Just go to http://soldersmoke.com. On that archive page, just click on the blue hyperlinks and your audio player should play that episode.
http://soldersmoke.com
There were a lot points in Eric's interview with Will that resonated with me:
-- Will told about how his very understanding and perceptive wife KNOWS when a homebrew project is not going well. Yea, we have the same situation here!
-- Will mentions the wisdom of Wes Hayward, Doug Demaw, and Pete Juliano.
-- Eric mentioned that there is a bit of his own blood in most of his homebrew projects. One slip of he screwdriver is often enough. My projects also often have a bit of my A+ in them. This adds soul to the new machine.
-- Will spoke of S-38s and HW-8s. I have both these devices here with me in the Dominican Republic. I have used both of them here.
-- Will mentioned the magic that comes when you listen with a receiver you built yourself. Yes.
-- NanoVNA. Yes, very useful.
Lots more great stuff in this interview. Thanks Eric and thanks Will.
Pavel CO7WT explained why Cuban hams used a process of thermal endurance to improved the frequency stability of their homebrew rigs:
--------------------
I'm CO7WT from Cuba, I started my endeavor in ham radio with a islander board.
They (FRC, like ARRL but in Cuba) made a print of a PCB to build the Islander, with component numbers and values, making construction fool proof, I think it was on the 90 or end of the 80...
Mine was built with scraps from an old KRIM 218 Russian B&W TV as Coro's explain, later on I get the 6bz6 and 6be6 tubes for the receiver (this worked better than the Russian parts) the VFO was transistorized, made with Russian components. A friend CO7CO Amaury, explain me a trick: thermal endurance:
For a week put a crust of ice on the VFO board by placing it in a frosty fridge during the night. Put them in the sun by day. This indeed improved stability, this was an old trick.
By thermal endurance I
mean improving thermal resistance vs tolerance, meaning that tolerance doesn't
vary as much with temperature changes.
It's crazy, but it
worked!!
I remember that my vfo
was on 7 MHz, with Russian kt315 as normal Russian transistors and capacitors,
nothing 1-5%, 20% at most, it ran several khz in 5-10 min, mounted on a Russian
"Formica" board (no PCB) and wired underneath.
After that treatment to
the complete board with components and everything, including the variable
capacitor; I managed to get it to "only" noticeably in the ear after
30-40 minutes.
To me it was magic!!
Basically, what I'm
describing is just "thermal annealing", but Cuban-style and with more
extreme limits.
In a refrigerator you
could easily reach -10 c and in the sun for a day in Cuba 60-80 celsius at
least.
In Cuba in the
1990s-2010s many designs of DSB radios proliferated, both direct conversion and
super heterodine (using an intermediate frequency)
At first tubes and then
transistors, mostly using salvaged parts, so it was common to find 465/500 kHz
(if common Russian) 455 khz and 10.7 Mhz with or without "wide"
filters since narrow filters for SSBs were not scarce: they were almost impossible
to get.
Not only that, crystals,
ifs, PCBs, transistors, etc.
Then, around the 2000s,
Russian 500 khz USB filters began to appear (from Polosa, Karat, etc. equipment
from companies that deregistered and switched to amateur radio) and that
contributed to improving... Even though at 7 MHz 500kc if is very close.
I made many modifications with the years mostly from 1998 to 2004 ish... better filters in front of the first RX stage (same IF described between stages) improved selectivity and out of band rejection, remember we had on that days broadcast as low as 7100 khz
Tx part was a pair of russian 6P7 (eq. RCA 807) in paralell, etc.
The Jagüey and others is
one of those evolutions...
This is something I
remember...
73 CO7WT
----------------
This is not as crazy as it sounds. We can find versions of the same technique in the writings of Roy Lewellan W7EL, Doug DeMaw W1FB, and Wes Hayward W7ZOI. I found this 2007 message from our friend Farhan VU2ESE:
I think the word 'annealing' is a bit of a misnomer. the idea is to thermally expand and contract the wiring a few times to relieve any mechanical stresses in the coil. after an extreme swing of tempuratures, the winding will be more settled. this techniques owes itself to w7EL. I first read about it in his article on the 'Optimized transceiver' pulished in 1992 or so. but all said and done, it is part of the lore. it needs a rigorous proof. - farhan
I can almost hear it, all the way from across the continent: Pete N6QW should, please, stop chuckling. Obviously these stabilization techniques are not necessary with his beloved Si5351. Some will see all this as evidence of the barbarity and backwardness of LC VFOs. But I see it as another example of lore, of art in the science of radio. (Even the FCC regs talk about "Advancing the radio art." ) This is sort of like the rules we follow for LC VFO stability: keep the frequency low, use NP0 or silver mica caps, use air core inductors, keep lead length short, and pay attention to mechanical stability. Sure, you don't have to do any of this with an Si5351. Then again, you don't have to do any of this to achieve stability in an Iphone. But there is NO SOUL in an Iphone, nor in an Si5351. Give me a Harley, a Colpitts, or a Pierce any day. But as I try to remember, this is a hobby. Some people like digital VFOs. "To each, his own."
Pete WB9FLW asked for this. This was an important article for me -- it paved the way for my entry into homebrew phone gear -- this article was the basis for my first DSB transmitter, built in the Azores.
I think Doug was a bit optimistic in saying that SSB operation was possible with this rig. Maybe it was possible for Doug, but for most of us DSB is just a LOT easier to get going than SSB. (I know that some people don't believe this, but I note that most of these folks have built neither DSB nor SSB rigs. It always seems easier before you start to melt solder.)
Be sure to check out the 10 meter DSB rig recently built by Mike WU2D. He has 6 or 7 good videos on this project, including this one: https://www.youtube.com/watch?v=xThoAMv4zrw
It is time to put aside (again!) all of the heated ideological arguments about the power level that defines "low power." Just sit back and enjoy this wonderful trip down QRP memory lane.
40673! TT2! And G3RJV's PW Severn - indeed, bow your heads!
Wow, the Ten Tec Power Mite (or Might!) -- I still want one. Same for the Argonaut -- what a great name (sounds like a "magic carpet), and with SSB to boot! I want to join the Argonaut cult!
I have both the HW-7 and HW-8 (the HW-8 is heading to the Dominican Republic). This video makes me want to fire up the HW-7. Maybe on 40.
Lee KD4RE of the Vienna Wireless Society has been talking about the Franklin oscillator. He has been telling us that it is very stable, and capable of stable operation up through the ten meter band. Lee wants to build an direct conversion receiver for all of the HF bands with one of these circuits.
I was skeptical. First, I'd never heard of this circuit. I'd grown up in ham radio on a steady diet of Hartley and Colpitts and Pierce. Vackar or Clapp were about as exotic as I got. And second, I'd come to accept that it is just not possible to build a good, stable, simple, analog VFO for frequencies above around 10 MHz. For example, in his Design Notebook, Doug DeMaw wrote, "VFOs that operate on fundamental frequencies above, say, 10 MHz are generally impractical for use in communications circuits that have receivers with narrow filters." DeMaw was known for resorting to variable crystal oscillators.
But then this month Mike Murphy WU2D put out two videos about his use of the Franklin oscillator circuit in a direct conversion receiver at 21 MHz. The VFO was shockingly stable. I began to believe Lee. I fired up my soldering iron and built one.
WU2D's Franklin Oscillator
Lee was right, it is in fact remarkably stable, even at higher frequencies. My build (see picture above) was a bit slap-dash and could be improved a bit, but even in these circumstances here is what I got. This was with a stable 6 Volt Supply and with only a cardboard box covering the circuit:
Local time Frequency
0543 19.1114 MHz (cold start)
0636 19.1116
0804 19.1117
1034 19.1118
1144 19.1117
I started digging around for references to the Franklin. There was nothing about it in Solid State Design for the Radio Amateur, nor in Experimental Methods of RF Design. Pat Hawker G3VA (SK) did discuss it in his Technical Topics column in RADCOM, February 1990. Pat gave a great bio on Charles S. Franklin (born in 1879 and a colleague of Guillermo Marconi). But tellingly, Pat writes that, "Despite its many advantages, the Franklin oscillator remains virtually unknown to the bulk of American amateurs."
QST "How's DX" August 1947
It wasn't always unknown. In the 1940s, we see articles about the Franklin oscillator circuit. There is a good one in the January 1940 issue of "Radio." The authorW6CEM notes that the circuit "is probably familiar to only a few amateurs." It shows up in the "How's DX" column (above). And the 1958/1959 issue of Don Stoner's New Sideband Handbook we see a lengthy description of the Franklin oscillator. Stoner wrote: "The author's favorite oscillator is the 'old time' Franklin, and it is believed to be the most stable of them all! This rock-solid device can put a quartz crystal to shame! Because it represents the ultimate in stability, it is the ideal VFO for sideband applications." And we see a PTO-tuned Franklin oscillator in the July 1964 QST. And it is in the fifth edition of the RSGB Handbook (1976).
Here is the January 1940 "Radio" with the Franklin oscillator article on page 41 by W6CEM:
Look, there may be reasons why the Franklin oscillator has been ignored. But the circuit sure seems to present a lot of advantages. Stable operation beyond the 10 MHz barrier is the big one. Simplicity is another. If there are problems and shortcomings, let's hear about them. But it seems as if the Franklin oscillator may provide the opportunity for us to build stable VFOs beyond 10 MHz without resort to complicated PLL stabilization techniques, and without opting to go with an Si5351 or other complex digital devices.
So let me ask: Why hasn't the Franklin oscillator been given more attention, and why haven't we seen more use of this circuit by hams or even by manufacturers?
Dxers Unlimited's mid week edition for 23-24 October 2007
By Arnie Coro
Radio Amateur CO2KK
...
My own personal experience with the original JAGUEY direct conversion
transceiver, designed way back in 1982, is that when used with a well
designed front end input circuit, those receivers provide amazing
sensitivity, with signals as low as 1 microvolt easily detected but,
they do have one drawback, their selectivity or ability to separated
between stations is very poor. The direct conversion radio receivers are
used for picking up CW Morse Code Signals , Digital Modes and Single
Side Band, but they are not good for receiving AM signals, and can't
pick up FM modulated signals at all...
The original JAGUEY 82 Cuban designed single band amateur transceiver, was tested against a sophisticated and really expensive factory built
transceiver. The tests showed that our design was at least as sensitive
as the very expensive professional equipment, registering a measured
sensitivity of less than one microvolt per meter, producing perfect CW
Morse Code copy of such a signal. Adding well engineered audio filtering
to a direct conversion receiver can turn it into a really wonderful
radio by all standards amigos.
Radio is a fun hobby, and believe me amigos, there is nothing more
magical than listening to a radio receiver you have just finished
building !!!
-----
Peter Parker VK3YE Found a nice description of the Jaguey by Cuban radio Amateur Jose Angel Amador from the BITX40 Facebook Group:
A translation. This was apparently in response to someone who thought they'd found a Jaguey schematic:
"That's not an original Jaguey, that was a simple, single band, unswitched, 5 watt, DSB, kit for beginners with no gear and needing something to put on the license.
Carbon microphone direct to balanced modulator, two stages with 20 dB gain, W1FB/W1CER style feedback, and final with 2 x 2N2102 class B. The receiver was more like that of the schematic, with a TAA263, easy to get from the FRC in 1978, and headphones. No need for an RF stage: the mixer was overloaded at night with European broadcasts above 7150. The VFO is also inspired by Solid State Design for the Amateur Radio, a Colpitts with 2SC372 and a low gain feedback buffer with two 2SC372s. Binocular ferrites were taken from Soviet TV baluns. The conditions of Cuba 1978. Today I would make an SSB rig with polyphase networks, mixer with 4066, and VFO Si5351. The big complication of BitX is the crystal filter, they either get it made, or stick to a recipe, but few have what is needed to measure and tinker with crystal filters.
I've said this before: I just seems so unfair. We just should be able to listen to DSB signals with our beautifully simple homebrew Direct Conversion receivers. I mean, building a DSB transmitter is a natural follow-on to DC receiver construction. And we are using AM shortwave broadcast stations (Radio Marti --I'm looking at you) to test our DC receivers for AM breakthrough. But when we tune these stations in, they sound, well, awful. So unfair! Why? Unfortunately it has to do with laws. Laws of physics and mathematics. Blame Fourier, not me.
Over the years there has been a lot of handwaving about this problem. From Doug DeMaw, for example:
In his "W1FB's Design Notebook," Doug wrote (p 171): "It is important to be aware that two DSSC (DSB) transmitters and two DC receivers in a single communication channel are unsatisfactory. Either one is suitable, however, when used with a station that is equipped for SSB transmissions or reception. The lack of compatibility between two DSSC (DSB) transmitters and two DC receivers results from the transmitter producing both USB and LSB energy while the DC receiver responds to or copies both sidebands at the same time."
That's correct, but for me, that explanation didn't really explain the situation. I mean we listen to AM signals all the time. They produce two sidebands, and our receivers respond to both sidebands, and the results are entirely satisfactory, right? Why can't we do this with our Direct Conversion receivers? I struggled with this question before: https://soldersmoke.blogspot.com/2015/07/peter-parker-reviews-dsb-kit-and.html You can see in that post that I was not quite sure I had the answer completely correct.
It took some discussion with a fellow Vienna Wireless Society member, and some Googling and Noodling for me to figure it out. But I think I've got it:
Imagine a station transmitting a DSB signal at 7100 kHz with a 1 kHz tone at the AF input. There will be signals at 7101 kHz and at 7099 kHz. Assume the carrier is completely suppressed.
We come along with our DC RX and try to tune in the signal.
Remember that they heart of the DC RX is a product detector, a mixer with the VFO (or PTO) running as close as we can get it to the suppressed carrier frequency (which we can't hear).
Lets assume that we can somehow get our VFO or PTO exactly on 7100 kHz. The incoming signals will mix with the VFO/PTO signal. We are looking for audio, so we will focus on the difference results and ignore the sum results of the mixing.
The difference between 7101 and 7000 is 1 kHz. Great! And the difference between 7099 and 7000 is 1 kHz also. Great again, right? We are getting the desired 1 kHz signal out of our product detector, right? So what's the problem?
Here it is: SIDEBAND INVERSION. Factoring in this part of the problem helps us see the cause of the distortion that plagues DSB-DC communication more clearly.
Remember the Hallas Rule: Whenever you subtract the modulated signal FROM the unmodulated signal, the sidebands invert. So, in this case, we are subtracting that 7099 "lower sideband" signal FROM the 7100 VFO/PTO signal. So it will invert. It will become an upper sideband signal at 1 kHz. We will have two identical 1 kHz signals at the output. Perfect right? Not so fast. Not so PERFECT really.
The perfect outcome described above assumes that our VFO/PTO signal is EXACTLY on 7100 kHz. And exactly in phase with the suppressed carrier of the transmitter. But if it is even SLIGHTLY off, you will end up with two different output frequencies, signals that will move in and out of alignment, causing a wobbling kind of rapid fade-in, fade-out distortion. You can HEAR this happening in this video by Peter Parker VK3YE, starting at 6:28:
And you can see it in this LTSpice simulation.
This LTSpice model just shows two diode ring mixers. The transmitter is on the top, the receiver is on the bottom. The transmitter has RF at 7100 kHz at L1 and audio at 1 kHz at R1. The receiver has the VFO at 7100.001 L7, DSB from the transmitter at L12 with audio appearing at R4. It is instructive to watch the output as you move the VFO frequency. If you move the VFO freq away from the transmit carrier osc frequency you will see the distortion. Here is the netlist for the LTSpice simulation:
On paper, using simple mixer arithmetic, you can tell that it will be there. With the VFO/PTO just 1 Hz (that's ONE cycle per second) off, you will end up with outputs at 1.001 kHz and at .999 kHz. Yuck. That won't sound good. These two different frequencies will be moving in and out of alignment -- you will hear them kind of thumping against each other. And that is with a mere deviation of 1 Hz in the VFO/PTO frequency! We are scornful when the SDR guys claim to be able to detect us being "40 Hz off." And before you start wondering if it would be possible to get EXACTLY on frequency and in phase, take a look at the frequency readout on my PTO.
Now consider what would happen if the incoming signal were SSB, lets say just a tone at 7101 kHz. We'd put our VFO at around 7100 kHz and we'd hear the signal just fine. If we were off a bit we'd hear it a bit higher or lower in tone but there would be no second audio frequency coming in to cause distortion. You can hear this in the VK3YE video: When Peter switches to SINGLE Sideband receiver, the DSB signals sound fine. Because he is receiving only one of the sidebands.
The same thing happens when we try to tune in an AM station using a Direct Conversion receiver: Radio Marti sounds awful on my DC RX, but SSB stations sound great.
My Drake 2-B allows another opportunity to explore the problem. I can set the bandwidth at 3.6 kHz on the 2-B, and set the passband so that I will be getting BOTH the upper and the lower sidebands of an AM signal. With the Product Detector and the BFO on, even with the carrier at zero beat AM sounds terrible. It sounds distorted. But -- with the Product Detector and BFO still on -- if I set the 2-B's passband to only allow ONE of the sidebands through, I can zero beat the carrier by ear, and the audio sounds fine.
There are solutions to this problem: If you REALLY want to listen to DSB with a DC receiver, build yourself a synchronous detector that gets the your receivers VFO EXACTLY on frequency and in phase with the transmitter's oscillator. But the synchronizing circuitry will be far more complex than the rest of the DC receiver.
For AM, you could just use a different kind of detector. That will be the subject of an upcoming blog post.
Please let me know if you think I've gotten any of this wrong. I'm not an expert -- I'm just a ham trying to understand the circuitry.
Take a look at the simple little mixer above. I think I first saw it in SPRAT. Thinking that it was really just a simplified version of the two diode Doug DeMaw mixer that I had been using for years, I couple of years ago I built it into a little Direct Conversion receiver. It worked great. But later, I began to have doubts about it. In the words of young James Clerk Maxwell, I started to wonder about "the particular go of it."
You see, the way the DeMaw mixer is set up, both of the diodes are simultaneously on and off. This has the effect of "chopping up" the incoming RF at a rate set by the VFO frequency. Boom. Fournier. Mixing. Great.
But look at the mixer at the top of this post. Here the VFO signal is coming in on the wiper of the 1k pot. The same signal is hitting both diodes at the same time. The diodes are not being fed differentially. So D1 and D2 are NOT both simultaneously tuning on and off. Instead, when the wiper goes positive, D2 turns on while D1 is off. On negative swings of the voltage at the wiper, D1 turns on while D2 is off. For me, this made it a "mystery mixer."
This reminded me of the sub-harmonic DC receiver I built earlier in the year: The VFO runs at half the operating frequency, but the diodes are set up to switch on and sample the RF TWICE each VFO cycle. This is the equivalent of having the VFO at the operating frequency.
Could it be that this was just a sub-harmonic mixer with the VFO at the operating frequency? (I should note that Doug DeMaw published a design that actually made this mistake. See: https://soldersmoke.blogspot.com/2011/07/doug-demay-and-polyakov.html ) I knew that this would sort of work, but it would not work very well. And the mystery mixer seemed to work very well. Hmmm.
Our beloved book, Solid State Design for the Radio Amateur (SSDRA) has an explanation of this circuit on page 74. But this explanation didn't seen to work for me. Check it out. YMMV.
Bottom line: I still couldn't figure this circuit out, so left it alone for while.
The other day I woke up and looked at it with fresh eyes. Suddenly it hit me. Although the VFO was hitting the diodes in the same non-differential way as is done in the sub-harmonic mixer, the RF (signal) is entering the mixer in a differential way. This means that the two diodes are taking turns sampling the upper side of L2, then bottom side of L2, via L1 and L2. This results in a complex repeating waveform that is similar to that of diode ring mixer. Within that complex repeating waveform, there are sum and difference frequencies. I did some noodling on this:
The key difference between this mixer and the sub-harmonic mixer is the way L2 is positioned: In the sub-harmonic mixer, there is no differential feed of the RF. Both diodes get the same polarity of RF. The VFO switches on D1, then D2. The RF is sampled at twice the VFO frequency. But in the mystery mixer that had me scratching my head, the RF is fed to the diodes in differential form. So while the diodes here are -- as in the sub-harmonic mixer -- being switched on and off sequentially, they are taking turns sampling the top and the bottom of L2. That provides the complex repeating waveform that we need to get the sum and difference frequencies. In a DC receiver the difference frequency is audio.
What do you guys think? Do I have this right? How would you characterize this mixer: Is it multiplying by 1 and 0? Or is it multiplying by 1 and -1?
This would be good mixer for a school project. It is simpler than a mixer with a tri-filar toroid.
I'm not exactly sure why I pulled this old rig off the shelf, but I'll write up what I did -- I often use this blog as a kind of notebook. I can look back and easily see what I did on my last encounter with the rig.
This rig is getting a bit long in the tooth: The receiver is built with 40673 Dual-Gate MOSFETs, an some of the transistor cans have gotten rusty. The frequency readout on the receiver is the top of a coffee can fitted onto the reduction drive behind the tuning knob from a Drake 2-B (not MY 2B!).
Here are two 2013 videos that I did on this receiver:
-- I put the crystal filter back in CW mode. I had widened it so that I could listen to 20 meter SSB, but I decided to go back to its original configuration. When I built the receiver in 1987, I didn't characterize the crystals -- I just used the capacitor values that Doug DeMaw had in his article. I pretty much did that again this time, just putting caps that are close in value to what Doug had. DeMaw used color burst crystals at 3.579 MHz. So I guess this would be a GREAT receiver for the Color Burst Liberation Army!
-- I used My Antuino (thanks Farhan!) to check the passband. Here is what it looks like. I just put the Antuino across the 10k resistors on either side of the input and output transformers. The coil cores had become very loose -- I just tried put them in the right place. I may need to put some wax in there to allow them to better stay in place. I think they could have used toroids instead -- that would have been easier. One of the transformer connections was open -- they don't work well that way, once I fixed that, the passband looks like this:
-- Each of the horizontal divisions is 500 Hz. The passband is not pretty, but it is OK, and I didn't feel like doing too much work on this to get it in better shape.
-- The filter peak was a bit lower in frequency than expected. I found that trimmer cap C3 in series with the BFO crystal would not allow me to lower its frequency sufficiently. So I moved C3 to a position in parallel with the crystal. With this mod, I could get the BFO frequency to 3578.69. This produces a 690 Hz tone when the received signal is at the peak of the IF passband. Opposite sideband rejection is quite good.
March 2013 Rebuild of the VXO 6 watter
-- I didn't have to do any real work on the transmitter. The RF amplifier in the transmitter had served for a time as the RF amp in by 17 meter DSB rig (I had added a bias circuit, which I removed when I put the amplifier back in Class C). Some time ago I rebuilt the oscillator circuit (which had been literally cut off the board when I used the amplifier in the DSB rig).
-- I did have to reconfigure the muting circuit -- the T/R switch in the transmitter switches the antenna and also -- through a two wire circuit -- cuts off 12 V DC to the transmitter when in receive mode.
-- For sidetone I just put a small piezo buzzer through a 1k resistor between 12 V DC and the key line.
It all worked fine -- I talked to three stations on the high end of the 20 meter CW band.
This is the DC receiver that I built back in 2017-2018. I had used a ceramic resonator in the VFO. That receiver was on the cover of SPRAT magazine. It may not have deserved the honor -- recently Dean KK4DAS and I discovered that the ceramic resonator VFO drifted rather badly. So Dean and I are now building real LC analog VFOs. This is kind of an aside to a Virginia Wireless Society -- Maker Group project. This video shows my receiver working yesterday on 40 using the VFO that was recently thrown together.
More details on the original project (that used the ceramic resonator) here:
The VFO circuit comes largely from W1FB's Design Notebook page 36. I followed most of the conventional tribal wisdom on VFOs: NP0 caps, often many of them in parallel. Air core coil (in my case wound on a cardboard coat hanger tube).
For C1 I used a big variable cap (with anti-backlash gears) that Pete N6QW advised me to buy on e-bay. Thanks Pete. L1 is on the cardboard tube. I only built the oscillator and the buffer -- I did not need the Q3 amplifier. (The water stain in the upper left is the result of a heavy rain in the Azores around 2002 -- water came pouting into the shack.)
I think the VFO is more stable than the Ceramic Resonator circuit. But I want to go back and give the ceramic resonator circuit another chance... Miguel PY2OHH has some really interesting ceramic resonator circuits on his site. Scroll down for the English translation: https://www.qsl.net/py2ohh/trx/vxo40e80/vxo40e80.htm
Dean KK4DAS commented that VFO construction is as much an art as a science. I agree -- there is a lot of cut and try, a lot of fitting the components you have on hand into the device you want to end up with. You have move both the frequency of the VFO AND the tuning range of the VFO. Mechanics (in the form of reduction drives) is often involved. And, of course you have to apply lots of tribal knowledge to get the thing stable. You could, of course, avoid all of this by using an Si5351, but I think that moves you away from the physics of the device, and is just less satisfying.
So, JOVO! LC JOVO! The Joy of VARIABLE Oscillation!
6 weeks in the DR for Bill One contact on uBITX. More SW listening. Repaired my Chrome Book in Santo Domingo! Christmas Present for All: James Web Space Telescope launch
More on this project in due course. Lots of soul in this machine.
I'd forgotten about this article -- thanks to Pete Eaton for reminding me. Click on the images for a better look at the article. For an even clearer view, download the images and then open them on your computer.
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.
"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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SolderSmoke Co-Host and Master Homebrewer
Dean Souleles KK4DAS
With beret and with a Michigan Mighty Mite in hand
Linux Mint, QRP, & C / C++ Compilers
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Greetings:
On the bench I'm studying PLL techniques using a sample & hold detector +
VHF circuitry. Currently, I've got nothing to post RF-wise. Another...
December 11, 2024. We take things for granted.
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We often take things for granted! You know, you snap on your homebrew rig
or appliance box, and it comes alive. Or that if you want a fresh salad,
there is...
MeSQUAREs alternative - 1/32" board
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MeSQUAREs are excellent. I've purchased them from QRPme in the past and
used them with great success. I get through them very quickly and find it a
bit unf...
HRWB 224 - 2024 Holiday Shopping Show
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In this episode we give you the buyer's guide to holiday cheer. The team
put their heads together to come up with many suggestions for the
workbench, ha...
The November - December 2024 SARC Communicator
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*Another BIG issue*
The final issue of the year. The November-December Communicator, digital
periodical of Surrey Amateur Radio Communications is now avail...
Hollow-State Design, 3rd Edition
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Hollow-State Design, 3rd Edition is available from: Lulu Press:
tinyurl.com/hollowstatedesign3 eBay: search for “hollow-state design”
Electric Radio bookst...
I Finally Bought My Dream Airplane
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Aviation has been a love of mine since I was a very little person. Living
in Nevada, seeing posters and ads for the Reno Air Races, specifically the
Texa...
2000 47pF Caps ...
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An unexpectged package arrive in the mail today. Did you ever wonder what
2000 47pF NP0 capacitors look like? Thanks to John, AB2XT I will never run ...
New QRP Cluster From OM0ET and OM6APN
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By DX EXPLORER
DX EXPLORER
Paul OM0ET and Peter OM6APN recently launched a new cluster dedicated to
QRP operations. Have a look and I hope you will enjoy...
Daylight Again – An all Analog Radio
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What’s all this? In 10 seconds, A high performance, 7MHz, 5 watt SSB rig
Draws just 24 mA of current 90 dB dynamic range, 80 dB close-in dynamic
range 3D ...
Digi-chirp! Digital synthesis of ‘nostalgic’ CW
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The bottom ends of 80, 40 and 20m are not what they used to be. For
starters, the busiest part is the digital segment where computers talk to
computers – l...
SMA Torque Wrench for the NanoVNA (uncalibrated)
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I have been using SMA connectors on most of my projects, and have
occasionaly gotten a slightly different reading than I had expected. Using
the NanoVNA, ...
40m SSB Tramping Rig
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Please see my YouTube channel for details of the build.
http://www.youtube.com/c/CharlieMorrisZL2CTM
*2N3904 Antenna Amplifier (initial)*
Voltage gain is ...
Modifications to the Dayton/FDIM-2019 Antuino
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The Dayton Antuino has sub-optimal performance. This is a short note on
improving it to an 80 db range of measurements. The trouble with Antuino
2.0 (the o...
Raduino as NBFM TX
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Here is a neat, 30 minute hack for your Raduino to turn the Si5351 into a
pretty stable, solid NBFM transmitter. The hack is to add a varactor diode
in ...
QRP Labs shop!
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[image: Shop]
All QRP Labs kits may be ordered online securely at the shop, with PayPal
payment.
*Click here to visit the shop!*
*Click!*
*Shop! Order...
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