QRM
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Bulletin issued by the Northern 20 Box 1010
Branches of the dJireless Institute Launceston
L of sustralis, Tas. 2ivision. Tase. 7250
June 1974
Vol. 4 No -3
Registered at GPO Hobart
for transmission by post Price 20¢
as a periodical. Category B.
et eto eet et et etet etet et et ee ee e eet et et
y As s8ll licensees are taken into consideration in computing the
final score in the R.D. contest, it is most inconsiderate of the
Federal Council not to allow the use of repeaters.
There are many limited licensees in isolated (VHF) areas who have
very little chance of getting a reasonable score without the use
of repeaters.
The #.I.A. lists repeaters as one of the benefits to members.
Last year they spent quite a large amount of money on a special
9 convention to sgree on a national freqguency plan.
Yet when it comes to a contest, to remember the amateurs who
gave their life in the fight for freedom, they become little
dictators and discriminate aggeinst limited licensees and country
areas.
Don't allow this to happen, protest, by writing to the Institute
and A.R., by talking to your Federal Councillor and even by
submitting a log of repeater contacts in this contest, wccompanied
by a note stating your reason for using the repesater.
W . John VK7JV
°
MESTINGS.
June Lth North West Branch, Lakins Hall, Ulverstone.
June {4th Northern Branch, AlB rooms, High st.
June 15th Council meeting at the QTH of VK7KK, 130 p.me.
149 Cambridge st. Launceston.
i YRCS
- June 8th & 22nd room 38, Kings Meadows High School.
QcRuI‘in June 19?)4‘
Northern notes by Reg VK /Ks. Page 2
I don't want this to sound like another editorial or a soap box
article but there are a few things worth saying.
There's no doubt that the branch has achieved much in the past
few years- the repesater, ¢RM and meeting attendances would be
the most notable features.
However there is one distinct lack of action, soclal activities.
Do you think its important that the UM's and XYL's (a nasty term!)
get together more often?
Do the wives feel that hubby has a hobby in which they want to -
but can't get involved in?
Should the wives get together now and again to organise social
events for the branch? Any bites?
Thanks to Frank and Brenda 74FR for the use of their GTH and
their efforts in preparation for the 25th.
Thanks also to those who attended to make the evening such a
SuUccesss
With a total around 50 (34 adults) it must rate as one of the
best attended yet.
It was great to see North West and Southern representation.
Seems there were a few worried OM's after signs of "cluckiness"
in a few XYL's present, guess reminders of the sleepless nights
and associated problems should've cured that.
The other major development concerns meeting activities, Wally
7ZWX has organised well and has activities planned until January:.
The fare includes talks by members to assist those amongst us
who are less experienced, outside visitors with both electronic
and non electronic expertise, and an occasional film.
Finally, it is proposed to hold regular executive meetings on
the Friday prior to branch meetings.
If you have any winges, ideas or brainwaves that's the place
to alr them.
Let's get everyone involved in making this branch serve you
even more effectively than it does at present. Ideas please.
The June meeting will include two BP films.
0il digger - shows the life of a rubberneck working on a oil
rig in the Gippsland area, it shows both the work and play side
of the job.
Soltice - is an aesthetic study of bird and animal life in the
Bass Strait region.
Whilst these are non-electronic films they're well worth seeing,
you dont need an activity to entice you to attend meetings,
this is just an added attraction.
000000000000000
John was adept as ever as auctioneer at the May meeting.
The clubhouse account was $30.00 better off as a result of a
donation of a percentage of the proceeds of 700's gear.
Seems the bottom's fallen out of the market in VK3!
Prices of equipment sold at the Geelong Hamfest were ridiculous,
Base stations sold for $5.00.
0000000UU000000
Qe
We must be breading literary talent in the Northern Branch.
O
First 7JV's QRM, next 74BY is Bulletin editor and now 7Down
from Matric College!
All we need now is IEB to move Northi
000000000000000
QeR.M. June 1974
Page 3
North West notes from hMax VK7MX.
Way I commence my notes with a word to the ladies, bless them.
The salt of the ham shack. The silent partner mostly, but now
is your chance to become voluble.
I refer to the ladies page in @rM, you can write some thoughts
on the subject of radio, any aspect, post them to QRM
PO Box 1010 Launceston, and give someone a shock when the
magazine arrives, its a great idea and we do look forward to
reading some interesting notes in the months to come.
We had a very well attended meeting this month and our
visitors included Brian VKLUZKF and his companion Darrel.
In addition four very interested young chaps came along and
we hope to see them at future meetings.
The usual business was transacted including a lengthy
discussion on the possibility of originating the Sunday
Broadcast from this aresa, more of that later.
5id 7SF came up with some interesting goodies which
disappeared in very quick time.
At the conclusion of the meeting Wayne Gibson gave a lecture
on the intricacies of the electronic keyer which he designed
and built for the beacon.
Wayne knew his subject allright and finished up with a very
confused audience. How do those things work ? Thanks iwayne.
We are appreciating the liason with council that we now
have through our councillor Graham 72AQ.
It is a new experience to our branch..-
We are all very sorry that David 7MS has had such bad luck
with his new HF rig, particularly when he received it back
from the mainland with a heap of broken glass rattling inside.
However David is now back on the air and we hope that 1t
stays that way.
There appears to be trouble over the hill. A racket came on
2 metres recently consisting of squaks, whistles and a paper
crackling sound and somewhere amongst it we resolved lan 72IE.
Whats with the new rig Ian ?
Which reminds me of some of Murphy's law which I think may
be appropriagte.
Probability of failure of a component, assembly or system
is inversely proportional to ease of repair or replacement.
A transistor protected by a fast acting fuse will protect
the'fuse by blowing first.
Isn't that the truth. See you next month
fax VK7MX
000000000000000
A reminder to our assocliate members that the next AOLCP
examinations are held on August 20th.
However your application will have to be at Radio Branch
before July 8th. T T
If you think you haven't a chance, try it anyway you may be
surprised and if you don't pass at least you'll be told how
much you have learned.
000000000000000
QsR.M. June 1974
DX notes by Den VK/DK. Page 4
I guess it is Jjust my luck, but the very evening I turned
in my notes for the May QRM,stating that 20 metres could
be forgotten as a night time Dx band, that European signals
were plentiful, but not strong.
SM, OH, DL, were but a few that were heard around 1200 Z
and about S5.
I have had very little chance this month, to listen on the
bands. For one week the gear wasn't even turned on whilst
g virilent wog dealt with me.
From what I have heard I haven't missed much, going through
the bands does not reveal any great DX news.
80 metres; have not had a chance to listen for DX
4O metres; the occasional openings to Europe is still there
around 1230 4, and again at 2400 Z, YU's and YO's
have been noted.
20 metres; 0300/0400 Z, HC20A, YS, W4's and VQI9M (long path)
0600/0800 4, G6PD, DJ9GD, stacks of I's, YS1AG,
MiD (89), VE7's and of all things, ST25A at S6
so dont overlook the possibility of an African
QS0.
15 metres; 0130 Z, W's and JA's would you believe?
73 Den
000000000000000
VHF notes by Joe VK7Z2Gd.
Dporadic B activity is almost non-existent, the only two
openings this month were on the 5th when Danny 74DA and
Kevin 7ZAH worked VK4QO and again on the 6th when Danny
worked VKH5SU.
Brian 7RR 1s once again active on 53.525 as well as myself
with a 50W base station.
A new station on 2 metres A.M. in Launceston is Graeme 7i4GG
running 20W input to a 3/12,
2 metres has been a little better with an extremely good
opening to VK3 on May 5th.when over 416 SSB stations were
worked by Denny 74DA and John 7JV, Danny also worked 20
stations via the ch.42 and 48 repeaters.
At the same time John worked VK3ZCG and VK3BDL on 6 metres.
That's about it for this month, don't forget to keep an
ear open for the mid winter 6 metre DX openings, it only
lasts a week or two but every VHF operator will be looking
for this so there should be plenty to work.
73 Me
000000000000000
Congratulations to Brenda and Frank VK7ZFR on the birth
of their daughter Katie Ann.
Congratulations to Angus Robertson and Margaret Cush on
their engagement.
Qe ReMe June 1974
fage 5
_ADIES PAGE
I thought that the ladies who belong to clubs, committees etc.
may like to hear about a way of raising a little extra money.
The committee of the pre-school my son atteands holds monthly
bingo evenings.
2ighteen people attended the last evening and just over $20.00
was raised.
The evenings are held at the homes of members and each is
asked to bring something for supper as well as & small
grocery item for prizes.
This way there is ro great expense on anyone and what money
is made is all profit.
e encourgge members to bring their friends along so we
have a few different faces each evening.
For those who haven't played bingo it goes something like
this, the cards are 5 cents each (so as not to make too big
a hole in the house keeping) there is no limit to the number
of cards a player can buy.
As the numbers are called out the player crosses them off
if they appear on her card, the first player to have all the
numbers crossed out, calls out Bingo. the card is then
checked and if correct is the winner.
Bvery one who comes agrees its a good evening out for just
over a dollar.
VK744H's XYL Judith
000000000000000
Festive Dip.
L4 oz Cream Cheese, softened at room temperature.
1 Table spoon of lemon Jjuice
1 Table spoon of finely grated onion
1/2 Tea spoon of salt
Good pinch of cayenne pepper
Milk
Beat the cream cheese until smooth, add lemon Jjuice, onion,
salt and cayenne pepper.
Blend in sufficient milk to make a dipping consistency,
spoon into small bowl and chill.
Judith VK74aH
0000000000000¢C0O
O.R.M. June 1974
Page 6
ALOW_NOISE PREAMPLIFIER
FOR 1296 Mhz.
by Daniel VKT7ZDA.
A low noise transistor preamplifier Tor 1296 Mhz is described
in this article using the Philips BFR91 NPN silicon planar
epitaxial transistor used in a grounded emitter circuit with
an approxiamate noise figure of 2.7 - 3db and approximate
gain of 10-12db.
The amplifier is constructed on a piece of 1/16" thick double
sided glass epoxy printed circuit board 3.5" long x 2" wide
with a $" wide stripline etched on one side and full copper
clad on the other sice.
The basic structure is a 50 ohm stripline with a transistor
inserted ncar the input connector and DC blocking capacitors
placed at the junction between coaxial connector and stripline.
No input tuning is »rovided since best noise performance is
obtained with a 50 ohm source impedance, this means that the
anténna and feedline must themselves be reasonably well
impedance matched at the operating frequency for optimum
performance,
The output of this transistor is tuned and matched to 50 ohms
by means of a sliding capacitor tuner.
In the finished design the capacitor is a tab of copper foil
who's area (capacitance) and position along the output line
are experimentaly adjusted for maximum gain at 1296 Mhz.
Under the cordition of 50 ohm input and output impedance the
gain will be approximately 10-12 db at midband and exhibit
a -3 db bandwith of severnl hundred Mhz.
Biasing: An important feature of this circuit is its
stability (freedom fron strplus oscillations) which is a
function of the elaborate bias nctwork shown on the schematic
diagram. This network corsists of a 56 ohm resistor in series
with a resonant choke for midband, the choke L consists of 6
turns of 30 gauge wire air wound on a 1/16" diameter former
with turn spacing of about one wire diameter, the overall
length of the winding is about §".
The small resistor is first soldered to the stripline (straight
upward away from the strip) with leads as short as possible.
The top of the resistor is now a terminal point for one end
of L, the other end of L is convected to a good UHF 1000 pf
bypass capacitor (low inductance).
These three components provide a good high impedance choke
at midband, 1296, and & good lossy impedance ouvt oi band. At
the lower frequencies in the VHF region the inductance is
small and the 56 ohm resistor loads the circuit heavily
preventing resonances of large cnought Q to start oscillations.
At still lower freguencies an additional R.C. network is
provided which essentially loads the transistor with a total
of 112 okms well into the HF region.
Q.R.M, June 1974
Page 7
Below the HF region the 10Cpf blocking capacitors roll off
the external circuit responce and 5 mf capacitor prevents
internal feedback. This combined action of components in
the bias network discourages external and internal circuit
resonances which may cause self oscillations. In addition
the bias network provides collector current stabilization
o
by means of negative fecdback through the 560 ohm collector
dropping resistor. When operating from 12 volts sunply the
minimum noise figure in this circuit occurs with a collector
current of 2.5-6 ma which is adjusted by the 25K ohm bias
adjust resistor.
BFR91 Data.
Vebo 15V
8 s Veeo 12V
Tc max 35 ma
’_VE Power dissipation 180 mW
Top ViEW
FT 5000 Mhz
Construction.
1) Circuit boavrd as shown in diagram A
2) End plates made of %" x " brass bar 2" long in which the
appropraite holes are drilled to mount the BNC connectors
and the support shelf for the circuit board.
Diagram B1 and B2.
3) Support shelf mounted to end plates by " whit. screws
or sweated ‘o it, made of " square by 2" long brass
and it supports the circuit board to stop movement away
from the BNC connectors, which would damage the input/output
coupling capacitors. Diagram C.
4) Emitter earthing block, 11" square by §" long brass as
shown in diagrsm D.
The overall cost of the project should be less than $10.00
as all components are available in Australia and the
construction can be carried out using the tools normally
found in the Ham shack without great difficulty.
I would 1like to thank Ron Wilkinson VK3AKC for supplying me
with information and the Crawford Hill VHF club technical
report 8 from which nearly all this information comes from.
@eReb June 1974
Page 8
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QeR. M. June 1974
Reprinted from 6UP, Vol.2 No.l Page 9
Subscriptions are $4.00 per year
from; 47 Ballast Point Rd. Birchgrove 2041
MIXERS for VHF SSB
by Mike Farrell VK2AM
There has been a dramatic increase in the use of SSB on VHF in the past
few years -~ SSB is certainly the dominant mode on six metres, and two metre SSB is
increasing. The latter no doubt is partly due to Dscar 6,
VHF sideband does have its problems,principally those of spurious products
appearing in-band which can be of much annoyance to ones (amateur) neighbours.
Qut—~of-band spurii annoy the other neighbours § If one considers the usual
"commercial” specification of —-60db spurious performance, and the fact that a
genuine S9+40db signal report would mean that a -60db spurious is S6 at the
receiver, the extent of the problem is readily appreciated. Figure 1, pinched from
the RSGB VHF manual, illustrates the problem.
Obviously a case can be made for spurious reduction of 80db,or even 100db.A
drive control on the transverter will enable the output power to be adjusted for
reasonable copy at the receiver. A report of 60 over S9 is good for the ego but
deflating when it is remembered that ones in-band crud is S9 !
The problem, of spurii, under discussion is usually produced by mixing
processes in the transmitter - it is therefore essential to be sure that the SSB
exciter is clean‘before tackling the transverter problem as higher order harmonics
from the exciter can cause problems on VHF, even though the HF transceiver etc is
0K on HF. The writer recently modified his 14MHz SSB exciter and found that the
modifications were creating a large spurious only 40db down from the main signal,
This turned out to be the 6th harmonic of the VFO mixing with the 5th harmonic of
the SSB generator on 9MHz to produce a reverse tuning spot on 14MHz - one cant be
too careful ! Harmonics from the SSB exciter should be considered also (28MHz x 5
comes out on 140MHz) and use of a bandpass filter is good practice.
Fig.l.
TRANSMITTER RECIEVER
100w
Line of sight signals
Distance Signal Level gL.o.S.l Attenuation of
50db will give
signal strength
of 5=
2 milesm 36mv S9 + 20db
8 miles 19mv s8
32 miles 2.25mv S6
Another problem is the spectral purity of the local oscillator chadin in the
transverter. Use of an oscillator and mutiplier on, say 144MHz, is not good enough
—— consider figure 2.
58MH: i
Osc.
28 MiHz
SSB
Fig.2.
58 x 2) + 28 = 144 (434333 x 3) + 14 = 144
§58 x 3) - 28 = 146 (434333 2 4) - (14 x 2) = 145,333
Q.R.M. June 1974
Page 10
The working Q of LG circuits at VHF is not high and undesirable harmonics
gan cause embarrassment. The local oscillator chain should be liberally supplied
with buffers and double tune circuits. Figure 3 would be the sort of thing required.
Use of a double balanced mixer in the transverter is almost mandatory,
especially where the local oscillator frequency approaches the desired output
frequency as in fig.3a. Where the local oscillator is far removed from the
desired output frequency, a simple single-endeé@ mixer may be used, provided
L.0.
out
130 MHz
116 MHz
“’m.forzsMHzSSB Drive
rost-mixer filtering is good.
A circuit popular in the US is seen in fig.4. An advantage here is that the
SSB drive can be applied at high impedance and low level. Linearity is good, but the
efficiency tends to fall off at 144MHz. A variation of this circuit is injection
of the local oscillator into the screen instead of the cathode.
Fig.4.
28MH2 12BY7
$SB
10p
This circuit
appears in the
RSGB manuals and
47k works well with
100 . excellent linearity
and output. About
lw L.0. injection
is needed with
24MHz (6m) somewhat less SSB
116 MHz (2m) drive.
Balanced Mixers
Balanced mixers are superior to fig.4. in all aspects and should be
used if at all possible. The most successful version uses a QQE02/5 with the SSB
drive applied in push-pull and the local oscillator applied in parallel, thus
" @ancelling the L.O. in the plate circuit. Several variations of this arrangement
are shown in fig.5.
Drive is adjusted from the S:B source and L.O. separately to produce 0.5 - 1lmA
grid current respectively,i.e. apply drive from one source and adjust level to
achieve grid current required,then from other source.One only at a time,
QeReM. June 1974
Page 11
QQE02-5
001 e
u
Fig.5b. /;;;
This circuit is reputed to be less
critical to adjust than 5ae. A more complicated version of 5b
with similar performance.
A QQE03/10 or 3/12 will work with the mixers in fig.5. but output and
linearity are down on the QQE02/5. A 6J6 may be used in a similar arrangement aa
in fig.6.
The mixer may be arranged to balance out the feedthrough of the HF SSB -
this may be of benefit when using 28MHz SSB to drive a six metre transverter, but
generally it is preferable to balance out the local oscillator - herewith for the
record, see fig.7. A UHF version which performs well appeared in "Ham Radio" a few
years ago. This circuit (or variations) is popular on 432MHz..
0Qe02-5
Solid State Mixers
All the forgoing circuits use, of course, valves. Since it is far easier and
cheaper to achieve power at VHF using valves rather than transistors one might as
well use valves throughout -~ although this problem is decreasing rapidly. For those
who subscribe to solid state for the sake of solid state, some transistors et al
are described in mixer service in fig.8.
Q.R.M. June 1974
Page 12
SSB
Junction FET Mixer...with L.0O. & SSB
injected into gates. Can give up to MOSFET Mixer. N.B. the SSB drive is
45db L.O. rejection. cancelled out, not the L.O.
Output is sufficient to drive MPF121-
2N3866 to l.5w output.
This circuit appears in Jessop's manual (RSGB) - 2N3819 FETs are used to
provide several microwatts of SSB on 144MHz (valves forever 1)
To tune up, carrier should be inserted at low level and all coils tuned for
maximam at 144MHz. Turn carrier off and decouple link from L.0O. chain. Note either S
source voltage reading (they should be equal - if not, adjust tle source resistora)
and couple the link back into the L.O. chain until the source voltage just starts
to rise,y then reduce slightly. The SSB drive should be adjusted for best output
commensurate with good quality.
Notwithstanding the above this circuit is straightforward but FETs should be
used in preference to bipolars as the intermodulation performance is superior,
Last year VK3ZUR published a circuit in the Victorian VHFer of an all solid
state SSB transmitter for 52MHz and used MPFl2ls in the mixer, but he did observe
that single gate FETs would have worked just as well and provided easier balancinge
The circuit is shown in fig.8.b. Note that the SOB drive is balanced out, not the
L.0. Output is sufficient to drive an MPF121 amp.-2N3866 driver to l.5watts output.
The ring diode arrangement would probably make an excellent double-balanced
mixer - for the lovers of hot-carrier diodes. See fig.8c.
’
L.0.
Fig.8¢c.
use high speed switching diodes
-
e.9: INP14, hp2800 > VHF SSB out
Summary
Well, there you have it. The golden rule with mixers is not to overdrive -
spurious products increase alarmingly - the proper place to increase the VHF SSB
signal level is after the mixer - a class A buffer will provide more than enough
“power to drive anything up to a 6/40 in ABl, so the prime requirement of the mixer
is quality, not quantity.
QeR.M. June 1974
Pgge 13
FOR _SALE
High fidelity audio equipment, AWA ST25 amplifier
7¢5 Watts rms per channel, fitted with quad decoder
&S per HE.A. must sell $#90.00
Joe Gelston, 40 Lavender Gr., Summer Hill
Phone 443882
1 only power transformer 240 volt primary, secondary
550 volt at 500 ma, 1400 volts at 500 ma $20.00
6 and 2metres combined AM transceiver, receiver
tunable, includes 6UP 6 metre and VK3 2 metre
converters, transmitter xtal locked $50.00
Trio TR2E 2 metre AM transceiver, has seperate
VFO's for transmit and receive, can also be '
xtal locked $150.00
Daniel Apted, 65 Upper Brougham st. Launceston
Vinten car phone, mod. MTR13, QQE03/42 final
fitted with NMOS FET preamp and xtal switching
for 6 channels (ref. A.R. May '74) fitted with
xtals for ch.40 and 48 (uses same xtals as AWA
and IGL) very good order $60.00
Vinten car phone, mod. MTR12, similar to above
but low band, fitted with xtals for 52.525 Mhz
also in good order $50. 00
Peter Dowde, Phone LL2047
s aEs oo
Playmaster 104 stereo amplifier, tuner and
2 - 8 inch twin cone speakers $50.00
Cabinet with smoked perspex cover to suit above -
negotiate price $3$4$%3
Also some transformers and a radio dial, what offers?
Carl Waldon, 11 Woolven st.Kings Meadows
W oB
LRSS s s eS o S e S s
I know Col 7KW doesn't like water but to use a bank of
Solar cells to power hig receiver to listen to the
Broadcast is carrying his dislike g bit far ¢
DON't forget the "TOWNSVILLE PACIFIC FESTIVAL CONTEST"
on 8th June. Rules can be found on page 25 in the May
issue of A.R.
Logs to be sent to; PO Box 964, Townsville, Qld 4810
Closing date for entries , 31st July 1974
2o
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