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May/J

une 2015

The Auguration of the Rooihuiskraal Repeater Site, with Pam ZS6APT and Johan

ZS6CAQ doing the Honours!

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CLUB INFORMATION Chairman Pam ZS6APT 083 770 9514 iti04256@mweb.co.za

Vice Chairman Gert ZR6BV 060 859 4071 corvus47@yahoo.com

Secretary Billy ZS6WPS 081 485 2120 billys@telkomsa.net

Treasurer Pam ZS6APT 083 770 9514 iti04256@mweb.co.za

Technical Johan ZS6CAQ 072 371 9854 keuldej@mweb.co.za

Bulletin Relays Jimmy ZS6APS 083 969 3967 iti04256@mweb.co.za

Editor Pam ZS6APT 083 770 9514 iti04256@mweb.co.za

Co-Editor Jimmy ZS6APS 083 969 3967 iti04256@mweb.co.za

Sunday Night Talks Pine ZS6GST 082 602 8880 aps@logica.co.za

Social Gert ZR6BV 060 859 4071 corvus47@yahoo.com

Club Fixed Activities and Venue

Club meetings : 14h00 Every second Saturday of the month

Club news bulletins: 07h30 Sundays on 145.775 MHz FM, 7.078 MHz LSB & 439.050 MHz

Sunday Night Talks: 19h30 on 145.775 MHz

Clubhouse address: Scout Hall, Springbok Street, Wierda Park

Correspondence: The Secretary, PO Box 14960, Lyttelton, 0140

Banking particulars: Centurion Radio Amateur Club, Standard Bank, Lyttelton

Branch Code - 010945 - Account No - 017366380

Web Site: www.cqcenturion.org

The Chairman, Committee and members of the Centurion Radio Amateur Club join

together in wishing you all a very HAPPY BIRTHDAY and congratulations on

your WEDDING ANNIVERSARY

Birthdays Wedding Anniversaries

2nd June Elma sw of Chris ZS6LOG 7th June Linda ZR6AWV and Egmond

12th June Erna sw of Whitey ZS6JJJ 9th July Daryl ZS6DLL and Kim

22nd June Joy sw of Dave ZS6AZP

22nd June Richard ZS6UK

25th June Sonja sw of Stephen ZS6SFW

26th June Dave ZS6AZP

30th June Elma sw of Gawie ZS6GJJ

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From the Chairman

As you will have noticed the advertisement which usually

appeared on page 2 (and has been there for many years), is no

longer there. Unfortunately this source of income has now

come to an end. Many thanks to Robbie Robberts and Allen

Joss Motors for their valued support over the years.

The AGM is on our doorstep, and the time has come to reflect on the

achievements of the club during the past months, and also to bear in mind that a

new committee needs to be elected at the AGM. The nomination forms, together

with the AGM notifications and Proxy forms will be sent out shortly.

During this past year our meetings have been well attended, and have always been

followed by interesting talks and demonstrations. Many thanks to all who

contributed to these discussions.

See you next time, and until then Happy Hamming and Gud DX!

73 de Pam ZS6APT

Pam ZS6APT

A new application for Transistors

Have you ever needed a zener diode to complete that project you have so diligently been working on and

just cannot find one in your jewel box? Well, fear not, help is at hand and you will not have to travel to

the nearest component supply store to buy one, just to find they are out of stock!

Use a transistor as shown in figure 1 instead. Figure 1

Table 1 shows the results of tests carried out on 5 samples of 3 different types of npn transistor (pnp

transistors can be used to generate a negative voltage reference!) which I had to hand, using the circuit of

Figure 1.

(Continued on page 8)……….

+ V (eg 12V)

Regulated output

R (eg 220)

Transistor used as a Zener diode

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Understanding Mr. Pierce’s Oscillator

I’ve recently spent some time struggling with a simple crystal controlled Pierce oscillator on a

frequency of 1.843 MHz as the frequency generation stage for a QRP Foxhunt transmitter I offered to

build (constructed Manhatten style) for the Centurion Radio Amateur Club. Such a simple circuit

(See Figure 1) but it just refused to oscillate until, in desperation, I touched the collector of the

BC107 (metal cased transistor with the collector connected to the case) and off it went – then the penny dropped, I needed additional capacitance between the collector and ground.

Figure 1 : Basic Pierce Oscillator (as used in the “ONER” transmitter detailed on page 19 of

reference 1)

I grabbed a 100pF capacitor (Cadd) that just happened to be lying on my workbench, soldered it in,

and low and behold the oscillator worked beautifully. This got me thinking – I drew out the

equivalent circuit, ( see Figure 2) with the assistance of Reference 2, and realised that the Pierce

design was actually a Colpitts circuit with the stray collector-to-emitter (CCE) and the base-to-emitter

(CBE) capacitances providing the feedback. In this case the collector-to-emitter capacitance needed to

be increased to allow sufficient feedback. Previous Pierce oscillators I have built have always been

for much higher frequencies which required lower values of feedback capacitor! The only other

1.843Mhz Pierce oscillator circuit I have built, many years ago, was constructed on Veroboard which clearly had sufficient stray capacitance between the various tracks to allow oscillation to occur. You

live and learn!

Figure 2 : Equivalent circuit of the Pierce Oscillator

This little exercise taught me a valuable lesson – never take anything for granted!

de ZS6AZP

References

“South African QRP Circuit Handbook”, Dave Smith ZS6AZP, 1989

“Understanding Amateur Radio”, Jay Rusgrove W1VD, Doug de Maw W1FB and George

Grammar W1DF, ARRL 1977

+ 12V

1.843MHz Xtal

BC107

100k

3k3

Output

1.843MHz Xtal

BC107

100k

3k3

Output

CBE

CCE

See text

Cadd

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Experiments with a VXO using a 3.58MHz Ceramic Resonator After trying many different circuits to build a satisfactory VXO (variable crystal oscillator) using

the very common 3.579545MHz American Colour Burst crystals I was never able to achieve a

stable frequency shift of more than about 1kHz – inadequate for using the VXO as the “BFO” in

a direct conversion receiver to use on the early morning 80m QRP CW net where the transmitting

frequencies of the various stations participating can vary in the range of 3.581 to 3.575MHz! As

a result I was forced to go for the VFO approach with all its inherent issues of long term and

thermal stability etc – a story for another time perhaps.

While browsing through my archives of many photocopies of “circuits which may come in useful

someday”, I came across an article by G4COL [1] which piqued my interest – maybe I could use

a ceramic resonator VXO , which seems to offer a much wider frequency pulling range than a

standard crystal, in place of my current 80m VFO and obtain the improved stability suggested in

the article.

Firstly, a comparison of the equivalent circuits of a quartz crystal (Figure 1) and a ceramic

resonator (Figure 2) will prove helpful in understanding the fundamental differences between

these two component types.

Figure 1 : Equivalent Circuit of a conventional quartz crystal

Figure 2 : Equivalent circuit of a 3.58Mz ceramic resonator

(Continued on page 6)

R1 L C1

C2

R1 – Equivalent series resistance

L – Dynamic or motional inductance

C1 – Dynamic or motional capacitance

C2 – Parallel or static capacitance

9 436µ 4p8

42p

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Quoting loosely from G4COL’s article:

Compared with a typical quartz crystal, the series resistance of a ceramic resonator is similar,

and the series capacitance higher by a factor of up to 100. The Series inductance and unloaded

Q are lower by a similar factor. The parallel capacitance of the resonator is higher than that of

the quartz crystal by a factor about 100.

What makes the ceramic resonator promising for use in a wide range VXO, in place of a

conventional VFO, is that its Q factor is several times higher than that of a high quality inductor

-capacitor tuned circuit, while its series equivalent inductance is much smaller than that of a

quartz crystal, which suggests a wider pulling range.

In addition, ceramic resonators are small (a bit smaller than one’s thumbnail), are readily

available at low cost and fortuitously are available (3.58Mz) for the 80m amateur band.

Given all the promising attributes, I built an experimental VXO (see Figure 3) and investigated

the performance of the five 3.58MHz resonators lurking in my “jewel box”.

Figure 3 : Experimental ceramic resonator VXO circuit

(Continued from page 5)

(Continued on page 7)

47k

100p

100p

100p 1k5

BC107B

0.01

3.58 Ceramic Resonator

LM78L08

+ 12V

output

82p

0.1 0.1

0

5p to

7

7

Some interesting results were obtained ( see Table 1):

The tuneable frequency range obtained with all the resonators tested were all in excess of

104kHz

With the capacitor in series with the resonator bypassed, there was a wide spread in the basic

operating frequency of the various devices, despite them all being marked with a

frequency of 3.58MHz!

Table 1 : Results Measured

I have been very impressed with the results obtained. This VXO design will definitely be finding

its way into a future 80m QRP transceiver. What a pity that suitable ceramic resonators do not

seem to be available for the 40m band!

Reference

[1] “Using Ceramic Resonators in Oscillators” : Ian Braithwaite, G4COL, RADIO

COMMUNICATION February 1994, page 38

73 de ZS6AZP (Tnx Dave)

(Continued from page 6)

Device Cap bypassed Cap at Max C Cap at Min C Freq. Range

1 3460khz 3493kHz 3599kHz 106kHz

2 3458kHz 3493kHz 3597kHz 104kHz

3 3508kHz 3543kHz 3650 107kHz

4 3464kHz 3499kHz 3605kZ 105kHz

5 3524kHz 3548kHz 3654kHz 106kHz

(Continued from page 3)

Table 1 : Regulated output voltage measured

A very useful, novel, trick is to use a transistor when you don’t have the needed zener diode. You just

have to be a bit patient and choose a suitable transistor from your jewel box!

Note: the regulated voltage can be increased in 0.7 volt steps by inserting one or more silicon diodes

(typically from the 1N400X family) in series with the common base/collector connection and ground.

de ZS6AZP

ref: “Carrying on the Practical way”, G3RJV, Practical Wireless, July 2009. (Tnx Dave)

Sample Number/Type BC107 2N2222 BSX59

1 7.47 7.62 7.26

2 6.03 7.51 7.53

3 10.10 7.42 8.91

4 8.31 7.38 7.42

5 9.85 7.34 6.18

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Removing Alternator Whine by Jim KB1MVX I recently installed a new transceiver in my truck. On the first day of using the new radio I got reports that I was transmitting very noticeable alternator whine. I could also hear it on receive and when the radio was quiet. I checked the diodes in the alternator, verified I had good grounds, and I even ran the truck with the alternator removed to be sure that the whine was indeed from the alternator. The alternator produces AC, which is rectified into DC. The problem is the rectification is not perfect. The DC output will have a small AC signal riding on it. That AC signal will have 9 cycles for each revolution of the alternator. Suppose your engine is idling at 600 RPM and the drive pulley ratio to your alternator is 1:3. At that engine speed your alternator is turning 1800 RPM, which is 30 rotations per second. Each rotation gives you 9 cycles of AC. Do the math and you get a 270 Hz sinusoid (not a perfect sinusoid but close enough). Cruise down the road at 2000 RPM and you get a 900 Hz sinusoid riding on your DC power supply.

I decided to figure out a filter design that could be built in less than an hour by anyone with basic tools, and handle a current of at least 20 Amps.

Directions below

1/2" Quick Link will be used as the inductor core. A fellow ham, Dave KC1LT, suggested using a shackle. I went to get a shackle and came across this quick link. I went with the quick link to make more efficient use of project box space.

(Continued on page 9)

Parts List:

1/2" Quick Link

6x3x2" project box

20' roll 12 gauge red hook up wire

4700 uF 35V capacitor

18" of black 16 gauge wire

electrical tape

GOOP or similar glue

3 zip ties

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If you use a torroid, as shown above, this instead of the oblong shaped shackle as the core to wrap, you might need to adjust the size of the plastic project box to accommodate the wrapped width of the core.

Beginning the winding

Wrap the hook up wire around the closed side of the quick link starting from the left as shown. Leave about 9" of wire free on the left end. Try to keep the winds as close together and tight as possible. On the last layer space the winds so that you have 9" of wire left on the right end. Use all 20' of wire.

(Continued from page 8)

(Continued on page 10)

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Above is the finished wrap

Wrap the coils in electrical tape and close the quick link. About 1.5" from the right end of the inductor strip 1/4" of insulation off the red wire and solder in the + lead of the capacitor. Make sure you observe the capacitor polarity. In the picture you can see the negative arrow on the capacitor pointing down. Solder the 18" piece of black wire to the negative lead of the

capacitor. (Above)

(Continued from page 9)

(Continued on page 11)

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Cover the solder connections and capacitor leads with electrical tape. Drill a 3/16" hole in both ends of the project box for the red wires. Drill a 1/8" hole in one end of the project box for the black wire. Run the wires through the holes. Put a zip tie on each of the three wires to limit how far the wires can be pulled out of the box. Make sure to leave a little slack in the wires inside the box. Using GOOP or some other thick strong adhesive, glue the capacitor and inductor into the project box. Leave the cover off until the glue dries.

+12V Side with the capacitor to radio Black Ground +12V to battery

Measured Filter Response:

I made this measurement using a low frequency signal generator and an oscilloscope. At 25 Hz the filter has better than 30 dB of attenuation. In other words for frequencies above 25 Hz the noise power has been knocked down by more than a factor of 1000.

73 de Jim KB1MVX (Thanks to Johan ZS6CAQ for supplying this article)

(Continued from page 10)