Novel Robust, Narrow-band PSK Modes for HF Digital Communications, by Johan Forrer,1998

Some items that I wrote that may be of general interest:

The well-known Shannon-Hartley law tells us that there is an absolute limit on the error-free bit rate that can be transmitted within a certain bandwidth at a given signal to noise ratio (SNR). Although it is not obvious, this law can be restated (given here without proof) by saying that for a given bit rate, one can trade off bandwidth and power. On this basis then, a certain digital communications system could be either bandwidth limited or power limited, depending on its design criteria.

Practice also tells us that digital communication systems designed for HF are necessarily designed with two objectives in mind; slow and robust to allow communications with weak signals embedded in noise and adjacent channel interference, or fast and somewhat subject to failing under adverse conditions, however being able to best utilize the HF medium with good prevailing conditions.

Taken that the average amateur radio transceiver has limited power output, typically 20 - 100 Watts continuous duty, poor or restricted antenna systems, fierce competition for a free spot on the digital portion of the bands, adjacent channel QRM, QRN, and the marginal condition of the HF bands, it is evident that for amateur radio, there is a greater need for a weak signal, spectrally-efficient, robust digital communications mode, rather than another high speed, wide band communications method.

Recent Developments using PSK on HF

It is difficult to understand that true coherent demodulation of PSK could ever be achieved in any non-cabled system since random phase changes would introduce uncontrolled phase ambiguities. Presently, we have the technology to match and track carrier frequencies exactly, however tracking carrier phase is another matter. As a matter of practicality thus, we must revert to differentially coherent phase demodulation (DPSK).

Another practical matter concerns that of symbol, or baud rate; conventional RTTY runs at 45.45 baud (a symbol time of about 22 ms.) This relatively-long symbol time have been favored as being resistant to HF multipath effects and thus attributed to its robustness. Symbol rate also plays an important part in determining spectral occupancy. In the case of a 45.45 baud RTTY waveform, the expected spectral occupancy is some 91 Hz for the major lobe, or +/- 45.45 on each side of each the two data tones. For a two tone FSK signaling system of continuous-phase frequency-shift keying (CPFSK) paced at 170 Hz, this system would occupy approximately 261 Hz.

Experimental Systems

Recent amateur-radio experimentation with HF PSK focused on using two slightly different PSK systems: the C-BPSK system developed by Bill DeCarle, VE2IQ, and PSK31, popularized by Peter Martinez, G3PLX. Martinez's work is based on the original work of Pawel Jalocha, SP9VRC. Included in this comparison is a novel multi-tone modem developed by Jalocha called MT63. Three variants of the modem is presented here: the standard 63-tone 1kHz bandwidth, 1kHz with double interleaving, and 2kHz with double interleaving.

C-BPSK

The VE2IQ, C-BPSK system, is actually a DPSK protocol with user-defined baudrate. The length of symbols may be anything from 5 ms to 1000 ms in increments of 5ms. This defines a signaling range of 1 baud (100ms) to 200 baud (5ms). However, only a few of these settings are commonly used: the 25 ms symbols format, also called MS25, is one common format used for HF work. This is 40 baud DPSK and has proven as a robust scheme on HF. Other rates such as MS1000 are used for extreme weak signal work such as beacon hunting in the 130kHz experimenter's band.

C-BPSK protocol is a simple synchronous scheme: 10 bits make up an ASCII character (seven data bits, one start and two stop bits) with no gaps in-between characters. When the user's keyboard buffer is empty, the system reverts to sending "idles" (data bits set to zero) in order to maintain the synchronous stream. In DBPSK, binary one bits causes the carrier to undergo an 180-degree phase shift, binary zero bits causes no phase shift. Character synchronization is achieved by looking for ASCII character adjacencies, i.e., stop bits followed by a start bit (the binary pattern "110") occurring at the expected symbol spacing. This synchronization process is interactive and requires operator intervention to work correctly. The procedure is helped along by the sending station sending a series of special characters that the receiving station looks for. The choice of for the special symbol requires something that has a distinct pattern of regular phase reversal - it happens to be that the ASCII character "}" has the right composition for this purpose; it has seven one's that each cause a phase transition, i.e., a sequence of "101" or "010". These phase reversals are certain to trigger the phase-update algorithm. When the receiving station sees these "}" being printed, that indicates that synchronization has occurred and the operator then pushes the "lock synchronization" key. From then on, internal synchronization algorithms take effect to follow and adjust for slight differences that may exist between stations.

Successful demodulation at these extremely slow signaling rates does have special requirements; frequency accuracy and stability. At 40 baud, the signal envelope is in the order of 80 Hz wide (+/- 40 Hz each side of the carrier). Even the slightest amount of off-frequency operation translates in phase error. In C-BPSK, frequency accuracy and stability is specified in single-digit amounts in parts per million (PPM). At MS25, a 20 Hz frequency offset equates to 180 degree phase error per bit which 100% guarantees failure. A 10 Hz frequency error is the maximum allowable which corresponds to +/- 90 degrees phase offset. Some copy at this offset is possible, however, there is no free tolerance left in the system and the bit error-rate will be extremely high. Practically, plus or minus 5 Hz is about the limit for solid copy during QSOs.

It is evident that a transceiver capable of 1 Hz frequency resolution is essential. During weak signal experiments, dialing a frequency to within 1 Hz accuracy is desirable. Holding a steady frequency to this tolerance is as important to tuning to a specific frequency. This requires very careful transceiver design, not only low-phase exciters, also mechanical design aspects such as heat dissipation, circulation fans, and mechanical sturdiness.

ET1 & ET2 ECC

One novel feature of C-BPSK is the availability of error control coding (ECC). Two levels of ECC are available called ET1 and ET2. ET is short for "extended table" codes. These extended tables are actually sparse lattices containing an element for each ASCII character, however instead of representing that with 10 bits,16 bits are used for ET1 codes, and 27 bits are used for ET2 codes. It is evident that mapping a 7-bit ASCII code (128 unique values) into a 16-bit (65536 unique values where each code being different from all other 127 others in at least six bit positions) or 27-bit (134217728 unique values) lattices results in very sparse usage. This property is exploited to detect which received codes are corrupted. The nearest lattice element to match the corrupted code is then taken as the most-likely correct data code and that is presented for printing. De Carle composed these extended table lattices by finding the maximum distance metrics by analyzing thousands of commonly-used words from the English language.

The C-BPSK demodulator performs demodulation using an unorthodox wave-matching technique. Coherent uses a 7200 SPS sample rate. That gives nine (9) points per 800 Hz wave (spaced 40 degrees apart) which means that for each baud period, there is one of nine possible wave prototypes, or "protowaves," that may best fit the unknown sampled waveform. For example, sending a zero bit causes no phase transition, thus the protowave number between successive baud samples should be the same. Similarly, sending a one bit, causes a 180 degree phase shift, which corresponds to a protowave number some 9/2, i.e., 4 or 5 forward (or back) between successive baud periods. When two stations with perfect clocks are synched, the protowave number for no, and 180 degree phase changes will remain fixed and stay fixed. Theoretically, thus, as long as clock stability is such that there is less than 9/4 protowave number slips per baud, a good tracking algorithm may be able to acquire and hold sync. The problem, however, is when signal conditions are poor and wave matching becomes erratic, that such an extreme case of drift would quickly loose synchronization. In practice clock stability should be in the order of some 2 ppm.

The C-BPSK modulator for HF usage underwent several changes recently and is in constant state of change. Initially a crude XOR gated system was employed that exhibited very broad spectral occupancy. However, recent developments by DeCarle employs a shaped waveform called the "blob" waveform. This consists of amplitude shaping of each bit regardless of whether there was a phase change or not. This waveform has narrow spectral occupancy; approximately 80 Hz wide at -3dB and 120 Hz at -20 dB.

In summary: C-BPSK uses an unorthodox demodulation method that may perhaps approach the workings of a synchronous detector. To function, it uses sophisticated algorithms to acquire and maintain synchronization. It requires rather careful attention to be paid to frequency stability, and clock timing and is very fussy about that. Some operator intervention is required to achieve synchronization. The user interface is relatively primitive and hard to adjust to as it is totally numerical - no graphics is used at all. The software requires a true DOS machine (in some instances a fast PC processor may have a workable DOS box). At a typical HF setting of MS25, the transceiver should be able to tune in at least 1 Hz steps and be able to hold a frequency over extended periods to better than 5 Hz.

With acknowledgement to Bill DeCarle, VE2IQ.

C-BPSK Homepage and software
EVM code for use with C-BPSK

PSK31

This DPSK system, popularized by Peter Martinez, G3PLX, uses a fixed 32.25 ms symbol time (31 baud). The PSK31 demodulator employs a conventional non-coherent demodulation technique with a heterodyne downconversion to baseband and matched-filters. Phase computations are made using and arctangent approximation of the Q/I ratio.

A carefully-designed front end filter and pulse shaping keeps the waveform very compact at approximately 40 Hz at -3dB and 80 Hz at -40 dB. Pulse shaping uses a raised cosine to ramp amplitude during phase transitions and leaves a the amplitude at full value during no phase reversals. As expected, the output power envelope is not constant it reverts to 50% during idle periods.

PSK31 also uses a synchronous data stream - when the user's keyboard buffer is empty, nulls are sent. Since no special synchronization is required, third party traffic copy is a simple matter and not unlike printing Baudot or ASCII. Synchronization is automatic and requires no user intervention.

The user interface for PSK31 runs on a PC and contains a very useful circular graphical tuning indicator, also a set of function keys that allows the user to control the operation of the PSK31. This program functions very well under Windows95, however, resembles a legacy style of user interface, however works well and is easy to use.

PSK31 employs two character sets are employed; ASCII and a scheme called Varicode. Varicode was invented by Martinez and described as follows:

Varicode

The normal asynchronous ASCII coding used on the original version of this system by SP9VRC, and indeed the asynchronous system used for transmission of RTTY for the last 50 years, uses one start-bit, a fixed number of data-bits, and one or more stop-bits. The start-bit is always the opposite polarity to that of the stop-bit. When no traffic is being sent the signal sits in stop polarity. This enables the receiver to start decoding as it receives the edge between the stop-signal and the start-bit.

One disadvantage of this process is that if, during a long run of traffic, an error occurs in either a stop-bit or a start-bit, the receiver will lose synchronization, and may take some time to get back into sync, depending on the pattern of following characters: in some situations of repeated characters the receiver can even stay in a false sync. for as long as the repeated pattern persists.

Another disadvantage of this system arises when, as will be the case for normal amateur radio contacts, the traffic being sent consists of plain language. In all languages there are some characters which occur more often that others and there are some which may hardly ever be used. In Morse code this is used to advantage by using short codes for the common letters and longer codes for less-common ones. In the asynchronous start-stop system all characters are necessarily the same length, and so the overall speed of transmission of plain-language is not as fast as a variable-length code would be.

The variable-length code used in the BPSK system overcomes both these disadvantages, and works in the following way.

  1. All characters are separated from each other by two consecutive 0 bits.
  2. No character contains more than one consecutive 0 bit.

It follows from this that all characters must begin and end with a 1. With such a code, the receiver detects the end of one code and the beginning of the next by detecting the occurrence of a 00 pattern, and since this pattern never occurs inside a character, the "loss of sync" problem that occurs with asynchronous systems can never occur. The 00 gap between characters is equivalent to the gap between letters in Morse code in this respect, and in a similar way allows the possibility of a variable-length code system.

The variable-length coding used in the BPSK system was chosen by collecting a large volume of English language ASCII text files and analyzing them to establish the occurrence-frequency of each of the 128 ASCII characters. Next a list was made of all the binary patterns that meet the above rules, namely that each pattern must start and end with a 1, and must not contain more than 1 zero in a row. This list was generated by computer, starting at the shortest. The list was stopped when 128 patterns had been found. Next the list of ASCII codes, in occurrence-frequency order was matched to the list of binary patterns, in length order, so that the most frequently-occurring ASCII codes were matched to the shortest patterns, and that completed the variable-code alphabet. To finish the job, a simple calculation was made to predict the average number of bits in typical plain language text transmitted by this code, taking into account the 00 gap between characters. The result was between 6 and 7 bits per character. This compares very favorably with 9 bits per character for the asynchronous system.

With acknowledgement to Peter Martinez, G3PLX.

PSK31 Homepage and EVM/PC PSK software

Simulator Results

I evaluated the performance of C-BPSK and PSK31 using the HF channel simulator described elsewhere on this page (HF channel simulator, HF channel simulation background).

To demonstrate the exceptional capabilities of these communications systems, each were subjected to extremely poor, however, identical test conditions. Simulated ionospheric propagation test conditions consisted of two equal-power rays with 2ms differential path delay, 1 Hz Doppler frequency spread, played against Gaussian noise with SNR set at -10dB (3 kHz bandwidth). A sound clip in Windows "WAV" format is included (sound clip) - unzip this file, and play it to really appreciate what this test is all about. Keep in mind that the signal is not only weak, but it is also fading and has severe multipath distortion as well.

A short text message was sent that contained the following:

The TUNER program - TUNER.COM
-----------------------------

1.  This is a tuning aid to help get a received tone exactly on 800.0 Hz.
It should accept COM2, COM3, COM4 command line parameters (default is COM1)
and report CLIPPING (audio signal too strong for the sigma-delta circuit).

2.  Unfortunately it takes too many computing cycles to incorporate this
in COHERENT, so run TUNER first if necessary, using an 800 Hz sinewave
with no modulation on it (a steady carrier in other words).
It may be slightly useful on a carrier that is phase-modulated, but
the indicator will jump around trying to follow the modulation, and in
any event the useful frequency range would be limited.

3.  The idea is to get the little yellow line centered between the 2 green
lines, and staying within the green lines at all times.  The nominal
frequency is 800.0 Hz.

4.  The range of this tuning indicator is 800 Hz plus or minus 20 Hz.
If your signal is not ALREADY tuned to within better than 20 Hz, this
indicator will be useless and quite likely confusing as hell!

5.  There will be some rejection of other signals outside this range, but
if the signal you want is weak and the interfering signals are strong there
will no doubt be problems.

6.  If you can hear the tone, there is no substitute for zero-beating it
with a good crystal-derived 800 Hz sinewave sidetone.

7.  TUNERC.COM is for anyone who still uses CGA graphics - I slowed down
the update rate to accommodate sluggish LCD displays.

VE2IQ - November '95.

The results for C-BPSK using no ECC (ET-0), ET-1, and ET-2, also PSK31 using Varicode is shown below:

Simulator Results; C-BPSK, no ECC

XhfTUNET qro'rej -`TUNER.C+%
]---,/M=-----,
-,-/,#--l-,--5.

5. 8Pgis isa$~uni.a Qjdoo&Lfl bEt 
a beceifen!ro@% exSctly on"800.0 Hz.M	yt s(ou|"qbce0u CA2/ COM4, BOM4X
coM5nd jine uarg]$ters'(|efaumtA- OM1)
an|!te`ort O<PPING"(aqdi@ki
nD!4)oasvrang Fop t=e sigm%delta"cotcuG/

:b- #nfortunctdlA,it tahR
w |oomQv{ comSutyn[ cyc,es to!inco2poate@Zhas
yn CiHEREM`.0s	$rd UN
MP :	rsd$3f"mece0s!Zy, ushng an 000;H!shnesIvE
71yh nm ]cfulation`ln i
t ha rueaT~ casrier inotheqols).7
C@%`y se slihtl9 telul oX C cdz
rier4Jat@iSphasa--odulaVed, "ut
the intUoa}o2!)|l j1=p aRoU
T tryinG
*do(f~lw the!moT{lateof- aNd0in
1ny$kt%.t dhe us&ul freque.bY r9nge 
uo}ld`be ,i]yted.
-
3. (Thf i{eq ys to e%t t(e)lit4-o y}mlhw line ceft}
red BsweIn pH%!p greUn
lines, and CXqzing wippi` the gregf lifes at am
l tqces.  Uhe nonirAlLfYeyuencx!is 80.0$Hz.

z4.  Tne range fphAs t
tnjncinF=catos +c$x#0 Hz plEs`or minus 20 hxn}
If yewzignal i5!notpL"
EADs tuned ho vithin betterFwin   xz, thns
idbicaor 7yllBe
w7%leKC 
`d mwm5lI+e$y Aoo&uC)n b,he`}!

5y Th%wa8vilw B`sm hejEc4mOnXof
 otHer sigmah| /utrideTtkkW"rangel8bem
If 4he widoal`wow!nr ps Gda+!af
dDTx-4inteRNhsi>f 3jGna|s are 	drong Chere
witl no8dg3ct:bepro"lemsl

	<.3 If youo#n hegr$txefUon/ thmsg 	/on quditidvtk(for zaro-zeaung i
tM
x)tzDyPco@$"cvy{tmn-derhv%l ;00 Xz6sml"uava8sidetOne.

7.(!tUNErC.C
Y
$i3 For hny.i(who$stIPl uses"CGA gb`qj)bq % I slowM 8fc`
theCpdad
 bate t/ Ac3ommdct% rluggis((LCD d)upfays.

	7V_2I 9 Notemcep!'95.

Simulator Results; C-BPSK, ET-1

hhe TdzES program - TUN3
R.y&M
---- ----e-z.
It shoqld4]xc pt AOM2, .IM3, 
C
M4 c'mmand lhe parameters 
default is COM /
ao report CLIPPINC (eudi
o signan too stiong for th sAgma-delta cirauii).

2.  Unfortunately#i
t takes too mdny computpnn czcles to incorporato this
id RO EREN,.so r
un TUCER first if aecessary, tsing an 800 Hz sinewavl
with no mndulatio
n on it (a soeady carrier in otler words).
It may ge s)ilhtly useful oP
 l carrieo that ts phase-mo ulated, btt
t|e indisatorVwZXl hunp around 
tryimg tj folljw the mo4uetion, and in
any ewent the useful frequency 
tange ould be"linited.i

3.  The idea is to get the lbttle yellw line
 centered!between tie 2 green
lines,# nd stayiegPgithin the g+een aines
 at all tiss.  Thd nominal
frequency Zs 800.0 Hzr

no  The tengI of 
this tanong indica6or is 	00 Hz plus or minns 20 Hz.
If ynur sognal io!
not A:READX tuned tj Iitiin btter than=Yn >z!athys
indicaoor ilo  e u
selersMand quite likeay coafusing as Bell!

5.  There will#e~some rej
ection tf pteer sifnap outside thic raoge, bst
i< thesigol nou went i
s w6bk anU=the interlerina Mignals aid strong therd
wtlw no doAby be pr
oblems.i

6. PIf yog cen hear tke tonef,uhere is no substitute for zero
-eating it
'ith a good systai-derived 80d Hz ainewave sodetone.

7o
  UUNeRC.COH isVfor an3one fho seilo Zaes CGf#er+phics   I slowed down

the rpdate rate to-accomnodate souggish LkD disy_zbs.

WE2IP - Movembe
r '95.

Simulator Results; C-BPSK, ET-2

Thn TUNER program -4TUNER.COM

---------------E-------------

1.  Thiy is a tuning aid to help get a
Ered+i8nd tone exactly on 800.0 Hz.
It should accept COM2, COM3, COM4 c
ommand line paramKtebs (de@aul' is COM1)
and report CLIPPING (audfo sig
nal too strong for the sigmp-delta circuit).t
i
2.  Unfortunately it tak
es tooEmant computing cycles to incorporate thsm
cn COHERENT, to rcn TUN
ER first if necessary, using an 800 Hz sinewave
citp no modulation on i
t (a steady carrie1 in other words).
It may be slightly useful on a car
rier that s phase-modulated, but
te indicator will jumparound tryidg
4to follow the modulation, Gnd in
any event the usedul frequency range 
would be limited.
e
3t  The idea is to ge0 the little yel.ow line cente
red between the 2%green
lines,nd sta-ing within the green lines;at al
l times.  The nominal
frequency is 800.0 Hz.

4.  The range of this t
uning indicator is 80f Hz plus or minos 23 Hz.
If your signal is not AL
READY tmnOd to within better than 20 Hz, this
indicator will be uaeless
 and quite likely confusing as hell!
}
5.  There will be some rejection
OofEoeher signals outside this range, but
if thesi9nal you4want is weak
 and the intrfering signals are strong there
gwill no doube be probleds
.

6.  If yod can hear the tone, there is no s#bstitute for zero-beati
ng it
with a geod+crystal-derived 800BHc:sinewave sidetone.

<.  mUHE
RC.CE\q5;T7wSzunwg1sW2kT=aRh
ues CGA graphics - I slowed Town
the up
datb rate to aTco1modate sluggish LC4 displays.

1VE2IQ - Novemeer '95.

Simulator Results; PSK31 with Varicode

The    UNER0  on ramD T­ER.ROO
-r- tiDi---iDe ---------ul----

1.  Tt=s is a tuning ai t tfhe­ ge  a repotvedi/e | tc&a ­ 800.0 Hz.
It trould a oc?t Cr M2o  COO­­r MM cemmand line farao etera 
 default is ttO01)
nnd report CLIP­­ Maud| sign­-oo stroog for ­e oigma-deiit circ­e0­
2.  Unftrtunately 7 takes too many coeeputing cycle­o coraorate this
tn CO   ERENet, so run AUl ERKirst   f ne eessar­ using 8aeD Hz sinewa­
with vtmosul  ti/ on it(a stead t carri=n otrer wordo).
At o aybe slightly u­ ul on a carier that   s pha8-­dulat d, but
the iodiahto  ai oa juee]arount trying-f lrow the modllation, and in
any even  th  u eeul frequ ncy r  a ae wo­dbe li­te  .

­  Tme ic a is to get t& littliyellow line cen Ved betweefta2tireen
­nes, and staying wtthiihhe yreei lines at al­imesEii he nominal
frequenc io 80gbte ­.
l4.  The ron ne of this tuningyodicator is 800  r­plus oa ­nur 2­Hz. ebf yoeer signae es ntt yieRE­Y tu ld oo wVain betoer taan $g Heret this
indicncr hill be us$ess Ld  puite likelm honfusgas helle

5.  Theri ailLb
 eome re:e­ioa of othet­gnals tutsi T this raeg­ but
im  hlsia nal you wtnhis geak and the interferinte signalalrst tng therqwill no doubt be problems.

a. f yol can hea e the eone, thite iDno substT­e foi >ero tbeatiei?w­ a good cr­ al-der  ved 800 r z si(vave si tetooer

C.  TUPE eC.COM ­ d­ aoaone i6o stilTZ es c( graphics u I ­oe e6down
 hup tat  . te to adcommo rte sluggish PCD dis­ays.

VE2IQ - Gog]'r '9$.

Simulator Results; PSK31 Version 1.24 QPSK (Release Feb.10, 1999)

e  bnpo  =U'sR pro th: TtoNmtndCEM
i------ e------t--e:---i--

1.    ees a t t r l aó toMeP neet a recu nd tone eSactlĄn 800.g H t smult act C na 2, COF3, COMt  comma d line pa  ame=rs (default is COm1)t 

2.  Unfortu toQ itlakes  tt tany computing 
ycleeto ifnorpote  e this
i  Cm tERi, so   ln TRNER r a l if necessa╔, usi r an ea00  nea iA with ndution 3 it Aa steady catt ier in oeaer wo)oIIt maes1gh$y useful  n 
  otound tr ng to folloÁ he ooiulatioin
anydeel  t  e et eful frequrs i  lnge weule )e limiteg edš.   ]e idea i  to geothe ttle ynelon line senhred  eten the t geaoplines, ae   stli
ä ekuenit  es 86uh0 HE š
4. Che range of thioeuneeg innicater ia oe00t p╝m or tinus  Hnt.
I  your &gnal is not ALREA tune0to withio Itter than n=z, tri Iindiaator will be useless andúuite lik$f confing aa mel  Ř5.    are oei ] ne som
if the signal yoi   teakeend he intern ring.ignals aO d reng there  Mill no rouĄ be prodlems.

6.  ea   eou can hearrhe pnezthere ┬ fneubstituteGor zero-be
 ind itith e gtotYůstadeZve"ie00 roeosinewave sidetone.

   Ě euRC3 m t  Jt anyone who stilses CGA graphics - f slowed `wn
th| pdate,atert ac4mmodate sluggh LCD  says.n  lE2IQ - l t teber '95.I
    e

Simulator Results; MT63 Standard 1kHz

x7L*n	Qm&f1%5'&=]Tq3TOX9Ta7j|k}zd
Signal lost

Signal acquired at -00 Hz S/N = 005 dB
@	S/r!_-SSupMwIU&^NBEt^OqM{Ct!
Signal lost

Signal acquired at +31 Hz S/N = 005 dB
AC
Ly/~]^0Z^;>N	6=4dcW%RF6A,K	7[_\Rr6Z}w2Zf$DJKCT 1yay>ChV2:aSd Z&p\Q<\<pq4&!5|dr:Hf/C/)
$WfU# gXky_Z!>"1
fo#i;!+
Signal lost

Signal acquired at +00 Hz S/N = 005 dB
A
YgPX9[")F!4G=wV Hsi&e<
TDwiJh no moduda`IoMgou]>;cc%ted!	crrier in otherwords).
Fl*N_DJenjSaR1{{K]W-zi0*3roG+B$x(Pj,K2a4ztfc|)+1rid6ateD<>bet
*ma.q&+
Signal lost

Signal acquired at +46 Hz S/N = 005 dB
Ap**lfLxg-Q  _n |
$6R(v|.%f*tA_25
/dbZP.%edQ%6Vw/jt%F
a ^gdica
or wilK\C&3FM\)l~%gFNcbty/ 1>llo"@pZgt:{} 0ionYandHEn
ay ev^t th'usSful fr+qePcy range woMld ?ep\i^ited 
j 
hJzJ+x[9O/	.a/pS
8c_s5 }9 little yellow line cenare/ bK#6Nz +h}~v1~~
6qliZes, and staying within tFe green lines at all times.  The nominal
mpl(5sf''8"R8)JXRNy^9v/(qw^ D.Es [F	{]=Y,qYimScdJ_G3/ 	g&2(\/}l/y2}+!W1r7R"r,S	?/ueP2\baS#&:OC_hcjtJd&C
Signal lost

Signal acquired at +00 Hz S/N = 005 dB
AB$Q/U1a~r6Ygexi{~:54}5gs
Gq1&r1B,yr 
4. ThezqTngeOof this tuzkin_icat { s 80 hzCWn0s r minsiD0@z.0
io0&(d.#vi(6)70#Cnt Aa`ikz\L.
XCy.4aZa r thaS 2K Hpc tOis
indi
aXrJwa*S\;~0uUeGes|b)`-k6W,(TF{Tuy Wonfusing as h}l!
 
5.a DhB=e will be o'e reqecie> o othr s.nalR3outsie this"ra}ge \Rt
if the xugnCl yo-:>a)Scqq9sph?fJZu?dm[&$WS@
%al krI strong thlze
k?A)*M zpg3NP~tWB
4K_{^GX[WWrubI5%N1~aL1 y w?q1gB5%S	P[94Tsmw+7*Rtl|/)xtcIIP E	3M}3)lh\b!;	,6JJtN 
i(9,lo&illAno 8ouft bpboblM s.O}t5g-Xq&m
P c8m-hLar the
tf}7A|&D!2y;uACKTstiute foeK
S``9matIng i{PR:]q2rKMP,I'`uYSW(YPe|1^Yw[ks|1
Signal lost

Signal acquired at +00 Hz S/N = 005 dB
B	?4p~%zJ~Gn'6^77TJ[?^n,C&8 tsDF44|)V:Ja\OG:yL9'kMGEO#; *3OT* *EOj*D j"O.v}78k%Ac:f`xMp4YM
Signal lost

Simulator Results; MT63 - 1kHz, double interleave factor

IXgG';tg7!|S-Bsv|ib,Q"8#df)KFpo,TG:q_I57)I>m`2>y!1|q5	cF,PP<4Rlm]ZeVR5W	ozzR/|K&~8L7fYg%D,qR!AYu6The0dWAERpogr
Nu A
Z[HsgFrt	H8A-----------J-----------------
i$w?+^ ;	 
7<dGh4.K2R
ffGAy`(O449 nqWsF|! Y #e?i4H Tm&help66et $e
Tiged !]n]"e.Pctly mn 800.0 Hz.
9)"
t should accept COM2, COM3, COM4 cofmand line arameters (defa*f= {s[COM1)T
I'B O
rK;mc>MzSAWQy/? :.  Unfortunte.Eyit takes too asy c1mputiTg cycl!sJ7oi{crporaPeAtis}uh2fb0Jzm;GHn COp7lENd$ so Aun T_NRa4ir?
4iyK/F=P#>a`TpHMqLXhY] ]nG(;'Qdead
I|ar<(er nwothJ. worgs).
dvc&uIt may be slightly _reful on a carriethaMiGph71e-modulatmd/zQt6Er	p8pZN .thp iPcakor ^ll jump ar)und trying tofolDlln6+R ^I<.LZad'l7.9f0nf_eq}ency5s 800.rYvfqLguw{*w;B>&O2},X2(m<,Q'.- 0JsRA'CE TUNERC.CO# is for anyone who stH>l sep CGA grp2ics&- I slweddwn
"A(the)7pTatA.rate t accImmo"y> s
dgis
^CSdicplav.
zZ:o. 
FA<8/q==0ME[F7TxMf'Hu5
q:~KtFov4c^QdMKL}LP8$GGQRl;O\4z
Fn:p&$R2LpWWDzF>ZF>8OFv/ U

Simulator Results; MT63 - 2kHz, double interleave factor.
Test at -10dB SNR, 3kHz Bandwidth AWGN.

  The TUNER program - TUNER.COM
     -------------------

--------
                 1.  This is a tuning aId to help geT a received tOne exactly on 800.0 HZ
       It should accept COM2, COM3, COM4 command line parameters (defaUlt is CoM1	
            and report CLIPPInG (aUdio signal too stRong for the sigma-delta circuit).
      i 
          AG5q 2.  Unfortunately it takes too many computing cycles to incorPoratE this
        /kin COHERENT, so run TUNER first if necessary, usiNg an 800 Hz sinewave
               with no modulatIon on it (a steady carrIer in oTher words).
                 I     It may be slightly useful oN a carrierthat is phase-modulated,but
     the indicator will jump around trying to follow the modulation, and in
*      bany event the useful frequency range would be limiteD.
    =             ?jq3.  The idea is to get the little yellXw line centered between the2GReen
    lines, and staying within the green lines at all times. Thenominal
   dfrequency is 800.0 Hz-
       
*     x       44.  The range of this tuning indicator is 800 Hz plus or minus 20 Hz.
9x         m   If your signAl is not ALREADY tuned to within better than 20 Hz, thIs
           x  m~lindicator will be useless aNd quite likely confusing as hell!
                  iQe    5.  There will be some rejection oFOtHer signAls outside this range, but
      if tHe siGnal you wAnT is weak and the interfering signals are strong there
         LB  ut5Jll l ll no doubt be problems.
                 
                    6.  If you can Hear the tone, there is No substitute for zero-beatingit
     u   with a goOd crystal-derived 80 Hz sInewave sidetone.-
  -
    6                   d2 7.  tUNERC.cOM is for anyOnEwho still uses CGA 
*        the update rate to accommodate slUggisH LCD disPlaYS.
    ~              iP        VE2IQ - November '95.
                 

Simulator Results; MT63 - 2kHz, double interleave factor.
Test at -5dB SNR, 3kHz Bandwidth AWGN.

The TUNER program - TUNER.COM
-----------------------------
 
     1.  This is a tuning aid to help get a received tone exactly on 800.0 Hz.
It should accept COM2, COM3, COM4 command line parameters (default is COM1)
and report CLIPPING (audio signal too strong for the sigma-delta circuit).
 
2.  Unfortunately it takes too many computing cycles to incorporate this
in COHERENT, so run TUNER first if necessary, using an 800 Hz sinewave
with no modulation on it (a steady carrier in other words).
It may be slightly useful on a carrier that is phase-modulated, but
the indicator will jump around trying to follow the modulation, and in
any event the useful frequency range would be limited.
 
3.  The idea is to get the little yellow line centered between the 2 green
lines, and staying within the green lines at all times.  The nominal
frequency is 800.0 Hz.
 
4.  The range of this tuning indicator is 800 Hz plus or minus 20 Hz.
If your signal is not ALREADY tuned to within better than 20 Hz, this
indicator will be useless and quite likely confusing as hell!
 
5.  There will be some rejection of other signals outside this range, but
if the signal you want is weak and the interfering signals are strong there
will no doubt be problems.
 
6.  If you can hear the tone, there is no substitute for zero-beating it
with a good crystal-derived 800 Hz sinewave sidetone.
 
7.  TUNERC.COM is for anyone who still uses CGA graphics - I slowed down
the update rate to accommodate sluggish LCD displays.
 
VE2IQ - November '95.

Summary

These results are encouraging. Evidently, there still remains further improvements and gains that can be made when using stronger ECC, perhaps by using Turbo codes. DeCarle, Martinez, and Jalocha have done commendable work.

In addition to these tests, be sure to look at Michael Keller's (DL6IAK) results of innovative PSK developments he has done. Link to DL6IAK HF-PSK work.

Back to home

Johan Forrer,1998 <forrerj@peak.org>