Broadcast - 13 July 2025
▫Hopefully no one turned up at the NTARC Club Rooms last Wednesday night, because we had all relocated to the Iron Horse Bistro - for the clubs mid-winter social get together. We all gathered about six pm for what ended up being an evening of excellent food, served in pleasant surroundings, with friends. It may have been a social evening, but as usual, much of the conversation was interspersed with radio and electronics, as always! HiHi. A great time was had by all and we eventually made our way home thoroughly satiated.
Friday morning tea came with an update from Trevor VK7TB, regarding a presentation earlier this month on crystal parameter measurements. Trevor brought in a plug in crystal test jig that he constructed fourteen years ago, consisting of an upturned printed circuit board with all the operational components fully accessible for soldering and tweaking, all mounted on top of a diecast enclosure which houses calibration and measurement switches as well as some external connectors. The test jig is complete with a sacrificial crystal socket and daughter board that can be replaced in case of any contact wear after testing many hundreds of crystals.
The design is based on a paper published by Chris Trask, N7ZWY from Sonoran Radio Research in Tempe, Arizona, USA. Titled “A Practical Test Set for Comprehensive Crystal Testing”, published in 2008. This is considered to be one of the definitive papers on the measurement of series resonant parameters of a crystal. The circuit is based on a differential Butler oscillator which in this case allows for parameter testing and measurement in a linear, non-saturated mode. External measurement ports for his Vector Voltmeter and Oscilloscope are also buffered from the crystal under test. The beauty of this particular design is the very high level of accuracy and repeatability of measurements. This confidence in results is paramount for the selection of crystals, to a very close tolerance, for the implementation of a ten pole ladder filter Trevor is designing.
For interest there is high end commercial test equipment by Hewlett-Packard / Agilent and others that accomplish the same result, however with a test jig like this you can test at a similar level of accuracy. The use of this type of “test jig” certainly is more labour intensive and slower but comes with the added bonus of not having to mortgage your house to afford the piece of Agilent test equipment. No doubt after a couple more hundred crystals are tested for his ten pole ladder filter project, Trevor will update us as to the progress.
As always pictures will be available on the NTARC Web site under “Blogs” for this broadcast. NTARC Blogs
UPCOMING EVENTS
On Air Test and Technical Net session - Every Wednesday, Test-Net and CW course on 3.580 MHz from 7 pm, then a Technical Net on 3.567 MHz from 7.30 pm till 8.30 pm. Your host for the evening is Nic VK7WW.
Club Room Technical night session - The next session will be Wednesday the 23rd July, from the usual time of 6.30 pm at the Club Room Archer Street, Rocherlea.
Coffee Morning - Held every Friday in the NTARC Club rooms. Time is from 10 am to noon.
Finally – If you have any items of news please email them to the Secretary at the following address news@ntarc.net all items to be received no later than 5 pm on the Friday prior to the Broadcast.
That’s all folks,
73, Stefan
