Lest You forget the Girlfriend and/or (both) the Wife, today is Valentines Day. A friend once changed his XYL's oil in her car on Valentines Day and declared to her that it was his present to her. Somehow Candy was at the top of her list. That act sure must have put a wrench into things and perhaps a while before he was no longer sleeping on the couch.
Our gift to you is a Phased Quadrature Oscillator WITHOUT an Arduino or Seed RP2040 or Si531. All you need is a handful of LC components plus one resistor and (gulp) a 14 MHz LC VFO*.
When QST used to be something other than an advertising brochure for foreign ham equipment manufacturers, they actually had "techie" stuff. Float back to September 1969 and the QST for that month featured a solid state phasing receiver and the all important how to create a simple quadrature LO. A Tip of the Cap to Richard Taylor W1DAX!
The Quadrature Hybrid Network with a 90 Degree Phase Shift.
There are four 0.47uh inductors, three 110pF Caps, one 220pF Cap , one 51 Ohm Resistor and one Variable Cap in the Range 55-300pF. Good only at 14 MHz and covers about 600 kHz with a 90 Degree shift. NOTE: Use of this circuit on any band other than 20M will not result in a 90 Degree shift.
This design may be scalable, but I do not know that for a fact. Try this circuit in LT Spice and then the answer may be evident. A start is 2X all values less the 51 Ohm resistance may yield the 40M network constants.
I was struck by the 51 Ohm resistor and parts of that circuitry that bear a resemblance to a Diplexer. The operative word is resemblance and I did not say that it definitively was a diplexer. We must be careful in what we say. There are those that watch!
While Taylor uses a B&W 2Q4 Audio Phase Shift network this can be replaced with real components (of better tolerance and precision) or just use Quad Net to design an op-amp phase shift network.
Taylor even describes how to turn this into a transceiver with just a few modifications. This project appeared in the ARRL Sideband Handbook but based on past history with QST, I would trust the Article versus the Book insofar as accuracy. Imagine a Phasing SSB Transceiver running off of your 14 MHz LC VFO and no micro-controllers, computers or software.
But as with most QST articles it is missing a big piece and that is the two mixer circuits that convert the RF signal to an audio base band. It does cite a reference of where to find this amazing Mixer stage (well you need two).
Wait for it, wait for it, as you are directed to the November 1968 QST (1 year earlier) and the article by Hayward and Bingham -- the seminal piece on Direct Conversion Receivers. That Home Brew DBM is lifted from W7ZOI and finds its way into the Phasing Receiver as the Mixer stage. Take a short cut and just slap ADE-1's in two places and call it a "Swifty". [Small, rich (in features) and sings (works) well.] Of particular note: the Hayward/Bingham publication title includes the words "a Neglected Technique", but not for long!
* If you want a stable signal with a digital readout on 20 Meters, you can program an Arduino or Seeed RP2040 and just feed CLK0 into the port where you feed the oscillator. Just saying, despite the LC proponents and advocates -- a stable 14MHz LC Oscillator is more difficult than you think.
This could be a real challenge to the FLEX and Apache SDR appliance operators! The I/Q approach to SDR is nothing more than two direct conversion receivers phased by 90 degrees with the "I" being In Phase and the "Q" being Quadrature. Do the math -- this phasing receiver project was done 55 years ago!
A Bonus Gift: You know that Hartley Oscillator Guy --well R V L Hartley was involved with the Phasing Method of SSB Modulation. So SDR may even go back to about 100 years ago.
RIP Bill Post who passed recently credited as the inventor of one of my most favorite foods: The Pop Tart!
73's
Pete N6QW
PS I searched on the Internet for the QST by the two issue dates and up they popped. If you go to ARRL for a reprint they want your credit card.
Fifty-Five years ago, there was a problem in our Hobby. Read: It Seems to Us from the September 1969 QST about Newcomers and lack thereof. Does anyone remember the ARRL Movie from Dave Bell on becoming a ham?
This was about the time of incentive licensing from ARRL and the start of literally giving away ham tickets. Now 50% of US hams do not have full HF Band privileges and many of the total ham population (770K) are not technically qualified to be hams -- something often openly admitted by them! We have all heard "just got my Extra but know nothing about Electronics!"
73's
Pete N6QW