VK amateurs assist in the Australian bushfires 2019 - 2020
An (incomplete) slideshow summary of communications assistance rendered by VK amateurs through WICEN groups in the 2019-2020 bushfires (no audio). Taken from social media posts. Articles on previous fires and what amateurs did in these Amateur Radio magazine archives linked below.
Video shows how easy it is to use a Nano VNA as a spectrum scope.
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https://www.youtube.com/watch?v=GX1qN0ywsSs
What happens if you use 12 volts as the high tension for a homebew valve receiver?
The answer is you lose the need for a mains power supply, eliminate AC hum problems and can prod around inside without getting bitten. Construction is also much quicker.
This video describes a 1 valve regenerative receiver using a 12AX7 mains valve. The filaments are wired in series and the whole lot is run from a 12 volt gel battery.
It tunes about 470 - 1900 kHz, allowing reception of signals on either side of the AM broadcast band. Eventually I'll add more coils for HF coverage.
The set was built in a day based on the refined Thames & Kosmos Radio Ace circuit available at:
http://members.iinet.net.au/~cool386/kits/ace.html I didn't need to change any component values as those given worked first time. An alternative link is http://www.vk6fh.com/vk6fh/12au7regen.htm
But I did (i) add an LM386 audio amplifier (22k plate resistor replaces the transformer primary) to provide speaker reception and (ii) wind the coil on a ferrite rod, complete with a winding for the antenna (about 70 turns with the tap at around 10 turns from ground).
If you don't want the LM386 stage, just wire some 2k impedance headphones instead of the transformer primary (satisfactory reception on local stations) or do like the original and use a power transformer to step down to low impedence phones.
As for valves, I agree that the 12AU7 provided the easiest regeneration. A 12AT7 was less active but could still be made to oscillate across the whole band. A 12AX7 also worked but only oscillated in the top half of the band with the coil tap used.
The performance achieved speaks for itself. But you won't need an external antenna unless planning to receive distant stations. The WIA's Amateur Radio magazine has full constructional details in its May 2012 issue.
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https://www.youtube.com/watch?v=orSlJ9oJ3d0
Dick Smith Funway 1 project construction continues with a Morse oscillator. More on Funway 1 here. https://vk3ye.com/historical.htm
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https://www.youtube.com/watch?v=qp4E2AeA8Mg
Testing a one transistor CW transmitter based on the desription by SV3ORA here with some variations http://www.qrp.gr/emtx Use the biggest crystal you have or several smaller crystals in parallel. I used a BD139 transistor but you can use whatever you have if it operates on HF. NOTE: my circuit had some decoupling from the supply rail (10nF and 10 uF). Also have 0.1uF across the key contacts.
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https://www.youtube.com/watch?v=h6xpug8mqzw
This is the last and best of this three-part series. Under a full moon I tune beacons from a park where the RF noise is lower than previous locations. This is a long video and is best played while doing something else. Use the double speed playback function to save time when watching. Note: KT (29:10) is a New Zealand beacon at Kaitaia near the northern tip of the north island.
List of beacons in Australia: http://vk6ysf.com/nbd_freq.htm
List of beacons in NZ: http://worldaerodata.com/nav/New_Zealand.php
Information about switch-off: http://www.flightsafetyaustralia.com/2016/05/switch-on-about-the-navaid-switch-off/
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https://www.youtube.com/watch?v=sULc8Y0hd38
Some simple HF antennas to try if you don't have much space at home.
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https://www.youtube.com/watch?v=YurFJMzB8xU
144 MHz pedestrian mobile SSB from the beach. Contact made up to approx 50 km distant. It was a Wednesday night with contacts made during or after the 144.150 MHz VK3 2m SSB net.
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https://www.youtube.com/watch?v=WnSa1_99QAE