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-R
BULLETIN ISSUED BY THE NCRTHERN ZCNES COF THE P.C.BCX 1010,
WIRELESS INSTITUTE CF AUSTRALTA TASMANTAN DIVISICN LAUNCESTCYM,
TAS, 7250.
FEBRUARY
VCL. 1 NC, 9
. ———
———————
-T—— .T .. < WA AG AR S W, TP At s BN
e A . AR
AN Ai T v
REGISTERED AT G,P.C, HCBART
for transmission by post as
e Periodicel, CATEGORY B, PRICE 5¢.
PAGE 1
FOR a few months now we have been printing basic circuits with
cxplanations on how they operate; to date we haven't had any corresponcence
to say that this meets a demand or whether it's a waste of time and space.
We co hear a lot of pecnle say that QRM fulfills the need for a Northem
bulletin and that it is very informative but very few of you take pen in hand
and drop us a line, How about yéu naking a New Year's rescluticn to help with
QRM by writing a few lines, Anything will help -~ from a couple cf lines about
scme new gear to a techmical article, editorial or cven a (isagreement with sone
of the material printed, So let's hear from you in the very near future,
JOHN VK7IV,
EDITCR.
333K
CCMING EVENTS
FEB. 1 N.W, MEETING, LAKIN'S HALL, ULVERSTCNE,
FEB, 11 NCRTHERN 7(NE MEETING AT A,E.B. ROCMS, 51 YORK ST, LAWCESI,
FEB, 27 MNYUAL PIQNIC, FIELD DAY AND CRICKET MATCH AT PORT SORELL,
FEB, 56 ARRL, PHCNE DX CCNTEST,
FEB.12~13 NATICNAL FIELD DAY CCNTEST 1972 - REF, NCV, A,R, PAGE 13,
The January mecting was well attenéed, hcvever there weren
office bearers present tc meet the quorum recuirements, We =
~ Peter 7PF acted as chairman,
It was revorted that the oHreblen with off frecuency tran
the repeater had been sclved, Scrme discussicn tock place cn consista
natters,
THE FEBRUARY MEETING WILL NCT BE AT 8 HIGH ST, THE RCCMS ARE
FESTIVAL OF TASVANIA ACTIVITIES.
THE MEETING WILL BE AT ADULT EDUCATICN BCARD RCCMS, 51 YCRK STREET,
HKFHFINHRK
We hope te have TIM 7ZX at Port Scrcll on the 27th to report on the rost
imoertant event of the ycar - THE CRICKET MATCH{
3 KK
H K
CCNGRATULATICNS to RCBIN HARWOCD whe passed his exams end now holds the
call 7RH. DRobin has been heard gquite a bit on 40 meters using his FT 200,
3K
TREVCR 7TD found that the protective covering around his FT 101 in the
ferm of a Helden Torana is not waternroof!
HHHHHHA
K
LEE PRETTY 7ZLP was home from VK3 cduring the helicdays, We had a chat with
hin abcut regulated power sun lics and active filters end he »remiscd that he
would send us on article on these subjccts for QRYM,
| HHIHK KKK
BRIAY 70R has given up travelling to Lawncesten end is now residing here
permanently,
RN
(UITE a few new veices heard on channel 4, including 7ZEC, 7LZ, 7AX, MZ,
7WH, 7PS, 7ZRO and cven VK3BBB (Brien) and 3ZXM (Max) cn Mt, Tassia are coming
through regularly,
FHIHFINN
NCRTH-WESTERY ZKE FCTES R
We trust thet all members and friends enjoyed their Christoss
and are on the threshold of a bright and prosperous Hew Year,
Good harming to all,
No neceting in January so news is scarce,
I met Bob 7ZAA awey in the bush the other cday, I believe he cane out
loaded with gen stones,
Harcld '7MZ is holidaying on the nmainland, visiting harronic I believe,
We miss hin on 2,
As loss to the zone is 3R who has left on the "Austrelian Tracder" for
an extended holiday, We will miss his checery weice, I understancd that Bill
Dunn 3ATD will be replacing Noel, Can't say if he has 2M gear,
Ken 7KH has been on helicday at Green's Beach, He has been on 20 and 40 ete,
1Hbile end the rig really works,
Lock out for Tony 74 on repeater channel, He gets through (X from Ulvcrstonc,
T necd abcut 200 wluntecrs with sicks and shovcls to move the hill which
is isclating me fron the repcater,
v Pcter 7PF spent a weck or two in our areca and certainly lcft a few grateful
cheps as a result of a few very useful jobs that hce fownd time for,
A couple of Southern boys carped in our arca rccently and we enjoyed 2M
contacts with them, Winston 7WH at Ulverstone end Jolm 7EJG at Devonport,
In Deccenber we efijoyed the cheery voice of Tonm 7AL dashing rounc the place
for a week, We arc always plecascd to welcome visitors to the arca,
Thosc whe were wisc and fortunatc enough to be at the Hanfecst all agree
that it was an excellent show, Great crcdit is due to the organisers with
a particular thanks to the ladics - after a great deal of chat about it, we
still can't figure how they did it, Thanks girls, fronm the I',W, Zone,
I hope to have sorme morc ncws after the ncxt mecting,
M™X,
AR
AMATEUR TELEVISICN . ATV. (PART 5)
IRANSMITTING 420~ 450 Mz 420- 450 Mz
LimsERR
. )' VINEVY _
—fi—"—J” DC—bMHZ
os<.
(ne nay tend £to censicder a T,V, transnittcr to be sirply a wideband wversion
of a souncd transmitter, Unfcrtunately this is nct quitc as casy as first q{qacctezl
fron rcascns belowse -
1. Normal video anc sound transmission requirc two scparatc tronsmitters,
the sound transmitter carrier being 5,5 MHz above the video transnitter carricr,
The video transritter is of the vestigial sicdebend type, i.c, the upper sideband
. P D
SauN
-»lus a proportion of the lower sicdchand, CARKIER
'Basic VESTIGAL SipEBAND
.
\/iDEO LARRIER
125z O 2.5 Mrz g 5,5 Mhz
If we arc intending te usc thc 420-450 1MHz band, it becomes cobvious that sc
long as we kec: to the centre of the band, therc is no reascn why double siceband
carmot be trensmitted, thus saving the ncccssity of fancy vestipgial sideband filters
c¢te, The souncd can siimnly be frequency rocdulated against o 5,5 MHz sub-cerricr and
mixed with the video in a rmecdulator and finally a» lied to the transmitter, This
icca “ccs not require the usc of a separatc sound transmitter, Refer te bBlock diagran
at beginning, The A, T.V, converter and T,V, rceciver can then be tuncd tc the uwper
sidebanc only,
2, Thc modulator needs special censiderations with regard to the D,C, corponent
cepeelially the YblackM level cte, | |
3. The widebandwidth required, reans that the cfficicney methods of
moculation arc ou‘i:. Plate and sercen rocdulation con, hewever, be used in the
transnitter at onc of the low level stages, This requires the usc of a power valuc
as a cathode follower in the modulator, In the main, most transmitters usc grid
mecdulation,
/MATEUR TELEVISICN - A.T.V. (contd,)
of a
From the above it can be appreciated that the largest degracation
. the
Tclevision signal within a television system, con casily occur through
trensmitter, (bandwidth, phase distortion, and non lincararity) being some of the
main problems, It is thus cssential to ronitor the signal sirml teneously
r)
before transmission (ronitor) and after trensmission, (normal T,V. with converte
to claluatc transmission quelity,
this serics
A s ort article next ronth re M"Aerisls for A, T.V." will conclude
of articles for the present, It is hoped to be able to list a few reference
articlcs also,
TONY (VK7AX/T)
HHRPHRIK
THOSE that participated in fox hunts in the days of AM, can wvouch for the
fin those events procluce.,
At the hemfest it was illustrated that directional fox hunts are feasable,
yvet there was a disappointing roll-up for the hunt arranged for the 21st January,
By corments héard, members went more activities to allow social contact; fox hunts
appear an idecal way to combine this with some challenging activity., Surcly there
arc plenty of members with channel B gear and the only other item reouired is a
bean described in December ORM, Have a go next time it's no disgrace to get lost,
You couldn't get into a bigger mess than Peter 7PF tangled up in the Glen Dhu Ceravan
Park at a late hour,
Your skill will improve with practice so let's sce you at the next hunt,
REG, 7KK,
3NN
FOR SALE
1 ONLY VK3, 144 Mc CONVERTER WITH XTAL FOR 15Mc I.F. - $15,00
1 ONLY VK3 432 Mc CONVERTER WITH XTAL FCR 6,3Mc. I.F. - 923,00
1 ONLY VK3 52 Mc CCNVERTER WITH DUAL GATE ICSFET PREAMP AND XTAL FCR 7Mc I.F. ~
$13,00
ALL I WORKING ORDER FROM JOE GELSTCN VK72GJ.
HH KKKH
WAN TED
5 FP7 CATHCDE RAY TUBES WITH CR WITHCUT YOKES AVD SHIELDS ..
JCIN VAT STAVEREN VI7JV
-
(ne of the sirplest forms of f.n, detection is = system cslled slcpe dcte
Slope ‘etection inwlves the use cf a simple AY, fctector, its theory cf cocraticn
can be casily ex-lained by a carcful study cf the ciagrass below,
R.F. appearing across the secondary parallecl resonant circuit is half
wave rectified, Audio is derived from the R.F., component by the low pass
filter, .
Most simplified circuits are subject to operating limitations, and the sin-lc
slepe cdetector is no cxeeptien,
1. It is very necessary (as iB with mest .f,n, cderccdulaters) that sufficient
lirmiting takes place in thc limiting stages ahead of the detector; the detector
rust sec a censtant level regardless of signal level being rcceived - reference
te diagram,
2. It is impertant that the deviation of f,n, signal remains within the
lincar porticns cf the resonance curve, if not, a disterted a,f, output sigal
will result, The typical rescnance curve scen by the detector, (sec diagram)
can handlc cnly a small armount of signal cue tc the shert length of the lincar
nerticn,
LA
REr o
FILTERS ' ALIDJD
ouT
Next renth rore on f.m, derodulators,
store weTEcTions SN TAKE PLACE o~ EITHER ygmTp,
stope S A.F OUTPUT
——
MAXIMLE
%
UNDISTORTED
ouTrur
Nonbimear
TorTion |
/ -
/ Liven® 3 £
Por T10m 2‘ b \
9 ~ &*
A W
5 3 R 3
Y5 ooy gT
THE CPERATICN CF A TCNE CPERATED SWITCH
(FULLY SCLID STATE)
The wnit was developed so that a tape recorder could be switched off a2t a
precetermined spot on the tepe, COFff the cuff the idea secmed quite a simle cne,
but aftcr some further thcught and scme hecurs of excerimenting it was founs, that
for a it to operate successfully a minimun of 10 semicenducters were neeessary,
Reascons -
1. The switch had to be a separate unit, with no interference or mdification
tc the tape rccorder.
2. It had to be 1004 reliable and not to be triggered intc the off state by
spuricus signals on the tape - (2 time delay nctwork),
3. Cnce triggercd it mst remain in that state mtil it is manually reset.
4Le Cn princinle it had to be fully solid state — (no rclays), The circuit
shown below is that of a practical working model; the parts used were
thosc that were availablc at the time of construction,
Circuit Cuecraticn
In
A,
audic signal of 10,5 Khz is recorded on the tape at the cdesired switch off
point ~ (of average level) end for a duration of abeut 10 seconds,
The tonc signal is taken -from the extensicn speaker socket, (cr across the
speeker at a load between 4 Chn and 15 Chr), The only irmportent factor at this
staze is that thc level from the tape recorder be at least 0,04 vep.p, Cn rost
tape recorders this level is often 10 times the above figure,
Q1 is a tuncd collector grcuriced base amplifier. Why grounded base.
1. The input impedance is low.
2e It has & high voltare gain,
3. Its high output impedance can bc connected directly acroes the parallcl
resonant circuit (10.5 Khz), L1 and L2 are ccils weund in a pot corc
fermer, The LC retic was selected to give a selectivity of about 3.0 Khz
(f;r switch operaticn), 12 is an wmtwned seconcary winding (weltage step
up) .
QR is a grouncded emitter clipping limiter; by driving Q2 to saturation
a constent veltage level will agrear across its collector, The square
wave information is rcctified by a voltage cdoubler and turns Q3 hard cng
the + woltage on Q3 collector falls to zere leaving Q4 in an uwnbiasecd
condition, With Q4 at zero bias the potentiel of Q4 ccllecter will rise
to almst full su~nly wveltege (9V), The C.R. nctwork of 1AK- Chr and 10cMF
presents a suitable delay of about 345 to 4 secends before the unijunction
transistor conducts, The wnijunection will firc when its emitter is at
6 volts + with respect to the negative rail,. When fired the wnijunction
will present a negative impedance across the capaciter "C", this will
discharge the "C" very cuickly and in sco doing will cause base current
to flow in the. 27 Ch~ end 470 Chn resistors. This base eurrent will
be seen as very short duration pulses (positive going across the 27 Chm),
It was thought at this stace that these + poing pulses (every 4 seconds
approx) would trigger the bi-stable mltivibrator directly; however
due to the low impecance circuitry of the biastable (Q7, Q8) 06 was
nee'ed as a trigger transister,
What is a histable miltivibrator.
Bricfly, it is an oscillator which has two stable states, and can be
suitably triggered frcem one stable state to another, The irrortant noint
here is that when it is triggercd into the second state where Q8
concducts, it will remain in that statc wntil it is rcset by S.W.1.
When Q8 conducts (9 will be turned off which will tum on Q10, The
ccllector of Q10 will be at earth potential, rermoving the firing veltage
fronm the gate ofthe triac; zecro current will flow in the load circuit -
the it will be switched off, It will rcermain in that state wmtil the
rulti-vibrater is reset, You might ask why use Q9 and 010, why not
the output fron the bistable tc trigger the gate directly, Recson -
the gate of a CD40 triac draws about 30 mA, this currant would load
the bistable tco heavily.,
!
REsET
rm
po ally £deséb
47K
QLLOK
A5
v
W
T4
36108 AUDIC ATFLIFIER
BC108 CLIPPIG LIKITER
O e
D.C, SWITCHES
3
- 04 BC108
QN O
W
212140 %.J.7, DELAY
-
»
0108 PI.5TASLE TRIGGER
o ¢ WD
AC128 + 08 AG127 BIL.STALLE IVLTIVIBRATCR : ¥
£8
2400 D,C. SYITCHES
2 b
15 | - :
(1
3k R L .
SR
|