Superhet crystal mixing schemes

 

Homebrew superheterodyne receivers/transceivers using a computer crystal ladder filter, BFO and  VXO offer the combination of simplicity and stability.  The key to this receiver pattern is the VXO.  I know VXOs are so ’90s, and that I should embrace digital and start banging out DDS VFOs with Arduinos, eBay AD9850 cards and AdaFruit si5351‘s.  I will soon, I promise.  In the mean time I just want to explore computer crystal mixing schemes a little longer.   Scratch-building a DDS VFO necessitates some new practices, such as getting the script you’ve picked from dozens online to compile and download to the controller, for the particular combination of display, Arduino and DDS chip in use.  I’m not saying it’s too difficult, I’m just observing that it isn’t trivial, and if you get stuck you may find yourself limited in your options to unpick it.  Crystals, on the other hand, are real, physical things, remarkable for their sharp resonant characteristics.  And these days they’re almost literally a dime a dozen.

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2.4GHz Wifi corner reflector 

First Harmonic (FH) was getting patchy wifi coverage to his desktop computer in his bedroom.  The obvious thing would be to invest in a new multiband wifi modem/router, one of those things that looks like a UFO with spiky antennas for its multiple bands.  But the situation presented a good opportunity for some basic UHF antenna experiments over this short unlicensed duplex data link. Discussion of the popular Cantenna suggested lower performance than many have claimed due to the small size of Pringles/Milo cans at 2.4GHz. A repurposed satellite TV dish of diameter 1.2m or more seems to be the best option.  Not having one, and needing a solution that would not turn FH’s bedroom into a junkyard, I opted for a homebrew corner reflector based on one of the many online designs.

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Hack Green online SDR service

As if listening to 75 meter AM from the US West Coast on the train going to work in Melbourne, Australia wasn’t entertaining enough, I googled to discover other WebSDR receivers, thinking an ear in central Europe or the UK might make for an interesting contrast. Websdr.org lists some of the world’s active online Software Defined Receivers.  One that looked promising was a station on the wonderfully named Hack Green in Cheshire UK.  Hack Green turns out to be a regional Cold War nuclear bunker, established in the 1950s and declassified in 1993.  Now the site hosts a popular online SDR.

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Mt Donna Buang (VK3/VC-002) and Mt Ritchie (VK3/VC-003)

A clear winter’s day was forecast on August 5th 2016 and with arrangements made I headed out early to Mt Donna Buang VK3/VC-002 with plans for Mt Ritchie VK3/VC-003 afterwards.  I left Melbourne’s eastern suburbs by 0710 and arrived at Donna Buang around 0845 to a frosty, clear, cold and calm summit, distrubing no fewer than 5 lyre birds on the final few kilometers before the car park.  A bonus for getting up there early was spectacular morning sunrays cutting through the mountain mist.

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Mt St Leonard VK3/VC-006 for the VK1 SOTA QSO Party 2016

The VK1 SOTA QSO Party is in its fourth year.  Mountain Goat Andrew VK1AD ex 1NAM does a fine job of promoting it and rallying VK1s onto hilltops.  On Friday 5th August he posted that there were 19 planned activations recorded at SOTAWatch involving activations across VK1, VK2, VK3, VK5, VK7 and ZL1.  It worked out that if I left early for a nearby summit and kept moving I could join the party on Mt St Leonard VK3/VC-006. Mt St Leonard is not much more than an hour’s drive from the eastern suburns of Melbourne.  I left at 0710 and arrived at the car park just over an hour later.  On the Yarra Glen-Healesville Road I passed the morning balloon departure.  I was on the summit by 0830, plenty of time.

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Artisan Printed Circuit Boards

I have been hand-making printed circuit boards since I was a teenager.  In the late 1970s I started with ‘proper’ PCBs, hand-drawn, hand-drilled, then painted with resist (bituminous paint) thinned with turpentine and applied with a tiny brush to form the copper traces, drilled holes on the copper side, etched in Ferric Chloride, cleaned and sprayed with a clear enamel to stop tarnish.  This was the way all circuit boards looked at that time, including commercially made ones in kits, and those inside transistor radios, digital clocks, televisions and ham radio transceivers.

Sometime in the 1980s I tried a ‘copper side up’ board, dispensing with the drilled holes, free-hand drawing on the copper side, painting and etching, then soldering the components directly to the copper pads. I’ve been making them this way ever since.

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Return to Mt Gordon VK3/VN-027 and Mt Strickland VK3/VN-030

Sunday 10th July 2016 turned out to be my first SOTA outing for several months.  Weather was windy, overcast with intermittent showers forecast, not the worst of winter, so I headed up to the northern end of the Yarra Ranges. First up was Mt Gordon VK3/VN-027 on the way to Marysville, turning off opposite the trout farm, my second visit here (the first one was on June 8th 2015).  The summit was windy and cold. I set up the dipole which performs better than the vertical. Self-spotting and going on air at 1430, conditions were average at best, the spot bought out two stations who I could not complete QSOs with, Matt VK1MA and Geoff VK3SQ Both were weak signals and faded right out on second overs. Five QSOs followed quickly, VKs 3GGG, 5IS, 2IO, 5EE and 2PX with my signals varying between 3×5 and 5×7.

Looking north from the Mt Gordon operating spot.

 

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FYBO 2016 at Kangaroo Ground

Sunday was the inaugural Freeze Your Butt Off (FYBO) context, devised by Ian VK5CZ to encourage portable (parks and SOTA) activity during the SOTA winter bonus period. The timing could not have been better for freezing one’s butt off, as an Antarctic blast of cold air swept up the east coast of Australia on Friday, just two days earlier, resulting in record low temperatures and snow falls down to 500 meters from Bathurst to Ballarat. Melbourne shivered through the coldest June day in almost 20 years on Friday with temperatures as low as 2C on Friday night. It was 4C at 9am Saturday. This is unseasonably cold.   I considered activating Melbourne’s nearest SOTA summit Mt Dandenong VK3/VC-025 (2 points) but my time was so short I opted for old favourite Kangaroo Ground which gives a clear take-off in all directions, has facilities, and can be reached in 30 minutes.

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Listening to West Coast AM on 75 meters

Standing on  a crowded commuter train, going home at the end of the work day in Melbourne Australia, listening to a late night west coast AM QSO on 75 meters, 3870khz, using my Samsung smart phone, via W7RNA’s web SDR.  This is just one of the miracles of SDR and the Internet — the ability to use someone else’s station anywhere in the world, from almost anywhere in the world. My old elmer from my school days in the 1970s, Moss VK5TU, would turn his tuning knob in his grave if he could see this. KB6 and WB6es chewing the rag, on big AM transmitters.  You can almost smell the burning dust on the ultraviolet glass envelopes.  Pressing the tiny audio buds into my ear to shield some of the ambient train noise I hear the tone of the transmitter, rounded low-mids and bass.  It could be 1972. It’s a nostalgic and beautiful sound.

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Return to Mt Bullfight (VN-002) and Pyramid Hill (VN-005)

The Sunday of ANZAC Day weekend emerged as my first full SOTA day for 2016 and with perfect weather forecast (low 20 degrees Celsius) I was keen to have a second try at Mount Bullfight  (VK3/VN-002), this time approaching it from the ridge, not the creek. Last time, on 2nd December last year, I arrived later in the day after having activated two other summits, Mt Mitchell (VK3/VN-012) and the scenic Sugarloaf Peak (VK3/VN-011). On that occasion I left Bullfight Track about 300 meters further on and encountered the creek and thick undergrowth — not easy. There is a description of the two approaches in my previous post, and a map with the two paths here.  There are no paths or tracks in the vicinity of Mount Bullfight summit, so no two climbers take exactly the same way.  This time I wanted to cut in from Bullfight Track earlier, close to Stillman’s Lookout sign, which others had reported as being relatively clear of the dense undergrowth that slowed me down. I also wanted to tackle it as the first summit of the day, not the second or third, with plenty of time to spare. Whichever way you take, the final ascent to Bullfight summit is a decent climb.

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Andrew VK1AD | Adventure & Radio from Mountain Tops | Bush Walking | Summits on the Air (SOTA)