I wish I could report that there has been some miracle happen that made the Phase Shift SSB Transmitter work properly.
I even spent a small fortune for some 1% SMD capacitors to mate with the 0.1% resistors that would be employed in an 8 Pole filter. I didn't even open the box from Mouser.
While one could easily be swayed to thinking this will finally do it. Realistically I just do not think I would see any different result other than poor opposite sideband suppression that I have been experiencing.
I have become very skeptical of those who have reported amazing results with their phase shift networks and put those comments in the same league as exaggerated gas mileage claims.
We have a great word in Italian --Basta. Enough!
But I am happy to report that I have successfully built a 2nd ZL2CTM Teensy 3.5 SDR transceiver. the Hilbert Transforms Rule and indeed opposite sideband suppression!
The why of the 2nd build is to have something presentable and not look like a bunch of wires hanging out all over the place and to eventually "harden" the build so there are no wires waiting to be shorted and no boards with cold solder joints.
Yesterday I had a QSO with a station running a FLEX 6700 --try as he might he just could not denigrate the signal. His parting shot was that it was indeed a solid build and sounded really well --for a homebrew rig!
73's
Pete N6QW
Thursday May 28th, 2020
Here is a series of tests that only leave me totally baffled.
I built a 6 Pole Audio Phase Shift Network using the Tonne Design Software but KK7B's Schematic. For a signal source I have a waveform generator and use this in the sine mode to cover frequencies in the range of 200 to 2800 Hertz at 200 Hertz intervals. The A and B channels were connected to my Rigol 100 MHz DSO set to read Lissajous figures.
There was a two fold purpose to the test the first of which to see if we got a circular pattern which is indicative of a 90 Degree Phase Shift. The second parameter was to see how that pattern held over the range 200 to 2800 Hz using a 200 Hz step evaluation.
Assuming satisfactory results then this piece can be eliminated as an issue in poor opposite sideband suppression. By poor maybe only 5-10 dB. Below is the test setup.
In the initialization stage, the signal level from the source is critical so you don't overdrive the mic amp and the follow on circuitry. It takes very little signal level! Secondly on the APSN is an input balance pot and that was found to greatly affect the "roundness" of the plot. It is not at the center of the range as you would perhaps think.
The following are the test results...
Reading at 200 Hz
Reading at 400 Hz
Reading at 600 Hz
Reading at 800 Hz
Reading at 1kHz
Reading at 1.2kHz
Reading at 1.4 kHz
Reading at 1.6 kHz
Reading at 1.8 kHz
Reading at 2.0 kHz
Reading at 2.2 kHz
Reading at 2.4 kHz
Reading at 2.6 kHz
Reading at 2.8 kHz
General observations:
At 200 Hz --a bit ragged but improving thereafter. No distortion, like at 200 Hz, but higher in frequency a definite pattern shift
Beyond 1500 Hz some shifting from circular to slightly elliptical
Very likely "not textbook" for 45 to 50 dB of opposite sideband suppression but I would venture certainly better than 5 to 10 Decibels.
The front end with the DBM's has been tested with a 2nd ZL2CTM Teensy 3.5 and the opposite sideband suppression is very evident.
So now for the head scratching -- why such poor opposite sideband suppression?
Think about the emperor (with a nearly invisible e) citing that there are only 100K deaths, 1.7M infected souls and 41 Million out of work and saying "I have done an amazing job managing this pandemic."
73's
Pete N6QW
Memorial Day ~ 2020
For those who served, Thank You for your service. For those who made the ultimate sacrifice, we are deeply indebted. For those now serving may you be safe and know we stand behind you!
For those who golf during this pandemic crisis while the country suffers an unfathomable loss of life and dire economic impact ... (readers can finish this sentence)
TL084 Eight Pole Filter, two DCR's, Summer, 74AC74, Band Pass Filter 4X7" Board
Regrettably I am stopping all work on the Phasing Transmitter Rig. After finishing the KK7B Rig following the 2Q4 sojourn, I am left with a pile of crap. I have been unsuccessful in making a suitable and working hardware based phasing transmitter.
The KK7B Board has a mysterious problem that I have been unable to resolve. So one option is to stop work today, as my efforts, so far, have failed to crack the code. Spending some time thinking about the why is more productive that just removing parts and soldering in new ones. So following a tip from N2CQR --put it aside and think, research and come up with possible resolutions.
I know this project has stirred some interest no more so than my own; but there comes a time to fold them and play another day.
73's
Pete N6QW
The QuadNet Software from Tonne Systems
May 10, 2020 ~ A story from WWII.
Failed to mention that May 8th, was the 75th Anniversary of VE Day. There was such great celebration across this nation on that day in 1945. Perhaps we all will live to see the same for Covid19.
There are some interesting stories from WWII. As the country geared up for war, there was a huge infrastructure construction build up to support the war effort. While the work was done by civilian contractors, the US Army oversaw the security for these sites. Everything going in or out of the facility was searched by the Army personnel.
So there was the contractor person that everyday would go through the gate pushing an empty wheelbarrow from the inside to the outside. The Security personnel would check over the wheelbarrow and seeing as it was empty would wave him on through the gate. What the security forces did not realize was that the worker was stealing wheelbarrows.
The posting from May 9th asked why were those frequencies chosen as it was not clear to me. Thanks to Joe, I have been enlightened. And what I am about to share is more than I really know.
Think about capacitors and their response to frequencies. If you impress DC on a Capacitor (think of it as "O" frequency) what do you have? It is like an open circuit to DC -- essentially DC is blocked. So OK now if you impress a Very High Frequency on a Capacitor it acts like a short circuit to ground. Capacitors have names where they are referred to generically as "Blocking Capacitors" and/or "By-Pass Capacitors"
Now since the non-inverting input has the capacitor affixed to it we have the input to Pin 3 being affected such that a phase shift may occur when the cap is blocking/bypassing.
I think this comes from an internet source (Wikipedia) regarding all pass networks...
This
implementation uses a low-pass filter at the non-inverting input to generate
the phase shift and negative feedback.
At high frequencies, the capacitor is a short circuit, creating an inverting
amplifier (i.e., 180° phase shift) with unity gain.
At low frequencies and DC, the capacitor is an open circuit, creating a
unity-gain voltage buffer (i.e., no phase shift).
At the corner frequency ω=1/RC of the low-pass filter (i.e., when input
frequency is 1/(2πRC)), the circuit introduces a 90° shift (i.e., output is in
quadrature with input; the output appears to be delayed by a quarter period
from the input).
In fact, the phase shift of the all-pass filter is double the phase shift of
the low-pass filter at its non-inverting input.
Much like our wheelbarrow story the focus is not so much the Frequency of the RC circuit but whether the capacitor looks open or shorted.
Another revelation from Joe, The filter elements can be in any order and not necessarily from low to high or high to low.
More parts on the board yesterday and maybe a finish today. Keep in mind this is NOT plain old perforated vector board but Single Sided Copper Vector Board so the top is a copper ground plane with all point to point wiring done on the reverse insulated side.
I even wear nitrile gloves when I work with the board as the acids in your hands will tarnish the copper surface of the board. If you look at the T2 -- it has a resemblance to KK7B's layout. How is that for guessing a bunch? I will take some photos of the underside as another objective is short direct connections (just like a PCB) and to minimize any cross overs.
Every penetration through the board and not to ground has the copper removed from around the hole to prevent shorting to ground. I use a 1/8 inch drill bit fitted with a handle. All ground connections are simply passed through the hole and soldered to the top. If you look closely you will see some of the ground connections.
This takes some effort but makes for an excellent alternative if you lack a CNC machine. The reason I chose this approach versus using my CNC is to achieve a very compact layout.
73's
Pete N6QW
May 9, 2020 ~ Does Science Meet Data or does Data Meet Science?
I have been pondering that question and suggest it depends. It depends if you want to implore science to verify and/or validate data. Or is it a that you have weird data and are looking to science to explain the why.
This leads me to a point made yesterday about the "odd ball" capacitor in the KK7B T2 schematic. It was pointed out to me (thanks Joe) that in the schematic for the individual op-amps in the network the only variable is the RC component values for the individual op-amp. You know the old time constant T = RC (in seconds) for discharging a capacitor.
So for a constant "T" the values of R and C can float all over the place just as long as their product remains a constant "T". There is of course a relationship between the Time and Frequency Domain which is why the time constant is so critical. Thus f = 1/T or 1/(RC). OK 1 millisecond is 1000 Hz and 1 microsecond = 1 Megahertz.
So did KK7B simply run out of 0.001 uf caps and then made a quick calculation and said Ahh this size 1% resistor will keep the T constant and boom there we go. I simply don't know!
If we look at that last capacitor resistor combination we have 0.0027uF times 649K and that product in seconds is 0.001753 seconds and thus 570.678 hertz. The other value of 0.001uF and 511K comes out to 1956.947 hertz.
Some of the other values have an interesting reveal. One combination is 0.001uF and 15K. Doing the math ~ 001uF * 15K = 0.000015 seconds which translates to 66.667 kHz. Yet another of 0.001uF * 232K which translates to 4.310 kHz. For the same value capacitor smaller resistors result in higher frequencies.
Keep in mind the T2 was developed in 1993,which is ancient technology (almost 30 years ago) so I am uncertain what tools were available then. Even the QuadNet is 15 years old; but certainly more interactive than would be available in 1993. The KK7B Values result in the following frequencies.
U2C = 66.67 kHz
U3D = 8.85 kHz
U3C = 1.956 kHz
U2B = 19.12 kHz
U3A = 4.31 kHz
U3B = 0.5707 kHz
At this point I have no clue as to the why these are the frequencies chosen by KK7B. Now lets look at the 6 pole filter used in the QuadNet where all capacitor values are the same at 0.01uf. I will use the same designations as in the KK7B.
U2C = 47.62 kHz
U3D = 5.24 kHz
U3C = 0.9524 kHz
U2B = 12.406 kHz
U3A = 2.262 kHz
U3B = 0.2551 kHz
Again not obvious the "why" of the values. The first three are in cascade on one output as are the second three in cascade for the second output. I am just not that versed on progressive filtering and the impact of values and what passes through the chain. [More learning opportunity.]
But the data does show the 1st grouping is passing a higher band of frequencies as in 66 kHz to 1.9 kHz and the second grouping 19 kHz to 0.5 kHz. That same relationship is evident in the Quadnet values.
Certainly it has to do with passing the same band of audio frequencies but out of phase by 90 degrees. Just doesn't jump right out at me and grabs me by the stacking swivel.
I was made aware of the stage to stage coupling in both the KK7B and the Quadnet model as being "AC" coupled via the 0.001uF in the KK7B and the 0.01uF in the Quadnet to Pin 3.
It was suggested that I swap the capacitor and resistor locations (just the R &C) so that the stages are now "DC" coupled to avert noise pick up issues. Initially I sort of gulped over switching the circuit location of R and C. But if you do a LT Spice Simulation the results are no different; but as we know --noise and op amps are like oil and water.
Thus for my first build I am switching the R's and C's. Keep in mind T still = R*C. I understand that W6JL in his magnificent build used this same approach. (Thanks Joe)
Below is the beginning work on the KK7B T2 Phasing Transmitter. I am using single sided copper vector board where the top of the perforated board is covered in copper (read expensive). At each location where there is not a ground connection using a 1/8 inch drill bit with a special handle I ream out the holes so the component or socket does not ground itself to the top surface. All hardwired connections are made on the underside. If a connection goes to ground don't ream the hole and solder right to the top of the board. Using the photo of how Campbell laid out his PC Board, I more or less followed his layout and away we go
As I well know from the 2Q4 this could go bust at any moment but at the very least there are now some analytical tools that let you have the very best of the Science and Data worlds.
SITS and HUAH.
73's
Pete N6QW
********************************************
Noteworthy I also do not see a direct mathematical relationship between the sets of values for the two filters.
There is much to be said about someone who discovers a new religion and suddenly is imbued with a terrible missionary zeal. Thanks to two hams (Joe and Dave) who suggested I look at the Tonne Systems QuadNet software as a design tool for op-amp audio phase shift networks. They were right!
First some important observations:
Unlike many tools this one is user friendly and intuitive. If you are a button pusher this will work for you.
It has some pretty nifty built in tools like the Monte Carlo Analysis to rapidly evaluate a network's response to an array of stimuli in graphical form.
It offers options on the precision of the network such as what happens if you use 5% resistors versus 0.1% resistors (It is dramatic!). If you really want 90 Degrees across an audio range at suppression levels >50 dB then 0.1% or better is required!
The default for the capacitors is all of the same value of 0.01uF . But you can readily change that to any value say 0.001uF or even a mixed set of values.
One of the outputs is a link to LT Spice so that the QuadNet Design automatically appears as a LT Spice design. Now that is a nice feature.
It also can be used in conjunction with LT Spice as an evaluation tool to compare networks. More on this.
You have options for the numbers of poles such as every integer up to 10. I must admit a 7 pole filter looks strange as we tend to think in an even number of poles.
Before being introduced to QuadNet (dragged is more like it) I had decided to build the KK7B phasing transmitter and ordered the parts which have since arrived. Since I now have a new found religion, I decided to use QuadNet to design a 6 pole filter which is what Campbell uses. The next step was to compare the QuadNet with the KK7B using LT Spice.
Campbell uses the NE5514 which is difficult or impossible to find let alone purchase. Yet the QuadNet uses a generic op-amp. I suspect you really cannot use just any op-amp; but one that is low noise, has good isolation between the sections and since this is audio having really wideband characteristics like 200 MHz is not so critical. Several candidates look promising as substitutes like the N35534, NE5532 and LM324. I happen to have all of these in the bins. Linear Technology has a slew of op-amps --but I just am not as familiar with those as I am with the three mentioned.
Noteworthy in the KK7B design is that five of the six capacitors are of the same value (0.001uF) and one is not (0.0027uF).
In one analysis I use with LT spice is to designate the I and Q outputs as "A" and "B" and tag them as such Then setting up the AC Analysis for the range of 100 Hz to 3kHz I look at A & B with reference to the V (audio input). I get two plots which shows the phase difference. Boom two parallel lines separated by 90 degrees over the audio range. Now here is the interesting part. If you use the KK7B values (with the one odd cap value) for the most part the output curves are parallel. But if you make that odd capacitor the same as the other five --the output curves are skewed and not parallel. So that odd capacitor value is there for a reason (A big one).
Above the plot with the same capacitor values
Above is the plot with the one odd ball capacitor.
The lines are for the most part parallel and 90 Degrees apart. But observe the skewing at the very low and high end of the range
Now if you use the QuadNet Values where all caps are the same at 0.01uF, then you get the two parallel lines BUT the lines are really appear parallel over the entire range whereas in the KK7B design appear a bit skewed at the extreme ends.
The QuadNet 6 pole all same cap value.
Note above that the very low end that the curves still remain parallel, whereas below (KK7B) there is a skewing. How much of an issue that is remains to be decided whether just a plot point or real issue. I suspect the 40M SDR police running their FLEX 6600's with 72 Inch LCD will tell you something about your signal at 100 Hertz when running the KK7B.
The KK7B plot, note the very low end skewing.
Bottom line is the use of the tools. I have parts on order for the 8 pole QuadNet and likely will build three versions. The two six poles for the transmitter and the 8 pole for a receiver.
BTW the 1% resistors can be had for 7 cents a piece in lots of 10 from DigiKey. Thus 60 piece of 1% resistors is less than a $5 bill. Of course the 0.1% cost more and are more readily found in the surface mount versus thru hole.
QuadNet is your best friend and a new found religion.
(By any chance could this be a Special Assistant to the emperor (undersized e) Whiz Kid Panel Member only in disguise so he doesn't have to explain to Wall Street about their misadventures in buying PPE.)
A PSA regarding Covid19. Summer is coming, thus we must never let our guard down and protect ourselves at all times. Social Distancing works! So does the use of masks and gloves such as ..
Easy to spot --- this is a YL as the foot covering and the flip flops are color coordinated. Another piece of evidence --- small feet. We all need a laugh in our day -- during this pandemic never lose your sense of humor!
[Yes, someone will point out the waste of precious PPE; but the emperor (with an undersized e) told a nurse yesterday there was not a PPE problem. Guess his "special adviser" told the "emp" that the whiz kids fixed all that!]
An 8 P0le Network from QuadNet ~ Tonne Software. A Free Download. Although have been advised this may have problems in the way you have to power the op-amps and the possibility of noise. I have also been made aware of an alternative to fix the power feed issue. Stay tuned. With 8 poles, QuadNet says this is >60 dB opposite Sideband Suppression. BUT -- that >60dB can only be achieved with extremely close tolerance parts. There are analytical tools in the Tonne software that enable that evaluation. The >60 dB requires 0.1% or better resistors and if you use 1% resistors that drops to the 45 to 50 dB range. Using 10% is not worth the effort! One approach is to use a combination of close tolerance resistors along with precision trim pots (like W6JL) to put the network dead on. With 10 poles --that is 10 trim pots.
10 % Tolerance Resistors about 25 dB of Suppression.
1% Tolerance Resistor about 45 to 50dB of Suppression
0.1% Tolerance Resistors about 60 dB of Suppression Once again this like most things in homebrew --this is not plug and play It is test, measure, re-test, tweak and then start breathing again. So if you simply go into the junk box and find a 10K 10% resistor and plug that in the 11K location on the schematic-- it ain't gonna work very well! But if it does --stop and go play the lottery as you are indeed full of luck!
Data and Science are extremely important. So today I gathered yet more data after using the SDR to test the opposite sideband suppression.
Luckily today I ran across a ham who lives only 2.5 miles from me and is an experienced ham having worked in the electronics industry building of all things high power phasing transmitters. Wow, was this the hand of God?
He pronounced my phasing transmitter as having "other sidebands" riding along and that the USB component while diminished in comparison to LSB was still very present some 2.5 miles away. Not good news; but HIGHLY Important News!
So is this beating the dead horse to death? Perhaps there may be other issues that are in play. Using LT Spice there were some identified issues with ideal parts.
Now mate the simulation with an electronic part that is at least 60 years old (have the sales receipt) or possibly 70 years old AND it is a used part.
The local ham said he heard signals 20 kHz away. Now that may indicate too much audio drive and the typical splatter effect. He had me reduce the audio gain; but the spurs were still heard although of lesser amplitude. When I added in the 100 watt amp -- like the Goonies --they were back with a vengeance or a bad case of Tourista!
Well I have ordered some precision resistors and capacitors in anticipation of building Rick Campbell's (KK7B) T2 rig. So the focus might shift to that approach.
Additionally note that the former email on the masthead had an out of body experience (craponthebench) as it stopped sending a receiving. Then mysteriously 40 emails showed up today some from two weeks ago. So I tried to answer your emails -- but lots in the inbox.
I did receive some circuit suggestion about how to fix the low end frequency response --it involves four op-amps. I also received some circuits similar to the T2 made from what was in the bins. Thank You. Some of these sharing circuits may find their way into the next build.
I guess we all like to take the shortest path and maybe reason 88% is really good. Well it's not! I was aware that even on a clear day standing on a tall ladder, about the best to be achieved with the 2Q4 was 35 dB and on a spectacular day perhaps 41 dB might be experienced. Well -- I did not even come close and the on the air test convinced me that with some significant redesign about the very best I could see was 40 dB.
So then I looked at the effort that might take and what could be done with op-amps and a clear picture was coming into focus.
Put a hold on the audio phase shift board and move to the op-amp approach. A lot of the hardware already is built like the phased Si5351 with Arduino/LCD Display, the ADE-1 DBM's, the Combiner Transformer, the Driver Stage and the Final RF Amp Board simply move over. This is yet another incentive since the op-amp build may not be that involved.
I plan on using the NE5532's as I have a small stock in the bins.
Perhaps later I can come back to the 2Q4 and figure the "why" such crappy performance. Don't overlook cockpit and pilot error issues!
73's
Pete, N6QW
*****************************
May 5, 2020 ~ Nailed the Sideband Suppression!
A friend in VK Land, (Greg) suggested in lieu of the Rigol DSO to use my SDR RADIG. Well that seems to bear some fruit as you can expand the scale and do all sorts of cool things like read frequencies and look for over driving the input.
I did that and can see that the Opposite Sideband Suppression if I stand on a tall ladder and squint my eyes is maybe hitting 30 DB. You can read that right off the SDR Spectrum plot. I also can see the impact of the small trim Pot in affecting the Suppression level.
So while this has been a cool exercise and learning journey -- have some very close tolerance parts to undertake building the T2. the Bottom line the 2Q4 was great in 1950 -- but 70 years later we have better ways to do it.
Please excuse the poor quality video --it is my garage and not the best place to shoot videos. 73's Pete N6QW
*********************
May 4, 2020 ~ Part #4 Test Results.
In one word: inconclusive.
Here is the test setup:
I fed a 1 kHz tone into the mic input keeping the signal at about the same level as the normal microphone input. In this case I am using an amplified D-104 Microphone.
The IRF510 was connected to a dummy load and the power output was 4 watts.
A fashioned a "snoop loop" out of a single turn of wire and passed that through the last toroid in the LPF and connected the DSO probe (Input #1) to the snoop loop.
I also had an outboard receiver (Ten Tec Omni VI + Opt 3) tuned to the operating frequency but only connected to a small chunk of wire.
Two series of tests were planned with the first not involving the DSO but rather the Omni VI. This test involved setting up the receiver tuned to the output in the LSB mode. A bit of fine tuning was involved so that I was copying the best quality signal and the read the S Meter. Next without touching the tuning on either the Phasing Rig or the Omni VI I left the Phasing rig in LSB and switched over to USB on the Omni. Noting the S Meter reading I tuned Trim Pot R16 so as the lowest reading was locked in and then I noted the S Meter reading. Switching back to LSB on the Omni VI, I then noted the S Meter reading.
The difference between the two readings was maybe 15 dB which of course is nowhere near 41dB. This first test and these results were disappointing. The good news is we have opposite sideband suppression; but the bad news it is pretty marginal.
So now to the second test is where I connected up the Rigol Scope in the FFT mode and again using the snoop loop looked at the output.
Quite honestly I am not sure of just exactly what I am seeing. So that may be an issue. But I did repeat introducing the 1kHz tone and then tried adjusting R16. I did have the Omni VI on as well and verified the null. But that null was not so obvious on the DSO.
I then simply talked into the Microphone to see if there was any evidence of the opposite sideband. Hard to tell just what I saw.
73's
Pete N6QW
May 4, 2010 ~ Part #2 Opposite Sideband
Today I will start testing for the opposite sideband suppression. In setting up for the tests my initial "look see" was not too promising.
Unlike the emperor (with a small e) predicting 100K will die; BUT I have done a great job doesn't fly. That will not be my approach. I note the emperor (with a microscopic e) is blaming everyone except the one person responsible --HIMSELF!
Why I say it is not too promising sans detailed measurements --the quick and dirty test of simply listening to the opposite side band shows it is present. In only looking at the outboard receiver S Meter --there is not 41 dB of difference between LSB and USB. But we need to quantify that with the measurements. Data and Science is the only sure quantification.
May 4, 2020 ~ Pt.#1 ~The KK7B Audio Filter.
I built the filter today and installed it on the board. Made some basic checks such as will it work in the audio chain and is the same level of power output achieved. Yes to both! But I have not as yet done the Opposite Sideband evaluation. Possibly tomorrow.
Watch this space.
73's
Pete N6QW
**********************************
May 3, 2020 ~ Parts arrived yesterday.
The parts I was awaiting, now here, were the components to build the audio filter used in the KK7B, T2 Multimode Phasing Transmitter (circa 1993). There seems to be a weight of evidence that supports having such a filter in ANY phasing rig and the direct correlation to opposite sideband suppression. See the schematic below.
Thus any Data and Science approach to systems evaluation should include the filter as a part of the measurement process. As you will recall the emperor (with a small e) very much dislikes Data and Science --it makes him look bad!
My plan is to build the audio filter on a small piece of single sided copper vector board which then can be soldered (vertically) to the main 2Q4 audio board. When that is done, I will proceed with the opposite sideband evaluation.
BTW there seems to be an unusual interest in a project of the past, The Simple SSB (TSS) which is found on my www.n6qw.com website. I guess folks don't read ... I specifically mention in the write up that if you want the code to email me. Use the email at the top of the blog.
You would be surprised at how many inquiries I get like -- have searched everywhere and can't find the code. Well I purposefully made it so you would have to contact me to get the code --this is just to gage the interest in the project.
Somehow -- a year later the amazing utility and performance of this rig has been discovered! Check out kk4das.blogspot.com and you will see unit #2. Dean has worked several European station on SSB (not CW) using the TSS at QRP power levels --like 3 watts! I think he said the best DX was 5000 miles and that is on 40M!
Stay tuned for more amusement and amazement from N6QW.
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I am awaiting arrival of some hardware so my project is temporarily "awaiting parts".
My friend Bill, N2CQR's reminded me about asuperb piece of Phasing craftsmanship from Don Huff, W6JL, which is QRO CW transceiver. This perhaps is the ne plus ultra of homebrew construction using advanced phasing technology circuit design to achieve superlative performance.
Most likely after my having visited the W6JL site I will never show another one of my breadboard projects. Hunk of Junk would be a kind description of what I do. The sheer magnificence of W6JL's work accompanied with data and science is a testament to skill, art and "knowing stuff".
Even the 40M FLEX 6700 SDR Police would be impressed. Just think 10 Pole tunable filters and the phrase "brick wall filtering" takes on a whole new meaning.
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