May 2, 2020 More on Phasing Rigs!
May 5, 2020 ~ There are other issues!
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
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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.
73's
Pete N6QW
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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
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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 a superb 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.
Ciao,
73's
Pete