Playing with Phasing - Part 3 - An experimental SSB/CW Transmitter (WIP)

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.   A photo of the TX "guts" as they currently stand, reveals that the same 50 ohm interface, modular approach used for the RX was also used, here.


 A few brief tests (using a TinySA Ultra with 60db attenuation in front of it for "protection") showed 48db carrier suppression and opposite sideband suppression on the order of 37 - 40db  (yes, I did correct for the attenuation).  Not spectacular, but usable, at least at QRP levels.  This performance could possibly be improved by careful adjustment of AF and LO levels at the 2 X DBM module.  I just haven't got there, yet!

To do:

1. Optimize AF/LO levels at DBM's for best possible carrier and opposite sideband suppression.

2. Determine if more than 200 taps are practical for the Hilbert filters.  Experiment with filter window type.

3. Make sure the TX amplifier chain has acceptable IMD performance.  I'm bumping up on gain compression in the TIA and pre-driver.  The SV1AFN driver amp seems pretty robust and doesn't gain compress much at 1 watt output.  Not cheap, but a real beast!

4. Actually put this gear on the air and see if it sounds good to the outside world.

5. Decide if I want to add any software-based "features". 

6. Remove the 10-turn pot and op-amp voltage source that were used to control various VCA's during initial development.  Using small-signal VCA's in this application did not turn out well.  Sometimes you have to learn the hard way....

_______________________________________________________________________________________________

The Teensy code (again, largely based on ZL2CTM's work) for this TX follows: 

 #include <_Teensy.h>

#include <Wire.h>  
#include <Audio.h>  // Teensy audio library

// Number of Filter Coefficients
#define NO_HILBERT_COEFFS 200

// Iowa Hills Hilbert transform filter coefficients
const short Hilbert_Plus_45_Coeffs[NO_HILBERT_COEFFS] = {
(short)(32768 *  0.00000187995362921356),
(short)(32768 *  0.00000101382681805262),
(short)(32768 * -0.00000041944920781134),
(short)(32768 * -0.00000206886261366890),
(short)(32768 * -0.00000328853616338165),
(short)(32768 * -0.00000322961068377481),
(short)(32768 * -0.00000104261721389776),
(short)(32768 *  0.00000383674523618538),
(short)(32768 *  0.00001138329298555618),
(short)(32768 *  0.00002075305565085728),
(short)(32768 *  0.00003022999953827821),
(short)(32768 *  0.00003742715125554241),
(short)(32768 *  0.00003976617153966799),
(short)(32768 *  0.00003518092489684932),
(short)(32768 *  0.00002290562406415120),
(short)(32768 *  0.00000414016449212795),
(short)(32768 * -0.00001763984073477332),
(short)(32768 * -0.00003692470636451617),
(short)(32768 * -0.00004705678293248639),
(short)(32768 * -0.00004169571548118256),
(short)(32768 * -0.00001661604801483918),
(short)(32768 *  0.00002856819992302917),
(short)(32768 *  0.00008924310532165691),
(short)(32768 *  0.00015566049842163920),
(short)(32768 *  0.00021412860951386392),
(short)(32768 *  0.00024954276159405708),
(short)(32768 *  0.00024891708744689822),
(short)(32768 *  0.00020523219427559525),
(short)(32768 *  0.00012067319039488211),
(short)(32768 *  0.00000828072279546177),
(short)(32768 * -0.00010876693704631180),
(short)(32768 * -0.00020058304653503001),
(short)(32768 * -0.00023643388703931123),
(short)(32768 * -0.00019207553123123944),
(short)(32768 * -0.00005703790884581394),
(short)(32768 *  0.00015996840375009924),
(short)(32768 *  0.00042924060835503042),
(short)(32768 *  0.00070302636595442891),
(short)(32768 *  0.00092342460993677378),
(short)(32768 *  0.00103426445275545120),
(short)(32768 *  0.00099482492078095675),
(short)(32768 *  0.00079241563798859715),
(short)(32768 *  0.00045058503746986389),
(short)(32768 *  0.00003020270378328860),
(short)(32768 * -0.00037809176137670875),
(short)(32768 * -0.00066977186361327767),
(short)(32768 * -0.00074829190270975232),
(short)(32768 * -0.00054877914953976870),
(short)(32768 * -0.00005827662607771344),
(short)(32768 *  0.00067276862682774663),
(short)(32768 *  0.00153185811359435320),
(short)(32768 *  0.00236034626141190529),
(short)(32768 *  0.00298246811144053936),
(short)(32768 *  0.00324279186315834522),
(short)(32768 *  0.00304473401047289371),
(short)(32768 *  0.00238144909963011742),
(short)(32768 *  0.00135089165996760130),
(short)(32768 *  0.00014931759505998343),
(short)(32768 * -0.00095839390996843576),
(short)(32768 * -0.00168814661446958780),
(short)(32768 * -0.00179734628181904554),
(short)(32768 * -0.00114480499178171158),
(short)(32768 *  0.00026374991284683347),
(short)(32768 *  0.00225671660155057907),
(short)(32768 *  0.00451200548559427261),
(short)(32768 *  0.00660791201516985893),
(short)(32768 *  0.00810285285115242004),
(short)(32768 *  0.00863009598106145859),
(short)(32768 *  0.00798853952437639236),
(short)(32768 *  0.00620909873396158218),
(short)(32768 *  0.00357905798591673374),
(short)(32768 *  0.00061377260135486722),
(short)(32768 * -0.00202476163394749165),
(short)(32768 * -0.00365150393918156624),
(short)(32768 * -0.00370277347974479198),
(short)(32768 * -0.00187310588080435991),
(short)(32768 *  0.00178553408477455378),
(short)(32768 *  0.00682784663513302803),
(short)(32768 *  0.01245793793350458145),
(short)(32768 *  0.01765142939984798431),
(short)(32768 *  0.02134133130311965942),
(short)(32768 *  0.02263728901743888855),
(short)(32768 *  0.02103775925934314728),
(short)(32768 *  0.01659170538187026978),
(short)(32768 *  0.00997202750295400620),
(short)(32768 *  0.00243640411645174026),
(short)(32768 * -0.00432921992614865303),
(short)(32768 * -0.00846713781356811523),
(short)(32768 * -0.00826646760106086731),
(short)(32768 * -0.00249097635969519615),
(short)(32768 *  0.00934264715760946274),
(short)(32768 *  0.02679026685655117035),
(short)(32768 *  0.04844862595200538635),
(short)(32768 *  0.07208253443241119385),
(short)(32768 *  0.09489956498146057129),
(short)(32768 *  0.11393431574106216431),
(short)(32768 *  0.12648330628871917725),
(short)(32768 *  0.13052044808864593506),
(short)(32768 *  0.12502384185791015625),
(short)(32768 *  0.11015775054693222046),
(short)(32768 *  0.08727697283029556274),
(short)(32768 *  0.05875028669834136963),
(short)(32768 *  0.02762975543737411499),
(short)(32768 * -0.00278118043206632137),
(short)(32768 * -0.02939149923622608185),
(short)(32768 * -0.04974408075213432312),
(short)(32768 * -0.06232902035117149353),
(short)(32768 * -0.06674224138259887695),
(short)(32768 * -0.06366980075836181641),
(short)(32768 * -0.05470800399780273438),
(short)(32768 * -0.04205619916319847107),
(short)(32768 * -0.02813878841698169708),
(short)(32768 * -0.01522193104028701782),
(short)(32768 * -0.00508764060214161873),
(short)(32768 *  0.00118558865506201982),
(short)(32768 *  0.00330774253234267235),
(short)(32768 *  0.00172494212165474892),
(short)(32768 * -0.00254931696690618992),
(short)(32768 * -0.00817991327494382858),
(short)(32768 * -0.01378324162214994431),
(short)(32768 * -0.01817758195102214813),
(short)(32768 * -0.02056903392076492310),
(short)(32768 * -0.02064667269587516785),
(short)(32768 * -0.01857941970229148865),
(short)(32768 * -0.01492566708475351334),
(short)(32768 * -0.01048160158097743988),
(short)(32768 * -0.00610282970592379570),
(short)(32768 * -0.00253540510311722755),
(short)(32768 * -0.00028686513542197645),
(short)(32768 *  0.00044281702139414847),
(short)(32768 * -0.00023613573284819722),
(short)(32768 * -0.00196024379692971706),
(short)(32768 * -0.00421178108081221581),
(short)(32768 * -0.00643614307045936584),
(short)(32768 * -0.00815287977457046509),
(short)(32768 * -0.00903960969299077988),
(short)(32768 * -0.00897559151053428650),
(short)(32768 * -0.00804105214774608612),
(short)(32768 * -0.00647746818140149117),
(short)(32768 * -0.00462108245119452477),
(short)(32768 * -0.00282579683698713779),
(short)(32768 * -0.00139185704756528139),
(short)(32768 * -0.00051368179265409708),
(short)(32768 * -0.00025485135847702622),
(short)(32768 * -0.00055192952277138829),
(short)(32768 * -0.00124285195488482714),
(short)(32768 * -0.00211122864857316017),
(short)(32768 * -0.00293577904812991619),
(short)(32768 * -0.00353441317565739155),
(short)(32768 * -0.00379485054872930050),
(short)(32768 * -0.00368738733232021332),
(short)(32768 * -0.00325958081521093845),
(short)(32768 * -0.00261628418229520321),
(short)(32768 * -0.00189098750706762075),
(short)(32768 * -0.00121538620442152023),
(short)(32768 * -0.00069354032166302204),
(short)(32768 * -0.00038519204827025533),
(short)(32768 * -0.00030032714130356908),
(short)(32768 * -0.00040448509389534593),
(short)(32768 * -0.00063220167066901922),
(short)(32768 * -0.00090467871632426977),
(short)(32768 * -0.00114747288171201944),
(short)(32768 * -0.00130460795480757952),
(short)(32768 * -0.00134678115136921406),
(short)(32768 * -0.00127289851661771536),
(short)(32768 * -0.00110566662624478340),
(short)(32768 * -0.00088308291742578149),
(short)(32768 * -0.00064822542481124401),
(short)(32768 * -0.00043971571722067893),
(short)(32768 * -0.00028470484539866447),
(short)(32768 * -0.00019540384528227150),
(short)(32768 * -0.00016927160322666168),
(short)(32768 * -0.00019218781380914152),
(short)(32768 * -0.00024342768301721662),
(short)(32768 * -0.00030108159990049899),
(short)(32768 * -0.00034670846071094275),
(short)(32768 * -0.00036839049425907433),
(short)(32768 * -0.00036184827331453562),
(short)(32768 * -0.00032975079375319183),
(short)(32768 * -0.00027971604140475392),
(short)(32768 * -0.00022168386203702539),
(short)(32768 * -0.00016534616588614881),
(short)(32768 * -0.00011817178165074438),
(short)(32768 * -0.00008432669710600749),
(short)(32768 * -0.00006453354581026360),
(short)(32768 * -0.00005669903839589097),
(short)(32768 * -0.00005700450492440723),
(short)(32768 * -0.00006111734546720982),
(short)(32768 * -0.00006522855983348563),
(short)(32768 * -0.00006672595918644220),
(short)(32768 * -0.00006443818710977212),
(short)(32768 * -0.00005849724766449071),
(short)(32768 * -0.00004994427581550553),
(short)(32768 * -0.00004023295696242712),
(short)(32768 * -0.00003077201108681038),
(short)(32768 * -0.00002260407563881017),
(short)(32768 * -0.00001626135053811595),
(short)(32768 * -0.00001178528145828750),
(short)(32768 * -0.00000886051384441089),
(short)(32768 * -0.00000699792735758820)
};

// Iowa Hills Hilbert transform filter coefficients
const short Hilbert_Minus_45_Coeffs[NO_HILBERT_COEFFS] = {
(short)(32768 * -0.00000699792735758820),
(short)(32768 * -0.00000886051384441089),
(short)(32768 * -0.00001178528145828750),
(short)(32768 * -0.00001626135053811595),
(short)(32768 * -0.00002260407563881017),
(short)(32768 * -0.00003077201108681038),
(short)(32768 * -0.00004023295696242712),
(short)(32768 * -0.00004994427581550553),
(short)(32768 * -0.00005849724766449071),
(short)(32768 * -0.00006443818710977212),
(short)(32768 * -0.00006672595918644220),
(short)(32768 * -0.00006522855983348563),
(short)(32768 * -0.00006111734546720982),
(short)(32768 * -0.00005700450492440723),
(short)(32768 * -0.00005669903839589097),
(short)(32768 * -0.00006453354581026360),
(short)(32768 * -0.00008432669710600749),
(short)(32768 * -0.00011817178165074438),
(short)(32768 * -0.00016534616588614881),
(short)(32768 * -0.00022168386203702539),
(short)(32768 * -0.00027971604140475392),
(short)(32768 * -0.00032975079375319183),
(short)(32768 * -0.00036184827331453562),
(short)(32768 * -0.00036839049425907433),
(short)(32768 * -0.00034670846071094275),
(short)(32768 * -0.00030108159990049899),
(short)(32768 * -0.00024342768301721662),
(short)(32768 * -0.00019218781380914152),
(short)(32768 * -0.00016927160322666168),
(short)(32768 * -0.00019540384528227150),
(short)(32768 * -0.00028470484539866447),
(short)(32768 * -0.00043971571722067893),
(short)(32768 * -0.00064822542481124401),
(short)(32768 * -0.00088308291742578149),
(short)(32768 * -0.00110566662624478340),
(short)(32768 * -0.00127289851661771536),
(short)(32768 * -0.00134678115136921406),
(short)(32768 * -0.00130460795480757952),
(short)(32768 * -0.00114747288171201944),
(short)(32768 * -0.00090467871632426977),
(short)(32768 * -0.00063220167066901922),
(short)(32768 * -0.00040448509389534593),
(short)(32768 * -0.00030032714130356908),
(short)(32768 * -0.00038519204827025533),
(short)(32768 * -0.00069354032166302204),
(short)(32768 * -0.00121538620442152023),
(short)(32768 * -0.00189098750706762075),
(short)(32768 * -0.00261628418229520321),
(short)(32768 * -0.00325958081521093845),
(short)(32768 * -0.00368738733232021332),
(short)(32768 * -0.00379485054872930050),
(short)(32768 * -0.00353441317565739155),
(short)(32768 * -0.00293577904812991619),
(short)(32768 * -0.00211122864857316017),
(short)(32768 * -0.00124285195488482714),
(short)(32768 * -0.00055192952277138829),
(short)(32768 * -0.00025485135847702622),
(short)(32768 * -0.00051368179265409708),
(short)(32768 * -0.00139185704756528139),
(short)(32768 * -0.00282579683698713779),
(short)(32768 * -0.00462108245119452477),
(short)(32768 * -0.00647746818140149117),
(short)(32768 * -0.00804105214774608612),
(short)(32768 * -0.00897559151053428650),
(short)(32768 * -0.00903960969299077988),
(short)(32768 * -0.00815287977457046509),
(short)(32768 * -0.00643614307045936584),
(short)(32768 * -0.00421178108081221581),
(short)(32768 * -0.00196024379692971706),
(short)(32768 * -0.00023613573284819722),
(short)(32768 *  0.00044281702139414847),
(short)(32768 * -0.00028686513542197645),
(short)(32768 * -0.00253540510311722755),
(short)(32768 * -0.00610282970592379570),
(short)(32768 * -0.01048160158097743988),
(short)(32768 * -0.01492566708475351334),
(short)(32768 * -0.01857941970229148865),
(short)(32768 * -0.02064667269587516785),
(short)(32768 * -0.02056903392076492310),
(short)(32768 * -0.01817758195102214813),
(short)(32768 * -0.01378324162214994431),
(short)(32768 * -0.00817991327494382858),
(short)(32768 * -0.00254931696690618992),
(short)(32768 *  0.00172494212165474892),
(short)(32768 *  0.00330774253234267235),
(short)(32768 *  0.00118558865506201982),
(short)(32768 * -0.00508764060214161873),
(short)(32768 * -0.01522193104028701782),
(short)(32768 * -0.02813878841698169708),
(short)(32768 * -0.04205619916319847107),
(short)(32768 * -0.05470800399780273438),
(short)(32768 * -0.06366980075836181641),
(short)(32768 * -0.06674224138259887695),
(short)(32768 * -0.06232902035117149353),
(short)(32768 * -0.04974408075213432312),
(short)(32768 * -0.02939149923622608185),
(short)(32768 * -0.00278118043206632137),
(short)(32768 *  0.02762975543737411499),
(short)(32768 *  0.05875028669834136963),
(short)(32768 *  0.08727697283029556274),
(short)(32768 *  0.11015775054693222046),
(short)(32768 *  0.12502384185791015625),
(short)(32768 *  0.13052044808864593506),
(short)(32768 *  0.12648330628871917725),
(short)(32768 *  0.11393431574106216431),
(short)(32768 *  0.09489956498146057129),
(short)(32768 *  0.07208253443241119385),
(short)(32768 *  0.04844862595200538635),
(short)(32768 *  0.02679026685655117035),
(short)(32768 *  0.00934264715760946274),
(short)(32768 * -0.00249097635969519615),
(short)(32768 * -0.00826646760106086731),
(short)(32768 * -0.00846713781356811523),
(short)(32768 * -0.00432921992614865303),
(short)(32768 *  0.00243640411645174026),
(short)(32768 *  0.00997202750295400620),
(short)(32768 *  0.01659170538187026978),
(short)(32768 *  0.02103775925934314728),
(short)(32768 *  0.02263728901743888855),
(short)(32768 *  0.02134133130311965942),
(short)(32768 *  0.01765142939984798431),
(short)(32768 *  0.01245793793350458145),
(short)(32768 *  0.00682784663513302803),
(short)(32768 *  0.00178553408477455378),
(short)(32768 * -0.00187310588080435991),
(short)(32768 * -0.00370277347974479198),
(short)(32768 * -0.00365150393918156624),
(short)(32768 * -0.00202476163394749165),
(short)(32768 *  0.00061377260135486722),
(short)(32768 *  0.00357905798591673374),
(short)(32768 *  0.00620909873396158218),
(short)(32768 *  0.00798853952437639236),
(short)(32768 *  0.00863009598106145859),
(short)(32768 *  0.00810285285115242004),
(short)(32768 *  0.00660791201516985893),
(short)(32768 *  0.00451200548559427261),
(short)(32768 *  0.00225671660155057907),
(short)(32768 *  0.00026374991284683347),
(short)(32768 * -0.00114480499178171158),
(short)(32768 * -0.00179734628181904554),
(short)(32768 * -0.00168814661446958780),
(short)(32768 * -0.00095839390996843576),
(short)(32768 *  0.00014931759505998343),
(short)(32768 *  0.00135089165996760130),
(short)(32768 *  0.00238144909963011742),
(short)(32768 *  0.00304473401047289371),
(short)(32768 *  0.00324279186315834522),
(short)(32768 *  0.00298246811144053936),
(short)(32768 *  0.00236034626141190529),
(short)(32768 *  0.00153185811359435320),
(short)(32768 *  0.00067276862682774663),
(short)(32768 * -0.00005827662607771344),
(short)(32768 * -0.00054877914953976870),
(short)(32768 * -0.00074829190270975232),
(short)(32768 * -0.00066977186361327767),
(short)(32768 * -0.00037809176137670875),
(short)(32768 *  0.00003020270378328860),
(short)(32768 *  0.00045058503746986389),
(short)(32768 *  0.00079241563798859715),
(short)(32768 *  0.00099482492078095675),
(short)(32768 *  0.00103426445275545120),
(short)(32768 *  0.00092342460993677378),
(short)(32768 *  0.00070302636595442891),
(short)(32768 *  0.00042924060835503042),
(short)(32768 *  0.00015996840375009924),
(short)(32768 * -0.00005703790884581394),
(short)(32768 * -0.00019207553123123944),
(short)(32768 * -0.00023643388703931123),
(short)(32768 * -0.00020058304653503001),
(short)(32768 * -0.00010876693704631180),
(short)(32768 *  0.00000828072279546177),
(short)(32768 *  0.00012067319039488211),
(short)(32768 *  0.00020523219427559525),
(short)(32768 *  0.00024891708744689822),
(short)(32768 *  0.00024954276159405708),
(short)(32768 *  0.00021412860951386392),
(short)(32768 *  0.00015566049842163920),
(short)(32768 *  0.00008924310532165691),
(short)(32768 *  0.00002856819992302917),
(short)(32768 * -0.00001661604801483918),
(short)(32768 * -0.00004169571548118256),
(short)(32768 * -0.00004705678293248639),
(short)(32768 * -0.00003692470636451617),
(short)(32768 * -0.00001763984073477332),
(short)(32768 *  0.00000414016449212795),
(short)(32768 *  0.00002290562406415120),
(short)(32768 *  0.00003518092489684932),
(short)(32768 *  0.00003976617153966799),
(short)(32768 *  0.00003742715125554241),
(short)(32768 *  0.00003022999953827821),
(short)(32768 *  0.00002075305565085728),
(short)(32768 *  0.00001138329298555618),
(short)(32768 *  0.00000383674523618538),
(short)(32768 * -0.00000104261721389776),
(short)(32768 * -0.00000322961068377481),
(short)(32768 * -0.00000328853616338165),
(short)(32768 * -0.00000206886261366890),
(short)(32768 * -0.00000041944920781134),
(short)(32768 *  0.00000101382681805262),
(short)(32768 *  0.00000187995362921356)
};


// Instantiate the Objects

AudioControlSGTL5000 audioShield;  // Name for the Teensy audio CODEC on the audio shield

// Audio shield
AudioInputI2S audioInput;    // Name for the input to the audio shield
AudioOutputI2S audioOutput;  // Name for the output of the audio shield

AudioFilterFIR RX_Hilbert_Plus_45;   // Name for the RX +45 Hilbert transform
AudioFilterFIR RX_Hilbert_Minus_45;  // Name for the RX +45 Hilbert transform
AudioFilterBiquad biquad1;
AudioFilterBiquad biquad2;
AudioAmplifier amp1;
AudioAmplifier amp2;


// Audio connections
AudioConnection patchCord5(audioInput, 0, RX_Hilbert_Plus_45, 0);
AudioConnection patchCord10(audioInput, 0, RX_Hilbert_Minus_45, 0);
AudioConnection patchCord15(RX_Hilbert_Plus_45, 0, biquad1, 0);
AudioConnection patchCord20(RX_Hilbert_Minus_45, 0, biquad2, 0);
AudioConnection patchCord30(biquad1, 0, amp1, 0);
AudioConnection patchCord35(biquad2, 0, amp2, 0);
AudioConnection patchCord40(amp1, 0, audioOutput, 0);
AudioConnection patchCord45(amp2, 0, audioOutput, 1);


void setup() {

  // Setup the audio shield
  AudioNoInterrupts();
  AudioMemory(16);
  audioShield.enable();
  audioShield.inputSelect(AUDIO_INPUT_MIC);
  audioShield.volume(1.0);
  audioShield.micGain(10);
  audioShield.lineOutLevel(13, 13);
  audioShield.audioPreProcessorEnable();
  audioShield.autoVolumeControl(0, 1, 0, -20, 0.5, 2.5);
  audioShield.autoVolumeEnable();
  AudioInterrupts();

  Turn_On_TX();
  //pinMode(SSB_SWITCH, INPUT_PULLUP);
  //pinMode(FILTER_SWITCH, INPUT_PULLUP);
  // Serial.begin(9600);
}

void loop() {
}

void Turn_On_TX() {
  AudioNoInterrupts();
  audioShield.muteHeadphone();  // Default is 5
  audioShield.unmuteLineout();
  RX_Hilbert_Plus_45.begin(Hilbert_Plus_45_Coeffs, NO_HILBERT_COEFFS);
  RX_Hilbert_Minus_45.begin(Hilbert_Minus_45_Coeffs, NO_HILBERT_COEFFS);
  biquad1.setBandpass(0, 1000, 0.4);
  biquad1.setBandpass(1, 1000, 0.4);
  biquad1.setBandpass(2, 1000, 0.4);
  biquad1.setBandpass(3, 1000, 0.4);
  biquad2.setBandpass(0, 1000, 0.4);
  biquad2.setBandpass(1, 1000, 0.4);
  biquad2.setBandpass(2, 1000, 0.4);
  biquad2.setBandpass(3, 1000, 0.4);
  amp1.gain(2.0);
  amp2.gain(2.0);
  AudioInterrupts();
}


 

Comments

Post a Comment

Popular posts from this blog

Even a Blind Pig finds an acorn once and a while (35 watt push-pull RD30HVF1 amp for HF)

Image
     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...
Read more

Playing with Phasing - part 1

Image
      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...
Read more

Playing with Phasing - part 2b - audio processing code

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)(...
Read more