Broadcast - 23 November 2025
NTARC News for Sunday Broadcast – 23rd November 2025
Last October Ross VK7ALH, brought in a Drake T-4XB, HF transmitter during a club technical night, a piece of archival equipment from his collection. It was one of those pieces of equipment that has that classic “eye appeal” about it. Once the outer cover was removed, it revealed its most striking feature, a glorious copper plated chassis! This unit was part of the T-4X series and was intended to pair with the R-4 receiver.
Fortuitously Ross came across an SPR-4 for sale, so naturally he purchased it and brought it in to the club rooms. It was also manufactured in the late-sixties or early-seventies along with its twin. This model was a bit of a pivotal moment for Drake as the SPR-4 was the company’s first fully solid-state general coverage receiver, marking a significant leap from tube-based designs. It stayed in production until 1978. Like its twin it still had its elegant analogue design and nostalgic incandescent backlighting appearance, but it didn’t have a copper plated chassis! However it did have 28 transistors, a superheterodyne triple-conversion design and a Long Wave Band to help make up for it, Hi-Hi. This model has a secret feature, the inclusion of a rubber bung covering a small hole in the lid. Directly under this hole, way down on the chassis, is a 6.5mm, headphone or guitar, style socket mounted on the chassis. Once the bung is removed a direction finder loop antenna can be inserted and pushed down towards the chassis and into the socket. The socket acts as a bearing and a 360 degree swivel point for the loop antenna, quite an ingenious and simple setup.
I don’t know how he finds them, but this one was also in absolute mint condition, thank you for the update Ross.
On the same club room technical night we were once again lucky enough to have a presentation by Colin VK7ZCF on the basics of 2 and 3 Dimensional CAD or Computer Aided Design, through to preparation for 3D printing.
Using FreeCAD version 2 as his designing software, Colin walked us through the steps of going from a blank 2D page, drawing a rectangle, dimensioning it then giving it a third dimension of thickness. It could then be rotated and turned at will. Colin then went on to show drillings through the object, both partial and full. He then moved up a gear and included rebates, radius on corners and edges as well as counter-sinking and threading of drillings. Once having being satisfied by our creation Colin saved the file and imported it into the next stage, preparation for 3D printing.
Preparation is accomplished by “slicer” software, the software that literally divides your object up into steps of the thickness of the hot filament being laid down in about 0.2 mm slices. That’s the concept but in theory it also has to consider how to put all the internal printed support honeycombed structure to give the object support for the walls and overall rigidity. We also covered sacrificial honeycomb that is used to hold up sections that have to be printed in mid-air, this honeycomb is removed after the print is completed. Colin used slicer software that was supplied with his particular Ender printer for our demonstration. We didn’t actually print our creation on the night but we now have the understanding and the method. If you went to Miena last weekend you would have seen a table of Colin’s handiwork.
From the presentation the key take home concepts were:
For beginners, reference everything from the 2 Dimensional X and Y axis crossings.
Start with a 2 Dimensional sketch as this is easily adjusted or modified.
Designs can be built from downloadable 2 and 3D sketches and are possibly alterable for your specific requirements before slicing.
In FreeCAD, constraints define relationships between geometry (like lengths, angles, or alignments). When a sketch is fully constrained, meaning all degrees of freedom are locked down, the geometry turns green.
In your sketch is showing green constraints, this is FreeCAD’s way of telling you the sketch is stable and mathematically consistent and won’t do funny things unexpectedly.
And for 3D printing:
Prototyping mode, where all the walls and inner strength webbing is printed at a minimum to conserve filament and time.
Prototyping is intended for proof of concept and to make sure that everything does indeed fit.
Once all the dimensions and bugs are figuratively ironed out, the final full strength printing can be undertaken, but remember the finished printing could take quite a few hours.
An excellent presentation Colin, it certainly created intense interest during the evening and I am sure will followed up later with some “deep dives” into CAD and 3D printing.
A reminder for the NTARC Christmas dinner that is now less than a month away, it will be on Thursday the 4th of December. As we have received a number of requests we are trialling a change from the usual Wednesday to a Thursday evening as this may be more manageable for members. Due to popular requests it will be held at the Iron Horse Bar and Grill located at 468 Westbury Rd, Prospect Vale.
Check your calendar! If you are free and wish to attend, now is the time to mark the date and RSVP to the secretary at: secretary@ntarc.net or jot your name and number of places required on the registration sheet next to the sign-in register at the club rooms.
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 - The next session will be this Wednesday the 26th of November and will commence at 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 VK7ZSB.
