Welcome to the March bulletin. Please forgive my ramblings in the last issue, but sometimes it is good to have a diversion from the usual routine.

This month we also continue with the development of the new remote keyer. We will be discussing the formulation and application of the input stages. I have not been able to come up with a suitable name for the keyer. So if any member would like to make a suggestion please let me know.

Of interest to all members is the annual field day which is scheduled for the 1st of April (No its not a joke we will be having one - honest). The details have been published later in the bulletin. It is hoped that all members will participate. If not to score points perhaps get on the air and make contact with those members who are participating in the competition. Why not have a chat to other members on an adjacent channel.

Sunday, 1 April, 2001.

1. The contest is open to all individual licensed amateurs. All bands above 50 MHz, and all licensed modes, may be used.

2. Points are scored for two way contacts between pairs of stations, at least one of which must be portable, and at least one of which must be in the VK6 call area. (Repeater contacts do not count towards the score, but may be used for liaison purposes.) For the purposes of the contest, a portable station is one which is being operated away from the usual station address and which is not powered from the AC mains. Mobile stations (including permanently mobile) count as portable, as does the

VHF Group station VK6WH.

3. CONTEST TIME: 1030-1500 WST (0230Z-0700Z) on Sunday, 1 April, 2001.

The contest is divided into 2 intervals of 2 hours each, 1030-1230 WST and 1300-1500 WST. These are separated by a half hour (1230-1300 WST) for lunch. Two stations may work each other for a scoring contact once on each band in each 2 hour interval.

4. The contest exchange will consist of a signal report, 3 digit serial number starting from 001, and the station location.

5. Each scoring monoband contact is worth 1 point times the following multipliers:

DISTANCE MULTIPLIER:

One point for each 25km or part thereof, up to a maximum of 15 points.

BAND MULTIPLIER:

PORTABLE TO PORTABLE MULTIPLIER: 2

PORTABLE TO COUNTRY FIXED STATION MULTIPLIER: 2

Contacts count double if both stations are portable, or if one is portable and the other is a country fixed station. A country station is one which is at least 100km from GPO Perth.

NOVICE STATION MULTIPLIER: 4

Contacts with Limited Novice and Novice stations count quadruple.

6. SECTIONS: 1. Portable (All band), 2. Portable (Single Band),

3. Fixed (All band), 4. Novice.

All portable contestants should submit with their logs, a tally of their score for each band (for section 2) and their total score (for section 1).

7. GROUP OPERATION: There is no section for club stations, but contacts with club stations count towards the scores of individual amateurs entering sections 1 to 4. Groups of up to 3 licensed amateurs may pool their equipment, and operate from a single portable site under their own individual call signs. (An exception is made for VK6WH, which is allowed multiple operators, and can enter the portable section even if operated from Wireless Hill.)

The use of multiple call signs by a single individual is not allowed.

8. CROSSBAND CONTACTS are permitted, but only score in special circumstances. If two stations work crossband from band A to some other band (B, say), but do not have a two way contact on band A in the relevant 2 hour time period, then once, and only once, in that period, each may claim towards their band A (and total) score half the points that would have resulted from a band A contact. This means that if they do not have a two way contact on band B in the time period, they may also claim (once

only) half the points that would have resulted from a band B contact.

9. LOGS should be sent by Monday, 23 April, 2001 (April Meeting night) to:

CONTEST MANAGER, WEST AUSTRALIAN VHF GROUP (INC),

PO BOX 189 APPLECROSS, W.A. 6953

The Contest Manager's decisions and interpretation of the rules are final.

REMEMBER: Contacts between a portable station, and a portable or country fixed station, count double. Contacts with Novice stations count quadruple.

If things get a bit quiet, some suggested frequencies to try are:

SSB: 50.175, 144.120, 432.120, 1296.120

FM: 52.525, 146.5, 434.0, 439.0

Liaison: 144.175 (SSB), 432.175 (SSB), 145.375 (FM)

I have received several e-mails from Christine Bastin VK6ZLZ depicting various internet sites to visit. These have been correlated below.

http://www.heavens-above.com/

This shows a site where you can select your current position by entering the country and city. The site then allows you to select a range of orbiting body data that will appear over your location. The data includes a 24hr prediction of amateur satellites, MIRs current location, planetary probes and even celestial bodies including the planets. This is a very interesting site not only for amateur but for budding astronomers.

http://www.qsl.net/g3zhi

This has the web page for G3ZHI. This also has additional links to other amateur sites.

http://spaceflight.nasa.gov/realdata/tracking/index.html

This contains realtime information as to the current location of the international space station. There are additional tabs for links to other NASA sites covering human space flight.

http://spaceflight.nasa.gov/realdata/sightings/SSapplications/Post/SightingData/sighting_index.html

This site calculates the predicted passes of the international space station with reference to the selected country and city.

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Wally VK6KZ also gave me a list of contacts that were received in Broome by VK6JQ. This will hopefully give scope to the range of contacts that can be achieved from out northern areas.

REMOTE KEYER

This month we will discuss the input section of the keyer. As was mentioned in previous articles it is all to easy to try and design a circuit that will try to be all things to all men. We are attempting to design a circuit which is as versatile a possible without losing track of our objective. Our circuit is designed such that the configuration may be changed by omitting components and adding jumpers between various blocks.

To begin we have assumed the available power supply is +12V. To allow for sufficient regulator overhead above the drop out voltage we have assumed an operating voltage for the analogue circuit of +8V. As secondary reference voltage of +5V may also be used if required. Otherwise U5 may be omitted and R1 set to 0 ohms.

To make an 8 channel system we have the option of using using semiconductors such as op amps and comparators that have either single circuits or up to 4 devices each internally. Using single circuits increases the size of the final PCB. Using multiple circuit devices does not substantially increase the cost as long as we use only the additional passive components as required. Dependent on the application, there may be cases where we only wish to use portions of the circuit. This configuration will allow us to activate those portions as required.

Referring to Figure 2, The signal we are trying to measure enters a Pi filter FILT1. This is to reduce any RF interference entering the circuit. Where a channel is not required, this component may be omitted.

The signal then enters a circuit which can be configured in several different ways. Varying the values of R1 and C3 allows us to provide a single pole low pass filter. Adding R2 provides a divider network to reduce any large signals to a level suitable for our circuit. D1 acts as input protection, clamping the signal level such that the devices are not overloaded.

Where a channel is not required, R1 and C3 may be omitted and R2 set to a short circuit such that the inputs to the remainder of the circuit is not floating.

Once the signal has passed the divider network we have the choice of either routing it to the amplifier U1A or directly to a comparator U2A. Shorting pins 1 and 2 of H1 will send the signal to U1A. Shorting pins 2 and 3 of H1 will send the signal to U2A.

Referring now to Figure 3. U1A is configured as a non inverting amplifier. The gain of the amplifier is set by the resistor ratio of R7 and R6 such that;

Gain = 1+(R7/R6)

By omitting R6 the circuit acts as a unity gain buffer. C2 can be used to reduce the gain at high frequencies.

Where a channel is not required, R6 may be omitted.

By shorting pins 1 and 2 on H2 the comparator U2A accepts its signal from the amplifier circuit. By shorting pins 2 and 3 the comparator accepts the signal from the divider network.

R4 and R10 provide a hysteresis circuit which prevents signals around the trigger point from oscillating the output. The ratio of R8, R9 and VR1 sets the trigger point for the comparator. The resistive divider may be powered by a reference voltage, which in this case is a precision reference of 5V. If this sort of accuracy is not required you can tie this point to the output of the 8V regulator.

As this type of comparator has an open collector output, R5 is used to pull-up to a 5V rail suitable for driving a digital input on the processor.