n3ajx radio experiments

Since the phasing RX (part 2) functioned reasonably well, I decided to build a companion phasing TX using the same general concepts as before. Phasing TX's anecdotally have a less than stellar reputation - poor carrier and opposite sideband suppression.  I wanted to see if replacing the usual op-amp based phase shifters (KK7B) with the Teensy4.0/SGTL5000 (ZL2CTM) combination would be practical.  As in the RX build, filtering at RF frequencies is done using external LP and BP LC filters of conventional design.  The TX concept is detailed, below:   The RX's switched quadrature LO is put to work in this build.  (The RX has the capability to offset the TX frequency for CW operation and the built-in FST3253 DPDT switch makes the LO signal available externally in the transmit state.)  PTT circuitry was implemented using old-school, discreet component switching for simplicity's sake.  The Teensy would be more than capable of accomplishing the same result....

Target is Teensy 4.0 + SGTL5000 audio shield.  Mostly ZL2CTM's code again - he's done some good stuff (IMO)!  Filter coefficients were generated using Oak Hills filter design program.  Oak Hills site is gone, but the GUI filter design program (Windows only, unfortunately) can be found by searching the interweb.  Same disclaimer as part 2a. _______________________________________________________________________________________________  #include <_Teensy.h> #include <Wire.h>                           #include <Audio.h>  // Teensy audio library // Number of Filter Coefficients #define NO_HILBERT_COEFFS 200   #define SSB_SWITCH 3 #define FILTER_SWITCH 4 // Iowa Hills Hilbert transform filter coefficients const short Hilbert_Plus_45_Coeffs[NO_HILBERT_COEFFS] = { (short)(32768 *  0.00000187995362921356), (short)(...

Code for Quadrature VFO control.  Credits to ZL2CTM and NT7S (and probably others..) Use at your own risk - If your radio starts to glow green and explodes from running this code, it's not my (or anyone else's) fault.  Target is Arduino Nano or Metro mini.  _______________________________________________________________________________________________  // #include <Rotary.h> #include <si5351.h> #include <Wire.h> #include "SSD1306Ascii.h" #include "SSD1306AsciiWire.h" #define I2C_ADDRESS 0x3C // Define proper RST_PIN if required. #define RST_PIN -1 SSD1306AsciiWire oled; #define ENCODER_A 3  // Encoder pin A #define ENCODER_B 2  // Encoder pin B #define ENCODER_BTN 11 #define RESET_BTN 12 #define TX_ON 6 #define OFFSET_ON 8 Si5351 si5351; Rotary r = Rotary(ENCODER_A, ENCODER_B); volatile uint32_t cw_offset = 0ULL; volatile uint32_t cwo_old = 0ULL; volatile uint32_t radix = 1000;  //start step size - change to suit boolean changed_f = 0...

      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...

     I spend (waste?) significant time looking for RF bargains on the auction site that you all know and love.  Recently, I found a US-based listing for Mitsubishi RD30HVF1 MOSFETs at a very reasonable price (<$12/piece for 4).  So I bought 4 and thought I'd put together a 35 - 50 watt HF amp for my Hermes Lite 2 that would perform a bit better than the typical IRF510/IRF530 designs that abound on the net.  A cursory search didn't reveal any examples to use for guidance.  So I looked at several RD15HVF1/RD16HHF1 designs that served as a starting point:  1.  A couple of examples from 60dbm.com 2. KK4DAS's design that had evolved from Skelton's (EI9GQ) design. I had actually built an example of Dean's design, and while it worked as advertised, I never quite got the input match a good as I wanted.  I figured that another try, using the RD30HVF1's, was in order.  The circuit I came up with lies below: A photo of the test build f...