Broadcast - 11 February 2024
As promised for this broadcast we will continue with the left-overs from the last technical night.
Trevor VK7TB has moved on from the traditional “Breadboard” designs for electronics into the new realm of “Baking Dish” designing. In fact he brought a baking dish in to the club…… no it was not full of food!
It had been repurposed for an electronic project that required a reasonably large flat top working area but did not require much height. Trevor turned the baking dish into a fully functioning thermionic valve tester. Evidently he found it quicker to make a purpose build unit than rush the restoration of an antique tester sitting on his storage shelf.
Visually it is very impressive and not your usual cobbled together breadboard setup that so often happens when testing is required. The non-stick coating on the baking dish gave the exterior a pleasing appearance.
Trevor was interested in particular valves that he is using in a project so there was no need for every valve socket known to man to be included. He settled on 7, 8 and 9 pin bases plus a Top Cap when needed.
The baking dish bottom side is now the front panel.
The middle area of the panel contains the three valve bases plus two rows of banana sockets to the right. The top row of banana sockets extend all the valve socket pins and the lower row of banana sockets extends the equipment test connections.
The lower third has two good sized digital LCD displays, volt meter mounted on the left with current meter mounted on the right hand side. In between there are switches for Screen and Anode voltage range selection, one potentiometer for Screen voltage adjustment and a multi turn counting potentiometer for fine Grid voltage adjustment. A short circuit indicator and ferrite rings on the Top Cap lead complete the unit.
One interesting construction feature is all the controls and patch point labelling is mounted on separately cut strips of metal that are in turn screwed onto the case.
Visually very effective and gives the unit an engineered feel. I can’t help wondering if this was an elegant solution because the stick on labels would not adhere to the non-stick surface on the baking dish? hihi
All in all this side project turned out to be a very nice solution to a “Test and Measurement” requirement for other ongoing projects. Thank you Trevor for bringing the home brew test equipment in and sharing it with us.
Peter VK7SP has been working on receiving and decoding terrestrially broadcast HF radio weather fax images. He has loaded up his Raspberry Pi with appropriate software and quickly strung up a temporary 7m long wire antenna at home. These are connected to his newly acquired Icom-IC705. Peter brought the IC705 and Pi into the club rooms to try the combination on some of the various club room antenna. Listening to VMC, Charleville located in Queensland on 13920 kHz, the club room multiband Dipole had marginally higher strength than the vertical. Both of these antenna appeared to be only a little better than measured signal strength at home with his long wire. Peter also has had limited success at home with this frequency as well as 11030 kHz and 5200 kHz. He also had a one off weather fax reception of VMW at Wiluna in Western Australia on 5755 kHz, a couple of weeks ago.
A work in progress that I wouldn’t be surprised to see ending up on a certain sailing boat. Thanks Peter and hopefully we will get to see some weather faxes in the near future.
Now continuing the tenuous marine theme, Ross VK7ALH brought in a mature radio called the “Sailor”, manufactured by S.P. Radio of Denmark. The name on the unit was very specific in that it was a “2182kHz Watch Keeping Receiver Type R501”.
To set the scene the Sailor R501 complies with the requirements of the international convention for SAFETY OF LIFE AT SEA, or SOLAS for short, ratified in 1974. It states that “on board all ships above 300 tons gross tonnage there must be continuous listening on the radiotelephonic emergency frequency of 2182 kHz”, end quote. One can only assume that a reasonably large ship gave the radio to Ross.
This Sailor R501 was manufactured about 1990. It is a single-channel telephony receiver designed to receive A2, A2H, A3, and A3H signals on the international emergency frequency.
The front panel is quite simple, it has a volume knob, speaker and five push buttons to select operating modes, timer reset and for testing with a simulated distress call.
It can operate as an unmuted receiver or in automatic volume mute mode that ensures the receiver is muted, but still listening, until a two-tone alarm signal or a navigation warning signal is received to un-mute the audio. Automatic mode also provides control of mute function and is timed to the international listening period. This is and I quote “To increase the chances of a weak distress transmission being received, 3 minute periods of radio silence are observed on the hour and half hour on distress channels. All transmissions must stop during silence periods except distress calls”, end quote. Now think back…. How many can remember watching the December REAST DATV night on the “Gibson Girl”, where Justin highlighted the analogue clock on the club room wall. It had these listening periods marked on its face.
This unit is a solid-state design and runs on 24 Volts DC with overall dimensions of 230 x 150 x 163 mm. It has a coated steel front panel with two internal chassis made of aluminium. The chassis are back to back, one opening facing up and the other facing down. With the speaker nestled between them. One chassis holds all the RF receiver side of things. The other side has a printed circuit board covered with of CMOS 4000-series digital logic integrated circuits. They are mainly counters, gates and shift registers, there is even a 555 timer and not a microprocessor to be seen. hihi
This was yet another interesting artefact from Ross’ expansive archival collection of equipment. This one did have one more secret on the radio side, it was equipped with a reasonably large huntsman spider hiding within, but it had well and truly, “Shuffled off this mortal coil”.
As always pictures, including the spider, will be available on the NTARC Web site under “Blogs” for this broadcast.
UPCOMING EVENTS
TestNet and TechNet session - Every Wednesday, TestNet/CW course on 3.580MHz from 7pm till 7.30pm…. and a TechNet on 3.567MHz from 7.30pm till about 8.30pm. Your host for the evening will probably not be Nic VK7WW this week, you will have to tune in to find out.
Coffee Morning - held every Friday in the NTARC Club rooms. Time is from 10am to noon and we look forward to seeing you all there. So why not pop in and join us for a cuppa, there is endless tea and coffee along with biscuits available for a donation.
Annual General Meeting & General Meeting – This Wednesday the 14th February 2024 at the NTARC Club Rooms, Rocherlea Scout Hall, Archer Street Rocherlea commencing at 19:30 hours (7.30 pm).
Club Room Technical night session - The next session will be on Wednesday the 28th of February and will commence at the usual time of 6.30 pm, running through to about 10 pm, at the Club room Archer Street, Rocherlea.
Finally - A reminder to all members that if you have any items of news you would like added to our weekly roundup, no matter how trivial, then please email them to the Secretary at the following address news@ntarc.net all items to be received no later than 5pm on the Friday prior to the Broadcast.
That’s all folks,
73 from Stefan, VK7ZSB, Secretary NTARC Inc.
