In a world of worsening noise floors, our workshop on RFI was eagerly awaited. Held on Sunday 3 November, from 1pm – 3pm at Bernard ZL2BD’s QTH (1 Winsley Tce, Churton Park) it was attended by 9 members.
Three speakers spoke about radio frequency interference. This is a growing problem for amateurs in urban environments and one that is not always easily able to be resolved.
The workshop was in three parts as follows:
RFI in Amateur Radio: Brief overview of RFI (Bob ZL2AVM). Hams as the culprits!
RF interference tracking (John ZL2XJ). Diagnostic guide and detection tools.
RFI Suppression: (Bernard ZL2BD). SMPS Suppression and earthing
Everybody stayed around to enjoy the tea, coffee, sausage rolls and biscuits.
Bernard ZL2BD gave a talk on how to safely switch between RX and TX antennas on your rig and demonstrated the circuit (which is probably not suitable for break-in keying). This circuit would allow us to use our active antenna or mag loop antenna on RX and our standard antenna on TX. The MFJ unit above is an alternative approach.
He also demonstrated a simple phasing circuit that works with two RX antennas to reduce noise levels or to peak a signal. Steering of a two antenna array throughout 360 degree is possible. Two active antennas can be used, or in fact, any two antennas spaced less than 1/4 wavelength apart can be steered (on RX) to reduce unwanted noise and maximise forward gain.
The following articles relate to the workshop:
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)