Shed Workshop – Page 9

August 4, 2019

Shed Workshop 4 August

Bernard talking about fake transistors, discovered during prototyping of the Active Antenna Kit

Bernard ZL2BD and John ZL2XJ launched the first of a pair of shed workshops covering the construction of an active antenna.

Bernard discussed why amateur operators should be interested in active antennas, the basic design elements that underpin the electronics, and the nature of the kit construction that members will be undertaking.

The designs all incorporate a FET followed by a bipolar transistor. They must transfer the very high impedance of a short whip antenna to the 50 ohm input of a typical receiver. They may also include filtering to reduce broadcast interference (BCI). They are fed using 12v over the coax, so they require a filtering system to separate RF from DC back in the shack.

We will meet on 1 September from 2pm -4pm since it will be Father’s Day and some may want to go out to lunch with family. We will be constructing our devices, so members will need to bring a soldering iron. The kits will be provided free of charge to members. If you didn’t attend the first session, please contact one of the committee to confirm you are coming to be sure we have sufficient kits available.

Active Whip Antennas Explained

1 file(s) 2.22 MB

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May 5, 2019May 27, 2019

Shed Workshop and RemoteDX AGM – 26 May

We held the June Shed Workshop a week earlier than usual on 26 May 2019. The event was held at Bernard ZL2BD’s QTH at 1 Winsley Tce, Churton Park, Wellington. The topic was Class D Audio Amplifiers. These audio amplifiers come very cheaply as modules and are incredibly small and light weight when combined with a switched mode power supply. They can also be scaled for different power outputs by simply changing the supply voltage. They have many good points, but there is a downside from an amateur radio perspective … they can generate a large amount of RF noise!

Bernard gave an excellent overview of the concept, the application and demonstrated the range of commercial modules available. His paper will be available here shortly to read.

The shed workshop was followed by a special afternoon tea at 2.30pm and then the AGM of RemoteDX Inc at 3pm. It was an excellent afternoon, with gorgeous late autumn weather.

Class D amplifiers

1 file(s) 2.70 MB

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April 25, 2019May 5, 2019

Shed Workshop – Vintage Radio #2

At our shed workshop on Sunday 5 May, George ZL2AG opened up his garage and museum to the club to host the second shed workshop on vintage radios. The talk this time was given by Don ZL2BL.

Don first spoke about his restoration of a vintage Eddystone HF receiver. This had been somewhat hacked about by a previous owner, but he has restored it to near the status of the original.

He then talked about a couple of vintage AM radios – one he had restored and one still to be restored. They are illustrated in the photo below

George ZL2AG also had a mystery piece of electronic equipment for us to ponder on. This is clearly something developed for military or government purposes. Our guess is was that it is something like a range finder unit, since it is marked “E”, “N”, and “H” on the three banks of dials. Perhaps “East-West”, “North-South” and “High-Low”?

March 21, 2019April 14, 2019

Shed Workshop: Vintage Radio

At our shed workshop in the afternoon of Saturday 13 April, George ZL2AG opened up his garage and museum to the club to host a workshop on vintage radios. We were intrigued by the progression in designs – from expensive crystal sets (with galenium cat’s whisker diodes, through to feedback designs like the TRF, before the age of superhets.

George ZL2AG talking to his homebrew vintage-style radio, with John ZL2XJ and Don ZL2BL assisting

There were also changes also in the shape of cabinetry – from cathedral, through to tombstone and chest designs. George was lamenting the sharp fall off in interest in vintage radio, and was concerned about where all the beautifully restored vintage sets will end up. Tea and coffee was served at the conclusion of the workshop. A further workshop on vintage radios will take place in May.