Bernard ZL2BD will talk to the challenges of switching between RX and TX antennas on your rig and demonstrate a simple circuit (not suitable for break-in keying) to allow us to use our active antenna or mag loop antenna on RX and our standard antenna on TX (or you can buy one like the MFJ unit above).
He will also demonstrate using a phasing circuit with two RX antennas (through a full 360 degrees) to reduce noise levels. This can be used with two active antennas, or in fact, any two antennas.
All welcome at Bernard’s QTH: 1 Winsley Tce, Churton Park. Sunday 6 October 2019 1pm -3pm. Tea and coffee available after the workshop talk.
To whet your appetite you may want to read the following introductory articles:
Receive Antenna Phasing and Noise Cancelling Explained
The second shed workshop on Active Antennas involved a construction day … with soldering irons out and smoke from the burnt plastic wafting through John ZL2XY’s QTH.
The kit was made available to all Branch 50 NZART members wanting to build an active antenna. This involves two enclosures – the active RX unit at the antenna site – where the whip antenna is mounted and powered over coax, and the shack unit that provides for the power over coax. Assemblers found they were able to build about half of the circuit in the allotted time, and the rest will be done at their own QTH.
With the next shed workshop on 6 October 2019 at Bernard ZL2BD’s QTH will focus on antenna switching and phasing of two RX antennas to reduce or eliminate noise. This is a logical follow on and should be of heightened interest with club members getting their active RX working over coming weeks.
Type 504 Active Antenna Kit - Construction notes (updated 9 Sept)
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.
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.