Happenings for July to December 2010

AGM

The AGM was held on Friday 20 August 2010 to a good turn out of members.

Reports were heard from committees. President Charles thanked all members for their support. A copy of his report will be placed here later.

President Charles presents the President's Appreciation Award to Tom VK5EE on behalf of the two recipients of the award this year. Wayne VK5ZX was the co-recipient but unable to attend the meeting. President Charles spoke of the terrific assistance both Tom and Wayne had provided him during his first year as President.

The Roy Goodwin award is to celebrate the great contribution many Foundation Licensees make to amateur radio. President Charles is seen here presenting this year's recipient, Ian VK3FNBL, with the award for his outstanding willingness to help at all club activities.

Our President for the coming year will be Charles VK5HD (his second year), Andrew VK5KET continues as secretary while James VK5HJP is our new treasurer. Our thanks go to these members for taking on these important roles.

Weathalert boxes

Weathalert units were a commercial product designed to provide weather warnings to fisherman and others. Transmitters were located at strategic places around the coast and the device was continually updated with weather information. For some reason the project was discontinued and large numbers of these boxes became available. The box contains a 148MHz receiver, various ICs for decoding the data and an LCD. The first project uses the receiver board while the second uses the LCD and many of the parts reclaimed from the board.

At the last meeting of SERG, John VK5DJ introduced the members to the Weathalert boxes. Boxes were distributed to those members who were interested in taking part in the project.

The main project was to use the 2 line display and make a transistor tester. In the meantime John has been busy examining the box in more detail. It contains a sensistive crystal controlled receiver for 2metres (148.0875 MHz to be exact).

The original crystal is on 68.69375MHz. (2*68.69375 + 10 .70 = 148.0875).

Trying various crystals around the shack that might get the receiver into our band met with no success - the oscillator didn't like them. So John changed the feedback capacitor on the bottom of the board by adding a ceramic 82pF cap between the emitter of the oscillator transistor and ground. This gave the necessary oomph to cause some old crystals once used in a Phillips 1680 to fire up. No adjustment of the oscillator tuning was required.

This shows the position of the extra cap (see top)

The crystal used was one for 146.90 RX and I assume it is an overtone crystal probably in the 45 MHz range. Anyway this combination produced an oscillation at 136.3 MHz which when adding the 10.7MHz IF resulted in a receiver on 147.00MHz. Success. A 0.1uV signal produced an audible tone in headphones, but a nicely saturated signal needed about 2uV. Not bad.

There is no mute in these receivers but the IF/Demodulator chip does have the facility. You'd need to read the Data sheet for the MC3357 to arrange this.

Of course no well meaning amateur would settle for leaving the adjustments where they are - so I fiddled with the series inductor (the one near the crystal) and this had very little effect on frequency.

I was able to peak the signal by adjusting the multiplier tank coil. A trick passed on to me by Brian VK5VI is to use a jewellers screwdriver and while holding it in position on the slug warm the shaft of the screwdriver with a soldering iron. Careful judgement and the wax melts and enables easy adjustment of the slug. A good trick to remember.

Top board. Crystal holder added, and two pins added.

The crystal socket is sildered to two pins made from a resistor's lead. A pin is soldered (a) into the active hole of the removed crystal and (b) another pin uses the earth hole of the second crystal which is not installed in this model. This was necessary because John used a socket that was too big to go into the original crystal's holes.

A power pin (5-9volts) is created near the end of R15 and an earth pin is added by soldering to the top of the board near TP1.

By this time all the unnecessary parts of the main board have been removed with a hacksaw - be gentle. John cut through the set of sockets nearest the receiver leaving just one row standing up. Although a cut could have been made on the receiver side of the socket this could have damaged some components.

Audio is taken from TP1 and earth. There is another earth pin in the corner of the board near the MC3357.

This photo shows the CRO lead on TP1, the power negative and CRO neg on the ground connection but with the +7V not connected so you can see the new pin by R15.

The CRO showing a nice sinewave received from the sig gen.

Now what to do with it? At this time the plan is to make a remote control for the 1296MHz beacon so that Chris VK5MC can point his dish east without interference when he wants to work the moon on the horizon.

Transistor tester

The next project with the WeathAlert boxes is the construction of a transistor tester. This project was developed by Gary Morton M1GRY and was described in Practical Wireless of August 2009. Brian VK5VI did the Veroboard layout on behalf of the North East Radio Club. Here is a zip file with the relevant information. When cutting away the traces on the veroboard use the Flip.jpg which is the view from the bottom of the board and will make it easier to get the gaps in the right spot. When adding the resistors R6,7,8,9,10,11 be aware you need to put some links in first. Before soldering the socket install the links that go under the socket. When the resistors are installed ensure that the leads do not foul the links, if necessary install the resistors a small distance above the veroboard. John VK5DJ will burn the PIC for you. He recommends a 28 pin socket for the PIC.

Shows where the tracks have been opened with a 3mm drill bit. If the board was flipped left to right it would look like the picture below.

The board is 30 holes across by 32 holes down. The traces are up and down in this picture.
Almost all the links have been installed in this photo( a link parallel with the top row of pins is missing which caused me some heartache until I worked out why the unit wasn't working). Note that two of the links go under the socket and so should be installed before the socket.
My socket (needs to be 28 pins) is made up from a 14 pin socket and a 16 pin socket as they fitted together nicely. Ideally a 28 pin socket should be purchased that is not too wide (some might cover another line of holes). Because mine is effectively a 30 pin socket I have 'blued' out the 2 pins I have to ignore. If you use this photo for reference remember to ignore the bottom pair of holes.

An internal photo of the working unit.
I relocated the position of the crystal because I like having short leads. The method in the photographs in the ZIP file works fine so use that.

The connections on the LCD are from bottom to top, That is pin 1 is closest to the centre of the LCD (it is marked on the other side)

Pin number Symbol Level I/O Function
1 Vss - - Power supply (GND)
2 Vcc - - Power supply (+5V)
3 Vee - - Contrast adjust (VO on the layout diagram)
4 RS -- reset
5 R/W -- read/write
6 E -- Enable signal
7 DB0 -unused
8 DB1 -unused
9 DB2 -unused
10 DB3 -unused
11 DB4
12 DB5
13 DB6
14 DB7

End view showing the exit for the test leads.

The finished device. Note On/Off switch added. A BC548 is attached to the leads showing a gain of 128.

I recycled a lot of the parts, this included the crystal from the WeathAlert, the bypass capacitors, the 100K pot. I installed the pot the reverse to the instructions as I wanted to be able to adjust it easily. So far it has taken me about 8 hours. The software is identical for any of the recommended PICs so even though the hex code is labelled for the 870 it works in the 876A. Many thanks to Gary Morton M1GRY for developing this project and sharing the details.

Rally Comms 3 July 2010

The club regularly provides the communications for the car rallies in the South East. The rallies are almost always conducted in the pine forests of the South East. The pine breaks as they are known provide rough sandy tracks ideal for rallying. SERG members provide safety communications at various points around the track and results to the organisers at a central point. Due to the absorption of UHF in the pines ordinary CB radios are not satisfactory but our club is able to provide reliable two metre communications from any point in each rally to the base. A very powerful safety measure.

Is it Tom VK5EE in a hurry to get to his checkpoint or a competitor in mid flight?

The rally boys try hard (photo: Ron VK5AKJ)

The SERG trailer, Andrew VK5KET adjusting the antenna mount while Andrew VK5FCLS supervises