Wow, really cool video from CuriousMarc and the guy who wrote the "Open Circuits" book. But fellows, you really need to be more careful with the high voltage. Remember poor Ross Hull. One hand behind the back would help. Volts jolt, but mills kill.
Tuesday, April 18, 2023
Sunday, April 16, 2023
Inside "Open Circuits"
Here is a cool video about a very cool book. I wasn't going to buy it, but when I saw it in a book store, I opened it up to a random page and found myself looking at the 2N3904. TRGHS. So I bought it.
Thursday, April 13, 2023
The Franklin Oscillator: A Super-Stable VFO. Why No Attention? Why So Little Use?
My Franklin VFO
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 author W6CEM 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:
Here is the July 1964 QST article:
There was an article about the Franklin oscillator in 73 magazine by W4LJC in February 1999:
The author notes that:
Much more recently (2022), Mike WN2A, modified his Mousefet transmitters (seen in QRP Classics in 1992) to include the use of the Franklin VFO circuit. Mike's documentation is really excellent. Kostas SV3ORA has a Franklin oscillator in his Super VFO circuit. Hans G0UPL has one on his site.
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?
Wednesday, April 12, 2023
Farhan's sBITX -- Taking Orders! (Video)
It is really looking great. Congratulations to Farhan for bringing yet another amazing rig to the amateur radio community.
Order yours here:
https://www.hfsignals.com/Tuesday, April 11, 2023
Arnie Coro: Jaguey Rig Designed in 1982, More info on the Rig
Jaguey, Matanzas, Cuba
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.
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