•
"Smart" Squelch for SSB
Editor's Note: W9M KV and W9YAN's "Smart Squelch" overwhelmed the competition to win the first 73 Magazine Hom.Brew Contest. The
authors receiYed II $250 prize In addition to the normal article payment. You can build this trend-settlrlg project; W9M KVoflers 8 PC board
lor $7.00 and a complete parts kit is availab le from Radloklt, Box 411 , Greenville NH 03048, lor $49.95. Congratulations to W9MKV and
W9YAN lor a Job well done.
frank S, Reid W9MKV
PO Box 528J
8loomin~lOn
IN 47401
David A Link W9 VA N
21J Westt'l"n Drive
Bloom ;ngton IN 47401
A sque lch turn s off receiver audio t o eli mi nate
annoy ing backgrou nd noise
w hen there is no signa l.
Squelch circuits in AM and
FM receivers are carrier-operated , On single sideband ,
which has no c a rr ie r,
squelch ing is more d ifficu lt.
T
his c ircu it detects the
hum an voice but ignor es noise, steady to nes,
a nd the Russi a n wood pecke r HF radar pulses . It requires no receiver mod ification a nd wo rks even when
vo ice signals are below the
noise le ve l.
Most SSB rigs with sq uelch,
e.g.. t he popu la r 2-mete r
mult im od e t ran sc e iver s,
use age (5-meter) vo ltage to
open sq uelch in SSB mode.
Age-operated sq uelch is adequate for st rong signa ls on
relatively quiet channels.
Agc and VOX-type squelch-
es open for a ny noise or hete rodyne that exceeds a prese t le vel . Weak si gna ls often a re missed because the
th res hold mu st be set
above the no ise level.
White noise sometimes
ca n ma ke you imagine t iny
voices in the noise, bu t it
won 't fo o l the Sm a rt
Sq uelc h. Detect ing unreada bly-wea k signa ls is worthwhile if a c ha nge of a ntenna d ire ct ion or re ce iver
control settings will ma ke
them usable.
The audio -ope rated
squelc h circuit described
here is sim ila r in prin cipl e
to Motor ola's "Consta nt Sined " squelch, a di scre tecomponent circuit with 22
transistor s.
Discriminating the
Human Voice
People no rmally spea k
a bout three syll a bles per
second. The sq ue lch work s
by detecting vo ice-ba nd e ne rgy (500-3000 H z) which is
varyi ng in frequency at a
rate of 0.5 to 3.25 H z .
The circuit is a type of
FM detector. It is insensitive to amplitude va riations
througho ut the range where
the input stage is not driven
to sa t u ra tio n b ut bac kgro u nd noi se is st ro ng
e no ugh to sa turate the limiter. The sq ue lc h wor ks
pro perly with most speakerle vel signa ls. You can connect it di rect ly to the receiver's detector output.
ad just ing ga in of inpu t buffe r a mpli fe r U1A as necessa ry.
Performance
Photo A. Squelch unit is atta ched to the right side o f the HF SSB transceiver. Rectangular
LEOs above the control knob indicate circuit status. (Pho to by KA9FJSj
44
73 Magazine· August, 1982
A re c e iver t un e d to
WW V pro vid e s a good
demonstration of th e circ uit's ca pabi lities. Squelch
opens fo r voice a nnouncements and igno res the rest
of the tra nsmissions.
The sq uelc h ca n turn on
well within th e first spoken
sylla ble. Speed of response
depends mostly upon th e
rise-time of ac tive low-pass
filte r U3A. The receiver is
mu ted one second af te r the
last voice detection. The
beginni ng of a steady tone
.. , f N- ..~ S S
•
- J"
I ,eoo
( 4 •
' .. '
_8 .
...
"
"
""
I.Lc~.
'000
f l O. .
( ~ 2 ' 6 - ' 7, .0'
( 1
4 ?OO
'"
'I.'
,,,
'"
'"
"'2
' IIQK
...
6 _• •
' '1.
"
'"
'"
'"
".
"
. ,To
,eOK
,
J:
~
"
t_
""
2 1.
."...
' ~;:; ' '''l''
....
...
... ...
,." .
C6
0 0'"
------;:~~ r. ~'f'
:~~~X
O1QNo s r . I1L £
~ ".
"'..•< "'
"
••
FlL',.
•.
•
."
"•
'J:'
- "'
'" ' "
.,"
~ 60 .
, • .l.
CO. O'"
"
..'."..-.
...""
· " . SS F it 'Ell
..
~,
N,
..
".
oc rrcroes
0.4/
'"
'W'
."
"
LOn H
"' 00',
'•'.'"
.,"
."
" .
."'"
."
..
'""
.
..
"
"2 V ' "
''.'"
,.
.,.
""
...
.,.
".
'- "
L [O '
l . s n ti- l1' 11
,.
."
'------i",
"0' "
,'."
."
"
,- SEC
""
,,
h:,
•
' ~2 . ') - OO '1
L.--j
-.e ' 10
.
r '~'
"H U
'2v '0 ....
[ " .lIL [
."
••
."
•
."
I"'T.-- .
O R' VC R
'"
Iv " [ G
"
1 .. 2 1 11
),'
Fig. 1. Schematic diagram.
open s the sq uelch only mom enta rily. l t o pens intermi ttently on music . Response
to CW depends o n code
speed and tone.
A si ngle squelc h c ircu it
can contro l mult ip le receiv-
ers, unsq uelching them a ll
when any rece iver detects a
vo ice signal. (We like to
monitor HF aircraft and mar ine frequencies plus 144.2
M Hz-t he 2-mete r sse
ca lling freq ue nc v.I
The sq ue lch is usefu l
wh en
rf
radiation
from
co m p uter system s ove rwhelms the normal sq ue lc h
in a VHF FM re cei ver. It' s
a lso good fo r moni toring
VHF/U HF mo b ile-te le phone c ha nne ls in systems
where a co nsta n t idle tone
is transmitted while no call
is in progress. The c ircu it
ha s o ther app licatio ns as a
" sma rt" VOX (voice-operated switc h) for transmitters,
recorders, intercoms, security system s, remote-ba se
systems, a nd repeater equipment .
Circuit Description
U1A is a u nity-gain summing ampl ifier, in p ut buffe r. a nd low-pass filter with
3-k Hz c utoff. U1A d rives
U1 8 , a th ird-order high-pa ss
act ive filter with 3-d B c utoff at 500 Hz. We c hose
high-perform an c e FET-input operational amplifiers
so that act ive filters co uld
use high re sista nce s and
sma ll capacito rs. The n 084
quad o p-a m p c hip is e q uiva le nt to the Nationa l lF357.
U1C and U1D a re limi ter
amplifiers with a combined
gai n of 85 d B. U1 D's output
is voice-ba nd a ud io turned
in to co nsta n t-a m pl it u d e
sq ua re wa ve s. The sq ua re
waves trigge r CMOS monostab le m ultivib ra to r U2 .
Output of U2 is a train o f
.33-m illise co nd pu lses. o ne
fo r ea c h aud io cycle. The
average voltage o f U2's o utpu t is proporti onal to the input freq uency. U2 a nd the
fo llo w ing low-pass filte r
form a fre quency-to-voltage converter, i.e ., FM d etecto r, somew hat sim ila r to
a n a uto mobile tachometer
ci rc uit.
Active low-pass f ilt er
U3A cuts off a t 3.25 Hz, the
best compromise betwee n
nolse-fals ing and the rate at
whi ch people spe a k svllables.' Note tha t U3A ha s no
bias network even though
the amp lifier use s a singlepola rity powe r supp ly. U2's
ave ra ged pulse s keep the
o utp ut o f U3A a t 5 to &
vo lts with normal noi se inp ut from the re ceiver. R1 7,
which sets U2's period. can
be va ried to keep U3A's quiescent o utp ut voltage ne a r
the c e nte r of its range .
On very quiet channel s
the re may no t be e noug h
pulse s from U2 to ke ep U3A
pro perl y bia sed . Fa lse dete c ts ma y o cc u r as U3A's
outpu t goes in a nd o ut o f its
linear range. You c a n inject
extra noi se or low-level
tone into the sq uelc h ci rc u it's a ux ilia ry input to
a chie ve the desired re sults
for your partic ul ar application .
U3A's output is ac-co upled to U3B. which a m plifies with a ga in o f 2, a nd
thenc e to U3C. a unity-ga in
inverte r. U3 B and U3C together fo rm a phase splitte r
w ith a gain o f 2. The pha se
73 Magazine. August ,1982
45
splitter provides posmvegoing outputs for positive
and negative frequency devia tions of the re c e ive r
audio.
Comparators U4A and
U4 B d e t e c t t he ra te -o fc ha nge-of-f req ue ncy signals fro m the phase-spl itter
outputs . If the vo ltage at
the inverting (-) input of
U4A o r U48 exceeds the reference voltage set by
squelch-threshold control
R30, then the low-going leve l at the compa rators' paralleled open-collector outputs disc ha rges C20
th rou gh R34 a nd D1 . The
disc ha rge time constant is
10 m illise co nds. C20. R35.
and comparator U4C form
a time-delay circuit which
holds squelch open during
its one-second period . Each
detector output longer than
10 milliseconds resets the
timer for another one seco nd. R35 controls length of
delay .
U4C's outp ut is t h e
squelc h-open signal (active
high). U4C tu rns o n hysteres is-sw itc h tran si st or Q1
(whic h lights LED2) a nd activates output-driver U4D.
As shown. U4D's o utput
goes high to unsquelch. We
used normally-closed relay
contacts so that the speaker
is enabled when the relay is
tu rned off o r if power is remo ved from the squelc h
c ircuit. To reve rse the se nse
of the o utput, exc ha nge t he
(+) a nd (-) inputs of U4D.
(J umpers a re provided o n
the PC board .) U4D's opencol lector output can drive a
relay in the speaker lead, as
shown. or a gated amplifier,
ana log gate, optoisolator.
talki ng. If there is too much
hysteresis , squelch threshold becomes hard to adjust
properly. Detector comparators U4A and U4B have
two le ve ls of hysteresis.
Po siti ve-fe e d ba ck res istor
R32 preve nts compa rato r
osc illation and lowers the
th res hold slightly d uring a
o r TT L o r CMOS logic ci rcuit. The comparator output can si nk 50 rnA maxrmum .
The sq uelc h is more sensitive a fter open ing than befo re. The se nsitivity c hange
is ca lled hysteresis . With no
hystere sis, the sq uelch may
d rop o ut while someone is
•~
I
_
_
I
( 14 _
1' 2 0 _
••
=
I
-.-
1I 1I :I
o'
A~
t
o
-
(7-
~_ I'ls . z l
..•
00 0
.... c:
J
I
sI
I
j.'
j
.
11:\ II A
..
...
,
..
..
r
o
e
•
•
•
,•
c;
---------1
z
,r•
I
•n<•
•
•
-
Fig. 2. PC board (fo il side).
48
73Magazine . August , 1982
Fig. J. Component layout
Pho to B. Circuit board and chassis detail. The only external connec tions required are receiver audio, speaker, and
12 volts dc. (Photo b y KA9F/5)
detec t. Q1 cond u c ts whil e
sq uelc h is o pen, furth er redu cing the threshold voltage via R42 a nd 02. R42 determ in es the amount o f hy steresi s. The 100k valu e
shown for R42 p rovide s
smooth sq ue lc h operation .
The ci rcu i t u ses 25-30 rnA
plu s relay current. The
eight-volt-regulator IC, US,
should be u sed f or mobile
o pe ration. Otherwise, the
entire circu it c an run from a
well-regulated 12-volt su pply . (O mit US and add a
jumper between input and
o u t p ut pins of US on the PC
board .)
Ad justment
LE01 lights w henever t he
d etector i s active. li sten to
a voice signal and ad ju st
the threshold co nt ro l until
LE01 bl ink s for every spoken syllab le, then make fine
ad j u st m ent s as necessary
for noi se conditions. T he
enable sw itch allows you to
adjust t he squelc h before
activating t he rel ay and allows you t o unsquel ch with-
o u t disturbing the threshold
setting . Sc ale mark in gs
around the cont rol knob
make it easier to reset an often-used level .
Construction
All-new parts c ost ab o ut
540, using referenced items
from Radio Shack and ECG.
Reso u rcefu l ham s can build
Parts List
Semiconductors
Ul ,U3
TL084CquadBIFET opamp
U2
C04047CMQS multiylbrator {ECG 4047)
U4
LM339quad comparat or
U5
7808 a-vert regu lator (opt ional- see text)
2N2222 or equiv. emcc n NPN trans istor
01
01,02
lN9l4 orequiY. silicondiode
D3
lN4002 0r equiY. slllcond iode
LEDl
Red LED (rec tangular)
LED2
Green LED (rec tangular)
Capacitors (All 20 V or more)
C12
68pF
ca. CS, C1 3
1000 pF
C7, C8
4700pF,5 %
C6
0.047uF, 5%
C2
O.056uF
C10, Cl1
0.1 uF
C1S
0.22uF,S%
0.47 uF, 5%
C14
Cl , C4, C20,
e21
1 uF, electrolytic
4.7 uF, non,polarlzed (RS 272-998)
C16
C18, C19
6 uF, electrolytic
C9, C17
47u F,elactrolytic
Resistors (All '/4 Watt; • = 5"10)
Rl,R2,R3,R33,A4l
48
73Magazine · August, 1982
lk
2
1
1
1
1
2
$ 5.98
1.49
1.50
.99
.1'
.20
1
1
.10
.49
1
.49
1
3
2
1
1
2
1
1
4
1
2
2
.12
.4'
.60
.30
.30
.30
.40
.40
1.60
.99
2.38
2.00
s
A11,A 14
A9, Rl 0, R23, A24
R4",A3 l
A30
R13, R16, A34, R36
A29
A40
A38
AS · , R6", R7, AS, A2l
R25, R26,R39, R42
A22, A27,R28
A18-, nrsA17
A20
R12, A15
R3S, R37
A32
Other
Ferrite beads
Miniature earphone jacks
Relay, tz-vott SPOT (AS 275-000)
Switch, miniatu re toggle SPST
Control knob
Hardware, PC board, chassis
Parts Tot al
2.7k
4.7k
6.8k
Sk, linearpot
10k
18k
47k
56'
68'
l OOk
130k
150k
160k (see text)
2
4
2
1
4
1
1
1
s
4
3
2
1
300'
360'
1
2
1M
2
2.4M
1
42 @ $.08 ea. = $3.28
2
3
1
1
1
.10
1.29
2.99
1.49
.49
10.00
$40.85
•
HAL'S SUMMER SPECIALS
HAl 2304 MI-Iz DClWN CONVERTERS IFRED AANGE zooceoo "'Hll
2304MOOEl It1Il;IT BASlCUNITW ~EA "'PLESS H()lJ$INQ .. FrTTlNGS
$34.$$
2304 MOOELnKIT I...'ll'1P1MmPl
S44.1l6
2304 MOOEllQ IUT I""'" H'll"G.!o,n Ple¥TIPl
SSoI.1l6
""lXlELS 2 & 3 WITH COAX FlmNGS IN" 0lJT AND WITH WEATHER·~EO DIE
CAST HOUSlNGS
BASlCPOWERSUPPl..V
POWER suPPLY I( IT FOH ABOVE WlTH CASE
FACTORY WIRED & TESTED
'1U5
$2....5
ANTENNAS" OTHER ACCESSORIES AVAILABLE SEND FOR MORE INFO
"'''
I
-.
HAlJOOPRE
HA1. 300 M"RE
HAL600PR E
HAL &00 MRE
S14.1l6
"'''
"'''
"'''
TOUCH TONE DECODER KIT
H JG Hl Y STABLE DECODER 11,11, COMES WITH 2 $IOED. PlATED THRU AND SOlDER
FLOWED G-l0 PC BOARD. 1·!:J6T's. 21.a2, AND ALL ELECTRONIC COMPONENTS
BOARD "'E"SURES l-112 ~ ~lI2I NCHES HAS 1211NESOUT
NEW- 1SlIN E OELUXE OECOOER
QNlY$39.1l6
569.9'5
DELUXE neUTTON TO UCHTONE ENCO DER KIT UTILIZI NG THE NEW leM 7200 CHIP
PROVIDES BOTH VISUAL AND AUDIO INDICAliON S' COMES WITH ITS OWN TWO-
TON E ANODIZED ALUMINUM CABINET MEA$ URES ONl Y 2' . -,3'. · COMPLET E WITH
TOUCH TON E PAD BOARO_CRYST AL. CHIP AND ALL NECESSARY COMPONENTS TO
FINISH THE KIT
PRICEDAT $29.95
N EW_16 LiN E DELUXE ENCOOER
$3I!l_95
HAL ECD- 16 liNE DELuxE ENCODER INCLUDES PC BOARD. ALL PARTS & CASE
"'''
HAL ECD- 12 liNE DELUXE ENCODER CQf.li>LETE WITH PC BOARO_ALL PARTS &
CASE
$29_95
the ci rcuit fo r su bstantia lly
le ss.
We built several prototypes on universal pri ntedci rcuit ca rds. The only c ritical a rea is U1, w here hig h
limiter-ampl ifier gain c a n
c a use feedback osci llation
in some layouts . Kee p component le ad s as short a s
possible . Use 5 % toleran ce
o r better for freque nc y-determ ining com ponents in
act ive filters . The Rad io
Shack rel ay's fra me must
be insu lated from ground .
Mounting the re la y on a
rubber pad quiets its c licking and isolates it from vibration.
ca n be preset to precise frequencies.
This ci rcuit can be a starting point for many experiments. You co uld, for example, insert an ana log delay
device between audio input
and o utput. If the delay
we re lo n ge r t ha n t he
squelc h re sponse time , then
sq ue lc h would o pen before
the fir st spo ke n sy lla b le
re a ches the lo ud spe ak er.
Digital techn iques could
perform the function of the
ana log ci rcu it described
here. perhaps with improvements su ch as adaptive
threshold and prog ram-controlled time c o nsta nts. We
a re ex perimenti ng with a
m i c r 0 p r o c e s s or-b a sed
voice de te c tor which may
be the sub ject of a future 73
a rt icle .•
Conclusion
Althoug h sque lch effect iveness may dimini sh o n
very c row de d amat eur
bands, a sensitive, d iscr iminating squelch is very useful for net ope ration s and
sched uled contacts, e specia lly with modern digitally-tuned re c e ive rs which
References
' Don lancaster, Active Filter
Cookbook, Howard W. Sams &
Co ., Inc., 1975.
' Moto rola Micom HF SSB Transceiver Service Manual, 1975.
A(;CUKEYER{krn THIS ACCUKEYER IS A REVISED VEFlSION OF THE VERY POPULAR
WB4IfVF ACCUKEYER ~INALLY DESCRlBED BY J AMES GARREn . IN 05T
I.AAGAZlN E AND THE 191!lRAOlOAMATEUASHAN09QOK
116.95
AC(;UKEYER-MEMORY OPTION KIT PROVIDES A SII.APLE. LOW COST METHOD OF
ADOING MEMOHYCAPABIliTY TO THE W8<lIfVF ACCUKEYER WH ILE DESIGNED FOR
DIRECT An ACHI.A ENT TO Tl-lE ABOVE ACCUKEYER IT CAN ALSO BE An ACHED TO
ANY STANDARQ ACCUKEYER BOARQWITH LinLE DIFFICULTY
116.9S
. " ....."...
BUY 80TH THE MEMORY AND THE KEYER AND SAVE
COMB IN ED PRICE ONLY $32,00
PRE-AMPLIFIER
HAl ·PA- 19 WIDE BAN D PRE-AMPliFIER, 2-200 MH l BANDWIDTHj _ JdB POINTSI 19 dB
GAIN
FULLY ASSEMBLED AN D TESTED 18_95
ONLY
$S
HAl·PA·I _. WIDE BAND PRE·AMPLI FIER, 10 MHl TO 1 . GHl 12dB GAIN
FULLY ASSEMBlE O 112.95
(i
603-883·5005
ERATES ON 12,VOI..T AC INOT SUPPLiEOI PAO\I1SIONS FOR OC
AND ALARM OPERATION
Attracttve ana {).JratNe. T~ Non Run t-rcoms Can u prPSS yOU(
Hats Are One SIze F:ts All .../ ~J1On Mes!', B.Jo: ~
6-DIOIT CLOCK·12124 HOUR
CQf.lPlETE KIT CONSISTING OF 2PCG-l0PAE·I)fUlED PC BOARDS. 1ClOCKCHIP.6
FNDCQf.lM CATM READOUTS. 13 TRANS . 3CAPS. 9 RESISTORS_S DIODES. 3 PUSHSWITCHES. POW£R TRANSFOl'lMER AND INSTRUCTIONS, lXlN -T BE
FOOLED BY PARTIAL KITS WHERE YOU HAVE TO BUY EVERYTHING EXTRA
PRICED AT 112.95
lint
emos
ST-_
HAL.TRONIX
P. o. BOX 1101
SOUTHGATE, MICH. 48195
PHONE (313) 2!l>1782
50
73 Magazine.
August, 1982
0
My
Own Logo
R(>d
Royal Blue llelley Green
LINE J
Introduced and the talk of the Oayton Hamfest th etlll AttraetiV1l and
Durable CALL LETTER HATS Ire [ust the thing for Hamfests, Field
day , Contests and other Club Activities. Me ..... a,. printed by com
puter and can btl up to thr.. targelines or six small lines of copy. For
orders of 12 or mOfe hats deduct 10"" a n d the club o r business logo :
will btl FREE" Phone oders shipped in one day , two d ays for special I
logo orders. Provide a good b&w copy of y ou logo.
I
" TWELVE-VOlT Ae LINE GOAD FOR THOSE WHO WISH TO OPERATE THE CLOCK
FFlOM II().VOlT Ae
WHEN PURCHASED WlTHCLOCK KlT $2.9S
...
~ey ~
LINE Z
SlX·DIGIT ALARM CLOCK KIT FOR HOME. CAMPER, RV. OR FIEL[} DAY USE,
OPERATES ON 12·VOLT AC OR DC, AND HAS ITS OWN 6I).H1 TIME BASE ON THE
BOARD, COMPLET E WITH ALL ELECTRONIC COMPONENTS AND TWO-PIECE. PRE DRILLED PC BDAJ:lOS BOARD SIZE . " x J " COMPLETE WITH SPEAKE R AND
SWITCHES IF OPERATED ON DC. THERE IS NOTHING MORE TO BUY·
PRICED AT $ Ul.95
SHIPPING lN FOl'lMATION 0l'l0ER5 OVER S25 WILL 8E SHIPPED POST-PAID EXCEPT
ON lTEIo4S WH ERE ADDITIONAL CHARGES ARE REOVESTEO ON ORDERS LESS THAN
$25. PLEASE INClUDE AOOfTIONAL 12,OO FOR HANOt.JNG AND Io4AIUNG CH ARGES
SEND 2011: STAMP FOR FREE FLYER
ClISTIll8UTOP FOP
_T_AP_
o
\ll"S5ilge
CIRCLE ONE
CLOCK CASE AVAILABLE AND WILL FIT ANY ONE OF THE ABOVE CLOCKS REGULAR
PRICE
S6SO BUT ONY $.f.S1I WHEN BOUGHT WITH CLOCK.
~ ~
61 Lowell Road
Hu dson, NH 03051
CLOCK KIT - HAL 79 FOUR-DtGlT SPEClAl_I1.9S. ce.
Ml._'..
ElE(TRONICS
:-- ----------~------------- ------ - ----------------~--:
I
I
II
:
I
Name
Address
SUte
City
Ck 0 Money Order 0 Charge Card D '
Slgnltur e To Validate Order
l a
O IlOEII 8U"lK
::c
PTIon,
Up
Exp. Oltl
Add $2 To Total Fo r Shipping Chl rges
~----------------------------------
I
:
II
I
I
:
.I