Just go to http://soldersmoke.com. On that archive page, just click on the blue hyperlinks and your audio player should play that episode.
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It is especially appropriate for us to use that Irish phrase because the design of the rig's new final amplifier is out of Ireland. Our friend Dean KK4DAS added a 16 watt RF amplifier based on a design by EI9GQ to his homebrew N6QW Simple SSB rig. Note the IBEW label on the top.
Here is Dean's blog post on this wonderful project (with video and more pictures).
I usually try to listen in on the Old Military Radio Net on Saturday mornings (3885 kc). Lately I listen with my Mate for the Mighty Midget receiver.
This morning's session was especially good. For me the highlight was when Masa AB9MQ called in from Normal, Illinois using his Central Electronics 20A (see below). That was one of the earliest SSB rigs. A phasing rig, it also ran AM (which was what Masa was using this morning). He had it paired up with a Central Electronics 458 VFO. You folks really need to check out Masa's QRZ.com page:
Three cheers for Alan Wolke W2AEW, truly one of the great guys of homebrew ham radio. Alan's wonderful YouTube videos have enlightened hams all around the world. He is always there to answer questions and help hams (like me) who are at times struggling to understand technical concepts.
Photo from the November 13, 2021 ARRL Hudson Division Awards Luncheon. That’s Alan with the ARRL CEO David Minster NA2AA, the Nobel Prize winning Dr. Joe Taylor K1JT, and 2021 Technical Achievement winner David DeCoons WO2X. Alan was presented with the division’s 2020 Technical Achievement award.
Wow, I was really pleased to learn that Peter Parker VK3YE was a 2021 inductee into the QRP Hall of Fame.
This is a richly deserved honor. Peter Parker has been making extraordinary contributions to QRP and homebrewing for many years. I remember reaching out to him when I was just getting started with homebrew phone gear. I considered him a guru of DSB. He helped me a lot. Peter Parker was interviewed on the SolderSmoke podcast in 2013:
Peter has published many books and has produced many YouTube videos. He hosts an annual QRP gathering in his beloved home-town of Melbourne Australia that gets attention from solder-melters around the world.
Jerry KI4IO is such an amazing homebrewer that he has been dubbed "The Wizard of Warrenton." The picture above shows Jerry during the early 1980s in the shack of Father Moran 9N1MM in Nepal. Jerry was also in India. (I previously posted the info on Jerry's time in India and Nepal, but I didn't have this picture. The picture makes it worthwhile to post the story again.) From Jerry's QRZ.com page:
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While in India I was licensed at VU2LHO and worked a lot of US hams with a 135' flat-top and open-wire feed. I had the antenna strung between two bamboo towers atop the embassy housing 2nd-story roof-top. I also put up a 3/8 wave vertical on the roof for 10 meters. That little antenna had 110 radials stapled into the roof screen and worked very well! The rig was a HW-101. I was in Kathmandu, Nepal from early 1980 to late 1982. I could not obtain a license there, but became good friends with Father Moran, 9N1MM, and would often spend time up at his place putting his Drake station on CW. Pretty cool being real DX! Back in the states in late 1982.
Here I am at one of my many visits to Father Moran's shack.
I got in touch with Jerry because Pete Eaton reminded me that Jerry had homebrewed a discrete transistor version of the NE602 Gilbert Cell Mixer, a device that I am very interested in. Nick G8INE also built one.
Armed now with a NanoVNA, I took a look at the passband of the 5 MHz filter in my Barebones Superhet (BBRX) W4OP built it on a Circuit Board Specialist Board. He put a 5 MHz CW filter in there; I broadened the passband for phone by changing the values of the capacitors. Here is what the passband now looks like in the NanoVNA:
This is what DeMaw would call an "LSB filter." You would get much better opposite sideband rejection by using it with an LSB signal, placing the BFO/Carrier Oscillator slightly above the passband, in this case near 5.002 MHz.
When I first built the down converter to get the 18.150 MHz signal down to the 7 MHz range (where I had the receiver running) I used an 11 MHz crystal for the NE602's local oscillator. But this created a big problem: 18.150 - 11 = 7.150 MHz. That is in the 40 meter band, but note: NO SIDEBAND INVERSION. Then in the BBRX 7.150 MHz - 2.150 MHz = 5 MHz (the filter frequency) but again: NO SIDEBAND INVERSION. The signal started as a USB signal and remained a USB signal.
I briefly tried shifting the BFO frequency to the other side of the filter passband. If I could get it to around 4.985 MHz, it might work, but because the filter passband was so large, and because the crystal frequency was so low, I was unable to shift the crystal frequency that far. In any case the results would have been less than ideal because of the "LSB" shape of the filter. Back to the drawing board.
I decided to cause one sideband inversion.
At first I put a 25.175 MHz crystal module in my down converter. This shifted the 17 meter phone band down to the 40 meter CW band. It worked, but I cold hear strong 40 meter CW signals being picked up by the wiring of the receiver (the box is plastic!). I went back to the module jar in search of frequency that would move 17 meter phone to the 40 meter area (so I would not have to re-build the BBRX front end) but outside the actual 40 meter band.
I ended up using a 25 MHz crystal in the down converter. 25 MHz - 18.150 MHz = 6.85 MHz WITH SIDEBAND INVERSION. After checking on the NA5B Web SDR to see that there are no strong signals in the 6.835 to 6.89 MHz range, I retuned the output circuit on the converter and tweaked the input capacitor on the Barebones. I shifted the VFO frequency down to 1.835 to 1.89 MHz and put the BFO at 5.002 MHz. The receiver was inhaling on 17 meter SSB.
One more change to the BBRX: in his June 1982 QST article, DeMaw warned that trying to get speaker level audio out of the 741 op amp that he used would result in audio distortion. And it did. So I put one of those little LM386 boards I have been using into the BBRX box. I just ran audio in from the wiper of the AF gain pot. It sounds good.
In effect this is my first double-conversion receiver. I usually prefer single conversion, but this project has highlighted for me one of the advantages of double conversion for someone like me who eschews digital VFOs: Starting with a crystal filter at 5 MHz, with double conversion I could keep the frequency of the LC VFO low enough to ensure frequency stability. That would have been impossible with a 5 MHz IF in a single conversion 17 meter rig. But if I were starting from scratch for a 17 meter rig, I could stick with single conversion by building the filter at 20 MHz, keeping the VFO in the manageable 2 MHz range.
Now, on to the SSB transmitter. The Swan 240 dual crystal lattice filter from the early 1960s needs some impedance matching.
I think the key to understanding the Gilbert Cell Double Balanced mixer is to separate out the three tasks that this device completes, and consider them one at a time, using different diagrams:
1) It mixes two signals to produce sum and difference outputs.
2) It balances out the RF input.
3) It balances out the LO input.
Task 1 -- Mixing
The Gilbert cell is like the diode ring mixer in that it switches the polarity of the input signal at a rate set by the Local Oscillator. Another way of saying this is that the mixer multiplies the input signal by 1 and by -1.
Steve Long of the University of California described the essence of this mixing this way (using the diagram above):
In an effort to see this for myself, I drew (noodled!) this diagram:
There are four transistors -- two differential pairs with RF coming into the bases of the pairs.
The LO is a square wave. The LO alternately turns on transistors 1 and 4, then 2 and 3. When 1 and 4 are on, we are in period 1 -- here there is no switching of polarity. Portions of the RF waveform are passed to the outputs. But when the LO turns on transistors 2 and 3, portions of the RF wave form are "crossed over" to the opposite output. Polarity is reversed. We see this in period number 2.
Take a look at the resulting output waveforms. This is the same waveform we see coming out of a diode ring mixer. I really like this drawing because in that complex waveform you can actually see the sum and difference frequencies:
I could see this diode ring waveform myself on my oscilloscope:
In a diode ring, and in other diode mixers, the balancing out of the input signals really takes place in the trifilar toroidal coils that are part of the circuit. Barrie Gilbert needed an integrated circuit mixer that did not use coils.
Again referring to the above diagram, Steve Long of the University of California put it this way:
The ideal balanced structure above cancels any output at the RF input
frequency since it will average to zero.
To fully understand this I find it helps to look at the Gilbert cell circuit drawn in a different way. Here is a drawing from Alan Wolke W2AEW that I found very helpful. It comes from his excellent YouTube video: https://www.youtube.com/watch?v=7nmmb0pqTU0
Suppose the RF waveform at I1 is causing the current through R1 and R2 to increase. At the same time, the opposite phase current through I2 will be causing the current through R1 and R2 to DECREASE. So there is no net effect of the RF signal at the output. The RF is balanced out.
TASK 3 - Balancing Out the Local Oscillator Signal
Here too I used my own drawing, and was guided by the words of Steve Long:
It also cancels out any LO frequency
component since we are taking the IF output as a differential signal and the LO
shows up as common mode.
The important thing to realize here is which transistors are being turned on and off by the local oscillator signal. On one half cycle of the LO, transistors 1 and 4 are on. So the LO signal at the LO frequency are both pulling the same amount of LO frequency current through the resistors. So you have the same change in voltage at the output terminals. And the output terminals are differential. The LO signal results in no voltage difference between the terminals. So the LO frequency is balanced out.
The same thing happens on the following half of the LO cycle. Here, transistors 2 and 3 are turned on. Again, both transistors pull the same amount of LO frequency current through the resistors. There is no differential voltage. So no LO frequency energy passes to the output. LO frequency is balanced out.
--------------------------------
I am surrounded by Gilbert Cell Mixers and I have been using them in my homebrew rigs for many years. I use them in up-converters for my RTL-SDR receivers. I have one in the downconverter for my 17 meter receiver and had one as the mixer in my first SSB transmitter. I built a 40 meter SSB transceiver with NE602s on either end of the crystal filter. Years ago, I built a DSB transceiver with several NE602s. My SST QRP CW transceiver is made with NE602s. I have on my bookshelf Rutledge's book "The Electronics of Radio" that is all about the NORCAL 40 transceiver, built using NE602 chips. But until now I really didn't know how these chips worked. Truth be told, for me they were mysterious little black boxes, and that bothered me. Now I feel a lot better about using these clever devices. I plan on stocking up on the old style (non-SMD) NE602s.
Apparently Barrie Gilbert rejected the idea that he invented the circuit that bears his name. It seems that Howard Jones first used this circuit in 1963, with Gilbert developing it independently (in an improved form) in 1967.
Barrie Gilbert was quite a guy, with electronic roots in the world of tinkering:
My old friend Mike EI0CL used to remind me that hams in Ireland are granted not just an amateur radio license, but an amateur radio experimenter's license, with an emphasis on experimentation. I think we can see that emphasis in the newsletter of the club. It has a remarkably high level of technical content. Check it out, and look at more information on the club:
Rarely if ever will we come across a high quality NETFLIX series built around a shortwave broadcast transmitter. But that is what we have in Gloria. It is really good. We were especially interested in it because we lived in Portugal for three years. In addition to all the intrigue and drama you will catch glimpses of broadcast antennas, big transmitting tubes, and one out-of-focus shot of what appears to be a Hallicrafters receiver (SX-42?)
Acharya Sir Jagadish Chandra Bose, was a Bengali polymath, physicist, biologist, botanist, archaeologist, as well as an early writer of science fiction. He pioneered the investigation of radio and microwave optics, made very significant contributions to plant science, and laid the foundations of experimental science in the Indian subcontinent. IEEE named him one of the fathers of radio science. He is also considered the father of Bengali science fiction. He also invented the crescograph.
Born in Bikrampur (present day Munshiganj District near Dhaka in Bangladesh) during the British Raj, Bose graduated from St. Xavier's College, Calcutta. He then went to the University of London to study medicine, but could not pursue studies in medicine due to health problems. Instead, he conducted his research with the Nobel Laureate Lord Rayleigh at Cambridge and returned to India. He then joined the Presidency College of University of Calcutta as a Professor of Physics. There, despite racial discrimination and a lack of funding and equipment, Bose carried on his scientific research. He made remarkable progress in his research of remote wireless signaling and was the first to use semiconductor junctions to detect radio signals. However, instead of trying to gain commercial benefit from this invention, Bose made his inventions public in order to allow others to further develop his research.
Bose subsequently made a number of pioneering discoveries in plant physiology. He used his own invention, the crescograph, to measure plant response to various stimuli, and thereby scientifically proved parallelism between animal and plant tissues. Although Bose filed for a patent for one of his inventions due to peer pressure, his reluctance to any form of patenting was well known. To facilitate his research, he constructed automatic recorders capable of registering extremely slight movements; these instruments produced some striking results, such as Bose's demonstration of an apparent power of feeling in plants, exemplified by the quivering of injured plants. His books include Response in the Living and Non-Living (1902) and The Nervous Mechanism of Plants (1926).
......Bose's education started in a vernacular school, because his father believed that one must know one's own mother tongue before beginning English, and that one should know also one's own people.
Speaking at the Bikrampur Conference in 1915, Bose said:
“At that time, sending children to English schools was an aristocratic status symbol. In the vernacular school, to which I was sent, the son of the Muslim attendant of my father sat on my right side, and the son of a fisherman sat on my left. They were my playmates. I listened spellbound to their stories of birds, animals and aquatic creatures. Perhaps these stories created in my mind a keen interest in investigating the workings of Nature. When I returned home from school accompanied by my school fellows, my mother welcomed and fed all of us without discrimination. Although she was an orthodox old-fashioned lady, she never considered herself guilty of impiety by treating these ‘untouchables’ as her own children. It was because of my childhood friendship with them that I could never feel that there were ‘creatures’ who might be labelled ‘low-caste’. I never realised that there existed a ‘problem’ common to the two communities, Hindus and Muslims.”
Oh man, I share this with much trepidation because the last time I posted something about the work of Mike KG7TR, Pete N6QW said he felt like putting all of his own work in the dumpster, so much better was the artistry of KG7TR. This receiver is so cool and so well-done that we now might have to post a guard outside the N6QW shack -- heck Mike even has an Arduino Uno and an Si5351 in there! Don't do it Pete!
I was led to this magnificent receiver by the very humble 6U8 tube. Scott WA9WFA and I have been learning (mostly from Grayson KJ7UM) that the much used and sometimes loved 6U8s (three of them in our "Mates for the Mighty Midget") might be a bit long in the tooth, old even by Thermatron standards. I was worried when I remembered that my Drake 2-B has a 6U8 in it -- V2, the first mixer. So I Googled for more info and was led to this amazing receiver, a 2018 creation by KG7TR. How did we NOT see this for almost four years?
As for the 6U8s, well Grayson says the tube has been getting something of a bum rap. And KG7TR has two of them in this receiver, so I will obviously have to give the 6U8 another chance.
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I didn't know that Lew McCoy had his own crystal and crystal filter company:
In SolderSmoke Podcast #234, I said that I was scrutinizing the filter from the Swan 240 that I had picked up around 1994 in the Dominican Republic. I cannibalized it out in the Azores in the early 2000s and used the parts to build -- among other things -- my first SSB transmitter. I never really focused much attention on the filter that I pulled out of that old rig -- I was just happy that it seemed to work. But I am now older and wiser, and I have some test gear that lets me look at the passband of that filter.
First, take a look at what it is supposed to look like. This is from the manual. Yikes! That passband looks far from flat. I can almost hear homebrewers around the world shrieking in horror and disgust.
Above is a description of the filter, and the schematic, again from the manual.
Here is what my extracted and somewhat re-built filter looked like in my NanoVNA (more shrieking!). The dip in the passband is a lot worse here -- it looks like 10 db vs. 3 db in the manual. This is probably because I'm not even attempting any impedance matching on the filter -- it is just seeing the 50 ohms in and out of the NanoVNA.
Here is my 2002 attempt to rebuild the filter and put it in my SSB transmitter, along with my more recent attempt to flatten the passband. I no longer had the adjustable coil L8, so I made my own coil based on guidance from Ben Vester W3TLN's January 1959 QST article on "Surplus-Crystal High-Frequency Filters." (Ben had an early influence on Pete Juliano's tube-rig designs.) In the picture above I have 1k pots between the filter and the input and the output of the NanoVNA, as described by Nick M0NTV.
Adjusting the 1 k pots, I could smooth out the passband quite a bit. Measuring the pots and adding the 50 ohms of the NanoVNA, it looks to me like this filter is smoother with about 280 ohms at the input and output. I may build two matching networks or some transformers. Some TIAs may also be needed.
"SolderSmoke -- Global Adventures in Wireless Electronics" is now available as an e-book for Amazon's Kindle.
Here's the site:
http://www.amazon.com/dp/B004V9FIVW
Bill's OTHER Book (Warning: Not About Radio)
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