Just setting up

 I'll write about some of my radio experiments once & a while.

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Playing with Phasing - part 1

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      Every so often it seems that some folks are lured into the less-populated territory of SSB reception and transmission using the phasing method.  Maybe it's the promise of simpler (?) circuitry, eliminating the need for crystal/mechanical filters, or perhaps as a gateway drug into SDR-land.   Rick Campbell's (KK7B) articles describing a single-signal direct conversion receiver (QST - Jan 1993), followed by a phasing transmitter (QST - April 1993) are seminal works that detail the implementation of the phasing method with modern (for the 1990's, at least) circuitry.  These papers also discuss design tradeoffs in terms that are easily understood.  Quite a few years ago, I actually built a R2/T2 transceiver, shamelessly copying those designs and adding a Si5351 quadrature LO along the lines of that described by ZL2CTM in his blog.  It worked OK, but the opamp-based, all-pass phase shifters required hand matching of the RC components fo...
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A Half-baked Fix for Si5351 Quadrature Issues

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In a previous post, I briefly described issues I had preserving quadrature output from an Si5351 board.  Allegedly, once a 5351 is programmed to provide a fixed phase offset on a second output,  it should maintain that phase shift across frequency excursions, provided the "even divisor" remained unchanged - No PLL reset needed until the a large enough frequency excursion requires a change in the "even divisor".  PLL resets caused annoying "pops" in the output of direct conversion front ends that I typically use for phasing-type receivers.  I was loathe to include a PLL reset on every frequency change because of that.  So, I (and many others) only do a PLL reset when the required integer "even divisor" was changed.  Many fewer "pops", but semi-random loss of LO quadrature within a relatively small frequency range.  I added a polled front-panel switch to my hardware that I use to manually reset the  PLL when my "ear detector" de...
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Revisiting the LT5517

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Some time ago (just before Linear Tech & Analog Devices merged), I requested a few samples of LT's 5517 quadrature demodulator and 5598 quadrature modulator.   They happily supplied a few samples of each, but the local LT rep also called me at work and asked if I'd also like to have a dc678a evaluation board ( https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards-kits/dc678a.html#eb-overview ).  Of course, I said, "Hell yes!" and it appeared in the mail soon after (no charge).  But then it sat unloved and unused for years until I recently decided to see how well it worked at HF. The 5517 board is the green one in the upper left corner.  A 2-channel baseband preamp is the Manhattan-style board next to it.  The board below the 5517 board is a split supply boost converter that powers a 100x gain, 2-channel baseband preamp using THAT1510 instrumentation amps.  These devices are very similar to the widely used INA217....
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