor filters over the years. Not that these filters in the 6000 series are poor, I don't have a way of accurately measuring them. I know the PSDR filter shape factors were highly dependent upon the sample rate and pan-adapter width selected, and there were plots given in the documentation to help us decide on the trade-offs to get decent shape factors without undue latency.
As I mentioned earlier, I'm not hearing "brick wall" performance of the CW filters, especially at the 50 and 100 hz widths. A crowded CW band in a contest can have signals often less than 50 hz separation, so filter shape factors of 1.05 to 1, or 1.1 to 1, would be close enough to "brick wall" to make a tremendous difference in competitive CW work. If there is a penalty to making really good shape factors at these narrow bandwidths, and trade-offs are necessary,just let us know so we can accept the best compromise and we can move on. I've seen great posts by Steve that are concise about engineering decisions that had to made in such areas, so maybe he can nail this down for us.
As I mentioned earlier, I'm not hearing "brick wall" performance of the CW filters, especially at the 50 and 100 hz widths. A crowded CW band in a contest can have signals often less than 50 hz separation, so filter shape factors of 1.05 to 1, or 1.1 to 1, would be close enough to "brick wall" to make a tremendous difference in competitive CW work. If there is a penalty to making really good shape factors at these narrow bandwidths, and trade-offs are necessary,just let us know so we can accept the best compromise and we can move on. I've seen great posts by Steve that are concise about engineering decisions that had to made in such areas, so maybe he can nail this down for us.
Charles,
Did you reach any conclusions about the shape factors? Did I miss
some info from Flex? The vs. 1.1 filters seem fine, but are there some numbers
we can quote on the air?
Ned, K1NJ
Did you reach any conclusions about the shape factors? Did I miss
some info from Flex? The vs. 1.1 filters seem fine, but are there some numbers
we can quote on the air?
Ned, K1NJ
Ned, look at Steve response to KA4B's post about Filter Quality vs Panadapter Bandwidth. Steve has a way of explaining why certain things are the way they are. As you noted, the 1.1 filters are improved over the 1.024, and I hope they continue to refine them with each new version. There is a time delay through a digital filter, the better the folter, the more the delay. Since I do not use QSK, delay is not that big a factor for me since the station listening to me can't reply until I finish anyway. Doubling the delay through the filter would not really affect CW ops like me who are non-qsk. However, they need to keep a balance for both qsk and non-qsk ops.
Paul Christensen, W9AC, Elmer
As a quick test, I used the Flex's S-meter and an HP signal generator. CW mode, 20m, 250 Hz default BW. No AGC, but it does not matter in this architecture when observing SSDR. Here are my -6dB/-60dB numbers:
f1 = 14,175.340 (-60 dB)
f2 = 14,175.370 (- 6 dB)
f3 = 14,175.630 (-6 dB)
f4 = 14,175.660 (-60 dB)
For the shape factor, use the formula [f4 - f1] / [f3 - f2]
[14,175.660 - 14,175.340] / [14,175.630 - 14,175.370]
The resulting shape factor is about 1.2 for the 250 Hz filter. A few important points that affect computed shape factor accuracy: First, I am unsure of Flex's S-meter accuracy over a 60 dB level span; and secondly, small changes of a few Hz make a huge difference with digital filters. Better accuracy will be observed when moving in 1 Hz increments, rather than 10 Hz (e.g., using DDUtil).
Paul, W9AC
f1 = 14,175.340 (-60 dB)
f2 = 14,175.370 (- 6 dB)
f3 = 14,175.630 (-6 dB)
f4 = 14,175.660 (-60 dB)
For the shape factor, use the formula [f4 - f1] / [f3 - f2]
[14,175.660 - 14,175.340] / [14,175.630 - 14,175.370]
The resulting shape factor is about 1.2 for the 250 Hz filter. A few important points that affect computed shape factor accuracy: First, I am unsure of Flex's S-meter accuracy over a 60 dB level span; and secondly, small changes of a few Hz make a huge difference with digital filters. Better accuracy will be observed when moving in 1 Hz increments, rather than 10 Hz (e.g., using DDUtil).
Paul, W9AC
(Edited)
Steve - N5AC, VP Engineering / CTO
In v1.1, the relative accuracy of the S-Meter should be better than 1/2dB. The absolute accuracy in v1.1 is +/-3dB. This should return to something like +/-1-2dB in a later release.
Also for CW the filter shape factor changes at 400, 1000 and 1500Hz to lower latency with a wider filter.
Also for CW the filter shape factor changes at 400, 1000 and 1500Hz to lower latency with a wider filter.
Steve - N5AC, VP Engineering / CTO
Off the top of my head I can't tell you if the shape factor is governed strictly by the number of taps in an FIR filter or if the chosen bandwidth plus the number of taps will set this. What I can tell you is that the number of taps in the filter goes down by a factor of two at each of these crossings at the present time and I know that will affect the shape factor. So there are two possibilities:
1) shape factor is independent of filter bandwidth chosen (I know how this sounds, but I believe it is a possibility since all that we are analyzing is one side of a skirt) in which case you will also see a 1.2 for the 100Hz filter. If this is the case than all filters in each range will have the same shape factor (0-400, 401-1000, 1001-1500, etc).
2) The other possibility is that the shape factor is bandwidth dependent in which case there will be a progression from 0-400 and then a jump to 401, a progression from 401-1000 and a jump at 1000, etc.
Let me know which it is because I'm curious too!
1) shape factor is independent of filter bandwidth chosen (I know how this sounds, but I believe it is a possibility since all that we are analyzing is one side of a skirt) in which case you will also see a 1.2 for the 100Hz filter. If this is the case than all filters in each range will have the same shape factor (0-400, 401-1000, 1001-1500, etc).
2) The other possibility is that the shape factor is bandwidth dependent in which case there will be a progression from 0-400 and then a jump to 401, a progression from 401-1000 and a jump at 1000, etc.
Let me know which it is because I'm curious too!
Paul,
Good idea......we frequently slow down a bit for the weak ones anyway. Either an option as you suggested or just automatically sharpen up when the speed is below a certain value (e.g. 25 WPM?)
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Good idea......we frequently slow down a bit for the weak ones anyway. Either an option as you suggested or just automatically sharpen up when the speed is below a certain value (e.g. 25 WPM?)
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Paul,
I just realized why the automatic option won't always work. The speed is only known when using the internal keyer. So your idea of the "sharp" option is better but I guess it also has a risk (increased latency) if engaged when QSK at high speeds.
Does that make sense?
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
I just realized why the automatic option won't always work. The speed is only known when using the internal keyer. So your idea of the "sharp" option is better but I guess it also has a risk (increased latency) if engaged when QSK at high speeds.
Does that make sense?
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Paul Christensen, W9AC, Elmer
Operationally, I think it makes sense to make it a manual change. But for Flex's software engineers, the coding may not be trivial!
Don't get hung up on the ratios. Both 100 and 250 wide have about 30hz from -6 to -60 on each side, only the initial width changes. The math makes the ratio worse.
Do this on a 10hz bandwidth and the ratio would look horrible.
Besides, without a slight slope I couldn't demodulate a 2M FM signal on an AM filter slope.
Thanks again Steve for pulling back the curtain a little so we know how it all fits together.
If I can summarize, from 50 hz to 399 hz the filter shape factor gets better and better as it approaches 1.1 to 1 at the 400 hz boundry, then goes back to something like 1.6 to 1 at 401 hz and gets better and better until it approaches the next boundry at 1000 where it will be around 1.1 to 1 again.
The 1.6 to 1 shape factor at 100 hz is pretty impressive. And what can I say about 1.02 to 1 for SSB filters. That is truly "brick wall".
As Al and Paul said above, a non-QSK operator would not mind a little more latency through a 50 or 100 hz filter, if doing so could produce a 1.1 shape factor. As you have probably witnessed on the recent DXpeditions, QRMers often get very close to the DX station's frequency. It may be possible to attenuate the QRMers enough to copy the DX station with a 50 or 75 hz filter that has a 1.1 to 1 shape factor. As for latency......"Latency is in the eyes of the beholder."
Good job with the Ver 1.1 filters Steve.
If I can summarize, from 50 hz to 399 hz the filter shape factor gets better and better as it approaches 1.1 to 1 at the 400 hz boundry, then goes back to something like 1.6 to 1 at 401 hz and gets better and better until it approaches the next boundry at 1000 where it will be around 1.1 to 1 again.
The 1.6 to 1 shape factor at 100 hz is pretty impressive. And what can I say about 1.02 to 1 for SSB filters. That is truly "brick wall".
As Al and Paul said above, a non-QSK operator would not mind a little more latency through a 50 or 100 hz filter, if doing so could produce a 1.1 shape factor. As you have probably witnessed on the recent DXpeditions, QRMers often get very close to the DX station's frequency. It may be possible to attenuate the QRMers enough to copy the DX station with a 50 or 75 hz filter that has a 1.1 to 1 shape factor. As for latency......"Latency is in the eyes of the beholder."
Good job with the Ver 1.1 filters Steve.
Paul Christensen, W9AC, Elmer
Good analysis, Charles. What you've shown also applies to crystal filters, but unlike the mathematical perfection attained in DSP, as the crystal filter's bandwidth decreases, even slight slope imperfections have an impact on shape factor and symmetry from center.
Putting this into perspective, look at the shape factor of the best INRAD crystal filters. Due to manufacturing cost and inability to attain repeatable tolerance, I don't believe they offer one under 250 Hz. Their typical 250 Hz filter (at 8 MHz) has a shape factor of 2.2.
https://www.inrad.net/product.php?productid=203&cat=90&page=1
In addition to nearly perfect control of the slope, the DSP filters are providing much better ultimate filtering well beyond the -60dB point where crystal filters are subject to degradation due to I/O isolation and other blow-by effects that limit ultimate filtering performance. Thru-loss also escalates as a crystal filter becomes narrow. Look at the schemes developed by competing manufacturers to compensate for that loss.
It would be interesting to plot an overlay of the Flex's filters on top of a comparable INRAD crystal filter.
(Edited)
Ken - NM9P, Elmer
NN4ZZ will probably have that graphic by tomorrow! He is really good at that stuff. [gauntlet dropped....grin]
(Edited)
Ken,
Here you go! Below is a graphic for the inrad 250 HZ filter in BLACK and the FLEX 250 Hz filter overlaid on it in RED using Paul's data.
6 Db = 260 HZ
60 Db = 320 Hz
The 1.2 shape looks very good to me!
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Here you go! Below is a graphic for the inrad 250 HZ filter in BLACK and the FLEX 250 Hz filter overlaid on it in RED using Paul's data.
6 Db = 260 HZ
60 Db = 320 Hz
The 1.2 shape looks very good to me!
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Paul Christensen, W9AC, Elmer
Nice work, Al. Probably the top portion on the Flex plot is flatter than shown. It would just require me to capture more data points on Hz-by-Hz basis between filter center and the -6 dB points.
Paul, W9AC
(Edited)
Paul,
This is probably more like it then....also moved the 60DB points slightly.
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
This is probably more like it then....also moved the 60DB points slightly.
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Ken - NM9P, Elmer
Thanks, Al.
I figured you would do it even without my challenge... ha.
Impressive performance.....
Now, can you superimpose a 50 or 24 Hz filter on top of the INRAD so we can REALLY brag?
I figured you would do it even without my challenge... ha.
Impressive performance.....
Now, can you superimpose a 50 or 24 Hz filter on top of the INRAD so we can REALLY brag?
Barry,
If there is a close by interfering signal, then the brick wall filter will be better. Assume the BLUE signal is the offending one in the snapshot below. The Yellow is the the overlap for the Inrad filter. Much less for the Flex filter. It probably makes a lot more difference when the signal you want to hear is a weak DX signal.
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
If there is a close by interfering signal, then the brick wall filter will be better. Assume the BLUE signal is the offending one in the snapshot below. The Yellow is the the overlap for the Inrad filter. Much less for the Flex filter. It probably makes a lot more difference when the signal you want to hear is a weak DX signal.
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Ken - NM9P, Elmer
Of course, no filter can remove junk from a crappy, phase noise ridden signal, CW, SSB or other, that is splattering the bands. The best we can do is make sure that our OWN receive chain - oscillators, filters, mixers, etc - do not add to the problem.
I demonstrated my 6500 to the local ham club last night. I had it connected to my 20 Meter Hustler mobile antenna with a long jumper fed through a window into the meeting room.
I started with the big pileup on 20 CW from one of the big DXpeditions.
I used the 3K wide filter and it was mayhem! and said "This is what most of our rigs would hear without a good CW filter.
Then I switched in the 250 Hz filter and said "This is what it sounds like with a good CW filter." There were still 3 or 4 signals in the passband, but several people said "Wow, pretty nice."
Then I said, "You haven't seen anything, yet."
I set the 50 Hz filter and the Audio Peak Filter and there was only ONE signal, weak, right beside a very strong signal. And it stood out from a practically noiseless background.
That turned some heads! And then I went A/B between the 3 Khz wide and 50 Hz filter several times. Going split with the 50 Hz filter on one frequency and a 400 Hz on another freq about 20 Khz away with one in the left ear and the other in the right polished off that part of the demo. "And that is how I worked the big DXpedition barefoot with a dipole! I can't wait for my T-11 up 55 ft.!)
I had to brag a little bit..... But as they say in Texas..."It ain't braggin' if ya can do it!"
And this FLEX can do it!
Ken - NM9P
I demonstrated my 6500 to the local ham club last night. I had it connected to my 20 Meter Hustler mobile antenna with a long jumper fed through a window into the meeting room.
I started with the big pileup on 20 CW from one of the big DXpeditions.
I used the 3K wide filter and it was mayhem! and said "This is what most of our rigs would hear without a good CW filter.
Then I switched in the 250 Hz filter and said "This is what it sounds like with a good CW filter." There were still 3 or 4 signals in the passband, but several people said "Wow, pretty nice."
Then I said, "You haven't seen anything, yet."
I set the 50 Hz filter and the Audio Peak Filter and there was only ONE signal, weak, right beside a very strong signal. And it stood out from a practically noiseless background.
That turned some heads! And then I went A/B between the 3 Khz wide and 50 Hz filter several times. Going split with the 50 Hz filter on one frequency and a 400 Hz on another freq about 20 Khz away with one in the left ear and the other in the right polished off that part of the demo. "And that is how I worked the big DXpedition barefoot with a dipole! I can't wait for my T-11 up 55 ft.!)
I had to brag a little bit..... But as they say in Texas..."It ain't braggin' if ya can do it!"
And this FLEX can do it!
Ken - NM9P
Paul Christensen, W9AC, Elmer
Al,
Here's what I have between the filter center and the -6dB points of the 250 Hz filter. I only plotted the upper frequencies from center. The lower frequencies will be a mirror image with DSP. I couldn't say that if this was a crystal filter.
14,175.000 = 0 dB
14,175.110 = -1 dB
14,175.116 = -2 dB
14,175.118 = - 3dB
14,175.120 = - 4dB
14,175.123 = -5dB
14, 175.125 = -6 dB
How does that look? The measurement is super touchy. As expected, just a few Hz means a couple dB change when we get close to the knee of curve.
Paul, W9AC
.
(Edited)
Yes Al, I believe you're correct and the steep filter is inherently superior. However in your diagram, would it more accurately reflect real world cw signals if that blue signal had much more gradual/shallow slopes? If so, those gradual slopes would translate into a smaller difference in performance between the rx filters.
(Edited)
Barry has an interesting point about the bandwidth of a CW signal signal. I don't know if there is a universally accepted number since I have read various opinions ranging from 100 hz to 500 hz. I think using a screen capture of the panadapter zoomed in on a steady CW signal would give us an accurate picture of what the width and slope of a typical CW carrier would look like. Then we could apply our filter curves superimposed on the CW curve to see the difference between effect the best crystal filters and our DSP filters would have on that CW signal. I would imagine you could cozy up to an offending CW signal much closer with a 50 hz DSP filter with a 2.3 to 1 shape factor than you could with a 250 hz crystal filter with approximately the same shape factor. But as you mentioned Barry, it difference would depend upon the slope of the CW carrier.
So, could someone out there get a screen capture of a panadapter zoomed in on a CW carrier to determine its width and slope so it can be reproduced on a graph for evaluating how DSP filters and crystal filters differ? With this last bit of information, we will be very close to really understanding and documenting the value of steep filter slopes for congested CW operation. Once this is graphed out, I think it will vindicate the programming effort and the processor clock cycles dedicated to achieving these steep filter slopes. Thanks to all who participated in this discussion.
So, could someone out there get a screen capture of a panadapter zoomed in on a CW carrier to determine its width and slope so it can be reproduced on a graph for evaluating how DSP filters and crystal filters differ? With this last bit of information, we will be very close to really understanding and documenting the value of steep filter slopes for congested CW operation. Once this is graphed out, I think it will vindicate the programming effort and the processor clock cycles dedicated to achieving these steep filter slopes. Thanks to all who participated in this discussion.
My previous reply seems to have disappeared. Using the last example spectral diagram that Al posted, I would suggest the signal in blue would have much shallower slopes. With the steep blue slopes shown, there is a 35-40dB improvement in rejection afforded by the steeply sloped rx filter. But if the true real world tx slope was much shallower, that improvement might only be 5dB for example.
Barry,
I think your previous comment is still there.....when there are a lot of comments, the community software collapses them. You have to click on the "view more comments." It's easy to miss.
I agree that representing real world conditions are much more complex. (wide CW, multiple signals close by, clicks, hash, etc). The blue one I added was just to show how the narrower filter could help compared to the inrad. Real world could be a lot different.
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
I think your previous comment is still there.....when there are a lot of comments, the community software collapses them. You have to click on the "view more comments." It's easy to miss.
I agree that representing real world conditions are much more complex. (wide CW, multiple signals close by, clicks, hash, etc). The blue one I added was just to show how the narrower filter could help compared to the inrad. Real world could be a lot different.
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Steve - N5AC, VP Engineering / CTO
Ken - NM9P, Elmer
Thanks, Al.
I figured you would do it even without my challenge... ha.
Impressive performance.....
Now, can you superimpose a 50 or 24 Hz filter on top of the INRAD so we can REALLY brag?
Ken,
Paul provided data for the 100 HZ Flex filter so I superimposed it on the INRAD 250 HZ filter. It should be a fair approximation and even at the 1.6 shape it looks brick wall in comparison. At this scale the FLEX 50 HZ filter would look similar just half as wide. It's easy to see why using a good 50 or 100 HZ filter (that doesn't ring) makes such a difference compared to the 250 HZ crystal filters.
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Thanks, Al.
I figured you would do it even without my challenge... ha.
Impressive performance.....
Now, can you superimpose a 50 or 24 Hz filter on top of the INRAD so we can REALLY brag?
Ken,
Paul provided data for the 100 HZ Flex filter so I superimposed it on the INRAD 250 HZ filter. It should be a fair approximation and even at the 1.6 shape it looks brick wall in comparison. At this scale the FLEX 50 HZ filter would look similar just half as wide. It's easy to see why using a good 50 or 100 HZ filter (that doesn't ring) makes such a difference compared to the 250 HZ crystal filters.
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Paul Christensen, W9AC, Elmer
Al,
Not sure if you missed it but I provided the detail of the 250 Hz filter in 1.0 dB steps between the center frequency and the -6 dB point. This will give you better detail of for the top graphical passband response. The message may be collapsed in between others.
Paul
Not sure if you missed it but I provided the detail of the 250 Hz filter in 1.0 dB steps between the center frequency and the -6 dB point. This will give you better detail of for the top graphical passband response. The message may be collapsed in between others.
Paul
Paul,
Yes overlooked it, but got it now. I'll redo the 250 HZ plot...
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Yes overlooked it, but got it now. I'll redo the 250 HZ plot...
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Paul,
Here is the updated 250 HZ filter with your additional close in data points. At the scale used for the Inrad filter graphic, it is hard to plot that level of detail very accurately. But as you suspected the top is much flatter than my first picture. .
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Here is the updated 250 HZ filter with your additional close in data points. At the scale used for the Inrad filter graphic, it is hard to plot that level of detail very accurately. But as you suspected the top is much flatter than my first picture. .
Regards, Al / NN4ZZ
al (at) nn4zz (dot) com
Here's a cheap and dirty research project protocol to determine the relative effectiveness of a 250 hz DSP filter with a 1.2 shape factor and an INRAD 250 hz filter wth a 2.2 shape factor:
1. Use a signal generator to insert a continuous carrier and use the 6500's 250 hz filter to determine the carrier's maximim S-meter reading. Then tune either above or below the carrier frequency until the 6500's S-meter is down 60 db. Write down that frequency.
2. Use a receiver with a good INRAD 250 hz filter, use the same signal generator set to the same frequency and signal level as above, and determine the maximum signal strength of the carrier on the S-meter. Now tune to the same frequency that the 6500 showed the carrier to be 60 db down from its maximum. Write down this S-meter reading and determine the difference in db from its maximum.
3. The difference between the INRAD filter differential S-meter reading, and the 6500's 60 db differential S-meter reading will illustrate how much more attenuation the DSP filter will provide in a real-world environment.
Yes, the S-meter in the INRAD receiver will not be as linear as the one in the 6500, yes it will be harder to read, yes the steady state carrier is not as real-world as a keyed CW signal.........but this protocol eill give a fair assessment of how these two filter types will perform in a real RX environment. We'll need Rob Sherwood to do the definitive tests, but this will give us a good idea of what to expect.
Thanks again to all that have made this such an interesting discussion.
1. Use a signal generator to insert a continuous carrier and use the 6500's 250 hz filter to determine the carrier's maximim S-meter reading. Then tune either above or below the carrier frequency until the 6500's S-meter is down 60 db. Write down that frequency.
2. Use a receiver with a good INRAD 250 hz filter, use the same signal generator set to the same frequency and signal level as above, and determine the maximum signal strength of the carrier on the S-meter. Now tune to the same frequency that the 6500 showed the carrier to be 60 db down from its maximum. Write down this S-meter reading and determine the difference in db from its maximum.
3. The difference between the INRAD filter differential S-meter reading, and the 6500's 60 db differential S-meter reading will illustrate how much more attenuation the DSP filter will provide in a real-world environment.
Yes, the S-meter in the INRAD receiver will not be as linear as the one in the 6500, yes it will be harder to read, yes the steady state carrier is not as real-world as a keyed CW signal.........but this protocol eill give a fair assessment of how these two filter types will perform in a real RX environment. We'll need Rob Sherwood to do the definitive tests, but this will give us a good idea of what to expect.
Thanks again to all that have made this such an interesting discussion.
Charles - K5UA
So why am I interested in this? Well, "brick wall filters" imply a filter shape factor of 1:1. I'm just not sure that the 6500 CW filters are ,at their current state, close to that very high standard. Tuning around CW signals with the 50 hz and 100 filters has given me reason to question the shape factors of these digital filters. That's why I would like someone with a signal generator to determine the actual shape factors of the 6500's CW filters. I'm not saying that they are not good or better than the competition, I just would like to know what the shape factors actually are since I am not hearing a "brick wall" response as I tune across a CW signal. I am not trying to be overly critical, I just would like to know what kind of filter performance we have in our arsenal.